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Sample records for ion drift velocity

  1. Negative Ion Drift Velocity and Longitudinal Diffusion in Mixtures of Carbon Disulfide and Methane

    NASA Technical Reports Server (NTRS)

    Dion, Michael P.; Son, S.; Hunter, S. D.; deNolfo, G. A.

    2011-01-01

    Negative ion drift velocity and longitudinal diffusion has been measured for gas mixtures of carbon disulfide (CS2) and methane (CH4)' Measurements were made as a function of total pressure, CS2 partial pressure and electric field. Constant mobility and thermal-limit longitudinal diffusion is observed for all gas mixtures tested. Gas gain for some of the mixtures is also included.

  2. Measurements of the ion drift velocities in the presheaths of plasmas with multiple ion species

    NASA Astrophysics Data System (ADS)

    Severn, G.; Yip, C.-S.; Hershkowitz, N.

    2013-11-01

    We have used a variety of diode lasers to perform laser-induced fluorescence (LIF) measurements that were the first to test the Bohm Criterion for multiple ion species plasmas. These measurements led to the discovery that a collective effect, ion-ion instability enhanced friction, is important for sheath formation in multiple ion species plasmas. New LIF schemes were pioneered in order to complete these experiments with diode lasers. With respect to a new LIF scheme for KrII, accessible to diode lasers, challenges remain fielding an ion flow diagnostic in low temperature plasmas.

  3. The role of external electric fields in enhancing ion mobility, drift velocity, and drift-diffusion rates in aqueous electrolyte solutions

    NASA Astrophysics Data System (ADS)

    Murad, Sohail

    2011-03-01

    Molecular simulations have been carried out using the method of molecular dynamics to investigate the role of external electric fields on the ion mobility, drift velocity, and drift-diffusion rate of ions in aqueous electrolyte solutions. These properties are critical for a range of processes including electrodialysis, electro-deionization, electrophoresis, and electroosmosis. Our results show that external electric fields relax the hydrated ion structure at significantly larger time scales (between 300 and 800 ps), than most other relaxation processes in solutions (generally of the order of 1 ps). Previous studies that did not account for the much longer relaxation times did not observe this behavior for ions even with very high electric fields. External electric fields must also overcome several (at least two or more) activation energy barriers to significantly change the structure of hydrated ions. As a result, the dynamic behavior changes almost in bands as a function of electric field strengths, rather than linearly. Finally, the effect of the field is much less dramatic on water than the ions. Thus electric fields will be of more significance in processes that involve the transport of ions (such as electro-deionization) than the transport of water (electroosmosis).

  4. Comparison of SuperDARN irregularity drift measurements and F-region ion velocities from the resolute bay ISR

    NASA Astrophysics Data System (ADS)

    Bahcivan, Hasan; Nicolls, Michael J.; Perry, Gareth

    2013-12-01

    A number of studies have addressed the principal assumption used by the SuperDARN network of HF radars that the scatter from F region field-aligned irregularities has a Doppler shift given by the cosine component of the EXB plasma drift. However, the slopes of the best-fit line to the measured points have consistently been low, perhaps implying contamination from irregularities with smaller amplitude drifts. This work is motivated by testing the same assumption on a more optimal experimental setting: using the north face of the Resolute Bay incoherent scatter radar (RISR-N), which provides high resolution magnitude and direction measurements of EXB drift in a region where the ionospheric flow is mostly uniform relative to auroral latitudes, thereby reducing echo mixing due to spatio-temporal structuring. We compared the EXB drift measured by RISR-N to the line-of-sight Doppler velocities measured PolarDARN which is composed of Rankin Inlet and Inuvik HF radars, both having a field of view over Resolute Bay. An aggregate scatter plot of all the echoes observed during a 5-day period in early May 2011 contains two distinct groups of echoes. The first group is hypothesized to be from the E region because the echoes appear above a threshold EXB drift and at small flow angles, which are characteristics of primary Farley-Buneman waves. The Doppler velocity of the second group of echoes increase linearly with the EXB drift and is identified here as F region echoes. A special joint fit showed a slope of 0.85 for the F region echoes. During the observation period, the F region electron density has large variations between 1 and 101011, in particular due to the polar cap patches. Considering a representative F region electron density of 51011 m-3, which has a refraction index of 0.86 at 12.5 MHz (for PolarDARN frequencies) and the fact that the measured velocity is the product of the actual velocity and the refractive index, the expected slope is 0.86, in agreement with our measurement. The fit for E region Doppler velocities shows a saturation speed at 170 m/s, while the data were spread between 100 and 300 m/s. Although the saturation speed is somewhat lower than the ion acoustic speed, it is acceptable considering earlier work attributing similarly low velocities to large aspect angles at the scattering altitudes.

  5. Laser induced fluorescence measurements of ion velocity and temperature of drift turbulence driven sheared plasma flow in a linear helicon plasma device

    SciTech Connect

    Chakraborty Thakur, S.; Fedorczak, N.; Manz, P.; Tynan, G. R.; Xu, M.; McCarren, D.; Scime, E. E.; Lee, T.

    2012-08-15

    Using laser induced fluorescence (LIF), radial profiles of azimuthal ion fluid velocity and ion temperature are measured in the controlled shear de-correlation experiment (CSDX) linear helicon plasma device. Ion velocities and temperatures are derived from the measured Doppler broadened velocity distribution functions of argon ions. The LIF system employs a portable, high power (>300 mW), narrowband ({approx}1 MHz) tunable diode laser-based system operating at 668.614 nm. Previous studies in CSDX have shown the existence of a radially sheared azimuthal flow as measured with time delay estimation methods and Mach probes. Here, we report the first LIF measurements of sheared plasma fluid flow in CSDX. Above a critical magnetic field, the ion fluid flow profile evolves from radially uniform to peaked on axis with a distinct reversed flow region at the boundary, indicating the development of a sheared azimuthal flow. Simultaneously, the ion temperature also evolves from a radially uniform profile to a profile with a gradient. Measurements in turbulent and coherent drift wave mode dominated plasmas are compared.

  6. Drift velocities of electrons in methane-inert-gas mixtures

    NASA Astrophysics Data System (ADS)

    Foreman, L.; Kleban, P.; Schmidt, L. D.; Davis, H. T.

    1981-03-01

    The drift of electrons in mixtures of methane with argon and helium is measured with a double shutter drift tube as a function of methane composition and electric field-pressure ratio Ep. At certain concentrations, inelastic scattering by methane causes a maximum in the drift velocity as a function of Ep. As the methane mole fraction decreases, the drift velocity maximum decreases and moves to lower values of Ep. In the argon mixtures, the drift velocity at low Ep is greater than it is in either pure gas. Comparision is made with direct numerical solutions of the Boltzmann equation for the mixtures. When the methane mole fractions are appropriately chosen, the data obey roughly a scaling law relating the electron drift velocity versus Ep in a methane-argon mixture with VD versus Ep in a methane-helium mixture.

  7. Two-stream instability with time-dependent drift velocity

    DOE PAGESBeta

    Qin, Hong; Davidson, Ronald C.

    2014-06-26

    The classical two-stream instability driven by a constant relative drift velocity between two plasma components is extended to the case with time-dependent drift velocity. A solution method is developed to rigorously define and calculate the instability growth rate for linear perturbations relative to the time-dependent unperturbed two-stream motions. The stability diagrams for the oscillating two-stream instability are presented over a large region of parameter space. It is shown that the growth rate for the classical two-stream instability can be significantly reduced by adding an oscillatory component to the relative drift velocity.

  8. Two-stream instability with time-dependent drift velocity

    SciTech Connect

    Qin, Hong; Davidson, Ronald C.

    2014-06-15

    The classical two-stream instability driven by a constant relative drift velocity between two plasma components is extended to the case with time-dependent drift velocity. A solution method is developed to rigorously define and calculate the instability growth rate for linear perturbations relative to the time-dependent unperturbed two-stream motions. Stability diagrams for the oscillating two-stream instability are presented over a large region of parameter space. It is shown that the growth rate for the classical two-stream instability can be significantly reduced by adding an oscillatory component to the relative drift velocity.

  9. Measuring the equatorial plasma bubble drift velocities over Morroco

    NASA Astrophysics Data System (ADS)

    Lagheryeb, Amine; Benkhaldoun, Zouhair; Makela, Jonathan J.; Harding, Brian; Kaab, Mohamed; Lazrek, Mohamed; Fisher, Daniel J.; Duly, Timothy M.; Bounhir, Aziza; Daassou, Ahmed

    2015-08-01

    In this work, we present a method to measure the drift velocities of equatorial plasma bubbles (EPBs) in the low latitude ionosphere. To calculate the EPB drift velocity, we use 630.0-nm airglow images collected by the Portable Ionospheric Camera and Small Scale Observatory (PICASSO) system deployed at the Oukkaimden observatory in Morocco. To extract the drift velocity, the individual images were processed by first spatially registering the images using the star field. After this, the stars were removed from the images using a point suppression methodology, the images were projected into geographic coordinates assuming an airglow emission altitude of 250 km. Once the images were projected into geographic coordinates, the intensities of the airglow along a line of constant geomagnetic latitude (31°) are used to detect the presence of an EPB, which shows up as a depletion in airglow intensity. To calculate the EPB drift velocity, we divide the spatial lag between depletions found in two images (found by the application of correlation analysis) by the time difference between these two images. With multiple images, we will have several velocity values and consequently we can draw the EPB drift velocity curve. Future analysis will compare the estimates of the plasma drift velocity with the thermospheric neutral wind velocity estimated by a collocated Fabry-Perot interferometer (FPI) at the observatory.

  10. C/NOFS Daytime ExB Drift Velocity Measurements Compared With Ground-based Magnetometer-inferred ExB Drift Velocity Observations in the Peruvian Sector

    NASA Astrophysics Data System (ADS)

    Anderson, D. N.; Heelis, R.; Pfaff, R. F.

    2008-12-01

    A technique to determine realistic, daytime, vertical ExB drift velocities in the equatorial, ionospheric F-region has recently been developed. It has been established that taking the difference in the horizontal components (H) between a ground-based magnetometer on the magnetic equator and one 6-9o away in magnetic latitude, provides these realistic velocities. Relationships between the H values from the magnetometers at Jicamarca, Peru (1o N. mag. lat.) and Piura, Peru (6.5o N. mag. lat.) and the observed daytime ExB drift velocities from the JULIA (Jicamarca Unattended Long-term Ionosphere Atmosphere) coherent scatter radar have been developed and then applied, on a day-to-day basis, to obtain daytime, vertical ExB drift velocities between 0700 and 1700 LT in the Peruvian longitude sector. We briefly describe the H-inferred ExB drift technique and demonstrate that the H vs ExB drift relationship obtained in the Peruvian sector can be applied in other longitude sectors where appropriately-placed magnetometers exist. We then describe a study where we compare the H-inferred ExB drift velocities obtained in the Peruvian sector with the CINDI/IVM (Ion Velocity Meter) and the DC VEFI (Vector Electric Field Experiment) observations in the Peruvian sector during the months of August, September and October, 2008. The local time of the observations range between 0900 and 1600 LT. The IVM velocity component and the VEFI electric fields perpendicular to B in the magnetic meridional plane are calculated and transformed to the apex altitude at the magnetic equator. The fact that daytime, vertical ExB drift velocities at the magnetic equator are essentially independent of altitude between 150 km and 800 km simplifies the comparisons with the H- inferred ExB drift observations. It is important to validate the IVM and VEFI observations with a number of different ground-based ExB drift measurements and, while the Jicamarca ISR and JULIA are available, they are sporadic and all in one longitude sector. In contrast, the magnetometer-inferred ExB drift technique is available, continuously, day-to-day. In addition, the same technique can be used to validate VEFI and IVM daytime observations at other longitude sectors such as the Brazilian, African, Indian, Philippine and Indonesian sectors where appropriately-placed magnetometers already exist.

  11. Drift compression of an intense neutralized ion beam

    SciTech Connect

    Roy, P.K.; Yu, S.S.; Henestroza, E.; Anders, A.; Bieniosek, F.M.; Coleman, J.; Eylon, S.; Greenway, W.G.; Leitner, M.; Logan, B.G.; Waldron, W.L.; Welch, D.R.; Thoma, C.; Sefkow, A.B.; Gilson, E.P.; Efthimion, P.C.; Davidson, R.C.

    2004-10-25

    Longitudinal compression of a tailored-velocity, intense neutralized ion beam has been demonstrated. The compression takes place in a 1-2 m drift section filled with plasma to provide space-charge neutralization. An induction cell produces a head-to-tail velocity ramp that longitudinally compresses the neutralized beam, enhancing the beam peak current by a factor of 50 and producing a pulse duration of about 3 ns. this measurement has been confirmed independently with two different diagnostic systems.

  12. Ion drift in a magnetic field under the combined action of LID and light pressure

    SciTech Connect

    Parkhomenko, A I

    2002-06-30

    The effect of magnetic field on the ion drift in a weakly ionised gas under the combined action of light-induced drift (LID) and light pressure is theoretically investigated. It is shown that the imposition of an external magnetic field may give rise to a velocity component of light-induced ion drift orthogonal to the direction of radiation propagation. The effect of light pressure in sufficiently strong magnetic fields is found to prevail over the LID effect, while the reverse is true for weak magnetic fields. The dependence of the ion drift velocity on the frequency detuning drastically changes in the magnetic field when ions experience the Lorenz force. It is predicted that the projection of the ion drift velocity on the direction of radiation propagation should change its sign with increasing magnetic field, and an anomalous LID can be observed. (laser applications and other topics in quantum electronics)

  13. Cap Bubble Drift Velocity in a Confined Test Section

    SciTech Connect

    Xiaodong Sun; Seungjin Kim; Mamoru Ishii; Frank W. Lincoln; Stephen G. Beus

    2002-10-09

    In the two-group interfacial area transport equation, bubbles are categorized into two groups, i.e., spherical/distorted bubbles as group 1 and cap/slug/churn-turbulent bubbles as group 2. The bubble rise velocities for both groups of bubbles may be estimated by the drift flux model by applying different distribution parameters and drift velocities for both groups. However, the drift velocity for group 2 bubbles is not always applicable (when the wall effect becomes important) as in the current test loop of interest where the flow channel is confined by two parallel flat walls, with a dimension of 200-mm in width and 10-mm in gap. The previous experiments indicated that no stable slug flow existed in this test section, which was designed to permit visualization of the flow patterns and bubble characteristics without the distortion associated with curved surfaces. In fact, distorted cap bubbly and churn-turbulent flow was observed. Therefore, it is essential to developed a correlation for cap bubble drift velocity in this confined flow channel. Since the rise velocity of a cap bubble depends on its size, a high-speed movie camera is used to capture images of cap bubbles to obtain the bubble size information. Meanwhile, the rise velocity of cap and elongated bubbles (called cap bubbles hereafter) is investigated by examining the captured images frame by frame. As a result, the conventional correlation of drift velocity for slug bubbles is modified and acceptable agreements between the measurements and correlation estimation are achieved.

  14. A new digital ion drift meter for thermal plasma measurement

    SciTech Connect

    Chaplin, C.P.; Rich, F.; Pakula, W.A.

    1996-12-31

    In the near-earth space environment, thermal plasmas are those near equilibrium with temperatures from 0.1 to 10 eV and densities from 1 to 10{sup 7} cm{sup {minus}3}. It is useful to consider the distinctions between common measurement methods for thermal and medium energy (10 to 10{sup 5} eV) plasmas. Distributions of medium energy plasmas are commonly measured differentially. That is, ions in small portions of velocity space are isolated by devices using static fields. These use charge multipliers for single-ion or digital detection. Complete distribution measurements are made, with some difficulty by moving or combining multiple detectors. In contrast, thermal plasmas are more easily measured in bulk, with differential information being more difficult to obtain. Retarding Potential Analyzers (RPAs) and Drift Meters (DMs) are often used to measure thermal ions. The Digital Ion Drift Meter (DIDM) is being developed as a replacement for analog spacecraft drift meters. It combines the single-ion counting capability of a Micro-Channel Plate (MCP) with a position-determining anode. Careful electrostatic design is needed to create an instrument that can simultaneously measure bulk and differential plasma properties at very low densities. Performance has been optimized by simulating the trajectories of ions entering the device.

  15. Linear and nonlinear coupled drift and ion acoustic waves in collisional pair ion-electron magnetoplasma

    SciTech Connect

    Mushtaq, A.; Saeed, R.; Haque, Q.

    2011-04-15

    Linear and nonlinear coupled electrostatic drift and ion acoustic waves are studied in inhomogeneous, collisional pair ion-electron plasma. The Korteweg-de Vries-Burgers (KdVB) equation for a medium where both dispersion and dissipation are present is derived. An attempt is made to obtain exact solution of KdVB equation by using modified tanh-coth method for arbitrary velocity of nonlinear drift wave. Another exact solution for KdVB is obtained, which gives a structure of shock wave. Korteweg-de Vries (KdV) and Burgers equations are derived in limiting cases with solitary and monotonic shock solutions, respectively. Effects of species density, magnetic field, obliqueness, and the acoustic to drift velocity ratio on the solitary and shock solutions are investigated. The results discussed are useful in understanding of low frequency electrostatic waves at laboratory pair ion plasmas.

  16. Variation of type I plasma wave phase velocity with electron drift velocity in the equatorial electrojet

    SciTech Connect

    Ravindran, S.; Reddy, C.A.

    1993-12-01

    The authors report the use of VHF coherent backscatter radar to detect the phase velocity variations of type I and type II plasma waves coming from the equatorial electrojet in conjunction with substorm and magnetic storm events. These plasma waves are generated by two-stream type instabilities. The authors observe a correlation between the phase velocity of the type I plasma waves and the electron drift velocity, which is consistent with present models which explain the generation of such waves.

  17. Filament velocity scaling laws for warm ions

    SciTech Connect

    Manz, P.; Max-Planck-Institut für Plasmaphysik, EURATOM Assoziation, Boltzmannstr. 2, 85748 Garching ; Carralero, D.; Birkenmeier, G.; Müller, H. W.; Scott, B. D.; Müller, S. H.; Fuchert, G.; Stroth, U.; Physik-Department E28, Technische Universität München, James-Franck-Str. 1, 85748 Garching

    2013-10-15

    The dynamics of filaments or blobs in the scrape-off layer of magnetic fusion devices are studied by magnitude estimates of a comprehensive drift-interchange-Alfvén fluid model. The standard blob models are reproduced in the cold ion case. Even though usually neglected, in the scrape-off layer, the ion temperature can exceed the electron temperature by an order of magnitude. The ion pressure affects the dynamics of filaments amongst others by adding up to the interchange drive and the polarisation current. It is shown how both effects modify the scaling laws for filament velocity in dependence of its size. Simplifications for experimentally relevant limit regimes are given. These are the sheath dissipation, collisional, and electromagnetic regime.

  18. Magnetometer-inferred, Equatorial, Daytime Vertical ExB Drift Velocities Observed in the African Longitude Sector

    NASA Astrophysics Data System (ADS)

    Anderson, D. N.; Yizengaw, E.

    2011-12-01

    A recent paper has investigated the sharp longitude gradients in the dayside ExB drift velocities associated with the 4-cell, non-migrating structures thought to be connected with the eastward propagating, diurnal, non-migrating (DE3) tides. Observations of vertical ExB drift velocities obtained from the Ion Velocity Meter (IVM) on the Communication/Navigation Outage Forecast System (C/NOFS) satellite were obtained in the Western Pacific, Eastern Pacific, Peruvian and Atlantic sectors for a few days during the months of October, March and December, 2009. Respective ExB drift velocity gradients at the cell boundaries for these 4 longitude sectors were a.) -1.3m/sec/degree, b.) 3m/sec/degree, c.) -4m/sec/degree and d.) 1m/sec/degree and were observed on a day-to-day basis. In this talk, we estimate the longitude gradients in the dayside, vertical ExB drift velocities from magnetometer H-component observations in the African sector. We briefly describe the technique for obtaining realistic ExB drift velocities associated with the difference in the H-component values between a magnetometer on the magnetic equator and one off the magnetic equator at 6 to 9 degrees dip latitude (delta H). We present magnetometer-inferred, dayside ExB drift velocities obtained from the AMBER (African Meridian B-field Education and Research) magnetometer chain in the East Africa (Ethiopian) longitude sector and the West African (Nigerian) longitude sector. We compare the longitude gradients in ExB drift velocities in the African sector with the C/NOFS- observed longitude gradients mentioned above. We also discuss the advantages of using ground-based magnetometer observations to infer ExB drift velocities compared with the C/NOFS satellite observations.

  19. Role of ionization and electron drift velocity profile to Rayleigh instability in a Hall thruster plasma

    SciTech Connect

    Singh, Sukhmander; Malik, Hitendra K.

    2012-07-01

    Role of ionization to Rayleigh instability is clarified in a Hall thruster plasma under the variety of profiles of electron drift velocity, namely, step-like profile (SLP) and two different super-Gaussian profiles (SGP1 and SGP2). For this, a relevant Rayleigh equation is derived and solved numerically using fourth-order Runge-Kutta method. Interestingly, an upper cutoff frequency of oscillations {omega}{sub max} is realized for the occurrence of the instability that shows dependence on the ionization rate {alpha}, electron drift velocity u{sub 0}, electron cyclotron frequency {Omega}, azimuthal wave number k{sub y}, plasma density n{sub 0}, density gradient {partial_derivative}n{sub 0}/{partial_derivative}x, ion (electron) thermal speed V{sub thI}(V{sub thE}), and ion (electron) plasma frequency {omega}{sub pi}({omega}{sub pe}). The frequency {omega}{sub max} follows the trend {omega}{sub max} (for SGP2) >{omega}{sub max} (for SLP) >{omega}{sub max} (for SGP1) and shows a similar behaviour with ionization for all types of the velocity profiles. The instability is found to grow faster for the higher {alpha} and the ion temperature but it acquires lower rate under the effect of the higher electron temperature; the perturbed potential also varies in accordance with the growth rate. The electron temperature influences the growth rate and cutoff frequency less significantly in comparison with the ion temperature.

  20. Dominance of the diurnal mode of horizontal drift velocities at F-region heights

    NASA Technical Reports Server (NTRS)

    Kirchhoff, V. W. J. H.; Carpenter, L. A.

    1975-01-01

    Drift measurements perpendicular to the magnetic field are examined, taking into account also some nighttime measurements. Nighttime measurements of drift velocities are more difficult because densities are lower. However, the uncertainty in the drift velocities can be optimized by making use of an approach reported by Kirchhoff (1973). The approach involves a careful selection of the elevation angle of the radar antenna. Measured velocities are discussed along with the magnetospheric perturbation effect. The measurements are compared with conclusions of the dynamo theories.

  1. Explaining the subpulse drift velocity of pulsar magnetosphere within the space-charge limited flow model

    NASA Astrophysics Data System (ADS)

    Morozova, Viktoriya S.; Ahmedov, Bobomurat J.; Zanotti, Olindo

    2014-10-01

    We try to explain the subpulse drift phenomena adopting the space-charge limited flow model and comparing the plasma drift velocity in the inner region of pulsar magnetospheres with the observed velocity of drifting subpulses. We apply the approach described in a recent paper of van Leeuwen & Timokhin, where it was shown that the standard estimation of the subpulse drift velocity through the total value of the scalar potential drop in the inner gap gives inaccurate results, while the exact expression relating the drift velocity to the gradient of the scalar potential should be used instead. After considering a selected sample of sources taken from the catalogue of Weltevrede et al. with coherently drifting subpulses and reasonably known observing geometry, we show that their subpulse drift velocities would correspond to the drift of the plasma located very close or above the pair formation front. Moreover, a detailed analysis of PSR B0826-34 and PSR B0818-41 reveals that the variation of the subpulse separation with the pulse longitude can be successfully explained by the dependence of the plasma drift velocity on the angular coordinates.

  2. Subpulse drift velocity of pulsar magnetosphere within the space-charge limited flow model

    NASA Astrophysics Data System (ADS)

    Ahmedov, Bobomurat; Morozova, Viktoriya; Zanotti, Olindo

    We attempt to explain the subpulse drift phenomena adopting the space-charge limited flow (SCLF) model and comparing the plasma drift velocity in the inner region of pulsar magnetospheres with the observed velocity of drifting subpulses. We apply the approach described in a recent paper of van Leeuwen & Timokhin (2012), where it was shown that the standard estimation of the subpulse drift velocity through the total value of the scalar potential drop in the inner gap gives inaccurate results, while the exact expression relating the drift velocity to the gradient of the scalar potential should be used instead. After considering a selected sample of sources taken from the catalog of Weltevrede, Edwards & Stappers (2006) with coherently drifting subpulses and reasonably known observing geometry, we show that their subpulse drift velocities would correspond to the drift of the plasma located very close or above the pair formation front. Moreover, a detailed analysis of PSR B0826-34 and PSR B0818-41 reveals that the variation of the subpulse separation with the pulse longitude can be successfully explained by the dependence of the plasma drift velocity on the angular coordinates.

  3. On Ion Drifts and Neutral Winds in Titan's Thermosphere

    NASA Astrophysics Data System (ADS)

    Shebanits, Oleg; Wahlund, Jan-Erik; Edberg, Niklas J. T.; Andrews, David J.; Crary, Frank J.; Wellbrock, Anne; Coates, Andrew; Mandt, Kathleen E.; Waite, J. Hunter, Jr.

    2015-04-01

    Saturn's largest moon Titan hosts an atmosphere with complex organic chemistry initiated in the ionosphere. The nightside chemistry may be influenced by the ion transport from the dayside ionosphere. In turn, ion transport (ion drifts) may be affected by the neutral winds, which cannot be measured directly by Cassini. In this study we derive the ion drifts along the spacecraft trajectories based on analysis of in-situ measurements of electron and ion fluxes, positive and negative ion masses and the magnetic field. Data from Titan flybys TA to T100 was included (Oct 2005 - Apr 2014), of which 55 flybys were below 1400 km and 48 below 1200 km altitude. From the electron and ion flux measurements three regions were observed: 1) above 1600 km, ions are ExB-drifting (frozen into the fields), 2) 1100-1600 km altitudes, dynamo-region, ions drift in opposite directions (perpendicular to B) and 3) 880-1100 km altitude (upper limit depends on convection electric field strength), ions are following neutrals and ion drifts translate to neutral winds of 0.5-2.5 km/s with weaker winds on the dayside of Titan's ionosphere.

  4. In situ measurements of plasma drift velocity and enhanced NO/+/ in the auroral electrojet by the Bennett spectrometer on AE-C. [Atmosphere Explorer-C satellite

    NASA Technical Reports Server (NTRS)

    Brinton, H. C.

    1975-01-01

    Simultaneous measurements of ion composition and plasma drift velocity by the Bennett mass spectrometer on the Atmosphere Explorer-C satellite reveal a direct correlation between enhancements in NO(+) concentration and ion drift velocity in the southern auroral oval. Low altitude (137 to 250 km) data obtained between 1700 and 2400 hr magnetic local time on October 22, 1974, reveal a region of westward plasma flow at velocities up to 1.3 km/s between 62 and 68 deg invariant latitude, with corresponding NO(+) enhancements of up to a factor of 20. A narrow region of reverse flow at about 0.9 km/s was also measured. These drift observations are consistent with convective flow patterns derived from electric field measurements, and their correlation with NO(+) appears to support the suggestion that NO(+) enhancements would be expected in regions of drift owing to the dependence on ion energy of the reaction O(+) + N2 yields NO(+) + N.

  5. The effect of plasma shear flow on drift Alfven instabilities of a finite beta plasma and on anomalous heating of ions by ion cyclotron turbulence

    NASA Astrophysics Data System (ADS)

    Jo, Young Hyun; Lee, Hae June; Mikhailenko, Vladimir V.; Mikhailenko, Vladimir S.

    2016-01-01

    It was derived that the drift-Alfven instabilities with the shear flow parallel to the magnetic field have significant difference from the drift-Alfven instabilities of a shearless plasma when the ion temperature is comparable with electron temperature for a finite plasma beta. The velocity shear not only modifies the frequency and the growth rate of the known drift-Alfven instability, which develops due to the inverse electron Landau damping, but also triggers a combined effect of the velocity shear and the inverse ion Landau damping, which manifests the development of the ion kinetic shear-flow-driven drift-Alfven instability. The excited unstable waves have the phase velocities along the magnetic field comparable with the ion thermal velocity, and the growth rate is comparable with the frequency. The development of this instability may be the efficient mechanism of the ion energization in shear flows. The levels of the drift--Alfven turbulence, resulted from the development of both instabilities, are determined from the renormalized nonlinear dispersion equation, which accounts for the nonlinear effect of the scattering of ions by the electromagnetic turbulence. The renormalized quasilinear equation for the ion distribution function, which accounts for the same effect of the scattering of ions by electromagnetic turbulence, is derived and employed for the analysis of the ion viscosity and ions heating, resulted from the interactions of ions with drift-Alfven turbulence. In the same way, the phenomena of the ion cyclotron turbulence and anomalous anisotropic heating of ions by ion cyclotron plasma turbulence has numerous practical applications in physics of the near-Earth space plasmas. Using the methodology of the shearing modes, the kinetic theory of the ion cyclotron turbulence of the plasma with transverse current with strong velocity shear has been developed.

  6. Measurement of the electron drift velocity for directional dark matter detectors

    NASA Astrophysics Data System (ADS)

    Mayet, F.; Billard, J.; Bosson, G.; Bourrion, O.; Guillaudin, O.; Lamblin, J.; Richer, J. P.; Riffard, Q.; Santos, D.; Iguaz, F. J.; Lebreton, L.; Maire, D.

    2013-12-01

    Three-dimensional track reconstruction is a key issue for directional Dark Matter detection. It requires a precise knowledge of the electron drift velocity. Magboltz simulations are known to give a good evaluation of this parameter. However, large TPC operated underground on long time scale may be characterized by an effective electron drift velocity that may differ from the value evaluated by simulation. In situ measurement of this key parameter is hence a way to avoid bias in the 3D track reconstruction. We present a dedicated method for the measurement of the electron drift velocity with the MIMAC detector. It is tested on two gas mixtures : CF4 and CF4 + CHF3. We also show that adding CHF3 allows us to lower the electron drift velocity while keeping almost the same Fluorine content of the gas mixture.

  7. Drift Compression and Final Focus Options for Heavy Ion Fusion

    SciTech Connect

    Hong Qin; Ronald C. Davidson; John J. Barnard; Edward P. Lee

    2005-02-14

    A drift compression and final focus lattice for heavy ion beams should focus the entire beam pulse onto the same focal spot on the target. We show that this requirement implies that the drift compression design needs to satisfy a self-similar symmetry condition. For un-neutralized beams, the Lie symmetry group analysis is applied to the warm-fluid model to systematically derive the self-similar drift compression solutions. For neutralized beams, the 1-D Vlasov equation is solved explicitly, and families of self-similar drift compression solutions are constructed. To compensate for the deviation from the self-similar symmetry condition due to the transverse emittance, four time-dependent magnets are introduced in the upstream of the drift compression such that the entire beam pulse can be focused onto the same focal spot.

  8. Ion Mass/Velocity/Charge Spectrometer

    NASA Technical Reports Server (NTRS)

    Neugebauer, M. M.; Clay, D. R.; Goldstein, B. E.

    1983-01-01

    Ion spectrometer distributes ions two-dimensionally and measures three characteristics of incident-ion beam: (1) mass/charge distribution, (2) ion velocity distribution, and (3) direction of incidence. Also useful for diagnosis in experimental plasma physics in collisionless regime. Ion spectrometer uses novel combination of standard electrostatic and magnetic deflection techniques to sort incident ions according to speed, diretion of incidence, and mass/ charge ratio.

  9. Effect of film elasticity on the drift velocity of capillary-gravity waves

    NASA Astrophysics Data System (ADS)

    Weber, Jan Erik; Saetra, yvind

    1995-02-01

    The effect of an insoluble, elastic surface film on the drift velocity of capillary-gravity waves is studied theoretically on the basis of a Lagrangian description of motion. There is no forcing from the atmosphere, and the wave amplitude is taken to attenuate in time. Defining a nondimensional parameter ?, which combines film elasticity, fluid viscosity, and wave frequency, maximum damping of the linear waves occurs when ?=1 (the Marangoni effect). In this case the frequency of capillary-gravity waves nearly coincides with that of elastic film waves. The nonlinear drift velocity is obtained for general values of ?. In particular, it is found that the absolute maximum of the transient drift current is located below the surface when ??2/3. At the surface, maximum drift velocity (in time domain) occurs for values of ? that are somewhat less than one.

  10. In situ measurement of the electron drift velocity for upcoming directional Dark Matter detectors

    NASA Astrophysics Data System (ADS)

    Billard, J.; Mayet, F.; Bosson, G.; Bourrion, O.; Guillaudin, O.; Lamblin, J.; Richer, J. P.; Riffard, Q.; Santos, D.; Iguaz, F. J.; Lebreton, L.; Maire, D.

    2014-01-01

    Three-dimensional track reconstruction is a key issue for directional Dark Matter detection and it requires a precise knowledge of the electron drift velocity. Magboltz simulations are known to give a good evaluation of this parameter. However, large TPC operated underground on long time scale may be characterized by an effective electron drift velocity that may differ from the value evaluated by simulation. In situ measurement of this key parameter is hence needed as it is a way to avoid bias in the 3D track reconstruction. We present a dedicated method for the measurement of the electron drift velocity with the MIMAC detector. It is tested on two gas mixtures: CF4 and CF4+CHF3. The latter has been chosen for the MIMAC detector as we expect that adding CHF3 to pure CF4 will lower the electron drift velocity. This is a key point for directional Dark Matter as the track sampling along the drift field will be improved while keeping almost the same Fluorine content of the gas mixture. We show that the drift velocity at 50 mbar is reduced by a factor of about 5 when adding 30% of CHF3.

  11. Ion Mobility Spectrometry Mass Spectrometry Performance Using Electrodynamic Ion Funnels and Elevated Drift Gas Pressures

    PubMed Central

    Baker, Erin Shammel; Clowers, Brian H.; Li, Fumin; Tang, Keqi; Tolmachev, Aleksey V.; Prior, David C.; Belov, Mikhail E.; Smith, Richard D.

    2012-01-01

    The ability of ion mobility spectrometry coupled with mass spectrometry (IMS-MS) to characterize biological mixtures has been illustrated over the past eight years. However, the challenges posed by the extreme complexity of many biological samples have demonstrated the need for higher resolution IMS-MS measurements. We have developed a higher resolution ESI-IMS-TOF MS by utilizing high pressure electrodynamic ion funnels at both ends of the IMS drift cell and operating the drift cell at an elevated pressure compared to that conventionally used. The ESI-IMS-TOF MS instrument consists of an ESI source, an hourglass ion funnel used for ion accumulation/injection into an 88 cm drift cell followed by a 10 cm ion funnel and a commercial orthogonal time-of-flight mass spectrometer providing high mass measurement accuracy. It was found that the rear ion funnel could be effectively operated as an extension of the drift cell when the DC fields were matched, providing an effective drift region of 98 cm. The resolution of the instrument was evaluated at pressures ranging from 4 to12 Torr and ion mobility drift voltages of 16 V/cm (4 Torr) to 43 V/cm (12 Torr). An increase in resolution from 55 to 80 was observed from 4 to 12 Torr nitrogen drift gas with no significant loss in sensitivity. The choice of drift gas was also shown to influence the degree of ion heating and relative trapping efficiency within the ion funnel. PMID:17512752

  12. EFFECT OF ION B DRIFT DIRECTION ON TURBULENCE FLOW AND FLOW SHEAR

    SciTech Connect

    FENZI,C; McKEE,G.R; BURRELL,K.H; CARLSTROM,T.N; FONCK,R.J; GROEBNER,R.J

    2003-07-01

    The divertor magnetic geometry has a significant effect on the poloidal flow and resulting flow shear of turbulence in the outer region of L-mode tokamak plasmas, as determined via two-dimensional measurements of density fluctuations with Beam Emission Spectroscopy on DIII-D. Plasmas with similar parameters, except that in one case the ion {del}B drift points towards the divertor X-point (lower single-null, LSN), and in the other case, the ion {del}B drift points away from the divertor X-point (upper single-null, USN), are compared. Inside of r/a=0.9, the turbulence characteristics (amplitude, flow direction, correlation lengths) are similar in both cases, while near r/a=0.92, a dramatic reversal of the poloidal flow of turbulence relative to the core flow direction is observed in plasmas with the ion {del}B drift pointing towards the divertor X-point. No such flow reversal is observed in plasmas with the ion {del}B drift pointing away from the divertor X-point. This poloidal flow reversal results in a significantly larger local shear in the poloidal turbulence flow velocity in plasmas with the ion {del}B drift pointing towards the divertor X-point. Additionally, these plasmas locally exhibit significant dispersion, with two distinct and counter-propagating turbulence modes. Likewise, the radial correlation length of the turbulence is reduced in these plasmas, consistent with biorthogonal decomposition measurements of dominant turbulence structures. The naturally occurring turbulence flow shear in these LSN plasmas may facilitate the LH transition that occurs at an input power of roughly one-half to one-third that of corresponding plasmas with the ion {del}B drift pointing away from the X-point.

  13. Hemispheric asymmetry of subauroral ion drifts: Statistical results

    NASA Astrophysics Data System (ADS)

    Zhang, Xiao-Xin; He, Fei; Wang, Wenbin; Chen, Bo

    2015-06-01

    A large database of more than 18,000 subauroral ion drift (SAID) events from DMSP observations from 1987 to 2012 is used to systematically investigate the features of SAID. SAID occurs mostly at ~62/-60 magnetic latitude (MLAT) and ~22:15/22:45 magnetic local time (MLT) for geomagnetically quiet conditions and at ~58/-56 MLAT and ~22:15/22:45 MLT for geomagnetically disturbed conditions in the North Hemisphere (NH)/South Hemisphere (SH), respectively. Significant north-south asymmetries in SAID occurrence, shape, and geomagnetic activity variations are found in this statistical study. The latitudinal width of a SAID is larger in the NH than in the SH. An interesting finding of this work is that the SAID occurrence probability peaks have an ~180 difference in longitude between the two hemispheres in the geographic coordinates for both geomagnetically quiet and disturbed conditions. The SAID width peaks in almost the same geomagnetic meridian zone with a geomagnetic longitude of ~80-120 in both hemispheres. Significant hemispheric asymmetries and spike signatures with sharp dips are found in all the latitudinal profiles of the horizontal velocities of SAIDs. The SAID is highly correlated to geomagnetic activity, indicating that the location and evolution of the SAID might be influenced by global geomagnetic activity, auroral dynamics, and the dynamics of ring currents.

  14. Ion Mobility Spectrometry – Mass Spectrometry Performance Using Electrodynamic Ion Funnels and Elevated Drift Gas Pressures

    SciTech Connect

    Baker, Erin Shammel; Clowers, Brian H.; Li, Fumin; Tang, Keqi; Tolmachev, Aleksey V.; Prior, David C.; Belov, Mikhail E.; Smith, Richard D.

    2007-06-28

    The ability of ion mobility spectrometry coupled with mass spectrometry (IMS-MS) to characterize biological mixtures has been illustrated over the past eight years. However, the challenges posed by the extreme complexity of many biological samples have demonstrated the need for higher resolution IMS-MS measurements. We have developed a higher resolution ESI-IMS-TOF MS by utilizing high pressure electrodynamic ion funnels at both ends of the IMS drift cell and operating the drift cell at an elevated pressure compared to a previous design. The ESI-IMS-TOF MS instrument consists of an ESI source, an hourglass ion funnel used for ion accumulation/injection into an 88 cm drift cell followed by a 10 cm ion funnel and a commercial orthogonal time-of-flight mass spectrometer providing high mass measurement accuracy. It was found that the rear (exit) ion funnel could be effectively operated as an extension of the drift cell when the DC fields were matched, allowing the instrument to have an effective drift region of 98 cm. Two differentially pumped quadrupole regions were used to couple the IMS and TOF MS to focus and minimize the ion transient time between the stages. The resolution of the instrument was evaluated at pressures ranging from 4 to12 Torr and ion mobility drift voltages of 16 V/cm (4 Torr) to 43 V/cm (12 Torr). An increase in resolution from 55 to 80 was observed from 4 to 12 Torr nitrogen drift gas with no loss in sensitivity. Given the increased usage of ion funnels prior to ion mobility separations, additional attention was directed towards the influence of drift gas on the observed ion populations trapped and transmitted using an electrodynamic ion funnel. The choice of drift gas was shown to influence the degree of ion heating and relative trapping efficiency within the ion funnel.

  15. Numerical simulation of drift waves and trapped ion modes

    SciTech Connect

    Kingsbury, O.T.; Waltz, R.E. )

    1994-07-01

    Two-dimensional numerical simulations are used to study the interaction of trapped electron drift waves (DW) and trapped ion modes (TIM). Wave-number ([ital k]) space is divided into long and short wave regions at a poloidal wave number corresponding to the ion bounce frequency. Two field models are used to describe trapped electron drift wave dynamics at short waves and trapped ion mode dynamics for long waves. The standard case has curvature effects and collisionality. The nonlinearity that couples the two regions includes a trapped ion banana width effect analogous to finite Larmor radius (FLR) polarization drift. The principal result of this study is that the TIM do not contribute to the diffusion significantly, regardless of the model for the nonlinear coupling to the DW. This conclusion is supported by a more general four field model that includes pressure dynamics and which allows ion temperature gradient (ITG) driven drift modes. When the collisionality is varied, the diffusion deviates from the [gamma]/[ital k][sup 2][sub [ital x

  16. Asymptotic velocity of one dimensional diffusions with periodic drift.

    PubMed

    Collet, P; Martnez, S

    2008-06-01

    We consider the asymptotic behavior of the solution of one dimensional stochastic differential equations and Langevin equations in periodic backgrounds with zero average. We prove that in several such models, there is generically a non-vanishing asymptotic velocity, despite of the fact that the average of the background is zero. PMID:17960387

  17. Ion composition and drift observations in the nighttime equatorial ionosphere

    NASA Technical Reports Server (NTRS)

    Goldberg, R. A.; Aikin, A. C.; Murthy, B. V. K.

    1974-01-01

    The first in situ measurements of ion composition in the nighttime equatorial E and F region ionospheres (90-300 km) are presented and discussed. These profiles were obtained by two rocket-borne ion mass spectrometers launched from Thumba, India on March 9-10, 1970 at solar zenith angles of 112 deg and 165 deg. Ionosonde data established that the composition was measured at times bounding a period of F region downward drift. During this period the ions O(+) and N(+) were enhanced by one to three orders of magnitude between 220 and 300 km. Below the drift region (200 km), O(+) ceased to be the major ionic constituent, but the concentrations of O(+) and N(+) remained larger than predicted from known radiation sources and loss processes. Here also, both the O2(+) and NO(+) profiles retained nearly the same shape and magnitude throughout the night in agreement with theories assuming scattered UV radiation to be the maintaining source. Light metallic ions including Mg(+), Na(+) and possibly Si(+) were observed to altitude approaching 300 km, while the heavier ions Ca(+) and K(+) were seen in reduced quantity to 200 km. All metal ion profiles exhibited changes which can be ascribed to vertical drifting.

  18. Oblique ion collection in the drift approximation: How magnetized Mach probes really work

    SciTech Connect

    Hutchinson, I. H.

    2008-12-15

    The anisotropic fluid equations governing a frictionless obliquely flowing plasma around an essentially arbitrarily shaped three-dimensional ion-absorbing object in a strong magnetic field are solved analytically in the quasineutral drift approximation, neglecting parallel temperature gradients. The effects of transverse displacements traversing the magnetic presheath are also quantified. It is shown that the parallel collection flux density dependence upon the external Mach number is n{sub {infinity}}c{sub s} exp[-1-(M{sub parallel}{infinity}-M{sub perpendicular}cot {theta})], where {theta} is the angle (in the plane of field and drift velocity) of the object-surface to the magnetic-field and M{sub parallel{infinity}} is the external parallel flow. The perpendicular drift, M{sub perpendicular}, appearing here consists of the external E and B drift plus a weighted sum of the ion and electron diamagnetic drifts that depends upon the total angle of the surface to the magnetic field. It is that somewhat counterintuitive combination that an oblique (transverse) Mach probe experiment measures.

  19. Transient ion-drift-induced capacitance signals in semiconductors

    SciTech Connect

    Heiser, T.; Weber, E.R.

    1998-08-01

    A theoretical model is developed that describes capacitance signals induced by drift of mobile ions in the space charge region of a Schottky diode. Pairing between the diffusing ion and the doping impurities is taken into account. The coupled partial differential equations are resolved numerically and the influence of key parameters on the signal shape is analyzed. Special emphasis is put on those features that enable transient ion-drift- (TID-) induced signals to be distinguished from capacitance transients caused by deep-level carrier emission processes. Relaxation kinetics and reverse bias dependence of the signal shape represent two reliable tools to verify the ion-drift nature of the signals. Methods for extracting quantitative information on both diffusion and pairing properties of the mobile ions are described. The question of whether pairing or diffusion is limiting the process is addressed. The influence of the doping level on the signal time constant is used to evaluate whether or not the diffusion is trap limited. A semiempirical model is described that permits the estimation of diffusion and pairing coefficients without resolving numerically the differential equations. Experiments are performed on interstitial copper in {ital p}-type silicon to test the predictions of the theoretical model. An overall agreement is found between theory and experiments. {copyright} {ital 1998} {ital The American Physical Society}

  20. Drift Compression of an Intense Neutralized Ion Beam

    SciTech Connect

    Roy, P.K.; Yu, S.S.; Henestroza, E.; Anders, A.; Bieniosek, F.M.; Coleman, J.; Eylon, S.; Greenway, W.G.; Leitner, M.; Logan, B.G.; Waldron, W.L.; Welch, D. R.; Thoma, C.; Sefkow, A.B.; Gilson, E.P.; Efthimion, P.C.; Davidson, R.C.

    2005-12-02

    Longitudinal compression of a velocity-tailored, intense neutralized K{sup +} beam at 300 keV, 25 mA has been demonstrated. The compression takes place in a 1-2 m drift section filled with plasma to provide space-charge neutralization. An induction cell produces a head-to-tail velocity ramp that longitudinally compresses the neutralized beam, enhancing the beam peak current by a factor of 50 and producing a pulse duration of about 3 ns. This measurement has been confirmed independently with two different diagnostic systems.

  1. Drift compression of an intense neutralized ion beam

    SciTech Connect

    Roy, P.K.; Yu, S.S.; Henestroza, E.; Anders, A.; Bieniosek, F.M.; Coleman, J.; Eylon, S.; Greenway, W. G.; Leitner, M.; Logan, B.G.; Waldron, W.L.; Welch, D.R.; Thoma, C.; Sefkow, A.B.; Gilson, E.P.; Efthimion, P.C.; Davidson, R.C.

    2005-09-08

    Longitudinal compression of a velocity-tailored, intense neutralized K{sup +} beam at 300 keV, 25 mA has been demonstrated. The compression takes place in a 1-2 m drift section filled with plasma to provide space-charge neutralization. An induction cell produces a head-to-tail velocity ramp that longitudinally compresses the neutralized beam, enhancing the beam peak current by a factor of 50 and producing a pulse duration of about 3 ns. This measurement has been confirmed independently with two different diagnostic systems.

  2. Linear ion source with closed drift and extended acceleration region

    SciTech Connect

    Park, Dong-Hee; Kim, Ji-Hwan; Ermakov, Yury; Choi, Won-Kook

    2008-02-15

    Ion source with closed drift, which is caused by ExB field, and extended acceleration region is discussed. Though conventional circular-type closed drift ion source has advantages of high efficiency of gas ionization and low ion beam energy, there is a limitation in enlarging the beam size. Linear ion source with horse-track shape with 270 mm ceramic channel width is newly designed and tested. Inert gas (Ar) and reactive gas (O{sub 2}) are discharged. Discharge is ignited with voltage of 90 V. Discharge current is proportional to discharge voltage and increases up to 16.3 A in argon and 15.6 A in oxygen at discharge voltage of 320 V. Extracted ion beam current is also proportional to discharge voltage and is saturated after 280 V for both gases. It is measured up to 0.78 mA/cm{sup 2} in argon beam and 0.73 mA/cm{sup 2} in oxygen beam at a distance of 100 mm from the ion source. Argon ion beam shows better space uniformity than oxygen across the beam extraction region.

  3. Ion behavior and interelectrode breakdown voltage of a drift tube

    NASA Astrophysics Data System (ADS)

    Geng, Hao; Zhao, Zhong-Jun; Duan, Yi-Xiang

    2015-05-01

    We experimentally studied ion behavior and interelectrode breakdown voltage. The ion behavior of a drift tube directly influences the detection of ion intensity, and then influences the detection sensitivity of a system. Interelectrode voltage and pressure directly influence the ion behavior. Gas discharge between electrodes influences the adjustments required for interelectrode voltage. The experimental results show: ion intensity increases exponentially with the increment of voltage between drift electrodes; ion intensity decreases exponentially as pressure increases; with the increment of pressure, the breakdown voltage at first decreases, and then increases; ion injection has a significant influence on breakdown voltage, and this influence depends on the pressure and shapes of the electrodes. We explain the results above through assumptions and by mathematical methods. Supported by Financial Support from the National Major Scientific Instruments and Equipment Development Special Funds (2011YQ030113), National Recruitment Program of Global Experts (NRPGE), the Hundred Talents Program of Sichuan Province (HTPSP) and the Startup Funding of Sichuan University for Setting up the Research Center of Analytical Instrumentation

  4. Measurement of the drift velocities of electrons and holes in high-ohmic < 100 > silicon

    NASA Astrophysics Data System (ADS)

    Scharf, C.; Klanner, R.

    2015-11-01

    Measurements of the drift velocities of electrons and holes as functions of electric field and temperature in high-purity n- and p-type silicon with < 100 > lattice orientation are presented. The measurements cover electric field values between 2.5 and 50 kV / cm and temperatures between 233 and 333 K. For both electrons and holes differences of more than 15 % are found between our < 100 > results and the < 111 > drift velocities from literature, which are frequently also used for simulating < 100 > sensors. For electrons, the < 100 > results agree with previous < 100 > measurements; however, for holes differences between 5 and 15% are observed for fields above 10 kV / cm. Combining our results with published data of low-field mobilities, we derive parametrizations of the drift velocities in high-ohmic < 100 > silicon for electrons and holes for fields up to 50 kV / cm, and temperatures between 233 and 333 K. In addition, new parametrizations for the drift velocities of electrons and holes are introduced, which provide somewhat better descriptions of existing data for < 111 > silicon than the standard parametrization.

  5. Global, low-latitude, vertical E B drift velocities inferred from daytime magnetometer observations

    NASA Astrophysics Data System (ADS)

    Anderson, David; Anghel, Adela; Chau, Jorge L.; Yumoto, Kiyohumi

    2006-08-01

    Navigation and communication, Department of Defense and civilian, customers rely on accurate, low-latitude specification of ionospheric parameters, globally, that are not currently realistic on a day-to-day basis. This paper describes, demonstrates, and speculates about the data sets that are required inputs to the operational ionospheric models that will correct these deficiencies. In order to investigate quiet time, vertical E B drift velocities at two different longitude sectors, magnetometer observations were obtained for the period between January 2001 and December 2004 from the magnetometers at Jicamarca (0.8N dip latitude) and Piura (6.8N dip latitude) in Peru and from Davao (1.4S dip latitude) and Muntinlupa (6.3N dip latitude) in the Philippine sector. We choose only geomagnetically "quiet" days, when the 3-hourly Kp value never exceeds a value of 3 over the entire day, and when the daily Ap value is less than 10. These are "binned" into three seasons, December solstice, equinox, and June solstice periods. A neural network trained for the Peruvian sector was applied to each of the days in both the Peruvian and Philippine sectors, providing ?H-inferred vertical E B drift velocities between 0700 and 1700 local time. For each season, the average E B drift velocity curves are compared with the Fejer-Scherliess, climatological E B drift velocity curves in both the Peruvian and Philippine sectors. In the Peruvian sector, the comparisons are excellent, and in the Philippine sector they are very good. We demonstrate that realistic magnetometer-inferred E B drifts can be obtained in the Peruvian sector on a day-to-day basis and speculate that on the basis of the average, quiet day comparisons, realistic E B drifts can be obtained on quiet days in the Philippine sector.

  6. 2-D Drift Velocities from the IMAGE EUV Plasmaspheric Imager

    NASA Technical Reports Server (NTRS)

    Gallagher, D.; Adrian, M.

    2007-01-01

    The IMAGE Mission extreme ultraviolet imager (EUY) observes He+ plasmaspheric ions throughout the inner magnetosphere. Limited by ionizing radiation and viewing close to the Sun, images of the He+ distribution are available every 10 minutes for many hours as the spacecraft passes through apogee in its highly elliptical orbit. As a consistent constituent at about 15%, He+ is an excellent surrogate for monitoring all of the processes that control the dynamics of plasmaspheric plasma. In particular, the motion ofHe+ transverse to the ambient magnetic field is a direct indication of convective electric fields. The analysis of boundary motions has already achieved new insights into the electrodynamic coupling processes taking place between energetic magnetospheric plasmas and the ionosphere. Yet to be fulfilled, however, is the original promise that global EUY images of the plasmasphere might yield two-dimensional pictures of meso-scale to macro-scale electric fields in the inner magnetosphere. This work details the technique and initial application of an IMAGE EUY analysis that appears capable of following thermal plasma motion on a global basis.

  7. NUCLEAR PHYSICS: Measurement of Electron-Drift Velocity in Ar+CH4 Mixtures Using Double-Grid Method

    NASA Astrophysics Data System (ADS)

    Zhang, Jia-Guo; Zhang, Guo-Hui; Chen, Jin-Xiang

    2009-11-01

    Based on analyzing the induced signals from the double-grids of an ionization chamber, the electron-drift time between the two grids is determined and the electron-drift velocity is derived. A waveform digitizer is employed to record pulses from the two grids of the ionization chamber. The electron-drift velocity is measured as a function of the reduced electric field E/p for eight different ratios of Ar+CH4 mixtures. By analyzing the experimental data of this study, self-consistency of experimental data is achieved, and formulae for calculating electron-drift velocity in any ratio of Ar+CH4 mixtures are obtained.

  8. Gyrokinetic particle simulation of ion temperature gradient drift instabilities

    SciTech Connect

    Lee, W.W.; Tang, W.M.

    1987-04-01

    Ion temperature gradient drift instabilities have been investigated using gyrokinetic particle simulation techniques for the purpose of identifying the mechanisms responsible for their nonlinear saturation as well as the associated anomalous transport. For simplicity, the simulation has been carried out in a shear-free slab geometry, where the background pressure gradient is held fixed in time to represent quasistatic profiles typical of tokamak discharges. It is found that the nonlinearly generated zero-frequency responses for the ion parallel momentum and pressure are the dominant mechanisms giving rise to saturation. This is supported by the excellent agreement between the simulation results and those obtained from mode coupling calculations.

  9. Augmenting Ion Trap Mass Spectrometers Using a Frequency Modulated Drift Tube Ion Mobility Spectrometer.

    PubMed

    Morrison, Kelsey A; Siems, William F; Clowers, Brian H

    2016-03-15

    Historically, high pressure ion mobility drift tubes have suffered from low ion duty cycles and this problem is magnified when such instrumentation is coupled with ion trap mass spectrometers. To significantly alleviate these issues, we outline the result from coupling an atmospheric pressure, dual-gate drift tube ion mobility spectrometer (IMS) to a linear ion trap mass spectrometer (LIT-MS) via modulation of the ion beam with a linear frequency chirp. The time-domain ion current, once Fourier transformed, reveals a standard ion mobility drift spectrum that corresponds to the standard mode of mobility analysis. By multiplexing the ion beam, it is possible to successfully obtain drift time spectra for an assortment of simple peptide and protein mixtures using an LIT-MS while showing improved signal intensity versus the more common signal averaging technique. Explored here are the effects of maximum injection time, solution concentration, total experiment time, and frequency swept on signal-to-noise ratios (SNRs) and resolving power. Increased inject time, concentration, and experiment time all generally led to an improvement in SNR, while a greater frequency swept increases the resolving power at the expense of SNR. Overall, chirp multiplexing of a dual-gate IMS system coupled to an LIT-MS improves ion transmission, lowers analyte detection limits, and improves spectral quality. PMID:26854901

  10. Measuring drift velocity and electric field in mirror machine by fast photography

    NASA Astrophysics Data System (ADS)

    Be'ery, I.; Seemann, O.; Fruchtman, A.; Fisher, A.; Nemirovsky, J.

    2013-02-01

    The flute instability in mirror machines is driven by spatial charge accumulation and the resulting E B plasma drift. On the other hand, E B drift due to external electrodes or coils can be used as a stabilizing feedback mechanism. Fast photography is used to visualize Hydrogen plasma in a small mirror machine and infer the plasma drift and the internal electric field distribution. Using incompressible flow and monotonic decay assumptions we obtain components of the velocity field from the temporal evolution of the plasma cross section. The electric field perpendicular to the density gradient is then deduced from E=-V B. With this technique we analyzed the electric field of flute perturbations and the field induced by electrodes immersed in the plasma.

  11. Measuring drift velocity and electric field in mirror machine by fast photography

    NASA Astrophysics Data System (ADS)

    Be'Ery, Ilan; Seemann, Omri; Fruchtman, Amnon; Fisher, Amnon; Ron, Amiram

    2012-10-01

    The flute instability in mirror machines is driven by spatial charge accumulation and the resulting ExB plasma drift. ExB drift due to external electrodes can be used as a stabilizing feedback mechanism. In order to measure the plasma drift and the internal electric field distribution we used fast photography to visualize Hydrogen plasma in a small mirror machine. We use incompressible flow and monotonic decay assumptions to deduce the velocity field from the evolution of the plasma cross section. The electric field perpendicular to the density gradient is then deduced from E=-VxB. Using this technique we measured the electric field of the flute instability and the field induced by electrodes immersed in the plasma.

  12. Estimating daytime vertical ExB drift velocities from equatorial magnetometer observations

    NASA Astrophysics Data System (ADS)

    Anderson, D.; Anghel, A.; Chau, J.; Veliz, O.; Richmond, A.; Maute, A.

    2003-04-01

    The daytime equatorial electrojet is a narrow band of enhanced eastward current flowing in the 100 to 120 km altitude region within +/- 2 degrees latitude of the dip equator. The strength of the electrojet varies considerably from day-to-day and has its origin in the Sq current dynamo mechanism and the penetration of electric fields from high latitudes. A unique way of determining the daytime strength of the electrojet is to observe the difference in the magnitudes of the Horizontal (H) component between a magnetometer placed directly on the magnetic equator and one displaced 6 to 9 degrees away. The difference between these measured H values provides a direct measure of the daytime electrojet current, and in turn, the magnitude of the vertical ExB drift velocity in the ionospheric F region. This paper discusses a recent study that has quantitatively established the seasonal relationships between the vertical daytime ExB drift velocity in the ionospheric F region and the daytime strength of the equatorial electrojet in the South American (west coast) longitude sector. Magnetometer H component observations from Jicamarca (0.8 N. dip lat.) and Piura (6.8 N. dip lat.) in Peru and daytime, vertical ExB drift velocities measured by the Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere (JULIA) radar have been used to establish these relationships. The magnetometer observations and the JULIA 150 km echo drift measurements were obtained for the period between August, 2001 and September, 2002. Plotting DH vs ExB drift values on a day-to-day basis yields a linear, least-squares straight line whose slope changes systematically with season. For days within each season, the slope is often the same but the "off-sets" vary day-to-day. The implications and theoretical basis for this seasonal and daily variability will be discussed.

  13. Coupled ion acoustic and drift waves in magnetized superthermal electron-positron-ion plasmas

    SciTech Connect

    Adnan, Muhammad; Qamar, Anisa; Mahmood, S.

    2014-09-15

    Linear and nonlinear coupled drift-ion acoustic waves are investigated in a nonuniform magnetoplasma having kappa distributed electrons and positrons. In the linear regime, the role of kappa distribution and positron content on the dispersion relation has been highlighted; it is found that strong superthermality (low value of κ) and addition of positrons lowers the phase velocity via decreasing the fundamental scalelengths of the plasmas. In the nonlinear regime, first, coherent nonlinear structure in the form of dipoles and monopoles are obtained and the boundary conditions (boundedness) in the context of superthermality and positron concentrations are discussed. Second, in case of scalar nonlinearity, a Korteweg–de Vries-type equation is obtained, which admit solitary wave solution. It is found that both compressive and rarefactive solitons are formed in the present model. The present work may be useful to understand the low frequency electrostatic modes in inhomogeneous electron positron ion plasmas, which exist in astrophysical plasma situations such as those found in the pulsar magnetosphere.

  14. Optimum drift velocity for single molecule fluorescence bursts in micro/nano-fluidic channels

    NASA Astrophysics Data System (ADS)

    Kish, Lazar L.; Kameoka, Jun; Granqvist, Claes G.; Kish, Laszlo B.

    2012-07-01

    Photonic burst histograms can be used to identify single protein molecules in micro/nano-fluidic channels provided the width of the histogram is narrow. Photonic shot noise and residence time fluctuations, caused by longitudinal diffusion, are the major sources of the histogram width. This paper is a sequel to an earlier one of ours [L. L. Kish et al., Appl. Phys. Lett. 99, 143121 (2011)] and demonstrates that, for a given diffusion coefficient, an increase of the drift velocity enhances the relative shot noise and decreases the relative residence time fluctuations. This leads to an optimum drift velocity that minimizes the histogram width and maximizes the ability to identify single molecules, which is an important result for applications.

  15. Higher Regularity of Hlder Continuous Solutions of Parabolic Equations with Singular Drift Velocities

    NASA Astrophysics Data System (ADS)

    Friedlander, Susan; Vicol, Vlad

    2012-06-01

    Motivated by an equation arising in magnetohydrodynamics, we prove that Hlder continuous weak solutions of a nonlinear parabolic equation with singular drift velocity are classical solutions. The result is proved using the space-time Besov spaces introduced by Chemin and Lerner (J Differ Equ 121(2):314-328, 1995), combined with energy estimates, without any minimality assumption on the Hlder exponent of the weak solutions.

  16. The effect of ion drifts on the properties of the tokamak scrape-off plasma

    SciTech Connect

    Petravic, M.; Kuo-Petravic, G.

    1988-09-01

    A plasma fluid model which takes into account ion drifts has been constructed and applied to the scrape-off layer of a tokamak with a poloidal divertor. This model predicts near-sonic toroidal velocities and large poloidal flows in most of the scrapeoff together with steep gradients in the pressure and electrostatic potential along the magnetic field near the X-point, contrary to the predictions of the standard model. The potential step at X-point should reduce parallel heat transport and could act as an H-mode trigger. 12 refs., 4 figs.

  17. Precision measurement of the carrier drift velocities in langle100rangle silicon

    NASA Astrophysics Data System (ADS)

    Scharf, C.; Klanner, R.

    2015-11-01

    Measurements of the drift velocities of electrons and holes as functions of electric field strength and temperature in high-purity n- and p-type silicon with langle100rangle crystal orientation are presented. The measurements cover electric field strengths between 2.4 and 50 kV/cm and temperatures between 233 and 333 K. Two methods have been used for extracting the drift velocities from current transient measurements: a time-of-flight (tof) method and fits of simulated transients to the measured transients, with the parameters describing the field and temperature dependence of the electron and hole mobilities as free parameters. A new mobility parametrization, which also provides a better description of existing data than previous ones, allowed an extension of the classical tof method to the situation of non-uniform field strengths. For the fit method, the use of the convolution theorem of Fourier transforms enabled us to precisely determine the electronics transfer function of the complete set-up, including the sensor properties. The agreement between the tof and the fit method is about 1%, which corresponds to a time-of-flight uncertainty of 30 ps for a pad diode of 200μ m thickness at the highest voltages. Combining our results with published data of low-field mobilities, we derive parameterizations of the drift velocities in high-ohmic langle100rangle silicon for electrons and holes for field strengths between 0 and 50 kV/cm and temperatures between 233 and 333 K.

  18. East-west ion drifts at mid-latitudes observed by Dynamics Explorer 2

    SciTech Connect

    Heelis, R.A.; Coley, W.R. )

    1992-12-01

    Zonal ion drifts measured from the polar orbiting DE 2 spacecraft are examined to determine the effects of dynamo electric fields and penetration of high latitude electric fields at middle latitudes. Construction of a local time distribution from satellite data results in a mixture of local time and season as well as a range of magnetic activity encompassing Kp [le] 2 and Kp [ge] 3. Thus some combination of magnetospheric effects, expected to dominate during disturbed times, are seen during both quiet and disturbed times and solar tidal influences are most easily observed during quiet times. During quiet times, at invariant latitudes near 25[degrees], the solar diurnal tide dominates the local time distribution of the ion drift. At latitudes above 50[degrees] a diurnal component of comparable magnitude is also present, but its magnetospheric origin produces a shift in phase of almost 180[degrees] from the lower latitude diurnal tide. In the intervening region, between 20[degrees] and 50[degrees] invariant latitude, semidurnal and terdiurnal components in the local time distribution of the drift velocity are also seen. These components are generally larger than those seen by ground based radars during quiet times and may be attributable in part to a difference in solar activity and in part to a combination of the solar tides and magnetospheric penetration fields.

  19. Impact of ion diamagnetic drift on ideal ballooning mode stability in rotating tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Aiba, N.

    2016-04-01

    Drift magnetohydrodynamic (MHD) equations have been derived in order to investigate the ion diamagnetic drift effect on the stability to ideal MHD modes in rotating plasmas. These drift MHD equations have been simplified with the Frieman-Rotenberg formalism under the incompressible assumption, and a new code, MINERVA-DI, has been developed to solve the derived extended Frieman-Rotenberg equation. Benchmark results of the MINERVA-DI code show good agreements with the analytic theory discussing the stability to an internal kink mode and that to a ballooning mode in static plasmas. The stability analyses of the ballooning mode with respect to toroidal rotation with the ion diamagnetic drift effect have been performed using MINERVA-DI. The stabilizing effect by the ion diamagnetic drift is found to be negligible when the rotation frequency is large compared to the ion diamagnetic drift frequency. The direction of plasma rotation affects the ballooning mode stability when the ion diamagnetic drift effect is taken into account. It is identified that there are two physics mechanisms responsible for the dependence of MHD stability on the rotation direction. One is the correction of the dynamic pressure effect on MHD stability by the ion diamagnetic drift, and the other is the change of the MHD eigenmode structure by the combined effect of plasma rotation and ion diamagnetic drift.

  20. Drift velocity of a Smoluchowski gas: A numerical demonstration of the fluctuation-dissipation theorem

    NASA Astrophysics Data System (ADS)

    Verbeek, Martijn G.

    2010-08-01

    This Brief Report shows that the Smoluchowski thermostat, a stochastic boundary condition used to mimic a diffusive gas-wall collision, produces the correct stationary nonequilibrium states. The stationary states are generated by placing an ideal gas coupled to a Smoluchowski thermostat in a constant external field. It is shown by simple numerical simulations that the resulting drift velocity is compatible with the definition of the gas particle mobility, satisfying the well-known fluctuation-dissipation theorem. As an interesting application, it is shown that species that are chemically identical but differ in surface momentum accommodation can be separated effectively in the Knudsen regime.

  1. Measurements of Electron Drift Velocity in Isobutane using the Pulsed Townsend Technique

    NASA Astrophysics Data System (ADS)

    Vivaldini, Tlio C.; Lima, Iara B.; Gonalves, Josemary A. C.; Botelho, Suzana; Ridenti, Marco A.; Fonte, Paulo; Mangiarotti, Alessio; Pascholati, Paulo R.; Tobias, Carmen C. Bueno

    2011-08-01

    In the present work we report on the preliminary results related to the dependence of the electron drift velocity for isobutane as function of the reduced electric field E/N in the range of 190 Td up to 211 Td. The employed method is based on the Pulsed Townsend technique. In our configuration the anode is of a high resistivity (2.1010???.m) glass, while the cathode is made of aluminum. In order to validate the technique, the initial measurements were carried out for nitrogen, which is a gas widely studied.

  2. A study of vacuum arc ion velocities using a linear set of probes

    SciTech Connect

    Hohenbild, Stefan; Grubel, Christoph; Yushkov, Georgy Yu.; Oks, Efim M.; Anders, Andre

    2008-07-15

    The most likely velocity of ions moving away from vacuum arc cathode spots was measured using a set of probes along the path of plasma expansion. The goal was to determine how much, if any, change of the ion drift velocity occurs in the expanded plasma. The arc discharge current was perturbed to create plasma density markers whose travel is picked up by the set of probes. It was found that the perturbation with current oscillations did not result in consistent data because ion current maxima and minima are not only determined by the plasma production but by the transients of the arc pulse and by the asymmetry of the ion velocity distribution function. Perturbation with a short current spike was more conclusive. The ion velocity was measured to be slightly reduced with increasing distance from the cathode, which can be explained by collisions of ions with the background of neutrals. The ion velocity was increased when the arc current was increased, which correlated with enhanced arc voltage and power dissipation. The ion velocity could be enhanced when the plasma was produced in a non-uniform magnetic field.

  3. Self-consistent analysis of high drift velocity measurements with the STARE system

    NASA Technical Reports Server (NTRS)

    Reinleitner, L. A.; Nielsen, E.

    1985-01-01

    The use of the STARE and SABRE coherent radar systems as valuable tools for geophysical research has been enhanced by a new technique called the Superimposed-Grid-Point method. This method permits an analysis of E-layer plasma irregularity phase velocity versus flow angle utilizing only STARE or SABRE data. As previous work with STARE has indicated, this analysis has clearly shown that the cosine law assumption breaks down for velocities near and exceeding the local ion acoustic velocities. Use of this method is improving understanding of naturally-occurring plasma irregularities in the E-layer.

  4. Sudden appearance of sub-keV structured ions in the inner magnetosphere within one hour: drift simulation

    NASA Astrophysics Data System (ADS)

    Yamauchi, Masatoshi; Ebihara, Yusuke; Dandouras, Iannis; Nilsson, Hans

    2014-05-01

    Energy-latitude dispersed structured sub-keV ions in the inner magnetosphere drifts very slowly in the noon-to-afternoon sectors because the eastward corotation and the westward magnetic drift balances to each other there. However, majority of Cluster ion observation by the Cluster Ion Spectrometry (CIS) COmposition DIstribution Function (CODIF) instrument during 2001-2006 showed significant development or intensification (by more than factor of 3) within 1-2 h in that sector during the Cluster perigee traversals that quickly scans latitudinal structure at a fixed local time (Yamauchi et al., 2013). The frequent observations of significant inbound-outbound differences in the wedge-like dispersed ions by Cluster indicates either new injections or high eastward drift velocity even in the afternoon sector. To examine the former possibility, i.e., whether such sudden appearances in the dayside can be explained by the drift motion of ions that are formed during substorm-related injections, we numerically simulated two such examples, one at noon (8 September 2002) and the other in the afternoon (9 July 2001), based on the same ion drift simulation model that has successfully reproduced the ion pattern of an inbound-outbound symmetric event at 5 MLT observed by the Cluster CIS/CODIF instrument. The model uses backward phase-space mapping to a boundary at the nightside 8 Earth radii and forward numerical simulation using re-constructed distribution function at that boundary. For both examples, the ion drift model with finite duration (limited to 1-2 hours) of proton source in the nightside can explain the observed large inbound-outbound differences in the sub-keV proton population without any new sources. Ion drift motion is thus able to cause rapid changes of complicated ion populations, at remote places from the source long time after the substorm activities, although this result does not eliminate the possibility of having independent ionospheric sources. References: Yamauchi, M. et al.: Cluster observation of few-hour-scale evolution of structured plasma in the inner magnetosphere, Ann. Geophys., 31, 1569-1578, doi:10.5194/angeo-31-1569-2013, 2013.

  5. Advanced numerical studies of the neutralized drift compression of intense ion beam pulses

    NASA Astrophysics Data System (ADS)

    Sefkow, Adam B.; Davidson, Ronald C.

    2007-10-01

    Longitudinal bunch compression of intense ion beams for warm dense matter and heavy ion fusion applications occurs by imposing an axial velocity tilt onto an ion beam across the acceleration gap of a linear induction accelerator, and subsequently allowing the beam to drift through plasma in order to neutralize its space-charge and current as the pulse compresses. The detailed physics and implications of acceleration gap effects and focusing aberration on optimum longitudinal compression are quantitatively reviewed using particle-in-cell simulations, showing their dependence on many system parameters. Finite-size gap effects are shown to result in compression reduction, due to an increase in the effective longitudinal temperature imparted to the beam, and a decrease in intended fractional tilt. Sensitivity of the focal plane quality to initial longitudinal beam temperature is explored, where slower particles are shown to experience increased levels of focusing aberration compared to faster particles. A plateau effect in axial compression is shown to occur for larger initial pulse lengths, where the increases in focusing aberration over the longer drift lengths involved dominate the increases in relative compression, indicating a trade-off between current compression and pulse duration. The dependence on intended fractional tilt is also discussed and agrees well with theory. A balance between longer initial pulse lengths and larger tilts is suggested, since both increase the current compression, but have opposite effects on the final pulse length, drift length, and amount of longitudinal focusing aberration. Quantitative examples are outlined that explore the sensitive dependence of compression on the initial kinetic energy and thermal distribution of the beam particles. Simultaneous transverse and longitudinal current density compression can be achieved in the laboratory using a strong final-focus solenoid, and simulations addressing the effects of focusing aberration in both directions are presented.

  6. Electrostatic ion cyclotron velocity shear instability

    SciTech Connect

    Lemons, D.S.; Winske, D.; Gary, S.P. )

    1992-12-01

    An electrostatic ion cyclotron instability driven by sheared velocity flow perpendicular to a uniform magnetic field is investigated in the local approximation. The dispersion equation, which includes all kinetic effects and involves only one important parameter, is cast in the form of Gordeyev integrals and solved numerically. The instability occurs roughly at multiples of the ion cyclotron frequency (but modified by the shear) with the growth rate of the individual harmonics overlapping in wavenumber. At small values of the shear parameter, the instability exists in two branches, one at long wavelength, [kappa][rho][sub i] [approximately] 0.5, and one at short wavelength, [kappa][rho][sub i] > 1.5 ([kappa][rho][sub i] is the wavenumber normalized to the ion gyroradius). At larger values of the shear parameter only the longer wavelength branch persists. The growth rate of the long wavelength mode, maximized over wavenumber and frequency, increases monotonically with the shear parameter. Properties of the instability are compared to those of Ganguli et al. obtained in the nonlocal limit.

  7. Ion mobility mass spectrometry of peptide, protein, and protein complex ions using a radio-frequency confining drift cell.

    PubMed

    Allen, Samuel J; Giles, Kevin; Gilbert, Tony; Bush, Matthew F

    2016-02-01

    Ion mobility mass spectrometry experiments enable the characterization of mass, assembly, and shape of biological molecules and assemblies. Here, a new radio-frequency confining drift cell is characterized and used to measure the mobilities of peptide, protein, and protein complex ions. The new drift cell replaced the traveling-wave ion mobility cell in a Waters Synapt G2 HDMS. Methods for operating the drift cell and determining collision cross section values using this experimental set up are presented within the context of the original instrument control software. Collision cross sections for 349 cations and anions are reported, 155 of which are for ions that have not been characterized previously using ion mobility. The values for the remaining ions are similar to those determined using a previous radio-frequency confining drift cell and drift tubes without radial confinement. Using this device under 2 Torr of helium gas and an optimized drift voltage, denatured and native-like ions exhibited average apparent resolving powers of 14.2 and 16.5, respectively. For ions with high mobility, which are also low in mass, the apparent resolving power is limited by contributions from ion gating. In contrast, the arrival-time distributions of low-mobility, native-like ions are not well explained using only contributions from ion gating and diffusion. For those species, the widths of arrival-time distributions are most consistent with the presence of multiple structures in the gas phase. PMID:26739109

  8. Dayside/nightside asymmetry of ion densities and velocities in Saturn's inner magnetosphere

    NASA Astrophysics Data System (ADS)

    Holmberg, M. K. G.; Wahlund, J.-E.; Morooka, M. W.

    2014-06-01

    We present Radio and Plasma Wave Science Langmuir probe measurements from 129 Cassini orbits, which show a day/night asymmetry in both ion density and ion velocity in the radial region 4-6 RS (1 RS = 60,268 km) from the center of Saturn. The ion densities ni vary from an average of 35 cm-3 around noon up to 70 cm-3 around midnight. The ion velocities vi,? vary from 28-32 km/s at the lowest dayside values to 36-40 km/s at the highest nightside values. The day/night asymmetry is suggested to be due to the radiation pressure force acting on negatively charged nanometer-sized dust of the E ring. This force will introduce an extra grain and ion drift component equivalent to the force of an additional electric field of 0.1-2 mV/m for 10-50 nm sized grains.

  9. Using different drift gases to change separation factors (alpha) in ion mobility spectrometry

    PubMed

    Asbury; Hill

    2000-02-01

    The use of different drift gases to alter separation factors (alpha) in ion mobility spectrometry has been demonstrated. The mobility of a series of low molecular weight compounds and three small peptides was determined in four different drift gases. The drift gases chosen were helium, argon, nitrogen, and carbon dioxide. These drift gases provide a range of polarizabilities and molecular weights. In all instances, the compounds showed the greatest mobility in helium and the lowest mobility in carbon dioxide; however the percentage change of mobility for each compound was different, effectively changing the alpha value. The alpha value changes were primarily due to differences in drift gas polarizability but were also influenced by the mass of the drift gas. In addition, gas-phase ion radii were calculated in each of the different drift gases. These radii were then plotted against drift gas polarizability producing linear plots with r2 values greater than 0.99. The intercept of these plots provides the gas-phase radius of an ion in a nonpolarizing environment, whereas the slope is indicative of the magnitude of the ion's mobility change related to polarizability. It therefore, should be possible to separate any two compounds that have different slopes with the appropriate drift gas. PMID:10695145

  10. Rapidly changing distribution of velocity and suspended materials under the drifting Arctic sea ice

    NASA Astrophysics Data System (ADS)

    Ha, Ho Kyung; Im, Jungho; Kim, Yong Hoon; Yae Son, Eun; Lee, Sanggyun

    2015-04-01

    In two summer seasons of 2011 and 2014, the short-term (1-4 days) ice-camp study has been conducted on the drifting Arctic sea ice. In particular, in 2014, the international collaboration with the Marginal Ice Zone program (sponsored by Office of Naval Research) has been integrated. The mooring package comprises the acoustic Doppler velocity profiler, holographic imaging camera, and conductivity-temperature-depth profiler, which are used to understand the dynamic behavior of sea ice and spatial-temporal variation of mixing layer (ML) and suspended particulate matters under the sea ice. Mooring data clearly shows the mixing and entrainment pattern in the upper ML in the marginal ice zone. When ice floes drift toward the pack ice, the upward entrainment from the seasonal pycnocline to sea ice-water boundary was induced by shear across ML and seasonal pycnocline. The entrainment speed was in the range of 0.25-2 m/hr, which matches well with thickening and thinning rate of ML during the near-inertial period (~12 hr). When ice floes drift toward the open ocean, the turbulent wakes at the advancing edge of ice were combined with the entrainment caused by near-inertial motion, which results in a complex mixing pattern of both upward and downward fluxes in the ML. Also, the acoustic backscatter observed by the acoustic Doppler current profiler and beam attenuation from transmissometer revealed the increased concentration of suspended particulate materials in the ML, which can be direct evidence visualizing the mixing pattern. Results suggest that the mixing and entrainment found in our study sustain particulate matters in suspension within the upper ML for a few months.

  11. The effect of the time interval used to calculate mean wind velocity on the calculated drift potential, relative drift potential, and resultant drift direction for sands from three deserts in northern China

    NASA Astrophysics Data System (ADS)

    Zhang, Zhengcai; Dong, Zhibao; Zhao, Aiguo

    2016-01-01

    Wind is the power behind many erosion processes and is responsible for many of the characteristics of arid zone geomorphology. Wind velocity is a key factor in determining the potential sand transport, but the nature of the wind velocity data can strongly affect assessments of the risk of blowing sand. In this study, we obtained real-time wind velocity data in a region of the Tengger Desert with shifting sands, in the Badain Jaran Desert, and in the Madoi desertification land, with the data obtained at 1-min intervals, and used the data to determine the influence of how the wind velocity was calculated (mean versus mid-point values and the averaging time used to calculate these values) on sand drift potential. In the three regions, for both the mean and the mid-point wind velocities, the estimated drift potential decreased with increasing averaging time. The relationships between velocities calculated using the different averaging time intervals and the value calculated using a 1-min interval could be expressed as linear functions. The drift potential calculated using the mid-point wind velocity was larger than that calculated using the mean wind velocity.

  12. Magnetohydrodynamic dynamo in reversed field pinch plasmas: Electrostatic drift nature of the dynamo velocity field

    SciTech Connect

    Cappello, S.; Bonfiglio, D.; Escande, D.F.

    2006-05-15

    Within the framework of magnetohydrodynamic (MHD) numerical modeling, the reversed field pinch (RFP) has been found to develop turbulent or laminar regimes switching from the former to the latter in a continuous way when the strength of dissipative forces increases. The laminar solution corresponds to a simple global helical deformation of the current channel and is associated with an electrostatic dynamo field. The related electrostatic drift yields the main component of the dynamo velocity field. While quite natural in the stationary helical state, this analysis is shown to extend also to the dynamic turbulent regime for an Ohmic RFP. The continuity of the transition between the two regimes suggests that the simple helical symmetric solution can provide a fruitful intuitive description of the RFP dynamo in general. Many of the MHD predictions are in good agreement with experimental findings.

  13. Electron drift velocities in He and water mixtures: Measurements and an assessment of the water vapour cross-section sets

    NASA Astrophysics Data System (ADS)

    de Urquijo, J.; Basurto, E.; Jurez, A. M.; Ness, K. F.; Robson, R. E.; Brunger, M. J.; White, R. D.

    2014-07-01

    The drift velocity of electrons in mixtures of gaseous water and helium is measured over the range of reduced electric fields 0.1-300 Td using a pulsed-Townsend technique. Admixtures of 1% and 2% water to helium are found to produce negative differential conductivity (NDC), despite NDC being absent from the pure gases. The measured drift velocities are used as a further discriminative assessment on the accuracy and completeness of a recently proposed set of electron-water vapour cross-sections [K. F. Ness, R. E. Robson, M. J. Brunger, and R. D. White, J. Chem. Phys. 136, 024318 (2012)]. A refinement of the momentum transfer cross-section for electron-water vapour scattering is presented, which ensures self-consistency with the measured drift velocities in mixtures with helium to within approximately 5% over the range of reduced fields considered.

  14. Electron drift velocities in He and water mixtures: measurements and an assessment of the water vapour cross-section sets.

    PubMed

    de Urquijo, J; Basurto, E; Jurez, A M; Ness, K F; Robson, R E; Brunger, M J; White, R D

    2014-07-01

    The drift velocity of electrons in mixtures of gaseous water and helium is measured over the range of reduced electric fields 0.1-300 Td using a pulsed-Townsend technique. Admixtures of 1% and 2% water to helium are found to produce negative differential conductivity (NDC), despite NDC being absent from the pure gases. The measured drift velocities are used as a further discriminative assessment on the accuracy and completeness of a recently proposed set of electron-water vapour cross-sections [K. F. Ness, R. E. Robson, M. J. Brunger, and R. D. White, J. Chem. Phys. 136, 024318 (2012)]. A refinement of the momentum transfer cross-section for electron-water vapour scattering is presented, which ensures self-consistency with the measured drift velocities in mixtures with helium to within approximately 5% over the range of reduced fields considered. PMID:25005290

  15. Electron drift velocities in He and water mixtures: Measurements and an assessment of the water vapour cross-section sets

    SciTech Connect

    Urquijo, J. de; Juárez, A. M.; Basurto, E.; Ness, K. F.; Robson, R. E.; White, R. D.; Brunger, M. J.

    2014-07-07

    The drift velocity of electrons in mixtures of gaseous water and helium is measured over the range of reduced electric fields 0.1–300 Td using a pulsed-Townsend technique. Admixtures of 1% and 2% water to helium are found to produce negative differential conductivity (NDC), despite NDC being absent from the pure gases. The measured drift velocities are used as a further discriminative assessment on the accuracy and completeness of a recently proposed set of electron-water vapour cross-sections [K. F. Ness, R. E. Robson, M. J. Brunger, and R. D. White, J. Chem. Phys. 136, 024318 (2012)]. A refinement of the momentum transfer cross-section for electron-water vapour scattering is presented, which ensures self-consistency with the measured drift velocities in mixtures with helium to within approximately 5% over the range of reduced fields considered.

  16. The Influence of Drift Gas Composition on the Separation Mechanism in Traveling Wave Ion Mobility Spectrometry: Insight from Electrodynamic Simulations.

    PubMed

    May, Jody C; McLean, John A

    2003-06-01

    The influence of three different drift gases (helium, nitrogen, and argon) on the separation mechanism in traveling wave ion mobility spectrometry is explored through ion trajectory simulations which include considerations for ion diffusion based on kinetic theory and the electrodynamic traveling wave potential. The model developed for this work is an accurate depiction of a second-generation commercial traveling wave instrument. Three ion systems (cocaine, MDMA, and amphetamine) whose reduced mobility values have previously been measured in different drift gases are represented in the simulation model. The simulation results presented here provide a fundamental understanding of the separation mechanism in traveling wave, which is characterized by three regions of ion motion: (1) ions surfing on a single wave, (2) ions exhibiting intermittent roll-over onto subsequent waves, and (3) ions experiencing a steady state roll-over which repeats every few wave cycles. These regions of ion motion are accessed through changes in the gas pressure, wave amplitude, and wave velocity. Resolving power values extracted from simulated arrival times suggest that momentum transfer in helium gas is generally insufficient to access regions (2) and (3) where ion mobility separations occur. Ion mobility separations by traveling wave are predicted to be effectual for both nitrogen and argon, with slightly lower resolving power values observed for argon as a result of band-broadening due to collisional scattering. For the simulation conditions studied here, the resolving power in traveling wave plateaus between regions (2) and (3), with further increases in wave velocity contributing only minor improvements in separations. PMID:23888124

  17. Ion Mobility Drift Spectrometer (IMDS) as a flight analytical instrument technique

    NASA Technical Reports Server (NTRS)

    Kojiro, D. R.; Carle, G. C.

    1986-01-01

    A detailed knowledge of the history and abundances of the biogenic elements and their compounds throughout the solar system can provide the exobiologists with a basis for understanding the conditions necessary for chemical evolution and the origin of life. The Ion Mobility Drift Spectrometer is an ion molecule reactor coupled with an ion drift spectrometer. Sample molecules are ionized to form product ions in the reactant region. An electric field moves the ions through a drift region against the flow of a drift gas where they are separated according to their size and structure producing an ion mobility spectrum. These spectra provide the IMDS with virtually universal sample identification capability. To conform to the rigid limits of weight, volume and consumables placed on flight instrumentation, several aspects of the IMDS must be studied and redesigned for flight use. In addition to miniaturization of the instrument, a reduction in the high flow rates used for the drift gas is an obvious necessary consideration. The effect of drastically reduced drift flow rates on IMDS spectra was investigated by lowering flow rates from 500ml/min to 50ml/min. Changes in peak shape, drift time and total spectra were studied at each flow rate.

  18. Designing Neutralized Drift Compression for Focusing of Intense Ion Beam Pulses in a Background Plasma

    SciTech Connect

    Kaganovich, I.D.; Davidson, R.C.; Dorf, M.; Startsev, E.A.; Barnard, J.J.; Friedman, A.; Lee, E.P.; Lidia, S.M.; Logan, B.G.; Roy, P.K.; Seidl, P.A.; Welch, D.R.; Sefkow, A.B.

    2009-04-28

    Neutralized drift compression offers an effective method for particle beam focusing and current amplification. In neutralized drift compression, a linear radial and longitudinal velocity drift is applied to a beam pulse, so that the beam pulse compresses as it drifts in the drift-compression section. The beam intensity can increase more than a factor of 100 in both the radial and longitudinal directions, resulting in more than 10,000 times increase in the beam number density during this process. The self-electric and self-magnetic fields can prevent tight ballistic focusing and have to be neutralized by supplying neutralizing electrons. This paper presents a survey of the present theoretical understanding of the drift compression process and plasma neutralization of intense particle beams. The optimal configuration of focusing and neutralizing elements is discussed in this paper.

  19. Coupled dispersive drift acoustic modes in inhomogeneous dusty plasmas with different nonthermal distributions for electrons and ions

    NASA Astrophysics Data System (ADS)

    Masood, W.; Ahmad, Ali

    2012-08-01

    Linear dispersion characteristics of the coupled drift acoustic modes are investigated in inhomogeneous dusty magnetoplasmas both when the dust is considered immobile and when the dust dynamics is taken into account in the presence of nonthermal population of electrons and ions. In this regard, Cairns and Kappa distributed electrons and ions are considered. It is found that the nonthermal distributions affect the phase velocities and the fundamental scalelengths of the plasma. It is found that for both the ion and dust dynamics driven waves, the phase velocities are highest for Cairns, intermediate for Kappa, whereas they are minimum for the Maxwellian distributed electrons. The work presented here may be useful to understand the low frequency electrostatic modes in inhomogeneous dusty plasmas such as those found in planetary environments.

  20. Evaluation of drift gas selection in complex sample analyses using a high performance drift tube ion mobility-QTOF mass spectrometer.

    PubMed

    Kurulugama, Ruwan T; Darland, Ed; Kuhlmann, Frank; Stafford, George; Fjeldsted, John

    2015-10-21

    A recently developed uniform-field high resolution ion mobility (IM) quadrupole time of flight (Q-TOF) mass spectrometer is used for evaluating the utility of alternate drift gases for complex sample analyses. This study provides collision cross section comparison for 275 total pesticides including structural isomers in nitrogen, helium, carbon dioxide, nitrous oxide and sulfur hexafluoride drift gases. Furthermore, a set of small molecules and Agilent tune mix compounds were used to study the trends in experimentally derived collision cross section values in argon and the alternate drift gases. Two isomeric trisaccharides, melezitose and raffinose, were used to evaluate the effect of the drift gasses for mobility separation. The hybrid ion mobility Q-TOF mass analyzer used in this study consists of a low pressure uniform field drift tube apparatus coupled to a high resolution Q-TOF mass spectrometer. Conventionally, low pressure ion mobility instruments are operated using helium drift gas to obtain optimal structural information and collision cross-section (CCS) values that compare to theoretical CCS values. The instrument employed in this study uses nitrogen as the standard drift gas but also allows the utility of alternate drift gases for improved structural analysis and selectivity under certain conditions. The use of alternate drift gases with a wide range of polarizabilities allows the evaluation of mobility separation power in terms of induced dipole interactions between the drift gas and the analyte ions. PMID:26178817

  1. EARLY-TIME VELOCITY AUTOCORRELATION FOR CHARGED PARTICLES DIFFUSION AND DRIFT IN STATIC MAGNETIC TURBULENCE

    SciTech Connect

    Fraschetti, F.; Giacalone, J.

    2012-08-20

    Using test-particle simulations, we investigate the temporal dependence of the two-point velocity correlation function for charged particles scattering in a time-independent spatially fluctuating magnetic field derived from a three-dimensional isotropic turbulence power spectrum. Such a correlation function allowed us to compute the spatial coefficients of diffusion both parallel and perpendicular to the average magnetic field. Our simulations confirm the dependence of the perpendicular diffusion coefficient on turbulence energy density and particle energy predicted previously by a model for early-time charged particle transport. Using the computed diffusion coefficients, we exploit the particle velocity autocorrelation to investigate the timescale over which the particles 'decorrelate' from the solution to the unperturbed equation of motion. Decorrelation timescales are evaluated for parallel and perpendicular motions, including the drift of the particles from the local magnetic field line. The regimes of strong and weak magnetic turbulence are compared for various values of the ratio of the particle gyroradius to the correlation length of the magnetic turbulence. Our simulation parameters can be applied to energetic particles in the interplanetary space, cosmic rays at the supernova shocks, and cosmic-rays transport in the intergalactic medium.

  2. Transportation of high-current ion and electron beams in the accelerator drift gap in the presence of an additional electron background

    NASA Astrophysics Data System (ADS)

    Karas', V. I.; Kornilov, E. A.; Manuilenko, O. V.; Tarakanov, V. P.; Fedorovskaya, O. V.

    2015-12-01

    The dynamics of a high-current ion beam propagating in the drift gap of a linear induction accelerator with collective focusing is studied using 3D numerical simulations in the framework of the full system of the Vlasov-Maxwell equations (code KARAT). The ion beam is neutralized by a comoving electron beam in the current density and, partially, in space charge, since the velocities of electrons and ions differ substantially. The dynamics of the high-current ion beam is investigated for different versions of additional neutralization of its space charge. It is established that, for a given configuration of the magnetic field and in the presence of a specially programmed injection of additional electrons from the boundary opposite to the ion injection boundary, the angular divergence of the ion beam almost vanishes, whereas the current of the ion beam at the exit from the accelerator drift gap changes insignificantly and the beam remains almost monoenergetic.

  3. Observations of Counter-Streaming Ion Velocity Distributions in LLBL

    NASA Technical Reports Server (NTRS)

    Vaisberg, O. L.; Avanonv, L. A.; Smirnov, V. N.; Moore, T. E.

    2003-01-01

    We analyze ion velocity distributions observed by Interball-Tail at two LLBL crossings under southward and variable magnetosheath magnetic field. These magnetic conditions lead to highly structured LLBL. D-shape ion velocity distributions were observed within LLBL structures along with other reconnection signatures. Another type of the ion velocity distributions observed within LLBL structures consists of two counter-streaming magnetosheath-type components. We consider two possible scenarios that may lead to development of these counterstreaming ion components: reflection of transmitted magnetosheath ions from the ionosphere and creation of these velocity distributions during formation of the LLBL. We argue that observed counter-streaming component could not be due to ionospheric reflection. The observations of these ion velocity distributions are in favor of the multiple reconnections between magnetosheath and magnetospheric flux tubes.

  4. Ion upflow enhanced by drifting F-region plasma structure along the nightside polar cap boundary

    NASA Astrophysics Data System (ADS)

    Semeter, J.; Heinselman, C. J.; Thayer, J. P.; Doe, R. A.; Frey, H. U.

    2003-11-01

    Conjugate observations by the incoherent scatter radar at Sondrestrom, Greenland, and the Wideband Imaging Camera (WIC) on the IMAGE satellite have been used to establish a causal relationship between drifting F-region plasma structure in the polar ionosphere and upward ion number flux near the poleward edge of the auroral oval. A longitudinally extended patch of enhanced F-region density was observed as it advected equatorward across the open-closed field line boundary and into a region of discrete auroral rays and strong ion upflow (Vi > 800 m/s at 900 km altitude). Upward velocities within the upflow region remained constant during the patch transit, such that the upflowing number flux was directly controlled by F-region density (both increased by a factor of 2 within the patch). Because polar cap patches and ion upflows are both longitudinally extended, quasi-stable features of the nightside polar cap boundary, the observed interaction can produce a global-scale increase in plasma density at higher altitudes where suprathermal outflows are initiated.

  5. Ionic Drift Velocity Measurements on A Nano-composite Polymer Electrolyte: 95[90PEO: 10AgNO3]: 5SiO2

    NASA Astrophysics Data System (ADS)

    Chandra, Angesh; Chandra, Archana; Thakur, S. S.; Chakrawarti, V.

    2011-11-01

    Ionic drift velocity (vd) measurements on a hot-press synthesized nano-composite polymer electrolyte (NCPE) membrane: 95[90PEO: 10AgNO3]: 5SiO2, are reported. The ionic transference number (tion) values were determined using dc polarization Transient Ionic Current (TIC) technique for vd measurement at different temperatures. The drift energy (Ed), involved in the thermally activated process was determined from the temperature dependent studies on ionic drift velocity using the log vd vs 1/T Arrhenius plot. At all the temperatures, the ionic drift velocity is directly proportional to the ionic mobility (?) at a fixed value of applied dc potential.

  6. Optimal transport of two ions under slow spring-constant drifts

    NASA Astrophysics Data System (ADS)

    Lu, Xiao-Jing; Palmero, Mikel; Ruschhaupt, Andreas; Chen, Xi; Gonzalo Muga, Juan

    2015-06-01

    We investigate the effect of slow spring-constant drifts of the trap used to shuttle two ions of different mass. We design transport protocols to suppress or mitigate the final excitation energy by applying invariant-based inverse engineering, perturbation theory, and a harmonic dynamical normal-mode approximation. A simple, explicit trigonometric protocol for the trap trajectory is found to be robust with respect to the spring-constant drifts.

  7. A Study of Ion Velocities Observed by TIDE and How It Relates to Magnetospheric Circulation

    NASA Technical Reports Server (NTRS)

    Elliott, H. A.; Comfort, R. H.; Craven, P. D.; Chandler, M. O.; Moore, T. E.

    1998-01-01

    The high-latitude ion velocities measured by the Thermal Ion Dynamics Experiment (TIDE) instrument on the Polar spacecraft will be examined in relation to magnetospheric circulation. TIDE derives ion velocities from moments of measured distribution functions. Hydrogen and oxygen ions are E X B drifting in the polar cap and cleft regions with a speed of about 5-20 km/s at apogee (approximately 9 Re) and a speed of 1-2 km/s at perigee (approximately 1.8 Re). At perigee 0+ is typically seen flowing down in the polar cap and outflowing from the cleft. At the transition from downflowing to upflowing there is also seen a reversal in the ion convection. The convection at perigee is consistent with standard ionospheric convection models for given Interplanetary Magnetic Field (IMF) conditions. Convection at high altitude (approximately 8.9 Re) polar regions has not been studied very much since there have not been many satellites in this region. Unlike previous missions to this region TIDE in conjunction the Plasma Source Instrument (PSI) can measure ions with as low an energy as several electron Volts. The outflowing ions observed by TIDE at apogee are believed to be important to the overall circulation of the magnetosphere. The convection of these outflowing ions at apogee will be related to the IMF. This study tries to answer the question of how the IMF response of the convection influences the overall circulation of the magnetosphere.

  8. Measurement of ion swarm distribution functions in miniature low-temperature co-fired ceramic ion mobility spectrometer drift tubes.

    PubMed

    Pfeifer, Kent B; Rumpf, Arthur N

    2005-08-15

    Measurements of the performance of a miniature, portable 12-mm-diameter, 57-mm-length low-temperature cofired ceramic (LTCC) ion mobility spectrometer drift tube were undertaken to verify models of ion transport and determine the physical shape of the ion "swarms" in the LTCC tube. Simplified two-dimensional Gaussian models of ion swarm shape were fit to measured data to extract geometrical shape parameters. Results indicate that tube-transfer function effects that produce asymmetric ion swarms are minimized in the tube reducing temporal dispersion. Data are presented that illustrate the swarm shape as a function of gate time, electric field magnitude, and total charge in the ion swarm. Characterization and understanding of the ion transport mechanisms and effects that limit the resolution and other performance parameters of miniature IMS drift tubes is essential to the development of practical, robust, portable systems for "first responder" and homeland security missions. PMID:16097761

  9. Ion mixing in the plasma sheet boundary layer by drift instabilities

    NASA Technical Reports Server (NTRS)

    Horton, W.; Dong, J. Q.; Su, X. N.; Tajima, T.

    1993-01-01

    The linear stability properties of collisionless drift instabilities are analyzed in a Harris equilibrium model of the plasma sheet boundary layer (PSBL). The strearmng ions with drift-type instabilities driven in the PSBL are considered. The fluid approximation leads to growth but predicts that the mode width approaches the gyroradius of the energetic ions. Thus an integral equation theory for the modes is developed taking into account that in the PSBL the curvature drift is weak compared with the grad-B drift. The exact wave particle resonance is kept in the nonlocal response functions. Plasma density, temperature, and magnetic gradient drift motions are taken into account. The drift modes produce an anomalous cross-field momentum transport mixing the PSBL ions on the time scale of tens of seconds. A nonlinear simulation is performed which shows the coalescence of the small scale, fast growing modes into large-scale vortices. The relation between these collective modes and plasma sheet transport phenomena is discussed including the comparison with the competing plasma mixing from single-particle stochasticity.

  10. Drift compression and final focus systems for heavy ion inertial fusion

    SciTech Connect

    de Hoon, M.J.L.

    2001-05-01

    Longitudinal compression of space-charge dominated beams can be achieved by imposing a head-to-tail velocity tilt on the beam. This tilt has to be carefully tailored, such that it is removed by the longitudinal space-charge repulsion by the time the beam reaches the end of the drift compression section. The transverse focusing lattice should be designed such that all parts of the beam stay approximately matched, while the beam smoothly expands transversely to the larger beam radius needed in the final focus system following drift compression. In this thesis, several drift compression systems were designed within these constraints, based on a given desired pulse shape at the end of drift compression systems were designed within these constraints, based on a given desired pulse shape at the end of drift compression. The occurrence of mismatches due to a rapidly increasing current was analyzed. In addition, the sensitivity of drift compression to errors in the initial velocity tilt and current profile was studied. These calculations were done using a new computer code that accurately calculates the longitudinal electric field in the space-charge dominated regime.

  11. Spectral anomalies of the light-induced drift of rubidium atoms caused by the velocity dependence of transport collision frequencies

    NASA Astrophysics Data System (ADS)

    Parkhomenko, A. I.; Shalagin, A. M.

    2014-02-01

    The spectral features of the light-induced drift (LID) velocity for rubidium atoms (85Rb and 87Rb) in an argon buffer medium and in binary buffer mixtures of noble gases (Ne + Ar, Ne + Kr, Ne + Xe, He + Ar, He + Kr, and He + Xe) have been investigated theoretically. A strong temperature dependence of the spectral shape of the LID signal for Rb atoms in an Ar atmosphere is predicted in the temperature range 450 K < T < 800 K. It is shown that the anomalous LID of Rb atoms in binary buffer mixtures of noble gases can be observed at almost any temperature (including the room one) depending on the fractions of neon or helium in these mixtures. The results obtained enable a highly accurate testing of the interatomic interaction potentials used to calculate the drift velocity for anomalous LID in LID experiments.

  12. Optimization of curved drift tubes for ultraviolet-ion mobility spectrometry

    NASA Astrophysics Data System (ADS)

    Ni, Kai; Ou, Guangli; Zhang, Xiaoguo; Yu, Zhou; Yu, Quan; Qian, Xiang; Wang, Xiaohao

    2015-08-01

    Ion mobility spectrometry (IMS) is a key trace detection technique for toxic pollutants and explosives in the atmosphere. Ultraviolet radiation photoionization source is widely used as an ionization source for IMS due to its advantages of high selectivity and non-radioactivity. However, UV-IMS bring problems that UV rays will be launched into the drift tube which will cause secondary ionization and lead to the photoelectric effect of the Faraday disk. So air is often used as working gas to reduce the effective distance of UV rays, but it will limit the application areas of UV-IMS. In this paper, we propose a new structure of curved drift tube, which can avoid abnormally incident UV rays. Furthermore, using curved drift tube may increase the length of drift tube and then improve the resolution of UV-IMS according to previous research. We studied the homogeneity of electric field in the curved drift tube, which determined the performance of UV-IMS. Numerical simulation of electric field in curved drift tube was conducted by SIMION in our study. In addition, modeling method and homogeneity standard for electric field were also presented. The influences of key parameters include radius of gyration, gap between electrode as well as inner diameter of curved drift tube, on the homogeneity of electric field were researched and some useful laws were summarized. Finally, an optimized curved drift tube is designed to achieve homogenous drift electric field. There is more than 98.75% of the region inside the curved drift tube where the fluctuation of the electric field strength along the radial direction is less than 0.2% of that along the axial direction.

  13. Ion velocities in a micro-cathode arc thruster

    SciTech Connect

    Zhuang Taisen; Shashurin, Alexey; Keidar, Michael; Beilis, Isak

    2012-06-15

    Ion velocities in the plasma jet generated by the micro-cathode arc thruster are studied by means of time-of-flight method using enhanced ion detection system (EIDS). The EIDS triggers perturbations (spikes) on arc current waveform, and the larger current in the spike generates denser plasma bunches propagating along with the mainstream plasma. The EIDS utilizes double electrostatic probes rather than single probes. The average Ti ion velocity is measured to be around 2 Multiplication-Sign 10{sup 4} m/s without a magnetic field. It was found that the application of a magnetic field does not change ion velocities in the interelectrode region while leads to ion acceleration in the free expanding plasma plume by a factor of about 2. Ion velocities of about 3.5 Multiplication-Sign 10{sup 4} m/s were detected for the magnetic field of about 300 mT at distance of about 100-200 mm from the cathode. It is proposed that plasma is accelerated due to Lorentz force. The average thrust is calculated using the ion velocity measurements and the cathode mass consumption rate, and its increase with the magnetic field is demonstrated.

  14. CRADA Final Report CRADA No. LB05-001820"Ion Beam Drift Compression Technology for NDCX"

    SciTech Connect

    First point Scientific, Inc.; E.O. Lawrence Berkeley National Laboratory; Waldron, William L.

    2009-10-05

    Summary of the specific research and project accomplishments: Through this collaboration, LBNL and FPSI determined the specific energy manipulations that apply to the Neutralized Drift Compression Experiment (NDCX) ion beam and developed the preliminary design of a Fast Induction Energy Corrector (FIEC). This effort was successfully completed, firmly establishing the technical feasibility of the proposed approach for regulating the longitudinal energy distribution of the NDCX ion beam. This is a critical step in achieving the NDCX goal of axial compression of the beam by a factor of 100 during neutralized drift.

  15. Low velocity ion stopping in binary ionic mixtures

    SciTech Connect

    Tashev, Bekbolat; Baimbetov, Fazylkhan; Deutsch, Claude; Fromy, Patrice

    2008-10-15

    Attention is focused on the low ion velocity stopping mechanisms in multicomponent and dense target plasmas built of quasiclassical electron fluids neutralizing binary ionic mixtures, such as, deuterium-tritium of current fusion interest, proton-heliumlike iron in the solar interior or proton-helium ions considered in planetology, as well as other mixtures of fiducial concern in the heavy ion beam production of warm dense matter at Bragg peak conditions. The target plasma is taken in a multicomponent dielectric formulation a la Fried-Conte. The occurrence of projectile ion velocities (so-called critical) for which target electron slowing down equals that of given target ion components is also considered. The corresponding multiquadrature computations, albeit rather heavy, can be monitored analytical through a very compact code operating a PC cluster. Slowing down results are systematically scanned with respect to target temperature and electron density, as well as ion composition.

  16. Velocity-dependent isotope fractionation in secondary-ion emission

    SciTech Connect

    Gnaser, H.; Hutcheon, I.D.

    1987-01-15

    The formation of secondary ions is subject to isotopic fractionation (differing ionization probabilities for two isotopes) that depends linearly on the inverse velocity of the ejected ions. Theoretically, such a correlation follows directly from an exponential dependence of the ionization probability P on v/sup -1/, Pproportionalexp(-v/sub 0//v). The parameter v/sub 0/, derived from the experiment, amounts to --2 x 10/sup 6/ cm/sec for B, Si, and Ca ions.

  17. Electrostatic ion cyclotron velocity shear instability

    NASA Technical Reports Server (NTRS)

    Lemons, D. S.; Winske, D.; Gary, S. P.

    1992-01-01

    A local electrostatic dispersion equation is derived for a shear flow perpendicular to an ambient magnetic field, which includes all kinetic effects and involves only one important parameter. The dispersion equation is cast in the form of Gordeyev integrals and is solved numerically. Numerical solutions indicate that an ion cyclotron instability is excited. The instability occurs roughly at multiples of the ion cyclotron frequency (modified by the shear), with the growth rate or the individual harmonics overlapping in the wavenumber. At large values of the shear parameter, the instability is confined to long wavelengths, but at smaller shear, a second distinct branch at shorter wavelengths also appears. The properties of the instability obtained are compared with those obtained in the nonlocal limit by Ganguli et al. (1985, 1988).

  18. Effect of the entrained air and initial droplet velocity on the release height parameter of a Gaussian spray drift model.

    PubMed

    Stainier, C; Destain, M F; Schiffers, B; Lebeau, F

    2006-01-01

    The increased concern about environmental effect of off-target deposits of pesticides use has resulted in the development of numerous spray drift models. Statistical models based on experimental field studies are used to estimate off-target deposits for different sprayers in various environmental conditions. Random-walk and computational fluid dynamics (CFD) models have been used to predict the effect of operational parameters and were extensively validated in wind tunnel. A third group, Gaussian dispersion models have been used for several years for the environmental assessment of the pesticide spray drift, mainly for aerial application. When these models were used for the evaluation of boom sprayer spray drift, their predictions were found unreliable in the short range, were the initial release conditions of the droplets have a significant effect on the spray deposits. For longer ranges, the results were found consistent with the field measurements as the characteristics of the source have a reduced influence on the small droplets drift. Three major parameters must be taken into account in order to define realistic initial conditions of the droplets in a spray drift model: the spray pattern of the nozzle, the boom movements and the effect of entrained air and droplet velocities. To take theses parameters into account in a Gaussian model, the nozzle droplet size distribution measured with a PIV setup to divide the nozzle output into several size classes. The spray deposits of each diameter class was computed for each successive position of the nozzle combining the nozzle spray distribution with drift computed with a Gaussian tilting plume model. The summation of these footprints resulted in the global drift of the nozzle. For increasing droplet size, the release height used in the Gaussian model was decreased from nozzle height to ground level using an experimental law to take into account the effect of entrained air and droplet initial velocity. The experimental law was adjusted on 2 m/s wind tunnel measurements and robustness was evaluated for 1 and 4 m/s. PMID:17390793

  19. Drift wave stabilized by an additional streaming ion or plasma population.

    PubMed

    Bashir, M F; Vranjes, J

    2015-03-01

    It is shown that the universally unstable kinetic drift wave in an electron-ion plasma can very effectively be suppressed by adding an extra flowing ion (or plasma) population. The effect of the flow of the added ions is essential, their response is of the type (vph-vf0)exp[-(vph-vf0)2], where vf0 is the flow speed and vph is the phase speed parallel to the magnetic field vector. The damping is strong and it is mainly due to this ion exponential term, and this remains so for vf0

  20. Spectral anomalies of the light-induced drift effect caused by the velocity dependence of the collision broadening and shift of the absorption line

    SciTech Connect

    Parkhomenko, A I; Shalagin, Anatolii M

    2013-02-28

    We have theoretically investigated the spectral features of the light-induced drift (LID) effect, arising due to the dependence of the collision broadening {gamma} and shift {Delta} of the absorption line on the velocity of resonance particles, {nu}. It is shown that under certain conditions, account of this dependence can radically change the spectral shape of the LID signal, up to the appearance of additional zeros in the dependence of the drift velocity on the radiation frequency. (nonlinear optical phenomena)

  1. Spectral anomalies of the light-induced drift effect caused by the velocity dependence of the collision broadening and shift of the absorption line

    NASA Astrophysics Data System (ADS)

    Parkhomenko, A. I.; Shalagin, Anatolii M.

    2013-02-01

    We have theoretically investigated the spectral features of the light-induced drift (LID) effect, arising due to the dependence of the collision broadening ? and shift ? of the absorption line on the velocity of resonance particles, ?. It is shown that under certain conditions, account of this dependence can radically change the spectral shape of the LID signal, up to the appearance of additional zeros in the dependence of the drift velocity on the radiation frequency.

  2. Studies of ions in a drift field: laser diagnostics of excited states and measurements of thermochemical properties at equilibrium

    SciTech Connect

    Castleman, A.W. Jr.; Keesee, R.G.

    1983-01-01

    A major technique for investigating the thermochemical properties of ions and their related clusters is the high pressure drift/mass spectrometer detection technique. A crucial question in this regard is the extent to which ions drifting in an electric field are thermalized. This paper is divided into two parts, one describing some laser techniques which are enabling an investigation of the possible presence of excited ions in a drift field, and secondly, a reporting of some recent findings and trends in the stability of ion clusters of single and mixed constituents.

  3. Determination of Joule dissipation and drift velocity in the kinematic-dynamo model with two differential rotations

    NASA Astrophysics Data System (ADS)

    Kropachev, E. P.

    1982-08-01

    The paper examines the generation of a constant magnetic field in a conductivity sphere in which the motion is prescribed in the form of rigid rotations about the different axes of an outer spherical shell and a spherical rotor somewhat displaced from the center of the system. The power necessary for the operation of the dynamo is calculated along with the drift velocity of the conductivity shell relative to the rest of the system under the effect of an electromagnetic moment. Dynamo processes in the earth's core are considered as an example.

  4. Poloidal velocity of impurity ions in neoclassical theory

    SciTech Connect

    Wong, S. K.; Chan, V. S.; Solomon, W. M.

    2008-08-15

    A formula for the poloidal velocity of impurity ions in a two-species plasma is derived from neoclassical theory in the banana regime, with corrections from the boundary layer separating the trapped and transiting ions. The formula is applicable to plasmas with toroidal rotations that can approach the thermal speeds of the ions. Using the formula to determine the poloidal velocity of C{sup +6} ions in a recently reported experiment [W. M. Solomon et al., Phys. Plasmas 13, 056116 (2006)] leads to agreement in the direction of the central region when it is otherwise from theories without strong toroidal rotations. Comparisons among these theories are made, demonstrating the degree of uncertainty of theoretical predictions.

  5. A mass-selective variable-temperature drift tube ion mobility-mass spectrometer for temperature dependent ion mobility studies.

    PubMed

    May, Jody C; Russell, David H

    2011-07-01

    A hybrid ion mobility-mass spectrometer (IM-MS) incorporating a variable-temperature (80-400K) drift tube is presented. The instrument utilizes an electron ionization (EI) source for fundamental small molecule studies. Ions are transferred to the IM-MS analyzer stages through a quadrupole, which can operate in either broad transmission or mass-selective mode. Ion beam modulation for the ion mobility experiment is accomplished by an electronic shutter gate. The variable-temperature ion mobility spectrometer consists of a 30.2cm uniform field drift tube enclosed within a thermal envelope. Subambient temperatures down to 80K are achievable through cryogenic cooling with liquid nitrogen, while elevated temperatures can be accessed through resistive heating of the envelope. Mobility separated ions are mass analyzed by an orthogonal time-of-flight (TOF) mass spectrometer. This report describes the technological considerations for operating the instrument at variable temperature, and preliminary results are presented for IM-MS analysis of several small mass ions. Specifically, mobility separations of benzene fragment ions generated by EI are used to illustrate significantly improved (greater than 50%) ion mobility resolution at low temperatures resulting from decreased diffusional broadening. Preliminary results on the separation of long-lived electronic states of Ti(+) formed by EI of TiCl(4) and hydration reactions of Ti(+) with residual water are presented. PMID:21953095

  6. Pickup Ion Velocity Distributions at Titan: Effects of Spatial Gradients

    NASA Astrophysics Data System (ADS)

    Hartle, R. E.; Sittler, E. C.

    2004-05-01

    The principle source of pickup ions at Titan is its neutral exosphere, extending well above the ionopause into the magnetosphere of Saturn or the solar wind, depending on the moon's orbital position. Thermal and nonthermal processes in the thermosphere generate the distribution of neutral atoms and molecules in the exosphere. The combination of these processes and the range of mass numbers, 1 to over 28, contribute to an exospheric source structure that produces pickup ions with gyroradii that are much larger or smaller than the corresponding scale heights of their neutral sources. The resulting phase space distributions are dependent on the spatial structure of the exosphere as well as that of the magnetic field and background plasma. When the pickup ion gyroradius is less than the source gas scale height, the pickup ion velocity distribution is characterized by a sharp cutoff near the maximum speed, which is twice that of the ambient plasma times the sine of the angle between the magnetic field and the flow velocity. This was the case for pickup H+ ions identified during the Voyager 1 flyby (1). In contrast, as the gyroradius becomes much larger than the scale height, the peak of the velocity distribution in the source region recedes from the maximum speed. In addition, the amplitude of the distribution near the maximum speed decreases. These more beam like distributions of heavy ions were not observed from Voyager 1, but should be observable by more sensitive instruments on future spacecraft, including Cassini. The finite gyroradius effects in the pickup ion velocity distributions are studied by including in the analysis the possible range of spatial structures in the neutral exosphere and background plasma. (1) Hartle, R. E., E. C. Sittler, Jr., K. W. Ogilvie, J. D. Scudder, A. J. Lazarus and S. K. Atrea, Titan's Ion Exosphere Observed from Voyager 1, J. Geophys. Res., 87, 1383-1394, 1982.

  7. Storm-to-storm main phase repeatability of the local time variation of disturbed low-latitude vertical ion drifts

    NASA Astrophysics Data System (ADS)

    Huang, Chao-Song

    2015-07-01

    Penetration electric field can be very strong during magnetic storms. However, the variation of penetration electric field with local time (LT) has not been well understood. The Communication/Navigation Outage Forecasting System (C/NOFS) satellite measures the plasma drift/electric field over all local times within ~100 min. In this paper, we present the first nearly simultaneous observations of the dependence of penetration electric field on local time. The meridional ion drift measured by C/NOFS during the main phase of five magnetic storms in 2012 is analyzed. The storm time ion drift shows a large enhancement around 1900 LT, a relatively small enhancement during daytime, and a deep decrease in the postmidnight sector with a peak around 0500 LT. The observed storm time variation of the meridional ion drift with local time represents the variation of the penetration electric field. The averaged ion drifts are in remarkable agreement with recent simulations.

  8. Pic Modeling of a Closed Drift Ion Source for Material Surface Processing

    NASA Astrophysics Data System (ADS)

    Schoessow, Paul; Cary, John; Shaw, Denis; Stoltz, Peter

    2005-10-01

    The closed drift ion source is a technology that uses a DC discharge in a gas cell (Ar, O2) to produce a uniform, linear 300-1500 eV ion beam for in-line surface treatment and cleaning of materials. Maximum ion beam currents are on the order of 1 A / meter of source length. A permanent dipole magnet forms a magnetic circuit with the ferromagnetic cathode enclosure, producing a focusing field in the ion extraction gap that confines electrons. The focusing field shape is controlled by the beveling of the gap. We have developed 2- and 3- dimensional PIC models of the closed drift ion source using the OOPIC Pro and Vorpal codes. We will present numerical results on the ion beam properties, including the ion energy spectrum on the target, and compare them to measurements. We will also investigate possible design modifications such as to the magnetic field shape and discharge electrode geometry that might lead to increased ion current.

  9. Analysis of drifting electron concentration in a self-magnetically insulated ion diode

    NASA Astrophysics Data System (ADS)

    Pushkarev, A. I.; Pak, V. G.

    2015-02-01

    The drifting electron concentration in a self-magnetically insulated ion diode is analyzed using a TEMP-4M accelerator operating in a double bipolar pulse regime with the first pulse (300-600 ns and 150-200 kV) being negative and the second (120 ns and 250-300 kV) being positive. The electron concentration in the drift region is shown to be 1013-1014 cm-3. It is established that the Lorentz force acting on electrons in crossed electric and magnetic fields is 150-200 times greater than the Coulomb repulsion force, which ensures a higher electron concentration in the drift region as compared with the space charge region.

  10. Lithium-ion drifting: Application to the study of point defects in floating-zone silicon

    NASA Technical Reports Server (NTRS)

    Walton, J. T.; Wong, Y. K.; Zulehner, W.

    1997-01-01

    The use of lithium-ion (Li(+)) drifting to study the properties of point defects in p-type Floating-Zone (FZ) silicon crystals is reported. The Li(+) drift technique is used to detect the presence of vacancy-related defects (D defects) in certain p-type FZ silicon crystals. SUPREM-IV modeling suggests that the silicon point defect diffusivities are considerably higher than those commonly accepted, but are in reasonable agreement with values recently proposed. These results demonstrate the utility of Li(+) drifting in the study of silicon point defect properties in p-type FZ crystals. Finally, a straightforward measurement of the Li(+) compensation depth is shown to yield estimates of the vacancy-related defect concentration in p-type FZ crystals.

  11. Observation of Anomalous Ion Heating by Broadband Drift-Wave Turbulence

    SciTech Connect

    Enge, S.; Birkenmeier, G.; Manz, P.; Ramisch, M.; Stroth, U.

    2010-10-22

    Using laser induced fluorescence and passive spectroscopy on a magnetically confined low-temperature plasma, anomalous ion heating is observed which exceeds collisional heating from the electrons by a factor of up to five. Direct wave heating due to the 2.45 GHz microwave as well as stochastic heating by large-amplitude fluctuations could be ruled out as explanations. Good quantitative agreement is found when comparing the missing power in the ion species with heating power due to the dissipation of drift-wave turbulence. This turbulent energy transfer into the ion channel could have important consequences for the interpretation of transport in fusion plasmas.

  12. Exact representation of the asymptotic drift speed and diffusion matrix for a class of velocity-jump processes

    NASA Astrophysics Data System (ADS)

    Mascia, Corrado

    2016-01-01

    This paper examines a class of linear hyperbolic systems which generalizes the Goldstein-Kac model to an arbitrary finite number of speeds vi with transition rates μij. Under the basic assumptions that the transition matrix is symmetric and irreducible, and the differences vi -vj generate all the space, the system exhibits a large-time behavior described by a parabolic advection-diffusion equation. The main contribution is to determine explicit formulas for the asymptotic drift speed and diffusion matrix in term of the kinetic parameters vi and μij, establishing a complete connection between microscopic and macroscopic coefficients. It is shown that the drift speed is the arithmetic mean of the velocities vi. The diffusion matrix has a more complicate representation, based on the graph with vertices the velocities vi and arcs weighted by the transition rates μij. The approach is based on an exhaustive analysis of the dispersion relation and on the application of a variant of the Kirchoff's matrix tree Theorem from graph theory.

  13. Selected Ion Flow-Drift Tube Mass Spectrometry: Quantification of Volatile Compounds in Air and Breath.

    PubMed

    Spesyvyi, Anatolii; Smith, David; pan?l, Patrik

    2015-12-15

    A selected ion flow-drift tube mass spectrometric analytical technique, SIFDT-MS, is described that extends the established selected ion flow tube mass spectrometry, SIFT-MS, by the inclusion of a static but variable E-field along the axis of the flow tube reactor in which the analytical ion-molecule chemistry occurs. The ion axial speed is increased in proportion to the reduced field strength E/N (N is the carrier gas number density), and the residence/reaction time, t, which is measured by Hadamard transform multiplexing, is correspondingly reduced. To ensure a proper understanding of the physics and ion chemistry underlying SIFDT-MS, ion diffusive loss to the walls of the flow-drift tube and the mobility of injected H3O(+) ions have been studied as a function of E/N. It is seen that the derived diffusion coefficient and mobility of H3O(+) ions are consistent with those previously reported. The rate coefficient has been determined at elevated E/N for the association reaction of the H3O(+) reagent ions with H2O molecules, which is the first step in the production of H3O(+)(H2O)1,2,3 reagent hydrate ions. The production of hydrated analyte ion was also experimentally investigated. The analytical performance of SIFDT-MS is demonstrated by the quantification of acetone and isoprene in exhaled breath. Finally, the essential features of SIFDT-MS and SIFT-MS are compared, notably pointing out that a much lower speed of the flow-drive pump is required for SIFDT-MS, which facilitates the development of smaller cost-effective analytical instruments for real time breath and fluid headspace analyses. PMID:26583448

  14. Experimental and theoretical determination of the strongly anisotropic velocity distribution functions of ions in the intrinsic gas plasma in strong fields

    NASA Astrophysics Data System (ADS)

    Mustafaev, A. S.; Sukhomlinov, V. S.; Ainov, M. A.

    2015-12-01

    The first seven coefficient of expansion of the energy and angular distribution functions in the Legendre polynomials for Hg+ ions in the Hg vapor plasma with parameter E/ P ? 400 V/(cm Torr) are measured for the first time using a planar one-sided probe. The analytic solution to the Boltzmann kinetic equation for ions in the plasma of their parent gas is obtained in the conditions when the resonant charge exchange is the predominant process, and an ion acquires on its mean free path a velocity much higher than the characteristic velocity of thermal motion of atoms. The presence of an ambipolar field of an arbitrary strength is taken into account. It is shown that the ion velocity distribution function is determined by two parameters and differs substantially from the Maxwellian distribution. Comparison of the results of calculation of the drift velocity of He+ ions in He, Ar+ in Ar, and Hg+ in Hg with the available experimental data shows their conformity. The results of calculation of the ion distribution function correctly describe the experimental data on its measurement. Analysis of the result shows that in spite of the presence of the strong field, the ion velocity distribution functions are isotropic for ion velocities lower than the average thermal velocity of atoms. With increasing ion velocity, the distribution becomes more and more extended in the direction of the electric field.

  15. Drift Velocity of Small-Scale Artificial Ionospheric Irregularities According to a Multifrequency HF Doppler Radar. II. Observation and Modeling Results

    NASA Astrophysics Data System (ADS)

    Vertogradov, G. G.; Uryadov, V. P.; Vertogradov, V. G.; Vertogradova, E. G.; Kubatko, S. V.

    2015-11-01

    We present the results of observations of the Doppler frequency shift for the radar radio signals of broadcast and exact-time RWM stations, which are scattered by small-scale artificial ionospheric irregularities. By the method described in our previous paper [1] and using the multifrequency HF Doppler radar, estimates were made for a three-dimensional vector of the drift velocity of irregularities. It is shown that the drift velocity of irregularities can vary considerably both in magnitude and direction for short periods of time. The velocity lies in a wide range of values, 20-270 m/s, but sometimes it exceeds 500-700 m/s. The most probable drift velocity ranges from 40 to 70 m/s.

  16. Transmission of a Drift Tube Ion Mobility Spectrometer, Connected with a Mass Spectrometer

    NASA Astrophysics Data System (ADS)

    Chernyshev, D. M.; Poteshin, S. S.; Karpov, A. V.; Sysoev, Alexey A.; Sysoev, Alexander A.

    In this work it is experimentally showed that transmission of atmospheric drift tube ion mobility spectrometer (DT-IMS), connected with mass spectrometer (MS), depends on ion mobility of investigated compounds, because of depletion effect of Bradbury-Nielson ion gate (IG), which previously has been approved only by standalone DT-IMS. Theoretical estimation of depletion width of IG is in good agreement with experimental data. Also it is found, that ion lost due to its pulsing work of IG are few times smaller, than its duty cycle. It's explained by difference in influence of coulomb repulsion at 100% and 1% duty cycle - in first case it's significant versus second case, when coulomb repulsion become negligibly small, that reduces lost of ions on entrance of MS interface.

  17. Closed electron drift in a self-magnetically insulated ion diode

    SciTech Connect

    Pushkarev, A. I.; Isakova, Y. I.

    2013-05-15

    The paper investigates a spiral geometry self-magnetically insulated ion diode with an explosive-emission cathode made from graphite. The experiments have been carried out using the TEMP-4M accelerator, with the accelerator configured to operate in double-pulse mode: the first negative pulse (300–500 ns, 100–150 kV) and the second positive pulse (150 ns, 250–300 kV). The ion beam energy density was 0.4–0.8 J/cm{sup 2} and the beam was composed of carbon ions (80%–85%) and protons. In order to increase the efficiency of ion current generation, we have developed a new diode with a spiral-shaped grounded electrode. Using this geometry, it seems possible to realize closed electron drift in a diode with self-magnetic insulation. In the spiral diode, the efficiency of accelerated ions is increased from 5%–9% (conventional self-insulated diodes) up to 30%–40%. The realization of closed electron drift in the diode increases the efficiency of C{sup +} ion generation up to 40–50 times the Childe-Langmuir limit, which is more than 4 times higher than with other known constructions of self-magnetically insulated diodes.

  18. Closed electron drift in a self-magnetically insulated ion diode

    NASA Astrophysics Data System (ADS)

    Pushkarev, A. I.; Isakova, Y. I.

    2013-05-01

    The paper investigates a spiral geometry self-magnetically insulated ion diode with an explosive-emission cathode made from graphite. The experiments have been carried out using the TEMP-4M accelerator, with the accelerator configured to operate in double-pulse mode: the first negative pulse (300-500 ns, 100-150 kV) and the second positive pulse (150 ns, 250-300 kV). The ion beam energy density was 0.4-0.8 J/cm2 and the beam was composed of carbon ions (80%-85%) and protons. In order to increase the efficiency of ion current generation, we have developed a new diode with a spiral-shaped grounded electrode. Using this geometry, it seems possible to realize closed electron drift in a diode with self-magnetic insulation. In the spiral diode, the efficiency of accelerated ions is increased from 5%-9% (conventional self-insulated diodes) up to 30%-40%. The realization of closed electron drift in the diode increases the efficiency of C+ ion generation up to 40-50 times the Childe-Langmuir limit, which is more than 4 times higher than with other known constructions of self-magnetically insulated diodes.

  19. Scavenging of atmospheric ions and aerosols by drifting snow in Antarctica

    NASA Astrophysics Data System (ADS)

    Kamra, A. K.; Siingh, Devendraa; Pant, Vimlesh

    2009-02-01

    Measurements of the small-, intermediate-, and large-ion concentrations and the air-earth current density along with simultaneous measurements of the concentration and size distribution of aerosol particles in the size ranges 4.4-163 nm and 0.5-20 ?m diameter are reported for a drifting snow period after the occurrence of a blizzard at a coastal station, Maitri, Antarctica. Ion concentrations of all categories and the air-earth current simultaneously decrease by approximately an order of magnitude as the wind speed increases from 5 to 10 ms - 1 . The rate of decrease is the highest for large ions, lowest for small ions and in-between the two for intermediate ions. Total aerosol number concentration decreases in the 4.4-163 nm size range but increases in the 0.5-20 ?m size range with wind speed. The size distribution of the nanometer particles shows a dominant maximum at ~ 30 nm diameter throughout the period of observations and the height of the maximum decreases with wind speed. However, larger particles show a maximum at ~ 0.7 ?m diameter but the height of the maximum increases with increasing wind speed. The results are explained in terms of scavenging of atmospheric ions and aerosols by the drifting snow particles.

  20. Distributed drift chamber design for rare particle detection in relativistic heavy ion collisions

    SciTech Connect

    Bellwied, R.; Bennett, M.J.; Bernardo, V.; Caines, H.; Christie, W.; Costa, S.; Crawford, H.J.; Cronqvist, M.; Debbe, R.; Dinnwiddie, R.; Engelage, J.; Flores, I.; Fuzesy, R.; Greiner, L.; Hallman, T.; Hoffmann, G.; Huang, H.Z.; Jensen, P.; Judd, E.G.; Kainz, K.; Kaplan, M.; Kelly, S.; Lindstrom, P.J; Llope, W.J.; LoCurto, G.; Longacre, R.; Milosevich, Z.; Mitchell, J.T.; Mitchell, J.W.; Mogavero, E.; Mutchler, G.; Paganis, S.; Platner, E.; Potenza, R.; Rotondo, F.; Russ, D.; Sakrejda, I.; Saulys, A.; Schambach, J.; Sheen, J.; Smirnoff, N.; Stokeley, C.; Tang, J.; Trattner, A.L.; Trentalange, S.; Visser, G.; Whitfield, J.P.; Witharm, F.; Witharm, R.; Wright, M.

    2001-10-02

    This report describes a multi-plane drift chamber that was designed and constructed to function as a topological detector for the BNL AGSE896 rare particle experiment. The chamber was optimized for good spatial resolution, two track separation, and a high uniform efficiency while operating in a 1.6 Tesla magnetic field and subjected to long term exposure from a 11.6 GeV/nucleon beam of 10**6 Au ions per second.

  1. Resonant-to-nonresonant transition in electrostatic ion-cyclotron wave phase velocity

    NASA Astrophysics Data System (ADS)

    Carroll, J. J., III; Koepke, M. E.; Zintl, M. W.; Gavrishchaka, V.

    Because of the implications for plasmas in the laboratory and in space, attention has been drawn to inhomogeneous energy-density driven (IEDD) waves that are sustained by velocity-shear-induced inhomogeneity in cross-field plasma flow. These waves have a frequency vr in the lab frame within an order of magnitude of the ion gyrofrequency vci, propagate nearly perpendicular to the magnetic field (kz /k^ << 1), and can be Landau resonant (0 < v1/kz < nd) with a parallel drifting electron population (drift speed nd), where subscripts 1 and r indicate frequency in the frame of flowing ions and in the lab frame, respectively, and kz is the parallel component of the wavevector. A transition in phase velocity from 0 < v1/kz < nd to 0 > v1/kz > nd for a pair of IEDD eigenmodes is observed as the degree of in-homogeneity in the transverse E B flow is increased in a magnetized plasma column. For weaker velocity shear, both eigenmodes are dissipative, i.e. in Landau resonance, with kz nd > 0. For stronger shear, both eigenmodes become reactive, with one's wavevector component kz remaining parallel, but with v1/kz > nd , and the other's wavevector component kz becoming anti-parallel, so that 0 > v1/kz . For both eigenmodes, the transition (1) involves a small frequency shift and (2) does not involve a sign change in the wave energy density, which is proportional to vr v1, both of which are previously unrecognized aspects of inhomogeneous energy-density driven waves.

  2. Study of daytime vertical E B drift velocities inferred from ground-based magnetometer observations of ?H, at low latitudes under geomagnetically disturbed conditions

    NASA Astrophysics Data System (ADS)

    Subhadra Devi, P. K.; Unnikrishnan, K.

    2014-03-01

    In this study, 30 storm sudden commencement (SSC) events during the period 2001-2007 for which daytime vertical E B drift velocities from JULIA radar, Jicamarca (geographic latitude 11.91S, geographic longitude 283.11E, 0.81N dip latitude), Peru and ?H component of geomagnetic field measured as the difference between the magnitudes of the horizontal (H) components between two magnetometers deployed at two different locations Jicamarca (geographic latitude 11.91S, geographic longitude 283.11E, 0.81N dip latitude) and Piura (geographic latitude 5.21S, geographic longitude 279.41E, 6.81N dip latitude), in Peru, were considered. It is observed that a positive correlation exists between peak value of daytime vertical E B drift velocity and peak value of ?H for the three consecutive days of SSC. A qualitative analysis made after selecting the peak values of daytime vertical E B drift velocity and ?H showed that 57% of the events have daytime vertical E B drift velocity peak in the magnitude range 20-30 m/s and 63% of the events have ?H peak in the range 80-100 nT. The maximum probable (45%) range of time of occurrence of peak value for both vertical E B drift velocity and ?H during the daytime hours were found to be the same, i.e., 10:00-12:00 LT. A strong positive correlation was also found to exist between the daytime vertical E B drift velocity and ?H for all the three consecutive days of SSC, for all the events considered. To establish a quantitative relationship between day time vertical E B drift velocity and ?H, linear and polynomial (order 2 and 3) regression analysis (Least Square Method (LSM)) were carried out, considering the fully disturbed day after the commencement of the storm as disturbed period for the SSC events selected for analysis. The formulae indicating the relationship between daytime vertical E B drift velocity and ?H, for the disturbed periods, obtained through the regression analysis were verified using the JULIA radar observed E B drift velocity for 3 selected events. Root Mean Square (RMS) error analysis carried out for each case suggest that polynomial regression (order 3) analysis provides a better agreement with the observations from among the linear, polynomial (order 2 and 3) analysis.

  3. Kinetic effects on the KelvinHelmholtz instability in ion-to-magnetohydrodynamic scale transverse velocity shear layers: Particle simulations

    PubMed Central

    Nakamura, T. K. M.; Hasegawa, H.; Shinohara, I.

    2010-01-01

    Ion-to-magnetohydrodynamic scale physics of the transverse velocity shear layer and associated KelvinHelmholtz instability (KHI) in a homogeneous, collisionless plasma are investigated by means of full particle simulations. The shear layer is broadened to reach a kinetic equilibrium when its initial thickness is close to the gyrodiameter of ions crossing the layer, namely, of ion-kinetic scale. The broadened thickness is larger in B??<0 case than in B??>0 case, where ? is the vorticity at the layer. This is because the convective electric field, which points out of (into) the layer for B??<0 (B??>0), extends (reduces) the gyrodiameters. Since the kinetic equilibrium is established before the KHI onset, the KHI growth rate depends on the broadened thickness. In the saturation phase of the KHI, the ion vortex flow is strengthened (weakened) for B??<0 (B??>0), due to ion centrifugal drift along the rotational plasma flow. In ion inertial scale vortices, this drift effect is crucial in altering the ion vortex size. These results indicate that the KHI at Mercury-like ion-scale magnetospheric boundaries could show clear dawn-dusk asymmetries in both its linear and nonlinear growth. PMID:20838425

  4. Locality of ion-drift wave spectra in weakly-turbulent dusty plasmas

    NASA Astrophysics Data System (ADS)

    Onishchenko, Oleg G.; Pokhotelov, Oleg A.; Pavlenko, Vladimir P.; Sagdeev, Roald Z.; Stenflo, Lennart; Shukla, Padma K.

    2001-11-01

    The locality of weakly turbulent Kolmogorov spectra for the ion-drift waves in dusty plasmas and the flute waves in electron-ion plasmas is analyzed. Using a standard kinetic approach for the description of the wave turbulence it is shown that the wave spectrum associated with the enstrophy flux is nonlocal whereas that related to the energy flux is local. The nonlocality of the wave enstrophy spectrum is associated with the long wavelength part of the turbulence. It is found that the wave energy flux is directed to smaller spatial scales.

  5. Solvable Examples of Drift and Diffusion of Ions in Non-uniform Electric Fields

    SciTech Connect

    Cahn, Robert; Cahn, Robert N.; Jackson, John David

    2008-05-30

    The drift and diffusion of a cloud of ions in a fluid are distorted by an inhomogeneous electric field. If the electric field carries the center of the distribution in a straight line and the field configuration is suitably symmetric, the distortion can be calculated analytically. We examine the specific examples of fields with cylindrical and spherical symmetry in detail assuming the ion distributions to be of a generally Gaussian form. The effects of differing diffusion coefficients in the transverse and longitudinal directions are included.

  6. On the velocity distribution of ion jets during substorm recovery

    NASA Technical Reports Server (NTRS)

    Birn, J.; Forbes, T. G.; Hones, E. W., Jr.; Bame, S. J.; Paschmann, G.

    1981-01-01

    The velocity distribution of earthward jetting ions that are observed principally during substorm recovery by satellites at approximately 15-35 earth radii in the magnetotail is quantitatively compared with two different theoretical models - the 'adiabatic deformation' of an initially flowing Maxwellian moving into higher magnetic field strength (model A) and the field-aligned electrostatic acceleration of an initially nonflowing isotropic Maxwellian including adiabatic deformation effects (model B). The assumption is made that the ions are protons or, more generally, that they consist of only one species. It is found that both models can explain the often observed concave-convex shape of isodensity contours of the distribution function.

  7. A method for determining the drift velocity of plasma depletions in the equatorial ionosphere using far-ultraviolet spacecraft observations

    NASA Astrophysics Data System (ADS)

    Park, S. H.; England, S. L.; Immel, T. J.; Frey, H. U.; Mende, S. B.

    2007-11-01

    The Far-Ultraviolet Imager (IMAGE-FUV) on board the NASA IMAGE satellite has been used to observe plasma depletions in the nightside equatorial ionosphere. Observations from periods around spacecraft apogee, during which equatorial regions are visible for several hours, have allowed the velocity of these plasma depletions to be determined. A new method for determining the velocity of these depletions using an image analysis technique, Tracking Of Airglow Depletions (TOAD), has been developed. TOAD allows the objective identification and tracking of depletions. The automation of this process has also allowed for the tracking of a greater number of depletions than previously achieved without requiring any human input, which shows that TOAD is suitable for use with large data sets and for future routine monitoring of the ionosphere from space. Furthermore, this automation allows the drift velocities of each bubble to be determined as a function of magnetic latitude, which will give us the capability of retrieving geophysically important parameters such as the electric field, which are believed to vary rapidly with magnetic latitude.

  8. Two-Dimensional Numerical Simulation of Trapped Ion Mode and Drift Wave Turbulence.

    NASA Astrophysics Data System (ADS)

    Kingsbury, Owen Todd

    The first chapter is the paper entitled "Two-dimensional numerical simulation of trapped electron mode turbulent transport in a tokamak". Trapped electrons are lumped into hot and cold fluids to treat temperature gradient effects. The ion temperature gradient and dissipative trapped electron modes were simultaneously present. A plasma particle pinch was found only at extremely low collisionalities and a heat conduction pinch was found at moderate collisionalities, although there was no energy flow pinch seen. The second chapter is the paper entitled "Two -dimensional numerical simulation of trapped ion mode turbulence in a tokamak". The simulation of long wavelength trapped ion mode turbulence was used to investigate Bohm (macroscopic) versus gyro-Bohm (microscopic) scaling behavior in tokamaks. A nonlinear two-field model of dissipative trapped ion turbulence evolving trapped ion and trapped electron density fluctuations showed gyro-Bohm-like scaling in contrast to earlier simulation work by Saison, Wimmel, and Sardei (Plasma Physics, Vol. 20, pp. 1 to 20, 1978). In fact nearly all features of trapped ion mode turbulence and transport originally posited by Kadomstev and Pogutse (Reviews of Plasma Physics, Vol. 5) were recovered. The third chapter is the paper entitled "Numerical simulation of drift waves and trapped ion modes". Simulations were used to study the interaction of trapped electron drift waves (DW) and trapped ion modes (TIM). Wavenumber (k) space was divided into long wave and short wave regions at a poloidal wavenumber corresponding to the ion bounce frequency. Two field models were used to describe trapped electron drift wave dynamics at short waves and trapped ion mode dynamics for long waves. The principal result of this study was that the TIM did not contribute to the diffusion significantly, regardless of the model for the nonlinear coupling to the DW. The appendix documents a sparsely populated k -space grid scheme that was invented to perform the TIM/DW simulations. The method did not give physical results and was not used. The argument in the appendix states that it is not possible to mock up the nonlinear convolutions in Fourier representation such that some of the modes need not be included.

  9. A method for determining the drift velocity of plasma depletions in the equatorial ionosphere using far-ultraviolet spacecraft observations: initial results

    NASA Astrophysics Data System (ADS)

    England, S. L.; Immel, T. J.; Park, S. H.; Frey, H. U.; Mende, S. B.

    2007-12-01

    The Far-Ultraviolet Imager (IMAGE-FUV) on-board the NASA IMAGE satellite has been used to observe plasma depletions in the nightside equatorial ionosphere. Observations from periods around spacecraft apogee, during which equatorial regions are visible for several hours, have allowed the velocity of these plasma depletions to be determined. A new method for determining the velocity of these depletions using an image analysis technique, Tracking Of Airglow Depletions (TOAD), has been developed. TOAD allows the objective identification and tracking of depletions. The automation of this process has also allowed for the tracking of a greater number of depletions than previously achieved without requiring any human input, which shows that TOAD is suitable for use with large data sets and for future routine monitoring of the ionosphere from space. Furthermore, this allows the drift velocities of each depletion to be determined as a function of magnetic latitude as well as local time. Previous ground-based airglow observations from a small number of locations have indicated that the drift velocities of depletions may vary rapidly with magnetic latitude. Here we shall present the first results from TOAD of this shear in drift velocities from our global sample of depletion drift velocities.

  10. Beam dynamics of the Neutralized Drift Compression Experiment-II, a novel pulse-compressing ion accelerator

    SciTech Connect

    Friedman, A.; Barnard, J. J.; Cohen, R. H.; Grote, D. P.; Lund, S. M.; Sharp, W. M.; Faltens, A.; Henestroza, E.; Jung, J.-Y.; Kwan, J. W.; Lee, E. P.; Leitner, M. A.; Logan, B. G.; Vay, J.-L.; Waldron, W. L.; Davidson, R. C.; Dorf, M.; Gilson, E. P.; Kaganovich, I. D.

    2010-05-15

    Intense beams of heavy ions are well suited for heating matter to regimes of emerging interest. A new facility, NDCX-II, will enable studies of warm dense matter at approx1 eV and near-solid density, and of heavy-ion inertial fusion target physics relevant to electric power production. For these applications the beam must deposit its energy rapidly, before the target can expand significantly. To form such pulses, ion beams are temporally compressed in neutralizing plasma; current amplification factors of approx50-100 are routinely obtained on the Neutralized Drift Compression Experiment (NDCX) at the Lawrence Berkeley National Laboratory. In the NDCX-II physics design, an initial non-neutralized compression renders the pulse short enough that existing high-voltage pulsed power can be employed. This compression is first halted and then reversed by the beam's longitudinal space-charge field. Downstream induction cells provide acceleration and impose the head-to-tail velocity gradient that leads to the final neutralized compression onto the target. This paper describes the discrete-particle simulation models (one-, two-, and three-dimensional) employed and the space-charge-dominated beam dynamics being realized.

  11. Beam dynamics of the Neutralized Drift Compression Experiment-II (NDCX-II), a novel pulse-compressing ion accelerator

    SciTech Connect

    Friedman, A; Barnard, J J; Cohen, R H; Grote, D P; Lund, S M; Sharp, W M; Faltens, A; Henestroza, E; Jung, J; Kwan, J W; Lee, E P; Leitner, M A; Logan, B G; Vay, J; Waldron, W L; Davidson, R C; Dorf, M; Gilson, E P; Kaganovich, I

    2009-11-19

    Intense beams of heavy ions are well suited for heating matter to regimes of emerging interest. A new facility, NDCX-II, will enable studies of warm dense matter at {approx}1 eV and near-solid density, and of heavy-ion inertial fusion target physics relevant to electric power production. For these applications the beam must deposit its energy rapidly, before the target can expand significantly. To form such pulses, ion beams are temporally compressed in neutralizing plasma; current amplification factors of {approx}50-100 are routinely obtained on the Neutralized Drift Compression Experiment (NDCX) at LBNL. In the NDCX-II physics design, an initial non-neutralized compression renders the pulse short enough that existing high-voltage pulsed power can be employed. This compression is first halted and then reversed by the beam's longitudinal space-charge field. Downstream induction cells provide acceleration and impose the head-to-tail velocity gradient that leads to the final neutralized compression onto the target. This paper describes the discrete-particle simulation models (1-D, 2-D, and 3-D) employed and the space-charge-dominated beam dynamics being realized.

  12. Beam dynamics of the Neutralized Drift Compression Experiment-II (NDCX-II),a novel pulse-compressing ion accelerator

    SciTech Connect

    Friedman, A.; Barnard, J.J.; Cohen, R.H.; Grote, D.P.; Lund, S.M.; Sharp, W.M.; Faltens, A.; Henestroza, E.; Jung, J.-Y.; Kwan, J.W.; Lee, E.P.; Leitner, M.A.; Logan, B.G.; Vay, J.-L.; Waldron, W.L.; Davidson, R.C.; Dorf, M.; Gilson, E.P.; Kaganovich, I.D.

    2009-12-19

    Intense beams of heavy ions are well suited for heating matter to regimes of emerging interest. A new facility, NDCX-II, will enable studies of warm dense matter at {approx}1 eV and near-solid density, and of heavy-ion inertial fusion target physics relevant to electric power production. For these applications the beam must deposit its energy rapidly, before the target can expand significantly. To form such pulses, ion beams are temporally compressed in neutralizing plasma; current amplification factors of {approx}50-100 are routinely obtained on the Neutralized Drift Compression Experiment (NDCX) at LBNL. In the NDCX-II physics design, an initial non-neutralized compression renders the pulse short enough that existing high-voltage pulsed power can be employed. This compression is first halted and then reversed by the beam's longitudinal space-charge field. Downstream induction cells provide acceleration and impose the head-to-tail velocity gradient that leads to the final neutralized compression onto the target. This paper describes the discrete-particle simulation models (1-D, 2-D, and 3-D) employed and the space-charge-dominated beam dynamics being realized.

  13. Development of An Ion-Drift Time-of-Flight Chemical Ionization Mass Spectrometry Technique for Measurements of Aerosol Precursor Gases

    NASA Astrophysics Data System (ADS)

    Zheng, J.; Ma, Y.; Chen, M.

    2012-12-01

    We have developed a new technique, i.e., ion-drift time-of-flight chemical ionization mass spectrometry (ID-ToF-CIMS) for measurements of aerosol precursor gases, including ammonia, amines, organic acids and oxygenated VOCs at pptv level with a response time less than 1 s. The ID-ToF-CIMS was modified from an Aerodyne high resolution ToF-CIMS with a custom-designed ion-drift tube, which can control the ion flight velocity and hence the ion-molecular reaction time. In addition, the tunable electric field generated by the drift tube can break up water clusters to select the major reagent ions. The advantages of the ID-ToF-CIMS over the traditional quadrupole-based ID-CIMS were the high mass-resolving power of the ToF mass analyzer and the capability of simultaneous measurement of the full mass range (typically up to 300 m/z) of product ions. Using hydronium ion based reagent ions, we demonstrated that the ID-ToF-CIMS can unambiguously measure ammonia (NH3) at 18.03 m/z, methyl amine (CH3NH2) at 32.05 m/z, formic acid (HCOOH) at 47.01 m/z and acetone (CH3COCH3) at 59.05 m/z. Calibrations were performed with both compressed commercial standard gases and permeation tubes and the results showed that the instrument detection limit can reach pptv level for 1 s average time or less. The ID-ToF-CIMS was also field tested in a mobile laboratory on the campus of Nanjing University of Information Science & Technology (NUIST). The preliminary results will be discussed.

  14. Verifying changes to ion velocity distribution functions described by Baalrud's instability enhanced collision theory

    NASA Astrophysics Data System (ADS)

    Yip, Chi-Shung

    Experiments testing the recent theory of instability enhanced collisional friction formulated by Baalrud et al. is presented. To test the theory predictions on two stream instability enhanced collisional friction, drift velocities of Ar and Xe ions were measured using laser induced fluorescence (LIF) in Ar-Xe and Xe-He plasmas combined with acoustic wave and plasma potential data for varying relative concentrations and temperatures. The experimental data were found to be in excellent agreement with the theoretical predictions that ions tends to almost reach the system sound velocity at the sheath-edge when the relative concentrations are close, and their own Bohm's velocity when the relative concentrations are very different. The generalized Bohm Criterion for two ion species plasmas is verified for a wider variety of relative ion concentrations than have previously been investigated. The Baalrud theory also predicted that in single ion species plasmas, non-Maxwellian tails of ion velocity distribution functions (ivdfs) occurred due to charge exchange will be thermalized into the Maxwellian distribution when ions approach the sheath-edge. This phenomenon is predicted to cease occurring if electron temperature or neutral pressure is sufficiently high. To test this prediction, LIF measurements of ivdfs on single species xenon plasmas were performed, the data of which provided good qualitative agreement with the Baalrud theory. In addition, MacKenzie's Maxwell's demon and its instability was also studied. Its operation was found to be similar to that of a small metal plate that has comparable total conductive surface area as the total surface area of the wires, although the wire array had a far higher anode spot onset voltage. This enabled wider temperature variance without fundamentally changing the plasma. The demon instability found by MacKenzie et al. was also studied in this work and was found to be the pulsing anode spot instability studied by Stenzel et al. and Bin Song et al. Time resolved measurements of the instability provided sufficient insight for a simple model of the relaxation time formulated in this work.

  15. An updated climatology of thermospheric neutral winds and F region ion drifts above Millstone Hill

    NASA Astrophysics Data System (ADS)

    Buonsanto, M. J.; Witasse, O. G.

    1999-11-01

    Incoherent scatter radar data from 63 experiments during the period 1984-1997 have been used to update earlier published climatologies of ion drifts and neutral thermospheric winds at Millstone Hill. Data are binned according to season, solar activity, geomagnetic activity, and local solar time. The derived ion drift patterns are similar to those previously published, but we now find that the main effect of the increased magnetic activity is an enhancement of the usual nighttime west-ward ion drift. A tidal decomposition of the winds from geomagnetically quiet conditions is carried out for each season/solar activity level to extract diurnal means, diurnal amplitudes and phases, and semidiurnal components. These winds are compared with previous results at Millstone Hill and the HWM-93 model. Using our expanded wind database, statistically significant semidiurnal components are now found in both summer and winter, at both solar maximum and solar minimum. Our bin-averaged results confirm earlier published findings that at all seasons the diurnal mean winds are more strongly equatorward and the diurnal amplitudes are stronger at solar cycle minimum than at solar cycle maximum. Diurnal amplitudes derived in the present work are larger than those found previously because we now use a smaller value for the O+,O collision frequency. Differences in the diurnal mean and diurnal amplitude between recent solar minimum data (1993-1997) and data from the previous solar minimum (1984-1986) are attributed to a difference in the EUV flux as inferred from Millstone Hill electron density data which one would not expect from the F10.7 index. This affects the ion drag and apparently also the relative importance of the EUV and high latitude heat sources.

  16. A Monte Carlo simulation of the effect of ion self-collisions on the ion velocity distribution function in the high-latitude F-region

    NASA Technical Reports Server (NTRS)

    Barghouthi, I. A.; Barakat, A. R.; Schunk, R. W.

    1994-01-01

    Non-Maxwellian ion velocity distribution functions have been theoretically predicted and confirmed by observations, to occur at high latitudes. These distributions deviate from Maxwellian due to the combined effect of the E x B drift and ion-neutral collisions. At high altitude and/or for solar maximum conditions, the ion-to-neutral density ratio increases and, hence, the role of ion self-collisions becomes appreciable. A Monte Carlo simulation was used to investigate the behavior of O(+) ions that are E x B-drifting through a background of neutral O, with the effect of O(+) (Coulomb) self-collisions included. Wide ranges of the ion-to-neutral density ratio n(sub i)/n(sub n) and the electrostatic field E were considered in order to investigate the change of ion behavior with solar cycle and with altitude. For low altitudes and/or solar minimum (n(sub i)/n(sub n) less than or equal to 10(exp -5)), the effect of self-collisions is negligible. For higher values of n(sub i)/n(sub n), the effect of self-collisions becomes significant and, hence, the non-Maxwellian features of the O(+) distribution are reduced. The Monte Carlo results were compared to those that used simplified collision models in order to assess their validity. In general, the simple collision models tend to be more accurate for low E and for high n(sub i)/n(sub n).

  17. Li{sup +} alumino-silicate ion source development for the neutralized drift compression experiment

    SciTech Connect

    Roy, Prabir K.; Greenway, Wayne G.; Kwan, Joe W.; Seidl, Peter A.; Waldron, William L.; Wu, James K.

    2011-01-15

    We report results on lithium alumino-silicate ion source development in preparation for warm dense matter heating experiments on the new neutralized drift compression experiment II. The practical limit to the current density for a lithium alumino-silicate source is determined by the maximum operating temperature that the ion source can withstand before running into problems of heat transfer, melting of the alumino-silicate material, and emission lifetime. Using small prototype emitters, at a temperature of {approx_equal}1275 deg. C, a space-charge limited Li{sup +} beam current density of J {approx_equal}1 mA/cm{sup 2} was obtained. The lifetime of the ion source was {approx_equal}50 h while pulsing at a rate of 0.033 Hz with a pulse duration of 5-6 {mu}s.

  18. Li+ alumino-silicate ion source development for the Neutralized Drift Compression Experiment (NDCX)

    SciTech Connect

    Roy, Prabir K.; Greenway, Wayne G.; Kwan, Joe W.; Seidl, Peter A.; Waldron, William L.; Wu, James K.

    2010-10-01

    We report results on lithium alumino-silicate ion source development in preparation for warmdense-matter heating experiments on the new Neutralized Drift Compression Experiment (NDCXII). The practical limit to the current density for a lithium alumino-silicate source is determined by the maximum operating temperature that the ion source can withstand before running into problems of heat transfer, melting of the alumino-silicate material, and emission lifetime. Using small prototype emitters, at a temperature of ~;;1275 oC, a space-charge-limited Li+ beam current density of J ~;;1 mA/cm2 was obtained. The lifetime of the ion source was ~;;50 hours while pulsing at a rate of 0.033 Hz with a pulse duration of 5-6 mu s.

  19. MeV ion sputtering of polymers: correlation between secondary ion radial velocity distributions and heavy ion track structure

    NASA Astrophysics Data System (ADS)

    Papalo, R. M.; Brinkmalm, G.; Feny, D.; Eriksson, J.; Kammer, H. F.; Demirev, P.; Hkansson, P.; Sundqvist, B. U. R.

    1994-06-01

    Systematic investigations of the initial radial velocity distributions of low mass positive and negative secondary ions, sputtered electronically from thin films of polyvinylidene fluoride and polystyrene, are reported. 72.3 MeV 127I13+ primary ions bombard the targets at 45 angle of incidence. Sputtered secondary ions in an individual MeV ion impact are analysed in a high resolution time-of-flight mass spectrometer. The accurate mass measurements of all ion peaks in the range from 1 to 100 m/z provide unequivocal determination of the chemical composition of these ions, forming homologous series, CnHm and CnHmFp. Plots of both the initial mean radial velocity () and kinetic energy (? ) as a function of the ion m/z results in a periodic pattern. Ions with lower hydrogen content exhibit wider velocity distributions (i.e. higher ) and () directed towards the primary ion trajectory. Ions with higher hydrogen content have lower mean kinetic energies and directed away from the incident ion trajectory. We argue that the and periodic behaviour, connected to the chemical constitution of the ions, reflects the radial profile of the deposited energy density in the heavy ion track.

  20. A gated atmospheric pressure drift tube ion mobility spectrometer-time-of-flight mass spectrometer.

    PubMed

    Heptner, Andre; Reinecke, Tobias; Langejuergen, Jens; Zimmermann, Stefan

    2014-08-22

    Identifying the compounds of an unknown gas mixture by using an ion mobility spectrometer (IMS) is a difficult task, because several ion species can be generated in the ionization process. One method to analyze the occurring peaks in an IMS spectrum is coupling an IMS to a mass spectrometer (MS). In our setup we coupled a (3)H drift tube IMS to a Bruker micrOTOF II. Therefore, the detector plate of the IMS is pierced and a transfer capillary is inserted. The ions are transferred via gas flow and electric fields into the MS. The transmission of the ions through the transfer capillary can be shuttered very precisely by increasing the electric potential of the detector generating a repulsive electric field. Thus, it is possible to transfer single ion clouds of generated IMS spectra into the mass spectrometer where a corresponding mass spectrum is generated. In this work we analyze the positive and negative IMS spectra of single analytes as well as gas mixtures and characterize the occurring ion species. PMID:25015244

  1. Anisotropy of the He+, C+, N+, O+, and Ne+ pickup ion velocity distribution functions

    NASA Astrophysics Data System (ADS)

    Drews, C.; Berger, L.; Taut, A.; Wimmer-Schweingruber, R. F.

    2016-04-01

    Context. Interstellar and inner-source pickup ions (PUIs) are produced by the ionization of neutral atoms that originate either outside or inside the heliosphere. Just after ionization, the singly charged ions are picked up by the magnetized solar wind plasma and develop strong anisotropic toroidal features in their velocity distribution functions (VDF). As the plasma parcel moves outwards with the solar wind, the pickup ion VDF gets more and more affected by resonant wave-particle interactions, changing heliospheric conditions, and plasma drifts, which lead to a gradual isotropization of the pickup ion VDF. Past investigations of the pickup ion torus distribution were limited to He+ pickup ions at 1 astronomical unit (AU). Aims: The aim of this study is to quantify the state of anisotropy of the He+, C+, N+, O+, and Ne+ pickup ion VDF at 1 AU. Changes between the state of anisotropy between PUIs of different mass-per-charges can be used to estimate the significance of resonant wave-particle interactions for the isotropization of their VDF, and to investigate the numerous simplifications that are generally made for the description of the phase-space transport of PUIs. Methods: Pulse height analysis data by the PLAsma and SupraThermal Ion Composition instrument (PLASTIC) on board the Solar Terrestrial RElations Observatory Ahead (STEREO A) is used to obtain velocity-spectra of He+, C+, N+, O+, and Ne+ relative to the solar wind, f(wsw). The wsw-spectra are sorted by two different configurations of the local magnetic field - one in which the torus distribution lies within the instrument's aperture, φ⊥, and one in which the torus distribution lies exclusively outside the instrument's field of view, φ∥. The ratio of the PUI spectra between φ⊥ and φ∥ is used to determine the degree of anisotropy of the PUI VDF. Results: The data shows that the formation of a torus distribution at 1 AU is significantly more prominent for O+ (and N+) than for He+ (and Ne+). This cannot be explained by resonant wave-particle interactions as the sole mechanism for the isotropization of the PUI VDF. The anisotropy of the O+ VDF compared to He+ is highly fluctuating but consistently higher over an observation period of six years and therefore unlikely to be related to either specific heliospheric conditions or solar activity variations. To our surprise, we also found a clear signature of a C+ torus distribution at 1 AU very similar to the one of He+, although as an inner-source PUI, C+ should have a considerably different spectral and spatial injection pattern than interstellar PUIs.

  2. Heat flux modeling using ion drift effects in DIII-D H-mode plasmas with resonant magnetic perturbations

    NASA Astrophysics Data System (ADS)

    Wingen, A.; Schmitz, O.; Evans, T. E.; Spatschek, K. H.

    2014-01-01

    The heat flux patterns measured in low-collisionality DIII-D H-mode plasmas strongly deviate from simultaneously measured CII emission patterns, used as indicator of particle flux, during applied resonant magnetic perturbations. While the CII emission clearly shows typical striations, which are similar to magnetic footprint patterns obtained from vacuum field line tracing, the heat flux is usually dominated by one large peak at the strike point position. The vacuum approximation, which only considers applied magnetic fields and neglects plasma response and plasma effects, cannot explain the shape of the observed heat flux pattern. One possible explanation is the effect of particle drifts. This is included in the field line equations and the results are discussed with reference to the measurement. Electrons and ions show different drift motions at thermal energy levels in a guiding center approximation. While electrons hardly deviate from the field lines, ions can drift several centimetres away from field line flux surfaces. A model is presented in which an ion heat flux, based on the ion drift motion from various kinetic energies as they contribute to a thermal Maxwellian distribution, is calculated. The simulated heat flux is directly compared to measurements with a varying edge safety factor q95. This analysis provides evidence for the dominate effect of high-energy ions in carrying heat from the plasma inside the separatrix to the target. High-energy ions are deposited close to the unperturbed strike line, while low-energy ions can travel into the striated magnetic topology.

  3. Threshold field for soft damage and electron drift velocity in InGaN two-dimensional channels

    NASA Astrophysics Data System (ADS)

    Ardaravi?ius, L.; Kiprijanovi?, O.; Liberis, J.; ermuknis, E.; Matulionis, A.; Ferreyra, R. A.; Avrutin, V.; zgr, .; Morko, H.

    2015-10-01

    Experimental investigation of electron transport along a two-dimensional channel confined in an InGaN alloy of Al{}0.82In{}0.18N/AlN/In{}0.1Ga{}0.9N/GaN structure was performed at room temperature under near-equilibrium thermal-bath temperature. A soft damage was observed at a threshold electric field applied in the channel plane. The threshold current for soft damage and the supplied electric power were lower in the channels with a higher electron density. The results are interpreted in terms of plasmon-assisted heat dissipation. In agreement with ultra-fast decay of hot phonons in the vicinity of the resonance with plasmons, the electron drift velocity acquires a highest value of ?2 107 cm s?1 at 180 kV cm?1 in channels with 1 1013 cm?2 and decreases as the electron density increases. No negative differential resistance is observed. The effective hot-phonon lifetime is estimated as ? 2 ps at 1.6 1013 cm?2 at low electric fields and is found to decrease as the field increases.

  4. Effects of drift gas on collision cross sections of a protein standard in linear drift tube and traveling wave ion mobility mass spectrometry.

    PubMed

    Jurneczko, Ewa; Kalapothakis, Jason; Campuzano, Iain D G; Morris, Michael; Barran, Perdita E

    2012-10-16

    There has been a significant increase in the use of ion mobility mass spectrometry (IM-MS) to investigate conformations of proteins and protein complexes following electrospray ionization. Investigations which employ traveling wave ion mobility mass spectrometry (TW IM-MS) instrumentation rely on the use of calibrants to convert the arrival times of ions to collision cross sections (CCS) providing "hard numbers" of use to structural biology. It is common to use nitrogen as the buffer gas in TW IM-MS instruments and to calibrate by extrapolating from CCS measured in helium via drift tube (DT) IM-MS. In this work, both DT and TW IM-MS instruments are used to investigate the effects of different drift gases (helium, neon, nitrogen, and argon) on the transport of multiply charged ions of the protein myoglobin, frequently used as a standard in TW IM-MS studies. Irrespective of the drift gas used, recorded mass spectra are found to be highly similar. In contrast, the recorded arrival time distributions and the derived CCS differ greatly. At low charge states (7 ? z ? 11) where the protein is compact, the CCS scale with the polarizability of the gas; this is also the case for higher charge states (12 ? z ? 22) where the protein is more unfolded for the heavy gases (neon, argon, and nitrogen) but not the case for helium. This is here interpreted as a different conformational landscape being sampled by the lighter gas and potentially attributable to increased field heating by helium. Under nanoelectrospray ionization (nESI) conditions, where myoglobin is sprayed from an aqueous solution buffered to pH 6.8 with 20 mM ammonium acetate, in the DT IM-MS instrument, each buffer gas can yield a different arrival time distribution (ATD) for any given charge state. PMID:22974196

  5. SIMULATIONS OF HIGH-VELOCITY CLOUDS. I. HYDRODYNAMICS AND HIGH-VELOCITY HIGH IONS

    SciTech Connect

    Kwak, Kyujin; Henley, David B.; Shelton, Robin L. E-mail: dbh@physast.uga.edu

    2011-09-20

    We present hydrodynamic simulations of high-velocity clouds (HVCs) traveling through the hot, tenuous medium in the Galactic halo. A suite of models was created using the FLASH hydrodynamics code, sampling various cloud sizes, densities, and velocities. In all cases, the cloud-halo interaction ablates material from the clouds. The ablated material falls behind the clouds where it mixes with the ambient medium to produce intermediate-temperature gas, some of which radiatively cools to less than 10,000 K. Using a non-equilibrium ionization algorithm, we track the ionization levels of carbon, nitrogen, and oxygen in the gas throughout the simulation period. We present observation-related predictions, including the expected H I and high ion (C IV, N V, and O VI) column densities on sightlines through the clouds as functions of evolutionary time and off-center distance. The predicted column densities overlap those observed for Complex C. The observations are best matched by clouds that have interacted with the Galactic environment for tens to hundreds of megayears. Given the large distances across which the clouds would travel during such time, our results are consistent with Complex C having an extragalactic origin. The destruction of HVCs is also of interest; the smallest cloud (initial mass {approx} 120 M{sub sun}) lost most of its mass during the simulation period (60 Myr), while the largest cloud (initial mass {approx} 4 x 10{sup 5} M{sub sun}) remained largely intact, although deformed, during its simulation period (240 Myr).

  6. Modeling of ion acceleration through drift and diffusion at interplanetary shocks

    NASA Technical Reports Server (NTRS)

    Decker, R. B.; Vlahos, L.

    1986-01-01

    A test particle simulation designed to model ion acceleration through drift and diffusion at interplanetary shocks is described. The technique consists of integrating along exact particle orbits in a system where the angle between the shock normal and mean upstream magnetic field, the level of magnetic fluctuations, and the energy of injected particles can assume a range of values. The technique makes it possible to study time-dependent shock acceleration under conditions not amenable to analytical techniques. To illustrate the capability of the numerical model, proton acceleration was considered under conditions appropriate for interplanetary shocks at 1 AU, including large-amplitude transverse magnetic fluctuations derived from power spectra of both ambient and shock-associated MHD waves.

  7. Relative ion expansion velocity in laser-produced plasmas

    SciTech Connect

    Goldsmith, S.; Moreno, J.C.; Griem, H.R.; Cohen, L.; Richardson, M.C.

    1988-07-15

    The spectra of highly ionized titanium, TiXIII through TiXXI, and CVI Lyman lines were excited in laser-produced plasmas. The plasma was produced by uniformly irradiating spherical glass microballoons coated with thin layers of titanium and parylene. The 24-beam Omega laser system produced short, 0.6 ns, and high intensity, 4 x 10/sup 14/ W/cm,/sup 2/ laser pulses at a wavelength of 351 nm. The measured wavelength for the 2p-3s TiXIII resonance lines had an average shift of +0.023 A relative to the CVI and TiXX spectral lines. No shift was found between the CVI, TiXIX, and TiXX lines. The shift is attributed to a Doppler effect, resulting from a difference of (2.6 +- 0.2) x 10/sup 7/ cm/s in the expansion velocities of TiXIX and TiXX ions compared to TiXIII ions.

  8. Relative ion expansion velocity in laser-produced plasmas

    NASA Technical Reports Server (NTRS)

    Goldsmith, S.; Moreno, J. C.; Griem, H. R.; Cohen, Leonard; Richardson, M. C.

    1988-01-01

    The spectra of highly ionized titanium, Ti XIII through Ti XXI, and C VI Lyman lines were excited in laser-produced plasmas. The plasma was produced by uniformly irradiating spherical glass microballoons coated with thin layers of titanium and parylene. The 24-beam Omega laser system produced short, 0.6 ns, and high-intensity, 4 x 10 to the 14th W/sq cm, laser pulses at a wavelength of 351 nm. The measured wavelength for the 2p-3s Ti XIII resonance lines had an average shift of + 0.023 A relative to the C VI and Ti XX spectral lines. No shift was found between the C VI, Ti XIX, and Ti XX lines. The shift is attributed to a Doppler effect, resulting from a difference of (2.6 + or - 0.2) x 10 to the 7th cm/s in the expansion velocities of Ti XIX and Ti XX ions compared to Ti XIII ions.

  9. Ion flux energy distributions in a hydrogen-filled drift tube at high E/N

    NASA Astrophysics Data System (ADS)

    Phelps, Arthur

    2008-10-01

    Ion flux energy distributions are calculated for H^+, H2^+, and H3^+ ions in H2 for low-current, uniform-electric-field drift tubes at 1 kTd < E/N < 10 kTd and 5x10^20 <=N d <=3x10^21 m^2, where E is the electric field, N is the gas density, and d is the electrode separation. We use updated cross sections in a multi-beam model of the spatial and energy dependent particle fluxes. Calculated distributions at the cathode are compared with experiments by Rao et al. and detailed theory by Bretagne et al. Hypothetical large increases in the total momentum transfer cross sections for H^+ and H3^+ at 100 to 1000 eV yield approximate fits to the relative experimental distributions at high energies at moderate E/N. However, these fitted distributions are much too small at low ion energies. Similar discrepancies occur for analytic solutions of the Boltzmann equations using simplified reaction cross sections and the almost free-fall conditions for H^+ at 10 kTd.

  10. Electron drift velocities and electron mobilities in fast room-temperature dielectric liquids and their corresponding vapors

    NASA Astrophysics Data System (ADS)

    Faidas, H.; Christophorou, L. G.; McCorkle, D. L.; Carter, J. G.

    1990-09-01

    The drift velocity, w, of excess electrons as a function of the applied uniform electric field, E, in liquid tetramethylsilane (TMS), 2,2,4,4-tetramethylpentane (TMP), tetramethyltin (TMT), and in mixtures of TMS with TMP (molar ratio, M = 1.31/1) and n-pentane ( M = 102/1; 17/1; 5.6/1) has been measured up to E-values of 10 5 V cm -1 or density ( N)-reduced ele ctric held E/ N-values of 3 10 -17 V cm 2. The maximum w attained for these liquids, and the corresponding values of E are: 7.2 10 6 cm s -1 at 125 kV cm -1 for TMS, 6.0 10 6 cm s -1 at 75 kV cm -1 for TMS, 2.6 10 6 cm s -1 at 115 kV cm -1 for TMP, 3.2 10 6 cm s -1 at 105 kV cm -1 for TMS/TMP ( M = 1.31/1), 6.8 10 6 cm s -1 at 105 kV cm -1 for TMS/n-pentane ( M = 102/1), 6.8 10 6 cm s -1 at 145 kV cm -1 for TMS/n-pentane ( M = 17/1), and 4.9 10 6 cm s -1 at 145 kV cm -1 for TMS/n-pentane ( M = 5.6/1). The thermal-electron mobilities in the above liquid media are respectively 119.3, 85.7, 31.8, 39.1, 118, 85, and 47.6 cm 2 s -1 V -1. Also, w was measured as a function of E/ N for TMS, TMP, and neopentane vapors at room temperature and is compared with that in the corresponding liquids. Properties of these media which make them desirable for radiation detectors are discussed.

  11. Kinetic water-bag model of global collisional drift waves and ion temperature gradient instabilities in cylindrical geometry

    SciTech Connect

    Gravier, E.; Plaut, E.

    2013-04-15

    Collisional drift waves and ion temperature gradient (ITG) instabilities are studied using a linear water-bag kinetic model [P. Morel et al., Phys. Plasmas 14, 112109 (2007)]. An efficient spectral method, already validated in the case of drift waves instabilities [E. Gravier et al., Eur. Phys. J. D 67, 7 (2013)], allows a fast solving of the global linear problem in cylindrical geometry. The comparison between the linear ITG instability properties thus computed and the ones given by the COLUMBIA experiment [R. G. Greaves et al., Plasma Phys. Controlled Fusion 34, 1253 (1992)] shows a qualitative agreement. Moreover, the transition between collisional drift waves and ITG instabilities is studied theoretically as a function of the ion temperature profile.

  12. Regime transition of ion Bernstein instability driven by ion shell velocity distributions

    NASA Astrophysics Data System (ADS)

    Min, Kyungguk; Liu, Kaijun

    2015-10-01

    Linear kinetic dispersion theory is used to investigate a regime transition of the ion Bernstein instability driven by a proton velocity distribution with positive slopes with respect to the perpendicular velocity, ?fp(v?0,v?)/?v?>0. The unstable waves arising from this instability are ion Bernstein waves with proton cyclotron harmonic dispersion. However, in the inner magnetosphere, particularly inside of the plasmapause where plasmas are dominated by a cold background, the instability leads to ion Bernstein waves which approximately follow the cold plasma dispersion relation for fast magnetosonic waves and are, therefore, fast magnetosonic-like. Subsequently, the relevant waves have been termed fast magnetosonic waves and many studies have assumed the cold plasma dispersion relation to describe them. On the other hand, how the dispersion properties of ion Bernstein waves become fast magnetosonic-like has not yet been well understood. To examine this regime transition of the instability, we perform linear dispersion analyses using a two-component proton model of fp(v) = fM(v) + fs(v), where fM is a Maxwellian velocity distribution and fs is an isotropic shell velocity distribution. The results show that the unstable waves are essentially ion Bernstein waves; however, when the shell proton concentration becomes sufficiently small (less than 10), the unstable waves approach the cold plasma dispersion relation for fast magnetosonic waves and become fast magnetosonic-like. Although a reduced proton-to-electron mass ratio of 100 has been used for convenience, which reduces the number of unstable modes involved by lowering the lower hybrid frequency, this does not change the overall regime transition picture revealed in this study.

  13. Mobility-Resolved Ion Selection in Uniform Drift Field Ion Mobility Spectrometry/Mass Spectrometry; Dynamic Switching in Structures for Lossless Ion Manipulations

    SciTech Connect

    Webb, Ian K.; Garimella, Venkata BS; Tolmachev, Aleksey V.; Chen, Tsung-Chi; Zhang, Xinyu; Cox, Jonathan T.; Norheim, Randolph V.; Prost, Spencer A.; Lamarche, Brian L.; Anderson, Gordon A.; Ibrahim, Yehia M.; Smith, Richard D.

    2014-10-07

    A Structures for Lossless Ion Manipulations (SLIM) module that allows ion mobility separations and the switching of ions between alternative drift paths is described. The SLIM switch component has a “Tee” configuration and allows switching of ions between a linear path and a 90-degree bend. By controlling switching times, ions can be deflected to an alternative channel as a function of their mobilities. In the initial evaluation the switch is used in a static mode and shown compatible with high performance ion mobility separations at 4 torr. In the “dynamic mode” we show that mobility-selected ions can be switched into the alternative channel, and that various ion species can be independently selected based on their mobilities for time-of-flight mass spectrometer (TOF MS) IMS detection and mass analysis. This development also provides the basis for e.g. the selection of specific mobilities for storage and accumulation, and key modules for the assembly of SLIM devices enabling much more complex sequences of ion manipulations.

  14. Effect of small-scale plasma turbulence on altitude profiles of electron drift velocity in the equatorial electrojet: An experimental study

    SciTech Connect

    Murthy, B.V.K.; Ravindran, S.

    1994-10-01

    The authors report recent observations of the effect of turbulence on the altitude behavior of the equatorial electrojet. Their results show that with an increase in observed turbulence that the altitude of maximum in the electron drift velocity shifts to higher altitudes. This is consistent with recent theoretical work which shows that small scale turbulence can produce large-scale changes in the dynamics of the equatorial electrojet.

  15. Track-membrane-based interface for field evaporation of ions from polar solutions in the diffusion-drift regime

    NASA Astrophysics Data System (ADS)

    Balakin, A. A.; Buido, E. A.

    2013-11-01

    The possibility of realization of barrier-free field evaporation regime for ions from polar solutions in the conditions when the flux of ions from the liquid is limited by their diffusion and drift from the bulk to the surface is considered. The strength of the electric field extracting ions is estimated by simulating electric fields in an ion source with a track membrane as the interface with allowance for the sizes of channels in the membrane and their density. It is shown that when time-dependent electric fields are used, the regime of barrier-free field evaporation can be realized with an appropriate choice of geometrical parameters of the membrane.

  16. Parametric Excitation of Geodesic Acoustic Modes by Electron Drift Waves and Ion Temperature Gradient Modes in Tokamak Plasmas

    SciTech Connect

    Guzdar, P. N.; Kleva, R. G.; Chakrabarti, N.; Kaw, P. K.; Singh, R.; Naulin, V.; Rasmussen, J. J.

    2008-11-01

    Geodesic Acoustic Modes (GAMs) have been predicted and subsequently observed in many toroidal plasma devices. Bicoherence studies on various devices have suggested three-wave mode coupling processes between GAMs and high frequency turbulence. Thus the parametric coupling of GAMS to drift waves and/or ion temperature gradient(ITG{r_brace} modes is a potential candidate for excitation of these modes. In this paper we discuss the resonant three-wave coupling mechanism for the excitation of GAMs by ITG and finite beta drift waves in homogeneous and inhomogeneous plasmas and compare theoretical predictions with observed characteristics of the GAMs.

  17. Spectroscopic measurement of ion temperature and ion velocity distributions in the flux-coil generated FRCa)

    NASA Astrophysics Data System (ADS)

    Gupta, D.; Bolte, N.; Gota, H.; Hayashi, R.; Kiyashko, V.; Marsili, P.; Morehouse, M.; Primavera, S.; Roche, T.; Wessel, F.

    2010-10-01

    One aim of the flux-coil generated field reversed configuration at Tri Alpha Energy (TAE) is to establish the plasma where the ion rotational energy is greater than the ion thermal energy. To verify this, an optical diagnostic was developed to simultaneously measure the Doppler velocity-shift and line-broadening using a 0.75 m, 1800 groves/mm, spectrometer. The output spectrum is magnified and imaged onto a 16-channel photomultiplier tube (PMT) array. The individual PMT outputs are coupled to high-gain, high-frequency, transimpedance amplifiers, providing fast-time response. The Doppler spectroscopy measurements, along with a survey spectrometer and photodiode-light detector, form a suite of diagnostics that provide insights into the time evolution of the plasma-ion distribution and current when accelerated by an azimuthal-electric field.

  18. Spectroscopic measurement of ion temperature and ion velocity distributions in the flux-coil generated FRC

    SciTech Connect

    Gupta, D.; Gota, H.; Hayashi, R.; Kiyashko, V.; Morehouse, M.; Primavera, S.; Bolte, N.; Marsili, P.; Roche, T.; Wessel, F.

    2010-10-15

    One aim of the flux-coil generated field reversed configuration at Tri Alpha Energy (TAE) is to establish the plasma where the ion rotational energy is greater than the ion thermal energy. To verify this, an optical diagnostic was developed to simultaneously measure the Doppler velocity-shift and line-broadening using a 0.75 m, 1800 groves/mm, spectrometer. The output spectrum is magnified and imaged onto a 16-channel photomultiplier tube (PMT) array. The individual PMT outputs are coupled to high-gain, high-frequency, transimpedance amplifiers, providing fast-time response. The Doppler spectroscopy measurements, along with a survey spectrometer and photodiode-light detector, form a suite of diagnostics that provide insights into the time evolution of the plasma-ion distribution and current when accelerated by an azimuthal-electric field.

  19. Li+ alumino-silicate ion source development for the Neutralized Drift Compression Experiment (NDCX-II)

    SciTech Connect

    LBNL; Roy, P.K.; Greenway, W.; Kwan, J.W.; Seidl, P.A.; Waldron, W.

    2011-04-20

    To heat targets to electron-volt temperatures for the study of warm dense matter with intense ion beams, low mass ions, such as lithium, have an energy loss peak (dE/dx) at a suitable kinetic energy. The Heavy Ion Fusion Sciences (HIFS) program at Lawrence Berkeley National Laboratory will carry out warm dense matter experiments using Li{sup +} ion beam with energy 1.2-4 MeV in order to achieve uniform heating up to 0.1-1 eV. The accelerator physics design of Neutralized Drift Compression Experiment (NDCX-II) has a pulse length at the ion source of about 0.5 {micro}s. Thus for producing 50 nC of beam charge, the required beam current is about 100 mA. Focusability requires a normalized (edge) emittance {approx}2 {pi}-mm-mrad. Here, lithium aluminosilicate ion sources, of {beta}-eucryptite, are being studied within the scope of NDCX-II construction. Several small (0.64 cm diameter) lithium aluminosilicate ion sources, on 70%-80% porous tungsten substrate, were operated in a pulsed mode. The distance between the source surface and the mid-plane of the extraction electrode (1 cm diameter aperture) was 1.48 cm. The source surface temperature was at 1220 C to 1300 C. A 5-6 {micro}s long beam pulsed was recorded by a Faraday cup (+300 V on the collector plate and -300 V on the suppressor ring). Figure 1 shows measured beam current density (J) vs. V{sup 3/2}. A space-charge limited beam density of {approx}1 mA/cm{sup 2} was measured at 1275 C temperature, after allowing a conditioning time of about {approx} 12 hours. Maximum emission limited beam current density of {ge} 1.8mA/cm{sup 2} was recorded at 1300 C with 10-kV extractions. Figure 2 shows the lifetime of two typical sources with space-charge limited beam current emission at a lower extraction voltage (1.75 kV) and at temperature of 1265 {+-} 7 C. These data demonstrate a constant, space-charge limited beam current for 20-50 hours. The lifetime of a source is determined by the loss of lithium from the alumino-silicate material either as ions or as neutral atoms. Our measurements suggest that for the low duty factor ({approx}10{sup -8}) required for NDCX-II, the lifetime of an emitter depends mostly on the duration that the emitter spends at elevated temperature, that is, at {ge} 1250 C. At this temperature, lithium loss is due mostly to neutral loss (not charged ion extraction). Extension of the lifetime of the source may be possible by lowering the temperature between beam pulses, when the idling time is sufficiently long between shots. The NDCX-II design seeks to operate the ion source at the maximum current density without running into heat management and lifetime problems. In preparation to fabricate a large (10.9 cm in diameter) source for the NDCXII experiment, recently a 7.6 cm diameter source has been fabricated. The method of fabrication of this larger source is similar to that of fabrication of a 6.3mm diameter source, except a longer furnace heating time was used due to mass differences. NDCX-II construction is in progress. Progress of lithium source study for NDCX-II is available in literature.

  20. Characteristics of equatorial plasma bubble zonal drift velocity and tilt based on Hong Kong GPS CORS network: From 2001 to 2012

    NASA Astrophysics Data System (ADS)

    Ji, Shengyue; Chen, Wu; Weng, Duojie; Wang, Zhenjie

    2015-08-01

    Hong Kong (22.3N, 114.2E, dip: 30.5N; geomagnetic 15.7N, 173.4W, declination: 2.7W) is a low-latitude area, and the Hong Kong Continuously Operating Reference Station (CORS) network has been developed and maintained by Lands Department of Hong Kong government since 2001. Based on the collected GPS observations of a whole solar cycle from 2001 to 2012, a method is proposed to estimate the zonal drift velocity as well as the tilt of the observed plasma bubbles, and the estimated results are statistically analyzed. It is found that although the plasma bubbles are basically vertical within the equatorial plane, the tilt can be as big as more than 60 eastward or westward sometimes. And, the tilt and the zonal drift velocity are correlated. When the velocity is large, the tilt is also large generally. Another finding is that large velocity and tilt generally occur in spring and autumn and in solar active years.

  1. Neoclassical polarization drift of collisionless single ions in a sheared radial electric field in a tokamak magnetic geometry

    SciTech Connect

    Baek, Hoyul; Ku, Seunghoe; Chang, C. S.

    2006-01-15

    Neoclassical polarization drift is known to play critical role in the dynamical behavior of a sheared radial electric field E{sub r} in a toroidal confinement device. However, basic studies on the effect of radial electric shear on neoclassical polarization drift have not yet appeared in the literature. In the present report, the neoclassical polarization drift speed V{sub NP} of collisionless single ions is studied using a guiding-center code in a time-varying, spatially sheared E{sub r} in a realistic tokamak geometry. It is found numerically that the V{sub NP} for single ions is not only a function of the time derivative {partial_derivative}E{sub r}/{partial_derivative}t, but also a strong function of the radial shear {delta}r{partial_derivative}E{sub r}/{partial_derivative}r if the shear length is on the same order as the ion banana width {delta}r. Comparison with an analytic investigation reveals that this effect is simply due to the finite banana modification to the orbital average E{sub r}. An approximate analytic formula has been presented for collisionless single banana ions in a conventional tokamak magnetic geometry. The trapped-passing boundary layer physics is not treated.

  2. Ion velocity distributions in the vicinity of the current sheet in Earth's distant magnetotail

    NASA Technical Reports Server (NTRS)

    Frank, L. A.; Paterson, W. R.; Ackerson, K. L.; Kokubun, S.; Kivelson, M. G.; Yamamoto, T.; Fairfield, D. H.

    1994-01-01

    Observations of the three-dimensional velocity distributions of positive ions and electrons have been recently gained for the first time in Earth's distant magnetotail with the Galileo and Geotail spacecraft. For this brief discussion of these exciting results the focus is on the overall character of the ion velocity distributions during substorm activity. The ion velocity distributions within and near the magnetotail current sheet are not accurately described as convecting, isotropic Maxwellians. The observed velocity distributions are characterized by at least two robust types. The first type is similar to the 'lima bean'-shaped velocity distributions that are expected from the nonadiabatic acceleration of ions which execute Speiser-type trajectories in the current sheet. The second distribution is associated with the presence of cold ion beams that presumably also arise from the acceleration of plasma mantle ions in the electric and weak magnetic fields in the current sheet. The ion velocity distributions in a magnetic field structure that is similar to that for plasmoids are also examined. Again the velocity distributions are not Maxwellian but are indicative of nonadiabatic acceleration. An example of the pressure tensor within the plasmoid-like event is also presented because it is anticipated that the off-diagonal elements are important in a description of magnetotail dynamics. Thus our concept of magnetotail dynamics must advance from the present assumption of co-moving electron and ion Maxwellian distributions into reformulations in terms of global kinematical models and nonadiabatic particle motion.

  3. Simulated ion velocity distribution and its incoherent scattering spectrum in the high-latitude ionosphere

    NASA Astrophysics Data System (ADS)

    Ma, Bao-Ke; Guo, Li-Xin; Su, Hong-Tao; Zhang, Bei-Chen

    2013-10-01

    If the relatively larger convection electric field and small the collision frequency between ions and neutrals in the high-latitude ionosphere are considered, the integral solution of the non-Maxwellian ion velocity distribution function for the relaxation collision model is simplified, and a torus distribution function of the ion velocity is obtained. Also, the feature of the torus velocity distribution function is analyzed and simulated with different parameters in high-latitude ionosphere. Furthermore, by using the electromagnetic radiation theory of Sheffield and taking into account the ion temperature anisotropy and its variation with the electric field, we simulate the incoherent scattering spectrum of ions in different directions. The research shows that the ionospheric convection electric field, the ion-neutral collision frequency and the ion anisotropic temperature distribution all have an effect on the incoherent scattering spectrum.

  4. Enhancing Biological Analyses with Three Dimensional Field Asymmetric Ion Mobility, Low Field Drift Time Ion Mobility and Mass Spectrometry (µFAIMS/IMS-MS) Separations

    SciTech Connect

    Zhang, Xing; Ibrahim, Yehia M.; Chen, Tsung-Chi; Kyle, Jennifer E.; Norheim, Randolph V.; Monroe, Matthew E.; Smith, Richard D.; Baker, Erin Shammel

    2015-06-30

    We report the first evaluation of a platform coupling a high speed field asymmetric ion mobility spectrometry microchip (µFAIMS) with drift tube ion mobility and mass spectrometry (IMS-MS). The µFAIMS/IMS-MS platform was used to analyze biological samples and simultaneously acquire multidimensional information of detected features from the measured FAIMS compensation fields and IMS drift times, while also obtaining accurate ion masses. These separations thereby increase the overall separation power, resulting increased information content, and provide more complete characterization of more complex samples. The separation conditions were optimized for sensitivity and resolving power by the selection of gas compositions and pressures in the FAIMS and IMS separation stages. The resulting performance provided three dimensional separations, benefitting both broad complex mixture studies and targeted analyses by e.g. improving isomeric separations and allowing detection of species obscured by “chemical noise” and other interfering peaks.

  5. Spectral anomalies of the effect of light-induced drift of caesium atoms caused by the velocity dependence of transport collision frequencies

    NASA Astrophysics Data System (ADS)

    Parkhomenko, A. I.; Shalagin, A. M.

    2014-10-01

    The spectral features of the light-induced drift (LID) velocity of caesium atoms in inert buffer gases are studied theoretically. A strong temperature dependence of the spectral LID line shape of Cs atoms in Ar or Kr atmosphere in the vicinity of T ~ 1000 K is predicted. It is shown that the anomalous LID of Cs atoms in binary buffer mixtures of two different inert gases can be observed at virtually any (including ambient) temperature, depending on the content of the components in these mixtures. The results obtained make it possible to precisely test the interatomic interaction potentials in the experiments on the anomalous LID.

  6. Drift Velocity of Small-Scale Artificial Ionospheric Irregularities According to Multifrequency HF Doppler Radar. I. Method of Calculation and Its Hardware Implementation

    NASA Astrophysics Data System (ADS)

    Vertogradov, G. G.; Uryadov, V. P.; Vertogradov, V. G.; Vertogradova, E. G.; Kubatko, S. V.

    2015-10-01

    The method of calculating the total drift velocity vector of small-scale artificial ionospheric irregularities as measured by the effective Doppler frequency shift of aspect-scattered signals from several diagnostic illumination transmitters operated at different frequencies is discussed. The technique of adaptive simulation of decameter radio waves propagating in an inhomogeneous magnetized ionosphere with allowance for the aspect scattering effects due to small-scale field-aligned irregularities is developed. A multifrequency HF Doppler radar for simultaneous measurement of the Doppler spectra of radio signals at a set of frequencies is described.

  7. Spectral anomalies of the effect of light-induced drift of caesium atoms caused by the velocity dependence of transport collision frequencies

    SciTech Connect

    Parkhomenko, A I; Shalagin, A M

    2014-10-31

    The spectral features of the light-induced drift (LID) velocity of caesium atoms in inert buffer gases are studied theoretically. A strong temperature dependence of the spectral LID line shape of Cs atoms in Ar or Kr atmosphere in the vicinity of T ∼ 1000 K is predicted. It is shown that the anomalous LID of Cs atoms in binary buffer mixtures of two different inert gases can be observed at virtually any (including ambient) temperature, depending on the content of the components in these mixtures. The results obtained make it possible to precisely test the interatomic interaction potentials in the experiments on the anomalous LID. (quantum optics)

  8. Experimental evidence for unstable waves in the lower E/Upper D-region excited near the bisector between the electric field and the drift velocity

    NASA Astrophysics Data System (ADS)

    Blix, T. A.; Thrane, E. V.; Kirkwood, S.; Dimant, Y. S.; Sudan, R. N.

    During the METAL campaign conducted at Andya Rocket Range in September-October 1991, detailed in situ measurements were performed by means of plasma probes in the TURBO rocket payload. During one of the salvoes (30 September 1991), strong plasma density fluctuations were detected above 78 km, especially on downleg. The results are shown to be in good agreement with the new instability predicted from the kinetic theory of Dimant and Sudan (1995). The new instability leads to the excitation of long wavelength plasma waves along the bisector between the drift velocity Vd and the electric field E.

  9. Effects of errors in velocity tilt on maximum longitudinal compression during neutralized drift compression of intense beam pulses: I. general description

    SciTech Connect

    Kaganovich, Igor D.; Massidda, Scottt; Startsev, Edward A.; Davidson, Ronald C.; Vay, Jean-Luc; Friedman, Alex

    2012-06-21

    Neutralized drift compression offers an effective means for particle beam pulse compression and current amplification. In neutralized drift compression, a linear longitudinal velocity tilt (head-to-tail gradient) is applied to the non-relativistic beam pulse, so that the beam pulse compresses as it drifts in the focusing section. The beam current can increase by more than a factor of 100 in the longitudinal direction. We have performed an analytical study of how errors in the velocity tilt acquired by the beam in the induction bunching module limit the maximum longitudinal compression. It is found that the compression ratio is determined by the relative errors in the velocity tilt. That is, one-percent errors may limit the compression to a factor of one hundred. However, a part of the beam pulse where the errors are small may compress to much higher values, which are determined by the initial thermal spread of the beam pulse. It is also shown that sharp jumps in the compressed current density profile can be produced due to overlaying of different parts of the pulse near the focal plane. Examples of slowly varying and rapidly varying errors compared to the beam pulse duration are studied. For beam velocity errors given by a cubic function, the compression ratio can be described analytically. In this limit, a significant portion of the beam pulse is located in the broad wings of the pulse and is poorly compressed. The central part of the compressed pulse is determined by the thermal spread. The scaling law for maximum compression ratio is derived. In addition to a smooth variation in the velocity tilt, fast-changing errors during the pulse may appear in the induction bunching module if the voltage pulse is formed by several pulsed elements. Different parts of the pulse compress nearly simultaneously at the target and the compressed profile may have many peaks. The maximum compression is a function of both thermal spread and the velocity errors. The effects of the finite gap width of the bunching module on compression are analyzed analytically.

  10. Notes on drift theory

    NASA Technical Reports Server (NTRS)

    Burger, R. A.; Moraal, H.; Webb, G. M.

    1985-01-01

    It is shown that there is a simpler way to derive the average guiding center drift of a distribution of particles than via the so-called single particle analysis. Based on this derivation it is shown that the entire drift formalism can be considerably simplified, and that results for low order anisotropies are more generally valid than is usually appreciated. This drift analysis leads to a natural alternative derivation of the drift velocity along a neutral sheet.

  11. An Effective Approach for Coupling Direct Analysis in Real Time with Atmospheric Pressure Drift Tube Ion Mobility Spectrometry

    NASA Astrophysics Data System (ADS)

    Keelor, Joel D.; Dwivedi, Prabha; Fernández, Facundo M.

    2014-09-01

    Drift tube ion mobility spectrometry (DTIMS) has evolved as a robust analytical platform routinely used for screening small molecules across a broad suite of chemistries ranging from food and pharmaceuticals to explosives and environmental toxins. Most modern atmospheric pressure IM detectors employ corona discharge, photoionization, radioactive, or electrospray ion sources for efficient ion production. Coupling standalone DTIMS with ambient plasma-based techniques, however, has proven to be an exceptional challenge. Device sensitivity with near-ground ambient plasma sources is hindered by poor ion transmission at the source-instrument interface, where ion repulsion is caused by the strong electric field barrier of the high potential ion mobility spectrometry (IMS) inlet. To overcome this shortfall, we introduce a new ion source design incorporating a repeller point electrode used to shape the electric field profile and enable ion transmission from a direct analysis in real time (DART) plasma ion source. Parameter space characterization studies of the DART DTIMS setup were performed to ascertain the optimal configuration for the source assembly favoring ion transport. Preliminary system capabilities for the direct screening of solid pharmaceuticals are briefly demonstrated.

  12. Superstatistical velocity distributions of cold trapped ions in molecular-dynamics simulations

    NASA Astrophysics Data System (ADS)

    Rouse, I.; Willitsch, S.

    2015-11-01

    We present a realistic molecular-dynamics treatment of laser-cooled ions in radio-frequency ion traps which avoids previously made simplifications such as modeling laser cooling as a friction force and combining individual heating mechanisms into a single effective heating force. Based on this implementation, we show that infrequent energetic collisions of single ions with background gas molecules lead to pronounced heating of the entire ion ensemble and a time-varying secular ensemble temperature, which manifests itself in a superstatistical time-averaged velocity distribution of the ions. The effect of this finding on the experimental determination of ion temperatures and rate constants for cold chemical reactions is discussed.

  13. Measurements of velocity shear and ion viscosity profile in a magnetohydrodynamic plasma jet

    SciTech Connect

    Dorf, L. A.; Intrator, T.; Sun, X.; Hendryx, J.; Wurden, G. A.; Furno, I; Lapenta, G.

    2010-10-15

    Time-dependent, two-dimensional profiles of the axial flow velocity, density, electron temperature, and magnetic field components are measured at two axial locations in a screw pinch plasma column of the reconnection scaling experiment. The results show that the ion momentum flux for a given column radius is dissipated by the ion-ion Coulomb scattering viscosity due to a significant radial shear of the axial velocity. By comparing the terms of the magnetohydrodynamic momentum balance equation, radial profile of ion viscosity is determined. Chord-integrated ion temperature measurements performed at several radial locations using Doppler broadening spectroscopy show ion temperature of about 1 eV. Measured ion viscosity agrees within a factor of 2 with the classical Braginskii expectations.

  14. Combination of fast-ion diagnostics in velocity-space tomographies

    NASA Astrophysics Data System (ADS)

    Salewski, M.; Geiger, B.; Nielsen, S. K.; Bindslev, H.; Garca-Muoz, M.; Heidbrink, W. W.; Korsholm, S. B.; Leipold, F.; Madsen, J.; Meo, F.; Michelsen, P. K.; Moseev, D.; Stejner, M.; Tardini, G.; the ASDEX Upgrade Team

    2013-06-01

    Fast-ion D? (FIDA) and collective Thomson scattering (CTS) diagnostics provide indirect measurements of fast-ion velocity distribution functions in magnetically confined plasmas. Here we present the first prescription for velocity-space tomographic inversion of CTS and FIDA measurements that can use CTS and FIDA measurements together and that takes uncertainties in such measurements into account. Our prescription is general and could be applied to other diagnostics. We demonstrate tomographic reconstructions of an ASDEX Upgrade beam ion velocity distribution function. First, we compute synthetic measurements from two CTS views and two FIDA views using a TRANSP/NUBEAM simulation, and then we compute joint tomographic inversions in velocity-space from these. The overall shape of the 2D velocity distribution function and the location of the maxima at full and half beam injection energy are well reproduced in velocity-space tomographic inversions, if the noise level in the measurements is below 10%. Our results suggest that 2D fast-ion velocity distribution functions can be directly inferred from fast-ion measurements and their uncertainties, even if the measurements are taken with different diagnostic methods.

  15. SIMULATIONS OF HIGH-VELOCITY CLOUDS. II. ABLATION FROM HIGH-VELOCITY CLOUDS AS A SOURCE OF LOW-VELOCITY HIGH IONS

    SciTech Connect

    Henley, David B.; Kwak, Kyujin; Shelton, Robin L. E-mail: rls@physast.uga.edu

    2012-07-01

    In order to determine if the material ablated from high-velocity clouds (HVCs) is a significant source of low-velocity high ions (C IV, N V, and O VI) such as those found in the Galactic halo, we simulate the hydrodynamics of the gas and the time-dependent ionization evolution of its carbon, nitrogen, and oxygen ions. Our suite of simulations examines the ablation of warm material from clouds of various sizes, densities, and velocities as they pass through the hot Galactic halo. The ablated material mixes with the environmental gas, producing an intermediate-temperature mixture that is rich in high ions and that slows to the speed of the surrounding gas. We find that the slow mixed material is a significant source of the low-velocity O VI that is observed in the halo, as it can account for at least {approx}1/3 of the observed O VI column density. Hence, any complete model of the high ions in the halo should include the contribution to the O VI from ablated HVC material. However, such material is unlikely to be a major source of the observed C IV, presumably because the observed C IV is affected by photoionization, which our models do not include. We discuss a composite model that includes contributions from HVCs, supernova remnants, a cooling Galactic fountain, and photoionization by an external radiation field. By design, this model matches the observed O VI column density. This model can also account for most or all of the observed C IV, but only half of the observed N V.

  16. A velocity map imaging spectrometer for electron?ion and ion?ion coincidence experiments with synchrotron radiation

    SciTech Connect

    Advanced Light Source; Kilcoyne, Arthur L; Rolles, D.; Pesic, Z.D.; Perri, M.; Bilodeau, R.C.; Ackerman, G.D.; Rude, B.S.; Kilcoyne, A.L.D.; Bozek, J.D.; Berrah, N.

    2007-04-27

    We have built a velocity imaging (VMI) spectrometer optimized for angle-resolved photoionization experiments with synchrotron radiation (SR) in the VUV and soft X-tay range. The spectrometer is equiped with four electrostatic lenses that focus the charged photoionization products onto a position-sensitive multi-hit delay-line anode. The use of two additional electrostatic lens elements as compared to the standard design of Eppink and Parker [T.J.B. Eppink and D.H. Parker, Rev. Sci. Instrum. 68 (1997) 3477]provides better focusing of an extended interaction region, which is crucial for most SR applications. Furthermore, the apparatus is equipped with a second micro-channel plate detector opposite to the VMI spectrometer, enabling electron-ion coincidence experiments and thereby mass-resolved ion spectroscopy independent of the time structure of the synchrotron radiation. First results for the photofragmentation of CO2 molecules are presented.

  17. Ion velocities in direct current arc plasma generated from compound cathodes

    NASA Astrophysics Data System (ADS)

    Zhirkov, I.; Eriksson, A. O.; Rosen, J.

    2013-12-01

    Arc plasma from Ti-C, Ti-Al, and Ti-Si cathodes was characterized with respect to charge-state-resolved ion energy. The evaluated peak velocities of different ion species in plasma generated from a compound cathode were found to be equal and independent on ion mass. Therefore, measured difference in kinetic energies can be inferred from the difference in ion mass, with no dependence on ion charge state. The latter is consistent with previous work. These findings can be explained by plasma quasineutrality, ion acceleration by pressure gradients, and electron-ion coupling. Increasing the C concentration in Ti-C cathodes resulted in increasing average and peak ion energies for all ion species. This effect can be explained by the "cohesive energy rule," where material and phases of higher cohesive energy generally result in increasing energies (velocities). This is also consistent with the here obtained peak velocities around 1.37, 1.42, and 1.55 (104 m/s) for ions from Ti0.84Al0.16, Ti0.90Si0.10, and Ti0.90C0.10 cathodes, respectively.

  18. Ion velocities in direct current arc plasma generated from compound cathodes

    SciTech Connect

    Zhirkov, I.; Rosen, J.; Eriksson, A. O.; Oerlikon Balzers Coating AG, Iramali 18, 9496 Balzers

    2013-12-07

    Arc plasma from Ti-C, Ti-Al, and Ti-Si cathodes was characterized with respect to charge-state-resolved ion energy. The evaluated peak velocities of different ion species in plasma generated from a compound cathode were found to be equal and independent on ion mass. Therefore, measured difference in kinetic energies can be inferred from the difference in ion mass, with no dependence on ion charge state. The latter is consistent with previous work. These findings can be explained by plasma quasineutrality, ion acceleration by pressure gradients, and electron-ion coupling. Increasing the C concentration in Ti-C cathodes resulted in increasing average and peak ion energies for all ion species. This effect can be explained by the cohesive energy rule, where material and phases of higher cohesive energy generally result in increasing energies (velocities). This is also consistent with the here obtained peak velocities around 1.37, 1.42, and 1.55 (10{sup 4} m/s) for ions from Ti{sub 0.84}Al{sub 0.16}, Ti{sub 0.90}Si{sub 0.10}, and Ti{sub 0.90}C{sub 0.10} cathodes, respectively.

  19. Electric and magnetic drift of non-adiabatic ions in the earth's geomagnetic tail current sheet

    NASA Technical Reports Server (NTRS)

    Beard, D. B.; Cowley, S. W. H.

    1985-01-01

    It has been shown recently that nonadiabatic particles in the earth's magnetotail drift across the tail roughly as predicted for adiabatic particles with 90 deg pitch angles. In this paper it is shown that this result implies the existence of an approximate invariant of the motion. Adding the effect of convection associated electric fields, the approximate bounce averaged motion of nonadiabatic particles in the magnetotail can be obtained. Thus the particle motion and energization due to combined magnetic and electric drifts in the magnetotail are easily predicted.

  20. Temperature dynamics and velocity scaling laws for interchange driven, warm ion plasma filaments

    NASA Astrophysics Data System (ADS)

    Olsen, Jeppe; Madsen, Jens; Nielsen, Anders Henry; Rasmussen, Jens Juul; Naulin, Volker

    2016-04-01

    The influence of electron and ion temperature dynamics on the radial convection of isolated structures in magnetically confined plasmas is investigated by means of numerical simulations. It is demonstrated that the maximum radial velocity of these plasma blobs roughly follows the inertial velocity scaling, which is proportional to the ion acoustic speed times the square root of the filament particle density times the sum of the electron and ion temperature perturbations. Only for small blobs the cross field convection does not follow this scaling. The influence of finite Larmor radius effects on the cross-field blob convection is shown not to depend strongly on the dynamical ion temperature field. The blob dynamics of constant finite and dynamical ion temperature blobs is similar. When the blob size is on the order of 10 times the ion Larmor radius the blobs stay coherent and decelerate slowly compared to larger blobs which dissipate faster due to fragmentation and turbulent mixing.

  1. Mass loading and velocity diffusion models for heavy pickup ions at comet Grigg-Skjellerup

    NASA Technical Reports Server (NTRS)

    Huddleston, D. E.; Coates, A. J.; Johnstone, A. D.; Neubauer, Fritz M.

    1993-01-01

    We compare model predictions of cometary water group ion densities and the solar wind slow down with measurements made by the Giotto Johnstone plasma analyzer implanted ion sensor at the encounter with comet Grigg-Skjellerup (G-S) on July 10, 1992. The observed slope of the ion density profile on approach to the comet is unexpectedly steep. Possible explanations for this are discussed. We present also a preliminary investigation of the quasilinear velocity-space diffusion of the implanted heavy ion population at G-S using a transport equation including souce, convection, adiabatic compression, and velocity diffusion terms. Resulting distributions are anisotropic, in agreement with observations. We consider theoretically the waves that may be generated by the diffusion process for the observed solar wind conditions. At initial ion injections, waves are generated at omega approximately Omega(sub i) the ion gyrofrequency, and lower frequencies are predicted for diffusion toward a bispherical shell.

  2. Selective Detection of Low-Velocity Ions Using Nuclear Emulsion Films

    NASA Astrophysics Data System (ADS)

    Naka, Tatsuhiro; Kuge, Ken'ichi; Nakamura, Mitsuhiro

    2013-11-01

    We focused on the difference between the photographic sensitivities of nuclear emulsion films by the electronic stopping power (ESP) and nuclear stopping power (NSP) of charged particles. The effects of high-velocity particles, in which ESP was dominant, and of low-velocity particles, where both ESP and NSP were effective, were compared. Low-velocity Kr ions formed internal latent images by the interaction with NSP. This may be due to the formation of crystal defects by atomic collisions along the route of these ions in silver halide crystals, and such defects are detected only by internal development. On the other hand, high-velocity ions like ?-rays did not form internal latent images in the emulsion with Au+S sensitization, because sensitization centers on the surface of crystals accumulated excited electrons by ESP and only surface latent images were formed. It is demonstrated that internal latent images are characteristic signals by NSP. Low-velocity ions are selectively detectable by the internal development, even in high background fields like ?-rays, ?-rays, or other high-velocity ions.

  3. Kr II and Xe II axial velocity distribution functions in a cross-field ion source

    SciTech Connect

    Lejeune, A.; Bourgeois, G.; Mazouffre, S.

    2012-07-15

    Laser induced fluorescence measurements were carried out in a cross-field ion source to examine the behaviour of the axial ion velocity distribution functions (VDFs) in the expanding plasma. In the present paper, we focus on the axial VDFs of Kr II and Xe II ions. We examine the contourplots in a 1D-phase space (x,v{sub x}) representation in front of the exhaust channel and along the centerline of the ion source. The main ion beam, whose momentum corresponds to the ions that are accelerated through the whole potential drop, is observed. A secondary structure reveals the ions coming from the opposite side of the channel. We show that the formation of the neutralized ion flow is governed by the annular geometry. The assumption of a collisionless shock or a double layer due to supersonic beam interaction is not necessary. A non-negligible fraction of slow ions originates in local ionization or charge-exchange collision events between ions of the expanding plasma and atoms of the background residual gas. Slow ions that are produced near the centerline in the vicinity of the exit plane are accelerated toward the source body with a negative velocity leading to a high sputtering of front face. On the contrary, the ions that are produced in the vicinity of the channel exit plane are partially accelerated by the extended electric field.

  4. Flute mode waves near the lower hybrid frequency excited by ion rings in velocity space

    NASA Technical Reports Server (NTRS)

    Cattell, C.; Hudson, M.

    1982-01-01

    Discrete emissions at the lower hybrid frequency are often seen on the S3-3 satellite. Simultaneous observation of perpendicularly heated ions suggests that these ions may provide the free energy necessary to drive the instability. Studies of the dispersion relation for flute modes excited by warm ion rings in velocity space show that waves are excited with real frequencies near the lower hybrid frequency and with growth rates ranging from about 0.01 to 1 times the ion cyclotron frequency. Numerical results are therefore consistent with the possibility that the observed ions are the free energy source for the observed waves.

  5. Ionospheric ion velocity distributions and associated transport properties in the presence of auroral electric field gradients

    SciTech Connect

    St. Maurice, J.P.; Winkler, E.; Hamza, A.M.

    1994-10-01

    The authors have done modeling of the response of ions in the F region to strong horizontal gradients in the convection electric field. They have used kinetic equations, and find in the boundary regions where the most rapid changes in the elctric field are experienced, that the ions exhibit a strongly asymmetric velocity distribution. The sign of the gradient also makes a big difference in the ions distribution functions.

  6. The Physics of High-Velocity Ions in the Hall Thruster Near-Field

    NASA Astrophysics Data System (ADS)

    Sullivan, Regina

    A study of the physics underlying high velocity ion trajectories within the near-field region of a Hall thruster plume is presented. In this context, "high velocity" ions are ions that have been accelerated through the full potential drop of the thruster (sometimes referred to as "primary energy" or "primary beam energy" ions). Results from an experimental survey of an SPT-70 thruster plume are shown, along with simulated data from a Hall thruster code and from a plasma sheath model. Two main features are examined: the central jet along the Hall thruster centerline, and the population of high velocity ions at high angles. In the experimental portion of the investigation, three diagnostic instruments were employed: (1) a Faraday probe for measuring ion current density, (2) an ExB velocity filter for mapping ions with the primary beam energy, and (3) a Retarding Potential Analyzer (RPA) for determining ion energy distributions. In the numerical portion, two codes were employed: (1) a hybrid-PIC Hall thruster code known as HPHall, and (2) a model of the plasma sheath near the exit plane of the thruster, which was developed by the author. A comparison between the measured and simulated data sets is made, to analyze the degree to which different mechanisms are responsible for the evolution of the thruster plume in the near-field region. This analysis shows that the central jet is both a function of symmetric expansion of the ion beam as well as asymmetry in the internal potential field of the thruster. Additionally, it is suggested that high energy, high angle ions could be generated given a specific internal electric field configuration, while oscillations are ruled out as the cause of these ions. The results from the sheath model show that while the sheath can change trajectory angles by 10 to 20 degrees, it can not fully explain the presence of high angle ions with high energies.

  7. Ion temperature and toroidal velocity edge transport barriers in KSTAR

    NASA Astrophysics Data System (ADS)

    Ko, Won-Ha; Ko, S. H.; Kwon, J. M.; Diamond, P. H.; Ida, K.; Jeon, Y. M.; Lee, J. H.; Yoon, S. W.; Kwak, J. G.

    2015-08-01

    The structure and evolution of the ion temperature ({{T}\\text{i}} ) and toroidal rotation ({{V}?} ) profile have been investigated in neutral beam injection (NBI)-heated KSTAR H-mode plasmas, both without and with resonant magnetic pertubations (RMPs). A clear disparity between the width of the {{V}?} -pedestal and that of the {{T}\\text{i}} -pedestal was observed. Also, it was found that there exists a close correlation and weak relative hysteresis between the pedestal \

  8. Magnetized plasma sheath with two positive ions where collision frequencies have a power law dependency on ions velocities

    NASA Astrophysics Data System (ADS)

    Masoudi, S. Farhad; Khoramabadi, Mansor

    2015-09-01

    We study the dynamics of collisional magnetized plasma sheath with two species of positive ions by using the plasma fluid model. The basic equations of the fluid model are solved numerically where the sheath is in the external magnetic field and the elastic collision between ions and neutrals has been taken into account. In our model, we assume that the collisional momentum transferring cross section has a power law dependency on ion flow velocity. Our analysis demonstrates that the sheath dynamics are sensitive to the power law dependency, especially for the ion with greater density.

  9. Phase velocities of irregularities in the equatorial electrojet.

    NASA Technical Reports Server (NTRS)

    Cohen, R.

    1973-01-01

    Spectral decomposition of the power spectrum of radar echoes at 50 MHz from the equatorial electrojet reveals information as to the phase velocities of several classes of electron density irregularities and permits inferences as to the electron drift velocity and the electron and ion temperatures in the electrojet. In particular, it is shown that the phase velocity of two-stream irregularities is comparable to the ion-acoustic speed and independent of the horizontal phase velocity of coexistent non-two-stream irregularities. The latter can exceed the ion-acoustic speed and is probably a measure of the electron drift velocity. Thus a probable inference is that the electron drift velocity can itself be supersonic, contrary to some existing theoretical opinions.

  10. Cold ion-polar-molecule reactions studied with a combined Stark-velocity-filter-ion-trap apparatus

    NASA Astrophysics Data System (ADS)

    Okada, Kunihiro; Suganuma, Takuya; Furukawa, Takahiro; Takayanagi, Toshinobu; Wada, Michiharu; Schuessler, Hans A.

    2013-04-01

    We have developed a combined Stark-velocity-filter-ion-trap apparatus for the purpose of reaction-rate measurements between cold trapped ions and slow polar molecules under ultrahigh vacuum conditions. The prerequisite steps such as the characterization of velocity-selected polar molecules (PM), namely ND3, H2CO, and CH3CN, were performed using time-of-flight (TOF) measurements. We confirmed the generation of slow ND3, H2CO, and CH3CN molecules having thermal energies of a few Kelvin. Additionally, the number densities of the slow velocity-filtered polar molecules were determined to be in the range of n=104 to 106 cm-3 by calibrating the TOF signals. In a first experiment, the Stark velocity filter was connected to a cryogenic linear Paul trap and reaction-rate measurements between laser-cooled Ca+ Coulomb crystals and velocity-selected polar molecules were carried out. The observed reaction rates are of the order of 10-5 s-1, which are much slower than typical reaction rates of molecular ion-polar-molecule reactions at low temperatures. The present results confirm that reaction-rate measurements between velocity-selected polar molecules and sympathetically cooled molecular ions cooled by a laser-cooled Ca+ Coulomb crystal can be performed. Next we measured the reaction rates between sympathetically cooled nonfluorescent stored ion molecules namely N2H+ ions and velocity-selected CH3CN molecules at the average reaction energy of about 3 K. The measured reaction rate of 2.0(2)10-3 s-1 is much faster than those of the Ca++PM reactions. This is strong evidence that the velocity-selected polar molecules undergo reactive collisions. We also confirmed that the present reaction-rate constant of CH3CN+N2H+ ? CH3CNH++N2 is consistent with the estimated values from the room temperature results and the trajectory-scaling formula of Su In the future, the present velocity-filter combined cryogenic trap apparatus will enable us to perform systematic measurements of cold ion-polar-molecule reactions, which are important problems from a fundamental viewpoint and also contribute to astrochemistry.

  11. Observation of coherent nonlinear interactions in the ion velocity distribution function

    SciTech Connect

    Uzun-Kaymak, Ilker Ue.; Skiff, Frederick

    2006-11-15

    Using laser induced fluorescence (LIF) and higher order spectral analysis, we present the first measurements of phase space resolved coherent nonlinear interactions among the components of low frequency density fluctuations ({omega}{<=}{omega}{sub ci}), in a linearly magnetized device. The bicoherence calculations employing the two point correlation technique suggest that there are two different coherent nonlinear wave-wave interactions in the measured spectrum. The first one, having a short correlation length and existing for slow moving ions, for which {upsilon}{sub iparallel}{<=}{upsilon}{sub ith}, is an interaction between fluctuations below the electron drift frequency, {omega}*. The second one is the strongest for fast moving ions, for which {upsilon}{sub iparallel}{>=}{upsilon}{sub ith}, and is a mode coupling between the azimuthal drift wave modes, m=1 and m=2. Combining these bispectral results with earlier linear analysis based on the power spectra of the fluctuations, we suggest that the nonlinear coupling observed between the spectral components below {omega}* for the case of slow moving ions is associated with the anomalous kinetic component. For slow moving ions, as we increase the neutral collision frequencies, the nonlinear interaction observed for spectral components below {omega}* decreases and the harmonic mode coupling for {omega}* takes over.

  12. The Impact of Ion-Cyclotron Wave Dissipation on Minor Ion Velocity Distributions in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Cranmer, S. R.; Field, G. B.; Noci, G.; Kohl, J. L.

    1997-12-01

    We present theoretical models of the acceleration and heating of minor ions in the solar wind, as well as detailed anisotropic velocity distribution functions computed numerically by solving the Boltzmann transport equation. We examine the compatibility between these models and spectroscopic measurements of the velocities and kinetic temperatures of various particle species in the solar corona. The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) has measured hydrogen kinetic temperatures in polar coronal holes in excess of 3 million K, and O VI ion kinetic temperatures of at least 200 million K. In addition, the velocity distributions parallel to the open magnetic field are smaller than those perpendicular to the field, possibly implying temperature anisotropy ratios of order 100 for minor ions. We examine various features of plasma heating by the dissipation of high-frequency ion-cyclotron resonance Alfven waves, which may be the most natural physical mechanism to produce the observed plasma conditions. The modeled ion velocity distributions depend sensitively on the assumed amplitudes and frequencies of the waves, and these computations can be used to accurately predict many quantitative features of the wave power spectrum. Indeed, the more ionic species that are observed spectroscopically, the greater the extent in frequency space the wave spectrum can be inferred. This work is supported by the National Aeronautics and Space Administration under grant NAG5-3192 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by Swiss funding agencies.

  13. Ionization of highly charged iodine ions near the Bohr velocity

    NASA Astrophysics Data System (ADS)

    Zhou, Xianming; Cheng, Rui; Lei, Yu; Sun, Yuanbo; Ren, Jieru; Liu, Shidong; Deng, Jiachuan; Zhao, Yongtao; Xiao, Guoqing

    2015-01-01

    We have measured the L-shell X-rays of iodine from the collisions of 3 MeV Iq+(q=15,20,22,25,26) ions with an iron target. It is found that the X-ray yield decreases with the increasing initial charge state. The energy of the subshell X-ray has a blue shift, which is independent of the projectile charge state. In addition, the relative intensity ratios of Lβ1,3,4 and Lβ2,15 to Lα1,2 X-ray are obtained and compared with the theoretical calculations. That they are larger than for a singly ionized atom can be understood by the multiple ionization effect of the outer-shell electrons.

  14. Tomography of fast-ion velocity-space distributions from synthetic CTS and FIDA measurements

    NASA Astrophysics Data System (ADS)

    Salewski, M.; Geiger, B.; Nielsen, S. K.; Bindslev, H.; Garca-Muoz, M.; Heidbrink, W. W.; Korsholm, S. B.; Leipold, F.; Meo, F.; Michelsen, P. K.; Moseev, D.; Stejner, M.; Tardini, G.; the ASDEX Upgrade Team

    2012-10-01

    We compute tomographies of 2D fast-ion velocity distribution functions from synthetic collective Thomson scattering (CTS) and fast-ion D? (FIDA) 1D measurements using a new reconstruction prescription. Contradicting conventional wisdom we demonstrate that one single 1D CTS or FIDA view suffices to compute accurate tomographies of arbitrary 2D functions under idealized conditions. Under simulated experimental conditions, single-view tomographies do not resemble the original fast-ion velocity distribution functions but nevertheless show their coarsest features. For CTS or FIDA systems with many simultaneous views on the same measurement volume, the resemblance improves with the number of available views, even if the resolution in each view is varied inversely proportional to the number of views, so that the total number of measurements in all views is the same. With a realistic four-view system, tomographies of a beam ion velocity distribution function at ASDEX Upgrade reproduce the general shape of the function and the location of the maxima at full and half injection energy of the beam ions. By applying our method to real many-view CTS or FIDA measurements, one could determine tomographies of 2D fast-ion velocity distribution functions experimentally.

  15. Temporally resolved ion velocity distribution measurements in a radio-frequency plasma sheath

    SciTech Connect

    Jacobs, B.; Gekelman, W.; Pribyl, P.; Barnes, M.

    2011-05-15

    The ion velocity distribution function (IVDF) above and within a radio-frequency (RF) biased plasma sheath is studied experimentally with a pulsed laser-induced fluorescence diagnostic in an industrial plasma etch tool. Temporally resolved measurements taken at eight different phases of the 2.2 MHz bias waveform show that the ion dynamics vary dramatically throughout the RF cycle (the ratio of the average ion transit time through the sheath to the RF period is {tau}{sub ion}/{tau}{sub RF} = 0.3). The position of the presheath/sheath edge is constant throughout the RF cycle and the time-averaged ion flux is conserved within the sheath region. The characteristic bimodal structure of the time-averaged ion distributions found in previous experiments is observed to arise from the time-dependent ion dynamics, in accord with existing theory. The large temporal variation of the IVDF has implications for the plasma chemistry and etching quality.

  16. Carrier gas and ion beam parameter effects on the structure and properties of a-C:H/SiOx films deposited employing closed drift ion beam source

    NASA Astrophysics Data System (ADS)

    Tamulevičienė, Asta; Meškinis, Šarūnas; Kopustinskas, Vitoldas; Tamulevičius, Sigitas

    2012-07-01

    In the present study closed drift ion beam source was used to deposit SiOx containing amorphous hydrogenated carbon films (a-C:H/SiOx) employing hexamethyldisiloxane and H2 or He carrier gas. The structure, optical and mechanical properties of a-C:H/SiOx films deposited using different ion beam energies (300-800 eV) and ion beam current densities (20-80 μA/cm2) were analyzed. Raman spectroscopy has shown that the structure of a-C:H/SiOx films deposited using different carrier gas differs. In the case of H2 carrier gas I(D)/I(G) ratio decreased from 1.1 to 1 with the increase of ion beam energy from 300 eV to 500 eV. It is shown that the increase tendency observed for I(D)/I(G) ratio dependence on the ion beam current density was influenced by the structural changes (Si-H bonds formation) observed in FTIR analysis. The films with maximum hardness (12.8 GPa for He and 11.9 GPa for H2 carrier gas) were formed at 500 eV ion beam energy for both carrier gas. The band gap and B parameter of the films (formed at 500 eV with H2 carrier gas) increase almost linearly with the ion beam current density.

  17. Using Ion Imaging to Measure Velocity Distributions in Surface Scattering Experiments.

    PubMed

    Harding, Dan J; Neugebohren, J; Auerbach, Daniel J; Kitsopoulos, T N; Wodtke, Alec M

    2015-12-17

    We present a new implementation of ion imaging for the study of surface scattering processes. The technique uses a combination of spatial ion imaging with laser slicing and delayed pulsed extraction. The scattering velocities of interest are parallel to the imaging plane, allowing speed and angular distributions to be extracted from a single image. The first results of direct scattering of N2 from a clean, single-crystal Au(111) surface are reported, and the speed resolution is shown to be competitive with current state-of-the-art time-of-flight methods for velocity measurements while providing simultaneous measurements of in-plane angular distributions. PMID:26418228

  18. One year variations in the near earth solar wind ion density and bulk flow velocity

    NASA Technical Reports Server (NTRS)

    Bolton, Scott J.

    1990-01-01

    One-year periodic variations in the near earth solar wind ion density and bulk flow velocity are reported. The variations show an inverse relationship between the ion velocity and density. The peak strength of the observed density variation ranges from 50-100 percent over the background. These variations imply either large scale mass loading inside the earth's orbit or intrinsic solar modulations. Analyses of both near earth and Pioneer Venus Orbiter spacecraft data provide a comparison at two different heliocentric distances. Several explanations for these variations are discussed.

  19. Velocity and Energy Distributions of Water Group Ion Around the Enceladus Plume

    NASA Astrophysics Data System (ADS)

    Sakai, S.; Cravens, T.; Pothapragada, S.; Kumar, A.

    2014-12-01

    Enceladus has a dynamic plume on its south pole which is emitting gas, including water vapor, and dust. The gas is ionized by solar EUV radiation and by electron impacts and extends throughout the inner magnetosphere of Saturn. The dust is negatively charged and forms the E ring. Hence, the inner magnetosphere within 10 RS contains a complex mixture of plasma, neutral gas and dust. Cassini observations show that the plasma velocities are less than the co-rotation velocity. The velocity and energy distributions of this need to be explained in order to understand the inner magnetospheric plasma physics. We have investigated the velocity and energy distributions of water group ions in the vicinity of Enceladus using test particle and Monte Carlo methods including collisional processes such as charge exchange and ion-neutral chemical reaction. The model results will be constrained by neutral and ion composition data from the Cassini Ion and Neutral Mass Spectrometer and ion energy spectra from the Plasma Spectrometer (CAPS). We will also discuss related plasma processed in the Enceladus torus.

  20. Ion velocity and plasma potential measurements of a cylindrical cusped field thruster

    SciTech Connect

    MacDonald, N. A.; Young, C. V.; Cappelli, M. A.; Hargus, W. A. Jr.

    2012-05-01

    Measurements of the most probable time-averaged axial ion velocities and plasma potential within the acceleration channel and in the plume of a straight-channeled cylindrical cusped field thruster operating on xenon are presented. Ion velocities for the thruster are derived from laser-induced fluorescence measurements of the 5d[4]{sub 7/2}-6p[3]{sub 5/2} xenon ion excited state transition centered at {lambda}=834.72nm. Plasma potential measurements are made using a floating emissive probe with a thoriated-tungsten filament. The thruster is operated in a power matched condition with 300 V applied anode potential for comparison to previous krypton plasma potential measurements, and a low power condition with 150 V applied anode potential. Correlations are seen between the plasma potential drop outside of the thruster and kinetic energy contours of the accelerating ions.

  1. Single trapped indium and barium ion optical frequency standards and a laboratory constraint on the drift of fundamental constants

    NASA Astrophysics Data System (ADS)

    Trimble, William

    2005-05-01

    Single trappped ions cooled to the Lamb-Dicke regime are spectroscopic systems free of many external perturbations and are therefore attractive as optical frequency standards. We report continued development of single indium ion and barium ion rf Paul-Straubel traps and laser cooling systems. The forbidden ^1S0<->^3P0 transition in In^+ at 237 nm has a quality factor of 10^15 and is immune to 1 Hz quadratic Stark shifts that can limit other systems. In addition, the extraordinarily long 5D3/2 lifetime (?80 s) in a single trapped barium ion yields an electric dipole forbidden 2051 nm 6S1/2<->5D3/2 transition with a quality factor of 10^16. Further, the odd isotope ^137Ba^+ (I = 3/2) has an excited state with total angular momentum F' = 0 so an optical frequency standard based on this transition also avoids significant quadratic Stark shifts. We present our latest experimental probes of these transitions using new low linewidth diode pumped solid state laser systems (a frequency quadrupled non-planar ring oscillator Nd:YAG at 946 nm and a diode pumped Tm,Ho:YLF at 2 ?m) and propose a laboratory constraint on fundamental constant drift.

  2. Electron-ion hybrid instabilities driven by velocity shear in a magnetized plasma

    NASA Technical Reports Server (NTRS)

    Romero, H.; Ganguli, G.; Lee, Y. C.; Palmadesso, P. J.

    1992-01-01

    The stability of a magnetized plasma is investigated in which a sheared electron flow channel is present. The flow's peak velocity and shear scale length are denoted by V and L, respectively. If the velocity channel is perpendicular to the confining magnetic field and L is less than the ion Larmor radius, an electrostatic instability develops whose frequency is on the order of the lower hybrid frequency. It is concluded that velocity shear is the only source of free energy. Further, it is shown that density gradients do not stabilize this mode. It follows that the mode presented in this work can not be identified with the well-known modified two-stream instability. If the velocity channel is parallel to the confining magnetic field and the plasma is weakly magnetized, an instability driven by velocity shear is shown to exist.

  3. Development of implicit kinetic simulation methods, and their application to ion beam propagation in current and future neutralized drift compression experiments

    NASA Astrophysics Data System (ADS)

    Markidis, Stefano

    Ion beams can be accelerated and focused to hit a target thus releasing high density power to achieve nuclear fusion. They can also be used to study phase transition from the solid to the Warm Dense Matter state. The Neutralized Drift Compression Experiment (NDCX) at the Lawrence Berkeley National Laboratory is being used to investigate the possibility of developing drivers for the heavy ion fusion reactors, and for Warm Dense Matter experiments. Because ion beams are positively charged, repulsive forces act on the beam ions. These electrostatic forces defocus the beam, increasing the beam size and degrading the applied compression and focus. Electrons are introduced via a preformed plasma to eliminate the electrostatic forces that defocus the beam in the NDCX. The spread of the background plasma electrons inside the beam, and the adjustment of their velocity to the beam propagation velocity is called neutralization process. Because collisions occur on time scales much larger than the time scales for the neutralization process, the plasma can be considered collision-less. Thus, the neutralization process is dominated by plasma-wave interactions instead of collisions, and the kinetic approach is required to model this phenomenon. In this dissertation, the neutralization process in the NDCX configuration is studied. The collision-less kinetic equations of plasma are solved numerically using two implicit Particle-in-Cell methods. The implicit nature of the time-differenced governing equations leads to unconditional numerical stability. The primary numerical scheme is based on an implicit moment Particle-in-Cell approach. It has been developed for the electromagnetic case and implemented in a 3D, parallel code to study the neutralization process. In addition, a fully implicit Particle-in-Cell method to solve the particle and field equations has been also developed and implemented for a simple one dimensional, electrostatic configuration. The goal of the fully implicit scheme was to demonstrate that a fully implicit scheme can indeed converge as it has been a challenge. It has been demonstrated that fully implicit schemes (at least 1D, electrostatic configuration) can in fact converge. The schemes developed and implemented are used extensively to study the neutralization dynamics. The aim of this study is to analyze the dynamics that governs the neutralization process in the NDCX configuration. It has been found that the neutralization is a transient phenomenon, typically occurring on time scales of tens of plasma periods. During this transient, the ion beam undergoes through large electron oscillations. The oscillations are damped by a sheath. This sheath regulates the electron flux into and out of the beam, and because it opposes the electron oscillations, it also oscillates. The forward moving and oscillating sheath persists after the transient, and forms an oscillating shock at the front of the ion beam. The shock is in the form of a moving and oscillating discontinuity in the electric field, the charge density, and the electron average velocity. It has been found that the background plasma and beam densities influence the neutralization process, changing the properties of the sheath at the beam-plasma interface. The damping of the oscillations is important when the background plasma and beam densities are close in value, while it is weaker when the background plasma density is higher than the beam density. Moreover, the magnetic field does not have a significant effect on the ion beam neutralization process in the current and future NDCX configurations, and the simulations can be carried out in the electrostatic limit, achieving the same results as those obtained using electromagnetic simulations. A comparison of the implicit Particle-in-Cell methods with the explicitly time differenced Particle-in-Cell method shows that the implicit moment and the fully implicit Particle-in-Cell methods are on average 4 to 40 times computationally more expensive if the same simulation time step is used. Because the ion beam neutralizati

  4. 2D He+ pickup ion velocity distribution functions: STEREO PLASTIC observations

    NASA Astrophysics Data System (ADS)

    Drews, C.; Berger, L.; Taut, A.; Peleikis, T.; Wimmer-Schweingruber, R. F.

    2015-03-01

    Context. He+ pickup ions are either born from the ionization of interstellar neutral helium inside our heliosphere, the so-called interstellar pickup ions, or through the interaction of solar wind ions with small dust particles, the so-called inner source of pickup ions. Until now, most observations of pickup ions were limited to reduced 1D velocity spectra, which are insufficient to study certain characteristics of the He+ velocity distribution function (VDF). Aims: It is generally assumed that rapid pitch-angle scattering of freshly created pickup ions quickly leads to a fully isotropic He+ VDF. In light of recent observations, this assumption has found to be oversimplified and needs to be reinvestigated. Methods: Using He+ pickup ion data from the PLASTIC instrument on board the STEREO A spacecraft, we reconstruct a reduced form of the He+ VDF in two dimensions. This allows us to study relative changes of the 2D He+ VDF as a function of the configuration of the heliospheric magnetic field. Results: Our observations show that the He+ VDF is highly anisotropic and even indicates that, at least for certain configurations of B, it is not fully gyrotropic. Our results further suggest, that the observed velocity and pitch angle of He+ depends strongly on the local solar magnetic field vector, B, the ecliptic longitude, ?, the solar wind speed, vsw, and the global distribution of B. Conclusions: We found two distinct signatures that systematically change as a function of the alignment of B: (1) a ring beam distribution that is most pronounced at wsw> 0.5 and likely attributed to interstellar He+; (2) a beam signature aligned parallel to B that is most pronounced at wsw < 0.5 and attributed to inner-source He+. The strong anisotropy and the aforementioned dependencies of the He+ VDF also imply that observations of 1D velocity spectra of He+ pickup ions are potentially deceiving.

  5. Effect of ion excape velocity and conversion surface material on H- production

    SciTech Connect

    Johnson, Kenneth F; Tarvainen, Olli A; Geros, E.; Stelzer, J.; Rouleau, G.; Kalvas, T.; Komppula, J.; Carmichael, J.

    2010-10-05

    According to generally accepted models surface production of negative ions depends on ion escape velocity and work function of the surface. We have conducted an experimental study addressing the role of the ion escape velocity on H{sup -} production. A converter-type ion source at Los Alamos Neutron Science Center was employed for the experiment. The ion escape velocity was changed by varying the bias voltage of the converter electrode. It was observed that due to enhanced stripping of H{sup -} no direct gain of extracted beam current can be achieved by increasing the converter voltage. At the same time the conversion efficiency of H{sup -} was observed to vary with converter voltage and follow the existing theories in qualitative manner. We discuss the role of surface material on H{sup -} formation probability and present calculations predicting relative H{sup -} yields from different cesiated surfaces. These calculations are compared with experimental observations from different types of H{sup -} ion sources. The effects caused by varying cesium coverage are also discussed. Finally, we present a novel idea of utilizing materials exhibiting so-called negative electron affinity in H{sup -}/D{sup -} production under UV-light exposure.

  6. Velocity and Density of Low Energy Ions in High-Latitude Magnetosphere

    NASA Technical Reports Server (NTRS)

    Elliott, Heather A.; Comfort, Richard H.; Chandler, M. O.; Craven, P. D.; Moore, T. E.

    1999-01-01

    This study examines the characteristics of low energy ions at the polar cap boundary and within the polar cap in relationship to the convection velocity. The source of low energy ions in the magnetosphere could be driven by solar wind/IMF (interplanetary magnetic fields) interactions affecting energization processes of ionospheric ions. The IMF also influences the convection pattern which is in part responsible for determining the path ions take as they leave the ionosphere and contribute to magnetospheric populations. The primary source of data for this study is the Thermal Ion Dynamics Experiment (TIDE) on board the Polar satellite. TIDE can measure 3-D velocities and covers an energy range ideal for examining the polar cap plasma (0-450 eV). Due to certain limitations, this study uses H+ measurements at apogee and O+ measurements at perigee. At apogee H+ is very field-aligned and outflowing, and at perigee O+ is often moving downward in the polar cap proper. The path highly field-aligned flows take across the polar cap are also affected by changes in the magnetic field line topology which varies with geophysical conditions. Convection near the polar cap boundary is of particular interest since often the convection there is highly structured, and convection reversals may play a role in causing ion outflow. This study will examine in particular the density structures of ions in relationship to the convection velocity. Examining such relationships may provide insight into understanding the consequences of the 3-D flow on the density of ions in the polar cap, and transport of ions across the polar cap.

  7. Regulation of ion drifts and anisotropies by parametrically unstable finite-amplitude Alfvén-cyclotron waves in the fast solar wind

    SciTech Connect

    Maneva, Y. G.; Araneda, J. A.; Marsch, E.

    2014-03-10

    We study the preferential heating and differential acceleration of minor ions by dissipation of ion-acoustic waves (IAWs) generated by parametric instabilities of a finite-amplitude monochromatic Alfvén-cyclotron pump wave. We consider the associated kinetic effects of Landau damping and nonlinear pitch-angle scattering of protons and α particles in the tenuous plasma of coronal holes and the fast solar wind. Various data collected by Wind spacecraft show signatures for a local transverse heating of the minor ions, presumably by Alfvén-cyclotron wave dissipation, and an unexpected parallel heating by a so far unknown mechanism. Here, we present the results from a set of 1.5 dimensional hybrid simulations in search for a plausible explanation for the observed field-aligned kinetic features in the fast solar wind minor ions. We investigate the origin and regulation of ion relative drifts and temperature anisotropies in low plasma β, fast solar wind conditions. Depending on their initial drifts, both ion species can heat up not only transversely through cyclotron resonance and non-resonant wave-particle interactions, but also strongly in the parallel direction by Landau damping of the daughter IAWs. We discuss the dependence of the relative ion drifts and temperature anisotropies on the plasma β of the individual species and we describe the effect of the pump wave amplitude on the ion heating and acceleration.

  8. A novel pH-dependent drift improvement method for zirconium dioxide gated pH-ion sensitive field effect transistors.

    PubMed

    Chang, Kow-Ming; Chang, Chih-Tien; Chao, Kuo-Yi; Lin, Chia-Hung

    2010-01-01

    A novel compensation method for Zirconium dioxide gated Ion Sensitive Field Effect Transistors (ISFETs) to improve pH-dependent drift was demonstrated. Through the sequential measurements for both the n-channel and p-channel ISFETs, 75-100% pH-dependent drift could be successfully suppressed for the first seven hours. As a result, a nearly constant drift rate versus pH value was obtained, which increases the accuracy of pH measurements. Meanwhile, the drawback of the hyperbolic-like change with time of the common drift behavior for ISFETs was improved. A state-of-the-art integrated scheme adopting this method was also illustrated. PMID:22399897

  9. On the nonlinear stability of a quasi-two-dimensional drift kinetic model for ion temperature gradient turbulence

    SciTech Connect

    Plunk, G. G.

    2015-04-15

    We study a quasi-two-dimensional electrostatic drift kinetic system as a model for near-marginal ion temperature gradient driven turbulence. A proof is given for the nonlinear stability of this system under conditions of linear stability. This proof is achieved using a transformation that diagonalizes the linear dynamics and also commutes with nonlinear E B advection. For the case when linear instability is present, a corollary is found that forbids nonlinear energy transfer between appropriately defined sets of stable and unstable modes. It is speculated that this may explain the preservation of linear eigenmodes in nonlinear gyrokinetic simulations. Based on this property, a dimensionally reduced (???1) system is derived that may be useful for understanding dynamics around the critical gradient of Dimits.

  10. Distribution of electrons, ions, and fine (dust) particles in cylindrical fine particle (dusty) plasmas: drift-diffusion analysis

    NASA Astrophysics Data System (ADS)

    Totsuji, Hiroo

    2016-04-01

    Based on the drift-diffusion equations, the behaviour of electrons, ions and fine particles in fine particle plasmas is analysed both analytically and numerically. The cylindrical symmetry of the system is assumed and the cases of up to two species (sizes) of fine particles are considered. It is shown that, in the domain where fine particles exist, the charge neutrality is satisfied to a much higher accuracy, so that the electrostatic potential and the electron distribution are almost flat, and the change in the negative charges due to fine particles is compensated by the ion distribution. This occurs when the charge density of particles multiplied by their charge number exceeds the electron and ion charge densities, and is analytically attributed to the participation of fine particles to the screening of the space charge. The condition for the formation of void at the centre is obtained and the behaviour of particle distribution for parameters around the condition is observed. In the case of two species, the possibility is shown that smaller particles are distributed inside of the domain of larger particles and, when the larger ones form a void, it is filled with smaller ones, the enhanced charge neutrality being recovered.

  11. Ultrafast spectroscopy diagnostic to measure localized ion temperature and toroidal velocity fluctuations

    SciTech Connect

    Uzun-Kaymak, I. U.; Fonck, R. J.; McKee, G. R.; Schoenbeck, N.; Smith, D.; Winz, G.; Yan, Z.

    2010-10-15

    A dual-channel high-efficiency, high-throughput custom spectroscopic system has been designed and implemented at DIII-D to measure localized ion thermal fluctuations associated with drift wave turbulence. A large-area prism-coupled transmission grating and high-throughput collection optics are employed to observe C VI emission centered near {lambda}=529 nm. The diagnostic achieves 0.25 nm resolution over a 2.0 nm spectral band via eight discrete spectral channels. A turbulence-relevant time resolution of 1 {mu}s is achieved using cooled high-speed avalanche photodiodes and ultralow-noise preamplifiers. The system sensitivity is designed to provide measurements of normalized ion temperature fluctuations on the order of {delta}T{sub i}/T{sub i}{<=}1%.

  12. Nonlinear electrostatic drift waves in dense electron-positron-ion plasmas

    SciTech Connect

    Haque, Q.; Mahmood, S.; Mushtaq, A.

    2008-08-15

    The Korteweg-de Vries-Burgers (KdVB)-type equation is obtained using the quantum hydrodynamic model in an inhomogeneous electron-positron-ion quantum magnetoplasma with neutral particles in the background. The KdV-type solitary waves, Burgers-type monotonic, and oscillatory shock like solutions are discussed in different limits. The quantum parameter is also dependent on the positron concentration in dense multicomponent plasmas. It is found that both solitary hump and dip are formed and their amplitude and width are dependent on percentage presence of positrons in electron-ion plasmas. The height of the monotonic shock is decreased with the increase of positron concentration and it is independent of the quantum parameter in electron-positron-ion magnetized quantum plasmas. However, the amplitude of the oscillatory shock is dependent on positron concentration and quantum parameter in electron-positron-ion plasmas.

  13. Non-solar UV produced ions observed optically from the 'Crit I' critical velocity ionization experiment

    NASA Technical Reports Server (NTRS)

    Stenbaek-Nielsen, H. C.; Wescott, E. M.; Rees, D.; Valenzuela, A.; Brenning, N.

    1990-01-01

    A critical velocity ionization experiment was carried out with a heavily instrumented rocket launched from Wallops Island on May 13, 1986. Two neutral barium beams were created by explosive shaped charges released from the rocket and detonated at 48 deg to B at altitudes near 400 km and below the solar UV cutoff. Critical velocity ionization was expected to form a detectable ion jet along the release field line, but, instead, an ion cloud of fairly uniform intensity was observed stretching from the release field line across to where the neutral barium jet reached sunlight. The process creating these ions must have been present from the time of the release; the efficiency is estimated to be equivalent to an ionization time constant of 1800 sec. This ionization is most likely from collisions between the neutral barium jet and the ambient atmospheric oxygen, and, if so, the cross section for collisional ionization is 9 x 10 to the -18th sq cm.

  14. Ion velocity distribution at the termination shock: 1-D PIC simulation

    SciTech Connect

    Lu Quanming; Yang Zhongwei; Lembege, Bertrand

    2012-11-20

    The Voyager 2 (V2) plasma observations of the proton temperature downstream of the quasi-perpendicular heliospheric termination shock (TS) showed that upstream thermal solar wind ions played little role in the shock dissipation mechanism and their downstream temperature is an order of magnitude smaller than predicted by MHD Rankine-Hugoniot conditions. While pickup ions (PUI) are generally expected to play an important role in energy dissipation at the shock, the details remain unclear. Here, one-dimensional (1-D) Particle-in-cell (PIC) code is used to examine kinetic properties and downstream velocity distribution functions of pickup ions (the hot supra-thermal component) and solar wind protons (SWs, the cold component) at the perpendicular heliospheric termination shock. The code treats the pickup ions self-consistently as a third component. Present results show that: (1) both of the incident SWs and PUIs can be separated into two parts: reflected (R) ions and directly transmitted (DT) ions, the energy gain of the R ions at the shock front is much larger than that of the DT ions; (2) the fraction of reflected SWs and their downstream temperature decrease with the relative percentage PUI%; (3) no matter how large the PUI% is, the downstream ion velocity distribution function always can be separated into three parts: 1. a high energy tail (i.e. the wings) dominated by the reflected PUIs, 2. a low energy core mainly contributed by the directly transmitted SWs, and 3. a middle energy part which is a complicated superposition of reflected SWs and directly transmitted PUIs. The significance of the presence of pickup ions on shock front micro-structure and nonstationarity is also discussed.

  15. The effective ionization coefficients and electron drift velocities in gas mixtures of CF3I with N2 and CO2 obtained from Boltzmann equation analysis

    NASA Astrophysics Data System (ADS)

    Deng, Yun-Kun; Xiao, Deng-Ming

    2013-03-01

    The electron swarm parameters including the density-normalized effective ionization coefficients (?-?)/N and the electron drift velocities Ve are calculated for a gas mixture of CF3I with N2 and CO2 by solving the Boltzmann equation in the condition of a steady-state Townsend (SST) experiment. The overall density-reduced electric field strength is from 100 Td to 1000 Td (1 Td = 10-17 Vcm2), while the CF3I content k in the gas mixture can be varied over the range from 0% to 100%. From the variation of (?-?)/N with the CF3I mixture ratio k, the limiting field strength (E/N)lim for each CF3I concentration is derived. It is found that for the mixtures with 70% CF3I, the values of (E/N)lim are essentially the same as that for pure SF6. Additionally, the global warming potential (GWP) and the liquefaction temperature of the gas mixtures are also taken into account to evaluate the possibility of application in the gas insulation of power equipment.

  16. Ion Flow Measurement Using a Directional Langmuir Probe in the Radio Frequency Plasma Source DT-ALPHA

    NASA Astrophysics Data System (ADS)

    Kumagai, Takahiro; Okamoto, Atsushi; Takahashi, Hiroyuki; Daibo, Akira; Takahashi, Takuya; Tsubota, Shimpei; Kitajima, Sumio

    A directional Langmuir probe was designed and fabricated for measurement of ion flow in the RF plasma source, DT-ALPHA, in order to understand plasma structure in divertor study. Radial distribution and circumferential distribution of ion saturation current for He plasma were measured using the directional Langmuir probe. Ion flow velocity was obtained. A calibration factor was determined by comparing the radial profile of the azimuthal ion flow with E B drift velocity and diamagnetic drift velocity.

  17. Theoretical evaluation of peak capacity improvements by use of liquid chromatography combined with drift tube ion mobility-mass spectrometry.

    PubMed

    Causon, Tim J; Hann, Stephan

    2015-10-16

    In the domain of liquid phase separations, the quality of separation obtainable is most readily gauged by consideration of classical chromatographic peak capacity theory. Column-based multidimensional strategies for liquid chromatography remain the most attractive and practical route for increasing the number of spatially resolved components in order to reduce stress on necessary mass spectrometric detection. However, the stress placed on a chromatographic separation step as a second dimension in a comprehensive online methodology (i.e. online LCLC) is rather high. As an alternative to online LCLC combinations, coupling of HPLC with ion mobility spectrometry hyphenated to mass spectrometry (IMS-MS) has emerged as an attractive approach to permit comprehensive sampling of first dimension chromatographic peaks and subsequent introduction to an orthogonal IMS separation prior to measurement of ions by a mass spectrometer. In the present work, utilization of classical peak capacity and ion mobility theory allows theoretical assessment of the potential of two- (LCIMS-MS) or even three-dimensional (LCLCIMS-MS) experimental setups to enhance peak capacity and, therefore, the number of correctly annotated features within the framework of complex, non-targeted analysis problems frequently addressed using HPLC-MS strategies. Theoretical calculations indicate that newly-available drift tube IMS-MS instrumentation can yield peak capacities of between 10 and 40 using nitrogen drift gas for typical non-targeted metabolomic, lipidomic and proteomic applications according to the expected reduced mobilities of components in the respective samples. Theoretically, this approach can significantly improve the overall peak capacity of conventional HPLC-(MS) methodologies to in excess of 10(4) depending upon the column length and gradient time employed. A more elaborate combination of LCLCIMS-MS would improve the ion suppression limitation and possibly allow access to theoretically even higher peak capacities, but such a combination may render the IMS separation practically redundant as well as imparting the well-known dilution problems associated with LCLC. Finally, some predictions for the separation of co-eluted isobaric compounds can also be made by considering the required peak-to-peak resolution for acceptable IMS separation. The here-described theoretical predication approach can be used to aid method development for HPLCIMS-MS and is also accompanied by some practical considerations that should be contemplated in associated non-targeted analysis workflows. PMID:26372446

  18. Analogous Saturation Mechanisms of the Ion and Electron Temperature Gradient Drift Wave Turbulence

    NASA Astrophysics Data System (ADS)

    Sokolov, V.; Sen, A. K.

    2014-08-01

    New experimental results and theoretical arguments indicate that a novel saturation mechanism of the electron temperature gradient modes is related to its coupling to a damped ion acoustic mode. The experimental bicoherence data show multimode coupling between two high frequency radial harmonics of electron temperature gradient in the vicinity of (2 MHz) and one low frequency ion acoustic (45 kHz) mode. A unique feedback diagnostic also verifies this coupling. It is pointed out that a near identical mechanism is responsible for ITG mode saturation [V. Sokolov, and A. K. Sen, Phys. Rev. Lett. 92, 165002 (2004)], indicating its plausible generic nature.

  19. Positive/negative ion velocity mapping apparatus for electron-molecule reactions

    SciTech Connect

    Wu Bin; Xia Lei; Li Hongkai; Zeng Xianjin; Tian Shanxi

    2012-01-15

    In molecular dissociative ionization by electron collisions and dissociative electron attachment to molecule, the respective positively and negatively charged fragments are the important products. A compact ion velocity mapping apparatus is developed for the angular distribution measurements of the positive or negative fragments produced in the electron-molecule reactions. This apparatus consists of a pulsed electron gun, a set of ion velocity mapping optic lenses, a two-dimensional position detector including two pieces of micro-channel plates, and a phosphor screen, and a charge-coupled-device camera for data acquisition. The positive and negative ion detections can be simply realized by changing the voltage polarity of ion optics and detector. Velocity sliced images can be directly recorded using a narrow voltage pulse applied on the rear micro-channel plate. The efficient performance of this system is evaluated by measuring the angular distribution of O{sup -} from the electron attachments to NO at 7.3 and 8.3 eV and O{sup +} from the electron collision with CO at 40.0 eV.

  20. Measurements of nitrous acid (HONO) using ion drift-chemical ionization mass spectrometry during the 2009 SHARP field campaign

    NASA Astrophysics Data System (ADS)

    Levy, Misti; Zhang, Renyi; Zheng, Jun; Zhang, Annie L.; Xu, Wen; Gomez-Hernandez, Mario; Wang, Yuan; Olaguer, Eduardo

    2014-09-01

    We have developed a novel approach for ambient measurements of nitrous acid (HONO) using ion drift-chemical ionization mass spectrometry (ID-CIMS). HONO is ionized using the sulfur hexafluoride anion, representing the first application of this reagent ion under humid tropospheric conditions. During the 2009 Study of Houston Atmospheric Radical Precursors (SHARP) Field Campaign, HONO measurements were continuously conducted from 1 May to 1 June at a site located on the campus of the University of Houston. Diurnally, HONO concentration accumulates in the late afternoon, reaches a nighttime maximum, and declines rapidly after sunrise. The nighttime HONO peaks show close correlations with the NO2 concentration, particle surface area, and soot mass concentration, indicating that the aerosol-phase chemistry likely contributes to HONO formation. A higher nighttime HONO peak concentration typically precedes a higher and earlier ozone peak concentration of the following day, by about 20 ppb higher and four hours earlier than those with a lower preceding HONO peak concentration. Because of its high detection sensitivity and fast-responding time, the ID-CIMS method described in this work may greatly facilitate HONO detection under typical tropospheric conditions.

  1. Benchmark and combined velocity-space tomography of fast-ion D-alpha spectroscopy and collective Thomson scattering measurements

    NASA Astrophysics Data System (ADS)

    Jacobsen, A. S.; Salewski, M.; Geiger, B.; Korsholm, S. B.; Leipold, F.; Nielsen, S. K.; Rasmussen, J.; Stejner, M.; Weiland, M.; the ASDEX Upgrade team

    2016-04-01

    We demonstrate the combination of fast-ion D-alpha spectroscopy (FIDA) and collective Thomson scattering (CTS) measurements to determine a common best estimate of the fast-ion velocity distribution function by velocity-space tomography. We further demonstrate a benchmark of FIDA tomography and CTS measurements without using a numerical simulation as common reference. Combined velocity-space tomographies from FIDA and CTS measurements confirm that sawtooth crashes reduce the fast-ion phase-space densities in the plasma center and affect ions with pitches close to one more strongly than those with pitches close to zero.

  2. Sub-Auroral Ion Drifts as a Source of Mid-Latitude Plasma Density Irregularities

    NASA Astrophysics Data System (ADS)

    Sotnikov, V.; Kim, T.; Mishin, E.; Paraschiv, I.; Rose, D.

    Ionospheric irregularities cause scintillations of electromagnetic signals that can severely affect navigation and transionospheric communication, in particular during space storms. At midlatitudes, such space weather events are caused mainly by subauroral electric field structures (SAID/SAPS) [1, 2]. SAID/SAPS -related shear flows and plasma density troughs point to interchange and Kelvin-Helmholtz type instabilities as a possible source of plasma irregularities. A model of nonlinear development of these instabilities based on the two-fluid hydrodynamic description with inclusion of finite Larmor radius effects will be presented. A numerical code in C language to solve the derived nonlinear equations for analysis of interchange and flow velocity shear instabilities in the ionosphere was developed. This code was used to analyze competition between interchange and Kelvin Helmholtz instabilities in the equatorial region [3]. The high-resolution simulations with continuous density and velocity profiles will be driven by the ambient conditions corresponding to the in situ Defence Military Satellite Program (DMSP) satellite low-resolution data [2] during UHF/GPS L-band subauroral scintillation events. [1] Mishin, E. (2013), Interaction of substorm injections with the subauroral geospace: 1. Multispacecraft observations of SAID, J. Geophys. Res. Space Phys., 118, 5782-5796, doi:10.1002/jgra.50548. [2] Mishin, E., and N. Blaunstein (2008), Irregularities within subauroral polarization stream-related troughs and GPS radio interference at midlatitudes. In: T. Fuller-Rowell et al. (eds), AGU Geophysical Monograph 181, MidLatitude Ionospheric Dynamics and Disturbances, pp. 291-295, doi:10.1029/181GM26, Washington, DC, USA. [3] V. Sotnikov, T. Kim, E. Mishin, T. Genoni, D. Rose, I. Paraschiv, Development of a Flow Velocity Shear Instability in the Presence of Finite Larmor Radius Effects, AGU Fall Meeting, San Francisco, 15 - 19 December, 2014.

  3. Inversion methods for fast-ion velocity-space tomography in fusion plasmas

    NASA Astrophysics Data System (ADS)

    Jacobsen, A. S.; Stagner, L.; Salewski, M.; Geiger, B.; Heidbrink, W. W.; Korsholm, S. B.; Leipold, F.; Nielsen, S. K.; Rasmussen, J.; Stejner, M.; Thomsen, H.; Weiland, M.; the ASDEX Upgrade team

    2016-04-01

    Velocity-space tomography has been used to infer 2D fast-ion velocity distribution functions. Here we compare the performance of five different tomographic inversion methods: truncated singular value decomposition, maximum entropy, minimum Fisher information and zeroth- and first-order Tikhonov regularization. The inversion methods are applied to fast-ion {{\\text{D}}α} measurements taken just before and just after a sawtooth crash in the ASDEX Upgrade tokamak as well as to synthetic measurements from different test distributions. We find that the methods regularizing by penalizing steep gradients or maximizing entropy perform best. We assess the uncertainty of the calculated inversions taking into account photon noise, uncertainties in the forward model as well as uncertainties introduced by the regularization which allows us to distinguish regions of high and low confidence in the tomographies. In high confidence regions, all methods agree that ions with pitch values close to zero, as well as ions with large pitch values, are ejected from the plasma center by the sawtooth crash, and that this ejection depletes the ion population with large pitch values more strongly.

  4. Double-modulation spectroscopy of molecular ions - Eliminating the background in velocity-modulation spectroscopy

    NASA Technical Reports Server (NTRS)

    Lan, Guang; Tholl, Hans Dieter; Farley, John W.

    1991-01-01

    Velocity-modulation spectroscopy is an established technique for performing laser absorption spectroscopy of molecular ions in a discharge. However, such experiments are often plagued by a coherent background signal arising from emission from the discharge or from electronic pickup. Fluctuations in the background can obscure the desired signal. A simple technique using amplitude modulation of the laser and two lock-in amplifiers in series to detect the signal is demonstrated. The background and background fluctuations are thereby eliminated, facilitating the detection of molecular ions.

  5. Velocity imaging photoionization coincidence apparatus for the study of angular correlations between electrons and fragment ions

    NASA Astrophysics Data System (ADS)

    Takahashi, M.; Cave, J. P.; Eland, J. H. D.

    2000-03-01

    A new apparatus has been developed to detect and measure angular correlations between energy-selected photoelectrons and coincident mass-analyzed fragment ions from photoionization at selected wavelengths. It achieves velocity imaging for electrons and ions simultaneously and has high collection efficiency for both particles, with moderate mass and energy resolution. Angular and energy correlations between the two particles are measured, as are the angular distributions of each particle independently relative to the light polarization direction. Fixed-molecule electron angular distributions are deduced in cases of pure axial recoil. Examples of angular distributions from photoionization of diatomic molecules are reported.

  6. Theoretical investigations on plasma processes in the Kaufman thruster. [electron and ion velocity distribution

    NASA Technical Reports Server (NTRS)

    Wilhelm, H. E.

    1974-01-01

    An analysis of the sputtering of metal surfaces and grids by ions of medium energies is given and it is shown that an exact, nonlinear, hyperbolic wave equation for the temperature field describes the transient transport of heat in metals. Quantum statistical and perturbation theoretical analysis of surface sputtering by low energy ions are used to develop the same expression for the sputtering rate. A transport model is formulated for the deposition of sputtered atoms on system components. Theoretical efforts in determining the potential distribution and the particle velocity distributions in low pressure discharges are briefly discussed.

  7. Conformational Ordering of Biomolecules in the Gas Phase: Nitrogen Collision Cross Sections Measured on a Prototype High Resolution Drift Tube Ion Mobility-Mass Spectrometer

    PubMed Central

    2014-01-01

    Ion mobility-mass spectrometry measurements which describe the gas-phase scaling of molecular size and mass are of both fundamental and pragmatic utility. Fundamentally, such measurements expand our understanding of intrinsic intramolecular folding forces in the absence of solvent. Practically, reproducible transport properties, such as gas-phase collision cross-section (CCS), are analytically useful metrics for identification and characterization purposes. Here, we report 594 CCS values obtained in nitrogen drift gas on an electrostatic drift tube ion mobility-mass spectrometry (IM-MS) instrument. The instrument platform is a newly developed prototype incorporating a uniform-field drift tube bracketed by electrodynamic ion funnels and coupled to a high resolution quadrupole time-of-flight mass spectrometer. The CCS values reported here are of high experimental precision (0.5% or better) and represent four chemically distinct classes of molecules (quaternary ammonium salts, lipids, peptides, and carbohydrates), which enables structural comparisons to be made between molecules of different chemical compositions for the rapid omni-omic characterization of complex biological samples. Comparisons made between helium and nitrogen-derived CCS measurements demonstrate that nitrogen CCS values are systematically larger than helium values; however, general separation trends between chemical classes are retained regardless of the drift gas. These results underscore that, for the highest CCS accuracy, care must be exercised when utilizing helium-derived CCS values to calibrate measurements obtained in nitrogen, as is the common practice in the field. PMID:24446877

  8. Conformational ordering of biomolecules in the gas phase: nitrogen collision cross sections measured on a prototype high resolution drift tube ion mobility-mass spectrometer.

    PubMed

    May, Jody C; Goodwin, Cody R; Lareau, Nichole M; Leaptrot, Katrina L; Morris, Caleb B; Kurulugama, Ruwan T; Mordehai, Alex; Klein, Christian; Barry, William; Darland, Ed; Overney, Gregor; Imatani, Kenneth; Stafford, George C; Fjeldsted, John C; McLean, John A

    2014-02-18

    Ion mobility-mass spectrometry measurements which describe the gas-phase scaling of molecular size and mass are of both fundamental and pragmatic utility. Fundamentally, such measurements expand our understanding of intrinsic intramolecular folding forces in the absence of solvent. Practically, reproducible transport properties, such as gas-phase collision cross-section (CCS), are analytically useful metrics for identification and characterization purposes. Here, we report 594 CCS values obtained in nitrogen drift gas on an electrostatic drift tube ion mobility-mass spectrometry (IM-MS) instrument. The instrument platform is a newly developed prototype incorporating a uniform-field drift tube bracketed by electrodynamic ion funnels and coupled to a high resolution quadrupole time-of-flight mass spectrometer. The CCS values reported here are of high experimental precision (0.5% or better) and represent four chemically distinct classes of molecules (quaternary ammonium salts, lipids, peptides, and carbohydrates), which enables structural comparisons to be made between molecules of different chemical compositions for the rapid "omni-omic" characterization of complex biological samples. Comparisons made between helium and nitrogen-derived CCS measurements demonstrate that nitrogen CCS values are systematically larger than helium values; however, general separation trends between chemical classes are retained regardless of the drift gas. These results underscore that, for the highest CCS accuracy, care must be exercised when utilizing helium-derived CCS values to calibrate measurements obtained in nitrogen, as is the common practice in the field. PMID:24446877

  9. Apparent Velocity Threshold in the Electronic Stopping of Slow Hydrogen Ions in LiF

    SciTech Connect

    Draxler, M.; Chenakin, S.P.; Markin, S.N.; Bauer, P.

    2005-09-09

    The electronic energy loss of hydrogen ions (protons and deuterons) in thin supported films of LiF has been studied in backscattering geometry for specific energies from 700 eV/u to 700 keV/u, using Rutherford backscattering spectroscopy and time-of-flight low-energy ion scattering spectroscopy. For specific energies below 8 keV/u, our data confirm velocity proportionality for the stopping cross section {epsilon} (like in a metal) down to 3.8 keV/u, as observed previously for protons and antiprotons despite the large band gap (14 eV) of LiF. Below 3.8 keV/u, the present results indicate an apparent velocity threshold at about 0.1 a.u. for the onset of electronic stopping.

  10. A Survey of Velocity Distributions of Solar Wind Ions : ACE/SWICS observations

    NASA Astrophysics Data System (ADS)

    Berger, L.; Marsch, E.; Wimmer-Schweingruber, R. F.

    2014-12-01

    The state of solar wind ions is generally described by a small set of state variables. In detail these aretotal density (or flux), center of mass (or bulk) velocity, and temperature. These variables are obtainedfrom measured velocity distributions either by fitting a Maxwell-Boltzmann distribution or by calculatingthe zeroth, first, and second order moments of the distribution. Obviously the first approach requires athermalized distribution to yield meaningful results, while the second approach is universally valid.However, in both cases the shape of the distribution can not be reproduced by the derived parameters.From observations of solar wind protons and alpha particles it is known that the assumption of a thermalized distribution is not valid, at least for the majority of observations. For heavy solar wind ions most observationsare severely limited by statistics and do not even allow to distinguish whether the distribution is thermal or not.This often insufficient characterization of the solar wind VDF severely limits the information which can beobtained for more detailed studies, especially about microscopic kinetic physics and the associatedwave-particle interactions. These naturally yield deviations from Maxwell-Boltzmann distributions.To address this problem we have analyzed ten years worth of data from the Solar Wind Ion Composition Spectrometer (SWICS)and the Magnetometer (MAG) on the Advanced Composition Explorer (ACE). From our analysis we obtained reduced 1D velocity spectra in 12 minute cadence for some 40 solar wind ions, from protons and alpha particles up to iron.Using the magnetic field vector information we were able to study periods where the reduced 1D spectra representthe parallel and perpendicular shape of the velocity distributions. We present our results and discussthem in the aforementioned context.

  11. A simulation study on the impact of altitudinal dependent vertical plasma drift on the equatorial ionosphere in the evening

    NASA Astrophysics Data System (ADS)

    Qian, Cheng; Lei, Jiuhou; Wang, Wenbin

    2015-04-01

    We carry out a simulation study on the impact of altitudinal dependent plasma drift on the equatorial ionosphere in the evening, under geomagnetically quiet conditions. Our study used the vertical plasma drift velocity data measured by an incoherent scatter radar at Jicamarca (11.95S, 76.87W). The data covered the local sunset period on 15 and 16 November 2004. The plasma drift had significant altitudinal variations in the vertical component, which is perpendicular to the magnetic field. We employed SAMI2 (SAMI2 is another model of the ionosphere) to evaluate the effect of the altitude-dependent ion drift on the equatorial ionosphere. Three types of plasma drift velocity inputs were used in our simulations. The first input is calculated from an empirical model, the second is a height-averaged drift obtained from the observed drift velocity, and the third one corresponds to the observed altitudinal dependent drift data. A strong equatorial ionization anomaly occurred in the results of all numerical experiments. Additional layers (F3 layers) in electron densities over the equatorial F region and "arch" latitudinal structures extending to lower middle latitudes were seen in the simulations driven by the observed altitudinal dependent drift. We further show that neutral winds do not have a significant effect on the simulated F3 layers. The results of our numerical experiments suggest that the simulated additional ionospheric layers and arch structures are associated with the altitudinal gradients in the vertical plasma drift velocity.

  12. A millimeter/submillimeter velocity modulation spectrometer for studies of molecular ions

    NASA Astrophysics Data System (ADS)

    Savage, C.; Ziurys, L. M.

    2005-04-01

    A millimeter/submillimeter direct absorption spectrometer has been constructed that employs velocity modulation to selectively detect molecular ions. The instrument consists of a phase-locked Gunn oscillator/Schottky diode multiplier source, a gas absorption cell, and an InSb hot-electron bolometer detector. The gas cell is a single-pass system with two ring-type discharge electrodes at either end, which are connected to an rf power supply. Modulation of the ac discharge at a rate of 50 kHz and phase-sensitive detection at 1f allows for selective observation of molecular ion signals and suppression of absorption from neutral species. The spectrometer can also be used in source-modulated mode, where the signal-to-noise ratio for signals generated in an ac plasma are significantly better than for dc discharges. Combining source modulation with the ac discharge for signal detection and velocity modulation for ion identification provides a powerful technique for molecular ion spectroscopy at millimeter/submillimeter wavelengths. This instrument has been used to measure the pure rotational spectra of CO+, HCO+, and SH+ with better precision than previous studies.

  13. Effect of trajectory fluctuations on nucleon drift and diffusion in deep inelastic heavy ion collisions

    SciTech Connect

    Chattopadhyay, S.; Pal, D. )

    1990-01-01

    The role of trajectory fluctuations on the first and second moments obtained in the mean trajectory approximation for the proton and neutron distributions of the projectile-like fragments produced in deep inelastic heavy ion collisions has been studied in the framework of stochastic transfer of single nucleons. At each instant of time the neutron and proton numbers of the colliding nuclei are considered to be given by dynamically evolving Gaussian distributions generating trajectory fluctuations. The first moments calculated in this method differ considerably from those obtained in the mean trajectory approximation for the systems with strong gradient in the driving force around the point of injection. The second moments, however, do not change appreciably for all the systems studied.

  14. Velocity space diffusion of pickup ions from the water group at Comet Halley

    SciTech Connect

    Coates, A.J.; Johnstone, A.D. ); Wilken, B.; Jockers, K. ); Glassmeier, K.H. )

    1989-08-01

    The authors have studied the diffusion in velocity space of cometary ions using the distributions of ions measured by the implanted ion spectrometer on Giotto during the inbound pass. The measurements were transformed into a frame comoving with the solar wind and oriented with the magnetic field. The observations show the evolution of the pitch angle distribution in the solar wind turbulence to form a shell from the initial ring. Diffusion in energy takes place simultaneously but on a longer time scale. Comparison with theory is inhibited by the lack of a suitable spatial model, but the simple arguments they can make indicate that pitch angle diffusion, and the process of parallel pickup, take place more slowly than theory suggests.

  15. Properties of energetic-particle continuum modes destabilized by energetic ions with beam-like velocity distributions

    SciTech Connect

    Todo, Y.

    2006-08-15

    Properties of energetic-particle continuum modes (EPMs) destabilized by energetic ions in tokamak plasmas were investigated using a hybrid simulation code for magnetohydrodynamics and energetic particles. The energetic ions are assumed to have beam-like velocity distributions for the purpose of clarifying the dependence on energetic ion velocity. It was found that for beam velocities lower than the Alfven velocity, the unstable modes are EPMs while the toroidal Alfven eigenmodes are unstable for the beam velocities well above the Alfven velocity. The EPMs destabilized by the copassing energetic ions and those destabilized by the counterpassing energetic ions differ in primary poloidal harmonics and spatial locations. The frequencies of the EPMs are located close to the shear Alfven continuous spectrum when they are compared at the spatial peak locations of the primary poloidal harmonic or compared at the spatial tails if the primary poloidal harmonic is m=1. The frequencies of the EPMs were carefully compared with the energetic-ion orbital frequencies. It was found that the frequencies of the EPMs are in good agreement with the energetic-ion orbital frequencies with a correction for the toroidal circulation frequency. This demonstrates that the energetic-ion orbital frequency determines the EPM frequency.

  16. Formation and velocity measurement of a low-energy Li + ion beam for precision laser spectroscopy

    NASA Astrophysics Data System (ADS)

    Rong, H.; Grafstrm, S.; Kowalski, J.; Neumann, R.; zu Putlitz, G.

    2002-01-01

    This paper reports the formation and parameter analysis of a low-energy Li + beam (with natural isotope abundance) developed for optical and optical-microwave precision spectroscopy. Electrons emitted from a ring-shaped tungsten-wire cathode ionize Li atoms by impact immediately when leaving the nozzle of an oven. Electrons and ions are accelerated to typically 300 eV by propagating counter to each other through the same electric field applied between cathode and oven orifice. A well-collimated ion beam, containing a 10 -3 fraction of ions in the metastable 1s2s 3S1 state, is shaped by an electrostatic lens system. The 2 3S1-2 3P1,2,0 transition at the wavelength ??5485 , representing the central target of numerous investigations in the helium-like Li + spectrum, provides a nondestructive access to kinematic beam parameters: The beam of a cw single-mode ring dye laser crosses the ion beam at an angle of roughly 12. The Doppler shift of the 2 3S1, F=5/2-2 3P2, F=7/2 hyperfine structure component (the most prominent of the multiplet) with respect to the intrinsic transition frequency ?0 and the Doppler profile are measured by frequency-tuning the laser over this line and registering the excitation profile with a photomultiplier via the reemitted fluorescence. The mean velocity ?, the velocity distribution, and the divergence of the ion beam are derived from this measurement. The determination of ? with an uncertainty of 4.510 -3 has made it possible to perform at this ion-beam facility a measurement of ?0 with a precision of about 210 -9 and thus to provide a new independent value of this frequency.

  17. Interpretation of nonlinear wave structures in the F-region of the ionosphere, registered by DE2 satellite as ion-cyclotron gradient-drift solitons with chirp

    NASA Astrophysics Data System (ADS)

    Kovaleva, Irina

    On the basis of satellite DE2 data in the middle latitude ionosphere authors show that wave fluctuations exhibit properties of nonlinear ion-cyclotron gradient-drift structures, theoretically considered by the authors earlier [1,2]. The main property of the structures is excitation on transversal gradient of single ion concentration. For geomagnetically calm days distributions of the fluctuations along satellite trajectory are analyzed. The total ion concentration monotonically grows or decreases and has no sharp gradients along trajectory but concentrations of O+, N+ or H+ ions has sharp gradients. The fluctuations power follow O+, N+ tranversal gradient in middle and low latitudes and H+, He+ gradient in subauroral latitudes. The variations of electric field do not influence the fluctuation power. The theoretical structure is composed of the ion concentration asymmetric hump or hole and wave packet (ion-cyclotron envelope soliton - oscilliton) on the trailing sharp edge of it. The spike form of experimental signal confirms this hypothesis. The authors give some examples (when instrument resolution is appropriate) where wave packets are situated on the sharp edge of density hump or hole. Analysis confirms the justification of the interpretation of these signals as ion-cyclotron gradient-drift solitons with chirp-oscillitons. [1]Kovaleva I.Kh.//Phys plasmas, 19, 102905, doi: 10.1063/1.4763561,2012 [2]Kovaleva I.Kh.//Plasma Phys Reports 39, 3, pp226-235, 2013

  18. Measurements of Nitrous Acid (HONO) Using Ion Drift - Chemical Ionization Mass Spectrometry during the 2009 SHARP Field Campaign

    NASA Astrophysics Data System (ADS)

    Levy, M. E.; Zhang, R.

    2013-12-01

    During the 2009 SHARP Field Campaign in Houston, TX, measurements of HONO were continuously conducted from May 1 to June 1 at a site located on the campus of the University of Houston. We have developed a novel approach for ambient measurements of nitrous acid (HONO) using ion drift - chemical ionization mass spectrometry (ID-CIMS). In our innovative method, HONO is ionized using the sulfur hexafluoride anion, representing the first application of this reagent ion under humid tropospheric conditions. In this presentation, we will discuss the temporal trends and sources of HONO, as well as, as the involvement of HONO in the formation of key atmospheric constituents, such as ozone. Diurnally, HONO concentration accumulates in the late afternoon, reaches a nighttime maximum, and declines rapidly after sunrise; the averaged daytime and nighttime concentrations are 0.15 0.05 and 0.26 0.04, respectively. The nighttime measured HONO peaks show strong correlations with the NO2 concentration, particle surface area, and soot mass concentration, indicating that the aerosol-phase chemistry represents a significant contributor to the HONO yield. A higher nighttime HONO peak concentration consistently precedes a higher and earlier ozone peak concentration of the following day, by about 20 ppb higher and four hours earlier than those with a lower preceding HONO peak concentration do. Using a kinetic approach, we estimate an uptake coefficient in the range of 6 x 10-4 to 2 x 10-3 for the heterogeneous conversion of NO2 to HONO on aerosol surfaces, which is necessary to account for the measured nighttime HONO peaks. Our results underscore the importance of aerosol heterogeneous chemistry in HONO production and the contributions of this non-photolytic HONO source to the radical budget and the photochemical ozone production in this region. Furthermore, because of its high detection sensitivity and fast-responding time, the ID-CIMS method described in this work may greatly facilitate HONO detection under typical tropospheric conditions.

  19. Giotto-IMS observations of ion flow velocities and temperatures outside the contact surface of Comet Halley. [Ion Mass Spectrometer (IMS)

    NASA Technical Reports Server (NTRS)

    Goldstein, B. E.; Neugebauer, M.; Balsiger, H.; Drake, J.; Fuselier, S. A.; Goldstein, R.; Ip, WING-H.; Rettenmund, U.; Rosenbauer, H.; Schwenn, R.

    1986-01-01

    Fluid parameters for He(++) ions obtained from the Giotto ion mass spectrometer are presented. Proton densities and velocities and thermal speeds of protons, alpha particles, and heavy ions in the hour before closest approach are discussed. A region of enhanced He(++) ion densities, and velocity, and decreased temperature is observed from 20:26 to 21:45. Sharp decreases in the proton density are observed at 23:30 and at 23:41. There is a relative flow velocity between alpha particles and oxygen ions of 30 km/sec during a period from 22:55 to 23:30; the difference in flow velocity is less than the experimental uncertainities. The flow properties of protons observed during this period are also discussed.

  20. Investigation of localized 2D convection mapping based on artificially generated Swarm ion drift data

    NASA Astrophysics Data System (ADS)

    Fiori, R. A. D.; Boteler, D. H.; Koustov, A. V.; Knudsen, D.; Burchill, J. K.

    2014-07-01

    Ionospheric plasma flow is an indicator of the interconnection between the solar wind, interplanetary magnetic field (IMF), and Earths magnetosphere. Ionospheric convection has been mapped in the past using either a widespread data set for instantaneous convection mapping over a short time period or data from an instrument measuring convection in a spatially confined region over a long time period for the purpose of building a statistically averaged convection pattern. This study explores convection mapping using a spherical cap harmonic analysis (SCHA) technique within a localized spherical cap based on data that will be available from the Swarm three-satellite constellation. Convection is mapped in the vicinity of hypothetical Swarm satellite tracks where it is adequately constrained by data. By using statistical models to emulate Swarm measurements, we demonstrate that such mapping can be successful based on data from the Swarm A and Swarm B satellites. Convection is divided into well constrained and poorly constrained subsets to determine parameters characterizing goodness-of-fit based on known quantities. Using the subset of well constrained maps, it is determined that convection is best mapped for a spherical cap having an angular radius of ?c=10. The difference between the maximum mapped convection and the maximum velocity measured along the satellite track (?v) is introduced to evaluate goodness-of-fit. For the examples presented in this paper, we show that a threshold value of ?v=281 m/s successfully differentiates between well and poorly constrained maps 77.6% of the time. It is shown that convection can be represented over a larger region through the use of multiple spherical caps.

  1. Laboratory Course on Drift Chambers

    SciTech Connect

    Garcia-Ferreira, Ix-B.; Garcia-Herrera, J.; Villasenor, L.

    2006-09-25

    Drift chambers play an important role in particle physics experiments as tracking detectors. We started this laboratory course with a brief review of the theoretical background and then moved on to the the experimental setup which consisted of a single-sided, single-cell drift chamber. We also used a plastic scintillator paddle, standard P-10 gas mixture (90% Ar, 10% CH4) and a collimated 90Sr source. During the laboratory session the students performend measurements of the following quantities: a) drift velocities and their variations as function of the drift field; b) gas gains and c) diffusion of electrons as they drifted in the gas.

  2. Atomic collision experiments utilizing low-velocity, highly-charged ion beams

    SciTech Connect

    Johnson, B.M.; Jones, K.W.; Meron, M.

    1982-01-01

    Intense beams of highly-stripped ions are now routinely produced at low velocities using the Brookhaven dual MP-tandens in a unique four-stage accel/decel mode. This mode of operation combines three stages of acceleration, stripping at high energy, and one stage of deceleration to near-zero velocity. To date, experiments have used 10-100 nA beams of bare and few-electron heavy ions at energies as low as 0.2 MeV/amu, and upgrades of the facility should push the lower limit below 0.1 MeV/amu. Recent experiments, such as measurements of charge transfer and x-ray production for S/sup 6-16+/ on He and Ar at 6 to 20 MeV and P(b) measurements for MO x-rays produced in Cl/sup 16 +/ + Ar collisions at 20, 10, and 5 MeV have demonstrated the usefulness of highly-stripped, low-velocity projectiles. These experiments and a few possibilities for future experiments are discussed.

  3. Extension of charge-state-distribution calculations for ion-solid collisions towards low velocities and many-electron ions

    NASA Astrophysics Data System (ADS)

    Lamour, E.; Fainstein, P. D.; Galassi, M.; Prigent, C.; Ramirez, C. A.; Rivarola, R. D.; Rozet, J.-P.; Trassinelli, M.; Vernhet, D.

    2015-10-01

    Knowledge of the detailed evolution of the whole charge-state distribution of projectile ions colliding with targets is required in several fields of research such as material science and atomic and nuclear physics but also in accelerator physics, and in particular in regard to the several foreseen large-scale facilities. However, there is a lack of data for collisions in the nonperturbative energy domain and that involve many-electron projectiles. Starting from the etacha model we developed [Rozet et al., Nucl. Instrum. Methods Phys. Res., Sect. B 107, 67 (1996), 10.1016/0168-583X(95)00800-4], we present an extension of its validity domain towards lower velocities and larger distortions. Moreover, the system of rate equations is able to take into account ions with up to 60 orbital states of electrons. The computed data from the different new versions of the etacha code are compared to some test collision systems. The improvements made are clearly illustrated by 28.9 MeV u-1P b56 + ions, and laser-generated carbon ion beams of 0.045 to 0.5 MeV u-1 , passing through carbon or aluminum targets, respectively. Hence, those new developments can efficiently sustain the experimental programs that are currently in progress on the "next-generation" accelerators or laser facilities.

  4. MEASUREMENTS OF ANISOTROPIC ION TEMPERATURES, NON-THERMAL VELOCITIES, AND DOPPLER SHIFTS IN A CORONAL HOLE

    SciTech Connect

    Hahn, M.; Savin, D. W.

    2013-02-15

    We present a new diagnostic allowing one to measure the anisotropy of ion temperatures and non-thermal velocities, as well as Doppler shifts with respect to the ambient magnetic field. This method provides new results, as well as an independent test for previous measurements obtained with other techniques. Our spectral data come from observations of a low-latitude, on-disk coronal hole. A potential field source surface model was used to calculate the angle between the magnetic field lines and the line of sight for each spatial bin of the observation. A fit was performed to determine the line widths and Doppler shifts parallel and perpendicular to the magnetic field. For each line width component we derived ion temperatures T {sub i,} and T {sub i, Parallel-To} and non-thermal velocities v {sub nt,} and v {sub nt, Parallel-To }. T {sub i,} was cooler than off-limb polar coronal hole measurements, suggesting increasing collisional cooling with decreasing height. T {sub i, Parallel-To} is consistent with a uniform temperature of (1.8 {+-} 0.2) Multiplication-Sign 10{sup 6} K for each ion. Since parallel ion heating is expected to be weak, this ion temperature should reflect the proton temperature. A comparison between our results and others implies a large proton temperature gradient around 1.02 R {sub Sun }. The non-thermal velocities are thought to be proportional to the amplitudes of various waves. Our results for v {sub nt,} agree with Alfven wave amplitudes inferred from off-limb polar coronal hole line width measurements. Our v {sub nt, Parallel-To} results are consistent with slow magnetosonic wave amplitudes inferred from Fourier analysis of time-varying intensity fluctuations. Doppler shift measurements yield outflows of Almost-Equal-To 5 km s{sup -1} for ions formed over a broad temperature range. This differs from other studies that found a strong Doppler shift dependence on formation temperature.

  5. Outflow velocity of the O+5 ions in polar coronal holes out to 5 R?

    NASA Astrophysics Data System (ADS)

    Telloni, D.; Antonucci, E.; Dodero, M. A.

    2007-09-01

    The purpose of the paper is to extend the measurement of the kinetic temperature and outflow velocity of the oxygen ions in the outer corona above polar holes out to 5 R_?. An analytical model of the solar corona at the minimum of activity has been employed in order to synthesize the spectral line profiles to be fitted with the data: the kinetic temperature of the O+5 ions on the plane of the sky is derived from the width of the O VI 1031.9 line by applying the ?2 minimization. The oxygen temperature peaks at about 2.9 R_?, reaching a value of 1.5 108 K, and further out it is somehow flattening. The outflow velocity of the oxygen component of the fast solar wind, derived from the intensity ratio of the Doppler dimmed O VI doublet, increases outward to reach 550-760 km s-1 at 5 R_?. The upper and lower limits of the outflow speed are due to the fact that its measurement depends on the velocity distribution of the oxygen ions which cannot be directly measured along the radial direction, but only along the line of sight. Hence the uncertainty is related to the temperature anisotropy assumed in the analysis. For this reason in this paper the measurement of the temperature anisotropy, found beyond 2 R_? according to the previous literature on UVCS results, has been as well extended at higher altitudes, and it is found that above 3.7 R_? anisotropy can still exist but not necessarily. The observations of the extended corona analyzed in this paper are performed with the Ultraviolet Coronagraph Spectrometer on board the Solar Heliospheric Observatory, during the solar minimum activity period 1996-1997.

  6. Effects of gamma-ray and high energy carbon ion irradiation on swimming velocity of Euglena gracilis

    NASA Astrophysics Data System (ADS)

    Sakashita, T.; Doi, M.; Yasuda, H.; Fuma, S.; Häder, D.-P.

    The effects of gamma-ray and high energy carbon ion irradiation on the swimming velocity of the photosynthetic flagellate Euglena gracilis strain Z were studied, focusing on a dose-effect relationship. Cells were exposed to 60Co gamma-rays at 6 doses of 10, 15, 20, 40, 100 and 200 Gy for water, and also to 290 MeV/amu carbon ions from the Heavy Ion Medical Accelerator in Chiba at 7 doses (5, 10, 15, 20, 50, 100 and 200 Gy for water). The swimming velocity was measured by a biomonitoring system, called ECOTOX. The swimming velocities of Euglena gracilis cells were significantly decreased by >40 Gy gamma-rays and >5 Gy carbon ions, respectively. The 50% effective doses for inhibition, 34±4 Gy (gamma-rays) and 13±1 Gy (290 MeV/amu carbon ions), were estimated from the best fit to data of the logistic model. The relative biological effectiveness (2.6±0.4) was calculated by the ratio of 50% effective doses. The inhibition of the swimming velocity of the cells irradiated with gamma-rays was still present after 3 days, while recovery of the swimming velocity was shown in the cells exposed to 290 MeV/amu carbon ions. It is suggested that ionizing radiation inhibits ATP production and/or increases frictional drag on beating of the flagellum, thus decreasing swimming velocity.

  7. Ion Bernstein waves in a plasma with a kappa velocity distribution

    SciTech Connect

    Nsengiyumva, F.; Mace, R. L.; Hellberg, M. A.

    2013-10-15

    Using a Vlasov-Poisson model, a numerical investigation of the dispersion relation for ion Bernstein waves in a kappa-distributed plasma has been carried out. The dispersion relation is found to depend significantly on the spectral index of the ions, κ{sub i}, the parameter whose smallness is a measure of the departure from thermal equilibrium of the distribution function. Over all cyclotron harmonics, the typical Bernstein wave curves are shifted to higher wavenumbers (k) if κ{sub i} is reduced. For waves whose frequency lies above the lower hybrid frequency, ω{sub LH}, an increasing excess of superthermal particles (decreasing κ{sub i}) reduces the frequency, ω{sub peak}, of the characteristic peak at which the group velocity vanishes, while the associated k{sub peak} is increased. As the ratio of ion plasma to cyclotron frequency (ω{sub pi}/ω{sub ci}) is increased, the fall-off of ω at large k is smaller for lower κ{sub i} and curves are shifted towards larger wavenumbers. In the lower hybrid frequency band and harmonic bands above it, the frequency in a low-κ{sub i} plasma spans only a part of the intraharmonic space, unlike the Maxwellian case, thus exhibiting considerably less coupling between adjacent bands for low κ{sub i}. It is suggested that the presence of the ensuing stopbands may be a useful diagnostic for the velocity distribution characteristics. The model is applied to the Earth's plasma sheet boundary layer in which waves propagating perpendicularly to the ambient magnetic field at frequencies between harmonics of the ion cyclotron frequency are frequently observed.

  8. Calculation of the Ion Distribution Function over Transverse Velocities under ICR Heating Conditions and Separation Parameters of a Collector of Heated Ions

    SciTech Connect

    Karchevskii, A.I.; Potanin, E.P.

    2004-12-15

    The ion distribution function over transverse velocities and the ion heating efficiency (which is defined as the fraction {eta} of ions heated above a certain energy W{sub min}) are calculated in the context of a plasma method for isotope separation on the basis of ion cyclotron resonance heating. The ion distribution function over longitudinal velocities is assumed to be linear in the range of low velocities. It is shown that, when the ions are heated to high energies, the averaged ion distribution function over transverse velocities becomes highly nonequilibrium and has two peaks. Results are presented from calculations of the ion heating efficiency {eta} for W{sub min} = 40 eV and for different values of the parameter p that characterizes the ratio of the wavelength {lambda} of the antenna electric field to the length L of the heating region. The relative roles of the time-of-flight and the Doppler broadening are analyzed, and the separation parameters of a collector of heated ions are estimated.

  9. Drift and Hysteresis Effects on AlN/SiO2 Gate pH Ion-Sensitive Field-Effect Transistor

    NASA Astrophysics Data System (ADS)

    Chiang, Jung-Lung; Chou, Jung-Chuan; Chen, Ying-Chung; Liau, Guo Shiang; Cheng, Chien-Chuan

    2003-08-01

    The nonideal and unstable factors of AlN-based ion-sensitive field-effect transistor (ISFET) devices including the drift and hysteresis effects have been investigated in this study. The drift and hysteresis of AlN-based pH-ISFET devices have been measured using a constant current constant voltage (CCCV) readout circuit. The drift rates were obtained by long-time monitoring for 12 h in pH = 1, 3, 5, 7, 9, and 11 buffer solutions, which indicated that the drift rate increased with the pH value. The hysteresis effect was investigated by exposing the AlN gate ISFET in pH = 7-3-7-11-7 loop cycles with loop times of 960 s, 1920 s and 3840 s, and the magnitudes of hysteresis of 1.0, 1.5 and 4.5 mV were obtained, respectively. The temperature coefficient of hysteresis was found to be approximately 0.234 mV/°C. In addition, it was also found that the hysteresis width with pH started from acid side is smaller than that started from basic side, which results in an asymmetric hysteresis effect.

  10. Studies of endothelial monolayer formation on irradiated poly-L-lactide acid with ions of different stopping power and velocity

    NASA Astrophysics Data System (ADS)

    Arbeitman, Claudia R.; del Grosso, Mariela F.; Ibañez, Irene L.; Behar, Moni; Grasselli, Mariano; Bermúdez, Gerardo García

    2015-12-01

    In this work we study cell viability, proliferation and morphology of bovine aortic endothelial cells (BAEC) cultured on poly-L-lactide acid (PLLA) modified by heavy ion irradiation. In a previous study comparing ions beams with the same stopping power we observed an increase in cell density and a better cell morphology at higher ion velocities. In the present work we continued this study using heavy ions beam with different stopping power and ion velocities. To this end thin films of 50 μm thickness were irradiated with 2 MeV/u and 0.10 MeV/u ion beams provided the Tandar (Buenos Aires, Argentina) and Tandetron (Porto Alegre, Brazil) accelerators, respectively. The results suggest that a more dense and elongated cell shapes, similar to the BAEC cells on the internal surface of bovine aorta, was obtained for stopping power of 18.2-22.1 MeV cm2 mg-1 and ion velocity of 2 MeV/u. On the other hand, for low ion velocity 0.10 MeV/u the cells present a more globular shapes.

  11. ION TEMPERATURE AND NON-THERMAL VELOCITY IN A SOLAR ACTIVE REGION: USING EMISSION LINES OF DIFFERENT ATOMIC SPECIES

    SciTech Connect

    Imada, S.; Hara, H.; Watanabe, T.

    2009-11-10

    We have studied the characteristics of the ion thermal temperature and non-thermal velocity in an active region observed by the EUV Imaging Spectrometer onboard Hinode. We used two emission lines of different atomic species (Fe XVI 262.98 A and S XIII 256.69 A) to distinguish the ion thermal velocity from the observed full width at half-maximum. We assumed that the sources of the two emission lines are the same thermal temperature. We also assumed that they have the same non-thermal velocity. With these assumptions, we could obtain the ion thermal temperature, after noting that M{sub sulfur} approx 0.6M{sub iron}. We have carried out the ion thermal temperature analysis in the active region where the photon counts are sufficient (>4500). What we found is as follows: (1) the common ion thermal temperatures obtained by Fe XVI and S XIII are approx2.5 MK, (2) the typical non-thermal velocities are approx13 km s{sup -1}, (3) the highest non-thermal velocities (>20 km s{sup -1}) are preferentially observed between the bright points in Fe XVI, while (4) the hottest material (>3 MK) is observed relatively inside the bright points compared with the highest non-thermal velocity region.

  12. Quantification of ions with identical mass-to-charge (m/z) ratios by velocity-map imaging mass spectrometry.

    PubMed

    Bull, James N; Lee, Jason W L; Vallance, Claire

    2013-09-01

    By integrating a velocity-map imaging lens and position sensitive detector into an electron-impact time-of-flight mass spectrometer, it becomes possible to record ion kinetic energy release (KER) distributions for each fragment ion alongside the time-of-flight mass spectrum. The KER distributions allow ions of identical mass-to-charge ratio to be distinguished and quantified. PMID:23860732

  13. Spectroscopy of L-shell Xenon for Ion Temperature and Velocity Measurements on ITER

    NASA Astrophysics Data System (ADS)

    Lepson, Jaan; Beiersdorfer, Peter; Chun, Hyun

    2014-05-01

    In the ITER tokamak, the ion temperature and bulk toroidal velocity will be measured as a function of plasma minor radius using an imaging crystal spectrometer. The diagnostic relies on measuring the Doppler broadening and shift of x-ray lines from embedded impurity ions. However, in line with current trends in magnetic fusion devices, the ITER plasma is designed to have few heavy impurity ions, limited to those of argon and tungsten. Neither element produces ions whose radiation can cover the broad range of temperatures that are expected for ITER plasmas between the core and a fractional minor radius of r / a < 0 . 8 , throughout which the diagnostic is to function. While L-shell tungsten lines, in particular those from neonlike W64+, can be employed to diagnose the hottest parts of the plasma, it has been suggested to inject iron in order to utilize its K-shell emission to diagnose the cooler regions. Here, we show that the L-shell x rays of neonlike Xe44+ can provide the same information as iron. Moreover, we show that L-shell xenon ions will also persist in the hottest part of ITER plasmas and thus can be used in lieu of tungsten or krypton, whose injection had also been suggested. Moreover, because xenon is a noble gas, it can be readily removed from the plasma withou This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  14. Patterns of equatorial drifts according to diverse observational probes

    NASA Astrophysics Data System (ADS)

    Oyekola, Oyedemi S.

    We examine morphological patterns of observational results of the equatorial vertical EB drifts obtained from different probing methods (VHF radar at Jicamarca, Ion Drift Meter on the AE-E satellite, drifts derived from ionosonde hF data at Ibadan (Nigeria) over 1-year, and HF Doppler at Trivandrum (India)) during the evening and nighttime periods for geomagnetic quiet-day and high solar activity conditions (F10.7 ranges from ~160-208 sfu) for three different seasonal periods. A direct comparison between these measurements and the International Reference Ionosphere 2007 (IRI-2007) model-predictions of equatorial vertical plasma drifts are also made. Our results show that while VHF, AE-E and ionosonde-inferred drifts generally exhibit the typical characteristic features of quiet-time equatorial electrodynamics but reveal substantial disparities in the observational techniques of F-region vertical drifts. The trends in the experimental data agree reasonably with the Scherliess-Fejer climatological curves for the three seasons. In contrast, an IRI representation grossly overestimates and show large departure from the Ibadan and Trivandrum Doppler drift patterns between 1500-0100 LT. The model peak velocity occurs at about two hours earlier than the ionosonde and HF-Doppler velocity peaks. The magnitudes of the velocity peak differ by approximately 28 percent. The dusk reversal times fluctuate significantly and occur between about 1800-2200 LT for all the drift techniques. On the other hand, reversal times near sunrise show less variation. The essential feature of equatorial electrodynamics is the evening prereversal enhancement (PRE) peak velocity; a key parameter required to trigger postsunset ionospheric irregularities. We demonstrate that the simulated PRE ranges between about 20-50 m/s with average value (standard deviation) of roughly 37+/-11 m/s; whereas Ibadan ionosonde PRE velocities vary from about 20 to 45 m/s, with typical average value (standard deviation) of about 29+/-6 m/s. Assessment of the association between model and ionosonde PRE velocities with solar F10.7 and geomagnetic Ap indices illustrate that both IRI and ionosonde-inferred PRE peak velocities illustrate no noticeable link with solar flux, but correlate well with geomagnetic activity. This high correlation is an unexpected result which might shed new light on sources of quiet-time variability of the equatorial PRE peak vertical plasma velocities.

  15. Photodissociation of the dibromomethane cation at 355 nm by means of ion velocity imaging

    NASA Astrophysics Data System (ADS)

    Huang, Jianhua; Xu, Dadong; Fink, William H.; Jackson, William M.

    2001-10-01

    The photodissociation dynamics of the dibromomethane cation, CH2Br2+, have been studied by means of ion velocity imaging and time-of-flight mass spectroscopy methods at 355 nm. The dibromomethane cation is produced through the direct ionization of the neutral molecule with a pulsed 118 nm laser. The translational energy distribution shows that the CH2Br+ fragment is formed in highly vibrationally excited states with two distinguished dissociation channels following a parallel excitation from 2b2 to 3b2 of the parent ion. The broad fast speed distribution is fit with two Gaussian functions, from which a branching ratio of Br*(2P1/2) to Br(2P3/2) is determined as 2.2:1. The sharp peak with very slow speed was modeled with a Boltzmann distribution with a temperature of 300 K. This channel contributes 4.5% to the reaction and is proposed to proceed on the ground state surface following internal conversion. Ab initio calculations for both the parent and the fragment ions have been performed that strongly support the proposed dissociation mechanisms.

  16. Absolute Wavelength Calibration of the IDSII Spectrometer for Impurity Ion Velocity Measurements in the MST

    NASA Astrophysics Data System (ADS)

    Baltzer, M.; Craig, D.; den Hartog, D. J.; Nornberg, M. D.; MST Team

    2014-10-01

    The MST operates two Ion Doppler Spectrometers (IDS) for high time-resolution passive and active measurements of impurity ion emission. Absolutely calibrated measurements of flow are difficult because the spectrometers record data within 0.3 nm of the line of interest, and commercial calibration lamps do not produce lines in this narrow range . Four calibration methods were investigated. First, emission along the chord bisecting the poloidal plane was measured as it should have no time-averaged Doppler shift. Second, a calibrated CCD spectrometer and the IDSII were used to observe the same plasma from opposing sides so as to measure opposite Doppler shifts. The unshifted line is located halfway between the two opposing measurements. Third, the two fibers of the IDSI were positioned to take absolute flow measurements using opposing views. Substituting the IDSII for one of the IDSI fibers, absolute measurements of flow from the IDSI were used to calibrate the IDSII. Finally, an optical system was designed to filter an ultraviolet LED, providing a known wavelength source within the spectral range covered by the IDSII. The optical train is composed of an air-gapped etalon and fused silica lenses. The quality of calibration for each of these methods is analyzed and their results compared. Preliminary impurity ion velocity measurements are shown. This work has been supported by the US DOE and the NSF.

  17. Effect of ion temperature on ion-acoustic solitary waves in a plasma with a q-nonextensive electron velocity distribution

    SciTech Connect

    Roy, Kaushik; Saha, Taraknath; Chatterjee, Prasanta

    2012-10-15

    The effect of ion temperature on the existence of arbitrary amplitude ion-acoustic solitary waves is studied in a two component plasma in presence of a q-nonextensive velocity distributed electrons by using Sagdeev's pseudo potential technique. The range of relevent parameters for which solitons may exist is discussed. It is observed that both q, the nonextensive parameter and the ion temperature {sigma}, play significant roles in the formation and existence of solitons.

  18. Linear dependence of the postsunset equatorial anomaly electron density on solar flux and its relation to the maximum prereversal E B drift velocity through its dependence on solar flux

    NASA Astrophysics Data System (ADS)

    Whalen, James A.

    2004-07-01

    The postsunset equatorial ionization anomaly, with maximum F layer electron density, Nemax, occurring near 2100 LT, has been found during solar maximum to be a linear function of the maximum prereversal E B drift velocity (E B drift). In order to examine this relation at all levels of solar flux, Nemax is measured during 13 years of an entire solar cycle by eight ionospheric sounders located in the anomaly in both north and south dip latitudes and in eastern Asia, the Pacific, and South America. At each location the monthly median Nemax increases linearly with the monthly average solar flux, Sa, over the range from 70 to 285 sfu. The linear function varies markedly with location and by month at each location. The relation to E B drift, which is also a linear function of Sa, is determined using measurements of Nemax versus Sa measured at Bogota in the anomaly plotted as a function of E B versus Sa measured at Jicamarca at the dip equator. The result is that Nemax is a linear function of E B, which is in agreement with that found previously during solar maximum. Accordingly, the Nemax versus E B relation is independent of Sa. The fact that Nemax is linear in Sa at each site implies Nemax is linear in E B at each but with a functional dependence that varies with latitude and longitude.

  19. Velocity space diffusion and nongyrotropy of pickup water group ions at comet Grigg-Skjellerup

    NASA Technical Reports Server (NTRS)

    Coates, A. J.; Johnstone, A. D.; Wilken, B.; Neubauer, Fritz M.

    1993-01-01

    The diffusion of water group cometary ions in velocity space at comet Grigg-Skjellerup was measured during the Giotto spacecraft encounter. The evolution of the collapsed pitch angle and energy distributions during the inbound and outbound passes shows that the timescale for energy diffusion may be similar to that for pitch angle diffusion. Fully isotropic pitch angle distributions were never seen. Also the bulk parameters of the three-dimensional distributions are examined. Transformation of these parameters into a field-aligned solar wind frame allows us to test the gyrotropy of the distributions. These observations imply that there were deviations from gyrotropy throughout the encounter becoming most important near to closest approach.

  20. Atomic physics effects on tokamak edge drift-tearing modes

    SciTech Connect

    Hahm, T.S.

    1993-03-01

    The effects of ionization and charge exchange on the linear stability of drift-tearing modes are analytically investigated. In particular, the linear instability threshold [Delta][sup Th], produced by ion sound wave coupling is modified. In the strongly collisional regime, the ionization breaks up the near cancellation of the perturbed electric field and the pressure gradient along the magnetic field, and increases the threshold. In the semi-collisional regime, both ionization and charge exchange act as drag on the ion parallel velocity, and consequently decrease the threshold by reducing the effectiveness of ion sound wave propagation.

  1. Atomic physics effects on tokamak edge drift-tearing modes

    SciTech Connect

    Hahm, T.S.

    1993-03-01

    The effects of ionization and charge exchange on the linear stability of drift-tearing modes are analytically investigated. In particular, the linear instability threshold {Delta}{sup Th}, produced by ion sound wave coupling is modified. In the strongly collisional regime, the ionization breaks up the near cancellation of the perturbed electric field and the pressure gradient along the magnetic field, and increases the threshold. In the semi-collisional regime, both ionization and charge exchange act as drag on the ion parallel velocity, and consequently decrease the threshold by reducing the effectiveness of ion sound wave propagation.

  2. Improved charge exchange spectroscopy on the Joint European Torus for ion temperature and rotation velocity profiles

    SciTech Connect

    Andrew, Yasmin; Hawkes, N. C.; Crombe, K.

    2006-10-15

    The Joint European Torus (JET) edge charge exchange recombination spectroscopy diagnostic has recently been enhanced to extend its spatial coverage and improve its time resolution. Two identical periscopes have been installed on opposite ports so that they have perfectly symmetrical views of the edge plasma. This matched viewing geometry allows both the poloidal and toroidal components of the impurity ion rotation velocity to be accurately resolved. These measurements play a crucial role in the understanding of the physics of edge phenomena such as edge transport barrier formation and enhanced light microscopes. The diagnostic also has a more central view of the plasma with a third periscope that faces up towards the top of the vessel. This is a new configuration for the diagnostic and allows the poloidal rotation velocity profile to be measured further in towards the plasma core than previously possible. The new upward facing, core plasma viewing arrangement provides the advantage that the spatial evolution of the internal transport barrier can be tracked from its formation. An additional spectrometer-detector system doubles the total number of charge exchange recombination spectroscopy lines of sight that are analyzed and improves time resolution from 50 to 10 ms.

  3. 2-dimensional ion velocity distributions measured by laser-induced fluorescence above a radio-frequency biased silicon wafer

    SciTech Connect

    Moore, Nathaniel B.; Gekelman, Walter; Pribyl, Patrick; Zhang, Yiting; Kushner, Mark J.

    2013-08-15

    The dynamics of ions traversing sheaths in low temperature plasmas are important to the formation of the ion energy distribution incident onto surfaces during microelectronics fabrication. Ion dynamics have been measured using laser-induced fluorescence (LIF) in the sheath above a 30 cm diameter, 2.2 MHz-biased silicon wafer in a commercial inductively coupled plasma processing reactor. The velocity distribution of argon ions was measured at thousands of positions above and radially along the surface of the wafer by utilizing a planar laser sheet from a pulsed, tunable dye laser. Velocities were measured both parallel and perpendicular to the wafer over an energy range of 0.4600 eV. The resulting fluorescence was recorded using a fast CCD camera, which provided resolution of 0.4 mm in space and 30 ns in time. Data were taken at eight different phases during the 2.2 MHz cycle. The ion velocity distributions (IVDs) in the sheath were found to be spatially non-uniform near the edge of the wafer and phase-dependent as a function of height. Several cm above the wafer the IVD is Maxwellian and independent of phase. Experimental results were compared with simulations. The experimental time-averaged ion energy distribution function as a function of height compare favorably with results from the computer model.

  4. Velocity fluctuations of a heavy particle interacting with a hot and cold gas: Applications to molecular ion traps

    NASA Astrophysics Data System (ADS)

    Vaca, Christian; Bruinsma, Robijn; Levine, Alex J.

    2014-03-01

    Understanding the stochastic motion of a heavy particle in a gas of lighter ones is a classic problem in statistical mechanics. Alkemade, MacDonald, and Van Kampen (AMvK) analyzed this problem in one dimension, computing the velocity distribution function of the heavy particle in a perturbation expansion using the ratio of mass of the light to the heavy particle as a small parameter. Novel tests of this theory are now being provided by modern molecular ion traps [arXiv:1310.5190]. In such experiments, the heavy molecular ion interacts with a cold gas used for sympathetic cooling and low density hot gasses that leak into the system. Thus, the heavy ion is maintained in a complex nonequilibrium state due to its interactions with the hot and cold gasses. In this talk, we present an extension of the AMvK model appropriate to these experiments. Using new analytic and computational techniques, we explore the time-dependent velocity distribution function of the molecular ion interacting with the gasses including higher order perturbative corrections necessary to discuss the case in which the ion's mass is not significantly larger than that of the other two species. Using this analysis we address the experimental observation of non-Gaussian velocity distributions of the heavy ions.

  5. Physics of a magnetic filter for negative ion sources. II. E Multiplication-Sign B drift through the filter in a real geometry

    SciTech Connect

    Boeuf, J. P.; Claustre, J.; Chaudhury, B.; Fubiani, G.

    2012-11-15

    The physics of a magnetic filter under conditions similar to those of the negative ion source for the ITER neutral beam injector is analyzed with the help of a two-dimensional particle-in-cell Monte Carlo Collisions model. A detailed analysis of the different terms of the electron momentum equations shows how diamagnetic and drift currents can be dominant in different regions of the filter. Electron transport through the filter is due to an E Multiplication-Sign B drift current on one side of the chamber induced by the presence of the chamber walls perpendicular to the electron diamagnetic current. The filter design of the ITER negative ion source, which does not allow a closed electron diamagnetic current, induces an asymmetry of the plasma that is analyzed with the particle model. It is shown that electron transport through the filter in this geometry is very different from the transport in an ideal, one-dimensional magnetic filter often considered in the literature and described in detail in the companion paper [Boeuf et al., Phys. Plasmas 19, 113509 (2012)].

  6. Drift-tearing magnetic islands in tokamak plasmas

    SciTech Connect

    Fitzpatrick, R.; Waelbroeck, F. L.

    2008-01-15

    A systematic fluid theory of nonlinear magnetic island dynamics in conventional low-{beta}, large aspect-ratio, circular cross-section tokamak plasmas is developed using an extended magnetohydrodynamics model that incorporates diamagnetic flows, ion gyroviscosity, fast parallel electron heat transport, the ion sound wave, the drift wave, and average magnetic field-line curvature. The model excludes the compressible Alfven wave, geodesic field-line curvature, neoclassical effects, and ion Landau damping. A collisional closure is used for plasma dynamics parallel to the magnetic field. Two distinct branches of island solutions are found, namely the 'sonic' and 'hypersonic' branches. Both branches are investigated analytically, using suitable ordering schemes, and in each case the problem is reduced to a relatively simple set of nonlinear differential equations that can be solved numerically via iteration. The solution determines the island phase velocity, relative to the plasma, and the effect of local currents on the island stability. Sonic islands are relatively wide, flatten both the temperature and density profiles, and tend to propagate close to the local ion fluid velocity. Hypersonic islands, on the other hand, are relatively narrow, only flatten the temperature profile, radiate drift-acoustic waves, and tend to propagate close to the local electron fluid velocity. The hypersonic solution branch ceases to exist above a critical island width. Under normal circumstances, both types of island are stabilized by local ion polarization currents.

  7. Broadband Velocity Modulation Spectroscopy of Molecular Ions for Use in the Jila Electron Edm Experiment

    NASA Astrophysics Data System (ADS)

    Gresh, Daniel N.; Cossel, Kevin C.; Cornell, Eric A.; Ye, Jun

    2013-06-01

    The JILA electron electric dipole moment (eEDM) experiment will use a low-lying, metastable ^3?_1 state in trapped molecular ions of HfF^+ or ThF^+. Prior to this work, the low-lying states of these molecules had been investigated by PFI-ZEKE spectroscopy. However, there were no detailed studies of the electronic structure. The recently developed technique of frequency comb velocity modulation spectroscopy (VMS) provides broad-bandwidth, high-resolution, ion-sensitive spectroscopy, allowing the acquisition of 150 cm^{-1} of continuous spectra in 30 minutes over 1500 simultaneous channels. By supplementing this technique with cw-laser VMS, we have investigated the electronic structure of HfF^+ in the frequency range of 9950 to 14600 cm^{-1}, accurately fitting and assigning 16 rovibronic transitions involving 8 different electronic states including the X^1?^+ and a^3?_1 states. In addition, an observed ^3?_{0+} state with coupling to both the X and a states has been used in the actual eEDM experiment to coherently transfer population from the rovibronic ground state of HfF^+ to the eEDM science state. Furthermore, we report on current efforts of applying frequency comb VMS at 700 - 900 nm to the study of ThF^+, which has a lower energy ^3?_1 state and a greater effective electric field, and will provide increased sensitivity for a measurement of the eEDM. A. E. Leanhardt et. al., Journal of Molecular Spectroscopy 270, 1-25 (2011). B. J. Barker, I. O. Antonov, M. C. Heaven, K. A. Peterson, Journal of Chemical Physics 136, 104305 (2012). L. C. Sinclair, K. C. Cossel, T. Coffey, J. Ye, E. A. Cornell, Physical Review Letters 107, 093002 (2011). K.C. Cossel et. al., Chemical Physics Letters 546, 1-11 (2012).

  8. Background and pickup ion velocity distribution dynamics in Titan's plasma environment: 3D hybrid simulation and comparison with CAPS's observations

    NASA Astrophysics Data System (ADS)

    Lipatov, Alexander; Sittler, Edward; Hartle, Richard; Simpson, David

    The wave-particle interactions play very important role in the plasma dynamics near Titan: mass loading, excitation of the low-frequency waves and the formation of the particle velocity distribution function, e.g. ring/shell-like distributions, etc. The kinetic approach is important for estimation of the collision processes e.g. a charge exchange. The particle velocity distri-bution also plays a key role for understanding the observed particle fluxes. In this report we discuss the ion velocity distribution dynamics from the 3D hybrid simulation. The simulations are based on recent analysis of the Cassini Plasma Spectrometer (CAPS) ion measurements during the T9 and T18 flybys through the induced magnetic tail of Titan [1]. In our model the background ions, all pickup ions, and ionospheric ions are considered as a particles, whereas the electrons are described as a fluid. Inhomogeneous photoionization, electron-impact ionization and charge exchange are included in our model. The temperature of the background electrons and pickup electrons was also included into the generalized Ohm's law. We also take into account the collisions between the ions and neutrals. The current simulation shows that mass + + + loading by pickup ions H + , H2 , CH4 and N2 is stronger than in the previous simulations. + We consider two models for the upstream composition: (a) only magnetospheric H + and H2 , + + (b) only H and H2 pickup ions. In our hybrid simulations we use Chamberlain profiles for the exosphere's components. We also include a simple ionosphere model with M = 28 ions that were generated inside the ionosphere. The moon is considered as weakly conducting body. Special attention will be paid to comparing the simulated pickup ion velocity distribution with CAPS's T9 and T18 observations. We also compare our realistic 3D kinetic simulation with 1D kinetic simulation that was performed with a fine spatial resolution [2]. References Sittler, E.C., et al., Saturn's Magnetospheric Interaction with Titan as Defined by Cassini Encounters T9 and T18: New Results, Planet. Space Sci., doi.10.1016/j.pss.2009.09.017. [2] Cowee, M.M., Tokar, R.L., Gary S.P., Wei, H.Y., Russell, C.T., and Sittler, E.C., 2009. 1D Hybrid Simulations of Ion Cyclotron Wave Generation by Pickup Ions at Titan, Fall AGU 2009 Meeting, 14-18 Dec., 2009, San Francisco, CA.

  9. Dynamics of pickup ion velocity distribution in Titan's plasma environment: 3D hybrid simulation and comparison with CAPS's observations

    NASA Astrophysics Data System (ADS)

    Simpson, D. G.; Lipatov, A. S.; Sittler, E. C.; Hartle, R. E.; Cooper, J. F.

    2010-12-01

    The wave-particle interactions play a very important role in the plasma dynamics near Titan: mass loading, excitation of the low-frequency waves and the formation of the particle velocity distribution function, e.g. ring/shell-like distributions, etc. The kinetic approach is important for estimation of the collision processes e.g. a charge exchange. The particle velocity distribution also plays a key role for understanding the observed particle fluxes. In this report we discuss the ion velocity distribution dynamics from the 3D hybrid simulation. The simulations are based on recent analysis of the Cassini Plasma Spectrometer (CAPS) ion measurements during the T9 flyby through the induced magnetic tail of Titan [1]. In our model the background ions, all pickup ions, and ionospheric ions are considered as a particles, whereas the electrons are described as a fluid. Inhomogeneous photoionization, electron-impact ionization and charge exchange are included in our model. The temperature of the background electrons and pickup electrons was also included into the generalized Ohm's law. We also take into account the collisions between the ions and neutrals. The current simulation shows that mass loading by pickup ions H+, H2+, CH4+ and N2+ is stronger than in the previous simulations. We consider two models for the upstream composition: (a) only magnetospheric H+ and H2+, (b) only H+ and H2+ pickup ions. In our hybrid simulations we use Chamberlain profiles for the exosphere's components. We also include a simple ionosphere model with M=28 ions that were generated inside the ionosphere. The moon is considered as weakly conducting body. Special attention will be paid to comparing the simulated pickup ion velocity distribution with CAPS's T9 (events 1 and 2) observations. We also compare our realistic 3D kinetic simulation with a 1D kinetic simulation that was performed with a fine spatial resolution [2]. References [1] Sittler, E.C., et al., Saturn's Magnetospheric Interaction with Titan as Defined by Cassini Encounters T9 and T18: New Results, Planet. Space Sci., doi.10.1016/j.pss.2009.09.017. [2] Cowee, M.M., Tokar, R.L., Gary S.P., Wei, H.Y., Russell, C.T., and Sittler, E.C., 2009. 1D Hybrid Simulations of Ion Cyclotron Wave Generation by Pickup Ions at Titan, Fall AGU 2009 Meeting, 14-18 Dec., 2009, San Francisco, CA.

  10. Drift wave vortices in nonuniform plasmas with sheared magnetic fields

    SciTech Connect

    Su, X.N.; Horton, W.; Morrison, P.J.

    1991-11-01

    Nonlinear coherent structures governed by the coupled drift wave-ion acoustic mode equations in nonuniform plasmas with sheared magnetic fields are studied analytically and numerically. A solitary vortex equation that includes the effects of density and temperature gradients, and magnetic shear is derived and analyzed. The analytic and numerical studies show that for a plasma in a sheared magnetic field, even without the temperature and drift velocity gradients, solitary vortex solutions are possible; however, these solutions are not exponentially localized due to the presence of a nonstructurally stable perturbative tail that connects to the core of the vortex. The new coherent vortex structures are dipole-like in their symmetry, but are not the modons of Larichev and Reznik. In the presence of a small temperature or drift velocity gradient, the new shear-induced dipole can not survive and will separate into monopoles, like the case of the modon in a sheared drift velocity as studied in Su et al. The solitary solutions are found from the nonlinear eigenvalue problem for the effective potential in a quasi-one-dimensional approximation. The numerical simulations are performed in 2-D with the coupled vorticity and parallel mass flow equations.

  11. Interpretation of neutral particle analyzer measurements on plasmas having azimuthal drift

    NASA Technical Reports Server (NTRS)

    Englert, G. W.; Reinmann, J. J.; Lauver, M. R.

    1975-01-01

    The theoretical model accounts for drift and cyclotron components of ion motion in a partially ionized plasma. Density and velocity distributions are systematically prescribed. The flux into the neutral particle analyzer (NPA) from this plasma is determined by summing over all charge exchange neutrals in phase space which are directed into apertures. Calculation of the process is continued through the NPA using appropriate cross section data to obtain analyzer output distributions. Theoretical results were compared with NPA measurements on four plasma heating devices having radial electric, E, and axial magnetic, B, fields. Drift velocity, in the azimuthal direction is identified with E/B. Selection of randomized cyclotron velocity distributions about mean azimuthal drift yield energy distributions which compare well with experiment.

  12. Analytical Solutions for the Nonlinear Longitudinal Drift Compression (Expansion) of Intense Charged Particle Beams

    SciTech Connect

    Edward A. Startsev; Ronald C. Davidson

    2004-04-09

    To achieve high focal spot intensities in heavy ion fusion, the ion beam must be compressed longitudinally by factors of ten to one hundred before it is focused onto the target. The longitudinal compression is achieved by imposing an initial velocity profile tilt on the drifting beam. In this paper, the problem of longitudinal drift compression of intense charged particle beams is solved analytically for the two important cases corresponding to a cold beam, and a pressure-dominated beam, using a one-dimensional warm-fluid model describing the longitudinal beam dynamics.

  13. The Relation between Relaxation Time, Mean Free Path, Collision Time and Drift Velocity--Pitfalls and a Proposal for an Approach Illustrating the Essentials

    ERIC Educational Resources Information Center

    Jakoby, Bernhard

    2009-01-01

    The collision model is frequently introduced to describe electronic conductivity in solids. Depending on the chosen approach, the introduction of the collision time can lead to erroneous results for the average velocity of the electrons, which enters the expression for the electrical conductivity. In other textbooks, correct results are obtained

  14. The Relation between Relaxation Time, Mean Free Path, Collision Time and Drift Velocity--Pitfalls and a Proposal for an Approach Illustrating the Essentials

    ERIC Educational Resources Information Center

    Jakoby, Bernhard

    2009-01-01

    The collision model is frequently introduced to describe electronic conductivity in solids. Depending on the chosen approach, the introduction of the collision time can lead to erroneous results for the average velocity of the electrons, which enters the expression for the electrical conductivity. In other textbooks, correct results are obtained…

  15. The Three-dimensional Evolution of Ion-scale Current Sheets: Tearing and Drift-kink Instabilities in the Presence of Proton Temperature Anisotropy

    NASA Astrophysics Data System (ADS)

    Gingell, P. W.; Burgess, D.; Matteini, L.

    2015-03-01

    We present the first three-dimensional (3D) hybrid simulations of the evolution of ion-scale current sheets, with an investigation of the role of temperature anisotropy and associated kinetic instabilities on the growth of the tearing instability and particle heating. We confirm the ability of the ion cyclotron and firehose instabilities to enhance or suppress reconnection, respectively. The simulations demonstrate the emergence of persistent 3D structures, including patchy reconnection sites and the fast growth of a narrow-band drift-kink instability, which suppresses reconnection for thin current sheets with weak guide fields. Potential observational signatures of the 3D evolution of solar wind current sheets are also discussed. We conclude that kinetic instabilities, arising from non-Maxwellian ion populations, are significant to the evolution of 3D current sheets, and two-dimensional studies of heating rates by reconnection may therefore over-estimate the ability of thin, ion-scale current sheets to heat the solar wind by reconnection.

  16. Following the movement of Cu ions in a SSZ-13 zeolite during dehydration, reduction and adsorption: a combined in situ TP-XRD, XANES/DRIFTS study

    SciTech Connect

    Kwak, Ja Hun; Varga, Tamas; Peden, Charles HF; Gao, Feng; Hanson, Jonathan C.; Szanyi, Janos

    2014-05-05

    Cu-SSZ-13 has been shown to possess high activity and superior N2 formation selectivity in the selective catalytic reduction of NOx under oxygen rich conditions. Here, a combination of synchrotron-based (XRD and XANES) and vibrational (DRIFTS) spectroscopy tools have been used to follow the changes in the location and coordination environment of copper ions in a Cu-SSZ-13 zeolite during calcinations, reduction with CO, and adsorption of CO and H2O. XANES spectra collected during these procedures provides critical information not only on the variation in the oxidation state of the copper species in the zeolite structure, but also on the changes in the coordination environment around these ions as they interact with the framework, and with different adsorbates (H2O and CO). Time-resolved XRD data indicate the movement of copper ions and the consequent variation of the unit cell parameters during dehydration. DRIFT spectra provide information about the adsorbed species present in the zeolite, as well as the oxidation states of and coordination environment around the copper ions. A careful analysis of the asymmetric T-O-T vibrations of the CHA framework perturbed by copper ions in different coordination environments proved to be especially informative. The results of this study will aid the identification of the location, coordination and oxidation states of copper ions obtained during in operando catalytic studies. Financial support was provided by the US Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program. Part of this work (sample preparation) was performed in the Environmental Molecular Sciences Laboratory (EMSL) at Pacific Northwest National Laboratory (PNNL). The EMSL is a national scientific user facility supported by the US DOE, Office of Biological and Environmental Research. PNNL is a multi-program national laboratory operated for the US DOE by Battelle. All of the spectroscopy work reported here was carried out at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory (BNL). NSLS is a national scientific user facility supported by the US DOE.

  17. Photodetachment Studies Of Atomic Negative Ions Through Velocity-Map Imaging Spectroscopy

    NASA Astrophysics Data System (ADS)

    Chartkunchand, Kiattichart

    The technique of velocity-map imaging (VMI) spectroscopy as been adapted to a keV-level negative ion beamline for studies of photon-negative ion collisions. The design and operation of the VMI spectrometer takes into consideration the use of continuous, fast-moving (5 keV to 10 keV) ion beams, as well as a continuous wave (CW) laser as the source of photons. The VMI spectrometer has been used in photodetachment studies of the Group 14 negative ions Ge--, Sn--, and Pb-- at a photon wavelength of 532 nm. Measurements of the photoelectron angular distributions and asymmetry parameters for Ge-- and Sn-- were benchmarked against those measured previously [W. W. Williams, D. L. Carpenter, A. M. Covington, and J. S. Thompson, Phys. Rev. A 59, 4368 (1999), V. T. Davis, J. Ashokkumar, and J. S. Thompson, Phys. Rev. A 65, 024702 (2002)], while fine-structure-resolved asymmetry parameters for Pb-- were measured for the first time. Definitive evidence of a "forbidden" 4S 3/2?1D2 transition was observed in both the Ge-- and Sn-- photoelectron kinetic energy spectra. This transition is explained in terms of the inadequacy of the single-configuration description for the 1D2 excited state in the corresponding neutral. Near-threshold photodetachment studies of S-- were carried out in order to measure the spectral dependence of the photoelectron angular distribution. The resulting asymmetry parameters were measured at several photon wavelengths in the range of 575 nm (2.156 eV photon energy) to 615 nm (2.016 eV photon energy). Comparison of the measurements to a qualitative model of p-electron photodetachment [D. Hanstorp, C. Bengtsson, and D. J. Larson, Phys. Rev. A 40, 670 (1989)] were made. Deviations of the measured asymmetry parameters from the Hanstorp model near photodetachment thresholds suggests a reduced degree of suppression of d partial-waves than predicted by models. Measurement of the electron affinity of terbium was performed along with a determination of the structure of Tb--. The energy scale for the Tb-- photoelectron kinetic energy spectrum was calibrated to the photoelectron kinetic energy spectrum of Cs-- , whose electron affinity is well-known [T. A. Patterson, H. Hotop, A. Kasdan, D. W. Norcross, and W. C. Lineberger, Phys. Rev. Lett. 32 , 189 (1974)]. Comparison to a previous experimental measurement of the electron affinity of terbium [S. S. Duvvuri, Ph. D. dissertation, University of Nevada, Reno (2006)] and to theoretical calculations of the electron affinity [S. M. O'Malley and D. R. Beck, Phys. Rev. A 79, 012511 (2009)] were made. In contrast to the [Xe]4f106 s2 5I8 ground state configuration proposed in the experimental study and the [Xe]4f 85d6s26p 9G7 ground state configuration proposed in the theoretical study, the present study suggests a Tb-- ground state of [Xe]4f96s 26p 7I3 and an electron affinity of 0.13 +/- 0.07 eV for terbium.

  18. Pseudochemotactic drifts of artificial microswimmers

    NASA Astrophysics Data System (ADS)

    Ghosh, Pulak K.; Li, Yunyun; Marchesoni, Fabio; Nori, Franco

    2015-07-01

    We numerically investigate the motion of active artificial microswimmers diffusing in a fuel concentration gradient. We observe that, in the steady state, their probability density accumulates in the low-concentration regions, whereas a tagged swimmer drifts with velocity depending in modulus and orientation on how the concentration gradient affects the self-propulsion mechanism. Under most experimentally accessible conditions, the particle drifts toward the high-concentration regions (pseudochemotactic drift). A correct interpretation of experimental data must account for such an "anti-Fickian" behavior.

  19. A velocity map ion imaging study of difluorobenzene-water complexes: Binding energies and recoil distributions

    NASA Astrophysics Data System (ADS)

    Bellm, Susan M.; Moulds, Rebecca J.; van Leeuwen, Matthew P.; Lawrance, Warren D.

    2008-03-01

    The binding energies of the p-, m-, and o-difluorobenzene-H2O complexes have been measured by velocity map ion imaging to be 92210, 94510, and 8914cm-1, respectively. The lack of variation provides circumstantial evidence for water binding to the three isomers via the same interaction, viz. an in-plane O-H⋯F hydrogen bond to one of the fluorine atoms on the ring, with a second, weaker interaction of the water O atom with an ortho hydrogen, as determined previously for the p-difluorobenzene-H2O complex [Kang et al., J. Phys. Chem. A 109, 767 (2005)]. The ground state binding energies for the difluorobenzene-H2O complexes are 5%-11% larger than that for benzene-H2O, where binding occurs to the ? electrons out-of-plane. However, in the S1 state the binding energies of the o- and p-difluorobenzene-H2O complexes are smaller than the benzene-H2O value, raising an interesting question about whether the geometry at the global energy minimum remains in-plane in the excited electronic states of these two complexes. Recoil energy distributions for dissociation of p-difluorobenzene-H2O have been measured from the 31, 52, and 3151 levels of the excited electronic state. These levels are 490, 880, and 1304cm-1, respectively, above the dissociation threshold. Within the experimental uncertainty, the recoil energy distributions are the same for dissociation from these three states, with average recoil energies of 100cm-1. These recoil energies are 60% larger than was observed for the dissociation of p-difluorobenzene-Ar, which is a substantially smaller increase than the 400% seen in a comparable study of dissociation within the triplet state for pyrazine-Ar, -H2O complexes. The majority of the available energy is partitioned into vibration and rotation of the fragments.

  20. Influence of H{sup -} velocity on H{sup -} extraction probability from a negative ion source

    SciTech Connect

    Matsumoto, Y.; Nishiura, M.; Shinto, K.; Yamaoka, H.; Sasao, M.; Wada, M.

    2010-02-15

    We investigate influence of H{sup -} initial transport direction and kinetic energy on H{sup -} extraction probability with three-dimensional Monte Carlo calculation. As a result, lower energy H{sup -} ions are strongly trapped by the electrical potential structure, so that initial condition of H{sup -} transport direction is cancelled by alignment of the electric field; thus, it has lower influence for H{sup -} extraction probability. Besides, the potential hill induced by the beam extraction voltage more effectively enhances H{sup -} extraction probability for the lower energy H{sup -} ions. The correlation between the magnitude of the local plasma potential near the extraction region and the mean velocity of H{sup -} ions in the region should determine the H{sup -} extraction probability from the ion source.

  1. Predictions for the energy loss of light ions in laser-generated plasmas at low and medium velocities

    NASA Astrophysics Data System (ADS)

    Cayzac, W.; Bagnoud, V.; Basko, M. M.; Blaevi?, A.; Frank, A.; Gericke, D. O.; Hallo, L.; Malka, G.; Ortner, A.; Tauschwitz, An.; Vorberger, J.; Roth, M.

    2015-11-01

    The energy loss of light ions in dense plasmas is investigated with special focus on low to medium projectile energies, i.e., at velocities where the maximum of the stopping power occurs. In this region, exceptionally large theoretical uncertainties remain and no conclusive experimental data are available. We perform simulations of beam-plasma configurations well suited for an experimental test of ion energy loss in highly ionized, laser-generated carbon plasmas. The plasma parameters are extracted from two-dimensional hydrodynamic simulations, and a Monte Carlo calculation of the charge-state distribution of the projectile ion beam determines the dynamics of the ion charge state over the whole plasma profile. We show that the discrepancies in the energy loss predicted by different theoretical models are as high as 20-30%, making these theories well distinguishable in suitable experiments.

  2. Predictions for the energy loss of light ions in laser-generated plasmas at low and medium velocities.

    PubMed

    Cayzac, W; Bagnoud, V; Basko, M M; Blažević, A; Frank, A; Gericke, D O; Hallo, L; Malka, G; Ortner, A; Tauschwitz, An; Vorberger, J; Roth, M

    2015-11-01

    The energy loss of light ions in dense plasmas is investigated with special focus on low to medium projectile energies, i.e., at velocities where the maximum of the stopping power occurs. In this region, exceptionally large theoretical uncertainties remain and no conclusive experimental data are available. We perform simulations of beam-plasma configurations well suited for an experimental test of ion energy loss in highly ionized, laser-generated carbon plasmas. The plasma parameters are extracted from two-dimensional hydrodynamic simulations, and a Monte Carlo calculation of the charge-state distribution of the projectile ion beam determines the dynamics of the ion charge state over the whole plasma profile. We show that the discrepancies in the energy loss predicted by different theoretical models are as high as 20-30%, making these theories well distinguishable in suitable experiments. PMID:26651804

  3. High-velocity, multistage, nozzled, ion driven wind generator and method of operation of the same adaptable to mesoscale realization

    NASA Technical Reports Server (NTRS)

    Dunn-Rankin, Derek (Inventor); Rickard, Matthew J. A. (Inventor)

    2011-01-01

    Gas flows of modest velocities are generated when an organized ion flux in an electric field initiates an ion-driven wind of neutral molecules. When a needle in ambient air is electrically charged to a potential sufficient to produce a corona discharge near its tip, such a gas flow can be utilized downstream of a ring-shaped or other permeable earthed electrode. In view of the potential practical applications of such devices, as they represent blowers with no moving parts, a methodology for increasing their flow velocities includes exploitation of the divergence of electric field lines, avoidance of regions of high curvature on the second electrode, control of atmospheric humidity, and the use of linear arrays of stages, terminating in a converging nozzle. The design becomes particularly advantageous when implemented in mesoscale domains.

  4. An Analytic Study of the Perpendicularly Propagating Electromagnetic Drift Instabilities in the Magnetic Reconnection Experiment

    SciTech Connect

    Wang, Y., Kulsrud, R., Ji, H

    2008-12-03

    A local linear theory is proposed for a perpendicularly propagating drift instability driven by relative drifts between electrons and ions. The theory takes into account local cross-field current, pressure gradients and modest collisions as in the Magnetic Reconnection Experiment (MRX) [10]. The unstable waves have very small group velocities in the direction of the pressure gradient, but have a large phase velocity near the relative drift velocity between electrons and ions in the direction of cross-field current. By taking into account the electron-ion collisions and applying the theory in the Harris sheet, we establish that this instability could be excited near the center of the Harris sheet and have enough efoldings to grow to large amplitude before it propagates out of the unstable region. Comparing with the other magnetic reconnection related instabilities (LHDI, MTSI et.) studied previously, we believe the instability we find is a favorable candidate to produce anomalous resistivity because of its unique wave characteristics, such as electromagnetic component, large phase velocity, and small group velocity in the cross current layer direction.

  5. Experimental Test of Instability-Enhanced Collisional Friction for Determining Ion Loss in Two Ion Species Plasmas

    SciTech Connect

    Yip, Chi-Shung; Hershkowitz, Noah; Severn, Greg

    2010-06-04

    Recent experiments have shown that ions in weakly collisional plasmas containing two ion species of comparable densities nearly reach a common velocity at the sheath edge. A new theory suggests that collisional friction between the two ion species enhanced by two stream instability reduces the drift velocity of each ion species relative to each other near the sheath edge and finds that the difference in velocities at the sheath edge depends on the relative concentrations of the species. It is small when the concentrations are comparable and is large, with each species reaching its own Bohm velocity, when the relative concentration differences are large. To test these findings, ion drift velocities were measured with laser-induced fluorescence in argon-xenon plasmas. We show that the predictions are in excellent agreement with the first experimental tests of the new model.

  6. Simulation of Collisions of Ions with Atoms by the PIC-MC Method. Comparative Estimates

    NASA Astrophysics Data System (ADS)

    Sysun, V. I.; Sysun, A. V.; Ignakhin, V. S.; Titov, V. O.

    2015-11-01

    Monte Carlo models which simulate ion-atom collisions are considered. Efficient models for calculating the time between collisions are proposed which take into account the velocity dependence of the cross sections and also the probability distribution of the velocities of the ions and the probability distribution of the angles after a collision. The simulation results are compared with theoretical values of the drift velocity of the ions.

  7. Empirically Determined Anisotropic Velocity Distributions and Outflows of O5+ Ions in a Coronal Streamer at Solar Minimum

    NASA Astrophysics Data System (ADS)

    Frazin, R. A.; Cranmer, S. R.; Kohl, J. L.

    2003-11-01

    Empirical constraints on the O5+ velocity distributions and outflow speeds in a solar minimum equatorial streamer between 2.6 and 5.1 Rsolar are determined using a spectral synthesis code that includes O VI Doppler dimming. These constraints follow directly from UV spectra taken on 1996 October 12 with the Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO) satellite and three-dimensional electron densities derived from tomography applied to a time series of polarized white-light images taken with the Large Angle and Spectrometric Coronagraph (LASCO) also on SOHO. Four conclusions result from this work: (1) our analysis shows O5+ velocity distribution anisotropy in the streamer legs and stalk and gives strong evidence that the microscopic velocity distribution (which excludes wave motions that equally affect all charged particles) is anisotropic, where the most probable speed perpendicular to the magnetic field direction exceeds that in the parallel direction; (2) there is preferential heating of the O5+ ions over the protons in the streamer stalk and legs; (3) there is no evidence for preferential O5+ heating in the core; and (4) the outflow velocity of the O5+ ions is determined at heights above 4.6 Rsolar. All results have a confidence level of at least 70%.

  8. Number-conserving linear-response study of low-velocity ion stopping in a collisional magnetized classical plasma.

    PubMed

    Nersisyan, Hrachya B; Deutsch, Claude; Das, Amal K

    2011-03-01

    The results of a theoretical investigation of the low-velocity stopping power of ions in a magnetized collisional and classical plasma are reported. The stopping power for an ion is calculated through the linear-response (LR) theory. The collisions, which lead to a damping of the excitations in the plasma, are taken into account through a number-conserving relaxation time approximation in the LR function. In order to highlight the effects of collisions and magnetic field, we present a comparison of our analytical and numerical results obtained for nonzero damping or magnetic field with those for vanishing damping or magnetic field. It is shown that the collisions remove the anomalous friction obtained previously [Nersisyan et al., Phys. Rev. E 61, 7022 (2000)] for the collisionless magnetized plasmas at low ion velocities. One of the major objectives of this paper is to compare and to contrast our theoretical results with those obtained through a diffusion coefficient formulation based on the Dufty-Berkovsky relation evaluated for a magnetized one-component plasma modeled with target ions and electrons. PMID:21517600

  9. Number-conserving linear-response study of low-velocity ion stopping in a collisional magnetized classical plasma

    SciTech Connect

    Nersisyan, Hrachya B.; Deutsch, Claude; Das, Amal K.

    2011-03-15

    The results of a theoretical investigation of the low-velocity stopping power of ions in a magnetized collisional and classical plasma are reported. The stopping power for an ion is calculated through the linear-response (LR) theory. The collisions, which lead to a damping of the excitations in the plasma, are taken into account through a number-conserving relaxation time approximation in the LR function. In order to highlight the effects of collisions and magnetic field, we present a comparison of our analytical and numerical results obtained for nonzero damping or magnetic field with those for vanishing damping or magnetic field. It is shown that the collisions remove the anomalous friction obtained previously [Nersisyan et al., Phys. Rev. E 61, 7022 (2000)] for the collisionless magnetized plasmas at low ion velocities. One of the major objectives of this paper is to compare and to contrast our theoretical results with those obtained through a diffusion coefficient formulation based on the Dufty-Berkovsky relation evaluated for a magnetized one-component plasma modeled with target ions and electrons.

  10. Search for auroral belt E-parallel fields with high-velocity barium ion injections

    NASA Technical Reports Server (NTRS)

    Heppner, J. P.; Ledley, B. G.; Miller, M. L.; Marionni, P. A.; Pongratz, M. B.

    1989-01-01

    In April 1984, four high-velocity shaped-charge Ba(+) injections were conducted from two sounding rockets at 770-975 km over northern Alaska under conditions of active auroral and magnetic disturbance. Spatial ionization (brightness) profiles of high-velocity Ba(+) clouds from photometric scans following each release were found to be consistent with the 28-sec theoretical time constant for Ba photoionization determined by Carlsten (1975). These observations therefore revealed no evidence of anomalous fast ionization predicted by the Alfven critical velocity hypothesis.

  11. Effects of large zonal plasma drifts on the subauroral ionosphere

    NASA Technical Reports Server (NTRS)

    Sellek, R.; Bailey, G. J.; Moffett, R. J.; Heelis, R. A.; Anderson, P. C.

    1991-01-01

    A model of the earth's ionosphere and plasmasphere is used to investigate the effects of an imposed westward plasma drift of maximum velocity 2 km/s. A closed subauroral tube of plasma is considered and the velocity spike persists for 10 min. Ion-neutral frictional heating causes rapid elevation of the F-region O(+) temperature. The F-layer O(+) concentration is decreased due to increased O(+) loss rate and rapid ion flows both upward and downward from the F-region. The upward flux of O(+) through the topside ionosphere can each 5 x 10 exp 9/sq cm/s; when the velocity spike ceases there is a return flow of O(+) that tends to replenish the F-layer. Most of the features revealed by the model for the F-region and topside ionosphere are in accord with observations of subauroral ion drifts. Downward flows that are predicted to be persistently present around the 300 km altitude level appear to agree with observations only occasionally; suggestions are made to resolve this discrepancy.

  12. Electron injection in semiconductor drift detectors

    SciTech Connect

    Rehak, P. ); Gatti, E.; Longoni, A.; Sampietro, M.; Castoldi, A. ); Vacchi, A. )

    1990-01-01

    The paper reports the first successful results of a simple MOS structure to inject electrons at a given position in Silicon Drift Detectors. The structure allows on-line calibration of the drift velocity of electrons within the detector. The calibration is a practical method to trace the temperature dependence of the electron mobility. Several of these injection structures can be implemented in silicon drift detectors without additional steps in the fabrication process. 5 refs., 11 figs.

  13. Latitudinal variation in the occurrence of GPS L-band scintillations associated with the day-to-day changes in TEC, h'F and the EB drift velocity and their impact on GPS satellite signals

    NASA Astrophysics Data System (ADS)

    Venkatesh, K.; Rao, P. V. S. Rama; Seemala, Gopi K.; Prasad, D. S. V. V. D.

    2015-04-01

    The present study describes the day-to-day variations in the occurrence of GPS L-band scintillations from equator to the anomaly crest location associated with the changes in TEC, hF and E B drift velocities. The GPS-TEC and S4 index data from an equatorial station, Trivandrum (8.47?N, 76.91?E), a low latitude station, Waltair (17.7?N, 83.3?E) and an anomaly crest location Kolkata (22.6?N, 88.4?E) during the low solar activity years of 2004 and 2005 are used. It is observed that the day-time ambient TEC is higher during scintillation days compared to that during the days on which there are no scintillations at the three different locations mentioned above. Further, the diurnal variation of TEC shows a rapid decay during 1700-2000 hr LT over the three different locations during scintillation days which is observed to be comparatively much less during no scintillation days. The average height of the F-layer in the post-sunset hours over Trivandrum is found to be higher, around 350 km during scintillation days while it is around 260 km during the days on which there is no scintillation activity. The average pre-reversal E B drift velocity observed around 19:00 hr LT is higher (20 m/s) during scintillation days, whereas during no scintillation days, it is found to be much less (7 m/s). Further, it is observed that the GPS receivers lose their locks whenever the S4 index exceeds 0.5 (>10 dB power level) and these loss of lock events are observed to be more around the anomaly crest location (Kolkata). It may be inferred from the present observations that the level of ambient ionization around noon-time, and a fast decay (collapse) of the ionization during afternoon hours followed by rapid increase in the height of the F-layer contributes significantly to the occurrence of scintillations. The present study further indicates that the S4 index at L-band frequencies increases with an increase in latitude maximizing around the crest of the equatorial ionization anomaly during the post-sunset hours resulting in more loss of lock events in the GPS receiver signals around the EIA crest region.

  14. Observations of ion-neutral collisional effects in the auroral E region

    NASA Technical Reports Server (NTRS)

    Watanabe, S.; Whalen, B. A.; Wallis, D. D.; Pfaff, R. F.

    1991-01-01

    Thermal ion energy distribution functions and local electric and magnetic fields were directly measured for the first time in the ionospheric E region. Measured ion distribution functions were fitted to shifted Maxwellian distributions, and their resulting ion drift velocities were compared with E x B/B-squared velocities from the double-probe electric field observations. The results show that the ion drift direction rotates with respect to the local electric field direction and that the ratio of the magnitudes of the ion velocity to the E x B/B-squared velocity decreases with decreasing altitudes. Using these observations, the quiet time ion-neutral collison frequencies and neutral wind velocities were estimated and found to be consistent with theoretical estimates. However, significant discrepancies between observations and theory are found in the disturbed E region near auroral particle precipitation regions. These data indicate that the auroral atmosphere is significantly perturbed due to Joule as well as particle heating effects.

  15. The latitudinal structure of the nightside outer magnetosphere of Saturn as revealed by velocity moments of thermal ions

    NASA Astrophysics Data System (ADS)

    Nemeth, Z.; Szego, K.; Foldy, L.; Kivelson, M. G.; Jia, X.; Ramer, K. M.; Cowley, S. W. H.; Provan, G.; Thomsen, M.

    2015-09-01

    In this study we investigate the latitudinal behavior of the azimuthal plasma velocities in the outer magnetosphere of Saturn using the numerical ion moments derived from the measurements of the Cassini Plasma Spectrometer. One of the new results presented is that although these moments display some scatter, a significant positive correlation is found to exist between the azimuthal velocity and the plasma density, such that on average, the higher the density the higher the rotation speed. We also found that both the azimuthal velocity and the density anticorrelate with the magnitude of the radial component of the magnetic field and drop rapidly with increasing distance from the magnetic equator. The azimuthal velocities show periodic behavior with a period near the planetary rotation period, which can also be explained by the strong dependence on magnetic latitude, taking into account the flapping of the magnetodisk. It is thus found that the dense plasma near the magnetic equator rotates around the planet at high speed, while the dilute plasma at higher latitudes in the northern and southern hemispheres rotates significantly slower. The latitudinal gradient observed in the azimuthal speed is suggested to be a direct consequence of the sub-corotation of the plasma in the outer magnetosphere, with highest speeds occurring on field lines at lowest latitudes mapping to the rapidly rotating inner regions of the plasma sheet, and the speed falling as one approaches the lobe, where the field lines are connected to strongly sub-corotating plasma.

  16. Dissociation of internal energy-selected methyl bromide ion revealed from threshold photoelectron-photoion coincidence velocity imaging

    SciTech Connect

    Tang, Xiaofeng; National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029 ; Zhou, Xiaoguo E-mail: yanbing@jlu.edu.cn; Liu, Shilin; Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 ; Sun, Zhongfa; Liu, Fuyi; Sheng, Liusi; Yan, Bing E-mail: yanbing@jlu.edu.cn

    2014-01-28

    Dissociative photoionization of methyl bromide (CH{sub 3}Br) in an excitation energy range of 10.4516.90 eV has been investigated by using threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging. The coincident time-of-flight mass spectra indicate that the ground state X{sup 2}E of CH{sub 3}Br{sup +} is stable, and both A{sup 2}A{sub 1} and B{sup 2}E ionic excited states are fully dissociative to produce the unique fragment ion of CH{sub 3}{sup +}. From TPEPICO 3D time-sliced velocity images of CH{sub 3}{sup +} dissociated from specific state-selected CH{sub 3}Br{sup +} ion, kinetic energy release distribution (KERD) and angular distribution of CH{sub 3}{sup +} fragment ion are directly obtained. Both spin-orbit states of Br({sup 2}P) atom can be clearly observed in fast dissociation of CH{sub 3}Br{sup +}(A{sup 2}A{sub 1}) ion along CBr rupture, while a KERD of Maxwell-Boltzmann profile is obtained in dissociation of CH{sub 3}Br{sup +}(B{sup 2}E) ion. With the aid of the re-calculated potential energy curves of CH{sub 3}Br{sup +} including spin-orbit coupling, dissociation mechanisms of CH{sub 3}Br{sup +} ion in A{sup 2}A{sub 1} and B{sup 2}E states along CBr rupture are revealed. For CH{sub 3}Br{sup +}(A{sup 2}A{sub 1}) ion, the CH{sub 3}{sup +} + Br({sup 2}P{sub 1/2}) channel is occurred via an adiabatic dissociation by vibration, while the Br({sup 2}P{sub 3/2}) formation is through vibronic coupling to the high vibrational level of X{sup 2}E state followed by rapid dissociation. CBr bond breaking of CH{sub 3}Br{sup +}(B{sup 2}E) ion can occur via slow internal conversion to the excited vibrational level of the lower electronic states and then dissociation.

  17. Pitch angle and velocity diffusions of newborn ions by turbulence in the solar wind

    NASA Technical Reports Server (NTRS)

    Ziebell, L. F.; Yoon, Peter H.

    1990-01-01

    The temporal evolution of the distribution function of newborn ions under the influence of intrinsic low-frequency solar wind turbulences is studied. In particular, an initial ring-beam distribution of newborn ions under the influence of hydromagnetic waves is considered. A simplified treatment of the resonance broadening effect is given, and its role in the pickup process is discussed. Two different configurations of wave polarization amd direction of propagation are considered. The conditions that lead either to the formation of anisotropic shells as a long-duration transient state or to rapid isotropization of the ion pitch angle distribution are discussed, as are the conditions which lead to significant acceleration of the ions.

  18. Long wavelength gradient drift instability in Hall plasma devices. II. Applications

    SciTech Connect

    Frias, Winston; Smolyakov, Andrei I.; Kaganovich, Igor D.; Raitses, Yevgeny

    2013-05-15

    Hall plasma devices with electron E B drift are subject to a class of long wavelength instabilities driven by the electron current, gradients of plasma density, temperature, and magnetic field. In the first companion paper [Frias et al., Phys. Plasmas 19, 072112 (2012)], the theory of these modes was revisited. In this paper, we apply analytical theory to show that modern Hall thrusters exhibit azimuthal and axial oscillations in the frequency spectrum from tens KHz to few MHz, often observed in experiments. The azimuthal phase velocity of these modes is typically one order of magnitude lower than the E B drift velocity. The growth rate of these modes scales inversely with the square root of the ion mass, ?1/?(m){sub i}. It is shown that several different thruster configurations share the same common feature: the gradient drift instabilities are localized in two separate regions, near the anode and in the plume region, and absent in the acceleration region. Our analytical results show complex interaction of plasma and magnetic field gradients and the E B drift flow as the sources of the instability. The special role of plasma density gradient is revealed and it is shown that the previous theory is not applicable in the region where the ion flux density is not uniform. This is particularly important for near anode region due to ionization and in the plume region due to diverging ion flux.

  19. Electron capture dissociation and drift tube ion mobility-mass spectrometry coupled with site directed mutations provide insights into the conformational diversity of a metamorphic protein.

    PubMed

    Harvey, Sophie R; Porrini, Massimiliano; Tyler, Robert C; MacPhee, Cait E; Volkman, Brian F; Barran, Perdita E

    2015-04-28

    Ion mobility mass spectrometry can be combined with data from top-down sequencing to discern adopted conformations of proteins in the absence of solvent. This multi-technique approach has particular applicability for conformationally dynamic systems. Previously, we demonstrated the use of drift tube ion mobility-mass spectrometry (DT IM-MS) and electron capture dissociation (ECD) to study the metamorphic protein lymphotactin (Ltn). Ltn exists in equilibrium between distinct monomeric (Ltn10) and dimeric (Ltn40) folds, both of which can be preserved and probed in the gas-phase. Here, we further test this mass spectrometric framework, by examining two site directed mutants of Ltn, designed to stabilise either distinct fold in solution, in addition to a truncated form consisting of a minimum model of structure for Ltn10. The truncated mutant has similar collision cross sections to the wild type (WT), for low charge states, and is resistant to ECD fragmentation. The monomer mutant (CC3) presents in similar conformational families as observed previously for the WT Ltn monomer. As with the WT, the CC3 mutant is resistant to ECD fragmentation at low charge states. The dimer mutant W55D is found here to exist as both a monomer and dimer. As a monomer W55D exhibits similar behaviour to the WT, but as a dimer presents a much larger charge state and collision cross section range than the WT dimer, suggesting a smaller interaction interface. In addition, ECD on the W55D mutant yields greater fragmentation than for the WT, suggesting a less stable ?-sheet core. The results highlight the power of MS to provide insight into dynamic proteins, providing further information on each distinct fold of Ltn. In addition we observe differences in the fold stability following single or double point mutations. This approach, therefore, has potential to be a useful tool to screen for the structural effects of mutagenesis, even when sample is limited. PMID:25805055

  20. Continuous wave cavity ring down spectroscopy measurements of velocity distribution functions of argon ions in a helicon plasma

    NASA Astrophysics Data System (ADS)

    Chakraborty Thakur, Saikat; McCarren, Dustin; Carr, Jerry; Scime, Earl E.

    2012-02-01

    We report continuous wave cavity ring down spectroscopy (CW-CRDS) measurements of ion velocity distribution functions (VDFs) in low pressure argon helicon plasma (magnetic field strength of 600 G, Te ? 4 eV and n ? 5 1011 cm-3). Laser induced fluorescence (LIF) is routinely used to measure VDFs of argon ions, argon neutrals, helium neutrals, and xenon ions in helicon sources. Here, we describe a CW-CRDS diagnostic based on a narrow line width, tunable diode laser as an alternative technique to measure VDFs in similar regimes but where LIF is inapplicable. Being an ultra-sensitive, cavity enhanced absorption spectroscopic technique; CW-CRDS can also provide a direct quantitative measurement of the absolute metastable state density. The proof of principle CW-CRDS measurements presented here are of the Doppler broadened absorption spectrum of Ar II at 668.6138 nm. Extrapolating from these initial measurements, it is expected that this diagnostic is suitable for neutrals and ions in plasmas ranging in density from 1 109 cm-3 to 1 1013 cm-3 and target species temperatures less than 20 eV.

  1. Continuous wave cavity ring down spectroscopy measurements of velocity distribution functions of argon ions in a helicon plasma.

    PubMed

    Chakraborty Thakur, Saikat; McCarren, Dustin; Carr, Jerry; Scime, Earl E

    2012-02-01

    We report continuous wave cavity ring down spectroscopy (CW-CRDS) measurements of ion velocity distribution functions (VDFs) in low pressure argon helicon plasma (magnetic field strength of 600 G, T(e) ? 4 eV and n ? 5 10(11) cm(-3)). Laser induced fluorescence (LIF) is routinely used to measure VDFs of argon ions, argon neutrals, helium neutrals, and xenon ions in helicon sources. Here, we describe a CW-CRDS diagnostic based on a narrow line width, tunable diode laser as an alternative technique to measure VDFs in similar regimes but where LIF is inapplicable. Being an ultra-sensitive, cavity enhanced absorption spectroscopic technique; CW-CRDS can also provide a direct quantitative measurement of the absolute metastable state density. The proof of principle CW-CRDS measurements presented here are of the Doppler broadened absorption spectrum of Ar II at 668.6138 nm. Extrapolating from these initial measurements, it is expected that this diagnostic is suitable for neutrals and ions in plasmas ranging in density from 1 10(9) cm(-3) to 1 10(13) cm(-3) and target species temperatures less than 20 eV. PMID:22380092

  2. Ion temperature gradient driven mode in presence of transverse velocity shear in magnetized plasmas

    SciTech Connect

    Chakrabarti, Nikhil; Rasmussen, Jens Juul; Michelsen, Poul

    2005-07-15

    The effect of sheared poloidal flow on the toroidal branch of the ion temperature gradient driven mode of magnetized nonuniform plasma is studied. A novel 'nonmodal' calculation is used to analyze the problem. It is shown that the transverse shear flow considerably reduced the growth of the instability. A small but finite amount of viscosity and/or diffusion enhanced the stabilization process.

  3. Hypersonic drift-tearing magnetic islands in tokamak plasmas

    SciTech Connect

    Fitzpatrick, R.; Waelbroeck, F. L.

    2007-12-15

    A two-fluid theory of long wavelength, hypersonic, drift-tearing magnetic islands in low-collisionality, low-{beta} plasmas possessing relatively weak magnetic shear is developed. The model assumes both slab geometry and cold ions, and neglects electron temperature and equilibrium current gradient effects. The problem is solved in three asymptotically matched regions. The 'inner region' contains the island. However, the island emits electrostatic drift-acoustic waves that propagate into the surrounding 'intermediate region', where they are absorbed by the plasma. Since the waves carry momentum, the inner region exerts a net force on the intermediate region, and vice versa, giving rise to strong velocity shear in the region immediately surrounding the island. The intermediate region is matched to the surrounding 'outer region', in which ideal magnetohydrodynamic holds. Isolated hypersonic islands propagate with a velocity that lies between those of the unperturbed local ion and electron fluids, but is much closer to the latter. The ion polarization current is stabilizing, and increases with increasing island width. Finally, the hypersonic branch of isolated island solutions ceases to exist above a certain critical island width. Hypersonic islands whose widths exceed the critical width are hypothesized to bifurcate to the so-called 'sonic' solution branch.

  4. Anomalous resistivity resulting from electrostatic ion cyclotron turbulence

    NASA Technical Reports Server (NTRS)

    Ionson, J. A.

    1976-01-01

    The paper considers the generation of electrostatic ion cyclotron turbulence in an isothermal isotropic magnetized plasma where the drift velocity is below that of the ion-acoustic threshold. The saturated turbulence spectrum is found to be that which results from anomalous nonlinear wave damping related to stochastic ion-orbit diffusion in configuration space. An expression is obtained for the collective electrical resistivity resulting from current-driven electrostatic ion cyclotron turbulence.

  5. Drift reduction with drift control adjuvants

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Numerous drift reduction adjuvants and spray deposition aids are available to applicators of crop production and protection chemicals. Performance of many of the newly introduced drift control adjuvants has not been well documented for aerial application. Four new drift control adjuvants were sele...

  6. Drift reduction with drift control adjuvants

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Numerous drift reduction adjuvants and spray deposition aids are available to applicators of crop production and protection chemicals. Performance of many of the newly introduced drift control adjuvants has not been well documented for aerial application. Five new drift control adjuvants were sele...

  7. Study of incomplete fusion for light heavy-ion systems using velocity distributions

    SciTech Connect

    Chan, Y.; Albiston, C.; Bantel, M.; Budzanowski, A.; DiGregorio, D.; Stokstad, R.G.; Wald, S.; Zhou, S.; Zhou, Z.

    1986-03-01

    Experimental results on incomplete fusion for light systems are discussed by studying the velocity distribution of fusion-like residues in the energy range of 6 to 20 MeV/nucleon. Original experimental work and results from other groups including the Hahn-Meitner Institute and the Argonne National Laboratory are also cited. Reactions between /sup 14/N, /sup 16/O, /sup 19/F, and /sup 20,22/Ne projectiles and /sup 24,26/Mg, /sup 27/Al, /sup 28/Si, /sup 40/Ca and /sup 58,60/Ni targets have been studied. 19 refs., 15 figs., 1 tab.

  8. Ionization of highly charged iodine ions in collisions near the Bohr velocity

    NASA Astrophysics Data System (ADS)

    Xianming, Zhou; Yongtao, Zhao; Rui, Cheng; Jieru, Ren; Yu, Lei; Yuanbo, Sun; Yuyu, Wang; Shidong, Liu; Ge, Xu; Guoqing, Xiao

    2014-04-01

    The L-shell X-rays of iodine induced by 3MeV Iq+(q=20,22,25,26) ions impacting on Fe target were measured. The results indicated that, in addition to the ionization of L-shell, the projectile M- and N-shell were multiply ionized. The ratios of the sub-shell X-ray relative intensity were also investigated.

  9. Multi-point, high-speed passive ion velocity distribution diagnostic on the Pegasus Toroidal Experiment

    SciTech Connect

    Burke, M. G.; Fonck, R. J.; Bongard, M. W.; Schlossberg, D. J.; Winz, G. R.

    2012-10-15

    A passive ion temperature polychromator has been deployed on Pegasus to study power balance and non-thermal ion distributions that arise during point source helicity injection. Spectra are recorded from a 1 m F/8.6 Czerny-Turner polychromator whose output is recorded by an intensified high-speed camera. The use of high orders allows for a dispersion of 0.02 A/mm in 4th order and a bandpass of 0.14 A ({approx}13 km/s) at 3131 A in 4th order with 100 {mu}m entrance slit. The instrument temperature of the spectrometer is 15 eV. Light from the output of an image intensifier in the spectrometer focal plane is coupled to a high-speed CMOS camera. The system can accommodate up to 20 spatial points recorded at 0.5 ms time resolution. During helicity injection, stochastic magnetic fields keep T{sub e} low ({approx}100 eV) and thus low ionization impurities penetrate to the core. Under these conditions, high core ion temperatures are measured (T{sub i} Almost-Equal-To 1.2 keV, T{sub e} Almost-Equal-To 0.1 keV) using spectral lines from carbon III, nitrogen III, and boron IV.

  10. Bulk properties and velocity distributions of water group ions at Comet Halley - Giotto measurements

    NASA Technical Reports Server (NTRS)

    Coates, A. J.; Johnstone, A. D.; Wilken, B.; Jockers, K.; Glassmeier, K.-H.

    1990-01-01

    In the region upstream of Comet Halley, pickup heavy ions of cometary origin were directly observed by the implanted ion spectrometer on Giotto. Diffusion of this population in pitch angle and in energy, during the approach to the comet and on the outbound leg is discussed. The two data sets are compared and qualitative ideas on scattering timescales are inferred. In addition the bulk parameters of these distributions have been computed and a comparison of the observed speed in the solar wind frame and the observed density with expectations is presented. Pitch angle scattering occurs more slowly than expected with filled shells appearing at 2,500,000 km, and significant energy diffusion does not occur until the bow shock region. Also the shell distributions downstream of the shock flow at the bispherical bulk speed (related to the Alfven speed) along the magnetic field with respect to the solar wind in accordance with conservation of energy between the pickup ions and the wave turbulence.

  11. Upstream gyrophase bunched ions - A mechanism for creation at the bow shock and the growth of velocity space structure through gyrophase mixing

    NASA Technical Reports Server (NTRS)

    Gurgiolo, C.; Parks, G. K.; Mauk, G. H.

    1983-01-01

    The conditions necessary for the production of gyrophase bunched ions at the bow shock are developed. The conditions are applied to the reflection mechanism presented by Paschmann et al. (1980), showing that when in their model a portion of the incident parallel velocity is converted into reflected perpendicular velocity, the reflected particles are gyrophase bunched. The growth of velocity space structure in the gyrophase bunched distribution through gyrophase mixing is also explored. The structure is found to be similar to that reported in diffuse and dispersed ion events. This together with the close correlation of the observation of gyrophase bunched ions with diffuse and dispersed ions has led us to speculate that these two populations may be closely related.

  12. Method for enhancing the resolving power of ion mobility separations over a limited mobility range

    DOEpatents

    Shvartsburg, Alexandre A; Tang, Keqi; Smith, Richard D

    2014-09-23

    A method for raising the resolving power, specificity, and peak capacity of conventional ion mobility spectrometry is disclosed. Ions are separated in a dynamic electric field comprising an oscillatory field wave and opposing static field, or at least two counter propagating waves with different parameters (amplitude, profile, frequency, or speed). As the functional dependencies of mean drift velocity on the ion mobility in a wave and static field or in unequal waves differ, only single species is equilibrated while others drift in either direction and are mobility-separated. An ion mobility spectrum over a limited range is then acquired by measuring ion drift times through a fixed distance inside the gas-filled enclosure. The resolving power in the vicinity of equilibrium mobility substantially exceeds that for known traveling-wave or drift-tube IMS separations, with spectra over wider ranges obtainable by stitching multiple segments. The approach also enables low-cutoff, high-cutoff, and bandpass ion mobility filters.

  13. Background and Pickup Ion Velocity Distribution Dynamics in Titan's Plasma Environment: 3D Hybrid Simulation and Comparison with CAPS T9 Observations

    NASA Technical Reports Server (NTRS)

    Lipatov, A. S.; Sittler, E. C., Jr.; Hartle, R. E.; Cooper, J. F.; Simpson, D. G.

    2011-01-01

    In this report we discuss the ion velocity distribution dynamics from the 3D hybrid simulation. In our model the background, pickup, and ionospheric ions are considered as a particles, whereas the electrons are described as a fluid. Inhomogeneous photoionization, electron-impact ionization and charge exchange are included in our model. We also take into account the collisions between the ions and neutrals. The current simulation shows that mass loading by pickup ions H(+); H2(+), CH4(+) and N2(+) is stronger than in the previous simulations when O+ ions are introduced into the background plasma. In our hybrid simulations we use Chamberlain profiles for the atmospheric components. We also include a simple ionosphere model with average mass M = 28 amu ions that were generated inside the ionosphere. The moon is considered as a weakly conducting body. Special attention will be paid to comparing the simulated pickup ion velocity distribution with CAPS T9 observations. Our simulation shows an asymmetry of the ion density distribution and the magnetic field, including the formation of the Alfve n wing-like structures. The simulation also shows that the ring-like velocity distribution for pickup ions relaxes to a Maxwellian core and a shell-like halo.

  14. Effect of ion orbit loss on the structure in the H-mode tokamak edge pedestal profiles of rotation velocity, radial electric field, density, and temperature

    SciTech Connect

    Stacey, Weston M.

    2013-09-15

    An investigation of the effect of ion orbit loss of thermal ions and the compensating return ion current directly on the radial ion flux flowing in the plasma, and thereby indirectly on the toroidal and poloidal rotation velocity profiles, the radial electric field, density, and temperature profiles, and the interpretation of diffusive and non-diffusive transport coefficients in the plasma edge, is described. Illustrative calculations for a high-confinement H-mode DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] plasma are presented and compared with experimental results. Taking into account, ion orbit loss of thermal ions and the compensating return ion current is found to have a significant effect on the structure of the radial profiles of these quantities in the edge plasma, indicating the necessity of taking ion orbit loss effects into account in interpreting or predicting these quantities.

  15. Drift-induced modifications to the dynamical polarization of graphene

    NASA Astrophysics Data System (ADS)

    Sabbaghi, Mohsen; Lee, Hyun-Woo; Stauber, Tobias; Kim, Kwang S.

    2015-11-01

    The response function of graphene is calculated in the presence of a constant current across the sample. For small drift velocities and finite chemical potential, analytic expressions are obtained and consequences on the plasmonic excitations are discussed. For general drift velocities and zero chemical potential, numerical results are presented and a plasmon gain region is identified that is related to interband transitions.

  16. Drift Kinetic Theory and Cosmic Rays

    NASA Astrophysics Data System (ADS)

    Webb, G. M.; Le Roux, J. A.; Zank, G. P.

    2009-11-01

    Starting from the Vlasov or Boltzmann equation for cosmic rays in a random and regular magnetic field, we introduce guiding center coordinates and transform the velocity to a frame moving at the electric field drift velocity. The resultant equation is written in terms of the parallel and perpendicular momentum and gyro-phase of the particle, and describes spatial particle transport in guiding center coordinates. Using the drift ordering in which the gyro-scale and gyro-period are assumed short compared to the background flow length and time scales, and averaging over the gyro-phase gives the drift kinetic equation in which the adiabatic moment and total particle energy in the inertial frame are used to describe the momentum and energy of the particle. If the parallel electric field is small, the adiabatic moment of the particles is conserved to lowest order in the drift ordering. The resultant drift kinetic equation properly takes into account the energy changes of the particles due to drifts along the electric field, and betatron acceleration, but contains only the lowest order approximation for the guiding center drift velocity to describe the spatial advection of the particles. A further transformation of variables, in which the particle momentum and pitch angle are specified in the local fluid frame, gives the focussed transport equation derived by Skilling [1] to describe particle transport in a moving plasma medium, such as the solar wind. The connections to previous derivations of the Skilling's pitch angle focussed transport equation are discussed.

  17. Ion acceleration from laser-driven electrostatic shocks

    SciTech Connect

    Fiuza, F.; Stockem, A.; Boella, E.; Fonseca, R. A.; Silva, L. O.; Haberberger, D.; Tochitsky, S.; Mori, W. B.; Joshi, C.

    2013-05-15

    Multi-dimensional particle-in-cell simulations are used to study the generation of electrostatic shocks in plasma and the reflection of background ions to produce high-quality and high-energy ion beams. Electrostatic shocks are driven by the interaction of two plasmas with different density and/or relative drift velocity. The energy and number of ions reflected by the shock increase with increasing density ratio and relative drift velocity between the two interacting plasmas. It is shown that the interaction of intense lasers with tailored near-critical density plasmas allows for the efficient heating of the plasma electrons and steepening of the plasma profile at the critical density interface, leading to the generation of high-velocity shock structures and high-energy ion beams. Our results indicate that high-quality 200 MeV shock-accelerated ion beams required for medical applications may be obtained with current laser systems.

  18. Measurements of HNO3 and N2O5 using ion drift-chemical ionization mass spectrometry during the MILAGRO/MCMA-2006 campaign

    NASA Astrophysics Data System (ADS)

    Zheng, J.; Zhang, R.; Fortner, E. C.; Volkamer, R. M.; Molina, L.; Aiken, A. C.; Jimenez, J. L.; Gaeggeler, K.; Dommen, J.; Dusanter, S.; Stevens, P. S.; Tie, X.

    2008-11-01

    An ion drift-chemical ionization mass spectrometer (ID-CIMS) was deployed in Mexico City between 7 and 31 March to measure gas-phase nitric acid (HNO3) and dinitrogen pentoxide (N2O5 during the Mexico City Metropolitan Area (MCMA)-2006 field campaign. The observation site was located at the Instituto Mexicano del Petrleo in the northern part of Mexico City urban area with major emissions of pollutants from residential, vehicular and industrial sources. Diurnally, HNO3 was less than 200 parts per trillion (ppt) during the night and early morning. The concentration of HNO3 increased steadily from around 09:00 a.m. central standard time (CST), reached a peak value of 0.5 to 3 parts per billion (ppb) in the early afternoon, and then declined sharply to less than half of the peak value near 05:00 p.m. CST. An inter-comparison between the ID-CIMS and an ion chromatograph/mass spectrometer (ICMS) showed a good agreement between the two HNO3 measurements (R2=0.75). The HNO3 mixing ratio was found to anti-correlate with submicron-sized aerosol nitrate, suggesting that the gas-particle partitioning process was a major factor in determining the gaseous HNO3 concentration. Losses by irreversible reactions with mineral dust and via dry deposition also could be important at this site. Most of the times during the MCMA 2006 field campaign, N2O5 was found to be below the detection limit (about 30 ppt for a 10 s integration time) of the ID-CIMS, because of high NO mixing ratio at the surface (>100 ppb) during the night. An exception occurred on 26 March 2006, when about 40 ppt N2O5 was observed during the late afternoon and early evening hours under cloudy conditions before the build-up of NO at the surface site. The results revealed that during the MCMA-2006 field campaign HNO3 was primarily produced from the reaction of OH with NO2 and regulated by gas/particle transfer and dry deposition. The production of HNO3 from N2O5 hydrolysis during the nighttime was small because of high NO and low O3 concentrations near the surface.

  19. Measurements of HNO3 and N2O5 using Ion drift - Chemical Ionization Mass Spectrometry during the MCMA - 2006 Campaign

    NASA Astrophysics Data System (ADS)

    Zheng, J.; Zhang, R.; Fortner, E. C.; Molina, L.; Aiken, A. C.; Jimenez, J. L.; Gggeler, K.; Dommen, J.; Dusanter, S.; Stevens, P. S.; Tie, X.

    2008-03-01

    An ion drift - chemical ionization mass spectrometry (ID-CIMS) was deployed in Mexico City between 5 and 31 March to measure HNO3 and N2O5 during the 2006 Mexico City Metropolitan Area (MCMA) field campaign. The observation site, T0, was located at the Instituto Mexicano del Petrleo at the center of the Mexico City Basin with major emissions of pollutants from both domestic and industrial sources. Diurnally, HNO3 was less than 200 parts per trillion (ppt) during the night and in the early morning, increased steadily from around 09:00 a.m. central standard time (CST), reached a peak value of 0.5 to 3 parts per billion (ppb) in the early afternoon, and declined sharply to less than half of the peak value near 05:00 p.m. CST. An inter-comparison between the ID-CIMS and an ion chromatograph/mass spectrometer (ICMS) showed a good correlation in the HNO3 measurements (R2=0.75). The HNO3 mixing ratio was found to anti-correlate with aerosol nitrate, suggesting that the gaseous HNO3 concentration was controlled by the gas-particle partitioning process. During most times of the MCMA 2006 field campaign, N2O5 was found to be under the detection limit (about 20 ppt for a 10 s integration time) of the ID-CIMS, because of high NO mixing ratio (>100 ppb) during the night. With one exception on 26 March 2006, about 40 ppt N2O5 was observed during the late afternoon and early evening hours under a cloudy condition, before NO built up at the surface site. The results revealed that during the 2006 MCMA field campaign HNO3 was primarily produced by the reaction of OH with NO2 and regulated by gas/particle partitioning, and HNO3 production from N2O5 hydrolysis during the nighttime was small because of high NO and low O3 concentrations near the surface.

  20. Radar and satellite investigations of equatorial evening vertical drifts and spread F

    NASA Astrophysics Data System (ADS)

    Smith, J. M.; Rodrigues, F. S.; de Paula, E. R.

    2015-11-01

    We analyzed pre-midnight equatorial F region observations made by the 30 MHz coherent backscatter radar of São Luis, Brazil between August 2010 and February 2012. These measurements were processed, and used to create monthly maps of the echo occurrence as a function of local time and height. The maps show the inter-annual variability associated with equatorial spread F (ESF) occurrence in the Brazilian longitude sector. We also constructed monthly curves of the evening vertical drifts, for the Brazilian sector, using measurements by the ion velocity meter (IVM) onboard the C/NOFS satellite. The IVM evening drifts show a good overall agreement with the Scherliess and Fejer (1999) empirical model. Measured and model drifts show the development of the pre-reversal enhancement (PRE) of the vertical plasma drifts during ESF season. Using joint radar and satellite measurements, we found that evening (18:00-18:30 LT) mean non-negative drifts provide a necessary but not sufficient condition for the occurrence of topside ESF echoes. Evening downward (negative) drifts preceded the absence of topside ESF irregularities.

  1. Temporal evolution of drift Alfvn waves and instabilities in an inhomogeneous plasma with homogeneous shear flow.

    PubMed

    Mikhailenko, Vladimir S; Mikhailenko, Vladimir V; Heyn, Martin F; Mahajan, Swadesh M

    2002-12-01

    The temporal evolution of drift Alfvn waves in an inhomogeneous plasma of low and finite pressure with homogeneous shear flow is studied as an initial value problem without the use of spectral expansion in time. The cases of plasma with cold and hot ions, weak and strong flow shear are considered separately. It is shown that the conventional modal structure of the stable and unstable drift and Alfvn waves holds only for a limited time in the initial stage of its evolution. For larger times, nonmodal effects due to the velocity shear define the development of drift Alfvn waves and drift Alfvn instabilities. For the regimes of low flow shear, which corresponds to the period of the low-to-high transition, the long time evolution of these instabilities as well as their saturation are determined by the nonlinear effects such as the nonlinear decorrelation effect. In contrast, the plasma with strong flow shear, which corresponds to the regime of the developed transport barriers, is stable against the development hydrodynamic drift Alfvn and resistive drift Alfvn instabilities. The frequency increase caused by the shear flow brings the Alfvn wave phase speed close to the electron thermal speed where strong electron Landau damping occurs. At this stage, a kinetic approach for the description of these waves becomes necessary. PMID:12513414

  2. A DRIFT ORDERED SHORT MEAN-FREE DESCRIPTION FOR PARTIALLY IONIZED MAGNETIZED PLASMA

    SciTech Connect

    SIMAKOV, ANDERI N.

    2007-02-08

    Effects of neutral particles, most prominently the associated heat flux and viscosity, can be very important or even dominant at the edge of a tokamak and so must be self-consistently accounted for in a description of magnetized tokamak edge plasma. To the best of our knowledge, this has only been done so far for short mean-free path plasma under MHD-like Braginskii's orderings i.e. assuming that species velocities are on the order of the ion thermal speed. Since plasma flows in modern tokamaks are usually slow compared with the ion thermal speed (at least in the absence of strong external momentum sources) it is more appropriate to use drift orderings in which the plasma flow velocity is instead comparable with the diamagnetic heat flow divided by pressure. Employing drift orderings and evaluating species distribution functions through second order in the small gyroradius and mean-free path expansion parameters allows accounting for the important effects of heat fluxes on species momentum transport (viscosities), which are missing from the large flow ordered treatments. In this work we consider short mean-free path plasma consisting of electrons and single species of singly-charged ions and neutrals. We neglect neutral-neutral and elastic electron-neutral collisions and approximate the neutral-ion charge-exchange cross-section with a constant. We employ drift orderings to evaluate ion, neutral, and electron heat fluxes, viscosity tensors, and momentum and energy exchange terms and formulate a self-consistent system of electron, ion, and neutral fluid equations, thereby generalizing the drift-ordered treatment of fully ionized plasma.

  3. A NOVEL X-RAY IMAGING CRYSTAL SPECTROMETER FOR DOPPLER MEASUREMENTS OF ION TEMPERATURE AND PLASMA ROTATION VELOCITY PROFILES

    SciTech Connect

    Bitter, M; Hill, K W; Scott, S; Ince-Cushman, A; Reinke, M; Rice, J E; Beiersdorfer, P; Gu, M F; Lee, S G; Broennimann, C; Eikenberry, E F

    2008-06-06

    A new type of X-ray imaging crystal spectrometer has been implemented on Alcator CMod for Doppler measurements of ion temperature and plasma rotation velocity profiles. The instrument consists of two spherically bent (102)-quartz crystals with radii of curvature of 1444 and 1385 mm and four 'PILATUS II' detector modules. It records spectra of He-like argon from the entire, 72 cm high, elongated plasma cross-section and spectra of H-like argon from a 20 cm high, central region of the plasma, with a spatial resolution of 1.3 cm and a time resolution of less than 20 ms. The new spectrometer concept is also of interest for the diagnosis of burning plasmas on future machines. This paper presents recent experimental results from Aclator C-Mod and discusses challenges in X-ray spectroscopy for the diagnosis of fusion plasmas on future machines.

  4. Cross sections for resonant charge transfer between atoms and their positive ions: Collision velocity approx lt 1 a. u

    SciTech Connect

    Sakabe, Shuji; Izawa, Yasukazu )

    1991-11-01

    Calculated cross sections for resonant charge transfer between atoms and their positive ions are presented in tables and graphs for all nontransition elements in the range of low and intermediate collision velocities ({approx lt}1 a.u.). Experimental data obtained since the 1930s are compiled. The cross sections have been calculated by the impact-parameter and close-coupling methods. To solve the one-electron, time-dependent, spinless electronic wave function in a two-atom system, the wave function was expanded, time-dependent, spinless electronic wave function in a two-atom system, the wave function was expanded in terms of a set traveling atomic wave functions centered about either nucleus. As the eigenfunction of each atom, Hartree-Fock-Slater wave functions were used. The calculated results are in fairly good agreement with the compiled experimental results for the thoroughly studied elements and thus provide a useful interpolation/extrapolation of the experimental data.

  5. Filamentation instability of nonextensive current-driven plasma in the ion acoustic frequency range

    SciTech Connect

    Khorashadizadeh, S. M. Rastbood, E.; Niknam, A. R.

    2014-12-15

    The filamentation and ion acoustic instabilities of nonextensive current-driven plasma in the ion acoustic frequency range have been studied using the Lorentz transformation formulas. Based on the kinetic theory, the possibility of filamentation instability and its growth rate as well as the ion acoustic instability have been investigated. The results of the research show that the possibility and growth rate of these instabilities are significantly dependent on the electron nonextensive parameter and drift velocity. Besides, the increase of electrons nonextensive parameter and drift velocity lead to the increase of the growth rates of both instabilities. In addition, the wavelength region in which the filamentation instability occurs is more stretched in the presence of higher values of drift velocity and nonextensive parameter. Finally, the results of filamentation and ion acoustic instabilities have been compared and the conditions for filamentation instability to be dominant mode of instability have been presented.

  6. Ionization of Ar11+ ions during collisions near the Bohr velocity

    NASA Astrophysics Data System (ADS)

    Zhou, Xianming; Cheng, Rui; Lei, Yu; Liu, Shidong; Deng, Jiachuan; Sun, Yuanbo; Ren, Jieru; Wang, Yuyu; Zhao, Yongtao; Xiao, Guoqing

    2014-12-01

    The K-shell X-rays of argon from the collisions of 1-3 MeV Ar11+ ions with V target were measured. It was found that the Kα X-ray shifts to the high energy by 52 eV, and the intensity ratio of Kβ/Kα was larger than the atomic data, owing to the presence of 2p multiple vacancies. The X-ray production cross sections were obtained and compared with BEA, PWBA and ECPSSR theoretical predictions. The BEA model, taking into account the ionic binding energy, coulomb repulsion and multiple ionization effect on fluorescence yield, presented a better agreement with the experimental cross section data.

  7. Electric field variations due to resonance between ground velocity and ions motion in the Earth's magnetic field

    NASA Astrophysics Data System (ADS)

    Matsushima, M.; Honkura, Y.; Kuriki, M.; Ogawa, Y.

    2011-12-01

    We have so far observed clear electric field variations coincident with the passage of seismic waves. Circular polarization of electric field is the distinguishing feature in this phenomenon which can be interpreted in terms of the so-called seismic dynamo effect proposed by Honkura et al. (2009). That is, circularly polarized electric field is caused by resonance-like motion of ion in groundwater under the Earth's magnetic field. Therefore, left-handed and right-handed circular polarizations, if seen towards the direction of the magnetic field, are associated with anions with negative charge and cations with positive charge, respectively. Such polarization may be inconsistent with seismoelectric signals due to the electrokinetic mechanism, because they are mainly found in the direction of transmission of seismic compressional waves, as pointed out by Strahser et al. (2007) who examined polarization of seismoelectric signals by recording the three components of electric field. However, even such circular polarization of electric field is somehow interpreted in terms of the electrokinetic mechanism. Therefore, further convincing evidence is required to support the seismic dynamo effect. On 25-26 July 2011, an experiment for studies of crustal seismic structure was made in central Japan. We carried out simultaneous observations of ground velocity and electric field on this occasion at three sites near a blasting point using 50 kg of dynamite; about 280 m east-southeast, about 190 m east, and about 360 m northwest from the blasting point. Taking into account typical frequencies of ground velocity for artificial earthquakes by blasting higher than those for natural earthquakes, we used data loggers with sampling rate of 1 kHz and could obtain the waveforms of ground velocity and electric field very clearly. We show characteristics of electric field variations, their dependence of azimuth angle with respect to the blasting point, and frequency response functions.

  8. Drift of 10 herbicides after tractor spray application. 2. Primary drift (droplet drift).

    PubMed

    Carlsen, S C K; Spliid, N H; Svensmark, B

    2006-07-01

    In the present study the primary drift of 10 herbicides was investigated in five field experiments, and the amount deposited per surface area was quantified outside the application area using simple passive dosimeters. In addition, samples for measuring a possible background value were taken upwind of the sprayed field. Deposits of spray drift were common to all spray equipment and spray was detected up to 150 m off-target. There were deposits of 0.1-9% of the applied amount close to the sprayed field (up to 2 m). But 3m from the spraying zone deposits were reduced to 0.02-4%. The amounts decreased exponentially when moving away from the field. The differences in drift could be described mainly by the different drop sizes, the wind velocity, the formulation and the filtering effect of vegetation on the sampling area. The tendency of the active ingredients to evaporate could also have an, although less important, influence on the drift. This is a factor, which ought to be exposed to a further study. The findings supported that it is the physical properties of the spray and the conditions of application (i.e. equipment and meteorology) that are the primary determinants of primary drift rather than the chemical property of the pure active ingredients. PMID:16337986

  9. Dynamics of positive probes in underdense, strongly magnetized, E×B drifting plasma: Particle-in-cell simulations

    SciTech Connect

    Heinrich, Jonathon R.; Cooke, David L.

    2013-09-15

    Electron trapping, electron heating, space-charge wings, wake eddies, and current collection by a positive probe in E×B drifting plasma were studied in three-dimensional electromagnetic particle-in-cell simulations. In these simulations, electrons and ions were magnetized with respect to the probe and the plasma was underdense (ω{sub pe}<ω{sub ce}). A large drift velocity (Mach 4.5 with respect to the ion acoustic speed) between the plasma and probe was created with background electric and magnetic fields. Four distinct regions developed in the presences of the positive probe: a quasi-trapped electron region, an electron-depletion wing, an ion-rich wing, and a wake region. We report on the observations of strong electron heating mechanisms, space-charge wings, ion cyclotron charge-density eddies in the wake, electron acceleration due to a magnetic presheath, and the current-voltage relationship.

  10. Drift of dislocation tripoles under ultrasound influence.

    PubMed

    Murzaev, R T; Bachurin, D V; Nazarov, A A

    2016-01-01

    Numerical simulations of dynamics of different stable dislocation tripoles under influence of monochromatic standing sound wave were performed. The basic conditions necessary for the drift and mutual rearrangements between dislocation structures were investigated. The dependence of the drift velocity of the dislocation tripoles as a function of the frequency and amplitude of the external influence was obtained. The results of the work can be useful in analysis of motion and self-organization of dislocation structure under ultrasound influence. PMID:26278625

  11. Plasma drifts and polarization electric fields associated with TID-like disturbances in the low-latitude ionosphere: C/NOFS observations

    NASA Astrophysics Data System (ADS)

    Huang, Chao-Song

    2016-02-01

    Medium-scale traveling ionospheric disturbances are often observed at the magnetically conjugate points in the nighttime midlatitude ionosphere. It has been suggested that gravity waves disturb the ionosphere and induce electric fields in one hemisphere and that the electric fields are amplified by the Perkins instability and transmitted along the geomagnetic field lines to the conjugate ionosphere, creating similar disturbances there. However, direct observations of electric fields associated with traveling ionospheric disturbances (TIDs) are very few. In this study, we present low-latitude TID-like disturbances observed by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. It is found that ion velocity perturbations are generated in the directions parallel and perpendicular to the geomagnetic field within TIDs. Both the parallel and perpendicular ion velocity perturbations show an in-phase correlation with the ion density perturbations. For nighttime TIDs, the amplitude of both the parallel and meridional ion velocity perturbations increases almost linearly with the amplitude of the ion density perturbations, and the meridional ion drift is proportional to the parallel ion velocity. For daytime TIDs, the parallel ion velocity perturbation increases with the ion density perturbation, but the meridional ion velocity perturbation does not change much. The observations provide evidence that polarization electric field is generated within TIDs at low latitudes and maps along the geomagnetic field lines over a large distance.

  12. Dynamics of pickup ion velocity distribution function in Titan's plasma environment (TA encounter): 3D hybrid kinetic modeling and comparison with CAPS observations

    NASA Astrophysics Data System (ADS)

    Simpson, D. G.; Lipatov, A. S.; Sittler, E. C.; Hartle, R. E.; Cooper, J. F.

    2013-12-01

    Wave-particle interactions play a very important role in the plasma dynamics near Titan: mass loading, excitation of the low-frequency waves and the formation of the particle velocity distribution function, e.g. ring/shell-like distributions, etc. The kinetic approach is important for estimation of the collision processes e.g. a charge exchange. The particle velocity distribution function also plays a key role for understanding the observed particle fluxes. In this report we discuss the ion velocity distribution function dynamics from 3D hybrid modeling. The modeling is based on recent analysis of the Cassini Plasma Spectrometer (CAPS) ion measurements during the TA flyby. In our model the background ions, all pickup ions, and ionospheric ions are considered as particles, whereas the electrons are described as a fluid. Inhomogeneous photoionization, electron-impact ionization and charge exchange are included in our model. The temperatures of the background electrons and pickup electrons were also included into the generalized Ohm's law. We also take into account the collisions between the ions and neutrals. We use Chamberlain profiles for the exosphere's components and include a simple ionosphere model with M=28 ions that were generated inside the ionosphere. The moon is considered as a weakly conducting body. Our modeling shows that interaction between background plasma and pickup ions H+, H2+, CH4+ and N2+ has a more complicated structure than was observed in the T9 flyby and modeling due to the large gyroradius of the background O+ ions [1,2,3,4]. Special attention will be paid to comparing the simulated pickup ion velocity distribution with CAPS TA observations. We also compare our kinetic modeling with other hybrid and MHD modeling of Titan's environment. References [1] Sittler, E.C., et al., Energy Deposition Processes in Titan's Upper Atmosphere and Its Induced Magnetosphere. In: Titan from Cassini-Huygens, Brown, R.H., Lebreton J.P., Waite, J.H., Eds., Springer, (Dordrecht, Heidelberg, London, New York, pp. 393-455, 2009). [2] Sittler, E.C., et al., Saturn's Magnetospheric Interaction with Titan as Defined by Cassini Encounters T9 and T18: New Results, Planet. Space Sci., doi.10.1016/j.pss.2009.09.017. [3] Coates, A.J., Interaction of Titan's ionosphere with Saturn's magnetosphere. Phil. Trans. R. Soc. A (2009) 367, 773-788, doi: 10.1098/rsta.2008.0248. [4] Lipatov, A.S., et al., Background and pickup ion velocity distribution dynamics in Titan's plasma environment: 3D hybrid simulation and comparison with CAPS T9 observations. Adv. Space Res. 48, 1114-1125, 2011.

  13. Drift mechanism for energetic charged particles at shocks

    SciTech Connect

    Webb, G.M.; Axford, W.I.; Terasawa, T.

    1983-07-15

    The energy changes of energetic charged particles at a plane shock due to the so-called drift mechanism are analyzed by using the ''adiabatic treatment.'' The analysis shows that for a fast MHD shock, particles lose energy owing to acceleration (curvature) drift in the magnetic field at the shock with the drift velocity being antiparallel to the electric field, and they gain energy owing to gradient drift parallel to the electric field. It is shown that particles with pitch angles aligned along the magnetic field which pass through the shock tend to lose energy owing to acceleration drift, whereas particles with pitch angles nonaligned to the magnetic field gain energy owing to gradient drift. Particles that are reflected by the shock always gain energy. Slow-mode shocks may be similarly analyzed, but in this case curvature drifts give rise to particle energy gains, and gradient drifts result in particle energy losses.

  14. Drift waves in stellarator geometry

    SciTech Connect

    Persson, M.; Nadeem, M.; Lewandowski, J.L.V.; Gardner, H.J.

    2000-02-07

    Drift waves are investigated in a real three-dimensional stellarator geometry. A linear system, based on the cold ion fluid model and a ballooning mode formalism, is solved numerically in the geometry of the stellarator H1-NF. The spectra of stable and unstable modes, as well as localization, are discussed. The dependence of the spectrum of the unstable modes on the wavevector, plasma density variation, and the location in the plasma is presented.

  15. The response of a spherical tissue-equivalent proportional counter to different heavy ions having similar velocities

    PubMed Central

    Taddei, Phillip J.; Borak, Thomas B.; Guetersloh, Stephen B.; Gersey, Brad B.; Zeitlin, Cary; Heilbronn, Lawrence; Miller, Jack; Murakami, Takeshi; Iwata, Yoshiyuki

    2008-01-01

    A tissue-equivalent proportional counter (TEPC) has been used as a dosimeter in mixed radiation fields. Since it does not measure LET directly, the response function must be characterized in order to estimate quality factor and thus equivalent dose for the incident radiation. The objectives of this study were to measure the response of a spherical TEPC for different high-energy heavy ions (HZE) having similar velocity and to determine how quality factors can be determined. Data were obtained at the HIMAC heavy ion accelerator for 4He and 12C at 220 5 MeV/nucleon (? = 0.59) and 12C, 16O, 28Si and 56Fe at 376 15 MeV/nucleon (? = 0.70). A particle spectrometer recorded the charge and position of each incident beam particle. Events with low energy deposition were observed for particles that passed through the wall of the TEPC but not through the sensitive volume. The frequency averaged lineal energy, ?f, was always less than the LET of the incident particles. The dose averaged lineal energy, ?D, was approximately equal to LET for particles with LET greater than 10 keV/?m, whereas ?D was larger than LET for the lighter particles with lower LET. Part of this effect is due to detector resolution and energy straggling that increases the variance of the response function. Although the TEPC is not a LET spectrometer, it can provide real time measurements of dose and provide estimates of quality factors for HZE particles using averaged values of lineal energy. PMID:19079798

  16. Verification of continuum drift kinetic equation solvers in NIMROD

    SciTech Connect

    Held, E. D.; Ji, J.-Y.; Kruger, S. E.; Belli, E. A.; Lyons, B. C.

    2015-03-15

    Verification of continuum solutions to the electron and ion drift kinetic equations (DKEs) in NIMROD [C. R. Sovinec et al., J. Comp. Phys. 195, 355 (2004)] is demonstrated through comparison with several neoclassical transport codes, most notably NEO [E. A. Belli and J. Candy, Plasma Phys. Controlled Fusion 54, 015015 (2012)]. The DKE solutions use NIMROD's spatial representation, 2D finite-elements in the poloidal plane and a 1D Fourier expansion in toroidal angle. For 2D velocity space, a novel 1D expansion in finite elements is applied for the pitch angle dependence and a collocation grid is used for the normalized speed coordinate. The full, linearized Coulomb collision operator is kept and shown to be important for obtaining quantitative results. Bootstrap currents, parallel ion flows, and radial particle and heat fluxes show quantitative agreement between NIMROD and NEO for a variety of tokamak equilibria. In addition, velocity space distribution function contours for ions and electrons show nearly identical detailed structure and agree quantitatively. A Θ-centered, implicit time discretization and a block-preconditioned, iterative linear algebra solver provide efficient electron and ion DKE solutions that ultimately will be used to obtain closures for NIMROD's evolving fluid model.

  17. Verification of continuum drift kinetic equation solvers in NIMROD

    NASA Astrophysics Data System (ADS)

    Held, E. D.; Kruger, S. E.; Ji, J.-Y.; Belli, E. A.; Lyons, B. C.

    2015-03-01

    Verification of continuum solutions to the electron and ion drift kinetic equations (DKEs) in NIMROD [C. R. Sovinec et al., J. Comp. Phys. 195, 355 (2004)] is demonstrated through comparison with several neoclassical transport codes, most notably NEO [E. A. Belli and J. Candy, Plasma Phys. Controlled Fusion 54, 015015 (2012)]. The DKE solutions use NIMROD's spatial representation, 2D finite-elements in the poloidal plane and a 1D Fourier expansion in toroidal angle. For 2D velocity space, a novel 1D expansion in finite elements is applied for the pitch angle dependence and a collocation grid is used for the normalized speed coordinate. The full, linearized Coulomb collision operator is kept and shown to be important for obtaining quantitative results. Bootstrap currents, parallel ion flows, and radial particle and heat fluxes show quantitative agreement between NIMROD and NEO for a variety of tokamak equilibria. In addition, velocity space distribution function contours for ions and electrons show nearly identical detailed structure and agree quantitatively. A ?-centered, implicit time discretization and a block-preconditioned, iterative linear algebra solver provide efficient electron and ion DKE solutions that ultimately will be used to obtain closures for NIMROD's evolving fluid model.

  18. Time-Resolved Laser-Induced Fluorescence Measurements of the Ion Velocity Distribution in the H6 Hall Thruster Plume

    NASA Astrophysics Data System (ADS)

    Durot, Christopher; Gallimore, Alec

    2013-09-01

    We developed a technique to measure time-resolved laser-induced fluorescence signals in plasma sources that have a relatively constant spectrum of oscillations in steady-state operation but are not periodically pulsed, such as Hall thrusters. We present the first results using the new technique to capture oscillations in a Hall Thruster. The ion velocity distribution function in the plume of the H6 Hall thruster is interrogated during breathing mode oscillations. The breathing mode is characterized by an oscillating depletion and replenishment of neutrals at a frequency of about 10-25 kHz. We use laser modulation on the order of megahertz, well above the time scale of interest (about 0.1 ms). Band-pass filtering and phase-sensitive detection (with a time constant on the order of microseconds) raise the signal-to-noise ratio and demodulate the signal while preserving time-resolved information. Following phase-sensitive detection, we average over transfer functions to finish recovering the signal. This technique has advantages such as a shorter dwell time than other techniques and the lack of a need for triggering for averaging in the time domain.

  19. Drift compression experiments on MBE-4 and related emittance growth phenomena

    SciTech Connect

    Eylon, S.; Faltens, A.; Fawley, W.; Garvey, T.; Hahn, K.; Henestroza, E.; Smith, L.

    1991-04-01

    We have recently conducted a series of experiments on the MBE-4 heavy ion accelerator in which a velocity tilt was placed on the beam in the first accelerating section beyond the injector, followed by drift compression over the remaining 11 meters. Depending upon the magnitude of the velocity tilt and the accompanying mismatch in the focusing lattice, emittance growth was observed, manifested by butterfly'' shapes in x {minus} x{prime} phase space. We discuss various analytical limits on ion beam compression and relate them to these experiments and also to a driver for a heavy ion fusion reactor. We also present numerical simulations which investigate various aspects of compression and consequent emittance growth. 2 refs., 3 figs., 1 tab.

  20. Stability of ion acoustic solitary waves in a magnetized plasma consisting of warm adiabatic ions and non-thermal electrons having vortex-like velocity distribution

    NASA Astrophysics Data System (ADS)

    Das, Jayasree; Bandyopadhyay, Anup; Das, K. P.; Das

    2014-02-01

    Schamel's modified Korteweg-de Vries-Zakharov-Kuznetsov (S-ZK) equation, governing the behavior of long wavelength, weak nonlinear ion acoustic waves propagating obliquely to an external uniform static magnetic field in a plasma consisting of warm adiabatic ions and non-thermal electrons (due to the presence of fast energetic electrons) having vortex-like velocity distribution function (due to the presence of trapped electrons), immersed in a uniform (space-independent) and static (time-independent) magnetic field, admits solitary wave solutions having a sech 4 profile. The higher order stability of this solitary wave solution of the S-ZK equation has been analyzed with the help of multiple-scale perturbation expansion method of Allen and Rowlands (Allen, M. A. and Rowlands, G. 1993 J. Plasma Phys. 50, 413; 1995 J. Plasma Phys. 53, 63). The growth rate of instability is obtained correct to the order k 2, where k is the wave number of a long wavelength plane wave perturbation. It is found that the lowest order (at the order k) instability condition is strongly sensitive to the angle of propagation (?) of the solitary wave with the external uniform static magnetic field, whereas at the next order (at the order k 2) the solitary wave solutions of the S-ZK equation are unstable irrespective of ?. It is also found that the growth rate of instability up to the order k 2 for the electrons having Boltzmann distribution is higher than that of the non-thermal electrons having vortex-like distribution for any fixed ?.

  1. Model Etch Profiles for Ion Energy Distribution Functions in an Inductively Coupled Plasma Reactor

    SciTech Connect

    Abraham-Shrauner, B.; Chen, W.; Woodworth, J.R.

    1998-12-14

    Rectangular trench profiles are modeled with analytic etch rates determined from measured ion distribution functions. The pattern transfer step for this plasma etch is for trilayer lithography. Argon and chlorine angular ion energy distribution functions measured by a spherical collector ring analyzer are fit to a sum of drifting Maxwellian velocity distribution functions with anisotropic temperatures. The fit of the model ion distribution functions by a simulated annealing optimization procedure converges adequately for only two drifting Maxwellians. The etch rates are proportional to analytic expressions for the ion energy flux. Numerical computation of the etch profiles by integration of the characteristic equations for profile points and connection of the profiles points is efficient.

  2. Physics-Based Model Driven by Plasma Drifts Obtained From the C/NOFS Satellite

    NASA Astrophysics Data System (ADS)

    Su, Y.; Retterer, J. M.; Stoneback, R.; de La Beaujardiere, O.; Roddy, P. A.; Heelis, R. A.; Pfaff, R. F.

    2010-12-01

    An important parameter in determining low-latitude ionospheric plasma density is the plasma drift. Two instruments on-board the Communication/Navigation Outage System (C/NOFS) satellite were designed to directly or indirectly measure the plasma drifts: the Ion Velocity Drift Meter (IVM) and the Vector Electric Field Instrument (VEFI). By using the electric field measurements obtained from VEFI, the physics-based model (PBMOD) developed at the Air Force Research Laboratory has been shown to qualitatively reproduce post-midnight density trenches observed in June 2008. In this presentation, we will demonstrate simulation results obtained from PBMOD driven by averaged IVM [Stoneback and Heelis, 2010] and VEFI data [Pfaff et al., 2010]. A wave-4 structure has been identified in averaged IVM data. Based on our preliminary study, the ion density output from IVM-driven PBMOD also presents a similar wave-four structure in geographical longitudes (GLON). In addition, the lowest density region occurs near 300 degree GLON for all seasons, where the magnetic equator declination is largest. Model results will be compared with those driven by the Scherliess-Fejer drift model, as well as in-situ density measurements obtained from the Planar Langmuir Probe (PLP). Stoneback, R. and R. Heelis (2010), Equatorial ion densities and meridional ion drifts in 2009, C/NOFS Science Workshop at Breckenridge, Colorado. Pfaff, R. , H. Freudenreich, J. Klenzing, D. Rowland, and K. Bromund (2010), DC electric fields as observed on the C/NOFS satellite during solar minimum conditions, C/NOFS Science Workshop at Breckenridge, Colorado.

  3. A time-resolved laser induced fluorescence study on the ion velocity distribution function in a Hall thruster after a fast current disruption

    SciTech Connect

    Mazouffre, S.; Gawron, D.; Sadeghi, N.

    2009-04-15

    The temporal characteristics of the Xe{sup +} ion axial velocity distribution function (VDF) were recorded in the course of low-frequency discharge current oscillations ({approx}14 kHz) of the 5 kW class PPS X000 Hall thruster. The evolution in time of the ion axial velocity component is monitored by means of a laser induced fluorescence diagnostic tool with a time resolution of 100 ns. As the number of fluorescence photons is very low during such a short time period, a homemade pulse-counting lock-in system was used to perform real-time discrimination between background photons and fluorescence photons. The evolution in time of the ion VDF was observed at three locations along the thruster channel axis after a fast shutdown of the thruster power. The anode discharge current is switched off at 2 kHz during 5 {mu}s without any synchronization with the current oscillation cycle. This approach allows to examine the temporal behavior of the ion VDF during decay and ignition of the discharge as well as during forced and natural plasma oscillations. Measurements show that the distribution function of the axial component of the Xe{sup +} ion does change periodically in time with a frequency close to the current oscillation frequency in both forced and natural cases. The ion density and the mean velocity are found to oscillate, whereas the velocity dispersion stays constant, which indicates that ionization and acceleration layers have identical dynamics. Finally, variations over time in the electric field are for the first time experimentally evidenced in a crossed-field discharge.

  4. Experimental test of instability enhanced collisional friction for determining ion loss in two ion species plasmas

    SciTech Connect

    Hershkowitz, N.; Yip, C.-S.; Severn, G. D.

    2011-05-15

    Recent experiments have shown that ions in weakly collisional plasmas containing two ion species of comparable densities approximately reach a common velocity at the sheath edge equal to the bulk plasma ion sound velocity. A recent theory [S. D. Baalrud, C. C. Hegna, and J. D. Callen, Phys. Rev. Lett. 103, 205002 (2009)] suggests that this is a consequence of collisional friction between the two ion species enhanced by the two stream instability. The theory finds that the difference in velocities at the sheath edge depends on the relative concentrations of the two ions. The difference in velocities is small, with both species approaching to the bulk sound velocity, when the concentrations are comparable, and is large, with each species reaching its own Bohm velocity, when the relative concentration differences are large. To test these findings, drift velocities of Ar and Xe ions were measured with laser-induced fluorescence in Ar-Xe and He-Xe plasmas and combined with ion acoustic wave and plasma potential data. In addition, electron temperature was varied by a Maxwell demon [K. R. MacKenzie et al., App. Phys. Lett. 18, 529 (1971)]. The predictions were found to be in excellent agreement with the experimental data. The generalized Bohm criterion in two ion species plasmas is also verified in a wider variety of relative ion concentrations.

  5. Development of a very-low-velocity superconducting linac

    SciTech Connect

    Shepard, K.W.

    1987-01-01

    Four types of superconducting accelerator structures are being developed for use in a low velocity positive-ion injector linac for the ATLAS heavy-ion accelerator. Prototypes of the first two of these have been tested. The structures are all variants of a quarter-wave line terminated with a four-gap interdigital drift-tube array. The two structure types so far tested operate at 48.5 mHz and have an active length of 10 cm (for the particle velocity - .008c type) and 16.5 cm (for the velocity - .014c type). Effective accelerating fields of 10 MV/m have been achieved with the 10 cm structure, corresponding to an effective accelerating potential of 1 MV. The 16.5 cm structure has been operated at field levels of 6 MV/m, also giving an effective potential of 1 MV. Prototypes of the remaining two resonant geometries are under construction.

  6. Adiabatic particle motion in a nearly drift-free magnetic field - Application to the geomagnetic tail

    NASA Technical Reports Server (NTRS)

    Stern, D. P.

    1978-01-01

    An investigation is made of the adiabatic particle motion occurring in an almost drift-free magnetic field. The dependence of the mean drift velocity on the equatorial pitch angle and the variation of the local drift velocity along the trajectories is studied. The fields considered are two-dimensional and resemble the geomagnetic tail. Derivations are presented for instantaneous and average drift velocities, bounce times, longitudinal invariants, and approximations to the adiabatic Hamiltonian. As expected, the mean drift velocity is significantly smaller than the instantaneous drift velocities found at typical points on the trajectory. The slow drift indicates that particles advance in the dawn-dusk direction rather slowly in the plasma sheet of the magnetospheric tail.

  7. Dependence of the relative backscatter cross section of 1-m density fluctuations in the auroral electrojet on the angle between electron drift and radar wave vector

    SciTech Connect

    Andre, D.

    1983-10-01

    With the STARE radar system it is possible to measure, with high spatial and temporal resolution the electron drift velocity V/sub D/ and the relative amplitude of electron density fluctuations of 1-m wavelength in the auroral electrojet. These density fluctuations are generated by the combined effects of the two-stream and the gradient drift instabilities. We have determined the angular dependence of the backscatter intensity (which is proportional to the square of the amplitude of the density fluctuations) on the angle theta betweeen the electron drift direction and the direction from the scattering volume to the radar in the plane perpendicular to the magnetic field. We find a fluctuation minimum for theta = 90/sup 0/ and an increase towards theta = 0/sup 0/ over the whole velocity range up to 1000 m/s. This increase is small for velocities below the ion acoustic velocity C/sub N/ but reaches over 20 dB gain in the backscatter intensity (corresponding to a density fluctuation more than 10 times as great) for higher velocities. We explain that the backscatter is caused mainly by two-stream instability in the range cos theta>C/sub S//V/sub d/ and by secondary gradient drift instability elsewhere.

  8. Reduction effect of neutral density on the excitation of turbulent drift waves in a linear magnetized plasma with flow

    SciTech Connect

    Saitou, Y.; Yonesu, A.; Shinohara, S.; Ignatenko, M. V.; Kasuya, N.; Kawaguchi, M.; Terasaka, K.; Nishijima, T.; Nagashima, Y.; Kawai, Y.; Yagi, M.; Itoh, S.-I.; Azumi, M.; Itoh, K.

    2007-07-15

    The importance of reducing the neutral density to reach strong drift wave turbulence is clarified from the results of the extended magnetohydrodynamics and Monte Carlo simulations in a linear magnetized plasma. An upper bound of the neutral density relating to the ion-neutral collision frequency for the excitation of drift wave instability is shown, and the necessary flow velocity to excite this instability is also estimated from the neutral distributions. Measurements of the Mach number and the electron density distributions using Mach probe in the large mirror device (LMD) of Kyushu University [S. Shinohara et al., Plasma Phys. Control. Fusion 37, 1015 (1995)] are reported as well. The obtained results show a controllability of the neutral density and provide the basis for neutral density reduction and a possibility to excite strong drift wave turbulence in the LMD.

  9. Influence of {kappa}-distributed ions on the two-stream instability

    SciTech Connect

    Langmayr, D.; Biernat, H.K.; Erkaev, N.V.

    2005-10-01

    This paper is the first approach for analyzing the influence of {kappa}-distributed particles on the modified two-stream instability (MTSI). It is assumed that the plasma consists of a magnetized Maxwellian electron contribution and unmagnetized {kappa}-distributed ions drifting across the electrons. Within an electrostatic approximation, the influence of the {kappa} parameter on the maximum growth rate of the MTSI is evaluated for the special case of parallel drift velocity and wave propagation.

  10. Drift-Ordered Fluid Equations in Collisional Plasmas with Strong Perpendicular Gradients

    NASA Astrophysics Data System (ADS)

    Simakov, Andrei

    2003-10-01

    The short mean-free path description of magnetized plasma as originally formulated by Braginskii [1] assumes that the ion mean flow and thermal speed are comparable. Mikhailovskii et al. [2] considered an alternate ordering in which the flow is on the order of the ion diamagnetic heat flux divided by the pressure. In this drift ordering the flow velocity is on the order of the diamagnetic drift velocity - the case of interest for most fusion devices, and the edge of many tokamaks. Indeed, most short mean-free path treatments of turbulence in magnetized plasmas must adopt the results of Mikhailovskii et al. to properly treat the temperature gradient terms in the expressions for charged particles viscosity. Using their description a reduced system of fully non-linear low-beta equations is derived for fluctuations with connection length parallel variations and pedestal width perpendicular variations. The resulting reduced equations for plasma density, vorticity (or, equivalently, electrostatic potential), and electron and ion parallel flow velocities and temperatures, supplemented with Ampere's law, modify and generalize the BOUT [3] and Zeiler et al. [4] equations used to model plasma edge turbulence. They are constructed to manifestly conserve number and total energy locally, and insure that the plasma current and magnetic field are divergence free. The reduced equations also allow standard neoclassical Pfirsch-Schlter results for the current, ion heat flux, and temperature gradient modified ion flow velocity to be recovered. [1] S. I. Braginskii, Sov. Phys. JETP 6, 358 (1958). [2] A. B. Mikhailovskii et al., Beitr. Plasmaphys. 24, 335 (1984). [3] X. Q. Xu et al., Phys. Plasmas 7, 1951 (2000). [4] A. Zeiler et al., Phys. Plasmas 4, 2134 (1997).

  11. Dike/Drift Interactions

    SciTech Connect

    E. Gaffiney

    2004-11-23

    This report presents and documents the model components and analyses that represent potential processes associated with propagation of a magma-filled crack (dike) migrating upward toward the surface, intersection of the dike with repository drifts, flow of magma in the drifts, and post-magma emplacement effects on repository performance. The processes that describe upward migration of a dike and magma flow down the drift are referred to as the dike intrusion submodel. The post-magma emplacement processes are referred to as the post-intrusion submodel. Collectively, these submodels are referred to as a conceptual model for dike/drift interaction. The model components and analyses of the dike/drift interaction conceptual model provide the technical basis for assessing the potential impacts of an igneous intrusion on repository performance, including those features, events, and processes (FEPs) related to dike/drift interaction (Section 6.1).

  12. Adiabatic particle motion in a nearly drift-free magnetic field: Application to the geomagnetic tail

    NASA Technical Reports Server (NTRS)

    Stern, D. P.

    1977-01-01

    The guiding center motion of particles in a nearly drift free magnetic field is analyzed in order to investigate the dependence of mean drift velocity on equatorial pitch angle, the variation of local drift velocity along the trajectory, and other properties. The mean drift for adiabatic particles is expressed by means of elliptic integrals. Approximations to the twice-averaged Hamiltonian W near z = O are derived, permitting simple representation of drift paths if an electric potential also exists. In addition, the use of W or of expressions for the longitudinal invariant allows the derivation of the twice averaged Liouville equation and of the corresponding Vlasov equation. Bounce times are calculated (using the drift-free approximation), as are instantaneous guiding center drift velocities, which are then used to provide a numerical check on the formulas for the mean drift.

  13. Development of a High Resolution X-Ray Imaging Crystal Spectrometer for Measurement of Ion-Temperature and Rotation-Velocity Profiles in Fusion Energy Research Plasmas

    SciTech Connect

    Hill, K W; Broennimann, Ch; Eikenberry, E F; Ince-Cushman, A; Lee, S G; Rice, J E; Scott, S

    2008-01-29

    A new imaging high resolution x-ray crystal spectrometer (XCS) has been developed to measure continuous profiles of ion temperature and rotation velocity in fusion plasmas. Following proof-of-principle tests on the Alcator C-Mod tokamak and the NSTX spherical tokamak, and successful testing of a new silicon, pixilated detector with 1 MHz count rate capability per pixel, an imaging XCS is being designed to measure full profiles of Ti and v? on C-Mod. The imaging XCS design has also been adopted for ITER. Ion-temperature uncertainty and minimum measurable rotation velocity are calculated for the C-Mod spectrometer. The affects of x-ray and uclear-radiation background on the measurement uncertainties are calculated to predict performance on ITER.

  14. Development of a High Resolution X-Ray Imaging Crystal Spectrometer for Measurement of Ion-Temperature and Rotation-Velocity Profiles in Fusion Energy Research Plasmas

    SciTech Connect

    Hill, K W; Broennimann, Ch; Eikenberry, E F; Ince-Cushman, A; Lee, S G; Rice, J E; Scott, S

    2008-02-27

    A new imaging high resolution x-ray crystal spectrometer (XCS) has been developed to measure continuous profiles of ion temperature and rotation velocity in fusion plasmas. Following proof-of-principle tests on the Alcator C-Mod tokamak and the NSTX spherical tokamak, and successful testing of a new silicon, pixilated detector with 1MHz count rate capability per pixel, an imaging XCS is being designed to measure full profiles of Ti and vφ on C-Mod. The imaging XCS design has also been adopted for ITER. Ion-temperature uncertainty and minimum measurable rotation velocity are calculated for the C-Mod spectrometer. The affects of x-ray and nuclear-radiation background on the measurement uncertainties are calculated to predict performance on ITER.

  15. Free Drifting Buoys

    NASA Technical Reports Server (NTRS)

    1974-01-01

    Information was exchanged between people directly involved with the development, use, and/or potential use of free drifting buoys. Tracking systems and techniques, where methods and accuracy of optical, radio, radar, satellite, and sonic tracking of free-drifting buoys were discussed. Deployment and retrieval covering methods currently used or planned in the deployment and retrieval of free-drifting buoys from boats, ships, helicopters, fixed platforms, and fixed-wing aircraft were reported. Simulation, sensors, and data emphasizing the status of water circulation modeling, and sensors useful on free-drifting buoys, and data display and analysis were described.

  16. Gradient drift eigenmodes in the equatorial electrojet

    SciTech Connect

    Wang, X.H.; Bhattacharjee, A.

    1994-07-01

    The problem of kilometer-scale irregularities in the daytime equatorial electrojet is revisited by means of an eigenmode analysis of the gradient drift instability. Realistic physical parameters are used, including the modeled altitude variations of ion and electron collision frequencies and mobilities. The full fourth-order system of two coupled differential equations (each of second order) for the density and electrostatic potential perturbations is solved numerically by a relaxation technique. Under some approximations, the fourth-order system can be shown to reduce to a second-order differential equation for the perturbed potential or density. The latter is solved using a shooter technique and provides initial guesses for numerical solutions to the full problem. It is shown that the linear growth rate peaks for kilometer-scale waves, contrary to the findings of recent initial-value studies. This occurs because the equilibrium velocity shear is much more effective as a damping mechanism for short-wavelength modes than it is for the longer, kilometer-scale modes. These results provide a natural qualitative explanation for the observed dominance of kilometer-scale structures in the daytime electrojet spectrum. 27 refs., 9 figs.

  17. Gradient drift eigenmodes in the equatorial electrojet

    NASA Technical Reports Server (NTRS)

    Wang, X.-H.; Bhattacharjee, A.

    1994-01-01

    The problem of kilometer-scale irregularities in the daytime equatorial electrojet is revisited by means of an eigenmode analysis of the gradient drift instability. Realistic physical parameters are used, including the modeled altitude variations of ion and electron collision frequencies and mobilities. The full fourth-order system of two coupled differential equations (each of second order) for the denisty and electrostatic potential perturbations is solved numerically by a relaxation technique. Under some approximations, the fourth-order system can be shown to reduce to a second-order differential equation for the perturbed potential or density. The latter is solved using a shooting technique and provides initial guesses for numerical solutions to the full problem. It is shown that the linear growth rate peaks for kilometer-scale waves, contrary to the findings of recent initial-value studies. This occurs because the equilibrium velocity shear is much more effective as a damping mechanism for short-wavelength modes than it is for the longer, kilometer-scale modes. These results provide a natural qualitative explanation for the observed dominance of kilometer-scale structures in the daytime electrojet spectrum.

  18. Magnetotail acceleration using generalized drift theory - A kinetic merging scenario

    NASA Technical Reports Server (NTRS)

    Whipple, E. C.; Rosenberg, M.; Brittnacher, M.

    1990-01-01

    It is possible to describe particle behavior in the magnetotail, including particle energization, by means of generalized drift theory. Generalized drift velocities are obtained by using the generalized first invariant which has been shown to be useful in such current sheet configurations. Particles whose generalized invariant is preserved gain energy entirely in the field-aligned direction. The form of the accelerated particle velocity distribution is obtained and self-consistency conditions are derived.

  19. Collisional effects on nonlinear ion drag force for small grains

    SciTech Connect

    Hutchinson, I. H.; Haakonsen, C. B.

    2013-08-15

    The ion drag force arising from plasma flow past an embedded spherical grain is calculated self-consistently and non-linearly using particle in cell codes, accounting for ion-neutral collisions. Using ion velocity distribution appropriate for ion drift driven by a force field gives wake potential and force greatly different from a shifted Maxwellian distribution, regardless of collisionality. The low-collisionality forces are shown to be consistent with estimates based upon cross-sections for scattering in a Yukawa (shielded) grain field, but only if non-linear shielding length is used. Finite collisionality initially enhances the drag force, but only by up to a factor of 2. Larger collisionality eventually reduces the drag force. In the collisional regime, the drift distribution gives larger drag than the shift distribution even at velocities where their collisionless drags are equal. Comprehensive practical analytic formulas for force that fit the calculations are provided.

  20. Ion heating mechanism in a modified Penning discharge

    NASA Technical Reports Server (NTRS)

    Roth, J. R.

    1972-01-01

    Ions with Maxwellian energy distributions and kinetic temperatures ranging from 20 eV to 7 keV have been observed in a modified Penning discharge operating in the steady state. Investigation of the plasma revealed two distinct spoke-like concentrations of charge rotating with different velocities in the sheath between the plasma and the anode ring. The faster spoke consists of electrons rotating with the E/B drift velocity, where E is the electric field and B is the magnetic field strength. The slow spoke consists of ions, the thermal velocity of which is observed to be proportional to the spoke velocity. The experimental data are consistent with a model whereby the ion drift velocity in this spoke, corresponding to kilovolt ion energies, is Maxwellianized by strong electrostatic turbulence in the sheath. Theoretical expressions are derived for the frequency of the electron and ion spoke rotation, for the ion kinetic temperature, and for the ion heating efficiency as functions of the discharge parameters. These expressions are shown to be consistent with extensive experimental data.

  1. Anomalous drift of spiral waves in heterogeneous excitable media

    NASA Astrophysics Data System (ADS)

    Sridhar, S.; Sinha, Sitabhra; Panfilov, Alexander V.

    2010-11-01

    We study the drift of spiral waves in a simple model of heterogeneous excitable medium, having gradients in the distribution of ion-channel expression or cellular coupling. We report the anomalous drift of spiral waves toward regions having shorter period or stronger coupling, in reaction-diffusion models of excitable media. Such anomalous drift can promote the onset of complex spatiotemporal patterns, e.g., those responsible for life-threatening arrhythmias in the heart.

  2. Digisonde Drift Analysis Software

    NASA Astrophysics Data System (ADS)

    Kozlov, Alexander V.; Paznukhov, Vadym V.

    2008-02-01

    This paper introduces a newly developed conceptual Java-based software package for the digisonde drift data analysis and visualization. This package replaced the less versatile Fortran-based applications previously developed at UMLCAR. A dedicated database intended for raw and processed drift data storage, access, and exchange has also been established and is described in this paper.

  3. Booktalking: Avoiding Summer Drift

    ERIC Educational Resources Information Center

    Whittingham, Jeff; Rickman, Wendy A.

    2015-01-01

    Summer drift, otherwise known as loss of reading comprehension skills or reading achievement, has been a well-known and well-documented phenomenon of public education for decades. Studies from the late twentieth century to the present have demonstrated a slowdown in summer drift attributed to specific summer reading programs addressing motivation

  4. Experimental test of instability enhanced collisional friction for determining ion loss in two ion species plasmas a)

    NASA Astrophysics Data System (ADS)

    Hershkowitz, N.; Yip, C.-S.; Severn, G. D.

    2011-05-01

    Recent experiments have shown that ions in weakly collisional plasmas containing two ion species of comparable densities approximately reach a common velocity at the sheath edge equal to the bulk plasma ion sound velocity. A recent theory [S. D. Baalrud, C. C. Hegna, and J. D. Callen, Phys. Rev. Lett. 103, 205002 (2009)] suggests that this is a consequence of collisional friction between the two ion species enhanced by the two stream instability. The theory finds that the difference in velocities at the sheath edge depends on the relative concentrations of the two ions. The difference in velocities is small, with both species approaching to the bulk sound velocity, when the concentrations are comparable, and is large, with each species reaching its own Bohm velocity, when the relative concentration differences are large. To test these findings, drift velocities of Ar and Xe ions were measured with laser-induced fluorescence in Ar-Xe and He-Xe plasmas and combined with ion acoustic wave and plasma potential data. In addition, electron temperature was varied by a Maxwell demon [K. R. MacKenzie et al., App. Phys. Lett. 18, 529 (1971)]. The predictions were found to be in excellent agreement with the experimental data. The generalized Bohm criterion in two ion species plasmas is also verified in a wider variety of relative ion concentrations.

  5. The ion experiment onboard the Interball-Aurora satellite; initial results on velocity-dispersed structures in the cleft and inside the auroral oval

    NASA Astrophysics Data System (ADS)

    Sauvaud, J. A.; Barthe, H.; Aoustin, C.; Thocaven, J. J.; Rouzaud, J.; Penou, E.; Popescu, D.; Kovrazhkin, R. A.; Afanasiev, K. G.

    1998-09-01

    The Toulouse ION experiment flown on the Russian Interball-Aurora mission performs simultaneous ion and electron measurements. Two mass spectrometers looking in opposing directions perpendicular to the satellite spin axis, which points toward the sun, measure ions in the mass and energy ranges 1-32 amu and ~0-14 000 eV. Two electron spectrometers also looking in opposing directions perform measurements in the energy range ~10 eV-20 000 eV. The Interball-Aurora spacecraft was launched on 29 August 1996 into a 62.8 inclination orbit with an apogee of ~3 RE. The satellite orbital period is 6 h, so that every four orbits the satellite sweeps about the same region of the auroral zone; the orbit plane drifts around the pole in ~9 months. We present a description of the ION experiment and discuss initial measurements performed in the cusp near noon, in the polar cleft at dusk, and inside the proton aurora at dawn. Ion-dispersed energy structures resulting from time-of-flight effects are observed both in the polar cleft at ~16 hours MLT and in the dawnside proton aurora close to 06 hours MLT. Magnetosheath plasma injections in the polar cleft, which appear as overlapping energy bands in particle energy-time spectrograms, are traced backwards in time using a particle trajectory model using 3D electric and magnetic field models. We found that the cleft ion source is located at distances of the order of 18 RE from the earth at about 19 MLT, i.e., on the flank of the magnetopause. These observations are in agreement with flux transfer events (FTE) occurring not only on the front part of the magnetopause but also in a region extending at least to dusk. We also show that, during quiet magnetic conditions, time-of-flight ion dispersions can also be measured inside the dawn proton aurora. A method similar to that used for the cleft is applied to these auroral energy dispersion signatures. Unexpectedly, the ion source is found to be at distances of the order of 60-80 RE, at the dawn flank of the magnetosphere. These results are discussed in terms of possible entry, acceleration, and precipitation mechanisms.

  6. Drift distance survey in DPIS for high current beam production

    SciTech Connect

    Kanesue,T.; Okamura, M.; Kondo, K.; Tamura, J.; Kashiwagi, H.; Zhang, Z.

    2009-09-20

    In a laser ion source, plasma drift distance is one of the most important design parameters. Ion current density and beam pulse width are defined by plasma drift distance between laser target and beam extraction position. In direct plasma injection scheme (DPIS), which uses a laser ion source and Radio Frequency Quadrupole (RFQ) linac, we can apply relatively higher electric field at the beam extraction due to the unique shape of a positively biased electrode. However, when we aim at very high current acceleration like several tens of mA, we observed mismatched beam extraction conditions. We tested three different ion current at ion extraction region by changing plasma drift distance to study better extraction condition. In this experiment, C{sup 6+} beam was accelerated. We confirmed that the matching condition can be improved by controlling plasma drift distance.

  7. Ion beams from laser-generated plasmas

    NASA Technical Reports Server (NTRS)

    Hughes, R. H.; Anderson, R. J.; Gray, L. G.; Rosenfeld, J. P.; Manka, C. K.; Carruth, M. R.

    1980-01-01

    The paper describes the space-charge-limited beams produced by the plasma blowoffs generated by 20-MW bursts of 1.06-micron radiation from an active Q-switched Nd:YAG laser. Laser power densities near 10 to the 11th/sq cm on solid targets generate thermalized plasma plumes which drift to a 15-kV gridded extraction gap where the ions are extracted, accelerated, and electrostatically focused; the spatially defined ion beams are then magnetically analyzed to determine the charge state content in the beams formed from carbon, aluminum, copper, and lead targets. This technique preserves time-of-flight (TOF) information in the plasma drift region, which permits plasma ion temperatures and mass flow velocities to be determined from the Maxwellian ion curve TOF shapes for the individual charge species.

  8. Abstraction of Drift Seepage

    SciTech Connect

    J.T. Birkholzer

    2004-11-01

    This model report documents the abstraction of drift seepage, conducted to provide seepage-relevant parameters and their probability distributions for use in Total System Performance Assessment for License Application (TSPA-LA). Drift seepage refers to the flow of liquid water into waste emplacement drifts. Water that seeps into drifts may contact waste packages and potentially mobilize radionuclides, and may result in advective transport of radionuclides through breached waste packages [''Risk Information to Support Prioritization of Performance Assessment Models'' (BSC 2003 [DIRS 168796], Section 3.3.2)]. The unsaturated rock layers overlying and hosting the repository form a natural barrier that reduces the amount of water entering emplacement drifts by natural subsurface processes. For example, drift seepage is limited by the capillary barrier forming at the drift crown, which decreases or even eliminates water flow from the unsaturated fractured rock into the drift. During the first few hundred years after waste emplacement, when above-boiling rock temperatures will develop as a result of heat generated by the decay of the radioactive waste, vaporization of percolation water is an additional factor limiting seepage. Estimating the effectiveness of these natural barrier capabilities and predicting the amount of seepage into drifts is an important aspect of assessing the performance of the repository. The TSPA-LA therefore includes a seepage component that calculates the amount of seepage into drifts [''Total System Performance Assessment (TSPA) Model/Analysis for the License Application'' (BSC 2004 [DIRS 168504], Section 6.3.3.1)]. The TSPA-LA calculation is performed with a probabilistic approach that accounts for the spatial and temporal variability and inherent uncertainty of seepage-relevant properties and processes. Results are used for subsequent TSPA-LA components that may handle, for example, waste package corrosion or radionuclide transport.

  9. The complex mixed Wentzel–Kramers–Brillouin-full-wave approach and its application to the two dimensional mode structure analysis of ion temperature gradient/collisionless trapped electron mode drift waves

    SciTech Connect

    Lu, Z. X.

    2015-05-15

    The complex mixed Wentzel–Kramers–Brillouin (WKB)-full-wave approach is applied to the 2D mode structure analysis of ion temperature gradient/collisionless trapped electron mode drift waves in tokamak plasmas. The parallel mode structure is calculated with the full-wave approach, while the radial envelope is calculated with the complex WKB method. The tilting of the global mode structure along radius is demonstrated analytically. The effects of the phase and amplitude variation of the radial envelope on the parallel mode structure are included in terms of a complex radial wave vector in the parallel mode equation. It is shown that the radial equilibrium non-uniformity leads to the asymmetry of the parallel mode structure not only in configuration space but also in spectrum space. The mixed approach provides a practical way to analyze the asymmetric component of the global mode structure due to radial equilibrium non-uniformity.

  10. Thermal Electron Contributions to Current-Driven Instabilities: SCIFER Observations in the 1400-km Cleft Ion Fountain and Their Implications to Thermal Ion Energization

    NASA Astrophysics Data System (ADS)

    Adrian, M. L.; Pollock, C. J.; Moore, T. E.; Kintner, P. M.; Arnoldy, R. L.

    2001-12-01

    SCIFER TECHS observations of the variations in the thermal electron distribution in the 1400-km altitude cleft are associated with periods of intense ion heating and field-aligned currents. Energization of the thermal ion plasma in the mid-altitude cleft occurs within density cavities accompanied by enhanced thermal electron temperatures, large field-aligned thermal electron plasma flows and broadband low-frequency electric fields. Variations in the thermal electron contribution to field-aligned current densities indicate small scale ( ~100's m) filamentary structure embedded within the ion energization periods. TECHS observations of the field-aligned drift velocities and temperatures of the thermal electron distribution are presented to evaluate the critical velocity thresholds necessary for the generation of electrostatic ion cyclotron and ion acoustic instabilities. This analysis suggests that, during periods of thermal ion energization, sufficient drift exists in the thermal electron distribution to excite the electrostatic ion cyclotron instability. In addition, brief periods exist within the same interval where the drift of the thermal electron distribution is sufficient to marginally excite the ion acoustic instability. In addition, the presence an enhancement in Langmuir emission at the plasma frequency at the center of the ion energization region, accompanied by the emission's second-harmonic, and collocated with observations of high-frequency electric field solitary structures suggest the presence of electron beam driven decay of Langmuir waves to ion acoustic modes as an additional free energy source for ion energization.

  11. Thermal Electron Contributions to Current-Driven Instabilities: SCIFER Observations in the 1400-km Cleft Ion Fountain and Their Implications to Thermal Ion Energization

    NASA Technical Reports Server (NTRS)

    Adrian, Mark L.; Pollock, C. J.; Moore, T. E.; Kintner, P. M.; Arnoldy, R. L.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    SCIFER TECHS observations of the variations in the thermal electron distribution in the 1400-km altitude cleft are associated with periods of intense ion heating and field-aligned currents. Energization of the thermal ion plasma in the mid-altitude cleft occurs within density cavities accompanied by enhanced thermal electron temperatures, large field-aligned thermal electron plasma flows and broadband low-frequency electric fields. Variations in the thermal electron contribution to field-aligned current densities indicate small scale (approximately 100's m) filamentary structure embedded within the ion energization periods. TECHS observations of the field-aligned drift velocities and temperatures of the thermal electron distribution are presented to evaluate the critical velocity thresholds necessary for the generation of electrostatic ion cyclotron and ion acoustic instabilities. This analysis suggests that, during periods of thermal ion energization, sufficient drift exists in the thermal electron distribution to excite the electrostatic ion cyclotron instability. In addition, brief periods exist within the same interval where the drift of the thermal electron distribution is sufficient to marginally excite the ion acoustic instability. In addition, the presence an enhancement in Langmuir emission at the plasma frequency at the center of the ion energization region, accompanied by the emission's second-harmonic, and collocated with observations of high-frequency electric field solitary structures suggest the presence of electron beam driven decay of Langmuir waves to ion acoustic modes as an additional free energy source for ion energization.

  12. Generalized Drift-Diffusion Model In Semiconductors

    SciTech Connect

    Mesbah, S.; Bendib-Kalache, K.; Bendib, A.

    2008-09-23

    A new drift-diffusion model is proposed based on the computation of the stationary nonlocal current density. The semi classical Boltzmann equation is solved keeping all the anisotropies of the distribution function with the use of the continued fractions. The conductivity is calculated in the linear approximation and for arbitrary collision frequency with respect to Kv{sub t} where K{sup -1} is the characteristic length scale of the system and V{sub t} is the thermal velocity. The nonlocal conductivity can be used to close the generalized drift-diffusion equations valid for arbitrary collisionality.

  13. Relative drifts and temperature anisotropies of protons and α particles in the expanding solar wind: 2.5D hybrid simulations

    NASA Astrophysics Data System (ADS)

    Maneva, Y. G.; Ofman, L.; Viñas, A.

    2015-06-01

    Context. We perform 2.5D hybrid simulations to investigate the origin and evolution of relative drift speeds between protons and α particles in the collisionless turbulent low- tildeβ solar wind plasma. Aims: We study the generation of differential streaming by wave-particle interactions and absorption of turbulent wave spectra. Next we focus on the role of the relative drifts for the turbulent heating and acceleration of ions in the collisionless fast solar wind streams. Methods: The energy source is given by an initial broad-band spectrum of parallel propagating Alfvén-cyclotron waves, which co-exists with the plasma and is self-consistently coupled to the perpendicular ion bulk velocities. We include the effect of a gradual solar wind expansion, which cools and decelerates the minor ions. We here consider for the first time the combined effect of self-consistently initialized dispersive turbulent Alfvénic spectra with differentially streaming protons and α particles in the expanding solar wind outflows within a 2.5D hybrid simulation study. Results: For differential streaming of Vαp < 0.5VA, the selected initial wave spectrum accelerates the minor ions in the non-expanding wind. At Vαp = 0.5VA the relative drift speed remains nearly steady. For ions that stream below this threshold value, the waves act to increase the magnitude of the relative drift speed. Ions that stream faster than the threshold value become subject to a nonlinear streaming instability, and as the system evolves, their bulk velocities decrease. We find that the solar wind expansion strongly affects the relative drift speed and significantly slows down both ion species for all values of the relative drift speeds considered in this study. The initial nonresonant wave spectra interact with the particles, resulting in preferential and anisotropic heating for the minor ions with a prominent increase of their perpendicular temperature, which overcomes the effect of the double-adiabatic cooling that is due to the solar wind expansion. Finally, the initial parallel spectra undergo a micro-turbulent nonlinear cascade during which oblique waves are generated, whose intensity depends on the value of the relative drift speed.

  14. Dust magneto-gravitational drift wave in g×B configuration

    SciTech Connect

    Salahshoor, M. Niknam, A. R.

    2014-11-15

    The dispersion relation of electrostatic waves in a magnetized complex plasma under gravity is presented. It is assumed that the waves propagate perpendicular to the external fields. The effects of weak electric field, neutral drag force, and ion drag force are also taken into account. The dispersion relation is numerically examined in an appropriate parameter space in which the gravity plays the dominant role in the dynamics of magnetized microparticles. The numerical results show that an unstable low frequency drift wave can be developed in the long wavelength limit. This unstable mode is transformed into an aperiodic stationary structure at a cut-off wavenumber. Furthermore, the influence of the external fields on the dispersion properties is analyzed. It is shown that the instability is essentially due to the E×B drift motion of plasma particles. However, in the absence of weak electric field, the g×B drift motion of microparticles can cause the instability in a wide range of wavenumbers. It is also found that by increasing the magnetic field strength, the wave frequency is first increased and then decreased. This behaviour is explained by the existence of an extremum point in the dust magneto-gravitational drift velocity.

  15. Origins of ion irradiation-induced Ga nanoparticle motion on GaAs surfaces

    SciTech Connect

    Kang, M.; Wu, J. H.; Chen, H. Y.; Thornton, K.; Goldman, R. S.; Sofferman, D. L.; Department of Physics, Adelphi University, Garden City, New York 11530-0701 ; Beskin, I.

    2013-08-12

    We have examined the origins of ion irradiation-induced nanoparticle (NP) motion. Focused-ion-beam irradiation of GaAs surfaces induces random walks of Ga NPs, which are biased in the direction opposite to that of ion beam scanning. Although the instantaneous NP velocities are constant, the NP drift velocities are dependent on the off-normal irradiation angle, likely due to a difference in surface non-stoichiometry induced by the irradiation angle dependence of the sputtering yield. It is hypothesized that the random walks are initiated by ion irradiation-induced thermal fluctuations, with biasing driven by anisotropic mass transport.

  16. Note on the electric splitting of drift shells. [in magnetospheric convection electric field

    NASA Technical Reports Server (NTRS)

    Kivelson, M. G.; Southwood, D. J.

    1975-01-01

    A nonrelativistic analysis is presented for the deviation of a particle from its dipole magnetic drift shell in the presence of an electric field. An alternative definition of weak shell splitting is introduced in which the corotation drift velocity need not be small with respect to the azimuthal magnetic drift velocity. Approximate explicit solutions are obtained for the asymmetry of drift shells in the strong shell splitting case, i.e., for the case where the cross-magnetosphere potential drop is not small compared to particle kinetic energy. Upper limits to drift shell asymmetry are obtained from considerations of the Alfven layer.

  17. Ionospheric vertical drifts over an Indian low latitude station and its comparison with IRI-2007 vertical drift model

    NASA Astrophysics Data System (ADS)

    Saranya, P. L.; Prasad, D. S. V. V. D.; Rama Rao, P. V. S.

    2014-09-01

    The vertical plasma drift velocity (Vz=dh‧F/dt) of the Ionospheric F-Region is calculated using the Ionosonde data over an Indian low latitude station, Waltair (17.7°N, 83.3°E, dip 20°N). The vertical drift velocities thus computed are compared with those of the IRI-2007 vertical drift model during the post sunset hours of the high sunspot period of 2001-2002. The vertical drift values are entirely downward between 2000 and 0700 h LT for the IRI-2007 vertical drift model compared to those derived using Ionosonde. The root mean square errors (RMSE) in the vertical drifts during the post sun-set hours computed between the IRI vertical drift model and Ionosonde measured values are found to be 13.54, 21.68 and 22.39 m/s for summer, equinox and winter seasons respectively. The average vertical drifts derived using Ionosonde showing pre-reversal enhancements during evening hours (1700-1900 h LT) over Waltair are found to be 8, 16 and 12 m/s, whereas the IRI-2007 model derived values show 15, 35 and 36 m/s during summer, equinox and winter seasons respectively. The correlation analysis of peak drift velocities derived using Ionosonde and those from IRI model with Rz and F10.7 shows more or less similar variation while they are differed in their variation with Ap index. A good correlation is observed between the vertical plasma drift obtained using Ionosonde and Equatorial Electrojet Strength (EEJ) except during winter, while the correlation coefficients computed using IRI model are little higher than those obtained using Ionosonde with maximum values during summer season. The percentage of deviation for IRI-model correlation coefficient and that of Ionosonde-inferred drift for equinoctial and summer months is around 50% and 25% respectively where as it is more than 100% for winter.

  18. Simulation of the DRIFT Experiment

    NASA Astrophysics Data System (ADS)

    Hyatt, Matt; Ayad, Rachid; Hanson-Hart, Zach; Katz-Hyman, Moshe; Posner, Aaron; Martoff, C. J.

    2003-04-01

    The DRIFT Experiment [1] is an underground search for WIMP Dark Matter using a novel detector invented for this purpose: the Negative Ion TPC (NITPC). To aid in interpreting the results, a simulation code system has been developed. The system uses the CERNLIB program GEANT [2] and the NRC package EGS4 [3] to simulate particle interactions in the detector. These are linked directly to the CERNLIB program GARFIELD, which simulates signal production in the NITPC. Finally the GARFIELD output is converted into the format of the DRIFT DAQ for presentation to the analysis code. The physics and software issues dealt with in this development will be discussed. [1] Low Pressure Negative Ion TPC for Dark Matter Search. D. P. Snowden-Ifft, C. J. Martoff, J. M. Burwell, Phys Rev. D. Rapid Comm. 61, 101301 (2000) [2] GEANT Manual, CERN Program Library Long Writeup W5013, Copyright CERN, Geneva, 1993 . [3] EGS4, National Research Council, Canada. Note PIRS-701. http://www.irs.inms.nrc.ca/inms/irs/EGS4/get_egs4.html . [4] GARFIELD Manual, version 7.04, CERN Program Library Long Writeup W5050, Copyright CERN, Geneva, 2001 .

  19. Drift and reactions of positive tetratomic ions in dry, atmospheric air: Their effects on the dynamics of primary and secondary streamers

    NASA Astrophysics Data System (ADS)

    Bekstein, A.; Yousfi, M.; Benhenni, M.; Ducasse, O.; Eichwald, O.

    2010-05-01

    The ion swarm data, namely, the reduced mobility, diffusion, and reaction rates of the positive tetratomic ions O4+ and N2O2+ in N2 and O2 have been determined from a Monte Carlo simulation using calculated and fitted elastic and inelastic cross sections. The elastic momentum transfer cross sections have been determined from a semiclassical Jeffreys-Wentzell-Kramers-Brilouin (JWKB) approximation based on a rigid core potential model well adapted for polyatomic ions. The inelastic cross sections have been approximated from considerations based on the N4+/O2 and N4+/N2 systems. The validated cross section sets in pure N2 and O2 have been used to determine the O4+ and N2O2+ swarm data in dry air over a large E/N range up to 1000 Td. However, due to the lack of experimental ion transport coefficients necessary for a more rigorous cross section validation, the present data, validated only at low E/N, should be regarded as a first approximation, susceptible to improvements as soon as measurements of ion transport coefficients become available in the literature. Then, the present data are used in a two-dimensional discharge dynamics fluid model for the simulation of the primary and secondary streamers for the case of a positive point-to-plane corona discharge in dry air. Relevant characteristics such as discharge current, charged particle densities, space charge electric field and the variation in active species like N and O radicals (very useful in many nonthermal plasma applications) are analyzed and discussed with and without the consideration of three positive tetratomic ions (N4+, O4+, and N2O2+). More particularly, the non-negligible effect of O4+, in the dynamics of the primary and secondary streamers during the discharge propagation and relaxation stages is highlighted with an emphasis on the role of the related kinetic reactions occurring between the different charged particles.

  20. Lithium drifted germanium system

    NASA Technical Reports Server (NTRS)

    Fjarlie, E. J.

    1969-01-01

    General characteristics of the lithium-drifted germanium photodiode-Dewar-preamplifier system and particular operating instructions for the device are given. Information is included on solving operational problems.

  1. Electronic Excitation and Charge Transfer Processes in Collisions of H+, H_2^+, and H_3^+ Ions with Carbon Monoxide at Typical Solar-wind Velocities

    NASA Astrophysics Data System (ADS)

    Werbowy, S.; Pranszke, B.

    2014-01-01

    Luminescence in the 200-580 nm spectral region was observed in the collisions of H+, H_2^+, and H_3^+ with CO in the 50-1000 eV projectile energy range. Using computer simulations, we have identified emission of the following products in the observed spectra: the CO+(A-X) comet-tail system, CO+(B-X) first negative system, CO+(B-A) Baldet-Johnson system, and CO(b-a) third positive system. Also, an emission from atomic hydrogen (H? line at 486nm) has been observed. From the analysis of the experimental spectra, we have determined the absolute emission cross-sections for the formation of the observed products. Computer simulations gave the excited-product population distributions over vibrational and rotational energy levels. The vibrational level distribution from the CO+(A-X) comet-tail system is compared with the data for CO excited by 100 eV electrons and extreme ultraviolet radiation (XUV) photons. We have used these data to analyze the excitation conditions in the comet Humason (1961e). From the vibrational population distributions observed in the comet, we found that this distribution can be reproduced if electrons produce 25%, protons 70%, and XUV photons produce 5% of the emitting molecules. We find that the ratio of the CO+(B-X) emission to the sum of two main emissions (CO+(A-X)+CO+(B-X)) is velocity dependent and does not depend on the projectile ion type. For small velocities (below 100 km s-1) the ratio is about 5%, while for higher velocities it increases to 30%. For these data, we have found an empirical formula that satisfactorily describes the experimental data: R = R max(1 - v th/v), (where R max = 33%, v th = 87 km s-1). This could be used to infer the velocity of ions producing the observed emission of CO+ products.

  2. Search for the best timing strategy in high-precision drift chambers

    SciTech Connect

    Va'vra, J.

    1983-06-01

    Computer simulated drift chamber pulses are used to investigate various possible timing strategies in the drift chambers. In particular, the leading edge, the multiple threshold and the flash ADC timing methods are compared. Although the presented method is general for any drift geometry, we concentrate our discussion on the jet chambers where the drift velocity is about 3 to 5 cm/..mu..sec and the individual ionization clusters are not resolved due to a finite speed of our electronics.

  3. Cross sections for electron capture from atomic hydrogen by fully stripped ions in the 0.05--1.00 a.u. impact velocity range

    SciTech Connect

    Harel, C.; Jouin, H.; Pons, B.

    1998-03-01

    The authors have calculated electron capture cross sections from atomic hydrogen with the molecular approach to atomic collisions for impact velocities between 0.05 and 1 a.u. The projectile ions are H{sup +}, He{sup 2+}, Li{sup 3+}, Be{sup 4+}, B{sup 5+}, C{sup 6+}, N{sup 7+}, and O{sup 8+}. For the four most strongly populated capture channels, cross sections are tabulated for each value of the final quantum numbers n, l, m, summed over m for the given n and l and over l and m for the given n.

  4. Computation of two-dimensional electric field from the ion laser induced fluorescence measurements

    SciTech Connect

    Spektor, Rostislav

    2010-09-15

    This paper presents a method of computing two-dimensional electric field from ion laser induced fluorescence (LIF) measurements in a plasma flow. The expression for the field is derived by taking velocity moments of the Boltzmann equation for ions. It was found that the pressure tensor, related to the width of the ion velocity distribution, plays a critical role in the computation of the electric field. Even with the assumption of cold ion flow, the pressure tensor contribution may be significant when velocity spread is caused by other forces. Such a situation occurs in the flow of a Hall thruster, where velocity spread is caused by the ions born at different potentials. LIF measurements of the cylindrical hall thruster plume were used to demonstrate practical application of the derived method. Whenever the pressure tensor components are small as compared to the mean ion drift velocity, the electric field calculations reduce to a simple expression given in terms of mean ion drift velocity and its divergence.

  5. Study of plasma meniscus and beam halo in negative ion sources using three dimension in real space and three dimension in velocity space particle in cell model

    SciTech Connect

    Nishioka, S. Goto, I.; Hatayama, A.; Miyamoto, K.; Okuda, S.; Fukano, A.

    2014-02-15

    Our previous study by two dimension in real space and three dimension in velocity space-particle in cell model shows that the curvature of the plasma meniscus causes the beam halo in the negative ion sources. The negative ions extracted from the periphery of the meniscus are over-focused in the extractor due to the electrostatic lens effect, and consequently become the beam halo. The purpose of this study is to verify this mechanism with the full 3D model. It is shown that the above mechanism is essentially unchanged even in the 3D model, while the fraction of the beam halo is significantly reduced to 6%. This value reasonably agrees with the experimental result.

  6. Continuous Wave Cavity Ring-Down Spectroscopy and Laser Induced Fluorescence Measurements of Argon Ion Velocity Distribution Functions in a Helicon Plasma

    NASA Astrophysics Data System (ADS)

    McCarren, Dustin; Vandervort, Robert; Soderholm, Mark; Scime, Earl

    2014-10-01

    LIF is an established and powerful technique, but suffers from the requirement that the initial state of the LIF sequence have a substantial density. This usually limits LIF to ions and atoms with large metastable state densities for the given plasma conditions. Cavity ring down spectroscopy (CRDS) is a proven, ultra-sensitive, cavity enhanced absorption spectroscopy technique and when combined with a continuous wavelength (CW) diode laser that has a sufficiently narrow line width, the Doppler broadened absorption line, i.e., the target specie velocity distribution function (VDFs), is measured. CW-CRDS is designed for measurements of ion and atom states inaccessible to conventional techniques such as LIF. However, being a line integrated technique, CW-CRDS lacks the spatial resolution of LIF. We present a comparison of CW-CRDS and spatially resolved LIF measurements of the VDFs in an argon plasma using the 668.614 nm (in vacuum) line of Ar II.

  7. A very wide bandwidth Faraday cup suitable for measuring gigahertz structure on ion beams with velocities down to. beta. lt 0. 01

    SciTech Connect

    Bogaty, J.M.; Pardo, R.C.; Clifft, B.E.

    1990-01-01

    A stripline Faraday Cup of exceptional bandwidth (DC to 6.1 gigahertz) has been developed. An electrostatic shield in the ground-plane geometry prevents electric-field coupling of incoming ions so that the time distribution of low-velocity ({beta} {approx gt} .01c) particles can be measured. The cup is very rugged compared to other detectors used for ion-bunch timing measurements. We have measured bunch widths of 400 picoseconds on 3.9 MeV {sup 84}Kr{sup +15} beams (200 nanoampere average). Bunch widths down to 100 picoseconds should be observable with a sampling oscilloscope. Beam bunch shapes have been monitored at current levels of 1.0 nanoampere to 10 microampere average.

  8. Study of plasma meniscus and beam halo in negative ion sources using three dimension in real space and three dimension in velocity space particle in cell model.

    PubMed

    Nishioka, S; Miyamoto, K; Okuda, S; Goto, I; Hatayama, A; Fukano, A

    2014-02-01

    Our previous study by two dimension in real space and three dimension in velocity space-particle in cell model shows that the curvature of the plasma meniscus causes the beam halo in the negative ion sources. The negative ions extracted from the periphery of the meniscus are over-focused in the extractor due to the electrostatic lens effect, and consequently become the beam halo. The purpose of this study is to verify this mechanism with the full 3D model. It is shown that the above mechanism is essentially unchanged even in the 3D model, while the fraction of the beam halo is significantly reduced to 6%. This value reasonably agrees with the experimental result. PMID:24593471

  9. Electromagnetic drift waves dispersion for arbitrarily collisional plasmas

    NASA Astrophysics Data System (ADS)

    Lee, Wonjae; Angus, J. R.; Krasheninnikov, Sergei I.

    2015-07-01

    The impacts of the electromagnetic effects on resistive and collisionless drift waves are studied. A local linear analysis on an electromagnetic drift-kinetic equation with Bhatnagar-Gross-Krook-like collision operator demonstrates that the model is valid for describing linear growth rates of drift wave instabilities in a wide range of plasma parameters showing convergence to reference models for limiting cases. The wave-particle interactions drive collisionless drift-Alfvn wave instability in low collisionality and high beta plasma regime. The Landau resonance effects not only excite collisionless drift wave modes but also suppress high frequency electron inertia modes observed from an electromagnetic fluid model in collisionless and low beta regime. Considering ion temperature effects, it is found that the impact of finite Larmor radius effects significantly reduces the growth rate of the drift-Alfvn wave instability with synergistic effects of high beta stabilization and Landau resonance.

  10. Drift Scale THM Model

    SciTech Connect

    J. Rutqvist

    2004-10-07

    This model report documents the drift scale coupled thermal-hydrological-mechanical (THM) processes model development and presents simulations of the THM behavior in fractured rock close to emplacement drifts. The modeling and analyses are used to evaluate the impact of THM processes on permeability and flow in the near-field of the emplacement drifts. The results from this report are used to assess the importance of THM processes on seepage and support in the model reports ''Seepage Model for PA Including Drift Collapse'' and ''Abstraction of Drift Seepage'', and to support arguments for exclusion of features, events, and processes (FEPs) in the analysis reports ''Features, Events, and Processes in Unsaturated Zone Flow and Transport and Features, Events, and Processes: Disruptive Events''. The total system performance assessment (TSPA) calculations do not use any output from this report. Specifically, the coupled THM process model is applied to simulate the impact of THM processes on hydrologic properties (permeability and capillary strength) and flow in the near-field rock around a heat-releasing emplacement drift. The heat generated by the decay of radioactive waste results in elevated rock temperatures for thousands of years after waste emplacement. Depending on the thermal load, these temperatures are high enough to cause boiling conditions in the rock, resulting in water redistribution and altered flow paths. These temperatures will also cause thermal expansion of the rock, with the potential of opening or closing fractures and thus changing fracture permeability in the near-field. Understanding the THM coupled processes is important for the performance of the repository because the thermally induced permeability changes potentially effect the magnitude and spatial distribution of percolation flux in the vicinity of the drift, and hence the seepage of water into the drift. This is important because a sufficient amount of water must be available within a drift to transport any exposed radionuclides out of the drift to the groundwater below, and eventually to people within the accessible environment. Absent sufficient water, radionuclides cannot be transported and there would be no significant health effect on people, even if radioactive waste containers were damaged or corroded to such an extent that radionuclides were exposed to water.

  11. Drag Coefficients of Drifting Waterbirds

    NASA Astrophysics Data System (ADS)

    von Ellenrieder, Karl; Kenow, Kevin; Qu, Huajin (Ariel); Su, Tsung-Chow (Joe)

    2013-11-01

    A series of towing tank experiments has been performed to support the development of a probabilistic source tracking model that can be used to estimate the origin of waterbird die-offs. While monitoring the appearance of waterbird carcasses on beaches provides the primary means of assessing the magnitude, as well as the spatial and temporal patterns of die-offs, interpreting the actual site of exposure to toxins is hampered by a lack of information on the drift patterns of carcasses and the confounding influences of wind/current. In this work, a series of experimental measurements were conducted on Common Loon and Lesser Scaup carcasses to obtain steady drag coefficients of representative waterbird species. The tests were designed to capture the drag coefficients associated with current speeds of between 0.2 and 0.8 meters per second and wind speeds of up to 10 meters per second at different levels of carcass submergence. Using the submerged frontal area of an ellipse, together with the frontal area of any submerged portions of the head and neck gives good similarity across the ranges of speeds and submergence levels tested. An example approach to determining waterbird drift velocity and direction from knowledge of the drag coefficients, wind and current is provided. This effort was supported by the US Geological Survey.

  12. Laser initiated reactions in N{sub 2}O clusters studied by time-sliced ion velocity imaging technique

    SciTech Connect

    Honma, Kenji

    2013-07-28

    Laser initiated reactions in N{sub 2}O clusters were studied by a time-sliced velocity imaging technique. The N{sub 2}O clusters, (N{sub 2}O){sub n}, generated by supersonic expansion were irradiated by an ultraviolet laser around 204 nm to convert reactant pairs, O({sup 1}D{sub 2})-(N{sub 2}O){sub n?1}. The NO molecules formed from these reactant pairs were ionized by the same laser pulse and their velocity distribution was determined by the time-sliced velocity imaging technique. At low nozzle pressure, lower than 1.5 atm, the speed distribution in the frame moving with the clusters consists of two components. These components were ascribed to the products appeared in the backward and forward directions in the center-of-mass frame, respectively. The former consists of the vibrational ground state and the latter consists of highly vibrational excited states. At higher nozzle pressure, a single broad speed distribution became dominant for the product NO. The pressure and laser power dependences suggested that this component is attributed to the product formed in the clusters larger than dimer, (N{sub 2}O){sub n} (n ? 3)

  13. Numerical simulation of drifting snow sublimation in the saltation layer

    PubMed Central

    Dai, Xiaoqing; Huang, Ning

    2014-01-01

    Snow sublimation is an important hydrological process and one of the main causes of the temporal and spatial variation of snow distribution. Compared with surface sublimation, drifting snow sublimation is more effective due to the greater surface exposure area of snow particles in the air. Previous studies of drifting snow sublimation have focused on suspended snow, and few have considered saltating snow, which is the main form of drifting snow. In this study, a numerical model is established to simulate the process of drifting snow sublimation in the saltation layer. The simulated results show 1) the average sublimation rate of drifting snow particles increases linearly with the friction velocity; 2) the sublimation rate gradient with the friction velocity increases with increases in the environmental temperature and the undersaturation of air; 3) when the friction velocity is less than 0.525?m/s, the snowdrift sublimation of saltating particles is greater than that of suspended particles; and 4) the snowdrift sublimation in the saltation layer is less than that of the suspended particles only when the friction velocity is greater than 0.625?m/s. Therefore, the drifting snow sublimation in the saltation layer constitutes a significant portion of the total snow sublimation. PMID:25312383

  14. Numerical simulation of drifting snow sublimation in the saltation layer

    NASA Astrophysics Data System (ADS)

    Dai, Xiaoqing; Huang, Ning

    2014-10-01

    Snow sublimation is an important hydrological process and one of the main causes of the temporal and spatial variation of snow distribution. Compared with surface sublimation, drifting snow sublimation is more effective due to the greater surface exposure area of snow particles in the air. Previous studies of drifting snow sublimation have focused on suspended snow, and few have considered saltating snow, which is the main form of drifting snow. In this study, a numerical model is established to simulate the process of drifting snow sublimation in the saltation layer. The simulated results show 1) the average sublimation rate of drifting snow particles increases linearly with the friction velocity; 2) the sublimation rate gradient with the friction velocity increases with increases in the environmental temperature and the undersaturation of air; 3) when the friction velocity is less than 0.525 m/s, the snowdrift sublimation of saltating particles is greater than that of suspended particles; and 4) the snowdrift sublimation in the saltation layer is less than that of the suspended particles only when the friction velocity is greater than 0.625 m/s. Therefore, the drifting snow sublimation in the saltation layer constitutes a significant portion of the total snow sublimation.

  15. Silicon drift detectors as tracking devices

    NASA Astrophysics Data System (ADS)

    Takahashi, J.; Bellwied, R.; Beuttenmuller, R.; Caines, H.; Chen, W.; Dyke, H.; Hoffmann, G. W.; Humanic, T.; Jensen, P.; Kuczewski, P.; Leonhardt, W.; Li, Z.; Lynn, D.; Curto, G. Lo; Minor, R.; Schambach, J.; Soja, R.; Sugarbaker, E.; Willson, R. M.; Pandey, S. U.

    2000-10-01

    Silicon drift detectors provide unambiguous two-dimensional position information for charged particle detection in a single detector layer. Like most other semi-conductor technologies, Silicon drift detectors are presently used in vertexing detectors. By taking into account, the drastic reduction in channel count compared to other silicon-based devices this specific technology is also well suited for large coverage tracking detectors. The first larger area Silicon Drift Tracker (6.3 cm6.3 cm) was developed as the inner tracking detector (SVT) of the STAR experiment at the RHIC collider. Advantages and limitations of this detector will be discussed. Recent results of detector performance based on an application in a heavy ion fixed target experiment at the BNL-AGS (E896) are presented.

  16. Ion-molecule reaction dynamics: Velocity map imaging studies of N+ and O+ with CD3OD

    NASA Astrophysics Data System (ADS)

    Pei, Linsen; Farrar, James M.

    2015-08-01

    We present a study of the charge transfer reactions of the atomic ions N+and O+ with methanol in the collision energy range from 2 to 4 eV. Charge transfer is driven primarily by energy resonance, although the widths of the product kinetic energy distributions suggest that significant interchange between relative translation and product vibration occurs. Charge transfer with CD3OD is more exoergic for N+, and the nascent parent ion products appear to be formed in excited B and C electronic states, and fragment to CD2OD+ by internal conversion and vibrational relaxation to the ground electronic state. The internal excitation imparted to the parent ion is sufficient to result in loss of one or two D atoms from the carbon atom. The less exoergic charge transfer reaction of O+ forms nascent parent ions in the excited A state, and internal conversion to the ground state only results in ejection of single D atom. Selected isotopomers of methanol were employed to identify reaction products, demonstrating that deuterium atom loss from nascent parent ions occurs by C-D bond cleavage. Comparison of the kinetic energy distributions for charge transfer to form CD3OD+ and CD2OD+ by D atom loss with the known dynamics for hydride abstraction from a carbon atom provides strong evidence that the D loss products are formed by dissociative charge transfer rather than hydride (deuteride) transfer. Isotopic labeling also demonstrates that chemical reaction in the N+ + CD3OD system to form NO+ + CD4 does not occur in the energy range of these experiments, contrary to earlier speculation in the literature.

  17. Drift Degradation Analysis

    SciTech Connect

    D. Kicker

    2004-09-16

    Degradation of underground openings as a function of time is a natural and expected occurrence for any subsurface excavation. Over time, changes occur to both the stress condition and the strength of the rock mass due to several interacting factors. Once the factors contributing to degradation are characterized, the effects of drift degradation can typically be mitigated through appropriate design and maintenance of the ground support system. However, for the emplacement drifts of the geologic repository at Yucca Mountain, it is necessary to characterize drift degradation over a 10,000-year period, which is well beyond the functional period of the ground support system. This document provides an analysis of the amount of drift degradation anticipated in repository emplacement drifts for discrete events and time increments extending throughout the 10,000-year regulatory period for postclosure performance. This revision of the drift degradation analysis was developed to support the license application and fulfill specific agreement items between the U.S. Nuclear Regulatory Commission (NRC) and the U.S. Department of Energy (DOE). The earlier versions of ''Drift Degradation Analysis'' (BSC 2001 [DIRS 156304]) relied primarily on the DRKBA numerical code, which provides for a probabilistic key-block assessment based on realistic fracture patterns determined from field mapping in the Exploratory Studies Facility (ESF) at Yucca Mountain. A key block is defined as a critical block in the surrounding rock mass of an excavation, which is removable and oriented in an unsafe manner such that it is likely to move into an opening unless support is provided. However, the use of the DRKBA code to determine potential rockfall data at the repository horizon during the postclosure period has several limitations: (1) The DRKBA code cannot explicitly apply dynamic loads due to seismic ground motion. (2) The DRKBA code cannot explicitly apply loads due to thermal stress. (3) The DRKBA code, which determines structurally controlled key-block failure, is not applicable for stress-controlled failure in the lithophysal units. To address these limitations, additional numerical codes have been included that can explicitly apply seismic and thermal loads, providing significant improvements to the analysis of drift degradation and extending the validity of drift degradation models.

  18. Spiral silicon drift detectors

    SciTech Connect

    Rehak, P.; Gatti, E.; Longoni, A.; Sampietro, M.; Holl, P.; Lutz, G.; Kemmer, J.; Prechtel, U.; Ziemann, T.

    1988-01-01

    An advanced large area silicon photodiode (and x-ray detector), called Spiral Drift Detector, was designed, produced and tested. The Spiral Detector belongs to the family of silicon drift detectors and is an improvement of the well known Cylindrical Drift Detector. In both detectors, signal electrons created in silicon by fast charged particles or photons are drifting toward a practically point-like collection anode. The capacitance of the anode is therefore kept at the minimum (0.1pF). The concentric rings of the cylindrical detector are replaced by a continuous spiral in the new detector. The spiral geometry detector design leads to a decrease of the detector leakage current. In the spiral detector all electrons generated at the silicon-silicon oxide interface are collected on a guard sink rather than contributing to the detector leakage current. The decrease of the leakage current reduces the parallel noise of the detector. This decrease of the leakage current and the very small capacities of the detector anode with a capacitively matched preamplifier may improve the energy resolution of Spiral Drift Detectors operating at room temperature down to about 50 electrons rms. This resolution is in the range attainable at present only by cooled semiconductor detectors. 5 refs., 10 figs.

  19. Computer simulations of H{sup +} and H{sub 3}{sup +} transport parameters in hydrogen drift tubes

    SciTech Connect

    Simko, T.; Martisovits, V.; Bretagne, J.; Gousset, G.

    1997-11-01

    The coupled transport of H{sup +} and H{sub 3}{sup +} ions in molecular hydrogen is theoretically studied by using drift-tube-like computer simulations. The drift velocity and the longitudinal and the transverse diffusion coefficients of these ions are calculated for the reduced electric field E/n (where n is the gas density) ranging from 10 to 600 Td (1 Td=10{sup {minus}17} Vcm{sup 2}). A large influence of the rotational and vibrational H{sup +}-H{sub 2} excitations is noted even at low E/n for H{sup +} ions. The presence of ion conversion reactions in collisions with background gas during the transport is shown to influence the transport parameters from about 150 Td. A comparison with experimentally determined transport parameters is performed with the aim of testing available scattering models: the collisional cross-section values are adjusted to get a good agreement with experimental ion mobilities. A relatively good agreement is obtained also for the longitudinal and the transverse diffusion coefficients, which indicates the consistency of the refined cross-section set. However, the transverse diffusion coefficient of H{sub 3}{sup +} ions exhibits larger deviation from experimental results at higher E/n; as a possible explanation the role of proton-transfer and vibrational-excitation channels in H{sub 3}{sup +}-H{sub 2} collisions is discussed. {copyright} {ital 1997} {ital The American Physical Society}

  20. Ballistic Mass And Velocity Analyzer

    NASA Technical Reports Server (NTRS)

    Chutjian, Ara; Smith, Steven J.; Hecht, Michael

    1996-01-01

    Proposed device for measuring distribution of masses and velocities of ions in plasma or ion beam of general type denoted variously as mass, velocity, and energy analyzers. Yields indications of charge-to-mass ratios and velocities; from these quantities, one computes masses and energies if one also either measures charges of ions by other means or else makes realistic assumption that each ion carries small number (usually 1) of fundamental units of electric charge. In comparison with older devices of this type, device smaller, and operates faster, yielding simultaneous indications of both charge-to-mass ratios and velocities.

  1. Charge state effect on the K-shell ionization of iron by xenon ions near the Bohr velocity

    NASA Astrophysics Data System (ADS)

    Zhou, Xian-Ming; Zhao, Yong-Tao; Ren, Jie-Ru; Cheng, Rui; Lei, Yu; Sun, Yuan-Bo; Xu, Ge; Wang, Yu-Yu; Liu, Shi-Dong; Xiao, Guo-Qing

    2013-11-01

    Fe K-shell ionization cross sections induced by 2.4-6.0 MeV Xe20+ are measured and compared with different binary-encounter-approximation (BEA) models. The results indicate that the BEA model corrected both by the Coulomb repulsion and by the effective nuclear charge (Zeff) agrees well with the experimental data. Comparison of Fe K-shell X-ray emission induced by 5 MeV xenon ions with different initial charge states (20+, 22+, 26+, 30+) verifies the applicability of the effective nuclear charge (Zeff) correction for the BEA model. It is found that Zeff correction is reasonable to describe direct ionization induced by xenon ions with no initial M-shell vacancies. However, when the M shell is opened, the Zeff corrected BEA model is unable to explain the inner-shell ionization, and the electron transfer by molecular-orbital promotion should be considered.

  2. Drift Wave Turbulence

    SciTech Connect

    Horton, W.; Kim, J.-H.; Asp, E.; Hoang, T.

    2008-05-14

    Drift waves occur universally in magnetized plasmas producing the dominant mechanism for transport of particles, energy and momentum across magnetic field lines. A wealth of information obtained from laboratory experiments for plasma confinement is reviewed for drift waves driven unstable by density gradients, temperature gradients and trapped particle effects. The modern understanding of origin of the scaling laws for Bohm and gyro-Bohm transport fluxes is discussed. The role of sheared flows and magnetic shear in reducing the transport fluxes is discussed and illustrated with large scale computer simulations. Plasmas turbulence models are derived with reduced magnetized fluid descriptions. The types of theoretical descriptions reviewed include weak turbulence theory and anisotropic Kolmogorov-like spectral indices, and the mixing length. A number of standard turbulent diffusivity formulas are given for the various space-time scales of the drift-wave turbulent mixing.

  3. Influence of plasma beta on the generation of lower hybrid and whistler waves by an ion velocity ring distribution

    DOE PAGESBeta

    Winske, D.; Daughton, W.

    2015-02-02

    We present results of three-dimensional electromagnetic particle-in-cell simulations of the lower hybrid ion ring instability, similar to our earlier results [D. Winske and W. Daughton, Phys. Plasma, 19, 072109, 2012], but at higher electron beta (βe = ratio of electron thermal pressure to magnetic pressure = 0.06, rather than at 0.006) with Ti = Te. At higher electron beta the level of lower hybrid waves at saturation normalized to the ion thermal energy (βi = 0.06 also) is only slightly smaller, but the corresponding magnetic fluctuations are about an order of magnitude larger, consistent with linear theory. After saturation, themore » waves evolve into whistler waves, through a number of possible mechanisms, with an average growth rate considerably smaller than the linear growth rate of the lower hybrid waves, to a peak fluctuation level that is about 20% above the lower hybrid wave saturation level. The ratio of the peak magnetic fluctuations associated with the whistler waves relative to those of the saturated lower hybrid waves, the ratio of the nonlinear growth rate of whistlers relative to the linear growth rate of lower hybrid waves, the amount of energy extracted from the ring and the amount of heating of the background ions and electrons are comparable to those in the lower electron beta 3-D simulation. This suggests that even at higher electron beta, the linear and nonlinear physics of the lower hybrid ion ring instability is dominated by electrostatic, wave-particle rather than wave-wave interactions.« less

  4. Experimental limits on the velocities of sodium atoms sputtered from solid surfaces by hydrogen ions. [Na cloud production around Io

    NASA Technical Reports Server (NTRS)

    Stoner, J. O., Jr.

    1976-01-01

    Optical emission at 589.0 nm by sodium atoms sputtered from solid targets by hydrogen molecular ions was observed, and no accompanying broadening or shifts of this line could be detected relative to that from a laboratory lamp. This allowed an upper limit of about 500,000 cm/sec on the mean speed of ejected sodium atoms to be calculated. The results are consistent with the hypothesis that the atomic sodium cloud surrounding Io is produced by this mechanism.

  5. Influence of plasma beta on the generation of lower hybrid and whistler waves by an ion velocity ring distribution

    SciTech Connect

    Winske, D.; Daughton, W.

    2015-02-02

    We present results of three-dimensional electromagnetic particle-in-cell simulations of the lower hybrid ion ring instability, similar to our earlier results [D. Winske and W. Daughton, Phys. Plasma, 19, 072109, 2012], but at higher electron beta (βe = ratio of electron thermal pressure to magnetic pressure = 0.06, rather than at 0.006) with Ti = Te. At higher electron beta the level of lower hybrid waves at saturation normalized to the ion thermal energy (βi = 0.06 also) is only slightly smaller, but the corresponding magnetic fluctuations are about an order of magnitude larger, consistent with linear theory. After saturation, the waves evolve into whistler waves, through a number of possible mechanisms, with an average growth rate considerably smaller than the linear growth rate of the lower hybrid waves, to a peak fluctuation level that is about 20% above the lower hybrid wave saturation level. The ratio of the peak magnetic fluctuations associated with the whistler waves relative to those of the saturated lower hybrid waves, the ratio of the nonlinear growth rate of whistlers relative to the linear growth rate of lower hybrid waves, the amount of energy extracted from the ring and the amount of heating of the background ions and electrons are comparable to those in the lower electron beta 3-D simulation. This suggests that even at higher electron beta, the linear and nonlinear physics of the lower hybrid ion ring instability is dominated by electrostatic, wave-particle rather than wave-wave interactions.

  6. Influence of plasma beta on the generation of lower hybrid and whistler waves by an ion velocity ring distribution

    SciTech Connect

    Winske, D. Daughton, W.

    2015-02-15

    We present results of three-dimensional electromagnetic particle-in-cell simulations of the lower hybrid ion ring instability, similar to our earlier results [D. Winske and W. Daughton, Phys. Plasma 19, 072109 (2012)], but at higher electron beta (?{sub e}?=?ratio of electron thermal pressure to magnetic pressure?=?0.06, rather than at 0.006) with T{sub i}?=?T{sub e}. At higher electron beta, the level of lower hybrid waves at saturation normalized to the ion thermal energy (?{sub i}?=?0.06 also) is only slightly smaller, but the corresponding magnetic fluctuations are about an order of magnitude larger, consistent with linear theory. After saturation, the waves evolve into whistler waves, through a number of possible mechanisms, with an average growth rate considerably smaller than the linear growth rate of the lower hybrid waves, to a peak fluctuation level that is about 20% above the lower hybrid wave saturation level. The ratio of the peak magnetic fluctuations associated with the whistler waves relative to those of the saturated lower hybrid waves, the ratio of the nonlinear growth rate of whistlers relative to the linear growth rate of lower hybrid waves, the amount of energy extracted from the ring, and the amount of heating of the background ions and electrons are comparable to those in the lower electron beta 3D simulation. This suggests that even at higher electron beta, the linear and nonlinear physics of the lower hybrid ion ring instability is dominated by electrostatic, wave-particle rather than wave-wave interactions.

  7. Hamiltonian fluid reductions of electromagnetic drift-kinetic equations for an arbitrary number of moments

    NASA Astrophysics Data System (ADS)

    Tassi, E.

    2015-11-01

    We present an infinite family of Hamiltonian electromagnetic fluid models for plasmas, derived from drift-kinetic equations. An infinite hierarchy of fluid equations is obtained from a Hamiltonian drift-kinetic system by taking moments of a generalized distribution function and using Hermite polynomials as weight functions of the velocity coordinate along the magnetic guide field. Each fluid model is then obtained by truncating the hierarchy to a finite number N + 1 of equations by means of a closure relation. We show that, for any positive N, a linear closure relation between the moment of order N + 1 and the moment of order N guarantees that the resulting fluid model possesses a Hamiltonian structure, thus respecting the Hamiltonian character of the parent drift-kinetic model. An orthogonal transformation is identified which maps the fluid moments to a new set of dynamical variables in terms of which the Poisson brackets of the fluid models become a direct sum and which unveils remarkable dynamical properties of the models in the two-dimensional (2D) limit. Indeed, when imposing translational symmetry with respect to the direction of the magnetic guide field, all models belonging to the infinite family can be reformulated as systems of advection equations for Lagrangian invariants transported by incompressible generalized velocities. These are reminiscent of the advection properties of the parent drift-kinetic model in the 2D limit and are related to the Casimirs of the Poisson brackets of the fluid models. The Hamiltonian structure of the generic fluid model belonging to the infinite family is illustrated treating a specific example of a fluid model retaining five moments in the electron dynamics and two in the ion dynamics. We also clarify the connection existing between the fluid models of this infinite family and some fluid models already present in the literature.

  8. Transient and steady drift currents in waves damped by surfactants

    NASA Astrophysics Data System (ADS)

    Christensen, Kai Haakon

    2005-04-01

    In this paper we study the Lagrangian mean drift induced by spatially damped capillary-gravity waves on a surface covered by an elastic film. The analysis is developed with regard to a typical laboratory setup, and explicit solutions for both transient and steady horizontal drift velocities are given. We consider a situation where the film covers the entire surface and is prevented from drifting away, e.g., by a film barrier. The drift below an inextensible film resembles the drift under an ice cover, with a jetlike current in the wave propagation direction just below the surface. If the film is elastic the solution changes drastically. For certain values of the film elasticity parameter the mean flow is in the direction opposite to that of wave propagation in the upper part of the water column.

  9. DC Electric Fields, Associated Plasma Drifts, and Irregularities Observed on the C/NOFS Satellite

    NASA Technical Reports Server (NTRS)

    Pfaff, R.; Freudenreich, H.; Klenzing, J.

    2011-01-01

    Results are presented from the Vector Electric Field Investigation (VEFI) on the Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite, a mission designed to understand, model, and forecast the presence of equatorial ionospheric irregularities. The VEFI instrument includes a vector DC electric field detector, a fixed-bias Langmuir probe operating in the ion saturation regime, a flux gate magnetometer, an optical lightning detector, and associated electronics including a burst memory. Compared to data obtained during more active solar conditions, the ambient DC electric fields and their associated E x B drifts are variable and somewhat weak, typically < 1 mV/m. Although average drift directions show similarities to those previously reported, eastward/outward during day and westward/downward at night, this pattern varies significantly with longitude and is not always present. Daytime vertical drifts near the magnetic equator are largest after sunrise, with smaller average velocities after noon. Little or no pre-reversal enhancement in the vertical drift near sunset is observed, attributable to the solar minimum conditions creating a much reduced neutral dynamo at the satellite altitude. The nighttime ionosphere is characterized by larger amplitude, structured electric fields, even where the plasma density appears nearly quiescent. Data from successive orbits reveal that the vertical drifts and plasma density are both clearly organized with longitude. The spread-F density depletions and corresponding electric fields that have been detected thus far have displayed a preponderance to appear between midnight and dawn. Associated with the narrow plasma depletions that are detected are broad spectra of electric field and plasma density irregularities for which a full vector set of measurements is available for detailed study. The VEFI data represents a new set of measurements that are germane to numerous fundamental aspects of the electrodynamics and irregularities inherent to the Earth s low latitude ionosphere.

  10. The "zebra stripes": An effect of F region zonal plasma drifts on the longitudinal distribution of radiation belt particles

    NASA Astrophysics Data System (ADS)

    Lejosne, Solène; Roederer, Juan G.

    2016-01-01

    We examine a characteristic effect, namely, the ubiquitous appearance of structured peaks and valleys called zebra stripes in the spectrograms of energetic electrons and ions trapped in the inner belt below L ~ 3. We propose an explanation of this phenomenon as a purely kinematic consequence of particle drift velocity modulation caused by F region zonal plasma drifts in the ionosphere. In other words, we amend the traditional assumption that the electric field associated with ionospheric plasma drives trapped particle distributions into rigid corotation with the Earth. An equation based on a simple first-order model is set up to determine quantitatively the appearance of zebra stripes as a function of magnetic time. Our numerical predictions are in agreement with measurements by the Radiation Belt Storm Probes Ion Composition Experiment detector onboard Van Allen Probes, namely: (1) the central energy of any peak identified in the spectrum on the dayside is the central energy of a spectral valley on the night side, and vice versa; (2) there is also an approximate peak-to-valley inversion when comparing the spectrum of trapped electrons with that of trapped ions in the same place; and (3) the actual energy separation between two consecutive peaks (or number of stripes) in the spectrogram of a trapped population is an indicator of the time spent by the particles drifting under quiet conditions.

  11. On the height variation of the equatorial F region vertical plasma drifts

    SciTech Connect

    Pingree, J.E.; Fejer, B.G. )

    1987-05-01

    The authors have used improved incoherent scatter radar measurements at the Jicamarca Radio Observatory to study the height variation of the F region vertical plasma drift velocity (driven by the zonal electric field) during moderately quiet conditions. Preliminary results indicate a nearly linear change of the vertical drift velocity with altitude between 200 and 700 km, but with considerable day-to-day variations in the value of the slope. On the average, the velocity gradients are positive in the late night and morning periods and negative during the afternoon and evening hours. Simultaneous vertical and zonal drift measurements confirm that the measured height variation of the vertical drift is consistent with the existence of a curl free electric field in the low latitude ionosphere. The time dependence of the Jicamarca vertical drifts extrapolated to higher altitudes closely resembles the diurnal variation of the drift component due to the zonal electric field observed at F region heights over Arecibo.

  12. Measuring the effect of ion-induced drift-gas polarization on the electrical mobilities of multiply-charged ionic liquid nanodrops in air.

    PubMed

    Fernndez-Garca, Juan; Fernndez de la Mora, Juan

    2013-12-01

    The electrical mobilities of multiply-charged nanodrops of the ionic liquid 1-ethyl, 3-methylimidazolium dicyanamide (EMI-N[CN]2) were accurately measured in air at 20 C for mass-selected clusters of composition [EMI-N[CN]2] n [EMI(+)] z , with 2 ? n ? 369 and 1 ? z ? 10. We confirm prior reports that the mobility Z of a globular ion of mass m is given approximately by the modified Stokes-Millikan law for spheres, Z? = ?Z SM,mod (d m ? + ?d g ,?z,?m), where d m ? = ?(6m/??)(1/3) is the nanodrop mass-diameter based on the density ? of the liquid (corrected for the capillary compression and electrostatic deformation of the nanodrop), and d g is an effective air molecule diameter. There is however a measurable (up to 7%) and systematic z-dependent departure of Z from Z SM,mod . As theoretically expected at small ? (*) , this effect is accurately described by a simple correction factor of the form Z/Z SM,mod ? = ??(1? - ??? (*)), where kT? (*) is the potential energy due to the ion-induced dipole (polarization) attraction between a perfectly-conducting charged nanodrop and a polarized neutral gas-molecule at a distance (d m ? + ?d g )/2 from its center. An excellent fit of this model to hundreds of data points is found for d g ? 0.26 nm, ? ? 0.36, and ? ? 0.954. Accounting for the effect of polarization decreases d g considerably with respect to values inferred from earlier nanodrop measurements that ignored this effect. In addition, and in spite of ambiguities in the mobility calibration scale, the measured constant ? smaller than unity increases Millikan's drag enhancement factor from the accepted value ? m ? 1.36 to the new value ? ? ? m /? ? 1.42? 0.03. PMID:24048890

  13. Measuring the Effect of Ion-Induced Drift-Gas Polarization on the Electrical Mobilities of Multiply-Charged Ionic Liquid Nanodrops in Air

    NASA Astrophysics Data System (ADS)

    Fernndez-Garca, Juan; Fernndez de la Mora, Juan

    2013-12-01

    The electrical mobilities of multiply-charged nanodrops of the ionic liquid 1-ethyl, 3-methylimidazolium dicyanamide (EMI-N[CN]2) were accurately measured in air at 20 C for mass-selected clusters of composition [EMI-N[CN]2] n [EMI+] z , with 2 ? n ? 369 and 1 ? z ? 10. We confirm prior reports that the mobility Z of a globular ion of mass m is given approximately by the modified Stokes-Millikan law for spheres, Z = Z SM, mod ( d m + d g , z, m), where d m = (6 m/ ??)1/3 is the nanodrop mass-diameter based on the density ? of the liquid (corrected for the capillary compression and electrostatic deformation of the nanodrop), and d g is an effective air molecule diameter. There is however a measurable (up to 7 %) and systematic z-dependent departure of Z from Z SM,mod . As theoretically expected at small ? * , this effect is accurately described by a simple correction factor of the form Z/ Z SM, mod = ?(1 - ?? *), where kT? * is the potential energy due to the ion-induced dipole ( polarization) attraction between a perfectly-conducting charged nanodrop and a polarized neutral gas-molecule at a distance ( d m + d g )/2 from its center. An excellent fit of this model to hundreds of data points is found for d g ? 0.26 nm, ? ? 0.36, and ? ? 0.954. Accounting for the effect of polarization decreases d g considerably with respect to values inferred from earlier nanodrop measurements that ignored this effect. In addition, and in spite of ambiguities in the mobility calibration scale, the measured constant ? smaller than unity increases Millikan's drag enhancement factor from the accepted value ? m ? 1.36 to the new value ? ? ? m / ? ? 1.42 0.03.

  14. Charged particle flows in the beam extraction region of a negative ion source for NBI

    NASA Astrophysics Data System (ADS)

    Geng, S.; Tsumori, K.; Nakano, H.; Kisaki, M.; Ikeda, K.; Osakabe, M.; Nagaoka, K.; Takeiri, Y.; Shibuya, M.; Kaneko, O.

    2016-02-01

    Experiments by a four-pin probe and photodetachment technique were carried out to investigate the charged particle flows in the beam extraction region of a negative hydrogen ion source for neutral beam injector. Electron and positive ion flows were obtained from the polar distribution of the probe saturation current. Negative hydrogen ion flow velocity and temperature were obtained by comparing the recovery times of the photodetachment signals at opposite probe tips. Electron and positive ions flows are dominated by crossed field drift and ambipolar diffusion. Negative hydrogen ion temperature is evaluated to be 0.12 eV.

  15. Control and generation of drifting patterns by asymmetrical Fourier filtering

    NASA Astrophysics Data System (ADS)

    Louvergneaux, E.; Odent, V.; Coulibaly, S.; Bortolozzo, U.; Residori, S.

    2016-01-01

    We report the theoretical and experimental demonstration of one-dimensional drifting patterns generated by asymmetrical Fourier filtering in the transverse plane of an optical feedback system with a Kerr type nonlinearity. We show, with good agreement between our theoretical (analytics and numerics) calculations and experimental observations that at the primary instability threshold the group velocity is always different from zero. Consequently, the system is convective at this threshold, then exhibits drifting patterns.

  16. Electrostatic ion-cyclotron waves in a nonuniform magnetic field

    NASA Technical Reports Server (NTRS)

    Cartier, S. L.; Dangelo, N.; Merlino, R. L.

    1985-01-01

    The properties of electrostatic ion-cyclotron waves excited in a single-ended cesium Q machine with a nonuniform magnetic field are described. The electrostatic ion-cyclotron waves are generated in the usual manner by drawing an electron current to a small exciter disk immersed in the plasma column. The parallel and perpendicular (to B) wavelengths and phase velocities are determined by mapping out two-dimensional wave phase contours. The wave frequency f depends on the location of the exciter disk in the nonuniform magnetic field, and propagating waves are only observed in the region where f is approximately greater than fci, where fci is the local ion-cyclotron frequency. The parallel phase velocity is in the direction of the electron drift. From measurements of the plasma properties along the axis, it is inferred that the electron drift velocity is not uniform along the entire current channel. The evidence suggests that the waves begin being excited at that axial position where the critical drift velocity is first exceeded, consistent with a current-driven excitation mechanism.

  17. SRA: a new ion accelerator scheme

    SciTech Connect

    Choe, J.Y.; Uhm, H.S.

    1983-08-01

    The space-charge resonance accelerator consists of a relativistic electron beam propagating through a dielectric loaded drift tube. In a range of physical parameters, the phase velocity of a self-growing space-charge wave increases slowly from zero to a large beam velocity as it propagates into the downstream region, thereby trapping and accelerating ions with its electric field. The self-growing mechanism of the space-charge wave is a typical Cherenkov radiation. This paper presents schematics and calculation methods which describe the accelerator, its dynamics, and its fields.

  18. Effects of centrifugal drift on hurricane structure and intensity

    NASA Astrophysics Data System (ADS)

    Tripoli, G. J.; Hashino, T.; Lewis, W.

    2009-04-01

    High (1km) resolution simulations of the 2005 hurricane Wilma were conducted using the UW-NMS which models the effect of horizontal precipitation drift due to centrifugal force. The extremely tight nature of Wilma's vortex suggests that there should be a measurable horizontal drift of precipitation, comparable to the vertical motion, that is due to centrifugal terminal velocity. These effects would likely unload the updraft in the central core of the storm. Explicit calculations of this effect will be presented at the oral presentation and implications of centrifugal horizontal drift to the general 3D structure of a tropical cyclone will be discussed.

  19. Lower Hybrid Drift in Simulations of Hypersonic Plasma

    NASA Astrophysics Data System (ADS)

    Niehoff, D.; Ashour-Abdalla, M.; Niemann, C.; Schriver, D.; Sotnikov, V. I.; Lapenta, G.

    2014-12-01

    It has been shown experimentally that hypersonic plasma (defined as moving with a bulk flow velocity of more than 5 to 10 times the Mach speed) traveling through a magnetic field will create a diamagnetic cavity, or bubble [1]. At the edge of the bubble, opposing field and density gradients can drive the lower hybrid drift instability [2]. We will explore two and a half dimensional (2 space and 3 velocity dimensions) simulations of hypersonic plasma within a parameter regime motivated by the aforementioned diamagnetic bubble experiments, wherein we find oscillations excited near the lower hybrid frequency propagating perpendicular to the bulk motion of the plasma and the background magnetic field. The simulations are run using the implicit PIC code iPIC3D so that we are able to capture dynamics of the plasma below ion scales, but not be forced to resolve all electron scales [3]. [1] Niemann et al, Phys. Plasmas 20, 012108 (2013) [2] Davidson et al, Phys. Fluids, Vol. 20, No. 2, February 1977 [3] S. Markidis et al, Math. Comput. Simul. (2009), doi 10.1016/j.matcom.2009.08.038

  20. IN DRIFT CORROSION PRODUCTS

    SciTech Connect

    D.M. Jolley

    1999-12-02

    As directed by a written development plan (CRWMS M&O 1999a), a conceptual model for steel and corrosion products in the engineered barrier system (EBS) is to be developed. The purpose of this conceptual model is to assist Performance Assessment Operations (PAO) and its Engineered Barrier Performance Department in modeling the geochemical environment within a repository drift, thus allowing PAO to provide a more detailed and complete in-drift geochemical model abstraction and to answer the key technical issues (KTI) raised in the NRC Issue Resolution Status Report (IRSR) for the Evolution of the Near-Field Environment (NFE) Revision 2 (NRC 1999). This document provides the conceptual framework for the in-drift corrosion products sub-model to be used in subsequent PAO analyses including the EBS physical and chemical model abstraction effort. This model has been developed to serve as a basis for the in-drift geochemical analyses performed by PAO. However, the concepts discussed within this report may also apply to some near and far-field geochemical processes and may have conceptual application within the unsaturated zone (UZ) and saturated zone (SZ) transport modeling efforts.

  1. Continental drift before 1900.

    PubMed

    Rupke, N A

    1970-07-25

    The idea that Francis Bacon and other seventeenth and eighteenth century thinkers first conceived the notion of continental drift does not stand up to close scrutiny. The few authors who expressed the idea viewed the process as a catastrophic event. PMID:16057953

  2. High resolution drift chambers

    SciTech Connect

    Va'vra, J.

    1985-07-01

    High precision drift chambers capable of achieving less than or equal to 50 ..mu..m resolutions are discussed. In particular, we compare so called cool and hot gases, various charge collection geometries, several timing techniques and we also discuss some systematic problems. We also present what we would consider an ''ultimate'' design of the vertex chamber. 50 refs., 36 figs., 6 tabs.

  3. A Benign, Low Z Electron Capture Agent for Negative Ion TPCs

    NASA Technical Reports Server (NTRS)

    Martoff, C. J.; Dion, M. P.; Hosack, M.; Barton, D.; Black, J. K.

    2008-01-01

    We have identified nitromethane (CH3NO2) as an effective electron capture agent for negative ion TPCs (NITPCs). We present drift velocity and longitudinal diffusion measurements for negative ion gas mixtures using nitromethane as the capture agent. Not only is nitromethane substantially more benign than the only other identified capture agent, CS2, but its low atomic number will enable the use of the NITPC as a photoelectric X-ray polarimeter in the 1-10 keV band.

  4. Dike Propagation Near Drifts

    SciTech Connect

    NA

    2002-03-04

    The purpose of this Analysis and Model Report (AMR) supporting the Site Recommendation/License Application (SR/LA) for the Yucca Mountain Project is the development of elementary analyses of the interactions of a hypothetical dike with a repository drift (i.e., tunnel) and with the drift contents at the potential Yucca Mountain repository. This effort is intended to support the analysis of disruptive events for Total System Performance Assessment (TSPA). This AMR supports the Process Model Report (PMR) on disruptive events (CRWMS M&O 2000a). This purpose is documented in the development plan (DP) ''Coordinate Modeling of Dike Propagation Near Drifts Consequences for TSPA-SR/LA'' (CRWMS M&O 2000b). Evaluation of that Development Plan and the work to be conducted to prepare Interim Change Notice (ICN) 1 of this report, which now includes the design option of ''Open'' drifts, indicated that no revision to that DP was needed. These analyses are intended to provide reasonable bounds for a number of expected effects: (1) Temperature changes to the waste package from exposure to magma; (2) The gas flow available to degrade waste containers during the intrusion; (3) Movement of the waste package as it is displaced by the gas, pyroclasts and magma from the intruding dike (the number of packages damaged); (4) Movement of the backfill (Backfill is treated here as a design option); (5) The nature of the mechanics of the dike/drift interaction. These analyses serve two objectives: to provide preliminary analyses needed to support evaluation of the consequences of an intrusive event and to provide a basis for addressing some of the concerns of the Nuclear Regulatory Commission (NRC) expressed in the Igneous Activity Issue Resolution Status Report.

  5. Differences in drift behavior between drouged and undrogued satellite-tracked drifting buoys

    NASA Astrophysics Data System (ADS)

    Brgge, B.; Dengg, J.

    1991-04-01

    Drift behavior of drogued and undrogued Hermes-type buoys is studied. After drogue loss, an increase in drift speed and acceleration is observed as well as improved correlations between drift and wind in both speed and direction. With these criteria, a method for the separation of large data sets into a drogued and an undrogued part has been developed. In most areas of the North Atlantic this works very well; problems arise in regions with strong surface currents and/or light winds. A statistical analysis is performed in a selected area to demonstrate the errors that can be caused by indiscriminate use of drogued and undrogued drifters. Mean and rms velocities as well as kinetic energies change significantly when undrogued buoys are considered. Therefore caution is essential when using surface drifters without drogues.

  6. Effects of particle drifts on the solar modulation of galactic cosmic rays

    NASA Technical Reports Server (NTRS)

    Jokipii, J. R.; Levy, E. H.

    1977-01-01

    Gradient and curvature drifts in an Archimedean-spiral magnetic field are shown to produce a significant effect on the modulation of galactic cosmic rays by the solar wind. The net modulation, heliocentric radial gradient, and average energy change of particles which reach the inner solar system are significantly reduced. The effects of drifts are due to the fact that cosmic rays for which the drift velocity is comparable to the wind velocity or larger, have more rapid access to the inner solar system than in the absence of drifts.

  7. Study of ion-ion plasma formation in negative ion sources by a three-dimensional in real space and three-dimensional in velocity space particle in cell model

    NASA Astrophysics Data System (ADS)

    Nishioka, S.; Goto, I.; Miyamoto, K.; Hatayama, A.; Fukano, A.

    2016-01-01

    Recently, in large-scale hydrogen negative ion sources, the experimental results have shown that ion-ion plasma is formed in the vicinity of the extraction hole under the surface negative ion production case. The purpose of this paper is to clarify the mechanism of the ion-ion plasma formation by our three dimensional particle-in-cell simulation. In the present model, the electron loss along the magnetic filter field is taken into account by the " √{τ///τ⊥ } model." The simulation results show that the ion-ion plasma formation is due to the electron loss along the magnetic filter field. Moreover, the potential profile for the ion-ion plasma case has been looked into carefully in order to discuss the ion-ion plasma formation. Our present results show that the potential drop of the virtual cathode in front of the plasma grid is large when the ion-ion plasma is formed. This tendency has been explained by a relationship between the virtual cathode depth and the net particle flux density at the virtual cathode.

  8. Pre-sheath density drop induced by ion-neutral friction along plasma blobs and implications for blob velocities

    SciTech Connect

    Furno, I.; Chabloz, V.; Fasoli, A.; Loizu, J.; Theiler, C.

    2014-01-15

    The pre-sheath density drop along the magnetic field in field-aligned, radially propagating plasma blobs is investigated in the TORPEX toroidal experiment [Fasoli et al., Plasma Phys. Controlled Fusion 52, 124020 (2010)]. Using Langmuir probes precisely aligned along the magnetic field, we measure the density n{sub se} at a poloidal limiter, where blobs are connected, and the upstream density n{sub 0} at a location half way to the other end of the blobs. The pre-sheath density drop n{sub se}/n{sub 0} is then computed and its dependence upon the neutral background gas pressure is studied. At low neutral gas pressures, the pre-sheath density drop is ≈0.4, close to the value of 0.5 expected in the collisionless case. In qualitative agreement with a simple model, this value decreases with increasing gas pressure. No significant dependence of the density drop upon the radial distance into the limiter shadow is observed. The effect of reduced blob density near the limiter on the blob radial velocity is measured and compared with predictions from a blob speed-versus-size scaling law [Theiler et al., Phys. Rev. Lett. 103, 065001 (2009)].

  9. Drift wave instability in the Io plasma torus

    NASA Technical Reports Server (NTRS)

    Huang, T. S.; Hill, T. W.

    1991-01-01

    A linear normal mode analysis of the drift wave instability in the Io plasma torus was carried out on the basis of the Richmond (1973) and Huang et al. (1990) analyses of drift waves in the vicinity of the earth's plasmapause. Results indicate that the outer torus boundary is linearly unstable to the growth of electrostatic drift waves. It is shown that the linear growth rate is proportional to the ion drift frequency and to the ratio of the flux tube charge content to the Jovian ionospheric Pedersen conductance. It is also shown that various theoretical models of global radial transport in Jupiter's atmosphere (including corotating convection, interchange diffusion, and transient flux tube convection) can be understood as plausible nonlinear evolutions of electrostatic drift waves.

  10. Dual mode ion mobility spectrometer and method for ion mobility spectrometry

    DOEpatents

    Scott, Jill R [Idaho Falls, ID; Dahl, David A [Idaho Falls, ID; Miller, Carla J [Idaho Falls, ID; Tremblay, Paul L [Idaho Falls, ID; McJunkin, Timothy R [Idaho Falls, ID

    2007-08-21

    Ion mobility spectrometer apparatus may include an ion interface that is operable to hold positive and negative ions and to simultaneously release positive and negative ions through respective positive and negative ion ports. A first drift chamber is operatively associated with the positive ion port of the ion interface and encloses an electric field therein. A first ion detector operatively associated with the first drift chamber detects positive ions from the first drift chamber. A second drift chamber is operatively associated with the negative ion port of the ion interface and encloses an electric field therein. A second ion detector operatively associated with the second drift chamber detects negative ions from said second drift chamber.

  11. Photodissociation of the BrO radical using velocity map ion imaging: Excited state dynamics and accurate D{sub 0}{sup 0}(BrO) evaluation

    SciTech Connect

    Kim, Hahkjoon; Dooley, Kristin S.; Johnson, Elizabeth R.; North, Simon W.

    2006-04-07

    We have studied the photodissociation dynamics of expansion-cooled BrO radical both above (278-281.5 nm) and below (355 nm) the A {sup 2}{pi}{sub 3/2} state threshold using velocity map ion imaging. A recently developed late-mixing flash pyrolytic reactor source was utilized to generate an intense BrO radical molecular beam. The relative electronic product branching ratios at 355 nm and from 278 to 281.5 nm were determined. We have investigated the excited state dynamics based on both the product branching and the photofragment angular distributions. We find that above the O({sup 1}D{sub 2}) threshold the contribution of the direct excitation to states other than the A {sup 2}{pi}{sub 3/2} state and the role of curve crossing is considerably larger in BrO compared to that observed for ClO, in agreement with recent theoretical studies. The measurement of low velocity photofragments resulting from photodissociation just above the O({sup 1}D{sub 2}) threshold provides an accurate and direct determination of the A {sup 2}{pi}{sub 3/2} state dissociation threshold of 35418{+-}35 cm{sup -1}, leading to a ground state bond energy of D{sub 0}{sup 0}(BrO)=55.9{+-}0.1 kcal/mol.

  12. Results from the DRIFT Dark Matter Search

    NASA Astrophysics Data System (ADS)

    Ayad, R.; Hyatt, M.; Hanson-Hart, Z.; Katz-Hyman, M.; Martoff, C. J.; Kirkpatrick, J.; Snowden-Ifft, D. P.; Lawson, T. B.; Lightfoot, P. K.; Morgan, B.; Paling, S. M.; Robinson, M.; Spooner, N. J. C.

    2004-05-01

    DRIFT [1] is the only direction-sensitive WIMP Dark Matter search experiment now running underground. It employs a novel detector invented for this purpose: the Negative Ion TPC (NITPC). Data is collected in the form of digitized time-records of signals received on each active anode wire of the NITPC endcap. New Results from 2002 data taking will be presented, especially on underground neutron calibration and background. [1] Low Pressure Negative Ion TPC for Dark Matter Search. D. P.Snowden-Ifft, C. J. Martoff, J. M. Burwell, Phys Rev. D. Rapid Comm. 61,101301 (2000).

  13. Gyrokinetic simulation of momentum transport with residual stress from diamagnetic level velocity shears

    SciTech Connect

    Waltz, R. E.; Staebler, G. M.; Solomon, W. M.

    2011-04-15

    Residual stress refers to the remaining toroidal angular momentum (TAM) flux (divided by major radius) when the shear in the equilibrium fluid toroidal velocity (and the velocity itself) vanishes. Previously [Waltz et al., Phys. Plasmas 14, 122507 (2007); errata 16, 079902 (2009)], we demonstrated with GYRO [Candy and Waltz, J. Comp. Phys. 186, 545 (2003)] gyrokinetic simulations that TAM pinching from (ion pressure gradient supported or diamagnetic level) equilibrium ExB velocity shear could provide some of the residual stress needed to support spontaneous toroidal rotation against normal diffusive loss. Here we show that diamagnetic level shear in the intrinsic drift wave velocities (or ''profile shear'' in the ion and electron density and temperature gradients) provides a comparable residual stress. The individual signed contributions of these small (rho-star level) ExB and profile velocity shear rates to the turbulence level and (rho-star squared) ion energy transport stabilization are additive if the rates are of the same sign. However because of the additive stabilization effect, the contributions to the small (rho-star cubed) residual stress is not always simply additive. If the rates differ in sign, the residual stress from one can buck out that from the other (and in some cases reduce the stabilization.) The residual stress from these diamagnetic velocity shear rates is quantified by the ratio of TAM flow to ion energy (power) flow (M/P) in a global GYRO core simulation of a ''null'' toroidal rotation DIII-D [Mahdavi and Luxon, Fusion Sci. Technol. 48, 2 (2005)] discharge by matching M/P profiles within experimental uncertainty. Comparison of global GYRO (ion and electron energy as well as particle) transport flow balance simulations of TAM transport flow in a high-rotation DIII-D L-mode quantifies and isolates the ExB shear and parallel velocity (Coriolis force) pinching components from the larger ''diffusive'' parallel velocity shear driven component and the much smaller profile shear residual stress component.

  14. Gyrokinetic simulation of momentum transport with residual stress from diamagnetic level velocity shears

    NASA Astrophysics Data System (ADS)

    Waltz, R. E.; Staebler, G. M.; Solomon, W. M.

    2011-04-01

    Residual stress refers to the remaining toroidal angular momentum (TAM) flux (divided by major radius) when the shear in the equilibrium fluid toroidal velocity (and the velocity itself) vanishes. Previously [Waltz et al., Phys. Plasmas 14, 122507 (2007); errata 16, 079902 (2009)], we demonstrated with GYRO [Candy and Waltz, J. Comp. Phys. 186, 545 (2003)] gyrokinetic simulations that TAM pinching from (ion pressure gradient supported or diamagnetic level) equilibrium E B velocity shear could provide some of the residual stress needed to support spontaneous toroidal rotation against normal diffusive loss. Here we show that diamagnetic level shear in the intrinsic drift wave velocities (or "profile shear" in the ion and electron density and temperature gradients) provides a comparable residual stress. The individual signed contributions of these small (rho-star level) E B and profile velocity shear rates to the turbulence level and (rho-star squared) ion energy transport stabilization are additive if the rates are of the same sign. However because of the additive stabilization effect, the contributions to the small (rho-star cubed) residual stress is not always simply additive. If the rates differ in sign, the residual stress from one can buck out that from the other (and in some cases reduce the stabilization.) The residual stress from these diamagnetic velocity shear rates is quantified by the ratio of TAM flow to ion energy (power) flow (M/P) in a global GYRO core simulation of a "null" toroidal rotation DIII-D [Mahdavi and Luxon, Fusion Sci. Technol. 48, 2 (2005)] discharge by matching M/P profiles within experimental uncertainty. Comparison of global GYRO (ion and electron energy as well as particle) transport flow balance simulations of TAM transport flow in a high-rotation DIII-D L-mode quantifies and isolates the E B shear and parallel velocity (Coriolis force) pinching components from the larger "diffusive" parallel velocity shear driven component and the much smaller profile shear residual stress component.

  15. Rotation of a tenuous plasma with a high toroidal velocity in a Tokamak

    NASA Astrophysics Data System (ADS)

    Mikhailovskii, A. B.

    The question of plasma rotation in a Tokamak is of interest for problems of neoclassical transport and also for instability theory. In recent years, the original inferences of the neoclassical transport theory have been placed in doubt in some papers, for the reason that the influence of poloidal rotation of the plasma on the transport was not taken into account previously. Earlier, the rotation problem in the Pfirsch-Schleuter regime was considered and it was demonstrated that even with an essentially radial electric field, the velocity of poloidal rotation cannot substantially exceed the drift-temperature velocity of the ions. It follows from this that there is no basis for reconsideration of the neoclassical transport theory in the said regime. The problem of plasma rotation in the plateau and banana regimes was examined and it was demonstrated that the velocity of poloidal rotation in these regimes is also of the order of the drift-temperature velocity of the ions and thus is immaterial for transport problems.

  16. Vertical characteristics of midlatitude E and F region ionospheric drifts during disturbed conditions..

    NASA Astrophysics Data System (ADS)

    Boska, Josef; Kouba, Daniel; Koucka Knizova, Petra; Potuznikova, Katerina

    2015-04-01

    Modern HF digisonde DPS-4 D (Digisonde Portable Sounder), which is in operation at the Pruhonice observatory of the Institute of Atmospheric Physics, Prague (IAP) from 2004, enables us to carry out standard ionospheric sounding and ionospheric drifts measurements. Using standard mode of automatic drift (autodrift mode) measurements the velocity of the F region drifts is usually determined in the vicinity of the peak of the electron density profile (N(h) profile). Since 2005 we are also measuring ionospheric drifts at the heights of the ionospheric E region. This new experimental arrangement makes possible to study vertical changes and profiles of the ionospheric drift velocity in two different ionospheric regions. From E region within the altitudinal interval of 90-150 km to F region in altitudes from 150 km up to height of the maximum electron density profile N(h). This paper present the results of the analysis of the plasma drifts velocity in two different ionospheric regions observed under quiet geomagnetic and ionospheric conditions and especially during ionospheric spread F conditions. These spread F conditions are often observed in the ionosphere as effect of travelling ionopheric disturbances TIDs. The presence of this TIDS can be detected from the F layer isoelectrondensity contours. The spread F conditions are often present also under moderate-to-intense ionospheric and geomagnetic storm conditions. Our results shows, that behavior of Es layer drifts can be different than drifts in E-layer. During winter geomagnetic storm -more dramatic increasing of all drift velocities components was observed (50 - 100 m/s vertical drift component). Different behaviour ionospheric drifts at the heights intervals 90 - 110 km and 110 - 130 km was observed during winter storm. Significant height changes of the drift velocity height profile in the interval of heights 90 - 130 km during winter event was observed. Our results shows that behavior of Es layer drifts can be different than drifts in E-layer. All components of the ionospheric F region drift velocity, measured during medium and strong geomagnetic events are strongly disturbed by storm conditions. Observed drift velocity components reached during strong storm values ~100- 150 m/s during summer and ~500 m/s during winter storms.

  17. A photodissociation study of CH{sub 2}BrCl in the A-band using the time-sliced ion velocity imaging method

    SciTech Connect

    Zhou Jingang; Lau, K.-C.; Hassanein, Elsayed; Xu Haifeng; Tian Shanxi; Jones, Brant; Ng, C.Y.

    2006-01-21

    Employing a high-resolution (velocity resolution {delta}{nu}/{nu}<1.5%) time-sliced ion velocity imaging apparatus, we have examined the photodissociation of CH{sub 2}BrCl in the photon energy range of 448.6-618.5 kJ/mol (193.3-266.6 nm). Precise translational and angular distributions for the dominant Br({sup 2}P{sub 3/2}) and Br({sup 2}P{sub 1/2}) channels have been determined from the ion images observed for Br({sup 2}P{sub 3/2}) and Br({sup 2}P{sub 1/2}). In confirmation with the previous studies, the kinetic-energy distributions for the Br({sup 2}P{sub 1/2}) channel are found to fit well with one Gaussian function, whereas the kinetic- energy distributions for the Br({sup 2}P{sub 3/2}) channel exhibit bimodal structures and can be decomposed into a slow and a fast Gaussian component. The observed kinetic-energy distributions are consistent with the conclusion that the formation of the Br({sup 2}P{sub 3/2}) and Br({sup 2}P{sub 1/2}) channels takes place on a repulsive potential-energy surface, resulting in a significant fraction (0.40-0.47) of available energy to appear as translational energy for the photofragments. On the basis of the detailed kinetic-energy distributions and anisotropy parameters obtained in the present study, together with the specific features and relative absorption cross sections of the excited 2A{sup '}, 1A{sup ''}, 3A{sup '}, 4A{sup '}, and 2A{sup ''} states estimated in previous studies, we have rationalized the dissociation pathways of CH{sub 2}BrCl in the A-band, leading to the formation of the Br({sup 2}P{sub 3/2}) and Br({sup 2}P{sub 1/2}) channels. The analysis of the ion images observed at 235 nm for Cl({sup 2}P{sub 3/2,1/2}) provides strong evidence that the formation of Cl mainly arises from the secondary photodissociation process CH{sub 2}Cl+h{nu}{yields}CH{sub 2}+Cl.

  18. Drift wave instability in a nonuniform quantum dusty magnetoplasma

    NASA Astrophysics Data System (ADS)

    Salimullah, M.; Jamil, M.; Zeba, I.; Uzma, Ch.; Shah, H. A.

    2009-03-01

    Using the quantum hydrodynamic model of plasmas and with quantum effects arising through the Bohm potential and the Fermi degenerate pressure, the possible drift waves and their instabilities have been investigated in considerable detail in a nonuniform dusty magnetoplasma. It is found that in the presence of a nonuniform ambient magnetic field, the drift waves grow in amplitude by taking energy from the streaming ions and density inhomogeneity. The implication of the drift wave instability for nonthermal electrostatic fluctuations to laboratory and astrophysical environments is also pointed out.

  19. Streamers generation by small-scale drift-Alfvn waves

    SciTech Connect

    Zhao, J. S.; Yu, M. Y.

    2014-10-15

    Excitation of streamers by modulationally unstable small-scale drift-Alfvn wave (SSDAW) is investigated. It is found that the excitation depends strongly on the propagation direction of the SSDAW, and the ion and electron diamagnetic drift waves are both unstable due to the generation of streamers. It is also shown that zonal flows can be effectively excited by the SSDAW with the propagation direction different from that for streamer excitation.

  20. Excitation of Zonal Flow by Drift Waves in Toroidal Plasmas

    SciTech Connect

    L. Chen; R. White; Z. Lin

    1999-11-01

    An analytical dispersion relation is derived which shows that, in toroidal plasmas, zonal flows can be spontaneously excited via modulations in the radial envelope of a single-n coherent drift wave, with n the toroidal mode number. Predicted instability features are verified by 3D global gyrokinetic simulations of the ion-temperature-gradient mode. Nonlinear equations for mode amplitudes demonstrate saturation of the linearly unstable pump wave and bursting behavior in the drift-wave intensity and zonal flows.

  1. Coupled-cavity drift-tube linac

    DOEpatents

    Billen, James H. (Los Alamos, NM)

    1996-01-01

    A coupled-cavity drift-tube linac (CCDTL) combines features of the Alvarez drift-tube linac (DTL) and the .pi.-mode coupled-cavity linac (CCL). In one embodiment, each accelerating cavity is a two-cell, 0-mode DTL. The center-to-center distance between accelerating gaps is .beta..lambda., where .lambda. is the free-space wavelength of the resonant mode. Adjacent accelerating cavities have oppositely directed electric fields, alternating in phase by 180 degrees. The chain of cavities operates in a .pi./2 structure mode so the coupling cavities are nominally unexcited. The CCDTL configuration provides an rf structure with high shunt impedance for intermediate velocity charged particles, i.e., particles with energies in the 20-200 MeV range.

  2. Coupled-cavity drift-tube linac

    DOEpatents

    Billen, J.H.

    1996-11-26

    A coupled-cavity drift-tube linac (CCDTL) combines features of the Alvarez drift-tube linac (DTL) and the {pi}-mode coupled-cavity linac (CCL). In one embodiment, each accelerating cavity is a two-cell, 0-mode DTL. The center-to-center distance between accelerating gaps is {beta}{lambda}, where {lambda} is the free-space wavelength of the resonant mode. Adjacent accelerating cavities have oppositely directed electric fields, alternating in phase by 180 degrees. The chain of cavities operates in a {pi}/2 structure mode so the coupling cavities are nominally unexcited. The CCDTL configuration provides an rf structure with high shunt impedance for intermediate velocity charged particles, i.e., particles with energies in the 20-200 MeV range. 5 figs.

  3. Collective capture of released lithium ions in the solar wind

    NASA Technical Reports Server (NTRS)

    Winske, D.; Wu, C. S.; Li, Y. Y.; Zhou, G. C.

    1984-01-01

    The capture of newly ionized lithium ions in the solar wind by means of electromagnetic instabilities is investigated through linear analysis and computer simulation. Three instabilities, driven by a lithium velocity ring perpendicular to and drifting along the magnetic field, are considered. The capture time of the lithium by the solar wind is roughly 10 linear growth times, regardless of whether resonant or nonresonant modes dominate initially. Possible implications of the results for the Active Magnetosphere Particle Tracer Explorer (AMPTE) mission are discussed.

  4. Fermilab drift tube Linac revisited

    SciTech Connect

    Milorad Popovic

    2004-05-12

    Using the PARMILA code running under PC-WINDOWS, the present performance of the Fermilab Drift Tube Linac has been analyzed in the light of new demands on the Linac/Booster complex (the Proton Source). The Fermilab Drift Tube Linac (DTL) was designed in the sixties as a proton linac with a final energy of 200 MeV and a peak current of 100mA. In the seventies, in order to enable multi-turn charge exchange injection into the Booster, the ion source was replaced by an H- source with a peak beam current of 25mA. Since then the peak beam current was steadily increased up to 55mA. In the early nineties, part of the drift tube structure was replaced with a side-coupled cavity structure in order to increase the final energy to 400 MeV. The original and still primary purpose of the linac is to serve as the injector for the Booster. As an added benefit, the Neutron Therapy Facility (NTF) was built in the middle seventies. It uses 66MeV protons from the Linac to produce neutrons for medical purposes. The Linac/Booster complex was designed to run at a fundamental cycling rate of 15Hz, but beam is accelerated on every cycle only when NTF is running. Until recently the demand from the High Energy Physics program resulted in an average linac beam repetition rate of order 1 Hz. With the MiniBoone experiment and the NuMI program, the demands on the Proton Source have changed, with emphasis on higher beam repetition rates up to 7.5Hz. Historically the beam losses in the linac were small, localized at one spot, so activation was not an important issue. With higher beam rate, this has the potential to become the dominant issue. Until today all tuning in the linac and Proton Source was governed by two goals: to maximize the peak beam current out of the linac and to minimize the beam losses in the linac. If maximal peak current from the linac is no longer a primary goal, then the linac quadrupoles can be adjusted differently to achieve different goals.

  5. Toroidal universal drift instability: A global gyrokinetic study

    SciTech Connect

    Chowdhury, J.; Ganesh, R.; Brunner, S.; Vaclavik, J.; Villard, L.

    2010-10-15

    An electron density gradient driven instability identified as the toroidal branch of the universal drift instability is studied using a global gyrokinetic model treating both electrons and ions fully nonadiabatically and valid at all orders in the ratio of the Larmor radius to the wavelength. The physics of the magnetic drift resonance, Landau resonance and transit resonance, which are considered to be important for the toroidal universal mode, are kept for both species. A systematic parametric study is carried out for the mode. The toroidal universal drift mode is observed to sustain finite temperature gradient and can thus coexist with the temperature gradient driven modes and may contribute to the observed particle transport along with other drift modes. Especially at intermediate scales between the ion temperature gradient driven mode and electron temperature gradient driven mode, this branch of the drift instability can also be a plausible candidate for the observed particle loss. The effect of magnetic fluctuations on the mode is also investigated. In contrast to the slab mode, the toroidal branch of the universal drift mode is found to be strongly stabilized by electromagnetic effects at finite plasma {beta}. Finally, the effect of trapped electrons on the universal mode is studied and compared with the other possible modes in the same parameter regime, namely, ion temperature gradient mode in the presence of trapped electrons and pure trapped electron modes.

  6. Emplacement Drift System Description Document

    SciTech Connect

    Eric Loros

    2001-07-31

    The Emplacement Drift System is part of the Engineered Barrier System and provides the interface between the various waste package (WP) systems and the Ground Control System. In conjunction with the various WPs, the Emplacement Drift System limits the release and transport of radionuclides from the WP to the Natural Barrier following waste emplacement. Collectively, the Emplacement Drift System consists of the structural support hardware (emplacement drift invert and WP emplacement pallet) and any performance-enhancing barriers (drip shields and invert ballast) installed or placed in the emplacement drifts. The Emplacement Drift System is entirely located within the emplacement drifts in the subsurface portion of the Monitored Geologic Repository (MGR); specifically, it is physically bounded by the Subsurface Facility System, the Ground Support System, and the Natural Barrier. The Emplacement Drift System supports the key MGR functions of limiting radionuclide release to the Natural Barrier, minimizing the likelihood of a criticality external to the WPs, limiting natural and induced environmental effects, and providing WP support. The Emplacement Drift System limits radionuclide release to the Natural Barrier by controlling the movement of radionuclides within the emplacement drift and to the Natural Barrier, and by limiting water contact with the WPs. The Emplacement Drift System provides physical support and barriers for emplaced WPs that reduce water contact. The Emplacement Drift WP spacing supports the thermal loading performance by complimenting drift layout and orientation as described in the system description document for the Subsurface Facility System. The Emplacement Drift System supports the WP and also provides an environment that aids in enhancing WP confinement performance. As part of the Engineered Barrier System, the Emplacement Drift System interfaces with the WP systems. The Emplacement Drift System also interfaces with the Natural Barrier, Subsurface Facility System, and Ground Control System for the space and location of emplaced WPs, for the controlled release of radionuclides, and for controlling the heat, chemical, and physical effects that interact between these systems. The Emplacement Drift System interfaces with the Subsurface Ventilation System for preclosure heat removal from WPs. The Emplacement Drift System interfaces with the Waste Emplacement/Retrieval System and the Performance Confirmation Emplacement Drift Monitoring System for equipment clearance for the emplacement, retrieval, and monitoring of waste.

  7. Drifts of electron orbits induced by toroidal electric field in tokamaks

    SciTech Connect

    Abdullaev, S. S.

    2015-03-15

    The drifts of electron orbits induced by the toroidal electric field in tokamaks are analyzed. Based on the relativistic Hamiltonian equations for guiding centre motion, the formula for the drift velocity v{sub dr} is derived. It describes the outward drift of passing particles as well as the inward drift (the Ware pinch) of trapped particles. Unlike the approximate formula for v{sub dr} given in Guan et al. [Phys. Plasmas 17, 092502 (2010)] for circular electron orbits, it describes qualitatively new features of the outward drift of electron orbits. Particularly, the new formula describes the evolution of the orbit's shape, the formation of X-point and the associated separatrix. It is shown that the outward drift velocity is proportional to the inverse aspect ratio of tokamaks.

  8. Effect of parallel electron heat transport on drift and drift-tearing modes in RFP plasmas

    NASA Astrophysics Data System (ADS)

    Mirnov, V. V.; Hegna, C. C.; Sauppe, J. P.; Sovinec, C. R.

    2014-10-01

    Linear numerical simulations were performed for plasma slab with cold ions and hot electrons in a doubly periodic box bounded by two perfectly conducting walls. Within this model, configurations with magnetic shear are unstable to current-driven drift-tearing instability. Additionally, there is an unstable pressure-gradient driven mode that is largely electrostatic in nature, suggestive of a resistive-drift type instability. The simultaneous presence of linear drift-like and tearing instabilities was observed using both two fluid extended modeling with NIMROD and analytical methods. The primary motivation for these studies is to understand the electrostatic transport thought to be present in Madison Symmetric Torus RFP experiments. Our previous analytical studies were performed either in the limit of infinitively large parallel electron heat conduction or in the pure adiabatic regime with an isentropic equilibrium. We report now on a general model with arbitrary equilibrium and finite parallel thermal conduction. Drift mode stability is sensitive to the ratio of density and temperature gradient scales and the instability exists even for pure transverse perturbations. Preliminary analytical results confirm some reduction of the drift-tearing mode growth rate caused by finite electron thermal conduction, consistent with previous works. Results of NIMROD simulations for different regimes of the electron thermal conduction are reported as well. The work is supported by the U. S. DOE and NSF.

  9. Nonlinear evolution of drift instabilities in the presence of collisions

    SciTech Connect

    Federici, J.F.; Lee, W.W.; Tang, W.M.

    1986-07-01

    Nonlinear evolution of drift instabilities in the presence of electron-ion collisions in a shear-free slab has been studied by using gyrokinetic particle simulation techniques as well as by solving, both numerically and analytically, model mode-coupling equations. The purpose of the investigation is to determine the mechanisms responsible for the nonlinear saturation of the instability and for the ensuing steady-state transport. Such an insight is very valuable for understanding drift wave problems in more complicated geometries. The results indicate that the electron E x B convection is the dominant mechanism for saturation. It is also found that the saturation amplitude and the associated quasilinear diffusion are greatly enhanced over their collisionless values as a result of weak collisions. In the highly collisional (fluid) limit, there is an upper bound for saturation with ephi/T/sub e/ approx. = (..omega../sub l//..cap omega../sub i/)/(k/sub perpendicular/rho/sub s/)/sup 2/. The associated quasilinear diffusion, which increases with collisionality, takes the form of D/sub ql/ approx. = ..gamma../sub l//k/sub perpendicular//sup 2/, where ..omega../sub l/ and ..gamma../sub l/ are the linear frequency and growth rate, respectively. In the steady state, the diffusion process becomes stochastic in nature. The relevant mechanisms here are related to the velocity-space nonlinearities and background fluctuations. The magnitude of the diffusion at this stage can be comparable to that of quasilinear diffusion in the presence of collisions, and it remains finite even in the collisionless limit.

  10. Cross-field potential hill arisen eccentrically in toroidal electron cyclotron resonance plasmas in the Low Aspect ratio Torus Experiment device to regulate electron and ion flows from source to boundary

    NASA Astrophysics Data System (ADS)

    Kuroda, Kengoh; Wada, Manato; Uchida, Masaki; Tanaka, Hitoshi; Maekawa, Takashi

    2015-07-01

    We have investigated the electron and ion flows in toroidal electron cyclotron resonance (ECR) plasmas maintained by a 2.45 GHz microwave power around 1 kW under a simple toroidal field in the low aspect ratio torus experiment (LATE) device. We have found that a vertically uniform ridge of electron pressure that also constitutes the source belt of electron impact ionization is formed along just lower field side of the ECR layer and a cross-field potential hill ({{V}S}\\cong 30?V while {{T}e}\\cong 10?eV), eccentrically shifted toward the corner formed by the top panel and the ECR layer, arises. Combination of the hill-driven E B drift and the vertical drift due to the field gradient and curvature, being referred to as vacuum toroidal field (VTF) drift, realizes steady flows of electrons and ions from the source to the boundary. In particular, the ions, of which VTF drift velocity is much slower than the electron VTF drift velocity near the source belt, are carried by the E B drift around the hill to the vicinity of the top panel, where the ion VTF drift is enhanced on the steep down slope of potential toward the top panel. On the other hand the electron temperature strongly decreases in this area. Thus the carrier of VTF drift current is replaced from the electrons to the ions before the top panel, enabling the current circulation through the top and bottom panels and the vessel (electrons mainly to the bottom and ions mainly to the top) that keeps the charge neutrality very high. A few percent of electrons from the source turn around the hill by 360 degree and reentry the source belt from the high field side as seed electrons for the impact ionization, keeping the discharge stable.

  11. Selected ion flow drift tube studies of the reaction of Si+ (2P) with C2H4. Observation of the ternary reaction with two channels: collisional stabilization and collisional dissociation

    NASA Astrophysics Data System (ADS)

    Glosik, J.; Zakouril, P.; Lindinger, W.

    1995-07-01

    A selected ion flow drift tube study on the reaction of ground state Si+(2P) with C2H4 has been carried out in the pressure range from 0.14 to 0.52 Torr for average relative centre-of-mass kinetic energies, KECM, from near thermal to [approximate] 2 eV. Two product ions have been observed, SiC2H3+ and SiC2H4+. The apparent binary ("effective") rate coefficient, keff, and the product distribution have been determined as functions of KECM. The reaction rate coefficients of the binary (kBIN) and ternary (k3) channels have been determined by two procedures, from the pressure dependence of keff (indicated by index "PRESSURE") and by using the observed product distribution (indicated by index "PROD"). For KECM < 0.1 eV k3 obtained by both methods, k3-PRESSURE and k3-PROD, are equal and their dependence on KECM can be expressed in the form: k3-PROD = k3-PRESSURE [is proportional to] (KECM)-0.5. It was observed that dependence of the reaction rate coefficient of the binary channel can be expressed also in the form kBIN-PRESSURE [is proportional to] (KECM)-0.5. This similarity in the dependence on KECM may indicate that both binary and ternary channels are proceeding via the same rate-determining process prior to separation into two channels. The situation is different for KECM > 0.1 eV. Here k3-PROD decreased more rapidly with KECM than k3-PRESSURE, indicating that in the collisions of He atoms with the excited intermediate collision complex the dissociation of (SiC2H4)+* to SiC2H3+ takes place. Here we report the first observation of a ternary reaction having two product channels--collisional stabilization (product (SiC2H4+) and "collision induced dissociation" (product SiC2H3) with probabilities [alpha]1 and [alpha]2 (where [alpha]2 = 1 - [alpha]1), respectively. [alpha]1 and [alpha]2 have been determined from k3-PROD and k3-PRESSURE. For KECM < 0.1 eV the stabilization channel is dominant ([alpha]1 >> [alpha]2), for KECM [approximate] 0.2 eV both channels have the same probability ([alpha]1 = [alpha]2), and for KECM > 0.2 eV the "collision induced dissociation" of the intermediate complex, producing SiC2H3+, is dominant ([alpha]2 > [alpha]1).

  12. The relationship between oblique double layers, ion cyclotron waves, ion phase space holes and cold ion beams

    NASA Astrophysics Data System (ADS)

    Main, D. S.; Newman, D. L.

    2012-12-01

    Observations of Earth's auroral upward current region (UCR) indicate the presence of many non-linear structures including a transition region (TR) separating the ionosphere from the auroral cavity, ion phase space holes and ion cyclotron waves. In addition, the UCR is characterized by a cold, anti-earthward traveling ion beam with typical drift energies of ~sim 1000 eV. Observations indicate that the TR is 2D with an inferred U-shaped potential profile, abrupt drop in density and simultaneous parallel (E?) and perpendicular (E?) electric fields. In 1D, E? and the density cavity are well modeled by a double layer (DL). However, in 2D it is not clear how the U-shaped potential profile forms and evolves. In this paper, we study oblique DLs and the resulting waves using a Particle-in-Cell (PIC) simulation initialized with two different methods. In method 1, we initialize a 2D PIC simulation with a non-oblique density cavity (i.e. the initial density drop has no perpendicular dependence), resulting in a U-shaped 2D DL whose obliqueness angle can evolve with time. The drift velocity of the anti-earthward ions is given a perpendicular velocity shear so that the drift velocity is largest at the ? borders and smallest at the center of the simulation domain. In method 2, we initialize a 2D PIC simulation with a magnetic field that lies oblique to an initial density drop resulting in an oblique DL whose angle is fixed with respect to earth's magnetic field. In both methods, the initial plasma is composed of hot magnetospheric electrons and H+ ions, cold ionospheric electrons, and cold ionospheric H + and O + ions which have an anti-earthward drift (all initially Maxwellian). In method 1, we show that as the U-shaped DL evolves, strong cyclotron waves initially form. As the simulation progresses, ion holes form which are localized both perpendicular and parallel to earth's magnetic field. Method 2 also results in the formation of strong cyclotron waves. We compare/contrast both methods with homogeneous simulations in which no DL is included and only the auroral cavity is included in the simulation domain. The homogeneous simulations represent a more typical linear scenario in which some linear instability leads to non-linear waves. We show that including an oblique DL in the simulation leads to much stronger cyclotron waves and more localized phase space holes (in the perpendicular direction) compared with homogeneous simulations. We also show that including the low altitude DL results in more coherent ion beams compared with homogenous simulations, consistent with FAST observations.

  13. On the validity of drift-reduced fluid models for tokamak plasma simulation

    NASA Astrophysics Data System (ADS)

    Leddy, Jarrod; Dudson, Ben; Romanelli, Michele; Contributors, JET

    2015-12-01

    Drift-reduced plasma fluid models are commonly used in plasma physics for analytic studies and simulations, so the validity of such models must be verified for the regions of parameter space in which tokamak plasmas exist. By deriving and comparing the linear dispersion relations for the drift-wave instability for both a drift-reduced model and a full-velocity model, the importance of the physics lost with the drift-reduction is examined. This analysis is generalised for typical tokamak parameter spaces and is then applied directly to JET data. It is found that drift-reduced models are generally more applicable to the edge plasma (<10% error), while the core plasma shows more significant disagreement (>30% error) particularly at mid-radius. The effect of drift-wave mode number and wavelength also play a key role in determining the accuracy of drift-reduced models.

  14. ABSTRACTION OF DRIFT SEEPAGE

    SciTech Connect

    Michael L. Wilson

    2001-02-08

    Drift seepage refers to flow of liquid water into repository emplacement drifts, where it can potentially contribute to degradation of the engineered systems and release and transport of radionuclides within the drifts. Because of these important effects, seepage into emplacement drifts is listed as a ''principal factor for the postclosure safety case'' in the screening criteria for grading of data in Attachment 1 of AP-3.15Q, Rev. 2, ''Managing Technical Product Inputs''. Abstraction refers to distillation of the essential components of a process model into a form suitable for use in total-system performance assessment (TSPA). Thus, the purpose of this analysis/model is to put the information generated by the seepage process modeling in a form appropriate for use in the TSPA for the Site Recommendation. This report also supports the Unsaturated-Zone Flow and Transport Process Model Report. The scope of the work is discussed below. This analysis/model is governed by the ''Technical Work Plan for Unsaturated Zone Flow and Transport Process Model Report'' (CRWMS M&O 2000a). Details of this activity are in Addendum A of the technical work plan. The original Work Direction and Planning Document is included as Attachment 7 of Addendum A. Note that the Work Direction and Planning Document contains tasks identified for both Performance Assessment Operations (PAO) and Natural Environment Program Operations (NEPO). Only the PAO tasks are documented here. The planning for the NEPO activities is now in Addendum D of the same technical work plan and the work is documented in a separate report (CRWMS M&O 2000b). The Project has been reorganized since the document was written. The responsible organizations in the new structure are the Performance Assessment Department and the Unsaturated Zone Department, respectively. The work plan for the seepage abstraction calls for determining an appropriate abstraction methodology, determining uncertainties in seepage, and providing probability distributions of seepage. These are all discussed in detail in this report. In addition, the work plan calls for evaluation of effects of episodic flow and thermal-hydrologic-chemical alteration of hydrologic properties. As discussed in Section 5, these effects are not addressed in detail in this report because they can be argued to be insignificant. Effects of thermal-mechanical alteration of hydrologic properties are also not addressed in detail in this report because suitable process-model results are not available at this time. If these effects are found to be important, they should be included in the seepage abstraction in a future revision.

  15. Ion cyclotron and spin-flip emissions from fusion products in tokamaks

    SciTech Connect

    Arunasalam, V.; Greene, G.J.; Young, K.M.

    1993-02-01

    Power emission by fusion products of tokamak plasmas in their ion cyclotron range of frequencies (ICRF) and at their spin-flip resonance frequency is calculated for some specific model fusion product velocity-space distribution functions. The background plasma of say deuterium (D) is assumed to be in equilibrium with a Maxwellian distribution both for the electrons and ions. The fusion product velocity distributions analyzed here are: (1) A monoenergetic velocity space ring distribution. (2) A monoenergetic velocity space spherical shell distribution. (3) An anisotropic Maxwellian distribution with T {perpendicular} {ne} T{parallel}and with appreciable drift velocity along the confining magnetic field. Single ``dressed`` test particle spontaneous emission calculations are presented first and the radiation temperature for ion cyclotron emission (ICE) is analyzed both for black-body emission and nonequilibrium conditions. Thresholds for instability and overstability conditions are then examined and quasilinear and nonlinear theories of the electromagnetic ion cyclotron modes are discussed. Distinctions between ``kinetic or causal instabilities`` and ``hydrodynamic instabilities`` are drawn and some numerical estimates are presented for typical tokamak parameters. Semiquantitative remarks are offered on wave accessibility, mode conversion, and parametric decay instabilities as possible for spatially localized ICE. Calculations are carried out both for k{parallel} = 0 for k{parallel} {ne} 0. The effects of the temperature anisotropy and large drift velocities in the parallel direction are also examined. Finally, proton spin-flip resonance emission and absorption calculations are also presented both for thermal equilibrium conditions and for an ``inverted`` population of states.

  16. Ion cyclotron and spin-flip emissions from fusion products in tokamaks

    SciTech Connect

    Arunasalam, V.; Greene, G.J.; Young, K.M.

    1993-02-01

    Power emission by fusion products of tokamak plasmas in their ion cyclotron range of frequencies (ICRF) and at their spin-flip resonance frequency is calculated for some specific model fusion product velocity-space distribution functions. The background plasma of say deuterium (D) is assumed to be in equilibrium with a Maxwellian distribution both for the electrons and ions. The fusion product velocity distributions analyzed here are: (1) A monoenergetic velocity space ring distribution. (2) A monoenergetic velocity space spherical shell distribution. (3) An anisotropic Maxwellian distribution with T [perpendicular] [ne] T[parallel]and with appreciable drift velocity along the confining magnetic field. Single dressed'' test particle spontaneous emission calculations are presented first and the radiation temperature for ion cyclotron emission (ICE) is analyzed both for black-body emission and nonequilibrium conditions. Thresholds for instability and overstability conditions are then examined and quasilinear and nonlinear theories of the electromagnetic ion cyclotron modes are discussed. Distinctions between kinetic or causal instabilities'' and hydrodynamic instabilities'' are drawn and some numerical estimates are presented for typical tokamak parameters. Semiquantitative remarks are offered on wave accessibility, mode conversion, and parametric decay instabilities as possible for spatially localized ICE. Calculations are carried out both for k[parallel] = 0 for k[parallel] [ne] 0. The effects of the temperature anisotropy and large drift velocities in the parallel direction are also examined. Finally, proton spin-flip resonance emission and absorption calculations are also presented both for thermal equilibrium conditions and for an inverted'' population of states.

  17. Strong impact of neutrals on anomalous inward drift and width of steep gradient zone

    NASA Astrophysics Data System (ADS)

    Becker, G.

    1999-01-01

    The fundamental properties of the anomalous inward drift and the width of the steep gradient zone in H mode plasmas are explored. A special version of the 1.5-D BALDUR transport code is used to determine the profiles of the electron heat diffusivity and vin/D by transport analysis. The strong rise with radius of vin/D in the edge region is explained by a linear dependence on the neutral deuterium density n0, resulting in a new scaling expression vin(x)/D(x) = F0Zeff(x)n0(x)2x/(ρwxs2). Applying this in simulations reproduces the empirical fit of the vin/D profile not only in the edge plasma but also in the bulk plasma. Modellings with this scaling yield the observed flattening of density profiles with rising line averaged density. The decreasing penetration of deuterium atoms to the core causes a decline of the inward drift. The new scaling is shown to be compatible with gas oscillation experiments, while n0-independent scalings are not. This further explains the strong density profile peaking and rise of vin/D during and after pellet injection by the increase in neutral density. The width of the steep gradient zone is found to be connected with the penetration of neutrals at the edge and the presence of high inward drift velocities. The anomalous inward drift is attributed to ion dynamics, i.e. to the friction between fluctuating deuterons and deuterium atoms diffusing inward. A more general vin/D scaling including impurity effects is presented.

  18. Quaternary Contourite Drifts of the Western Spitsbergen Margin

    NASA Astrophysics Data System (ADS)

    Laberg, J. S.; Rebesco, M.; Wahlin, A.; Schauer, U.; Beszczynska-Möller, A.; Lucchi, R. G.; Noormets, R.; Accettella, D.; Zarayskaya, Y.; Diviacco, P.

    2014-12-01

    The study of contourite drifts is an increasingly used tool for understanding the climate history of the oceans. In this paper we analyse two contourite drifts along the continental margin west of Spitsbergen, just south of the Fram Strait where significant water mass exchanges impact the Arctic climate. We detail the internal geometry and the morphologic characteristics of the two drifts on the base of multichannel seismic reflection data, sub-bottom profiles and bathymetry. These mounded features, that we propose to name Isfjorden and Bellsund drifts, are located on the continental slope between 1200 and 1800 m depth, whereas the upper slope is characterized by reduced- or non-deposition. The more distinct Isfjorden Drift is about 25 km wide and 45 km long, and over 200 ms TWT thick. We revise the 13 years-long time series of velocity, temperature, and salinity obtained from a mooring array across the Fram Strait. Two distinct current cores are visible in the long-term average. The shallower current core has an average northward velocity of about 20 cm/s, while the deeper bottom current core at about 1450 m depth has an average northward velocity of about 9 cm/s. We consider Norwegian Sea Deep Water episodically ventilated by relatively dense and turbid shelf water from the Barents Sea responsible for the accumulation of the contourites. The onset of the drift growth west of Spitsbergen is inferred to be about 1.3 Ma and related to the Early Pleistocene glacial expansion recorded in the area. The lack of mounded contouritic deposits on the continental slope of the Storfjorden is related to consecutive erosion by glacigenic debris flows. The Isfjorden and Bellsund drifts are inferred to contain the record of the regional palaeoceanography and glacial history and may constitute an excellent target of future scientific drilling.

  19. Particle-in-cell simulations of the critical ionization velocity effect in finite size clouds

    NASA Technical Reports Server (NTRS)

    Moghaddam-Taaheri, E.; Lu, G.; Goertz, C. K.; Nishikawa, K. - I.

    1994-01-01

    The critical ionization velocity (CIV) mechanism in a finite size cloud is studied with a series of electrostatic particle-in-cell simulations. It is observed that an initial seed ionization, produced by non-CIV mechanisms, generates a cross-field ion beam which excites a modified beam-plasma instability (MBPI) with frequency in the range of the lower hybrid frequency. The excited waves accelerate electrons along the magnetic field up to the ion drift energy that exceeds the ionization energy of the neutral atoms. The heated electrons in turn enhance the ion beam by electron-neutral impact ionization, which establishes a positive feedback loop in maintaining the CIV process. It is also found that the efficiency of the CIV mechanism depends on the finite size of the gas cloud in the following ways: (1) Along the ambient magnetic field the finite size of the cloud, L (sub parallel), restricts the growth of the fastest growing mode, with a wavelength lambda (sub m parallel), of the MBPI. The parallel electron heating at wave saturation scales approximately as (L (sub parallel)/lambda (sub m parallel)) (exp 1/2); (2) Momentum coupling between the cloud and the ambient plasma via the Alfven waves occurs as a result of the finite size of the cloud in the direction perpendicular to both the ambient magnetic field and the neutral drift. This reduces exponentially with time the relative drift between the ambient plasma and the neutrals. The timescale is inversely proportional to the Alfven velocity. (3) The transvers e charge separation field across the cloud was found to result in the modulation of the beam velocity which reduces the parallel heating of electrons and increases the transverse acceleration of electrons. (4) Some energetic electrons are lost from the cloud along the magnetic field at a rate characterized by the acoustic velocity, instead of the electron thermal velocity. The loss of energetic electrons from the cloud seems to be larger in the direction of plasma drift relative to the neutrals, where the loss rate is characterized by the neutral drift velocity. It is also shown that a factor of 4 increase in the ambient plasma density, increases the CIV ionization yield by almost 2 orders of magnitude at the end of a typical run. It is concluded that a larger ambient plasma density can result in a larger CIV yield because of (1) larger seed ion production by non-CIV mechanisms, (2) smaller Alfven velocity and hence weak momentum coupling, and (3) smaller ratio of the ion beam density to the ambient ion density, and therefore a weaker modulation of the beam velocity. The simulation results are used to interpret various chemical release experiments in space.

  20. Laced permanent magnet quadrupole drift tube magnets

    SciTech Connect

    Feinberg, B.; Behrsing, G.U.; Halbach, K.; Marks, J.S.; Morrison, M.E.; Nelson, D.H.

    1989-03-01

    Twenty-three laced permanent magnet quadrupole drift tube magnets have been constructed, tested, and installed in the SuperHILAC heavy ion linear accelerator at LBL, marking the first accelerator use of this new type of quadrupole. The magnets consist of conventional tape-wound quadrupole electromagnets, using iron pole-pieces, with permanent magnet material (samarium cobalt) inserted between the poles to reduce the effects of saturation. The iron is preloaded with magnetic flux generated by the permanent magnet material, resulting in an asymmetrical saturation curve. Since the polarity of the individual quadrupole magnets in a drift tube linac is never reversed, we can take advantage of this asymmetrical saturation to provide about 20% greater focusing strength than is available with conventional quadrupoles, while replacing the vanadium permendur poletips with iron poletips. Comparisons between these magnets and conventional tape-wound quadrupoles will be presented. 3 refs., 5 figs.

  1. Electromagnetic nonlinear gyrokinetics with polarization drift

    SciTech Connect

    Duthoit, F.-X.; Hahm, T. S.; Wang, Lu

    2014-08-15

    A set of new nonlinear electromagnetic gyrokinetic Vlasov equation with polarization drift and gyrokinetic Maxwell equations is systematically derived by using the Lie-transform perturbation method in toroidal geometry. For the first time, we recover the drift-kinetic expression for parallel acceleration [R. M. Kulsrud, in Basic Plasma Physics, edited by A. A. Galeev and R. N. Sudan (North-Holland, Amsterdam, 1983)] from the nonlinear gyrokinetic equations, thereby bridging a gap between the two formulations. This formalism should be useful in addressing nonlinear ion Compton scattering of intermediate-mode-number toroidal Alfvén eigenmodes for which the polarization current nonlinearity [T. S. Hahm and L. Chen, Phys. Rev. Lett. 74, 266 (1995)] and the usual finite Larmor radius effects should compete.

  2. Manifestation of the light-induced drift effect in chemically peculiar stellar atmospheres

    NASA Astrophysics Data System (ADS)

    Parkhomenko, A. I.; Shalagin, A. M.

    2013-02-01

    We have calculated the factor ( ? g - ? e )/ ? g in the temperature range T = 300-20 000 K for the ions Be+, Mg+, Ca+, C+ in atomic hydrogen and for the ions Mg+ in atomic argon using the known interaction potentials. Here ? e and ? g are the transport collision frequencies for excited- and ground-state particles respectively. Calculations have shown that at T = 10 000-20 000 K, typical temperatures of the atmospheres of chemically peculiar (CP) stars, the values | ? g - ? e |/ ? g ? 0.1-0.2 can be reached for ions. This causes the light-induced drift (LID) velocity of ions up to 0.1 cm/s in the atmospheres of CP stars with temperatures T < 10 000 K. Therefore the separation of chemical elements due to the LID of ions under the conditions of the atmospheres of such CP stars can be an order of magnitude more efficient in comparison with the separation caused by the radiation pressure. In the atmosphere of more hot stars (20 000 K > T > 10 000 K) it is possible to expect approximately identical magnitude of the LID effect and that of radiation pressure. In the very hot stars ( T >20 000 K) the LID effect is manifested very weakly.

  3. Magnetic conjugate point observations of kilometer and hundred-meter scale irregularities and zonal drifts

    NASA Astrophysics Data System (ADS)

    de Paula, E. R.; Muella, M. T. A. H.; Sobral, J. H. A.; Abdu, M. A.; Batista, I. S.; Beach, T. L.; Groves, K. M.

    2010-08-01

    The Conjugate Point Equatorial Experiment (COPEX) campaign was carried out in Brazil, between October and December 2002, to study the conjugate nature of plasma bubble irregularities and to investigate their generation mechanisms, development characteristics, spatial-temporal distribution, and dynamics. In this work we will focus mainly on the zonal spaced GPS (1.575 GHz) and VHF (250 MHz) receivers' data collected simultaneously at two magnetic conjugate sites of the COPEX geometry: Boa Vista and Campo Grande. These GPS/VHF receivers were set up to detect the equatorial scintillations and to measure ionospheric scintillation pattern velocities. Then, the zonal irregularity drift velocities were estimated by applying a methodology that corrects the effects caused by vertical drifts and geometrical factors. The results reveal the coexistence of kilometer- (VHF) and hundred-meter-scale (GPS L-band) irregularities into the underlying depletion structure. Over the conjugate site of Campo Grande, the average zonal velocity at VHF seems to be consistently larger than the estimated GPS velocities until ˜0200 UT, whereas over Boa Vista the irregularities detected from both techniques are drifting with comparable velocities. The hundred-meter-scale structures causing L-band scintillations appear to be drifting with comparable velocities over both the conjugate sites, whereas the kilometer-scale structures are drifting over Campo Grande with larger average velocities (before 0300 UT). Complementary data of ionospheric parameters scaled from collocated digital ionosondes are used in the analysis to explain differences/similarities on the scintillation/zonal drift results.

  4. Fingermark ridge drift.

    PubMed

    De Alcaraz-Fossoul, Josep; Roberts, Katherine A; Feixat, Carme Barrot; Hogrebe, Gregory G; Badia, Manel Gené

    2016-01-01

    Distortions of the fingermark topography are usually considered when comparing latent and exemplar fingerprints. These alterations are characterized as caused by an extrinsic action, which affects entire areas of the deposition and alters the overall flow of a series of contiguous ridges. Here we introduce a novel visual phenomenon that does not follow these principles, named fingermark ridge drift. An experiment was designed that included variables such as type of secretion (eccrine and sebaceous), substrate (glass and polystyrene), and degrees of exposure to natural light (darkness, shade, and direct light) indoors. Fingermarks were sequentially visualized with titanium dioxide powder, photographed and analyzed. The comparison between fresh and aged depositions revealed that under certain environmental conditions an individual ridge could randomly change its original position regardless of its unaltered adjacent ridges. The causes of the drift phenomenon are not well understood. We believe it is exclusively associated with intrinsic natural aging processes of latent fingermarks. This discovery will help explain the detection of certain dissimilarities at the minutiae/ridge level; determine more accurate "hits"; identify potentially erroneous corresponding points; and rethink identification protocols, especially the criteria of "no single minutiae discrepancy" for a positive identification. PMID:26646735

  5. A new rf structure for intermediate-velocity particles

    SciTech Connect

    Billen, J.H.; Krawczyk, F.L.; Wood, R.L.; Young, L.M.

    1994-09-01

    This paper describes an rf structure with high shunt impedance and good field stability for particle velocities o.1 {le} {beta} {le} 0.5. Traditionally, the drift-tube linac (DTL) has been the structure of choice for this velocity range. The new structure, called a coupled-cavity drift-tube linac (CCDTL), combines features of the Alvarez DTL and the {pi}-mode coupled-cavity linac (CCL). Each accelerating cavity is a two-cell, 0-mode DTL. The center-to-center distance between gaps is {gamma}{lambda}. Adjacent accelerating cavities have oppositely directed electric fields, alternating in phase by 180{degrees}. The chain of cavities operates in a {pi}/2 structure mode so the coupling cavities are nominally unexcited. We will discuss 2-D and 3-D electromagnetic code calculations, and some initial measurements on a low-power model of a CCDTL. We will compare shunt impedance calculations for DTL, CCL, and CCDTL structures. The CCDTL has potential application for a wide range of ion linacs. For example, high-intensity proton linacs could use the CCDTL instead of a DTL up to an energy of about 200 MeV. Another example is a stand-alone, low-duty, low-current, very high gradient, proton, cancer therapy machine. The advantage for this application would be a saving in the cost of the machine because the linac would be short.

  6. Flow shear induced Compton scattering of electron drift instability

    SciTech Connect

    Hahm, T.S.

    1992-02-01

    Plasma flow shear effects on nonlinear saturation of electron drift waves are analyzed in the weak turbulence regime. Flow shear can enhance ion Compton scattering of long wavelength electron drift waves not only by modifying the beat wave-ion resonance condition, but also via the radial dependence of linear susceptibility. A nonlinear dispersion relation is obtained as a solution of the radially nonlocal nonlinear eigenmode equation. At nonlinear saturation, the spectral intensity of the fluctuations scales with flow shear as ({partial_derivative}V{var_phi}/{partial_derivative}r){sup {minus}2} in addition to the linear dependence on the linear growth rate.

  7. Zonal flow excitation by drift waves in toroidal plasmas

    SciTech Connect

    L Chen; Z. Lin; R. White

    2000-06-13

    Recent 3D gyrokinetic and gyrofluid simulations in toroidal plasmas have demonstrated that zonal flows play a crucial role in regulating the nonlinear evolution of electrostatic drift-wave instabilities such as the ion temperature gradient (ITG) modes and, as a consequence, the level of the anomalous ion thermal transport, and that zonal flows could be spontaneously excited by ITG turbulence, suggesting parametric instability processes as the generation mechanism. Diamond et. al. have proposed the modulational instability of drift-wave turbulence ( plasmons ) in a slab-geometry treatment.

  8. Drift-Scale Radionuclide Transport

    SciTech Connect

    J. Houseworth

    2004-09-22

    The purpose of this model report is to document the drift scale radionuclide transport model, taking into account the effects of emplacement drifts on flow and transport in the vicinity of the drift, which are not captured in the mountain-scale unsaturated zone (UZ) flow and transport models ''UZ Flow Models and Submodels'' (BSC 2004 [DIRS 169861]), ''Radionuclide Transport Models Under Ambient Conditions'' (BSC 2004 [DIRS 164500]), and ''Particle Tracking Model and Abstraction of Transport Process'' (BSC 2004 [DIRS 170041]). The drift scale radionuclide transport model is intended to be used as an alternative model for comparison with the engineered barrier system (EBS) radionuclide transport model ''EBS Radionuclide Transport Abstraction'' (BSC 2004 [DIRS 169868]). For that purpose, two alternative models have been developed for drift-scale radionuclide transport. One of the alternative models is a dual continuum flow and transport model called the drift shadow model. The effects of variations in the flow field and fracture-matrix interaction in the vicinity of a waste emplacement drift are investigated through sensitivity studies using the drift shadow model (Houseworth et al. 2003 [DIRS 164394]). In this model, the flow is significantly perturbed (reduced) beneath the waste emplacement drifts. However, comparisons of transport in this perturbed flow field with transport in an unperturbed flow field show similar results if the transport is initiated in the rock matrix. This has led to a second alternative model, called the fracture-matrix partitioning model, that focuses on the partitioning of radionuclide transport between the fractures and matrix upon exiting the waste emplacement drift. The fracture-matrix partitioning model computes the partitioning, between fractures and matrix, of diffusive radionuclide transport from the invert (for drifts without seepage) into the rock water. The invert is the structure constructed in a drift to provide the floor of the drift. The reason for introducing the fracture-matrix partitioning model is to broaden the conceptual model for flow beneath waste emplacement drifts in a way that does not rely on the specific flow behavior predicted by a dual continuum model and to ensure that radionuclide transport is not underestimated. The fracture-matrix partitioning model provides an alternative method of computing the partitioning of radionuclide releases from drifts without seepage into rock fractures and rock matrix. Drifts without seepage are much more likely to have a significant fraction of radionuclide releases into the rock matrix, and therefore warrant additional attention in terms of the partitioning model used for TSPA.

  9. Concepts and development of drift pumping for the Tandem Mirror Experiment-Upgrade (TMX-U)

    SciTech Connect

    Kane, R.J.; Pedrotti, L.R.; Brooksby, C.A.; Cummins, W.F.; Jackson, M.C.; Poulsen, P.; ver Planck, P.

    1985-11-11

    Low-energy ions trapped in the thermal barrier region of the TMX-U plasma cause a potential reduction which results in increased scattering and less thermal isolation between regions of the plasma. A method of removing these ions using magnetic field perturbations at the ion drift frequency has been developed. The concepts of ''drift pumping'' and hardware development are described in this paper. 5 refs., 7 figs.

  10. Relationship between vertical ExB drift and F2-layer characteristics in the equatorial ionosphere at solar minimum conditions

    NASA Astrophysics Data System (ADS)

    Oyekola, Oyedemi S.

    2012-07-01

    Equatorial and low-latitude electrodynamics plays a dominant role in determining the structure and dynamics of the equatorial and low-latitude ionospheric F-region. Thus, they constitute essential input parameters for quantitative global and regional modeling studies. In this work, hourly median value of ionosonde measurements namely, peak height F2-layer (hmF2), F2-layer critical frequency (foF2) and propagation factor M(3000)F2 made at near equatorial dip latitude, Ouagadougou, Burkina Faso (12oN, 1.5oW; dip: 1.5oN) and relevant F2-layer parameters such as thickness parameter (Bo), electron temperature (Te), ion temperature (Ti), total electron content (TEC) and electron density (Ne, at the fixed altitude of 300 km) provided by the International Reference Ionosphere (IRI) model for the longitude of Ouagadougou are contrasted with the IRI vertical drift model to explore in detail the monthly climatological behavior of equatorial ionosphere and the effects of equatorial vertical plasma drift velocities on the diurnal structure of F2-layer parameters. The analysis period covers four months representative of solstitial and equinoctial seasonal periods during solar minimum year of 1987 for geomagnetically quiet-day. We show that month-by-month morphological patterns between vertical EB drifts and F2-layer parameters range from worst to reasonably good and are largely seasonally dependent. A cross-correlation analysis conducted between equatorial drift and F2-layer characteristics yield statistically significant correlations for equatorial vertical drift and IRI-Bo, IRI-Te and IRI-TEC, whereas little or no acceptable correlation is obtained with observational evidence. Assessment of the association between measured foF2, hmF2 and M(3000)F2 illustrates consistent much more smaller correlation coefficients with no systematic linkage. In general, our research indicates strong departure from simple electrodynamically controlled behavior.

  11. Model etch profiles for ion energy distribution functions in an inductively coupled plasma reactor

    SciTech Connect

    Chen, W.; Abraham-Shrauner, B.; Woodworth, J.R.

    1999-09-01

    Rectangular trench profiles are modeled with analytic etch rates determined from measured ion distribution functions. The pattern transfer step for this plasma etch is for trilayer lithography. Argon and chlorine angular ion energy distribution functions measured by a spherical collector ring analyzer are fit to a sum of drifting Maxwellian velocity distribution functions with anisotropic temperatures. The fit of the model ion distribution functions by a simulated annealing optimization procedure converges adequately for only two drifting Maxwellians. The etch rates are proportional to analytic expressions for the ion energy flux. Numerical computation of the etch profiles by integration of the characteristic equations for profile points and connection of the profiles points is efficient. {copyright} {ital 1999 American Vacuum Society.}

  12. Progress in semiconductor drift detectors

    SciTech Connect

    Rehak, P.; Walton, J.; Gatti, E.; Longoni, A.; Sanpietro, M.; Kemmer, J.; Dietl, H.; Holl, P.; Klanner, R.; Lutz, G.

    1985-01-01

    Progress in testing semiconductor drift detectors is reported. Generally better position and energy resolutions were obtained than resolutions published previously. The improvement is mostly due to new electronics better matched to different detectors. It is shown that semiconductor drift detectors are becoming versatile and reliable detectors for position and energy measurements.

  13. Interferometric phase velocity measurements in the auroral electrojet

    NASA Technical Reports Server (NTRS)

    Labelle, J.; Kintner, P. M.; Kelley, M. C.

    1986-01-01

    A double-probe electric field detector and two spatially separated fixed-bias Langmuir probes were flown on a Taurus-Tomahawk sounding rocket launched from Poker Flat Research Range in March 1982. Interesting wave data have been obtained from about 10s of the downleg portion of the flight during which the rocket passed through the auroral electrojet. Here the electric field receiver and both density fluctuation (delta-n/n) receivers responded to a broad band of turbulence centered at 105 km-altitude and at frequencies generally below 4 kHz. Closer examination of the two delta-n/n turbulent waveforms reveals that they are correlated; from the phase difference between the two signals, the phase velocity of the waves in the rocket reference frame is inferred. The magnitude and direction of the observed phase velocity are consistent either with waves which travel at the ion sound speed or with waves which travel at the electron drift velocity. The observed phase velocity varies by about 50 percent over a 5 km altitude range, an effect which probably results from shear in the zonal neutral wind, although, unfortunately, no simultaneous neutral wind measurements exist to confirm this.

  14. Drift dynamics of larval pallid sturgeon and shovelnose sturgeon in a natural side channel of the Upper Missouri River, Montana

    USGS Publications Warehouse

    Braaten, P.J.; Fuller, D.B.; Holte, L.D.; Lott, R.D.; Viste, W.; Brandt, T.F.; Legare, R.G.

    2008-01-01

    The drift dynamics of larval shovelnose sturgeon Scaphirhynchus platorynchus (1, 2, 6, and 10 d posthatch [dph]) and pallid sturgeon S. albus (1, 2, 5, 9, 11, and 17 dph) were examined in a natural side channel of the Missouri River to quantify the vertical drift location of larvae in the water column, determine the drift velocity of larvae relative to water velocity, and simulate the cumulative distance (km) drifted by larvae during ontogenetic development. Larvae were released at the side-channel inlet and sampled at points 100, 500, 900, and 1,300 m downstream. Larvae drifted primarily near the riverbed, as 58-79% of recaptured shovelnose sturgeon and 63-89% of recaptured pallid sturgeon were sampled in the lower 0.5 m of the water column. The transition from the drifting to the benthic life stage was initiated at 6 dph (mean length, 15.6 mm) for shovelnose sturgeon and at 11-17 dph (mean length, 18.1-20.3 mm) for pallid sturgeon. Across ages, the drift rates of larval shovelnose sturgeon averaged 0.09-0.16 m/s slower than the mean water column velocity. The drift rates of pallid sturgeon were similar to or slightly slower (0.03-0.07 m/s) than the mean water column velocity for 1-11-dph larvae. Conversely, 17-dph larval pallid sturgeon dispersed downstream at a much slower rate (mean, 0.20 m/s slower than the mean water column velocity) owing to their transition to benthic habitats. Drift simulations indicated that the average larval shovelnose sturgeon may drift from 94 to 250 km and the average larval pallid sturgeon may drift from 245 to 530 km, depending on water velocity. Differences in larval drift dynamics between species provide a possible explanation for differences in recruitment between shovelnose sturgeon and pallid sturgeon in the upper Missouri River. ?? Copyright by the American Fisheries Society 2008.

  15. Strange Attractors in Drift Wave Turbulence

    SciTech Connect

    Jerome L.V. Lewandowski

    2003-09-03

    There are growing experimental, numerical and theoretical evidences that the anomalous transport observed in tokamaks and stellarators is caused by slow, drift-type modes (such as trapped electron modes and ion-temperature gradient-driven modes). Although typical collision frequencies in hot, magnetized fusion plasmas can be quite low in absolute values, collisional effects are nevertheless important since they act as dissipative sinks. As it is well known, dissipative systems with many (strictly speaking more than two) degrees of freedom are often chaotic and may evolve towards a so-called attractor.

  16. A drift model of interchange instability

    SciTech Connect

    Benilov, E. S.; Power, O. A.

    2007-08-15

    A set of asymptotic equations is derived, describing the dynamics of the flute mode in a magnetized plasma with cold ions, under a 'local' approximation (i.e., near a particular point). The asymptotic set is then used to calculate the growth rate of interchange instability in the slab model. It is shown that, unlike the magnetohydrodynamic ordering, the drift one allows instability to occur for either sign of the pressure gradient (i.e., for both 'bad' and 'good' curvature of the magnetic field). It is also demonstrated that finite beta gives rise to an extra instability that does not exist in the small-beta limit.

  17. Effects of grids in drift tubes

    SciTech Connect

    Okamura M.; Yamauchi, H.

    2012-05-20

    In 2011, we upgraded a 201 MHz buncher in the proton injector for the alternating gradient synchrotron (AGS) - relativistic heavy ion collider (RHIC) complex. In the buncher we installed four grids made of tungsten to improve the transit time factor. The grid installed drift tubes have 32 mm of inner diameter and the each grid consists of four quadrants. The quadrants were cut out precisely from 1mm thick tungsten plates by a computerized numerically controlled (CNC) wire cutting electrical discharge machining (EDM). The 3D electric field of the grid was simulated.

  18. Instability Caused by Dust Drift and the Observed Polar Mesospheric Summer Echoes (PMSE's)

    NASA Astrophysics Data System (ADS)

    Tsytovich, V. N.; Havnes, O.

    2002-12-01

    Observations show that the Polar Mesopause Summer Echoes (PMSE's) radar scattering layers near the Earth mesopause are strongly linked to the dust layer in the same hight region [1]. No single mechanism has been found which is capable of explaining the PMSE over large frequency range and different atmospheric conditions at which it has been observed. One possible explanation in the high frequency range around 1 GH is the non-coherent scattering on the non-linear plasma screening clouds around dust particles [2]. This requires that a < λD (a is the size of the grains, λD is the Debye radius) and that P = ndZd/ni is close to 1. New simultaneous and common volume observations by radars at 50 MHz and by rockets show that PMSE can also occur for P << 1 and that the reflected signal rise rapidly with dust charge density as P increases in the range below about 0.1. This may be an indication that some instability caused by dust is developing. In the regions of PMSE's the ion-dust mean free path λid = λD2/aP is 6 orders of magnitude larger than the ion-neutral mean free path λin and most instabilities are damped by high rate of ion-neutral collisions. We investigate the role of gravity forced dust drift in typical conditions (nn ≈ 1014 cm-3, T ≈ 100° K, a ≈ 0.01 μm with the falling velocity ≈ 20cm/s thermal dust velocity of the order of 50 cm/s). The gravity balance, the condition of charge neutrality and the balance of ionization and absorption on dust is taken into account. In the dispersion equation we include account the changes in dust charges, the ion-neutral collisions, the ion and electron pressures, the dust-ion drag and the dust inertia. We find an instability of dissipative type caused by the dust drift, dust charge variations and dust drag. The instability develops in broad range of wave lengths with threshold for typical parameters being estimated as λ > 10cm(1/√P ). For P = 0.01 (approximately the lowest value observed) this corresponds to 1 m which is much shorter than the wavelength (6 m) at which the observations of PMSE for the low P-value were done. The growth rate is estimated to be developing in ≈ 200 s during which the dust falls 50m while the thickness of PMSE layer is from several hundred meters to several kilometers. The instability operates till λmax ≈ 30 m.

  19. Effect of ion and ion-beam mass ratio on the formation of ion-acoustic solitons in magnetized plasma in the presence of electron inertia

    SciTech Connect

    Kalita, B. C.; Barman, S. N.

    2009-05-15

    The propagation of ion-acoustic solitary waves in magnetized plasma with cold ions and ion-beams together with electron inertia has been investigated theoretically through the Korteweg-de Vries equation. Subject to the drift velocity of the ion beam, the existence of compressive solitons is found to become extinct as {alpha} (=cold ion mass/ion-beam mass) tends to 0.01 when {gamma}=0.985 ({gamma} is the beam velocity/phase velocity). Interestingly, a transitional direction of propagation of solitary waves has been unearthed for change over, from compressive solitons to rarefactive solitons based on {alpha} and {sigma}{sub {upsilon}}(=cosine of the angle {theta} made by the wave propagation direction {xi} with the direction of the magnetic field) for fixed Q(=electron mass/ion mass). Further, the direction of propagation of ion-acoustic waves is found to be the deterministic factor to admit compressive or rarefactive solitons subject to beam outsource.

  20. Effect of solenoidal magnetic field on drifting laser plasma

    SciTech Connect

    Takahashi, Kazumasa; Sekine, Megumi; Okamura, Masahiro; Cushing, Eric; Jandovitz, Peter

    2013-04-19

    An ion source for accelerators requires to provide a stable waveform with a certain pulse length appropriate to the application. The pulse length of laser ion source is easy to control because it is expected to be proportional to plasma drifting distance. However, current density decay is proportional to the cube of the drifting distance, so large current loss will occur under unconfined drift. We investigated the stability and current decay of a Nd:YAG laser generated copper plasma confined by a solenoidal field using a Faraday cup to measure the current waveform. It was found that the plasma was unstable at certain magnetic field strengths, so a baffle was introduced to limit the plasma diameter at injection and improve the stability. Magnetic field, solenoid length, and plasma diameter were varied in order to find the conditions that minimize current decay and maximize stability.

  1. Relativistic wave-function effect on the K-shell ionization of Sb, Gd, Yb, Au, and Bi by low- to intermediate-velocity F ions

    NASA Astrophysics Data System (ADS)

    Mitra, D.; Singh, Yeshpal; Tribedi, Lokesh C.; Tandon, P. N.; Trautmann, D.

    2001-07-01

    We have measured absolute cross sections for the K-shell ionization of medium- and high-Z targets of Sb, Gd, Yb, Au, and Bi induced by low- to intermediate-velocity F ions having energies between 2.5 and 5.8 MeV/u. Our main interest is to see the effect of the relativistic nature of the K-shell electrons of these target atoms on the ionization cross sections. The information on the degree of relativistic effect has been obtained by comparing the measured data with different theoretical calculations with and without including the relativistic corrections. A comparative study of the two different models such as SCA (semiclassical approximation) and ECPSSR [perturbed stationary state (PSS) including the corrections for energy (E) loss, Coulomb (C) deflection, and relativistic (R) effects] is presented. It is shown that the SCA calculations with the relativistic wave function predict an ionization cross section that is at least an order of magnitude higher compared to that given by the nonrelativistic calculation for Bi target. This factor is reduced to about 2 in the case of Sb. The ECPSSR, however, predicts lower ratios for the relativistic to nonrelativistic calculations. The experimental results, in general, are in good agreement with the SCA calculations using relativistic wave functions as well as with the ECPSSR model. For high-Z targets the SCA gives slightly better agreement with the data compared to the ECPSSR. In addition, it is shown that in the ECPSSR formalism the ionization cross sections of high-Z (with large relativistic effect) as well as low-Z targets (with less relativistic effect) can be scaled approximately to follow a universal curve after including the relativistic correction.

  2. The role of grain boundary structure on electromigration-induced drift in pure Al and Al(0.5 wt% Cu)

    SciTech Connect

    Proost, J.; Maex, K.; Samajdar, I.; Verlinden, B.; Van Houtte, P.; Delaey, L.

    1998-09-15

    The effect of microstructure on the electromigration performance of aluminum-based metallizations in integrated circuits has been extensively investigated over the past three decades. Besides grain size, grain size distribution and precipitate morphology, crystallographic texture has been documented to have a major impact on the electromigration (EM) lifetime. The authors present here, for the first time, a direct relation between the aluminum microtexture and EM-induced drift velocities, both for different alloys (pure Al vs Al(Cu)) and different metallization technologies (reactive ion etching or RIE vs. damascene).

  3. East-west ionospheric drifts at the magnetic equator.

    NASA Technical Reports Server (NTRS)

    Woodman, R. F.

    1972-01-01

    A technique has been developed to measure the electromagnetic east-west drift velocity of the F region ionosphere by means of the Jicamarca incoherent scatter radar. Results show a fairly consistent behavior from day to day even during a magnetically disturbed day. Velocities are westward with a maximum of the order of 50 m/sec during the day, and eastward with a maximum of the order of 135 m/sec during the night. They are shown as experimental evidence for the superrotation of the neutral atmosphere at equatorial latitudes, but with a velocity smaller than the values inferred from satellite drag.

  4. Electrodeless drift chambers with 50-cm drift distance

    SciTech Connect

    Ayres, D.S.; Price, L.E.

    1982-08-01

    The electrodeless drift-chamber technique is potentially very useful in applications requiring the drifting of ionization in gas over long distances in narrow channels. Chamber construction is simple and cheap; the technique is well suited to very large detectors operating in low-rate environments. Prototype tests on planar chambers reveal excellent drifting characteristics after the initial charging, but show a substantial degradation of pulse height from cosmic rays over a two-week period. The loss of efficiency appears to be caused by excess charge buildup on the dielectric surfaces of the chamber. Several solutions are suggested.

  5. An experimental test and models of drift and dispersal processes of pallid sturgeon (Scaphirhynchus albus) free embryos in the Missouri River

    USGS Publications Warehouse

    Braaten, P.J.; Fuller, D.B.; Lott, R.D.; Ruggles, M.P.; Brandt, T.F.; Legare, R.G.; Holm, R.J.

    2012-01-01

    Free embryos of wild pallid sturgeon Scaphirhynchus albus were released in the Missouri River and captured at downstream sites through a 180-km reach of the river to examine ontogenetic drift and dispersal processes. Free embryos drifted primarily in the fastest portion of the river channel, and initial drift velocities for all age groups (mean = 0.66–0.70 m s−1) were only slightly slower than mean water column velocity (0.72 m s−1). During the multi-day long-distance drift period, drift velocities of all age groups declined an average of 9.7% day−1. Younger free embryos remained in the drift upon termination of the study; whereas, older age groups transitioned from drifting to settling during the study. Models based on growth of free embryos, drift behavior, size-related variations in drift rates, and channel hydraulic characteristics were developed to estimate cumulative distance drifted during ontogenetic development through a range of simulated water temperatures and velocity conditions. Those models indicated that the average free embryo would be expected to drift several hundred km during ontogenetic development. Empirical data and model results highlight the long-duration, long-distance drift and dispersal processes for pallid sturgeon early life stages. In addition, results provide a likely mechanism for lack of pallid sturgeon recruitment in fragmented river reaches where dams and reservoirs reduce the length of free-flowing river available for pallid sturgeon free embryos during ontogenetic development.

  6. A parametric study of the drift-tearing mode using an extended-magnetohydrodynamic model

    SciTech Connect

    King, J. R.; Kruger, S. E.

    2014-10-15

    The linear, collisional, constant-ψ drift-tearing mode is analyzed for different regimes of the plasma-β, ion-skin-depth parameter space with an unreduced, extended-magnetohydrodynamic model. New dispersion relations are found at moderate plasma β and previous drift-tearing results are classified as applicable at small plasma β.

  7. Theory of semicollisional drift-interchange modes in cylindrical plasmas

    SciTech Connect

    Hahm, T.S.; Chen, L.

    1985-01-01

    Resistive interchange instabilities in cylindrical plasmas are studied, including the effects of electron diamagnetic drift, perpendicular resistivity, and plasma compression. The analyses are pertinent to the semicollisional regime where the effective ion gyro-radius is larger than the resistive layer width. Both analytical and numerical results show that the modes can be completely stabilized by the perpendicular plasma transport. Ion sound effects, meanwhile, are found to be negligible in the semicollisional regime.

  8. Ion distributions in the fast solar wind and associated kinetic instabilities: Ulysses observations

    NASA Astrophysics Data System (ADS)

    Matteini, L.; Hellinger, P.; Goldstein, B. E.; Landi, S.; Velli, M. M.

    2011-12-01

    We investigate properties of ions in the fast solar wind using Ulysses observations and we compare the results with linear theory predictions. An analysis of ion distribution functions, which are characterized by temperature anisotropy and differential velocities, based on drifting bi-Maxwellians (Goldstein et al. 2010) is reported. The stability of the plasma, composed by the core and beam proton populations and the alpha particles, is investigated with respect to kinetic instabilities driven by temperature anisotropies and/or by drift velocities between different species. We find that while the total global distribution of protons appears constrained by a fire hose instability, in agreement with previous studies, the core of distributions is anisotropic with the perpendicular temperature that is larger then the parallel one, thus possibly exciting an ion-cyclotron or mirror instability. At the same time, signatures of ion-beam instabilities are found, suggesting that such instabilities play a role in the regulation of the ion drifts during the solar wind expansion. These Ulysses observations suggest that wave-particle interactions driven by kinetic instabilities are most of the time at work in the fast solar wind, influencing the plasma thermodynamics and providing also a possible explanation for recent magnetic field spectra observations (Wicks et al. 2010).

  9. Fast Correction Optics to Reduce Chromatic Aberrations in Longitudinally Compressed Ion Beams

    SciTech Connect

    Lidia, S.M.; Lee, E.P.; Ogata, D.; Seidl, P.A.; Waldron, W.L.; Lund, S.M.

    2009-04-30

    Longitudinally compressed ion beam pulses are currently employed in ion-beam based warm dense matter studies [1]. Compression arises from an imposed time-dependent longitudinal velocity ramp followed by drift in a neutralized channel. Chromatic aberrations in the final focusing system arising from this chirp increase the attainable beam spot and reduce the effective fluence on target. We report recent work on fast correction optics that remove the time-dependent beam envelope divergence and minimizes the beam spot on target. We present models of the optical element design and predicted ion beam fluence.

  10. Space-charge limiting currents in magnetically focused intense relativistic beams with an ion channel

    SciTech Connect

    Li Jianqing; Mo Yuanlong

    2006-12-15

    The intense relativistic beam propagation through the drift tube filled with background plasma is investigated. The self-consistent differential equations, which describe the laminar-flow equilibria state in magnetically focused relativistic beams with an ion channel, are presented. By solving these equations using the Runge-Kutta method, the azimuthal velocity, the axial velocity, and the electron beam density, which are functions of radial position, can be calculated. Then the space-charge limiting current and the externally applied magnetic field can be obtained for solid beams and hollow beams. In the case of plasma fill, the axial velocity of the laminar flow is a nonuniform radial profile. The simulated results show that the background plasma can increase the space-charge limiting current, reduce the externally applied magnetic field, and improve the electron beam propagation through the drift tube.

  11. A statistical analysis of systematic errors in temperature and ram velocity estimates from satellite-borne retarding potential analyzers

    SciTech Connect

    Klenzing, J. H.; Earle, G. D.; Heelis, R. A.; Coley, W. R.

    2009-05-15

    The use of biased grids as energy filters for charged particles is common in satellite-borne instruments such as a planar retarding potential analyzer (RPA). Planar RPAs are currently flown on missions such as the Communications/Navigation Outage Forecast System and the Defense Meteorological Satellites Program to obtain estimates of geophysical parameters including ion velocity and temperature. It has been shown previously that the use of biased grids in such instruments creates a nonuniform potential in the grid plane, which leads to inherent errors in the inferred parameters. A simulation of ion interactions with various configurations of biased grids has been developed using a commercial finite-element analysis software package. Using a statistical approach, the simulation calculates collected flux from Maxwellian ion distributions with three-dimensional drift relative to the instrument. Perturbations in the performance of flight instrumentation relative to expectations from the idealized RPA flux equation are discussed. Both single grid and dual-grid systems are modeled to investigate design considerations. Relative errors in the inferred parameters for each geometry are characterized as functions of ion temperature and drift velocity.

  12. DRIFT-INDUCED PERPENDICULAR TRANSPORT OF SOLAR ENERGETIC PARTICLES

    SciTech Connect

    Marsh, M. S.; Dalla, S.; Kelly, J.; Laitinen, T.

    2013-09-01

    Drifts are known to play a role in galactic cosmic ray transport within the heliosphere and are a standard component of cosmic ray propagation models. However, the current paradigm of solar energetic particle (SEP) propagation holds the effects of drifts to be negligible, and they are not accounted for in most current SEP modeling efforts. We present full-orbit test particle simulations of SEP propagation in a Parker spiral interplanetary magnetic field (IMF), which demonstrate that high-energy particle drifts cause significant asymmetric propagation perpendicular to the IMF. Thus in many cases the assumption of field-aligned propagation of SEPs may not be valid. We show that SEP drifts have dependencies on energy, heliographic latitude, and charge-to-mass ratio that are capable of transporting energetic particles perpendicular to the field over significant distances within interplanetary space, e.g., protons of initial energy 100 MeV propagate distances across the field on the order of 1 AU, over timescales typical of a gradual SEP event. Our results demonstrate the need for current models of SEP events to include the effects of particle drift. We show that the drift is considerably stronger for heavy ion SEPs due to their larger mass-to-charge ratio. This paradigm shift has important consequences for the modeling of SEP events and is crucial to the understanding and interpretation of in situ observations.

  13. Drift-Kinetic Simulations of Neoclassical Transport

    SciTech Connect

    Belli, E. A.; Candy, J.

    2008-11-01

    We present results from numerical studies of neoclassical transport for multi-species plasmas. The code, NEO, provides a first-principles based calculation of the neoclassical transport coefficients directly from solution of the distribution function by solving a hierarchy of equations derived by expanding the fundamental drift-kinetic equation in powers of {rho}{sub *i}, the ratio of the ion gyroradius to system size. It extends previous studies by including the self-consistent coupling of electrons and multiple ion species and strong toroidal rotation effects. Systematic calculations of the second-order particle and energy fluxes and first-order plasma flows and bootstrap current and comparisons with existing theories are given for multi-species plasmas. The ambipolar relation {sigma}{sub a}z{sub a}{gamma}{sub a} = 0, which can only be maintained with complete cross-species collisional coupling, is confirmed. The effects of plasma shaping are also explored.

  14. Imaging and Rapid-Scanning Ion Mass Spectrometer (IRM) for the CASSIOPE e-POP Mission

    NASA Astrophysics Data System (ADS)

    Yau, Andrew W.; Howarth, Andrew; White, Andrew; Enno, Greg; Amerl, Peter

    2015-06-01

    The imaging and rapid-scanning ion mass spectrometer (IRM) is part of the Enhanced Polar Outflow Probe (e-POP) instrument suite on the Canadian CASSIOPE small satellite. Designed to measure the composition and detailed velocity distributions of ions in the 1-100 eV/q range on a non-spinning spacecraft, the IRM sensor consists of a planar entrance aperture, a pair of electrostatic deflectors, a time-of-flight (TOF) gate, a hemispherical electrostatic analyzer, and a micro-channel plate (MCP) detector. The TOF gate measures the transit time of each detected ion inside the sensor. The hemispherical analyzer disperses incident ions by their energy-per-charge and azimuth in the aperture plane onto the detector. The two electrostatic deflectors may be optionally programmed to step through a sequence of deflector voltages, to deflect ions of different incident elevation out of the aperture plane and energy-per-charge into the sensor aperture for sampling. The position and time of arrival of each detected ion at the detector are measured, to produce an image of 2-dimensional (2D), mass-resolved ion velocity distribution up to 100 times per second, or to construct a composite 3D velocity distribution by combining successive images in a deflector voltage sequence. The measured distributions are then used to investigate ion composition, density, drift velocity and temperature in polar ion outflows and related acceleration and transport processes in the topside ionosphere.

  15. ON PLASMA ROTATION AND DRIFTING SUBPULSES IN PULSARS: USING ALIGNED PULSAR B0826-34 AS A VOLTMETER

    SciTech Connect

    Van Leeuwen, J.; Timokhin, A. N. E-mail: andrey.timokhin@nasa.gov

    2012-06-20

    We derive the exact drift velocity of plasma in the pulsar polar cap, in contrast to the order-of-magnitude expressions presented by Ruderman and Sutherland and generally used throughout the literature. We emphasize that the drift velocity depends not on the absolute value, as is generally used, but on the variation of the accelerating potential across the polar cap. If we assume that drifting subpulses in pulsars are indeed due to this plasma drift, several observed subpulse-drift phenomena that are incompatible with the Ruderman and Sutherland family of models can now be explained: we show that variations of drift rate, outright drift reversals, and the connection between drift rates and mode changes have natural explanations within the frame of the 'standard' pulsar model, when derived exactly. We apply this model for drifting subpulses to the case of PSR B0826-34, an aligned pulsar with two separate subpulse-drift regions emitted at two different colatitudes. Careful measurement of the changing and reversing drift rate in each band independently sets limits on the variation of the accelerating potential drop. The derived variation is small, {approx}10{sup -3} times the vacuum potential drop voltage. We discuss the implications of this result for pulsar modeling.

  16. The electron forewake: Shadowing and drift-energization as flowing magnetized plasma encounters an obstacle

    NASA Astrophysics Data System (ADS)

    Haakonsen, Christian Bernt; Hutchinson, Ian H.

    2015-10-01

    Flow of magnetized plasma past an obstacle creates a traditional wake, but also a forewake region arising from shadowing of electrons. The electron forewakes resulting from supersonic flows past insulating and floating-potential obstacles are explored with 2D electrostatic particle-in-cell simulations, using a physical ion to electron mass ratio. Drift-energization is discovered to give rise to modifications to the electron velocity-distribution, including a slope-reversal, providing a novel drive of forewake instability. The slope-reversal is present at certain locations in all the simulations, and appears to be quite robustly generated. Wings of enhanced electron density are observed in some of the simulations, also associated with drift-energization. In the simulations with a floating-potential obstacle, the specific potential structure behind that obstacle allows fast electrons to cross the wake, giving rise to a more traditional shadowing-driven two-stream instability. Fluctuations associated with such instability are observed in the simulations, but this instability-mechanism is expected to be more sensitive to the plasma parameters than that associated with the slope-reversal.

  17. Gyrokinetic theory of electrostatic lower-hybrid drift instabilities in a current sheet with guide field

    SciTech Connect

    Tummel, K.; Chen, L.; Department of Physics and Astronomy, University of California at Irvine, Irvine, California 92697 ; Wang, Z.; Wang, X. Y.; Lin, Y.

    2014-05-15

    A kinetic electrostatic eigenvalue equation for the lower-hybrid drift instability (LHDI) in a thin Harris current sheet with a guide field is derived based on the gyrokinetic electron and fully kinetic ion(GeFi) description. Three-dimensional nonlocal analyses are carried out to investigate the influence of a guide field on the stabilization of the LHDI by finite parallel wavenumber, k{sub ?}. Detailed stability properties are first analyzed locally, and then as a nonlocal eigenvalue problem. Our results indicate that at large equilibrium drift velocities, the LHDI is further destabilized by finite k{sub ?} in the short-wavelength domain. This is demonstrated in a local stability analysis and confirmed by the peak in the eigenfunction amplitude. We find the most unstable modes localized at the current sheet edges, and our results agree well with simulations employing the GeFi code developed by Lin et al. [Plasma Phys. Controlled Fusion 47, 657 (2005); Plasma Phys. Controlled Fusion 53, 054013 (2011)].

  18. Pulsed Drift Tube Accelerator

    SciTech Connect

    Faltens, A.

    2004-10-25

    The pulsed drift-tube accelerator (DTA) concept was revived by Joe Kwan and John Staples and is being considered for the HEDP/WDM application. It could be used to reach the full energy or as an intermediate accelerator between the diode and a high gradient accelerator such as multi-beam r.f. In the earliest LBNL HIF proposals and conceptual drivers it was used as an extended injector to reach energies where an induction linac with magnetic quadrupoles is the best choice. For HEDP, because of the very short pulse duration, the DTA could provide an acceleration rate of about 1MV/m. This note is divided into two parts: the first, a design based on existing experience; the second, an optimistic extrapolation. The first accelerates 16 parallel K{sup +} beams at a constant line charge density of 0.25{micro} C/m per beam to 10 MeV; the second uses a stripper and charge selector at around 4MeV followed by further acceleration to reach 40 MeV. Both benefit from more compact sources than the present 2MV injector source, although that beam is the basis of the first design and is a viable option. A pulsed drift-tube accelerator was the first major HIF experiment at LBNL. It was designed to produce a 2{micro}s rectangular 1 Ampere C{sub s}{sup +} beam at 2MeV. It ran comfortably at 1.6MeV for several years, then at lower voltages and currents for other experiments, and remnants of that experiment are in use in present experiments, still running 25 years later. The 1A current, completely equivalent to 1.8A K{sup +}, was chosen to be intermediate between the beamlets appropriate for a multi-beam accelerator, and a single beam of, say, 10A, at injection energies. The original driver scenarios using one large beam on each side of the reactor rapidly fell out of favor because of the very high transverse and longitudinal fields from the beam space charge, circa 1MV/cm and 250 kV/cm respectively, near the chamber and because of aberrations in focusing a large diameter beam down to a 1mm radius spot at a distance of 10m. Almost all subsequent work and the present concept have invoked multiple beams. For HEDP the major differences are that the focal distance can be centimeters instead of meters, provided strong-enough lenses exist and they do, thereby allowing much higher transverse and longitudinal emittances than driver concepts, and focusing parallel small beams is easier than one big beam.

  19. SPIV measurements around the DELFT 372 catamaran in steady drift

    NASA Astrophysics Data System (ADS)

    Falchi, M.; Felli, M.; Grizzi, S.; Aloisio, G.; Broglia, R.; Stern, F.

    2014-11-01

    The present work concerns the experimental measurements of the velocity field around a catamaran advancing in static drift. The main aim of the paper was to investigate the dynamics of the vortices generated by catamaran hulls with particular emphasis on the mechanisms of generation, detachment, downstream evolution and destabilization. In this context, a Stereo-PIV campaign has been performed to map the velocity fields on some cross-planes along and downstream of the catamaran. Froude numbers equal to 0.4 and 0.5 at drift angles as large as 6 and 9 have been selected as testing conditions. In all the tests, the model has been fixed at the dynamical values of trim and sinkage, measured in a preliminary static drift experiments. Major geometrical and kinematical characteristics of the keel vortices have been documented in the paper through the analysis of the mean and fluctuating components of the velocity and vorticity field. Vortex interaction with the wave pattern has been investigated as well through the use of a conditional average technique of the velocity snapshots with the free surface elevation. As a secondary, but important, outcome, a valuable experimental dataset for CFD benchmarking in severe off-design conditions has been collected.

  20. Quantum diffusion with drift and the Einstein relation. I

    SciTech Connect

    De Roeck, Wojciech; Frhlich, Jrg; Schnelli, Kevin

    2014-07-15

    We study the dynamics of a quantum particle hopping on a simple cubic lattice and driven by a constant external force. It is coupled to an array of identical, independent thermal reservoirs consisting of free, massless Bose fields, one at each site of the lattice. When the particle visits a site x of the lattice it can emit or absorb field quanta of the reservoir at x. Under the assumption that the coupling between the particle and the reservoirs and the driving force are sufficiently small, we establish the following results: The ergodic average over time of the state of the particle approaches a non-equilibrium steady state describing a non-zero mean drift of the particle. Its motion around the mean drift is diffusive, and the diffusion constant and the drift velocity are related to one another by the Einstein relation.