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1

Ion acoustic solitons in a plasma with finite temperature drifting ions: Limit on ion drift velocity  

Microsoft Academic Search

Propagation of ion acoustic solitons in a plasma consisting of finite temperature drifting ions and nondrifting electrons has been studied. It is shown that in addition to the electron inertia and weak relativistic effects, the ion temperature also modifies the soliton behavior. By including the finite ion temperature, limit for the ion drift velocity [ital u][sub 0] for which the

H. K. Malik; Sanjay Singh; R. P. Dahiya

1994-01-01

2

Ion acoustic solitons in a plasma with finite temperature drifting ions: Limit on ion drift velocity  

SciTech Connect

Propagation of ion acoustic solitons in a plasma consisting of finite temperature drifting ions and nondrifting electrons has been studied. It is shown that in addition to the electron inertia and weak relativistic effects, the ion temperature also modifies the soliton behavior. By including the finite ion temperature, limit for the ion drift velocity [ital u][sub 0] for which the ion acoustic solitons are possible, is obtained. The solitons can exist for [ital v][sub [ital Te

Malik, H.K.; Singh, S.; Dahiya, R.P. (Centre for Energy Studies, Indian Institute of Technology, New Delhi-110016 (India))

1994-05-01

3

Negative ion drift velocity and longitudinal diffusion in mixtures of carbon disulfide and methane  

NASA Astrophysics Data System (ADS)

Negative ion drift velocity and longitudinal diffusion have 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 are observed for all gas mixtures tested. Gas gain for some of the mixtures is also included.

Dion, M. P.; Son, S.; Hunter, S. D.; de Nolfo, G. A.

2011-08-01

4

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

NASA Technical Reports Server (NTRS)

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.

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

2011-01-01

5

Drift velocity of ions and electrons in non-polar dielectric liquids at high electric field strengths  

Microsoft Academic Search

Ionic and electronic charge carriers are usually in- jected into dielectric liquids either by ionization by high energy radiation or by photoelectric effect at an electrode. Here, we summarize and discuss data on the drift velocity as a function of applied electric field obtained with these methods. While the drift of ions can be described by Stokes' law of laminar

Werner F. Schmidt; George Bakale; Alexey Khrapak; Katsumi Yoshino

2011-01-01

6

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)

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).

Murad, Sohail

2011-03-01

7

Effects of ion drift on small-amplitude ion-acoustic solitons  

Microsoft Academic Search

Some properties of small-amplitude ion-acoustic solitons in a plasma consisting of nondrifting electrons and drifting ions are investigated. Electron inertia effects are shown to be considerably more important than relativistic effects. It is also shown that ion-acoustic soliton solutions exist only if the ion drift velocity is less than the electron thermal velocity.

H. H. Kuehl; C. Y. Zhang

1991-01-01

8

Comparison of drift velocities of nighttime equatorial plasma depletions with the ambient plasma drifts and the thermospheric neutral winds  

NASA Astrophysics Data System (ADS)

This study is for the first time to analyze satellite observations and compare the plasma depletion drifts with the ambient plasma drifts and the neutral winds in the post-sunset equatorial ionosphere. The local time and latitude variations of the drift velocities of O+ plasma depletions at 350--400 km altitude are derived from the observations of the Far Ultraviolet Imager (FUV) operated on the IMAGE satellite during March 10-June 7, 2002. The variations are compared with the simultaneous measurements of the ion drift velocities and the neutral winds by the ROCSAT-1 and the CHAMP satellites for a similar time period. The analysis shows that the zonal drift velocity of plasma depletions is smaller than both the ambient ion zonal drift velocity and the neutral zonal wind at 18-20 hour magnetic local time and after 21 hour the variations of these velocities are similar. The analysis also shows that the difference of the plasma depletion drift with the background is small at low latitudes. This is the first-ever satellite comparison of the plasma depletion drift with the ambient plasma drift as well as the neutral wind for a global scale, explaining many previous observations at single locations. Furthermore, the zonal drift velocity of the depletion is found in this study to have a large latitudinal gradient specifically at 12°-18° magnetic latitude, which again does not match the ambient ion drift and the neutral wind. This latitudinal difference has been reported by previous studies, but these studies use models and they only compare the depletion drifts with the modeled neutral winds. This study compares the satellite observations, and compares with both the neutral winds and the plasma drifts. The study provides a measure of the difference that has never been provided before by any study using global observations. It has been suggested that vertical polarization electric fields inside the plasma depletions are responsible for the eastward drift of the depletion structures. The difference in the latitudinal gradients seen here in this study could also be explained by the polarization electric fields. For the C-shaped depletion, the polarization electric fields drive a westward drift of plasma particles inside the depletion and this drift velocity changes with increasing latitude. Consequently, the depletion drifts eastward and the depletion drift has a larger latitudinal gradient than the ambient plasma drift.

Liu, G.; England, S.; Frey, H. U.; Immel, T. J.; Lin, C. S.; Pacheco, E.; Haeusler, K.; Doornbos, E.

2013-12-01

9

Two-stream instability with time-dependent drift velocity  

DOE PAGESBeta

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.

Qin, Hong [PPPL; Davidson, Ronald C. [PPPL

2014-01-01

10

Two-stream instability with time-dependent drift velocity  

NASA Astrophysics Data System (ADS)

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.

Qin, Hong; Davidson, Ronald C.

2014-06-01

11

Two-stream instability with time-dependent drift velocity  

SciTech Connect

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.

Qin, Hong [Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States); Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Davidson, Ronald C. [Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)

2014-06-15

12

Cap Bubble Drift Velocity in a Confined Test Section  

SciTech Connect

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.

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

2002-10-09

13

Height dependence of spread F bubble drift velocities  

NASA Technical Reports Server (NTRS)

Vertical bubble velocities in equatorial spread F have been investigated analytically by Ott (1978), Osakow and Chaturvedi (1978), all of whom found a proportionality of the vertical velocity to bubble depletion density. The paper presents radar data from two equatorial sites which support theoretical predictions that vertical drift velocities of spread F bubbles increase with height on the bottomside of the F layer. This increase is shown to result from the proportionality of bubble drift velocity to density depletion amplitude, which itself increases with height. The measured rate of increase is found to be dU/dh equals about 2 m/s km. It is concluded that this is consistent with numerical simulation results within a factor of 2.

Hudson, M. K.; Balsley, B. B.

1979-01-01

14

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

SciTech Connect

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.

Mushtaq, A. [Theoretical Plasma Physics Division, Pakistan Institute of Nuclear Science and Technology (PINSTECH), Nilore, Islamabad 45660 (Pakistan); School of Physics, University of Sydney, New South Wales 2006 (Australia); Saeed, R.; Haque, Q. [Theoretical Plasma Physics Division, Pakistan Institute of Nuclear Science and Technology (PINSTECH), Nilore, Islamabad 45660 (Pakistan)

2011-04-15

15

WINCS v.2 for the Neutral Wind and Ion-drift in the Thermosphere/Ionosphere  

NASA Astrophysics Data System (ADS)

The Wind Ion-drift Neutral Composition Suite (WINCS) has been updated to increase sensitivity to wind/ion-drift change and to further reduce risk and cost. Description of the new neutral wind/ion-drift spectrometer component of WINCS will be given with data results from simulations and laboratory tests of WINCS version 2. A 20-fold increase in wind/ion-drift sensitivity brings their uncertainties to about × 0.5 m/s; corresponding to a pointing uncertainty of × 0.005°. This precision improves accuracy in the wind/ion-drift when used with new star cameras that provide ×0.005° or better pointing accuracy; thus allowing vertical wind and vertical ion-drift measurements over broad regions of the upper atmosphere. The new design uses a larger aperture (0.1cm diameter instead of the 0.02cm diameter of WINCS v.1), and replaces the energy-scanning energy analyzer with a 30° PPA (parallel plate analyzer) energy spectrograph that simultaneously measures all energies of interest. These two features increase the signal to enable the new wind/ion-drift precisions stated above. Risk and cost reduction follow from the new electro-mechanical format that combines spectrometer mechanical mounting with the actual electrical connection. The presentation will close with discussion of cross-track and in-track wind and ion-drift components to emphasize the requirement of the energy analyzer in obtaining the magnitude of the total velocity in both cross-track and in-track winds and ion-drifts - that is, the total velocity of the neutrals or ions incident upon WINCS.

Herrero, F. A.; Nicholas, A. C.

2013-12-01

16

Identifying equatorial ionospheric irregularities using in situ ion drifts  

NASA Astrophysics Data System (ADS)

Previous climatological investigations of ionospheric irregularity occurrence in the equatorial ionosphere have utilized in situ measurements of plasma density to identify the presence of an irregularity. Here we use the Morlet wavelet and C/NOFS to isolate perturbations in meridional ion drifts and generate irregularity occurrence maps as a function of local time, longitude, season, and solar activity. For the low solar activity levels in 2008, the distributions identified by velocity perturbations follow normalized density perturbation (?N/N) maps with large occurrences after midnight into dawn over all longitudes. The velocity and normalized density occurrence maps contract in both local time and longitude with increasing solar activity. By 2011 irregularities are confined to particular longitudes expected by alignment and a few hours of local time after sunset. The variation in the occurrence of the late night irregularities with solar activity is consistent with the presence of gravity wave seeding.

Stoneback, R. A.; Heelis, R. A.

2014-04-01

17

Drift and ion acoustic wave driven vortices with superthermal electrons  

SciTech Connect

Linear and nonlinear analysis of coupled drift and acoustic mode is presented in an inhomogeneous electron-ion plasma with {kappa}-distributed electrons. A linear dispersion relation is found which shows that the phase speed of both the drift wave and the ion acoustic wave decreases in the presence of superthermal electrons. Several limiting cases are also discussed. In the nonlinear regime, stationary solutions in the form of dipolar and monopolar vortices are obtained. It is shown that the condition for the boundedness of the solution implies that the speed of drift wave driven vortices reduces with increase in superthermality effect. Ignoring density inhomogeniety, it is investigated that the lower and upper limits on the speed of the ion acoustic driven vortices spread with the inclusion of high energy electrons. The importance of results with reference to space plasmas is also pointed out.

Ali Shan, S. [Theoretical Plasma Physics Division, PINSTECH, P.O. Nilore, Islamabad (Pakistan); National Centre For Physics (NCP), Shahdra Valley Road, QAU Campus, 44000 Islamabad (Pakistan); Pakistan Institute of Engineering and Applied Sciences (PIEAS), Islamabad (Pakistan); Haque, Q. [Theoretical Plasma Physics Division, PINSTECH, P.O. Nilore, Islamabad (Pakistan); National Centre For Physics (NCP), Shahdra Valley Road, QAU Campus, 44000 Islamabad (Pakistan)

2012-08-15

18

Vertical drift velocities during the polarization jet observations by the ground-based ionospheric data  

NASA Astrophysics Data System (ADS)

Polarization jet (PJ) or narrow band of rapid westward drift of ionospheric plasma at subauroral latitudes has a horizontal velocity from hundreds of meters to a few kilometers per second. The PJ is clearly identified on the ground-based ionograms as an additional characteristic reflection trace from ionospheric heights. According to the Doppler measurements at the Yakutsk meridian chain of subauroral ionospheric stations the vertical drifts during registration PJ are investigated. It is shown that in periods of PJ observation vertical drift velocity is higher than the background level, and there is a variation of the ionospheric plasma flow direction from the upward to the downward and back.

Bondar, Elena; Stepanov, Alexandr; Khalipov, Victor

19

Electrostatic drift-wave instability in a nonuniform quantum magnetoplasma with parallel velocity shear flows  

SciTech Connect

The propagation of high and low frequency (in comparison with the cyclotron frequency) electrostatic drift-waves is investigated in a nonuniform, dense magnetoplasma (composed of electrons and ions), in the presence of parallel shear flow, by employing the quantum magnetohydrodynamic (QMHD) model. Using QMHD model, a new set of equations is presented in order to investigate linear properties of electrostatic drift-waves with sheared plasma flows for dense plasmas. In this regard, dispersion relations for coupled electron-thermal and drift-ion acoustic modes are derived and several interesting limiting cases are discussed. For instance, it is found that sheared ion flow parallel to the external magnetic field can drive the quantum drift-ion acoustic wave unstable, etc. The present investigation may have relevance in dense astrophysical environments where quantum effects are significant.

Tariq, Sabeen; Mirza, Arshad M. [Department of Physics, Theoretical Plasma Physics Group, Quaid-i-Azam University, Islamabad 45320 (Pakistan); Masood, W. [Theoretical Plasma Physics Division, PINSTECH, P.O. Box. Nilore, Islamabad 44000, Pakistan and National Center for Physics (NCP), Islamabad 45320 (Pakistan)

2010-10-15

20

Ion drifts in a snowflake divertor  

SciTech Connect

Prompt losses of ions having turning points in the vicinity of the poloidal field null of a snowflake divertor are analyzed. Classification of the ion trajectories is presented. It is concluded that prompt losses in a snowflake affect a broader zone than in the standard X-point divertor. The size of the phase-space 'hole' produced by prompt losses is evaluated.

Ryutov, D. D.; Umansky, M. V. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States)

2010-01-15

21

The drift velocity of oil film on the sea  

Microsoft Academic Search

To make surface seawater flow, the shear stress of the wind blowing on the sea must overcome the work of cohesion of seawaterW\\u000a c. Oil film on the sea will drift along the wind direction so long as the shear stress of the wind overcomes the work of adhesion\\u000a between the water and the oilW\\u000a a or the work of

Xinglun Kang

1990-01-01

22

Effect of burst ions on the excitation of ion-acoustic solitons in a drifting plasma  

Microsoft Academic Search

The characteristics of fast burst ions and ion-acoustic solitons in a drifting plasma, as well as their interaction, are investigated experimentally. It is shown that the soliton evolves from the normal fast ion-beam mode excited locally in the presheath region of an excitation grid. The burst ions are created by applying a positive ramp voltage to the grid. Adjusting the

De-Long Xiao; J. X. Ma; Yi-Ren Li; Yang-Fang Li; M. Y. Yu

2007-01-01

23

Drift ion acoustic solitons in an inhomogeneous 2-D quantum magnetoplasma  

Microsoft Academic Search

Linear and nonlinear propagation characteristics of quantum drift ion acoustic waves are investigated in an inhomogeneous two-dimensional plasma employing the quantum hydrodynamic (QHD) model. In this regard, the dispersion relation of the drift ion acoustic waves is derived and limiting cases are discussed. In order to study the drift ion acoustic solitons, nonlinear quantum Kadomstev–Petviashvilli (KP) equation in an inhomogeneous

W. Masood

2009-01-01

24

Observation of large electron drift velocities in InN by ultrafast Raman spectroscopy  

Microsoft Academic Search

Electron transport in an InN film grown on GaN has been studied by transient Raman spectroscopy at T=300 K. Our experimental results demonstrate that under the subpicosecond laser excitation and probing, electron drift velocity of carriers in the ? valley can exceed its steady-state value by as much as 40%. Electron velocities have been found to cut off at around

K. T. Tsen; C. Poweleit; D. K. Ferry; Hai Lu; William J. Schaff

2005-01-01

25

Observation of large electron drift velocities in InN by ultrafast Raman spectroscopy  

Microsoft Academic Search

Electron transport in an InN film grown on GaN has been studied by transient Raman spectroscopy at T=300 K. Our experimental results demonstrate that under the subpicosecond laser excitation and probing, electron drift velocity of carriers in the Gamma valley can exceed its steady-state value by as much as 40%. Electron velocities have been found to cut off at around

K. T. Tsen; C. Poweleit; D. K. Ferry; Hai Lu; William J. Schaff

2005-01-01

26

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

NASA Astrophysics Data System (ADS)

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 (0.8°N dip latitude) and Piura (6.8°N dip latitude) in Peru and from Davao (1.4°S dip latitude) and Muntinlupa (6.3°N 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.

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

2006-08-01

27

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

NASA Astrophysics Data System (ADS)

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.

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

2009-11-01

28

On the study of ion-acoustic solitary waves and double-layers in a drift multicomponent plasma with electron-inertia  

NASA Astrophysics Data System (ADS)

Using the pseudopotential method, theoretical investigation has been made on the first-order Korteweg-deVries ion-acoustic solitons in a multicomponent plasma consisting of warm positive ions, negative ions and isothermal electrons. The effects of electron-inertia and drift motion of the ions on the amplitudes and widths of the solitons have been studied in a plasma having (H^+, Cl^-), (H^+, O^-), (He^+, H^-) and (He^+, O^-) ions. Ion-acoustic double-layers have also been investigated for such plasmas. It has been found that drift velocity and electron-inertia have significant contribution on the formation of double-layers in multicomponent plasma.

Paul, S. N.; Chattopadhyaya, S.; Bhattacharya, S. K.; Bera, B.

2003-06-01

29

The wind-induced drift velocity of the freshwater layer on the sea's surface  

NASA Astrophysics Data System (ADS)

The effect of an unsteady river plume on the wind drift was studied. Initially, the plume occurs as a horizontal homogeneous near-surface layer with a low density and different thicknesses being washed around by the wind in the course of time due to the vertical mixing with the underlying waters. This process is described using the one-dimensional Princeton Ocean Model (POM) with the integrated turbulence submodel. A series of numerical experiments yielded the empirical dependence of the normalized surface drift velocity modulus on the nondimensional parameters: the Ekman numbers and the relations between the buoyancy and Coriolis forces.

Zhurbas, N. V.

2013-03-01

30

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

SciTech Connect

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 ?) 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.

Adnan, Muhammad; Qamar, Anisa [Institute of Physics and Electronics, University of Peshawar, Peshawar 25000 (Pakistan); National Center for Physics, Quaid-i-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan); Mahmood, S. [National Center for Physics, Quaid-i-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan); Theoretical Physics Division, PINSTECH P.O. Nilore Islamabad 44000 (Pakistan); Physics Institute, Federal University of Rio Grande do Sul (UFRGS), 915051-970, Porto Alegre, RS (Brazil)

2014-09-15

31

Comparison of nighttime zonal neutral winds and equatorial plasma bubble drift velocities over Brazil  

NASA Astrophysics Data System (ADS)

We present results from the first extended period of coincident observations of thermospheric zonal neutral winds and equatorial plasma bubble (EPB) zonal drift velocities over northeastern Brazil during the October to December months of 2009 and 2010. The EPB zonal drift velocities are estimated utilizing images of the O I 630.0 nm emissions recorded by a wide-angle imaging system at Cajazeiras. Thermospheric neutral wind estimates are based upon common volume observations made by a bistatic Fabry-Perot interferometer (FPI) experiment using FPIs located at Cajazeiras and Cariri in Brazil observing the Doppler shift of the O I 630.0 nm emission. The results illustrate a similar pattern of nighttime and night-to-night variations in the zonal neutral winds and EPB zonal drift velocities. In general, the geomagnetic zonal neutral winds and the EPB velocities show an excellent agreement illustrating that the F region dynamo is fully developed. However, in the early evening hours the EPB zonal speed is slower than that of the background winds on several occasions. We conclude that this indicates that during the bubble evolution period in the early evening the F region dynamo is not fully activated.

Chapagain, Narayan P.; Makela, Jonathan J.; Meriwether, John W.; Fisher, Daniel J.; Buriti, Ricardo A.; Medeiros, Amauri F.

2012-06-01

32

Intersaccadic drift velocity is sensitive to short-term hypobaric hypoxia.  

PubMed

Hypoxia, defined as decreased availability of oxygen in the body's tissues, can lead to dyspnea, rapid pulse, syncope, visual dysfunction, mental disturbances such as delirium or euphoria, and even death. It is considered to be one of the most serious hazards during flight. Thus, early and objective detection of the physiological effects of hypoxia is critical to prevent catastrophes in civil and military aviation. The few studies that have addressed the effects of hypoxia on objective oculomotor metrics have had inconsistent results, however. Thus, the question of whether hypoxia modulates eye movement behavior remains open. Here we examined the effects of short-term hypobaric hypoxia on the velocity of saccadic eye movements and intersaccadic drift of Spanish Air Force pilots and flight engineers, compared with a control group that did not experience hypoxia. Saccadic velocity decreased with time-on-duty in both groups, in correlation with subjective fatigue. Intersaccadic drift velocity increased in the hypoxia group only, suggesting that acute hypoxia diminishes eye stability, independently of fatigue. Our results suggest that intersaccadic drift velocity could serve as a biomarker of acute hypoxia. These findings may also contribute to our understanding of the relationship between hypoxia episodes and central nervous system impairments. PMID:24877213

Di Stasi, Leandro L; Cabestrero, Raúl; McCamy, Michael B; Ríos, Francisco; Catena, Andrés; Quirós, Pilar; Lopez, Jose A; Saez, Carolina; Macknik, Stephen L; Martinez-Conde, Susana

2014-04-01

33

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

SciTech Connect

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.

Heelis, R.A.; Coley, W.R. (Univ. of Texas, Richardson (United States))

1992-12-01

34

High Resolution Ion Mobility Spectrometry with Increased Ion Transmission: Exploring the Analytical Utility of Periodic-Focusing DC Ion Guide Drift Cells  

E-print Network

Drift tube ion mobility spectrometry (IMS) is a powerful, post-ionization separation that yields structural information of ions through an ion-neutral collision cross section. The ion-neutral collision cross section is governed by the collision...

Blase, Ryan Christopher

2012-02-14

35

Drift velocity of the ionospheric irregularities measured by closely-spaced GNSS receivers in Tromsoe, Norway  

NASA Astrophysics Data System (ADS)

A radio signal passing through small-scale irregularities in the ionospheric electron density fluctuates in amplitude and phase because the irregularities act as diffraction gratings. This phenomenon is known as scintillation. The GNSS (Global Navigation Satellite System) scintillation is caused by irregularities with a scale-size of several hundred meters. In this study, we use three GNSS receivers at the EISCAT radar site in Tromsoe, Norway, where optical and radio measurements are carried out. On January, 2012, we have installed a GNSS receiver at EISCAT radar site in Tromsoe, Norway. The receiver measures phase and signal-to-noise ratio of the radio wave from the GNSS satellites at dual frequency (L1 and L2) at 50 Hz, so that total electron content (TEC) and phase and amplitude scintillations of the ionosphere can be obtained. On September, 2012, we have installed two more receivers at Tromsoe. The distances between the three GNSS receivers are 172m, 242m and 218m, respectively. Drift velocities of irregularities can be measured using cross-correlation analysis for the time series of the GNSS signal intensity and phase obtained from the three receivers. Weak scintillation with an S4 index of 0.15 was observed at 1545 - 1605 UT on November 20, 2012. Period of the signal intensity variation was approximately 0.5 seconds. Since the scale-size of the irregularity causing the GPS scintillation, which corresponds to the Fresnel scale, is approximately 200 m, drift velocity of the irregularity causing the scintillation is estimated 400 m/s. On the other hand, the drift velocity was also estimated to be 350-400 m/s west-northwestward using cross-correlation analysis with the time series of the GPS signal intensity obtained from the three receivers. This velocity is similar to that estimated from the period of the signal intensity variation. The direction of aurora movement observed simultaneously using a digital camera at Tromsoe is also similar to that of the velocity estimated from the closely-spaced GNSS receivers. In this presentation, we discuss relationship of the irregularity drift velocity with aurora structure and movement based on these observations.

Ito, Y.; Otsuka, Y.; Shiokawa, K.; Hosokawa, K.; Ogawa, Y.

2013-12-01

36

Electron attachment, effective ionization coefficient, and electron drift velocity for CF 4 gas mixtures  

NASA Astrophysics Data System (ADS)

For tracking in a SSC experiment with wire chambers, CF 4 gas mixtures are very advantageous from the point of view of aging, drift velocity, and spatial resolution. However, they are also known to suffer from considerable electron attachment. This attachment can cause serious inefficiencies in the collection of electrons liberated near the anode wire, and causes broadening of the pulse-height spectrum for all ionization electrons. Two bench-top setups have been used to study electron attachment of CF 4 gas mixtures, and related properties such as the gas gain difference between single-electron avalanches and 55Fe X-ray initiated avalanches, the degradation of the energy resolution due to electron attachment, and the effective ionization coefficient overline?(? ? - ?) . A set of three prototype straw-tube modules each containing an 8 × 8 bundle of straws has been constructed and tested at a Fermilab test beam with various CF 4 gas mixtures. Some preliminary results on the drift velocity and drift time for these gas mixtures are reported.

Anderson, W. S.; Armitage, J. C.; Dunn, E.; Heinrich, J. G.; Lu, C.; McDonald, K. T.; Weckel, J.; Zhu, Y.

1992-12-01

37

A large enhancement of the maximum drift velocity of electrons in the channel of a field-effect heterotransistor  

SciTech Connect

It is shown that the optical-phonon momentum quantization in a GaAs quantum well resulting from the introduction of an InAs quantum-dot barrier layer provides for the elimination of inelastic scattering of electrons by optical phonons and, thus, makes the acceleration of electrons above the saturation drift velocity possible. It is shown experimentally that the maximum drift velocity of electrons in high electric fields in AlGaAs/GaAs heterostructure with InAs quantum-dot barriers introduced into the GaAs quantum well exceeds the saturation drift velocity in bulk GaAs by as much as a factor of 10. Such a rise in the maximum drift velocity of electrons ensures increased maximum current density, transconductance, and cutoff frequency of the heterostructure field-effect transistor with quantum dots.

Pozela, J. K. [Semiconductor Physics Institute (Lithuania)], E-mail: pozela@spi.pfi.lt; Mokerov, V. G. [Russian Academy of Sciences, Institute of the Microwave Semiconductor Electronics (Russian Federation)

2006-03-15

38

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

39

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

SciTech Connect

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.

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

2008-07-15

40

Graphene, a material for high temperature devices – intrinsic carrier density, carrier drift velocity, and lattice energy  

PubMed Central

Heat has always been a killing matter for traditional semiconductor machines. The underlining physical reason is that the intrinsic carrier density of a device made from a traditional semiconductor material increases very fast with a rising temperature. Once reaching a temperature, the density surpasses the chemical doping or gating effect, any p-n junction or transistor made from the semiconductor will fail to function. Here, we measure the intrinsic Fermi level (|EF| = 2.93?kBT) or intrinsic carrier density (nin = 3.87 × 106?cm?2K?2·T2), carrier drift velocity, and G mode phonon energy of graphene devices and their temperature dependencies up to 2400?K. Our results show intrinsic carrier density of graphene is an order of magnitude less sensitive to temperature than those of Si or Ge, and reveal the great potentials of graphene as a material for high temperature devices. We also observe a linear decline of saturation drift velocity with increasing temperature, and identify the temperature coefficients of the intrinsic G mode phonon energy. Above knowledge is vital in understanding the physical phenomena of graphene under high power or high temperature. PMID:25044003

Yin, Yan; Cheng, Zengguang; Wang, Li; Jin, Kuijuan; Wang, Wenzhong

2014-01-01

41

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

NASA Technical Reports Server (NTRS)

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.

Reinleitner, L. A.; Nielsen, E.

1985-01-01

42

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

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

43

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

SciTech Connect

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.

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

44

Behaviour of ion velocity distributions for a simple collision model  

NASA Technical Reports Server (NTRS)

Calculation of the ion velocity distributions for a weakly ionized plasma subjected to crossed electric and magnetic fields. An exact solution to Boltzmann's equation has been obtained by replacing the Boltzmann collision integral with a simple relaxation model. At altitudes above about 150 km, where the ion collision frequency is much less than the ion cyclotron frequency, the ion distribution takes the shape of a torus in velocity space for electric fields greater than 40 mV/m. This shape persists for one to two hours after application of the electric field. At altitudes where the ion collision and cyclotron frequencies are approximately equal (about 120 km), the ion velocity distribution is shaped like a bean for large electric field strengths. This bean-shaped distribution persists throughout the lifetime of ionospheric electric fields. These highly non-Maxwellian ion velocity distributions may have an appreciable affect on the interpretation of ion temperature measurements.

St-Maurice, J.-P.; Schunk, R. W.

1974-01-01

45

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

SciTech Connect

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.

Fraschetti, F.; Giacalone, J. [Department of Planetary Sciences and Astronomy, University of Arizona, Tucson, AZ 85721 (United States)

2012-08-20

46

Vertical Drift Velocities and East-West Electric Fields at the Magnetic Equator  

Microsoft Academic Search

Incoherent scatter observations of vertical drifts taken at Jicamarca (2 ø dip) are presented. Vertical drifts are found to be nearly constant as a function of height. These vertical drifts can also be taken as a direct measurement of the east-west electric fields at the magnetic equator. Their daily and seasonal behavior is presented. The effect of geomagnetic activity is

Ronald F. Woodman

1970-01-01

47

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

NASA Astrophysics Data System (ADS)

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.

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

2011-11-01

48

A New TDDB Degradation Model Based on Cu Ion Drift in Cu Interconnect Dielectrics  

Microsoft Academic Search

A new physical model of time-dependent dielectric breakdown (TDDB) in Cu interconnect dielectrics is proposed. TDDB occurs due to the drift of Cu ions under an electric field E. An activation energy analysis of the leakage current demonstrates that these injected Cu ions affect the conduction mechanism of electrons. The dominant electron conduction mechanism changes from Poole-Frenkel electron current through

N. Suzumura; S. Yamamoto; D. Kodama; K. Makabe; J. Komori; E. Murakami; S. Maegawa; K. Kubota

2006-01-01

49

Stationary Plasma Thruster Ion Velocity Distribution  

NASA Technical Reports Server (NTRS)

A nonintrusive velocity diagnostic based on laser induced fluorescence of the 5d4F(5/2)-6p4D(5/2) singly ionized xenon transition was used to interrogate the exhaust of a 1.5 kW Stationary Plasma Thruster (SPT). A detailed map of plume velocity vectors was obtained using a simplified, cost-effective, nonintrusive, semiconductor laser based scheme. Circumferential velocities on the order of 250 m/s were measured which implied induced momentum torques of approximately 5 x 10(exp -2) N-cm. Axial and radial velocities were evaluated one mm downstream of the cathode at several locations across the width of the annular acceleration channel. Radial velocities varied linearly with radial distance. A maximum radial velocity of 7500 m/s was measured 8 mm from the center of the channel. Axial velocities as large as 16,500 m/s were measured.

Manzella, David H.

1994-01-01

50

Optimal transport of two ions under slow spring-constant drifts  

E-print Network

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.

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

2015-02-05

51

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

NASA Technical Reports Server (NTRS)

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.

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

1998-01-01

52

Spectator-velocity pions from heavy ions  

SciTech Connect

The discussion centers on pions in the velocity regions of target and projectile, where strong spectral features appear. The topics covered include stopped-pion studies, and convoy pions in the projectile frame. (GHT)

Rasmussen, J.; Ridout, J.; Murphy, D.; Radi, H.M.A.

1982-11-01

53

The functional response of drift-feeding Arctic grayling: the effects of prey density, water velocity, and location efficiency  

Microsoft Academic Search

An important aspect of a predator-prey system is the functional response of the predator to changing prey densities. We studied the feeding rate response of drift-feeding Arctic grayling ( Thymallus arcticus) on a small inverte- brate prey, Daphnia middendorffiana, at densities ranging from 0.01 L-1 to 1.8 L-1 and current velocities of 25, 32, and 40 cm·s-1. We videotaped the

W. John O'Brien; Michael Barfield; Karen Sigler

2001-01-01

54

Ion velocities in a micro-cathode arc thruster  

SciTech Connect

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.

Zhuang Taisen; Shashurin, Alexey; Keidar, Michael [The George Washington University, Washington, DC 22202 (United States); Beilis, Isak [Tel Aviv University, Tel Aviv (Israel)

2012-06-15

55

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

Microsoft Academic Search

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

R.A. Heelis; W. R. Coley

1992-01-01

56

Nonuniform charging effects on ion drag force in drifting dusty plasmas  

SciTech Connect

The nonuniform polarization charging effects on the ion drag force are investigated in drifting dusty plasmas. The ion drag force due to the ion-dust grain interaction is obtained as a function of the dust charge, ion charge, plasma temperature, Mach number, Debye length, and collision energy. The result shows that the nonuniform charging effects enhance the momentum transfer cross section as well as the ion drag force. It is found that the momentum transfer cross section and the ion drag force including nonuniform polarization charging effects increase with increasing the Mach number and also the ion drag force increases with increasing the temperature. In addition, it is found that the ion drag force is slightly decreasing with an increase of the Debye length.

Chang, Dong-Man; Chang, Won-Seok; Jung, Young-Dae [Department of Applied Physics, Hanyang University, Ansan, Kyunggi-Do 426-791 (Korea, Republic of)

2006-03-01

57

TEERAHERTZ LASER VELOCITY MODULATION SPECTROSCOPY OF IONS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Velocity modulation spectroscopy has been investigated in the terahertz region, employing pure rotational transitions of ArH+ and rotation-tunneling transitions of H3O+ to study the competition between pressure broadening and Doppler broadening on the lineshapes, neutral suppression and modulation e...

58

Low velocity ion stopping in binary ionic mixtures  

SciTech Connect

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.

Tashev, Bekbolat; Baimbetov, Fazylkhan [Department of Physics, Kazakh National University, Tole Bi 96, Almaty 480012 (Kazakhstan); Deutsch, Claude [LPGP (UMR-CNRS 8578), Universite Paris XI, 91405 Orsay (France); Fromy, Patrice [Direction de l'Informatique, Universite Paris XI, 91405 Orsay (France)

2008-10-15

59

Ion velocity measurements for laser mass ablation studies  

NASA Astrophysics Data System (ADS)

The measurements used 10 J, 1.7 ns (FWHM), 1.06 micrometers laser pulse to irradiate flat Al targets. A range of lenses with focal lengths from 75 mm to 2000 mm were used to focus 50 mm diameter beam on target, resulting in a range of optical spot diameters from 30 micrometers to 3.5 mm. Irradiance on target was varied by inserting calibrated glass Nd filters in the main beam. Ion velocities were recorded using six time-of-flight Faraday cup collectors arrayed in the horizontal plane from 10 deg to 80 deg to the target normal at distances approx. 40 cm from the plasma. The focal spot size was measured by imaging the focal plane distribution onto infrared film. Ion velocities were calculated from the arrival time of the peak ion current. Polar ion velocity plots were extrapolated to determine the ion velocity normal to the target surface. These normal velocities were then plotted against irradiance I for each spot size. Random shots onto plastic targets showed no significant difference in measured velocities.

Pina, L.

1981-10-01

60

Comparison of azimuthal ion velocity profiles using Mach probes, time delay estimation, and laser induced fluorescence in a linear plasma device.  

PubMed

We compare measurements of radially sheared azimuthal plasma flow based on time delay estimation (TDE) between two spatially separated Langmuir probes, Mach probes and laser induced fluorescence (LIF). TDE measurements cannot distinguish between ion fluid velocities and phase velocities. TDE and Mach probes are perturbative, so we compare the results against LIF, a non-perturbative, spatially resolved diagnostic technique that provides direct measurements of the ion velocity distribution functions. The bulk ion flow is determined from the Doppler shift of the Argon absorption line at 668.6139 nm. We compare results from all the three diagnostics, at various magnetic fields, which acts as a control knob for development of drift wave turbulence. We find that while Mach probes and LIF give similar profiles, TDE measurements typically overestimate the velocities and are also sensitive to the drift wave modes being investigated. PMID:23126882

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

2012-10-01

61

Prediction of peptide drift time in ion mobility mass spectrometry from sequence-based features  

PubMed Central

Background Ion mobility-mass spectrometry (IMMS), an analytical technique which combines the features of ion mobility spectrometry (IMS) and mass spectrometry (MS), can rapidly separates ions on a millisecond time-scale. IMMS becomes a powerful tool to analyzing complex mixtures, especially for the analysis of peptides in proteomics. The high-throughput nature of this technique provides a challenge for the identification of peptides in complex biological samples. As an important parameter, peptide drift time can be used for enhancing downstream data analysis in IMMS-based proteomics. Results In this paper, a model is presented based on least square support vectors regression (LS-SVR) method to predict peptide ion drift time in IMMS from the sequence-based features of peptide. Four descriptors were extracted from peptide sequence to represent peptide ions by a 34-component vector. The parameters of LS-SVR were selected by a grid searching strategy, and a 10-fold cross-validation approach was employed for the model training and testing. Our proposed method was tested on three datasets with different charge states. The high prediction performance achieve demonstrate the effectiveness and efficiency of the prediction model. Conclusions Our proposed LS-SVR model can predict peptide drift time from sequence information in relative high prediction accuracy by a test on a dataset of 595 peptides. This work can enhance the confidence of protein identification by combining with current protein searching techniques. PMID:23815343

2013-01-01

62

Electrostatic ion cyclotron velocity shear instability  

NASA Technical Reports Server (NTRS)

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).

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

1992-01-01

63

A Mass-Selective Variable-Temperature Drift Tube Ion Mobility-Mass Spectrometer for Temperature Dependent Ion Mobility Studies  

NASA Astrophysics Data System (ADS)

A hybrid ion mobility-mass spectrometer (IM-MS) incorporating a variable-temperature (80-400 K) 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 30.2 cm uniform field drift tube enclosed within a thermal envelope. Subambient temperatures down to 80 K 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 TiCl4 and hydration reactions of Ti+ with residual water are presented.

May, Jody C.; Russell, David H.

2011-07-01

64

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

NASA Technical Reports Server (NTRS)

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.

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

1997-01-01

65

Observation of Anomalous Ion Heating by Broadband Drift-Wave Turbulence  

SciTech Connect

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.

Enge, S.; Birkenmeier, G.; Manz, P.; Ramisch, M.; Stroth, U. [Institut fuer Plasmaforschung, Universitaet Stuttgart, 70569 Stuttgart (Germany)

2010-10-22

66

A pulsed drift cavity to capture 30 keV ion bunches at ground potential  

NASA Astrophysics Data System (ADS)

To capture radioactive ion beams of tens of keV in an ion trap, the use of a pulsed drift cavity allows one to avoid placing the complete setup on a high voltage (HV) platform. By pulsing down the voltage on a long electrode while the ion bunch is inside it, the electric potential zero level can be shifted down over a range equal to the initial beam energy, thus allowing the ions to be captured in a trap at ground potential. The pulsed drift cavity of the WITCH setup, which is completely HV-platform free, is described here. It is demonstrated that bunched beams with energies of typically 30-60 keV, as will become available to all users at the ISOLDE facility after the installation of an RFQ buncher, can be transported over distances of tens of meters to the experiments and by means of a pulsed drift cavity directly be injected into a purification Penning trap. Simulation work showing the efficiency of such a system is discussed and tests showing the feasibility of such a system are presented. An estimate of the pulse down time is made from TOF spectra. An outlook on how the system can be improved is presented too.

Coeck, S.; Delauré, B.; Herbane, M.; Beck, M.; Golovko, V. V.; Kopecky, S.; Kozlov, V. Yu.; Kraev, I. S.; Lindroth, A.; Phalet, T.; Beck, D.; Delahaye, P.; Herlert, A.; Wenander, F.; Severijns, N.

2007-03-01

67

Closed electron drift in a self-magnetically insulated ion diode  

SciTech Connect

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.

Pushkarev, A. I.; Isakova, Y. I. [Tomsk Polytechnic University, 2a Lenin Ave., Tomsk 634050 (Russian Federation)] [Tomsk Polytechnic University, 2a Lenin Ave., Tomsk 634050 (Russian Federation)

2013-05-15

68

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

SciTech Connect

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.

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

69

Analysis of a drift-diffusion model with velocity saturation for spin-polarized transport in semiconductors  

E-print Network

A system of drift-diffusion equations with electric field under Dirichlet boundary conditions is analyzed. The system of strongly coupled parabolic equations for particle density and spin density vector describes the spin-polarized semi-classical electron transport in ferromagnetic semiconductors. The presence of a nonconstant and nonsmooth magnetization vector, solution of the Landau-Lifshitz equation, causes the diffusion matrix to be dependent from space and time and to have in general poor regularity properties, thus making the analysis challenging. To partially overcome the analytical difficulties the velocity saturation hypothesis is made, which results in a bounded drift velocity. The global-in-time existence and uniqueness of weak solutions is shown by means of a semi-discretization in time, which yields an elliptic semilinear problem, and a quadratic entropy inequality, which allow for the limit of vanishing time step size. The convergence of the weak solutions to the steady state, under some restrictions on the parameters and data, is shown. Finally the higher regularity of solutions for a smooth magnetization in two space dimensions is shown through a diagonalization argument, which allows to get rid of the cross diffusion terms in the fluid equations, and the iterative application of Gagliardo-Nirenberg inequalities and a generalized version of Aubin lemma.

Nicola Zamponi

2014-02-25

70

Pickup Ion Velocity Distributions at Titan: Effects of Spatial Gradients  

NASA Technical Reports Server (NTRS)

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(sup +) ions identified during the Voyager 1 flyby. 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. Iri 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.

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

2004-01-01

71

Simulating Ion Permeation Through the ompF Porin Ion Channel Using Three-Dimensional Drift-Diffusion Theory  

Microsoft Academic Search

Ionic channels, natural nanotubes found in biological cells, are interesting to the electronics community because they display a range of device-like functions. The purpose of this paper is to illustrate how the solution methodology, developed for 3-D drift-diffusion models of semiconductor devices, can be applied to ion permeation in ionic channels. For this study we select the ompF porin channel,

T. A. van der Straaten; J. M. Tang; U. Ravaioli; R. S. Eisenberg; N. R. Aluru

2003-01-01

72

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

SciTech Connect

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.

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

2008-05-30

73

Ion Temperature and Rotational Velocity Measurement in SSPX  

NASA Astrophysics Data System (ADS)

Lawrence Livermore National Laboratory, Livermore, CA 94550, USA. Anomalous ion heating and acceleration has been observed in spheromaks, although the precise mechanism that gives rise to this phenomenon is still unclear. In order to elucidate this, an ion Doppler spectrometer (IDS) has been designed and constructed to measure the ion temperatures and rotational velocities of impurity ions in SSPX plasmas. The IDS consists of a telescope, spectrometer with a grating density of 2400 lines/inch, and a 16 channel PMT. The output from the PMT is digitized and fit to a Gaussian curve, from which the ion temperature and Doppler-shift of the line is obtained. A dispersion of 0.02 nm/mm is calculated at the spectrometer output, allowing ion temperatures to 800 eV to be measured. This work follows on from initial investigations made last year, in which ion temperatures of 600eV and rotational velocities of 2km/s were observed in SSPX (Nagata et al Bull. Am. Phys. Soc. Seattle, 1999) This work was performed under the auspices of US DOE by the University of California Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.

Auerbach, D. W.; Hill, D. N.; McLean, H. S.; Sspx Team

2000-10-01

74

Superconducting accelerating structures for very low velocity ion beams  

SciTech Connect

This paper presents designs for four types of very-low-velocity superconducting accelerating cavity capable of providing several MV of accelerating potential per cavity, and suitable for particle velocities in the range 0.006 < v/c < 0.06. Superconducting TEM-class cavities have been widely applied to CW acceleration of ion beams. SC linacs can be formed as an array of independently-phased cavities, enabling a variable velocity profile to maximize the output energy for each of a number of different ion species. Several laboratories in the US and Europe are planning exotic beam facilities based on SC linacs. The cavity designs presented here are intended for the front-end of such linacs, particularly for the post-acceleration of rare isotopes of low charge state. Several types of SC cavities have been developed recently to cover particle velocities above 0.06c. Superconducting four-gap quarter-wave resonators for velocities 0.008 < {beta} = v/c < 0.05 were developed about two decades ago and have been successfully operated at the ATLAS SC linac at Argonne National Laboratory. Since that time, progress in simulation tools, cavity fabrication and processing have increased SC cavity gradients by a factor of 3-4. This paper applies these tools to optimize the design of a four-gap quarter-wave resonator for exotic beam facilities and other low-velocity applications.

Xu, J.; Shepard, K.W.; Ostroumov, P.N.; Fuerst, J.D.; Waldschmidt, G.; /Argonne; Gonin, I.V.; /Fermilab

2008-01-01

75

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

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

76

Machine learning based prediction for peptide drift times in ion mobility spectrometry  

PubMed Central

Motivation: Ion mobility spectrometry (IMS) has gained significant traction over the past few years for rapid, high-resolution separations of analytes based upon gas-phase ion structure, with significant potential impacts in the field of proteomic analysis. IMS coupled with mass spectrometry (MS) affords multiple improvements over traditional proteomics techniques, such as in the elucidation of secondary structure information, identification of post-translational modifications, as well as higher identification rates with reduced experiment times. The high throughput nature of this technique benefits from accurate calculation of cross sections, mobilities and associated drift times of peptides, thereby enhancing downstream data analysis. Here, we present a model that uses physicochemical properties of peptides to accurately predict a peptide's drift time directly from its amino acid sequence. This model is used in conjunction with two mathematical techniques, a partial least squares regression and a support vector regression setting. Results: When tested on an experimentally created high confidence database of 8675 peptide sequences with measured drift times, both techniques statistically significantly outperform the intrinsic size parameters-based calculations, the currently held practice in the field, on all charge states (+2, +3 and +4). Availability: The software executable, imPredict, is available for download from http:/omics.pnl.gov/software/imPredict.php Contact: rds@pnl.gov Supplementary information: Supplementary data are available at Bioinformatics online. PMID:20495001

Shah, Anuj R.; Agarwal, Khushbu; Baker, Erin S.; Singhal, Mudita; Mayampurath, Anoop M.; Ibrahim, Yehia M.; Kangas, Lars J.; Monroe, Matthew E.; Zhao, Rui; Belov, Mikhail E.; Anderson, Gordon A.; Smith, Richard D.

2010-01-01

77

Coulomb explosion at low and high ion velocities  

NASA Astrophysics Data System (ADS)

The ion-induced electric field is calculated for estimating the effect of the Coulomb explosion (CE) mechanism. The increase of the kinetic energy of lattice ions in the electric field of the track core is ?? ? (q(0))4, where q(r) is the induced initial charge density. Estimates are made for the irradiation of SiO2 by 2 MeV/nucleon Kr beam: the mean energy of lattice ions reaches 8.1 eV within 4 fs in the track core. The Lorentzian and Gaussian charge density distributions lead to similar results. The type of solids affects ?? through the charge neutralization time. As a result of the decrease of q(0), ?? is reduced by about an order of magnitude in the range 2-8 MeV/nucleon. The projectile velocity may affect the formation of ion-induced tracks by the CE mechanism.

Szenes, G.

2013-03-01

78

The effects of hyper-velocity dust-particle impacts on the LOFT Silicon Drift Detectors  

NASA Astrophysics Data System (ADS)

Solid-state detectors that operate in orbit are required to withstand harsh space environment conditions. Among the various phenomena able to damage the sensors, X-ray detectors are subjected to impacts of orbital debris and micrometeoroids whenever, to be sensitive to low energy photons, they need to be ``directly'' exposed to the sky. The LOFT mission, proposed for the M3 class opportunity of the ESA Cosmic Vision, has a very-large sensitive area (greater than 10 m2) made of Silicon Drift Detectors (SDD). Moreover, the satellite includes an X-ray Wide-Field Monitor based on the same SDD detectors. Here we present the results of a test campaign at the Cosmic Dust Accelerator Facility at MPIK in Heidelberg aimed at the space qualification of the detectors with respect to this phenomenon.

Zampa, G.; Del Monte, E.; Perinati, E.; Rashevskaya, I.; Rachevski, A.; Zampa, N.; Bugiel, S.; Kendziorra, E.; Tenzer, C.; Feroci, M.; Santangelo, A.; Vacchi, A.

2014-07-01

79

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)

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.

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

2007-12-01

80

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

NASA Astrophysics Data System (ADS)

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.

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

2007-11-01

81

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

NASA Astrophysics Data System (ADS)

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.

Yip, Chi-Shung

82

Amplification of ion acoustic wave in an inhomogeneous plasma through nonlinear wave-particle interaction with drift wave turbulence  

SciTech Connect

A study on the amplification of ion acoustic wave in an inhomogeneous plasma has been made on the basis of a nonlinear wave-particle interaction process called plasma maser effect. The drift wave instability, which is a universal phenomenon of an inhomogeneous confined plasma system, is found to be strongly in phase relation with thermal particles and may transfer its wave energy nonlinearly through a modulated field to ion acoustic wave. Considering a Maxwellian distribution function model for inhomogeneous plasmas under the standard local approximation, we have estimated the growth rate for ion acoustic wave, which is obtained by using the nonlinear dispersion relation. It has been found that amplification of ion acoustic wave is possible at the expense of drift wave turbulent energy. This result may be particularly important for stability of various drift modes in magnetically confined plasma as well as for transport of momentum and energy in such inhomogeneous systems.

Deka, P. N.; Borgohain, A. [Department of Mathematics, Dibrugarh University, Dibrugarh-786004, Assam (India)

2011-04-15

83

Drift orbit topology of fast ions in tokamaks Plasma Science and Fusion Centre, Massachusetts Institute of Technology,  

E-print Network

Drift orbit topology of fast ions in tokamaks J. Egedal Plasma Science and Fusion Centre methods are developed by which the guiding centre orbit topology of fast ions in tokamaks is e#ciently obtained and displayed. For constant energy we characterize the orbits by a new set of constant of motion

Egedal, Jan

84

Drift orbit topology of fast ions in tokamaks Plasma Science and Fusion Centre, Massachusetts Institute of Technology,  

E-print Network

Drift orbit topology of fast ions in tokamaks J. Egedal Plasma Science and Fusion Centre methods are developed by which the guiding centre orbit topology of fast ions in tokamaks is efficiently obtained and displayed. For constant energy we characterize the orbits by a new set of constant of motion

Egedal, Jan

85

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

PubMed

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

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

2014-08-22

86

Preferential acceleration of heavy ions from thermal velocities D. B. MELROSE  

E-print Network

Preferential acceleration of heavy ions from thermal velocities D. B. MELROSE #12;Preferential acceleration of heavy ions from thermal velocities1 D. B. MELROSE Belfer Graduate School of Science, Yeshiva University, New York, N.Y., U.S.A. Received June 15, 1967 The acceleration of ions from thermal velocities

Melrose, Don

87

Plasma-Enhanced-Polymerization Thin-Film as a Drift Barrier for Cu Ions  

NASA Astrophysics Data System (ADS)

The barrier properties of divinyl siloxane-benzocyclobutene (DVS-BCB) films formed by plasma-enhanced polymerization were studied for ultralow-k porous silica (po-SiO) interlayer dielectrics. Time-dependent dielectric breakdown (TDDB) measurements of blanket Cu/BCB/Si metal-insulator-semiconductor (MIS) capacitors showed no polarity dependence of the bias-temperature stresses at 200 °C under 2 MV/cm, indicating that Cu ions hardly drifted into the BCB film with the positive bias stress. On the other hand, Cu/SiOC/Si MIS capacitors under the positively biased Cu showed a significant degradation in the TDDB lifetime compared with the negative bias case. The barrier effect of the thin BCB was confirmed from the TDDB measurements using Cu/BCB/ultralow-k-po-SiO/Si stacked MIS structures. The TDDB lifetime of the stacked MIS capacitor was improved more than 30-fold by the use of 15-nm-thick BCB on po-SiO. The electric field and temperature dependences of the TDDB lifetime of the stacked MIS structure indicated that the TDDB lifetime of po-SiO capped with 15-nm-thick BCB is longer than 10 years at 125 °C and 1.4 MV/cm. We conclude that the barrier property of BCB that is as thin as 15 nm is effective for preventing Cu ion drift into interlayer dielectrics.

Yoshino, Takenobu; Hata, Nobuhiro; Kawahara, Jun; Shishida, Yoshinori; Kikkawa, Takamaro

2007-04-01

88

Detailed measurements of anisotropic mirror plasma ion energy distributions during drift cyclotron loss-cone instability  

SciTech Connect

Using improved computer filtering and a reconstruction analysis we have been able to extract additional details on a mirror plasma's midplane ion energy distribution from the current--voltage (I--V) curve of a voltage-swept electrostatic end loss analyzer (ELA). For the University of Maryland's MIX-1 plasma (Phys. Fluids 23, 3439 (1976)), the diagnostic technique has provided us with important information on the ''loss-cone region'' of an anisotropic ion distribution during drift cyclotron loss-cone (DCLC) instability experiments. Observations include convincing verification of ion distribution modification during DCLC evolution and an enhancement of the loss-region boundary over that predicted by simplified trapping theory. The reconstruction analysis involves matching the differentiated I--V curves (i.e., dI/dV vs V) to theoretically predicted curves based on model midplane ion distribution functions. The theoretical curves are obtained from the model midplane distributions by a mapping transformation based on conservation of magnetic moment and total energy of each ion along lines of magnetic flux.

Booske, J.H.; McCarrick, M.J.; Ellis, R.F.; Paquette, J.A.

1988-02-01

89

Scavenging of atmospheric ions and aerosols by drifting snow in Antarctica  

E-print Network

Measurements of the small,intermediate, and large ion concentrations and the airearth current density along with simultaneous measurements of the concentration and size-distribution of aerosol particles in the size ranges 4.4 to 163 nm and 0.5 to 20 micrometer diameters 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 airearth current simultaneously decrease by approximately an order of magnitude as the wind speed increases from 5 to 10 meter per sec. 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 to 163 nm size range but increases in 0.5 to 20 micrmetr size range with wind speed. Size distribution of the nanometer particles show a dominant maximum at 30 nm diameter throughout the period of observations and the height of the maximum decreases with wind speed. However, lar...

Kamra, A K; Pant, Vimlesh; 10.1016/j.atmosres.2008.02.018

2009-01-01

90

Velocity of auroral arcs drifting equatorward from the polar cap P. J. S. Williams, C. F. del Pozo, I. Hiscock, R. Fallows  

E-print Network

Velocity of auroral arcs drifting equatorward from the polar cap P. J. S. Williams, C. F. del Pozo. Magnetospheric physics (auroral phenomena; electric ®elds; plasma convection) 1 Introduction In recent years, as measured by EISCAT, was less than 300 m sA1 . The authors concluded that during active substorm periods arc

Paris-Sud XI, Université de

91

Analysis of Microturbulence within the Foot of Supercritical Quasiperpendicular Shocks for Different reflected ion vs electron Drifts  

NASA Astrophysics Data System (ADS)

Supercritical shocks are characterized by a fraction of the incoming ions which is reflected at the steep front and stream across the magnetic field in the foot. These ions accumulate and are responsible for the shock front self-reformation. The drift of the reflected ion beam versus the electrons can easily destabilize waves in the electron cyclotron frequency range. By means of linear analysis, we show that several Bernstein harmonics can be unstable, their number being proportional to the drift, yet limited by the ion beam's temperature. Separate electromagnetic PIC simulations restricted to the ion and electron populations of the foot region are performed for various drifts in order to investigate with high spatial resolution and high particle statistics the nonlinear characteristics of these waves. For drifts less than (T_e/m)^{1/2}, the waves saturate at weak intensity levels. For larger drifts, yet still below the ion acoustic threshold, they reach significant levels and exhibit an interesting nonlinear evolution. First, high cyclotron harmonics develop in good agreement with linear dispersion properties and over timescales much shorter than the period of the shock front self-reformation. Second, as the high k-modes saturate by trapping ions of the reflected beam, the spectral power shifts toward lower k-modes to eventually accumulate on the first harmonic in a process that appears like an inverse cascade. Third, one surprising result in the late phase is the development of a magnetic component to a spectrum that had so far been mostly electrostatic. The late phase also exhibits a significant energy transfer from the ion beam to the electrons which experience a marked increase in temperature.

Muschietti, L.; Lembege, B.

2011-12-01

92

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

PubMed

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

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

2012-10-16

93

Unexpected transverse velocity component of Xe{sup +} ions near the exit plane of a Hall thruster  

SciTech Connect

The velocity component of singly charged xenon ions in a plane perpendicular to the thrust axis of the 1 kW-class PPS100-ML Hall effect thruster is deduced from laser induced fluorescence measurements on the 5d {sup 2}F{sub 7/2}{yields}6p {sup 2}D{sub 5/2}{sup 0} electronic transition at 834.72 nm. Measurements are carried out at several locations in the near field of the channel exhaust. Thruster operating parameters, such as magnetic field strength, discharge voltage, and xenon mass flow rate, are varied over a wide range. The initial aim of this work was to measure the azimuthal velocity of the ions due to their weak magnetic deflection. Surprisingly, experimental results cannot be explained by the one and only Lorentz force acting on Xe{sup +} ions. A realistic picture of the ion trajectory in the ExB drift plane is obtained when adding a velocity component directed toward the external cathode.

Bourgeois, G.; Mazouffre, S. [ICARE, CNRS, 1C Avenue de la Recherche Scientifique, 45071 Orleans (France); Sadeghi, N. [LSP, Joseph Fourier University and CNRS, 140 Ave. de la Physique, 38402 St. Martin d'Heres (France)

2010-11-15

94

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

SciTech Connect

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.

Gravier, E. [Institut Jean Lamour, UMR 7198 CNRS-Universite de Lorraine, Bd des Aiguillettes, 54 506 Vandoeuvre-les-Nancy Cedex (France); Plaut, E. [LEMTA, UMR 7563 CNRS-Universite de Lorraine, 2, av. de la Foret de Haye, 54 518 Vandoeuvre-les-Nancy Cedex (France)

2013-04-15

95

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

SciTech Connect

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.

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.

2014-09-26

96

Periodic modulation of ion velocities within the magnetodisk of Saturn  

NASA Astrophysics Data System (ADS)

The results of recent numerical simulations [Jia and Kivelson, 2012] show that in the magnetodisk of Saturn fluctuating magnetic field perturbations are accompanied by other oscillatory phenomena. They investigated the magnetotail response for a dual periodicity driver in the case when the solar wind flow was perpendicular to the rotation axis. As demonstrated in Fig. 7 of their paper the components of the flow velocity extracted at different radial distances plotted versus time exhibit periodic modulation. Andrews et al. [2012] and Provan et al. [2012] investigated magnetic field modulations in Saturn's magnetosphere. They have shown that in the high latitude regions single period modulations can be observed, but near the current sheet dual periodicities are characteristic. In this study we investigate periodicities in the azimuthal flow velocities using the numerical ion moments derived from the measurements of Cassini Plasma Spectrometer. Ramer et al. [2012] investigated these periodicities in the inner magnetosphere near the equatorial plane. We extend our study to include higher latitude passes in the outer magnetosphere to the orbit of Titan and beyond. To have a close match with the model assumptions of Jia and Kivelson, we investigated the behaviour of the ion velocities in the time range DOY 092-285, 2009, around Saturnian equinox, along different passes all containing a Titan flyby, and crossing the magnetodisk at different angles. We have found that the azimuthal velocities show oscillatory behavior. The amplitude of the oscillation is comparable with the corrotation speed. We have also compared the structure of the velocity variations to the variations of ion densities along the different passes, and compared those to the model as well. The results of the current study is reported in this presentation. References Andrews, D. J., S. W. H. Cowley, M. K. Dougherty, L. Lamy, G. Provan, and D. J. Southwood (2012), Planetary period oscillations in Saturn's magnetosphere: Evolution of magnetic oscillation properties from southern summer to postequinox, J. Geophys. Res., 117, A04224, doi:10.1029/2011JA017444. Jia and Kivelson (2012),Driving Saturn's magnetospheric periodicities from the upper atmosphere/ionosphere: Magnetotail response to dual sources, J. Geophys. Res., 117, A11219, doi:10.1029/2012JA018183. Ramer, K. M., M. G. Kivelson1, K. K. Khurana, N. Sergis, R. J. Walke1, X. Jia (2012), Forces and Phases: An Investigation of Azimuthal Plasma and Field Periodicities in Saturn's Inner Magnetosphere, AGU Fall Meeting 2012, SM51B-2303 Provan, G., D. J. Andrews, C. S. Arridge, A. J. Coates, S. W. H. Cowley, G. Cox, M. K. Dougherty, and C. M. Jackman (2012), Dual periodicities in planetary-period magnetic field oscillations in Saturn's tail, J. Geophys. Res., 117, A01209, doi:10.1029/2011JA017104.

Nemeth, Zoltan; Szego, Karoly; Foldy, Lajos; Kivelson, Margaret; Jia, Xianzhe; Ramer, Katherine; Cowley, Stanley W. H.; Provan, Gabrielle

2013-04-01

97

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

SciTech Connect

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).

Kwak, Kyujin; Henley, David B.; Shelton, Robin L., E-mail: kkwak@physast.uga.edu, E-mail: dbh@physast.uga.edu, E-mail: rls@physast.uga.edu [Department of Physics and Astronomy, University of Georgia, Athens, GA 30602 (United States)

2011-09-20

98

Theoretical relationship between maximum value of the post-sunset drift velocity and peak-to-valley ratio of anomaly TEC  

Microsoft Academic Search

Theoretical study of electron density distribution in the nighttime equatorial ionosphere shows that linear relationships with statistically significant correlation coefficients exist between the maximum value of the post-sunset plasma drift velocity and the peak-to-valley ratio of anomaly TEC. The study is based on the low-latitude density model of Air Force Research Laboratory (AFRL) and the obtained relationships are valid for

B. Basu; J. M. Retterer; O. de La Beaujardière; C. E. Valladares; E. Kudeki

2004-01-01

99

Solar cycle, seasonal, and diurnal variations of subauroral ion drifts: Statistical results  

NASA Astrophysics Data System (ADS)

solar cycle, seasonal, and diurnal variations of the subauroral ion drifts (SAIDs) are investigated for the first time to use such a large database of 18,226 SAID events observed by the DMSP satellites during 1987-2012. Statistical results show that SAIDs occur mostly at 60.1° invariant latitude and 2230 magnetic local time with a typical half width of 0.57°, move equatorward during high solar activities with large widths, and have two occurrence peaks in spring and fall equinoxes and two valleys in summer and winter solstices. The seasonal variation of SAID latitude has two valleys in spring and fall, and SAID width has a valley distribution with a minimum in summer. SAIDs exhibit a clear day-to-night difference in latitude. The diurnal variation of SAID width has a morning valley and an afternoon peak. The generation mechanism of SAID associated with the electron precipitation and the downward field-aligned current is also supported in this study.

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

2014-06-01

100

The UV photodissociation dynamics of ClO radical using velocity map ion imaging  

E-print Network

threshold. The formation of O 3 PJ fragments with positive anisotropy is evidence of curve crossing fromThe UV photodissociation dynamics of ClO radical using velocity map ion imaging Hahkjoon Kim, Jiho 235 to 291 nm using velocity map ion imaging. We find that Cl 2 P3/2 +O 1 D2 is the dominant channel

North, Simon W.

101

Application of time-sliced ion velocity imaging to crossed molecular beam experiments  

NASA Astrophysics Data System (ADS)

A three-dimensional (3D) ion velocity imaging method was developed to measure the product velocity distributions in crossed molecular beam experiments. While maintaining conventional two-dimension velocity mapping, the third velocity component was mapped linearly to the ion time of flight. A weak extraction field was used to spread the ion turnaround time to several hundred nanoseconds, which permits good resolution for selection of the longitudinal velocity. A fast gated (?5 ns) intensified charge coupled device camera was used to record time-sliced ion images. Calibration of the apparatus was done by measuring O+ images from the multiphoton dissociation/ionization of O2. The resolution in velocity achieved was about 1% (?v/v) in slicing through the center of a Newton sphere. The overall performance was examined by observing product ion images from the F+CD4?DF+CD3 reaction. To detect CD3+ with kinetic energy release of about 1 eV, 50 ns time slicing provides sufficient velocity resolution, such that resolution of the image is mainly limited by the spread in velocity of the two molecular beams. These ion optics can focus on a large volume of ion cloud, which is crucial in crossed molecular beam experiments. Direct 3D imaging also simplifies data analysis. This direct 3D ion imaging method provides a powerful tool with which to study systems with no cylindrical symmetry.

Lin, Jim J.; Zhou, Jingang; Shiu, Weicheng; Liu, Kopin

2003-04-01

102

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

NASA Astrophysics Data System (ADS)

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.

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

2014-09-01

103

An effective approach for coupling direct analysis in real time with atmospheric pressure drift tube ion mobility spectrometry.  

PubMed

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. PMID:24903510

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

2014-09-01

104

Ion temperature gradient driven mode in presence of transverse velocity-shear in magnetized plasmas  

E-print Network

Ion temperature gradient driven mode in presence of transverse velocity-shear in magnetized plasmas flow on the toroidal branch of the ion temperature gradient driven mode of magnetized nonuniform plasma has significant effects on the linear Ion Tem- perature Gradient (ITG) mode also. In this paper, we

105

Thermal iron ions in high speed solar wind streams. II - Temperatures and bulk velocities  

NASA Technical Reports Server (NTRS)

Mitchel and Roelof (1980) reported the detection of iron in high speed solar wind flows using the small, but finite sensitivity of solid state detectors to Fe ions in the low energy (50-200 keV protons) L1 channel of the NOAA/JHU energetic particle experiment (EPE). In the current investigation, the EPE response is modeled to a convected Maxwellian to obtain the thermal velocity, flow angle, and bulk velocity of the iron distribution. It is assumed that the iron bulk flow velocity can be represented as a vector sum of the hydrogen bulk velocity and an interplanetary magnetic field (IMF) aligned velocity increment. It is found that the velocity increment is smaller than the local Alfven speed in magnitude, and that the iron thermal velocity is comparable with or greater than the proton thermal velocity, with the 'thermal' velocity defined as the square root of 2kT/m.

Mitchell, D. G.; Roelof, E. C.; Feldman, W. C.; Bame, S. J.; Williams, D. J.

1981-01-01

106

Comparative analysis of nocturnal vertical plasma drift velocities inferred from ground-based ionosonde measurements of hmF2 and h?F  

NASA Astrophysics Data System (ADS)

Variations in the evening/nighttime ionosonde vertical plasma drift velocities inferred from the time rate of change of both the base of the F-layer height (Vz(h?F)) and height of the peak electron density (Vz(hmF2)) from an equatorial station were compared for better description of the E×B drifts. For better interpretation, both results were compared with the Incoherent Scatter (IS) radar observations (Vz(ISR)) which is taken to be the most accurate method of measuring drift, and therefore the data of reference level. An equinoctial maximum and June solstice minimum in post-sunset pre-reversal enhancement (PRE) was observed for Vz(hmF2), Vz(ISR), and Vz(h?F). The percentage correlation between VzhmF2 and Vzh?F ranges within 55-70%. While PRE for Vz(hmF2) peaked at 19 LT for all seasons, Vz(h?F) peaked at 18 LT for September equinox and December solstice, and start earlier. The nighttime downward reversal peak magnitudes for Vz(hmF2) and Vz(h?F) are respectively within the range of -4 to -14 and -2 to -14 m/s; whereas Vz(ISR) ranges within -12 and -34 m/s; and the peak time was reached earlier with the ionosonde observations than for the ISR. The PRE peak magnitude for Vz(hmF2), Vz(h?F) and Vz(ISR) varies between 3-14, 2-14, and 4-14 m/s for the entire seasons. Our results revealed higher drift correlation coefficients in both Vz(hmF2) vs. Vz(ISR) (0.983) and Vz(h?F) vs. Vz(ISR) (0.833) relationships during the equinoxes between 16-20 LT, at which time the F-layer altitude is higher than the 300 km threshold value; and lower for solstice period (0.326 and 0.410 in similar order). A better linear relationship between Vz(hmF2) and Vz(h?F2) was observed during the reversal (19-21 LT) phase period. PRE velocity was shown to be seasonal and solar activity dependent. Both VzhmF2 and Vzh?F compares almost equally with the ISR measurement. However, the PRE peak magnitude for the drift inferred using h?F2 is closer to the corresponding ISR magnitude during the equinoxes; whereas the drift inferred from hmF2 best represent the ISR magnitude for solstices. We established that both VzhmF2 and Vzh?F are governed by the same mechanism at nighttime, and as such any of them can be used to infer vertical drift as long as the 300 km threshold value condition is considered, otherwise chemical correction may be required for the F-layer uplift.

Adebesin, B. O.; Adeniyi, J. O.; Adimula, I. A.; Oladipo, O. A.; Olawepo, A. O.; Reinisch, B. W.

2015-01-01

107

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

NASA Technical Reports Server (NTRS)

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.

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

1985-01-01

108

Rocket-based measurements of ion velocity, neutral wind, and electric field in the collisional transition region of the auroral ionosphere  

NASA Astrophysics Data System (ADS)

The JOULE-II sounding rocket salvo was launched from Poker Flat Rocket Range into weak pulsating aurora following a moderate substorm at 0345 LT on 19 January 2007. We present in situ measurements of ion flow velocity and electric and magnetic fields combined with neutral wind observations derived from ground observations of in situ chemical tracers. Measured ion drifts in the 150-198 km and 92-105 km altitude ranges are consistent with ${\\vec{E} × ${\\vec{B} motion to within 16 m s-1 rms and with neutral wind velocity to within 20 m s-1, respectively. From these measurements we have calculated the ratio $\\kappa$ of the ion cyclotron and ion collision frequencies, finding $\\kappa$ = 1 at an altitude of 118 ± 0.3 km. Using direct measurements of ion current, we calculate the Joule heating rate and Pedersen and Hall conductivity profiles for this moderately active event and find height-integrated values of 390 W km-2 and 0.59 and 2.22 S, respectively. We also find that these values would have errors of up to tens of percent without coincident neutral wind measurements, and presumably more so during more active conditions. Ion flow vectors were measured at a rate of 125 s-1 however, no significant fluctuations were observed at spatial/temporal scales below ˜350 m and 0.5 s. Observational limits were 5.5 m and 0.016 s.

Sangalli, L.; Knudsen, D. J.; Larsen, M. F.; Zhan, T.; Pfaff, R. F.; Rowland, D.

2009-04-01

109

Ion velocities in direct current arc plasma generated from compound cathodes  

SciTech Connect

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.

Zhirkov, I.; Rosen, J. [Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping (Sweden)] [Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping (Sweden); Eriksson, A. O. [Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping (Sweden) [Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping (Sweden); Oerlikon Balzers Coating AG, Iramali 18, 9496 Balzers (Liechtenstein)

2013-12-07

110

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

E-print Network

with existing theory. The large temporal variation of the IVDF has implications for the plasma chemistry and increases the energy of ions incident upon the sub- strate. For industrial plasma processing of poorlyTemporally resolved ion velocity distribution measurements in a radio-frequency plasma sheath B

California at Los Angles, University of

111

The ion experiment onboard the Interball-Aurora satellite; initial results on velocity-dispersed structures  

E-print Network

The ion experiment onboard the Interball-Aurora satellite; initial results on velocity / Accepted: 10 March 1998 Abstract. The Toulouse ION experiment ¯own on the Russian Interball-Aurora mission perform measurements in the energy range $10 eV±20 000 eV. The Interball- Aurora spacecraft was launched

Paris-Sud XI, Université de

112

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

SciTech Connect

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.

Henley, David B.; Kwak, Kyujin; Shelton, Robin L., E-mail: dbh@physast.uga.edu, E-mail: rls@physast.uga.edu, E-mail: kkwak@kasi.re.kr [Department of Physics and Astronomy, University of Georgia, Athens, GA 30602 (United States)

2012-07-01

113

Plasma structuring by the gradient drift instability at high latitudes and comparison with velocity shear driven processes  

NASA Technical Reports Server (NTRS)

Using results of the in situ measurements made by the DE 2 satellite, the nature of plasma structuring at high latitudes, caused by the gradient drift instability process, is described. Using noon-midnight and dawn-dusk orbits of the DE 2 satellite, it was possible to examine the simultaneous density and electric field spectra of convecting large-scale plasma density enhancements in the polar cap known as 'patches', in directions parallel and perpendicular to their antisunward convection. The results provide evidence for the existence of at least two generic classes of instabilities operating in the high-latitude ionosphere: one driven by large-scale density gradients in a homogeneous convection field with respect to the neutrals, and the other driven by the structured convection field itself in an ambient ionosphere where density fluctuations are ubiquitous.

Basu, Sunanda; Mackenzie, E.; Basu, S.; Coley, W. R.; Sharber, J. R.; Hoegy, W. R.

1990-01-01

114

Energy of secondary ions desorbed from insulating films by MeV heavy ions as a function of projectile velocity  

NASA Astrophysics Data System (ADS)

The influence of projectile velocity on the axial energy distribution and mean axial energy of secondary ions was measured with a double-field time-of-flight method at the GSI accelerator-system. The secondary ions were ejected from thin layers ( ~ 150 nm) of CsI, MgO, CaF2, valine and phenylalanine irradiated with Sn and U projectiles. The mean energy of ions like Cs + and Mg + clearly increases in the velocity range from 0.3 to 1.5 cm/ns, whereas the energy of cluster ions remains almost constant. In most cases an influence of the cluster size on the mean ion energy was not observed. The results are discussed in relevance to desorption models and their significance for the optimum design of time-of-flight mass spectrometers.

Becker, O.; Wien, K.

1986-07-01

115

Selective Detection of Low-Velocity Ions Using Nuclear Emulsion Films  

NASA Astrophysics Data System (ADS)

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.

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

2013-11-01

116

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

NASA Astrophysics Data System (ADS)

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.

Sullivan, Regina

117

Kinetic theory and atomic physics corrections for determination of ion velocities from charge-exchange spectroscopy  

NASA Astrophysics Data System (ADS)

Charge-exchange spectroscopy is a powerful diagnostic tool for determining ion temperatures, densities and rotational velocities in tokamak plasmas. This technique depends on detailed understanding of the atomic physics processes that affect the measured apparent velocities with respect to the true ion rotational velocities. These atomic effects are mainly due to energy dependence of the charge-exchange cross-sections, and in the case of poloidal velocities, due to gyro-motion of the ion during the finite lifetime of the excited states. Accurate lifetimes are necessary for correct interpretation of measured poloidal velocities, specially for high density plasma regimes on machines such as ITER, where l-mixing effects must be taken into account. In this work, a full nl-resolved atomic collisional radiative model coupled with a full kinetic calculation that includes the effects of electric and magnetic fields on the ion gyro-motion is presented for the first time. The model directly calculates from atomic physics first principles the excited state lifetimes that are necessary to evaluate the gyro-orbit effects. It is shown that even for low density plasmas where l-mixing effects are unimportant and coronal conditions can be assumed, the nl-resolved model is necessary for an accurate description of the gyro-motion effects to determine poloidal velocities. This solution shows good agreement when compared to three QH-mode shots on DIII-D, which contain a wide range of toroidal velocities and high ion temperatures where greater atomic corrections are needed. The velocities obtained from the model are compared to experimental velocities determined from co- and counter-injection of neutral beams on DIII-D.

Muñoz Burgos, J. M.; Burrell, K. H.; Solomon, W. M.; Grierson, B. A.; Loch, S. D.; Ballance, C. P.; Chrystal, C.

2013-09-01

118

Ion collection by a conducting sphere in a magnetized or drifting collisional plasma  

E-print Network

Ion collection by dust grains and probes in plasmas with a neutral background is of interest in the study of both space and terrestrial plasmas, where charge-exchange collisions can play an important role in ion collection. ...

Haakonsen, Christian Bernt, 1985-

2011-01-01

119

Velocity dependence of heavy-ion stopping below the maximum  

NASA Astrophysics Data System (ADS)

In the slowing-down of heavy ions in materials, the standard description by Lindhard and Scharff assumes the electronic stopping cross section to be proportional to the projectile speed v up to close to a stopping maximum, which is related to the Thomas-Fermi speed vTF . It is well known that strict proportionality with v is rarely observed, but little is known about the systematics of observed deviations. In this study we try to identify factors that determine positive or negative curvature of stopping cross sections on the basis of experimental data and of binary stopping theory. We estimate the influence of shell structure of the target and of the equilibrium charge of the ion and comment the role of dynamic screening.

Sigmund, P.; Schinner, A.

2015-01-01

120

Verifying effects of instability enhanced ion–ion Coulomb collisions on ion velocity distribution functions near the sheath edge in low temperature plasmas  

NASA Astrophysics Data System (ADS)

Experiments have shown that ion velocity distribution functions (ivdfs) with non-Maxwellian tails created by ion–neutral collisions and ionizations along pre-sheaths in weakly collisional plasmas can be thermalized into Maxwellian distributions near the sheath edge. A recent theory suggests that ion–ion collisions enhanced by ion-acoustic instabilities can rapidly thermalize ions near the sheath edge into Maxwellian distributions and that increasing either electron temperature or neutral pressure of a plasma suppresses the growth of instabilities and eliminates the thermalization process. Measurements of ivdfs by laser induced fluorescence showed qualitative agreement between experimental data and a marginal stability curve inferred from the new theory.

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

2015-02-01

121

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

NASA Astrophysics Data System (ADS)

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.

Salewski, M.; Geiger, B.; Nielsen, S. K.; Bindslev, H.; García-Muñoz, 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

122

Analysis of high-altitude planetary ion velocity space distributions detected by the Ion Mass Analyzer aboard Mars Express  

NASA Astrophysics Data System (ADS)

We present observations of planetary ion velocity space distributions from the Ion Mass Analyzer (IMA) onboard Mars Express (MEX). The magnetometer data from Mars Global Surveyor is used to obtain a rough estimate of the interplanetary magnetic field (IMF) orientation. Characteristic features of the velocity space distributions will be examined and discussed for orbits aligned with the convective electric field and those in the Mars terminator plane. This study will focus on the high (keV) energy ions, as well as the relative importance of a high-altitude magnetosheath source of escaping planetary ions. Furthermore, this paper will examine various methods for converting the IMA detector counts to species-specific fluxes. After mimicking the methods previously used by researchers, we apply each of these methods of species extraction to data collected during the same time intervals. We discuss the implications for planetary ion motion around Mars, using the details of the velocity space observations to better understand the solar wind interaction with Mars. Comparisons to virtual detections using a test particle simulation will also provide insight into ion origins and trajectories.

Johnson, B. C.; Liemohn, M. W.; Fraenz, M.; Curry, S.; Mitchell, D. L.

2012-12-01

123

The vacuum spark as a source of metal ions with variable velocity  

NASA Astrophysics Data System (ADS)

Results of the time-of-flight measurements of the cathode plasma jet velocity in a low voltage vacuum spark are presented. It is found that the mean velocity of ions in the plasma jet varies over a wide range of values. When the discharge current increases from 0.6 to 11 kA the ion velocity at a distance of 35 cm from the copper cathode goes up to 7×104 m s-1, i.e. exceeds nearly six times the corresponding value of 1.3×104 m s-1 for the dc arc. The intensity of the ion beam in this case increases by more than two orders of magnitude.

Gorbunov, S. P.; Krasov, V. P.; Krinberg, I. A.; Paperny, V. L.

2003-08-01

124

Ionization of highly charged iodine ions near the Bohr velocity  

NASA Astrophysics Data System (ADS)

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 L?1,3,4 and L?2,15 to L?1,2 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.

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

2015-01-01

125

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

E-print Network

We study a quasi-two-dimensional electrostatic drift kinetic system as a model for near-marginal ion temperature gradient (ITG) driven turbulence. A proof is given of 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 $E\\times B$ 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 ($\\infty\\times\\infty \\rightarrow 1$) system is derived that may be useful for understanding dynamics around the critical gradient of Dimits.

Plunk, G G

2015-01-01

126

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

SciTech Connect

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.

MacDonald, N. A.; Young, C. V.; Cappelli, M. A. [Stanford Plasma Physics Laboratory, Stanford University, Stanford, California 94305 (United States); Hargus, W. A. Jr. [Spacecraft Propulsion Branch, Air Force Research Laboratory, Edwards AFB, California 93524 (United States)

2012-05-01

127

Negative ion productions in high velocity collision between small carbon clusters and Helium atom target  

NASA Astrophysics Data System (ADS)

We measured absolute double capture cross section of Cn+ ions (n=1,5) colliding, at 2.3 and 2.6 a.u velocities, with an Helium target atom and the branching ratios of fragmentation of the so formed electronically excited anions Cn-*. We also measured absolute cross section for the electronic attachment on neutral Cn clusters colliding at same velocities with He atom. This is to our knowledge the first measurement of neutral-neutral charge exchange in high velocity collision.

M, Chabot; K, Béroff; T, Pino; G, Féraud; N, Dothi; Padellec A, Le; G, Martinet; S, Bouneau; Y, Carpentier

2012-11-01

128

Thermal Plasma Imager (TPI): An Imaging Thermal Ion Mass and 3-D Velocity Analyzer  

NASA Astrophysics Data System (ADS)

The Thermal Plasma Imager (TPI) is an imaging thermal ion mass and 3-dimensional (3-D) velocity analyzer. It is designed to measure the instantaneous mass composition and detailed, mass-resolved, 3-dimensional, velocity distributions of thermal-energy (0.5-50 eV/q) ions on a 3-axis stabilized spacecraft. It consists of a pair of semi-toroidal deflection and fast-switching time-of-flight (TOF) electrodes, a hemispherical electrostatic analyzer (HEA), and a micro-channel plate (MCP) detector. It uses the TOF electrodes to clock the flight times of individual incident ions, and the HEA to focus ions of a given energy-per-charge and incident angle (elevation and azimuth) onto a single point on the MCP. The TOF/HEA combination produces an instantaneous and mass-resolved "image" of a 2-D cone of the 3-D velocity distribution for each ion species, and combines a sequence of concentric 2-D conical samples into a 3-D distribution covering 360° in azimuth and 120° in elevation. It is currently under development for the Enhanced Polar Outflow Probe (e-POP) and Planet-C Venus missions. It is an improved, "3-dimensional" version of the SS520-2 Thermal Suprathermal Analyzer (TSA), which samples ions in its entrance aperture plane and uses the spacecraft spin to achieve 3-D ion sampling. In this paper, we present its detailed design characteristics and prototype instrument performance, and compare these with the ion velocity measurement performances from its 2-D TSA predecessor on SS520-2.

Yau, A. W.; Amerl, P. V.; King, E. P.; Miyake, W.; Abe, T.

2003-04-01

129

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

SciTech Connect

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.

Haque, Q.; Mahmood, S.; Mushtaq, A. [Theoretical Plasma Physics Division, PINSTECH, P.O. Nilore Islamabad (Pakistan)

2008-08-15

130

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

NASA Technical Reports Server (NTRS)

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.

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

1999-01-01

131

Effects of the ion-beam density and velocity on the excitation of multimode soliton  

SciTech Connect

Multimode solitons are observed to be excited in an ion-beam{endash}plasma system. But, the excitation of some mode solitons of these is found to be suppressed under a certain condition depending on the density and velocity of a low-energy ion beam, produced by the applied negative pulse. Furthermore, weak interaction between the slow-beam soliton and ion-acoustic soliton is also observed to cause small time lags in their trajectories on the distance{endash}time plane. {copyright} {ital 1996 American Institute of Physics.}

Nagasawa, T.; Honzawa, T. [Department of Electric and Electronic Engineering, Utsunomiya University, Utsunomiya 321 (Japan)] [Department of Electric and Electronic Engineering, Utsunomiya University, Utsunomiya 321 (Japan)

1996-08-01

132

Millimeter-wave Velocity Modulation Spectroscopy as a Technique to Selectively Detect Molecular Ions  

NASA Astrophysics Data System (ADS)

Molecular ions are usually very unstable and reactive species. As a result, their spectroscopic features can be difficult to identify and distinguish from those of neutral species, which tend to be more stable and thus have stronger signals. The technique of velocity modulation allows this disadvantage to be removed. This method uses the alternating plus and minus polarity of an electric field created by an AC discharge, which also produces the molecular ions, to selectively detect the molecular ions, while eliminating the neutral features. This technique has been applied at infrared and optical wavelengths for many years with much success. Recently, we designed and built a millimeter-wave velocity modulation spectrometer, the first ever constructed. This instrument has been used to create and study multiple molecular ions, including metal-bearing molecular ions. The rotational spectrum of these species, such as TiCl^+, VCl^+, TiF^+, FeO^+, FeCO^+, and SiCl^+, has been investigated with this new machine in our laboratory. Results of these studies along with a description of the velocity modulation technique and instrument will be presented.

Halfen, Dewayne; Ziurys, Lucy

2009-05-01

133

Quasi-linear velocity space diffusion of heavy cometary pickup ions on bispherical diffusion characteristics  

NASA Technical Reports Server (NTRS)

We consider an ion transport equation describing the source, convection, adiabatic acceleration, and quasi-linear velocity diffusion of cometary pickup ions. The equation is solved numerically along solar wind plasma flow lines for the environment of Comet Halley, to obtain distributions at positions on the Giotto spacecraft trajectory which may be compared with observations. We obtain full two-dimensional (pitch angle and velocity) numerical distributions which show pitch angle scattering about the wave scattering centers at +/- V(A), where V(A) is the Alfven wave speed in the solar wind frame. Peak ion phase-space densities approximately follow the bispherical shell geometry. The energy distributions F(v) agree well with Giotto observations at lower v, but in the high-energy tail there is evidence possibly for the first-order Fermi acceleration mechanism taking place in the Comet Halley foreshock region.

Huddleston, D. E.; Coates, A. J.; Johnstone, A. D.

1992-01-01

134

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

NASA Astrophysics Data System (ADS)

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.

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

2014-09-01

135

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

SciTech Connect

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.

Lu Quanming; Yang Zhongwei; Lembege, Bertrand [CAS Key Laboratory of Basic Plasma Physics, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026 (China); SOA Key Laboratory for Polar Science, Polar Research Institute of China, Shanghai 200136 (China); LATMOS-UVSQ-IPSL-CNRS, Guyancourt 78280 (France)

2012-11-20

136

Stokes Drift for Random Gravity Waves  

Microsoft Academic Search

Introduction. The modified form of the Stokes drift velocity [Stokes, 1847] for a random sea is briefly considered. For a statistically stationary and horizontally homogeneous wave field, the total wave drift is the sum of the drifts of the individual wave components. The expression for the Stokes drift, given here in terms of the full two-dimensionM energy spectrum for arbitrary

Kern E. Kenyon

1969-01-01

137

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)

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

Kovaleva, Irina

138

Temperature dependent sound velocity in hydrodynamic equations for relativistic heavy-ion collisions  

E-print Network

We analyze the effects of different forms of the sound-velocity function cs(T) on the hydrodynamic evolution of matter formed in the central region of relativistic heavy-ion collisions. At high temperatures (above the critical temperature Tc) the sound velocity is calculated from the recent lattice simulations of QCD, while in the low temperature region it is obtained from the hadron gas model. In the intermediate region we use different interpolations characterized by the values of the sound velocity at the local maximum (at T = 0.4 Tc) and local minimum (at T = Tc). In all considered cases the temperature dependent sound velocity functions yield the entropy density, which is consistent with the lattice QCD simulations at high temperature. Our calculations show that the presence of a distinct minimum of the sound velocity leads to a very long (about 20 fm/c) evolution time of the system, which is not compatible with the recent estimates based on the HBT interferometry. Hence, we conclude that the hydrodynamic description is favored in the case where the cross-over phase transition renders the smooth sound velocity function with a possible shallow minimum at Tc.

Mikolaj Chojnacki

2007-09-11

139

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

SciTech Connect

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.

Draxler, M.; Chenakin, S.P.; Markin, S.N.; Bauer, P. [Institut fuer Experimentalphysik, Johannes-Kepler Universitaet, Altenbergerstr. 69, A-4040 Linz (Austria)

2005-09-09

140

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

NASA Astrophysics Data System (ADS)

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.

Levy, M. E.; Zhang, R.

2013-12-01

141

Edge Ion Velocity and Temperature Measurements in NSTX T.M. Biewer, R.E. Bell, D. W. Johnson  

E-print Network

Edge Ion Velocity and Temperature Measurements in NSTX T.M. Biewer, R.E. Bell, D. W. JohnsonBeam Trajectories RF antenna Ion dynamics from C III, C IV, and He II are studied. C III triplet 47.88 eV ionization Waves (HHFW) are launched by the RF antenna into similar plasmas, a two-population distribution of ions

Biewer, Theodore

142

Double ionization of helium by high-velocity U sup 90+ ions  

SciTech Connect

Double ionization of helium is investigated for 60-, 120-, and 420-MeV/u ({ital v}/{ital c}=0.34--0.72)U{sup 90+}-ion impact. The measured double-to-single ionization ratios indicate that, even for these very high velocities, double ionization of the He target results predominantly from independent interactions of the projectile with both target electrons. It is concluded that the asymptotic high-velocity regime for one-step double ionization (i.e., shakeoff'') has not yet been reached even for U{sup 90+} projectiles at 420 MeV/u, and, in fact, cannot be reached for projectiles with {ital q}{approx gt}7, thereby verifying that the ionic charge is fully as important as the velocity in determining the importance of a given ionization mechanism.

Berg, H.; Jagutzki, O.; Doerner, R.; DuBois, R.D.; Kelbch, C.; Schmidt-Boecking, H. (Institut fuer Kernphysik, Universitaet Frankfurt, D6000 Frankfurt (Germany)); Ullrich, J. (Gesellschaft fuer Schwerionenforschung, D6000 Darmstadt (Germany)); Tanis, J.A. (Western Michigan University, Kalamazoo, Michigan 49008 (United States)); Schlachter, A.S.; Blumenfeld, L.; d'Etat, B. (Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States)); Hagmann, S.; Gonzales, A.; Quinteros, T. (Kansas State University, Manhattan, Kansas 66506 (United States))

1992-11-01

143

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

NASA Astrophysics Data System (ADS)

Ionospheric plasma flow is an indicator of the interconnection between the solar wind, interplanetary magnetic field (IMF), and Earth’s 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.

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

2014-07-01

144

Drifting Continents  

NSDL National Science Digital Library

This activity is a teacher-led demonstration of continental drift and includes a math worksheet for students involving the calculation of continental drift over time. Students will understand what continental drift is, why it occurs, and how earthquakes occur because of it.

Integrated Teaching And Learning Program

145

Measurement of ion temperature and flow velocity by using LIF and electric probe methods in K2H and DiPS propulsion simulators  

NASA Astrophysics Data System (ADS)

Ion temperature, plasma flow velocity and plasma density are measured in DiPS (Diversified Plasma Simulator) and K2H (KBSI-KAIST-Hanyang University) propulsion simulators by a laser induced fluorescence (LIF) method and a fast scanning electric probe system, which consists of an rf-compensated single probe and a Mach probe. In both devices helicon plasmas were stably generated with m=+1 right-helical antenna at 13.56 MHz with powers of 1 - 3kW (DiPS) and 0.5 - 1kW (K2H), and open ended magnetic configurations are utilized. The measured plasma parameters are as follows: plasma densities of 10^11 -- 10^13 cm-3 (K2H) and 10^12 -- 10^13 cm-3 (DiPS), electron temperatures of 3 -- 9 eV (K2H) and 2 -- 4 eV (DiPS), ion temperatures of 0.14 -- 0. 17 eV (K2H) and 0.05 -- 0.2 eV (DiPS) and drift velocities of 0.8 -- 1.6 km/s (k2H) and 0.2 -- 0.5 km/s (DiPS).

Choi, Geun-Sig; Chung, Kyu-Sun; Woo, Hyun-Jong; Seo, Young Jun; Lee, Myoung-Jae; Lho, Taihyeop; Jung, Yong Ho; Lee, Bong Ju

2006-10-01

146

A comparison study of zonal drift velocities measurements as seen by MF spaced antenna and HF Doppler radar in the Indian dip equatorial mesospheric and lower thermospheric (80-100 km) region  

NASA Astrophysics Data System (ADS)

The simultaneous measurements of zonal drift velocities, observed in the heights of 84-98 km in the Indian geomagnetic dip equatorial region by an medium frequency (MF, 1.98 MHz) spaced antenna and a high-frequency (HF, 18 MHz) Doppler radars, are compared on selected few days in the solar maximum years of 1998, 1999, and 2000. The agreement between the two radar measurements is found to be good below about 88 km, where the neutral turbulence induced ionospheric irregularities are more predominant. Above 90 km, however, the agreement becomes poor and at the highest height of 98 km it becomes the least. At this height, more often the HF Doppler radar shows a westward drift of about 200 m/s whereas the MF spaced antenna radar values lie within ±10 m/s and sometimes attain maximum values of ±50 m/s. Detailed discussions are made on the possible sources of underestimation of the drift velocities measured by the MF radar and the nature of scattering irregularities that are produced because of large neutral turbulences and plasma instabilities. It is suggested that these neutral and plasma turbulences (particularly type II plasma irregularities) contribute in a different manner to different radar frequencies and techniques and hence very different drift velocities in the heights of 90-100 km particularly in the geomagnetic dip equatorial region. Discussions are also made on (1) the real atmospheric and ionospheric physical process prevailing in the 90-100 km region and (2) the technical aspects of the radars that limits them to measure only particular types of motion in this region.

Ramkumar, T. K.; Gurubaran, S.; Rajaram, R.; Tiwari, D.; Viswanathan, K. S.

2010-02-01

147

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

SciTech Connect

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.

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

1982-01-01

148

Collective Thomson scattering for ion temperature and velocity measurements on Magnum-PSI: a feasibility study  

NASA Astrophysics Data System (ADS)

In this paper, collective Thomson scattering (CTS) is proposed for measuring the ion temperature and axial/rotational velocity of a plasma jet in the linear plasma generator Magnum-PSI, where ITER-relevant plasma conditions will be simulated. CTS is feasible at Magnum-PSI, because high electron densities (ne) can be obtained at low electron temperatures, which means that small Debye lengths are achievable. Calculations show that CTS is possible at the fundamental wavelength (1064 nm) of a Nd : YAG laser. At this wavelength, a scattering angle of 17-35° is sufficiently small to achieve a scattering parameter 1 < ? < 3. The estimated observational error in the ion temperature Ti is expected to be below 10% at ne = 5.0 × 1020 m-3 and Ti = 2.5 eV, for a scattering volume with a length of 2.4 mm using an accumulated scattering energy of 12 J (10 pulses of 1.2 J at 10 Hz). The accuracy in the determination of axial velocity is expected to be about 15%. Setting the required accuracy for ion temperature measurements at 15%, single pulse CTS is expected to be feasible for ne > 1.5 × 1021 m-3. The design considerations of the CTS diagnostic are described in this paper.

van der Meiden, H. J.

2010-04-01

149

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

SciTech Connect

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.

Hahn, M.; Savin, D. W. [Columbia Astrophysics Laboratory, Columbia University, MC 5247, 550 West 120th Street, New York, NY 10027 (United States)] [Columbia Astrophysics Laboratory, Columbia University, MC 5247, 550 West 120th Street, New York, NY 10027 (United States)

2013-02-15

150

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

NASA Astrophysics Data System (ADS)

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.

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

151

On velocity-space sensitivity of fast-ion D-alpha spectroscopy  

NASA Astrophysics Data System (ADS)

The velocity-space observation regions and sensitivities in fast-ion D? (FIDA) spectroscopy measurements are often described by so-called weight functions. Here we derive expressions for FIDA weight functions accounting for the Doppler shift, Stark splitting, and the charge-exchange reaction and electron transition probabilities. Our approach yields an efficient way to calculate correctly scaled FIDA weight functions and implies simple analytic expressions for their boundaries that separate the triangular observable regions in (v?, v?)-space from the unobservable regions. These boundaries are determined by the Doppler shift and Stark splitting and could until now only be found by numeric simulation.

Salewski, M.; Geiger, B.; Moseev, D.; Heidbrink, W. W.; Jacobsen, A. S.; Korsholm, S. B.; Leipold, F.; Madsen, J.; Nielsen, S. K.; Rasmussen, J.; Stejner, M.; Weiland, M.; the ASDEX Upgrade Team

2014-10-01

152

Ion drift meter research  

NASA Technical Reports Server (NTRS)

The final activity period for the DE project has been particularly productive. This period has seen the final delivery of geophysical data sets to the National Space Science Data Center, the granting of three Ph.D. degrees from cumulative work on the project, the operation of automatic data access and display routines for the data, and an increased effort in research and publication of the data. As before the research activities, largely devoted to studies involving the dynamics of the ionosphere, utilize data from the IDM and the RPA and thus the work is not easily attributable to one or the other of these separately funded efforts. In this final report we provide brief descriptions of the work accomplished in the final phase of the program. The Dynamics Explorer program has provided a significant opportunity for much of the community to participate in the data analysis and interpretation. The data, now residing in the national space science data center, are a great legacy that should continue to yield important results for many years.

Heelis, Roderick A.

1994-01-01

153

On Pitch-Angle Scattering Rates of Interstellar Pickup Ions as Determined by in Situ Measurement of Velocity Distributions  

Microsoft Academic Search

Newly ionized interstellar atoms are acted upon by electromagnetic forces in the solar wind. Measurements of these pickup ions enable study of the transport processes controlling the evolution of charged particle populations in solar wind plasma. Data from the CELIAS instruments on board the SOHO spacecraft allow measurement of the velocity distribution of singly charged helium ions. These observations are

Lukas Saul; Eberhard Möbius; Philip Isenberg; Peter Bochsler

2007-01-01

154

Climatology and Morphology of the Early Morning Upward Drift (Invited)  

NASA Astrophysics Data System (ADS)

During the recent solar minimum, a large amount of satellite measurements at equatorial latitudes have revealed an upward drift that occurs in the early morning near dawn (between 4 LT and 7 LT), before the occurrence of the regular upward drift in the daytime. An upward drift near dawn has also been shown from previous radar measurements, but has not yet been emphasized or explained. In this study, the simulations using the coupled Whole Atmosphere Model and Global Ionosphere Plasmasphere Model (WAM/GIP) are conducted to investigate the unusual upward drift and to obtain its climatology. The climatology from the simulations is then compared with observations from Ion Velocity Meter (IVM) instrument onboard the Communications/Navigation Outage Forecasting System (CNOFS) satellite during year 2010. The morphology and characteristics of the early morning upward drift are studied through analyzing the neutral winds, field-line integrated conductivities and currents in the electrodynamics solver. We also compare the conditions of the early morning upward drift with the pre-reversal enhancement (PRE) to further understand the causal mechanisms.

Fang, T.; Richmond, A. D.; Stoneback, R.; Wang, H.; Wu, F.

2013-12-01

155

Ion Beam Heating in the Auroral Zone  

NASA Technical Reports Server (NTRS)

Recent satellite observations at high altitudes (greater than 5000 km) in the auroral zone have shown the existence of hybrid or bimodal ion beam distributions that are evidence of both parallel and perpendicular ion acceleration. Acceleration parallel to the magnetic field is most likely due to quasi-static electric fields (double layers) which can create outflowing ion beams; since ions of different mass will have different drift speeds due to this acceleration, a plasma configuration unstable to the ion-ion two-stream acoustic mode develops. When the net drift velocity (U) between the two ion species is greater than the sound speed (C(sub 0)), the ion-ion instability has maximum growth at oblique wave propagation. To study the nonlinear effects of the ion-ion instability in terms of plasma heating, a numerical simulation parametric study has been performed. It was found that the parallel acceleration that forms the ion beams occurs on a time scale faster than ion- ion wave growth at low drifts; thus ion-ion wave growth is expected to occur primarily for higher drift speeds (U greater than C(sub 0)) which results in strong oblique heating of the ions (both hydrogen and oxygen) forming elevated ion conics (sometimes called 'bowl' distributions). Also, strong parallel electron heating in the direction of the ion beams can occur, and electrons near the top of the acceleration region may attain a net upward drift along with the elevated ion conics. Variation of the oxygen density greatly affects the ion heating due to the ion-ion instability; as the oxygen density decreases, oxygen heating increases, in agreement with observations (Collin et al., 1987). Ion-ion electrostatic wave properties and the plasma heating that results over a wide range of auroral zone parameters are included.

Schriver, David; Ashour-Abdalla, Maha; Collin, Henry; Lallande, Nicole

1990-01-01

156

Interpretation of neutral particle analyzer measurements on plasmas having azimuthal drift  

NASA Technical Reports Server (NTRS)

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.

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

1975-01-01

157

Drift wave vortices in nonuniform plasmas with sheared magnetic fields  

SciTech Connect

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.

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

1991-11-01

158

Generation of lower hybrid and whistler waves by an ion velocity ring distribution  

SciTech Connect

Using fully kinetic simulations in two and three spatial dimensions, we consider the generation and nonlinear evolution of lower hybrid waves produced by a cold ion ring velocity distribution in a low beta plasma. We show that the initial development of the instability is very similar in two and three dimensions and not significantly modified by electromagnetic effects, consistent with linear theory. At saturation, the level of electric field fluctuations is a small fraction of the background thermal energy; the electric field and corresponding density fluctuations consist of long, field-aligned striations. Energy extracted from the ring goes primarily into heating the background ions and the electrons at comparable rates. The initial growth and saturation of the magnetic components of the lower hybrid waves are related to the electric field components, consistent with linear theory. As the growing electric field fluctuations saturate, parallel propagating whistler waves develop by the interaction of two lower hybrid waves. At later times, these whistlers are replaced by longer wavelength, parallel propagating whistlers that grow through the decay of the lower hybrid fluctuations. Wave matching conditions demonstrate these conversion processes of lower hybrid waves to whistler waves. The conversion efficiency (=ratio of the whistler wave energy to the energy in the saturated lower hybrid waves) is computed and found to be significant ({approx}15%) for the parameters of the three-dimensional simulation (and even larger in the two-dimensional simulation), although when normalized in terms of the initial kinetic energy in the ring ions the overall efficiency is very small (<10{sup -4}). The results are compared with relevant linear and nonlinear theory.

Winske, D.; Daughton, W. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2012-07-15

159

Ionic liquid lubrication: influence of ion structure, surface potential and sliding velocity.  

PubMed

Colloid probe atomic force microscopy (AFM) has been employed to investigate the nanotribology of the ionic liquid (IL)-Au(111) interface. Data is presented for four ILs, 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([EMIM] FAP), 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([BMIM] FAP), 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([HMIM] FAP) and 1-butyl-3-methylimidazolium iodide ([BMIM] I), at different Au(111) surface potentials. Lateral forces vary as a function of applied surface potential and ion structure because the composition of the confined ion layer changes from cation-enriched (at negative potentials) to mixed (at 0 V), and to anion-enriched (at positive potentials). ILs with FAP(-) anions all exhibit similar nanotribology: low friction at negative potentials and higher friction at positive potentials. [BMIM] I displays the opposite behaviour, as an I(-) anion-enriched layer is more lubricating than either the [BMIM](+) or FAP(-) layers. The effect of cation charged group (charge-delocalised versus charged-localised) was investigated by comparing [BMIM] FAP with 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate ([Py(1,4)] FAP). [BMIM] FAP is less lubricating at negative potentials, but more lubricating at positive potentials. This indicated that even at positive potentials the cation concentration in the boundary layer is sufficiently high to influence lubricity. The influence of sliding velocity on lateral force was investigated for the [EMIM] FAP-Au(111) system. At neutral potentials the behaviour is consistent with a discontinuous sliding process. When a positive or negative potential bias is applied, this effect is less pronounced as the colloid probe slides along a better defined ion plane. PMID:23836254

Li, Hua; Rutland, Mark W; Atkin, Rob

2013-09-21

160

Wind Drift Compensation in Migrating Dragonflies Pantala (Odonata: Libellulidae)  

Microsoft Academic Search

Tailwind drift compensation serves to maximize a migrant's flight distance on a given amount of energy, and crosswind drift compensation serves to hold a course true and minimize the distance flown. With full or part compensation, airspeeds are predicted to increase with greater crosswind drift. To test whether migrating dragonflies compensated for wind drift, I measured the velocity and heading

Robert B. Srygley

2003-01-01

161

Wind Drift Compensation in Migrating Dragonfiles Pantala (Odonata: Libellulidae)  

Microsoft Academic Search

Q1 Tailwind drift compensation serves to maximize a migrant's flight distance on a given amount of energy, and crosswind drift compensation serves to hold a course true and minimize the distance flown. With full or part com- pensation, airspeeds are predicted to increase with greater crosswind drift. To test whether migrating dragonflies compensated for wind drift, I measured the velocity

Robert B. Srygley

2003-01-01

162

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

SciTech Connect

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 0.4–600 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.

Moore, Nathaniel B.; Gekelman, Walter; Pribyl, Patrick [Department of Physics and Astronomy, University of California, Los Angeles, California 90095 (United States)] [Department of Physics and Astronomy, University of California, Los Angeles, California 90095 (United States); Zhang, Yiting; Kushner, Mark J. [Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Ave., Ann Arbor, Michigan 48109-2122 (United States)] [Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Ave., Ann Arbor, Michigan 48109-2122 (United States)

2013-08-15

163

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

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.

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

2014-05-05

164

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

NASA Astrophysics Data System (ADS)

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).

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

2013-06-01

165

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

SciTech Connect

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.

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

2008-12-03

166

Genetic Drift  

NSDL National Science Digital Library

In this biology simulation, students use a mathematical simulation of genetic drift to answer questions about the factors that influence this evolutionary process. Students run a series of simulations varying allele frequency and population size and then analyze their data and propose a model to explain their results.

Scott Cooper

167

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

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…

Jakoby, Bernhard

2009-01-01

168

Stopping power for low-velocity heavy ions: (0-1.0)MeV\\/nucleon Mg ions in 17 (Z=22-79) elemental solids  

Microsoft Academic Search

The stopping power for 24,26Mg ions in 17 (Z=22-79) elemental solids has been studied in the energy region 0-1.0 MeV\\/nucleon by application of the Doppler-shift attenuation method. At velocities 2v0velocity), the scaling factors 1.10 (Ti), 0.90 (V), 0.93 (Fe), 0.97 (Co), 0.99 (Ni), 1.03 (Cu), 1.05 (Ge), 1.05 (Nb), 1.15 (Mo), 1.05 (Pd), 1.08 (Ag), 1.09

K. Arstila; J. Keinonen; P. Tikkanen

1990-01-01

169

Invertebrate drift — A review  

Microsoft Academic Search

This paper reviews the literature on invertebrate drift in running waters, emphasising papers published during the last 10–15 years. The terms constant drift, catastrophic drift, behavioural drift, active drift and distributional drift are defined, but their use should be limited as much confusion has arisen. Sampling methods are briefly reviewed.

John E. Brittain; Tor Jan Eikeland

1988-01-01

170

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

NASA Astrophysics Data System (ADS)

The binding energies of the p-, m-, and o-difluorobenzene-H2O complexes have been measured by velocity map ion imaging to be 922±10, 945±10, and 891±4cm-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.

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

2008-03-01

171

Electron injection in semiconductor drift detectors  

SciTech Connect

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.

Rehak, P. (Brookhaven National Lab., Upton, NY (USA)); Gatti, E.; Longoni, A.; Sampietro, M.; Castoldi, A. (Politecnico di Milano, Milan (Italy)); Vacchi, A. (Rockefeller Univ., New York, NY (USA))

1990-01-01

172

Effect of Cross-Field Drifts and Core Rotation on Flows in the Main Scrape-Off Layer of DIII-D L-mode Plasmas  

SciTech Connect

The flow velocities of deuterons and low charge-state carbon ions have been measured simultaneously for the first time at the crown of the main SOL for low-density plasmas in DIII-D. The dependences of the flow fields on the direction of the cross-field drifts (E x B and B x {del}B) and core plasma rotation were investigated. The measurements indicate that the carbon ion flow direction and magnitude along the magnetic field lines are not necessarily determined by the deuteron flow field, but other physics must also play a role. The deuteron velocities at the plasma crown are high (20-30 km/s) in configurations with the ion B x {del}B drift toward the divertor X-point, while nearly zero in configurations with the opposite B x {del}B drift direction. The flow velocities of doubly charged carbon ions are independent of the ion B x {del}B drift direction, and the measurements suggest a stagnation point in the flow field at the crown of the plasma. Both deuteron and carbon ion flow velocities in the SOL were found to be independent of the direction of core plasma rotation. Simulations with the UEDGE code have been carried out to better understand the underlying physics processes. Including the cross-field drifts in the simulations produced divertor solutions that are in significantly closer agreement with the measurements. They do not, however, reproduce the measured flow fields at the crown for the configuration with the ion B x {del}B drift toward the divertor X-point.

Groth, M; Boedo, J A; Brooks, N H; Isler, R C; Leonard, A W; Porter, G D; Watkins, J G; West, W P; Bray, B D; Fenstermacher, M E; Groebner, R J; Moyer, R A; Rudakov, D L; Yu, J H; Zeng, L

2008-10-13

173

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

NASA Technical Reports Server (NTRS)

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.

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

2011-01-01

174

Equatorial F2-layer peak height and correlation with vertical ion drift and M(3000)F2  

NASA Astrophysics Data System (ADS)

Ionosonde data recorded at Korhogo, Côte-d'Ivoire (Latitude +9.3; Longitude -5.4, Dip -0.67) during a year of low solar activity (1995) were used to investigate ways of improving the representation of equatorial F2 peak height (hmF2) in the International Reference Ionosphere (IRI). For this purpose we have studied the correlation between hmF2 and the equatorial F region vertical drift as given by the model of Scherliess and Fejer (1999). The positive correlation found during nighttime could be helpful in representing the post-sunset peak of hmF2 that is currently not represented by IRI. We have also investigated the reliability of the CCIR model for the propagation factor M(3000)F2 model since the IRI hmF2 model is based on the strong anti-correlation between hmF2 and M(3000)F2. Overall the CCIR model represents the diurnal variation of M(3000)F2 quite well but does not represent small-scale features. With the M(3000)F2 values deduced from the Korhogo ionograms as input, the IRI hmF2 model provides an excellent representation of the observed diurnal structure including the post-sunset peak.

Obrou, O. K.; Bilitza, D.; Adeniyi, J. O.; Radicella, S. M.

175

Continental Drift  

NSDL National Science Digital Library

This lesson plan is part of the DiscoverySchool.com lesson plan library for grades 6-8. It focuses on Alfred Wegener's theory of Continental Drift and the evidence used to support it. Using fossil types and maps, students view similarities between continents that led Wegener to conclude that they had once been together as a supercontinent, Pangea. Included are objectives, materials, procedures, discussion questions, evaluation ideas, suggested readings, and vocabulary. There are videos available to order which complement this lesson, and links to teaching tools for making custom quizzes, worksheets, puzzles and lesson plans.

176

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

SciTech Connect

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.

Nersisyan, Hrachya B. [Institute of Radiophysics and Electronics, 0203 Ashtarak (Armenia); Centre of Strong Fields Physics, Yerevan State University, Alex Manoogian Street 1, 0025 Yerevan (Armenia); Deutsch, Claude [LPGP - UMR-CNRS 8578, Universite Paris XI, F-91405 Orsay (France); Das, Amal K. [Department of Physics, Dalhousie University, Halifax, Nova Scotia B3H 3J5 (Canada)

2011-03-15

177

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

SciTech Connect

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.

Frias, Winston; Smolyakov, Andrei I. [Department of Physics and Engineering Physics, University of Saskatchewan, 116 Science Place, Saskatoon SK S7N 5E2 (Canada)] [Department of Physics and Engineering Physics, University of Saskatchewan, 116 Science Place, Saskatoon SK S7N 5E2 (Canada); Kaganovich, Igor D.; Raitses, Yevgeny [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)] [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

2013-05-15

178

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

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

179

Method for enhancing the resolving power of ion mobility separations over a limited mobility range  

DOEpatents

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.

Shvartsburg, Alexandre A; Tang, Keqi; Smith, Richard D

2014-09-23

180

Fast ion collective Thomson scattering diagnostic for ITER S.B. Korsholm1,2, H. Bindslev1, F. Leipold1, F. Meo1, P.K. Michelsen1,  

E-print Network

Fast ion collective Thomson scattering diagnostic for ITER S.B. Korsholm1,2, H. Bindslev1, F, 2007 Outline of the talk · ITER measurement requirements for confined fast ions · Overview of the 60 to misalignment · Measurements of fuel ion ratio and bulk ion drift velocity by CTS · Future work #12;ITPA

181

Stopping power of low-velocity ions in solids: inhomogeneous electron gas model  

Microsoft Academic Search

A self-consistent model for the calculation of electron scattering and stopping coefficients of slow ions in a non-homogeneous electron gas is developed. The model permits to account for realistic electron density profiles in the evaluation of the average energy loss of slow ions in solids. The screening parameter in the potential and the scattering phase shifts are calculated in a

J. Calera-Rubio; A. Gras-Martí; N. R. Arista

1994-01-01

182

Dust magneto-gravitational drift wave in g ×B configuration  

NASA Astrophysics Data System (ADS)

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.

Salahshoor, M.; Niknam, A. R.

2014-11-01

183

A comparison of ion velocity measurements from retarding field energy analyzer (RFEA) and laser induced fluorescence (LIF) in expanding helicon plasma  

NASA Astrophysics Data System (ADS)

We present a comparison of ion velocity measurements from RFEA and LIF where we specially focus on the ability to diagnose flow and ion beams due to current free double layers in expanding helicon plasma. An RFEA in a plasma will be surrounded by a sheath so the velocities measured by the RFEA will be the velocities of the ions after they have been accelerated by the sheath and any potential drops inside the probe. Different methods exist to relate the velocities measured by the RFEA to the velocities in the plasma. Most of them include some simple assumptions about the acceleration in the sheath. We will compare measurements from two different RFEAs, one with a grounded front grid and one with a floating front grid, with LIF measurements to assess the validity of these simple models.

Gulbrandsen, Njål; Fredriksen, Åshild; Carr, Jerry, Jr.; Scime, Earl; McCarren, Dustin W.; Vandervort, Robert; Galante, Matthew E.; Magee, Richard M.; Lusk, Greg; Sears, Stephanie H.; Miloch, Wojciech J.

2012-10-01

184

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

SciTech Connect

Dissociative photoionization of methyl bromide (CH{sub 3}Br) in an excitation energy range of 10.45–16.90 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 C–Br 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 C–Br 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. C–Br 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.

Tang, Xiaofeng [Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China) [Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China); National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029 (China); Zhou, Xiaoguo, E-mail: xzhou@ustc.edu.cn, E-mail: yanbing@jlu.edu.cn; Liu, Shilin [Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China) [Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Sun, Zhongfa [Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China)] [Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China); Liu, Fuyi; Sheng, Liusi [National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029 (China)] [National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029 (China); Yan, Bing, E-mail: xzhou@ustc.edu.cn, E-mail: yanbing@jlu.edu.cn [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China)] [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China)

2014-01-28

185

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

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

186

Measurements of Ion Temperature and Velocity in HIT-SI with Comparison to NIMROD Calculations, Development of Piezoelectric Valve  

NASA Astrophysics Data System (ADS)

A one meter ion Doppler spectrometer has been upgraded to multichord capability using an image intensifier and high-speed camera. Two linear arrays of 36 fibers each simultaneously collect light across a toroidal and poloidal section of HIT-SI. Temperature and velocity data will be presented and compared with NIMROD calculation results. Additionally, a fast, piezoelectric valve has been developed which achieves a gas flow rates of over 325 Torr liters per second and response time of approximately 0.5 ms. Flow rate is proportional to voltage, so the valve will offer arbitrary fueling profile for HIT-SI3. Work supported by USDoE and ARRA.

Hossack, A. C.; Akcay, C.; Jarboe, T. R.; Rogers, J. A.; Kirkpatrick, A. M.; Smith, R. J.

2012-10-01

187

Ion acceleration from laser-driven electrostatic shocksa)  

NASA Astrophysics Data System (ADS)

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.

Fiuza, F.; Stockem, A.; Boella, E.; Fonseca, R. A.; Silva, L. O.; Haberberger, D.; Tochitsky, S.; Mori, W. B.; Joshi, C.

2013-05-01

188

Ion acceleration from laser-driven electrostatic shocks  

SciTech Connect

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.

Fiuza, F.; Stockem, A.; Boella, E.; Fonseca, R. A.; Silva, L. O. [GoLP—Instituto de Plasmas e Fusão Nuclear—Laboratório Associado, Instituto Superior Técnico, 1049-001 Lisbon (Portugal)] [GoLP—Instituto de Plasmas e Fusão Nuclear—Laboratório Associado, Instituto Superior Técnico, 1049-001 Lisbon (Portugal); Haberberger, D.; Tochitsky, S.; Mori, W. B.; Joshi, C. [Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States)] [Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States)

2013-05-15

189

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...

190

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...

191

Filamentation instability of nonextensive current-driven plasma in the ion acoustic frequency range  

NASA Astrophysics Data System (ADS)

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.

Khorashadizadeh, S. M.; Rastbood, E.; Niknam, A. R.

2014-12-01

192

Plasma edge transport phenomena caused by particle drifts and sources in TEXTOR  

NASA Astrophysics Data System (ADS)

The parallel and radial transport properties of the plasma edge of TEXTOR are studied using radial electron density and temperature profiles as well as ion temperatures and poloidal velocities in the scrape-off layer (SOL). These quantities are measured by thermal helium beams at the low (LFS) and high field side (HFS) by emission and beam driven charge exchange recombination spectroscopy. We investigate the influence of the safety factor and of a magnetic field reversal on these edge parameters. Especially the field reversal leads to clear effects: a decrease of the density at the LFS, a significant change in the poloidal density distribution, which is identified by comparing LFS and HFS densities, and an increase in the density e-folding length at both poloidal positions. The poloidal ion rotation changes sign in reversed field configuration and thus gives a hint on the role of poloidal drifts in the SOL. For further analysis, we present a simple fluid model including poloidal drift velocities and local ionization sources. With this model we can show that the poloidal E×B drift clearly influences the poloidal density distribution. However, although the model results show the same tendencies as the experimental findings, the impact of the field reversal on the density asymmetry is not that pronounced as in the experiment. The dependence of the density e-folding length on the poloidal and radial drifts as well as on the source distribution is discussed within the frame of analytical estimates.

Lehnen, M.; Brix, M.; Samm, U.; Schweer, B.; Unterberg, B.; TEXTOR-team

2003-03-01

193

Shear driven electromagnetic drift-waves in a nonuniform dense magnetoplasma  

SciTech Connect

Linear characteristic properties of high- and low-frequency (in comparison with the cyclotron frequency) electromagnetic drift-waves are studied in a nonuniform, dense magnetoplasma (composed of electrons and ions), in the presence of parallel (magnetic field-aligned) velocity shear, by using quantum magnetohydrodynamic model. By applying the drift-approximation (viz., |{partial_derivative} {sub t}|<<{omega}{sub ci}<<{omega}{sub ce}) to the quantum momentum equations, together with the continuity equations and the Poisson equation, we derive the governing equations for electromagnetic drift-waves with the shear flow. These linear equations are then Fourier transformed to obtain the dispersion relation in both high-frequency and low-frequency regimes. The dispersion relations are then discussed under various limiting cases.

Tariq, Sabeen; Mirza, Arshad M. [Theoretical Plasma Physics Group, Department of Physics, Quaid-i-Azam University, Islamabad 45320 (Pakistan); Masood, Waqas [Theoretical Plasma Physics Division, PINSTECH, P. O. Nilore, Islamabad 44000 (Pakistan); National Center for Physics (NCP), Islamabad 44000 (Pakistan)

2011-08-15

194

Stopping power of Mylar for low-velocity 11B, 12C, and 16O ions  

NASA Astrophysics Data System (ADS)

The energy loss and stopping powers of 1.0-6.0 MeV 11B, 12C, and 16O ions in Mylar foil were determined in a transmission geometry. The experimental data were compared to the commonly used semiempirical theoretical predictions of Ziegler, Biersack, and Littmark and significant deviations were observed. The stopping powers were determined to an accuracy of 4%.

Changwen, Jin; Xiting, Lu; Xiaojing, Huang; Yanlin, Ye; Zonghuang, Xia; Hongtao, Liu; Dongxing, Jiang

1993-09-01

195

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)

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.

Gurgiolo, C.; Parks, G. K.; Mauk, G. H.

1983-01-01

196

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)

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.

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

2011-01-01

197

Extraordinarily High Electron Densities Observed in the Crest of the Post-sunset Equatorial Anomaly, Their Persistence with Solar Rotation and the Evidence of an Enhancement of Maximum Pre-reversal ExB Drift Velocity  

NASA Astrophysics Data System (ADS)

Extremely high F layer electron densities, possibly the highest ever recorded, were observed in the crests of latitudinal profiles of maximum electron density in the post sunset equatorial anomaly. A chain of ionospheric sounders located in western America recorded values of NmF2 of 6.9, 6.5 and >6.5 x106 el/cm3 on the 3 days, Feb 14, Mar 13 and Apr 11, 1958. These days were 27 and 29 days apart, so were nearly the same day in 3 successive Carrington solar rotations. The levels indicate extremely high levels of maximum pre-reversal ExB drift velocity (ExBmax) as does the fact that equatorial bubbles were observed on 2 of the days and a bubble was likely to have occurred on the third. However, conditions which are associated with high ExBmax, low Kp and high F10.7, were present, but not at levels that were unusual in relation to the other days in the period. Dst and daytime NmE are also ordinary on these days. Each of the 3 days lies in a period of IMF "away" and possibly near a sector boundary as indicated by high latitude magnetograms. Proximity to a boundary is also not unique to these 3 days, but the recurrence with solar rotation suggests that sector structure may play a role. In addition to the remarkable recurrence in solar rotation, the significance of these observations is that they indicate the presence of some not yet understood mechanism that enhances the eastward electric field, hence ExBmax. Its presence at other times could contribute to the largely unexplained variability of ExBmax, of equatorial bubbles and of the resulting scintillation, so that its understanding could lead to much improved forecasts.

Whalen, J. A.

2004-12-01

198

Measurements of HNO3 and N2O5 using ion drift-chemical ionization mass spectrometry during the MILAGRO/MCMA-2006 campaign  

NASA Astrophysics Data System (ADS)

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 Petróleo 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.

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

199

Measurements of HNO3 and N2O5 using Ion drift - Chemical Ionization Mass Spectrometry during the MCMA - 2006 Campaign  

NASA Astrophysics Data System (ADS)

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 Petróleo 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.

Zheng, J.; Zhang, R.; Fortner, E. C.; Molina, L.; Aiken, A. C.; Jimenez, J. L.; Gäggeler, K.; Dommen, J.; Dusanter, S.; Stevens, P. S.; Tie, X.

2008-03-01

200

ORNL 2012-G00549/tcc Resistive-Glass Drift Tube for Use as a Controlled  

E-print Network

ORNL 2012-G00549/tcc 06.2012 Resistive-Glass Drift Tube for Use as a Controlled Kinetic Energy Ion systems. The subject invention is a resistive-glass ion drift tube for controlling the mean kinetic energy drift tube in the device slows down ions both by pressure on the tube and the voltage applied

Pennycook, Steve

201

Dynamics of positive probes in underdense, strongly magnetized, E×B drifting plasma: Particle-in-cell simulations  

SciTech Connect

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 (?{sub pe}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.

Heinrich, Jonathon R.; Cooke, David L. [Air Force Research Laboratory, Kirtland Air Force Base, New Mexico 87117 (United States)] [Air Force Research Laboratory, Kirtland Air Force Base, New Mexico 87117 (United States)

2013-09-15

202

Experimental Observation of Ion-Cyclotron Turbulence in the Presence of Transverse-Velocity Shear  

Microsoft Academic Search

This laboratory investigation documents the influence of transverse, localized, dc electric fields (TLE) on the excitation of ion-cyclotron waves driven by magnetic-field -aligned current (FAC) in a Q-machine plasma device. A segmented disk electrode, located on axis at the end of the plasma column, is used to independently control TLE and FAC in the plasma (potassium plasma, n~ 10^9 cm^{-3},

William E. Amatucci

1994-01-01

203

Multi-point, high-speed passive ion velocity distribution diagnostic on the Pegasus Toroidal Experiment  

SciTech Connect

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.

Burke, M. G.; Fonck, R. J.; Bongard, M. W.; Schlossberg, D. J.; Winz, G. R. [Department of Engineering Physics, University of Wisconsin, Madison, Wisconsin 53706 (United States)

2012-10-15

204

Bulk properties and velocity distributions of water group ions at Comet Halley - Giotto measurements  

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

205

Bulk properties and velocity distributions of water group ions at Comet Halley - Giotto measurements  

NASA Astrophysics Data System (ADS)

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.

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

1990-07-01

206

Experimental Observation of Ion-Cyclotron Turbulence in the Presence of Transverse-Velocity Shear.  

NASA Astrophysics Data System (ADS)

This laboratory investigation documents the influence of transverse, localized, dc electric fields (TLE) on the excitation of ion-cyclotron waves driven by magnetic-field -aligned current (FAC) in a Q-machine plasma device. A segmented disk electrode, located on axis at the end of the plasma column, is used to independently control TLE and FAC in the plasma (potassium plasma, n~ 10^9 cm^{-3}, rho_{i} ~ 0.2 cm, T_{e} = T_{i} ~ 0.2 eV). Ion-cyclotron waves have been characterized in both the weak-TLE and large-FAC regime and the strong-TLE and small-FAC regime. The existence of a new category of oscillation identified as the inhomogeneous energy-density driven (IEDD) instability is verified based on the properties of the waves in the latter regime. In the weak-TLE regime, current-driven electrostatic ion-cyclotron (CDEIC) waves with features in qualitative agreement with previous laboratory results have been observed at sufficiently large FAC. These waves have a frequency spectrum with a single narrow spectral feature located slightly above the ion-cyclotron frequency (omega ~ 1.2Omega_{rm i}) . The waves are standing in the radial direction with peak oscillation amplitude located in the center of the FAC channel and are azimuthally symmetric (m = 0). Small magnitude TLE were found to have negligible effect on the characteristics of the waves. In the strong-TLE regime, a decrease in the threshold FAC level is observed. This transition in the instability threshold is accompanied by changes in the frequency spectra, propagation characteristics, and mode amplitude profiles. In the presence of strong-TLE, the ion-cyclotron waves propagate azimuthally in the vec{E} times vec{B} direction with k_thetarho_{i} = 0.4 and m = 1. The frequency spectrum becomes broadband and spiky, and shifts with the applied TLE strength. In contrast to CDEIC waves, the IEDD wave spectrum can extend to frequencies below Omega_{ rm i}. The waves have peak oscillation amplitude located off-axis in the region of maximum TLE.

Amatucci, William E.

207

Profile Measurement of Ion Temperature and Toroidal Rotation Velocity with Charge Exchange Recombination Spectroscopy Diagnostics in the HL-2A Tokamak  

NASA Astrophysics Data System (ADS)

This paper deals with the profile measurement of impurity ion temperature and toroidal rotation velocity that can be achieved by using the charge exchange recombination spectrum (CXRS) diagnostics tool built on the HL-2A tokamak. By using CXRS, an accurate impurity ion temperature and toroidal plasma rotation velocity profile can be achieved under the condition of neutral beam injection (NBI) heating. Considering the edge effect of the line of CVI 529.06 nm (n = 8~7), which contains three lines (active exciting spectral line (ACX), passivity exciting spectral line (PCX) and electron exciting spectral line (ICE)), and using three Gaussian fitted curves, we obtain the following experimental results: the core ion temperature of HL-2A device is nearly thousands of eV, and the plasma rotation velocity reaches about 104 m · s-1. At the end of paper, some explanations are presented for the relationship between the curves and the inner physical mechanism.

Wu, Jing; Yao, Lieming; Zhu, Jianhua; Han, Xiaoyu; Li, Wenzhu

2012-11-01

208

Ionization of Ar11+ ions during collisions near the Bohr velocity  

NASA Astrophysics Data System (ADS)

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 K? X-ray shifts to the high energy by 52 eV, and the intensity ratio of K?/K? 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.

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

2014-12-01

209

Spin drift in highly doped n-type Si  

SciTech Connect

A quantitative estimation of spin drift velocity in highly doped n-type silicon (Si) at 8?K is presented in this letter. A local two-terminal Hanle measurement enables the detection of a modulation of spin signals from the Si as a function of an external electric field, and this modulation is analyzed by using a spin drift-diffusion equation and an analytical solution of the Hanle-type spin precession. The analyses reveal that the spin drift velocity is linearly proportional to the electric field. The contribution of the spin drift effect to the spin signals is crosschecked by introducing a modified nonlocal four-terminal method.

Kameno, Makoto; Ando, Yuichiro; Shinjo, Teruya [Graduate School of Engineering Science, Osaka University Osaka (Japan); Koike, Hayato; Sasaki, Tomoyuki; Oikawa, Tohru [Advanced Technology Development Center, TDK Cooperation, Chiba (Japan); Suzuki, Toshio [AIT, Akita Research Institute of Advanced Technology, Akita (Japan); Shiraishi, Masashi, E-mail: mshiraishi@kuee.kyoto-u.ac.jp [Graduate School of Engineering Science, Osaka University Osaka (Japan); Graduate School of Engineering, Kyoto University, Kyoto (Japan)

2014-03-03

210

Spin drift in highly doped n-type Si  

NASA Astrophysics Data System (ADS)

A quantitative estimation of spin drift velocity in highly doped n-type silicon (Si) at 8 K is presented in this letter. A local two-terminal Hanle measurement enables the detection of a modulation of spin signals from the Si as a function of an external electric field, and this modulation is analyzed by using a spin drift-diffusion equation and an analytical solution of the Hanle-type spin precession. The analyses reveal that the spin drift velocity is linearly proportional to the electric field. The contribution of the spin drift effect to the spin signals is crosschecked by introducing a modified nonlocal four-terminal method.

Kameno, Makoto; Ando, Yuichiro; Shinjo, Teruya; Koike, Hayato; Sasaki, Tomoyuki; Oikawa, Tohru; Suzuki, Toshio; Shiraishi, Masashi

2014-03-01

211

Drift waves in stellarator geometry  

SciTech Connect

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.

Persson, M.; Nadeem, M.; Lewandowski, J.L.V.; Gardner, H.J.

2000-02-07

212

Drift compression experiments on MBE-4 and related emittance growth phenomena  

SciTech Connect

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.

Eylon, S.; Faltens, A.; Fawley, W.; Garvey, T.; Hahn, K.; Henestroza, E.; Smith, L.

1991-04-01

213

Experimental test of instability enhanced collisional friction for determining ion loss in two ion species plasmas  

SciTech Connect

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.

Hershkowitz, N.; Yip, C.-S. [Department of Engineering Physics, University of Wisconsin, Madison, Madison, Wisconsin 53706 (United States); Severn, G. D. [Department of Physics, University of San Diego, San Diego, California 92110 (United States)

2011-05-15

214

An assessment of the role of the centrifugal acceleration mechanism in high altitude polar cap oxygen ion outflow  

Microsoft Academic Search

The role of the centrifugal acceleration mechanism for ion outflow at high altitude above the polar cap has been investigated. Magnetometer data from the four Cluster spacecraft has been used to obtain an estimate of magnetic field gradients. This is combined with ion moment data of the convection drift and the field-aligned particle velocity. Thus all spatial terms in the

H. Nilsson; M. Waara; O. Marghitu; M. Yamauchi; R. Lundin; H. Rème; J.-A. Sauvaud; I. Dandouras; E. Lucek; L. M. Kistler; B. Klecker; C. W. Carlson; M. B. Bavassano-Cattaneo; A. Korth

2008-01-01

215

A refocusing modified velocity map imaging electron/ion spectrometer adapted to synchrotron radiation studies  

SciTech Connect

We present a modified velocity map imaging (VMI) spectrometer to be used in angle-resolved molecular photoionization studies in the gas phase with synchrotron radiation (SR) in the VUV/soft x-ray range. The main modifications as compared to the original design of Eppink and Parker [A. T. J. B. Eppink and D. H. Parker, Rev. Sci. Instrum. 68, 3477 (1997)] are an open repeller which allows the VMI spectrometer to be coupled to an independent dispersive electrostatic analyzer for combined operation in coincidence mode experiments, and the introduction of a coupled double Einzel lens in the flight tube in order to collect the full 4{pi} solid angle for higher kinetic energy particles. The length and position of the lenses have been optimized by a genetic algorithm to obtain the maximum kinetic energy possible without compromising the energy resolution. Ray-tracing simulations and SR experiments show that the lenses can increase the kinetic energy bandwidth by a factor of up to 2.5. Furthermore, a remarkable improvement in the radial focusing of the particles' momenta can be achieved when the lens array is operated in optimum fashion. The accuracy in the determination of the angular parameters, already satisfactory in the original VMI design, is not compromised by the lens operation. Experimentally, we succeeded in collecting 4{pi} electrons with 14 eV kinetic energy and 6% relative energy resolution with a detector of 36 mm effective diameter, despite the larger ionization volume given by the SR as compared to laser multiphoton experiments. We predict that, by changing to a detector diameter of 70 mm and reducing the focal length by a third, particles with energies up to 200 eV could be collected by applying 10 kV to the repeller electrode.

Garcia, Gustavo A.; Nahon, Laurent; Harding, Chris J.; Mikajlo, Elisabeth A.; Powis, Ivan [Laboratoire L.U.R.E., Bat 209D, Universite de Paris Sud, 91898 Orsay Cedex (France); School of Chemistry, University of Nottingham, NG7 2RD Nottingham (United Kingdom)

2005-05-15

216

NO+ formation pathways in dissociation of N2O+ ions at the C2Sigma+ state revealed from threshold photoelectron-photoion coincidence velocity imaging  

Microsoft Academic Search

Using the novel threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging technique, the dissociative photoionization of N2O molecule via the C2Sigma+ ionic state has been investigated. Four fragment ions, NO+, N2+, O+, and N+, are observed, respectively, and the NO+ and N+ ions are always dominant in the whole excitation energy range of the C2Sigma+ ionic state. Subsequently, the TPEPICO three-dimensional time-sliced

Xiaofeng Tang; Mingli Niu; Xiaoguo Zhou; Shilin Liu; Fuyi Liu; Xiaobin Shan; Liusi Sheng

2011-01-01

217

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)

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.

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

2013-12-01

218

The response of a spherical tissue-equivalent proportional counter to different heavy ions having similar velocities  

PubMed Central

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

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

219

Ion heating mechanism in a modified Penning discharge  

NASA Technical Reports Server (NTRS)

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.

Roth, J. R.

1972-01-01

220

Ion acceleration in plasmas emerging from a helicon-heated magnetic-mirror device  

Microsoft Academic Search

Using laser-induced fluorescence, measurements have been made of metastable argon-ion, Ar+*(3d4F7\\/2), velocity distributions on the major axis of an axisymmetric magnetic-mirror device whose plasma is sustained by helicon wave absorption. Within the mirror, these ions have sub-eV temperature and, at most, a subthermal axial drift. In the region outside the mirror coils, conditions are found where these ions have a

S. A. Cohen; N. S. Siefert; S. Stange; R. F. Boivin; E. E. Scime; F. M. Levinton

2003-01-01

221

Ion beams from laser-generated plasmas  

NASA Technical Reports Server (NTRS)

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.

Hughes, R. H.; Anderson, R. J.; Gray, L. G.; Rosenfeld, J. P.; Manka, C. K.; Carruth, M. R.

1980-01-01

222

Magnetotail acceleration using generalized drift theory - A kinetic merging scenario  

NASA Technical Reports Server (NTRS)

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.

Whipple, E. C.; Rosenberg, M.; Brittnacher, M.

1990-01-01

223

Drift distance survey in DPIS for high current beam production  

SciTech Connect

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.

Kanesue,T.; Okamura, M.; Kondo, K.; Tamura, J.; Kashiwagi, H.; Zhang, Z.

2009-09-20

224

Generation of electromagnetic structures via modulational instability of drift waves  

SciTech Connect

Generation mechanism for large scale electromagnetic structures (blobs) is considered by employing the technique of four-wave interactions (modulational instability). It is shown that primary electrostatic turbulence may generate elongated electromagnetic structures with poloidal modulations. Such structures are principally related to drift-Alfven waves. The analysis fully takes into account finite ion temperature effects and associated diamagnetic contributions to Reynolds stress. The turbulent generation of blobs has instability growth rates which scale similar to the zonal flow instabilities, {gamma}{approx}, where q is a characteristic wave vector of large scale modes, and V-tilde is a characteristic amplitude of the velocity of turbulent fluctuations. This analysis is shown to be fully consistent with results of an earlier analysis by using the wave kinetic equation.

Smolyakov, A. I. [Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2 (Canada); Nuclear Fusion Institute, Russian Research Center 'Kurchatov Institute', 1 Kurchatov Square, 123182, Moscow (Russian Federation); Krasheninnikov, S. I. [University of California at San Diego, 9500 Gilman Dr., La Jolla, California 92093 (United States)

2008-07-15

225

Excitonic luminescence in the drift of excess electrons through liquid and solid rare gases  

NASA Astrophysics Data System (ADS)

It is shown that the excitation of electronic states is the main channel of energy loss of excess electrons drifting in moderate (?103V/cm) electric fields through condensed heavy rare gases (Rg). These losses, together with scattering on resonances of metastable negative ions (Rg*)-, determine the dependence of the average energy of the electrons and their drift velocity vd on the electric field E both in condensed Rg and in dense gases. In particular, explanations are given for the constancy of vd at large E and for the transformation of the electroluminescence spectrum upon changes in the density of heavy particles and their temperature. Thus it is predicted that localized excitons can be efficiently excited in the bulk of crystalline and liquid Xe, Kr, and Ar, with a yield of around 102 excitons (and UV photons) per electron.

Gordon, E. B.; Shestakov, A. F.

2001-09-01

226

Origins of ion irradiation-induced Ga nanoparticle motion on GaAs surfaces  

SciTech Connect

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.

Kang, M.; Wu, J. H.; Chen, H. Y.; Thornton, K.; Goldman, R. S. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)] [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Sofferman, D. L. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States) [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Department of Physics, Adelphi University, Garden City, New York 11530-0701 (United States); Beskin, I. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040 (United States)] [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040 (United States)

2013-08-12

227

Determination of the interstitial electron density in liquid metals: Basic quantity to calculate the ion collective-mode velocity and related properties  

NASA Astrophysics Data System (ADS)

Considering that various investigations identified a correlation between the interstitial electron density in crystalline metals and some ground-state properties, including the compressibility, we propose a procedure to estimate the interstitial electron density in liquid metals starting from the experimental static structure factor. From the calculated electron density, starting from the standard approximation, which describes a liquid metal as made up of a homogeneous classic ion plasma with Coulomb interaction and a homogeneous interacting electron gas, we determine the ion collective mode velocity. The so-derived collective mode velocity is compared to the experimental data and a coherent view in different metallic systems at the melting point is obtained. Some guess about the collective mode damping is also presented because of the connection to the local static fluctuations of the interstitial electron density.

Sani, L.; Petrillo, C.; Sacchetti, F.

2014-07-01

228

Radar and satellite global equatorial F region vertical drift model  

Microsoft Academic Search

We present the first global empirical model for the quiet time F region equatorial vertical drifts based on combined incoherent scatter radar observations at Jicamarca and Ion Drift Meter observations on board the Atmospheric Explorer E satellite. This analytical model, based on products of cubic-B splines and with nearly conservative electric fields, describes the diurnal and seasonal variations of the

L. Scherliess

1999-01-01

229

Comment on ``Nonplanar dust-ion acoustic Gardner solitons in a dusty plasma with q-nonextensive electron velocity distribution'' [Phys. Plasmas 19, 033703 (2012)  

NASA Astrophysics Data System (ADS)

The basic characteristics of cylindrical and spherical dust-ion acoustic Gardner solitary waves in a dusty plasma with q-nonextensive electron velocity distribution have been represented by Ghosh et al. [Phys. Plasmas 19, 033703 (2012)]. In this manuscript, they use the double layer stationary solution of the standard Gardner equation but they explain the whole article in terms of Gardner solitons which is completely incorrect.

Mannan, A.; Tanjia, F.; Yasmin, S.

2013-04-01

230

Comment on 'Nonplanar dust-ion acoustic Gardner solitons in a dusty plasma with q-nonextensive electron velocity distribution' [Phys. Plasmas 19, 033703 (2012)  

SciTech Connect

The basic characteristics of cylindrical and spherical dust-ion acoustic Gardner solitary waves in a dusty plasma with q-nonextensive electron velocity distribution have been represented by Ghosh et al.[Phys. Plasmas 19, 033703 (2012)]. In this manuscript, they use the double layer stationary solution of the standard Gardner equation but they explain the whole article in terms of Gardner solitons which is completely incorrect.

Mannan, A. [Dipartimento di Matematica e Fisica, Seconda Universita degli Studi di Napoli, Caserta (Italy); Tanjia, F. [Dipartimento di Scienze Fisiche, Universita di Napoli 'Federico II' and INFN Napoli (Italy); Yasmin, S. [Department of Physics, Jahangirnagar University, Savar, Dhaka 1342 (Bangladesh)

2013-04-15

231

Variable-energy drift-tube linacs  

Microsoft Academic Search

Practical applications of ion linacs are more viable now than ever before because of the recent development of the radio-frequency quadrupole accelerating structure, as well as other technological advances developed under the Pion Generator for Medical Irradiations program. This report describes a practical technique for varying the energy of drift-tube linacs and thus further broadening the possibilities for linac applications.

D. A. Swenson; T. J. Boyd; J. M. Potter; J. E. Stovall

1981-01-01

232

Variable-energy drift-tube linacs  

Microsoft Academic Search

Practical applications of ion linacs are more viable now than ever before because of the recent development of the radio-frequency quadrupole accelerating structure, as well as other technological advances developed under the Pion Generator for Medical Irradiations program. A practical technique for varying the energy of drift-tube linacs and thus further broadening the possibilities for linac applications is described. This

D. A. Swenson; T. J. Jr. Boyd; J. M. Potter; J. E. Stovall

1981-01-01

233

NO+ formation pathways in dissociation of N2O+ ions at the C2?+ state revealed from threshold photoelectron-photoion coincidence velocity imaging  

NASA Astrophysics Data System (ADS)

Using the novel threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging technique, the dissociative photoionization of N2O molecule via the C2?+ ionic state has been investigated. Four fragment ions, NO+, N2+, O+, and N+, are observed, respectively, and the NO+ and N+ ions are always dominant in the whole excitation energy range of the C2?+ ionic state. Subsequently, the TPEPICO three-dimensional time-sliced velocity images of NO+ dissociated from the vibrational state-selected N2O+(C2?+) ions have been recorded. Thus the kinetic and internal energy distributions of the NO+ fragments have been obtained directly as the bimodal distributions, suggesting that the NO+ fragments are formed via both NO+(X1?+) + N(2P) and NO+(X1?+) + N(2D) dissociation channels. Almost the same vibrational population reversions are identified for both dissociation pathways. Interestingly, the obtained branching ratios of the two channels exhibit some dependence on the excited vibrational mode for N2O+(C2?+), in which the excited asymmetrical stretching potentially promotes dissociation possibility along the NO+(X1?+) + N(2D) pathway. In addition, the measured anisotropic parameters of NO+ are close to 0.5, indicating that the C2?+ state of N2O+ is fully predissociative, indeed, with a tendency of parallel dissociation, and therefore, the corresponding predissociation mechanisms for the N2O+(C2?+) ions are depicted.

Tang, Xiaofeng; Niu, Mingli; Zhou, Xiaoguo; Liu, Shilin; Liu, Fuyi; Shan, Xiaobin; Sheng, Liusi

2011-02-01

234

NO+ formation pathways in dissociation of N2O+ ions at the C2?+ state revealed from threshold photoelectron-photoion coincidence velocity imaging.  

PubMed

Using the novel threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging technique, the dissociative photoionization of N(2)O molecule via the C(2)?(+) ionic state has been investigated. Four fragment ions, NO(+), N(2)(+), O(+), and N(+), are observed, respectively, and the NO(+) and N(+) ions are always dominant in the whole excitation energy range of the C(2)?(+) ionic state. Subsequently, the TPEPICO three-dimensional time-sliced velocity images of NO(+) dissociated from the vibrational state-selected N(2)O(+)(C(2)?(+)) ions have been recorded. Thus the kinetic and internal energy distributions of the NO(+) fragments have been obtained directly as the bimodal distributions, suggesting that the NO(+) fragments are formed via both NO(+)(X(1)?(+)) + N((2)P) and NO(+)(X(1)?(+)) + N((2)D) dissociation channels. Almost the same vibrational population reversions are identified for both dissociation pathways. Interestingly, the obtained branching ratios of the two channels exhibit some dependence on the excited vibrational mode for N(2)O(+)(C(2)?(+)), in which the excited asymmetrical stretching potentially promotes dissociation possibility along the NO(+)(X(1)?(+)) + N((2)D) pathway. In addition, the measured anisotropic parameters of NO(+) are close to 0.5, indicating that the C(2)?(+) state of N(2)O(+) is fully predissociative, indeed, with a tendency of parallel dissociation, and therefore, the corresponding predissociation mechanisms for the N(2)O(+)(C(2)?(+)) ions are depicted. PMID:21303125

Tang, Xiaofeng; Niu, Mingli; Zhou, Xiaoguo; Liu, Shilin; Liu, Fuyi; Shan, Xiaobin; Sheng, Liusi

2011-02-01

235

Search for the best timing strategy in high-precision drift chambers  

SciTech Connect

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.

Va'vra, J.

1983-06-01

236

Numerical simulation of drifting snow sublimation in the saltation layer  

NASA Astrophysics Data System (ADS)

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.

Dai, Xiaoqing; Huang, Ning

2014-10-01

237

The influence of finite ion temperature on plasma blob dynamics  

NASA Astrophysics Data System (ADS)

In the scrape-off layer of magnetically confined fusion devices, the ion temperature is at least as high as the electron temperature and usually even much higher. The effects of the finite ion temperature enhance the blob drive and modify the vorticity. Recently developed scaling laws for blob velocity independent of its size, based on the full drift-interchange-Alfvén fluid equations are compared with recent experiments on the ASDEX Upgrade tokamak and gyrofluid simulations, showing remarkable agreement for the blob sizes and reasonable agreement for the blob velocities.

Manz, P.; Birkenmeier, G.; Carralero, D.; Fuchert, G.; Müller, H. W.; Müller, S. H.; Scott, B. D.; Stroth, U.; Ribeiro, T. T.; Wolfrum, E.

2015-01-01

238

Drift Scale THM Model  

SciTech Connect

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.

J. Rutqvist

2004-10-07

239

Alternative dust-ion acoustic waves in a magnetized charge varying dusty plasma with nonthermal electrons having a vortex-like velocity distribution  

NASA Astrophysics Data System (ADS)

Alternative localized dust-ion acoustic waves are investigated in a magnetized charge varying dusty plasma with nonthermal electrons having a vortex-like velocity distribution. The correct non-Maxwellian charging currents are obtained based on the well-known orbit limited motion theory. Following the standard reductive perturbation technique, a Schamel-Zakharov Kuznetsov Burgers (S-ZKB) equation is derived. It is shown that due to an interplay between trapping and nonthermality, our dusty plasma model may support solitary as well as shock waves the main quantities (phase velocity, amplitude and width) of which are drastically influenced by trapping, nonthermality and charge variation. Due to the flexibility provided by the outlined distribution function (two concepts of non isothermality), we stress that our model should provide a good fit of the space observations.

Hadjaz, Idir; Tribeche, Mouloud

2014-06-01

240

drift and selection a) selection, no genetic drift b) large population, drift + selection  

E-print Network

1 drift and selection a) selection, no genetic drift b) large population, drift + selection c) small population, drift + selection nonrandom mating affects genotypic frequencies of a population continental "mainland" population to a smaller island population pt+1 = pt + m (pm - pt ) p = pt+1 - pt = m

Dever, Jennifer A.

241

A vertical drift chamber as a high resolution focal plane detector for heavy ion spectroscopy with the Enge split-pole spectrometer  

E-print Network

these chamber gases have comparatively high specific ionization, high track ionization density I results, and resolution degradation due to statistical fluctuations in the number of primary ion pairs produced is small. As shown in Fig. 5, electrons in argon... 25 26 3O A. Prototype Design Considerations B. Construction C. Initial Tests 1. IS Source 2. Initial Tests with a Cyclotron Beam 30 31 IV SPECTRA FROM THE VDC A. Measurements l. Experimental Runs 2. Electronics 3. Data Acquisition Code B...

Yates, Kenneth Warren

2012-06-07

242

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

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.

Nishioka, S., E-mail: nishioka@ppl.appi.keio.ac.jp; Goto, I.; Hatayama, A. [Graduate School of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan)] [Graduate School of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan); Miyamoto, K. [School of Natural and Living Sciences Education, Naruto University of Education, 748 Nakashima, Takashima, Naruto-cho, Naruto-shi, Tokushima 772-8502 (Japan)] [School of Natural and Living Sciences Education, Naruto University of Education, 748 Nakashima, Takashima, Naruto-cho, Naruto-shi, Tokushima 772-8502 (Japan); Okuda, S.; Fukano, A. [Toshiba, 33 Isogo-chou, Isogo-ku, Yokohama-shi, Kanagawa 235-001 (Japan)] [Toshiba, 33 Isogo-chou, Isogo-ku, Yokohama-shi, Kanagawa 235-001 (Japan)

2014-02-15

243

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

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

Nishioka, S; Miyamoto, K; Okuda, S; Goto, I; Hatayama, A; Fukano, A

2014-02-01

244

Slow drift mirror kinetic instability at a finite electron temperature in a nonmaxwellian space plasma  

NASA Astrophysics Data System (ADS)

A slow drift mirror (SDM) instability has been analyzed in the scope of kinetic approximation, with accounting for the electron pressure for different particle distribution functions. The dependence of the SDM instability increment growth rate on the parameters of the anisotropic ? distribution with the loss cone, which is used to model real space plasma particle distributions, has been studied. An analysis indicated that the appearance of the loss cone in the ion distribution function results in a decrease in the SDM mode frequency, and an enhancement of the suprathermal tail (a decrease in ?) increases the SDM mode frequency as compared to the Maxwellian distribution. In other words, particle redistribution from the region of low velocities into that of high velocities results in an increase in the SDM mode frequency.

Feygin, F. Z.; Khabazin, Yu. G.

2014-11-01

245

Drift Degradation Analysis  

SciTech Connect

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.

D. Kicker

2004-09-16

246

A Benign, Low Z Electron Capture Agent for Negative Ion TPCs  

NASA Technical Reports Server (NTRS)

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.

Martoff, C. J.; Dion, M. P.; Hosack, M.; Barton, D.; Black, J. K.

2008-01-01

247

Spiral silicon drift detectors  

SciTech Connect

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.

Rehak, P.; Gatti, E.; Longoni, A.; Sampietro, M.; Holl, P.; Lutz, G.; Kemmer, J.; Prechtel, U.; Ziemann, T.

1988-01-01

248

Mapping climatological seasonal variations of surface currents in the tropical Atlantic using ship drifts  

Microsoft Academic Search

The seasonal variability of current velocities in the tropical Atlantic was studied by grouping ship drift velocity observations into 2°×5° boxes and calculating monthly mean velocity values. These values were used to calculate and map the annual mean velocity, the seasonal variation about the mean, the annual and semiannual harmonics, and the first two empirical orthogonal functions (EOFs).The seasonal variation

Philip L. Richardson; David Walsh

1986-01-01

249

Drift Wave Turbulence  

SciTech Connect

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.

Horton, W.; Kim, J.-H. [Institute for Fusion Studies, University of Texas at Austin (United States); Asp, E. [Ecole Polytechnique Federale de Lausanne, Centre de Recherches en Physique des Plasmas Association Euratom-Confederation Suisse, CH-1015 Lausanne (Switzerland); Hoang, T. [Assoc. Euratom-CEA, CEA/DSM/DRFC Cadarache, 13108 St Paul-Lez-Durance (France); Watanabe, T.-H.; Sugama, H. [National Institute for Fusion Science/Graduate University for Advanced Studies (Japan)

2008-05-14

250

Laser initiated reactions in N{sub 2}O clusters studied by time-sliced ion velocity imaging technique  

SciTech Connect

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)

Honma, Kenji [Graduate School of Material Science, University of Hyogo, 3-2-1 Kohto, Kamigori, Hyogo 678-1297 (Japan)] [Graduate School of Material Science, University of Hyogo, 3-2-1 Kohto, Kamigori, Hyogo 678-1297 (Japan)

2013-07-28

251

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)

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.

Fernández-García, Juan; Fernández de la Mora, Juan

2013-12-01

252

Measuring the effect of ion-induced drift-gas polarization on the electrical mobilities of multiply-charged ionic liquid nanodrops in air.  

PubMed

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

Fernández-García, Juan; Fernández de la Mora, Juan

2013-12-01

253

HIV envelope drift  

SciTech Connect

The consensus sequences for (HIV) the Human Immunodeficiency Virus,envelope proteins can also be examined with regard to what might be called differential drift. Conserved and hypervariable regions, or domains, of the envelope were defined in 1986, when the extent of conspicuous HIV variation began to be noticed. Although a large fraction of the envelope residues are subject to drift, once substition at some particular site begins, constraints will most likely naturally arise in relation to which residues will admit of substitution thereafater. Thus, we should not expect that the type 1 and type 2 HIVs will manifest identical patterns of conservation and hypervariability. They already reveal significant differences in the number of cysteine residues, for example; although it is far less obvious, there is some indication that with the sequences analyzed thus far that the Zairean and North American HIVs may be differentially drifting as a direct consequence of their high rates of diversification. What makes this case of drift so extraordinary is the rapid pace which appears to be characteristic of the HIV speciation, stemming from not merely the high mutation rate, but also from proliferation in what might be for these viruses a relatively new ecological niche. 3 figs.

Myers, G.

1988-01-01

254

IN DRIFT CORROSION PRODUCTS  

SciTech Connect

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.

D.M. Jolley

1999-12-02

255

High resolution drift chambers  

SciTech Connect

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.

Va'vra, J.

1985-07-01

256

Charge state effect on the K-shell ionization of iron by xenon ions near the Bohr velocity  

NASA Astrophysics Data System (ADS)

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.

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

257

Two-fluid models for stationary dust driven winds. II. The grain size distribution in consideration of drift.  

NASA Astrophysics Data System (ADS)

A multi-component method for the description of the evolution of the grain size distribution in consideration of a size dependent grain drift and growth rate is applied in order to model dust driven winds around cool C-stars. Grain drift introduces several modifications concerning dust growth: On the one hand the residence time in the region of efficient growth is reduced, on the other hand the growth efficiency is higher due to an increased collisional rate. For carbon grains the surface density of radical sites is increased, but on the other hand there is a reduction of the sticking efficiency of the growth species for drift velocities larger than ~5km/s. Furthermore, nonthermal sputtering may become relevant for high drift velocities. It is found that the consideration of drift results in a considerable distortion of the size distribution as compared to the case of zero drift velocity. Generally, there are less, but larger grains if drift is included.

Krueger, D.; Sedlmayr, E.

1997-05-01

258

Experimental observation of ion-cyclotron turbulence in the presence of transverse-velocity shear. Ph.D. Thesis  

Microsoft Academic Search

This laboratory investigation documents the influence of transverse, localized, dc electric fields (TLE) on the excitation of ion-cyclotron waves driven by magnetic field-aligned current (FAC) in a Q-machine plasma device. A segmented disk electrode, located on axis at the end of the plasma column, is used to independently control TLE and FAC in the plasma (potassium plasma, n approximately equals

Amatucci

1994-01-01

259

Tidal decomposition of zonal neutral and ion flows in the earth's upper equatorial thermosphere  

NASA Technical Reports Server (NTRS)

Evidence is presented for strong coupling between the diurnal components of zonal neutral winds and ion drifts, suggesting that the relative importance of the E- and F-region dynamos be reevaluated. Measurements of zonal neutral winds in the equatorial region of the earth's thermosphere at an average altitude of about 350 km show that the nighttime zonal winds are very similar to the zonal ion-drifts. That similarity is examined, comparing the corresponding tidal components of the 24 hr variations of these two parameters. The amplitude spectrum of the neutral winds exhibits primary and secondary maxima at the diurnal and ter-diurnal frequencies respectively, while the ion-drift spectrum shows only the diurnal maximum. It is found that the simularity between neutral winds and ion-drifts is strongest in the diurnal mode where the phases differ by less than one half hour, the amplitude of the ion-drift being between 70 percent and 80 percent that of the neutral wind, suggesting a first-order relation between the two quantities. The largest difference is found in the steady component representing superrotation; under similar conditions of solar activity, the ions superrotate with a velocity of about 30 m/s and the neutrals with 10 m/s. For the ions, the steady component, the phase of the semi-diurnal component and the amplitude of the ter-diurnal component appear to be sensitive to solar activity and are responsible for the observed solar cycle variations in the times of eastward-to-westward reversals between 0400 and 0700 LT. The ion-drift diurnal amplitude and phase are relatively insensitive to changes in solar activity.

Herrero, F. A.; Mayr, H. G.

1986-01-01

260

Drift wave instability in a nonuniform quantum dusty magnetoplasma  

SciTech Connect

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.

Salimullah, M.; Jamil, M.; Zeba, I.; Uzma, Ch.; Shah, H. A. [Department of Physics, GC University, Lahore 54000 (Pakistan)

2009-03-15

261

Experimental observation of ion-cyclotron turbulence in the presence of transverse-velocity shear. Ph.D. Thesis  

SciTech Connect

This laboratory investigation documents the influence of transverse, localized, dc electric fields (TLE) on the excitation of ion-cyclotron waves driven by magnetic field-aligned current (FAC) in a Q-machine plasma device. A segmented disk electrode, located on axis at the end of the plasma column, is used to independently control TLE and FAC in the plasma (potassium plasma, n approximately equals 10(exp 9) cm(exp {minus}3), rho(i) approximately equals 0.2 cm, T(e) = T(i) approximately equals 0.2 eV). Ion-cyclotron waves have been characterized in both the weak-TLE and large-FAC regime and the strong-TLE and small-FAC regime. The existence of a new category of oscillation identified as the inhomogeneous energy-density driven (IEDD) instability is verified based on the properties of the waves in the latter regime. In the weak-TLE regime, current-driven electrostatic ion-cyclotron (CDEIC) waves with features in qualitative agreement with previous laboratory results have been observed at sufficiently large FAC. These waves have a frequency spectrum with a single narrow spectral feature located slightly above the ion-cyclotron frequency (omega approximately equals 1.2 Omega(i)). The waves are standing in the radial direction with peak oscillation amplitude located in the center of the FAC channel and are azimuthally symmetric (m = 0). Small magnitude TLE were found to have negligible effect on the characteristics of the waves. In the strong-TLE regime, a decrease in the threshold FAC level is observed. This transition in the instability threshold is accompanied by changes in the frequency spectra, propagation characteristics, and mode amplitude profiles. In the presence of strong-TLE, the ion-cyclotron waves propagate azimuthally in the E x B direction with k(theta) rho(i) = 0.4 and m = 1. The frequency spectrum becomes broadband and spiky, and shifts with the applied TLE strength.

Amatucci, W.E.

1994-01-01

262

Streamers generation by small-scale drift-Alfvén waves  

SciTech Connect

Excitation of streamers by modulationally unstable small-scale drift-Alfvén 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.

Zhao, J. S. [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China); Yu, M. Y. [Institute for Fusion Theory and Simulation and Department of Physics, Zhejiang University, Hangzhou 310027, China and Institute for Theoretical Physics I, Ruhr University, D-44780 Bochum (Germany)

2014-10-15

263

Stopping power for low-velocity heavy ions: (0.01-0.9) MeV/nucleon Si ions in 18 ( Z = 13-79) metals  

NASA Astrophysics Data System (ADS)

The stopping power for 29Si ions in Al, Ti, V, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ag, Hf, Ta, W, Re, Pt and Au has been studied in the energy region (0.01-0.9) MeV/nucleon by application of a technique of nuclear physics, the inverted analysis of Doppler-shift attenuation data. Generally, the measured values are considerably higher at low energies (less than 0.4 MeV/nucleon) and show different energy dependence than the predictions of the commonly used empirical electronic stopping powers by Ziegler, Biersack and Littmark [1] [The Stopping and Ranges of Ions in Matter (Pergamon, New York, 1985) Vol. 1]. The uncertainty of the electronic stopping powers determined is typically ±6%.

Arstila, K.; Keinonen, J.; Tikkanen, P.

1995-08-01

264

Toroidal universal drift instability: A global gyrokinetic study  

SciTech Connect

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.

Chowdhury, J.; Ganesh, R. [Institute for Plasma Research, Bhat, Gandhinagar 382428 (India); Brunner, S.; Vaclavik, J.; Villard, L. [CRPP, Association EURATOM-Confederation Suisse, EPFL, 1015 Lausanne (Switzerland)

2010-10-15

265

Modulational instability of ion-acoustic waves in a plasma with a q-nonextensive electron velocity distribution  

SciTech Connect

The modulational instability (MI) of ion-acoustic waves (IAWs) in a two-component plasma is investigated in the context of the nonextensive statistics proposed by Tsallis [J. Stat. Phys. 52, 479 (1988)]. Using the reductive perturbation method, the nonlinear Schroedinger equation (NLSE) which governs the MI of the IAWs is obtained. The presence of the nonextensive electron distribution is shown to influence the MI of the waves. Three different ranges of the nonextensive q-parameter are considered and in each case the MI sets in under different conditions. Furthermore, the effects of the q-parameter on the growth rate of MI are discussed in detail.

Bains, A. S.; Gill, T. S. [Department of Physics, Guru Nanak Dev University, Amritsar 143005 (India); Tribeche, Mouloud [Plasma Physics Group (PPG), Theoretical Physics Laboratory (TPL), Faculty of Sciences-Physics, University of Bab-Ezzouar, U.S.T.H.B, B.P. 32, El Alia, Algiers 16111 (Algeria)

2011-02-15

266

Coupled-cavity drift-tube linac  

DOEpatents

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.

Billen, J.H.

1996-11-26

267

Molecular Communication Using Brownian Motion with Drift  

E-print Network

Inspired by biological communication systems, molecular communication has been proposed as a viable scheme to communicate between nano-sized devices separated by a very short distance. Here, molecules are released by the transmitter into the medium, which are then sensed by the receiver. This paper develops a preliminary version of such a communication system focusing on the release of either one or two molecules into a fluid medium with drift. We analyze the mutual information between transmitter and the receiver when information is encoded in the time of release of the molecule. Simplifying assumptions are required in order to calculate the mutual information, and theoretical results are provided to show that these calculations are upper bounds on the true mutual information. Furthermore, optimized degree distributions are provided, which suggest transmission strategies for a variety of drift velocities.

Kadloor, Sachin; Eckford, Andrew W

2010-01-01

268

Coupled-cavity drift-tube linac  

DOEpatents

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.

Billen, James H. (Los Alamos, NM)

1996-01-01

269

The KLOE drift chamber  

Microsoft Academic Search

The tracking detector of the KLOE experiment is 4m diameter, 3.3m length drift chamber, designed to contain a large fraction of the decays of low-energy KL produced at the Frascati DA?NE ?-factory. The chamber is made by a thin carbon fiber structure and operated with a helium-based gas mixture in order to minimise conversion of low-energy photons and multiple scattering

M. Adinolfi; A. Aloisio; F. Ambrosino; A. Andryakov; A. Antonelli; M. Antonelli; F. Anulli; C. Bacci; A. Bankamp; G. Barbiellini; F. Bellini; G. Bencivenni; S. Bertolucci; C. Bini; C. Bloise; V. Bocci; F. Bossi; P. Branchini; S. A. Bulychjov; G. Cabibbo; A. Calcaterra; R. Caloi; P. Campana; G. Capon; G. Carboni; A. Cardini; M. Casarsa; G. Cataldi; F. Ceradini; F. Cervelli; F. Cevenini; G. Chiefari; P. Ciambrone; S. Conetti; S. Conticelli; E. De Lucia; G. De Robertis; R. De Sangro; P. De Simone; G. De Zorzi; S. Dell'Agnello; A. Denig; A. Di Domenico; C. Di Donato; S. Di Falco; A. Doria; E. Drago; V. Elia; O. Erriquez; A. Farilla; G. Felici; A. Ferrari; M. L. Ferrer; G. Finocchiaro; C. Forti; A. Franceschi; P. Franzini; M. L. Gao; C. Gatti; P. Gauzzi; S. Giovannella; V. Golovatyuk; E. Gorini; F. Grancagnolo; W. Grandegger; E. Graziani; P. Guarnaccia; U. v. Hagel; H. G. Han; S. W. Han; X. Huang; M. Incagli; L. Ingrosso; Y. Y. Jang; W. Kim; W. Kluge; V. Kulikov; F. Lacava; G. Lanfranchi; J. Lee-Franzini; F. Lomtadze; C. Luisi; C. S. Mao; M. Martemianov; M. Matsyuk; W. Mei; L. Merola; R. Messi; S. Miscetti; A. Moalem; S. Moccia; M. Moulson; S. Mueller; F. Murtas; M. Napolitano; A. Nedosekin; M. Panareo; L. Pacciani; P. Pagès; M. Palutan; L. Paoluzi; E. Pasqualucci; L. Passalacqua; M. Passaseo; A. Passeri; V. Patera; E. Petrolo; G. Petrucci; D. Picca; G. Pirozzi; C. Pistillo; M. Pollack; L. Pontecorvo; M. Primavera; F. Ruggieri; P. Santangelo; E. Santovetti; G. Saracino; R. D. Schamberger; C. Schwick; B. Sciascia; A. Sciubba; F. Scuri; I. Sfiligoi; J. Shan; P. Silano; T. Spadaro; S. Spagnolo; E. Spiriti; C. Stanescu; G. L. Tong; L. Tortora; E. Valente; P. Valente; B. Valeriani; G. Venanzoni; S. Veneziano; Y. Wu; Y. G. Xie; P. P. Zhao; Y. Zhou

2001-01-01

270

Fermilab drift tube Linac revisited  

SciTech Connect

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.

Milorad Popovic

2004-05-12

271

Ion cyclotron and spin-flip emissions from fusion products in tokamaks  

SciTech Connect

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.

Arunasalam, V.; Greene, G.J.; Young, K.M.

1993-02-01

272

Ion cyclotron and spin-flip emissions from fusion products in tokamaks  

SciTech Connect

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.

Arunasalam, V.; Greene, G.J.; Young, K.M.

1993-02-01

273

Photodissociation of the BrO radical using velocity map ion imaging: Excited state dynamics and accurate D{sub 0}{sup 0}(BrO) evaluation  

SciTech Connect

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.

Kim, Hahkjoon; Dooley, Kristin S.; Johnson, Elizabeth R.; North, Simon W. [Department of Chemistry, Texas A and M University, College Station, Texas 77842 (United States)

2006-04-07

274

Emplacement Drift System Description Document  

SciTech Connect

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.

Eric Loros

2001-07-31

275

The Electron Drift Technique for Measuring Electric and Magnetic Fields  

NASA Technical Reports Server (NTRS)

The electron drift technique is based on sensing the drift of a weak beam of test electrons that is caused by electric fields and/or gradients in the magnetic field. These quantities can, by use of different electron energies, in principle be determined separately. Depending on the ratio of drift speed to magnetic field strength, the drift velocity can be determined either from the two emission directions that cause the electrons to gyrate back to detectors placed some distance from the emitting guns, or from measurements of the time of flight of the electrons. As a by-product of the time-of-flight measurements, the magnetic field strength is also determined. The paper describes strengths and weaknesses of the method as well as technical constraints.

Paschmann, G.; McIlwain, C. E.; Quinn, J. M.; Torbert, R. B.; Whipple, E. C.; Christensen, John (Technical Monitor)

1998-01-01

276

Pre-sheath density drop induced by ion-neutral friction along plasma blobs and implications for blob velocities  

SciTech Connect

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)].

Furno, I.; Chabloz, V.; Fasoli, A.; Loizu, J. [Centre de Recherches en Physique des Plasmas-Ecole Polytechnique Fédérale de Lausanne, Association EURATOM-Confédération Suisse, CH-1015 Lausanne (Switzerland)] [Centre de Recherches en Physique des Plasmas-Ecole Polytechnique Fédérale de Lausanne, Association EURATOM-Confédération Suisse, CH-1015 Lausanne (Switzerland); Theiler, C. [MIT Plasma Science and Fusion Center, Cambridge, Massachusetts 02139 (United States)] [MIT Plasma Science and Fusion Center, Cambridge, Massachusetts 02139 (United States)

2014-01-15

277

D. phi. vertex drift chamber construction and test results  

SciTech Connect

A jet-cell based vertex chamber has been built for the D{O} experiment at Fermilab and operated in a test beam there. Low drift velocity and diffusion properties were achieved using CO{sub 2}(95%)-ethane(5%) at atmospheric pressure. The drift velocity is found to be consistent with (9.74+8.68( E -1.25)) {mu}m/nsec where E is the electric field strength in (kV/cm < E z 1.6 kV/cm.) An intrinsic spatial resolution of 60 {mu}m or better for drift distances greater than 2 mm is measured. The track pair efficiency is estimated to be better than 90% for separations greater than 630 {mu}m. 8 refs., 6 figs., 1 tab.

Clark, A.R.; Goozen, F.; Grudberg, P.; Klopfenstein, C.; Kerth, L.T.; Loken, S.C.; Oltman, E.; Strovink, M.; Trippe, T.G.

1991-05-01

278

Electromagnetic nonlinear gyrokinetics with polarization drift  

SciTech Connect

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.

Duthoit, F.-X. [SNU Division of Graduate Education for Sustainabilization of Foundation Energy, Seoul National University, Gwanak-ro 1, Gwanak-gu, 151-744 Seoul (Korea, Republic of); Hahm, T. S., E-mail: tshahm@snu.ac.kr [Department of Nuclear Engineering, Seoul National University, Gwanak-ro 1, Gwanak-gu, 151-744 Seoul (Korea, Republic of); Wang, Lu [College of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China)

2014-08-15

279

Electromagnetic nonlinear gyrokinetics with polarization drift  

NASA Astrophysics Data System (ADS)

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.

Duthoit, F.-X.; Hahm, T. S.; Wang, Lu

2014-08-01

280

Dispersion characteristics of kinetic Alfven waves in a multi-ion cometary plasma  

NASA Astrophysics Data System (ADS)

We have studied the stability of the kinetic Alfven wave in a plasma composed of hydrogen and positively and negatively charged oxygen ions and electrons which approximates very well the plasma environment around comet Halley. In the direction parallel to the magnetic field, the electrons have been modelled by a drifting Maxwellian distribution. In the perpendicular direction, another ring simulated by a loss cone type distribution, obtained by subtracting two Maxwellians with different temperatures, model all the constituents of the plasma. The dispersion relation derived for KAWs is a generalisation of the pioneering dispersion relation of Hasegawa on two counts: it has been extended to a plasma described by a generalised distribution function and to a multi - ion plasma containing positively and negatively charged ions. We find that the dispersion characteristics of the KAW can be made independent of the heavy ion parameters by an appropriate choice of densities and temperatures. The source of free energy for the instability is the drift velocity of the electrons; the growth rate increases with increasing drift velocity of the electrons. The positively charged heavier ions enhance the instability while the negatively charged heavier ions tend to damp the wave.

Jayapal, R.; Abraham, Noble P.; Blesson, Jose; Antony, S.; Anilkumar, C. P.; Venugopal, Chandu

281

Magnetic conjugate point observations of kilometer and hundred-meter scale irregularities and zonal drifts  

NASA Astrophysics Data System (ADS)

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.

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

282

A Parametric Study of Extended-MHD Drift Tearing  

E-print Network

The linear drift-tearing mode is analyzed for different regimes of the plasma-$\\beta$, ion-skin-depth parameter space with an unreduced, extended-MHD model. New dispersion relations are found at moderate plasma $\\beta$ and previous drift-tearing results are classified as applicable at small plasma $\\beta$. The drift stabilization of the mode in the regimes varies from non-existent/weak to complete. As the diamagnetic-drift frequency is proportional to the plasma $\\beta$, verification exercises with unreduced, extended-MHD models in the small plasma-$\\beta$ regimes are impractical. The new dispersion relations in the moderate plasma-$\\beta$ regimes are used to verify the extended-MHD implementation of the NIMROD code [C. R. Sovinec et al., J. Comput. Phys. 195, 355 (2004)]. Given the small boundary-layer skin depth, discussion of the validity of the first-order finite-Larmour-radius model is presented.

King, Jacob R

2014-01-01

283

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

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.

Kalita, B. C. [Department of Mathematics, Gauhati University, Guwahati 781 014, Assam (India); Barman, S. N. [Department of Mathematics, Arya Vidyapeeth College, Guwahati 781 016, Assam (India)

2009-05-15

284

A magnetospheric critical velocity experiment - Particle results  

NASA Technical Reports Server (NTRS)

In March of 1983, a barium injection sounding rocket experiment (The Star of Lima) was conducted to investigate Alfven's critical ionization velocity (CIV) hypothesis in space. Included in the instrumented payload was a particle detection experiment consisting of five retarding potential analyzers. Despite conditions that appeared to be optimal for the critical velocity effect, the particle data, in agreement with optical observations, indicates that a fractional ionization of only approximately .0005 was observed, indicating that the conditions required for the effect to occur are still not well understood. However many of the required phenomena associated with the CIV effect were observed; in particular a superthermal electron population was formed at the expense of ion drift kinetic energy in the presence of intense electrostatic waves near the lower hybrid frequency. The amount of ionization produced is plausibly consistent with the observed electron flux, but could also be accounted for by residual solar UV at the injection point. It is shown based on the data set that one obvious explanation for the low ionization efficiency, namely that the ionizing superthermal electrons may rapidly escape along field lines, can be ruled out.

Torbert, R. B.; Newell, P. T.

1986-01-01

285

Suppression of hot electrons in threshold photoelectron photoion coincidence spectroscopy using velocity focusing optics  

NASA Astrophysics Data System (ADS)

Velocity focusing of electrons is combined with photoelectron photoion coincidence (PEPICO) spectroscopy to achieve a true threshold PEPICO signal without contributions from energetic electrons. Ions are generated by a continuous vacuum ultraviolet light source. Electrons, extracted by a field of 20 V/cm, pass through a 13 cm drift region and are dispersed in space on a multichannel plate detector by velocity focusing optics. The ions are extracted in the opposite direction by the same electric field, further accelerated by a second field, and collected after passing through a 30 cm drift region. Ions are measured in coincidence with electrons collected from the central 3.2 mm electrode as well as a ring electrode (inner and outer diameters of 5.6 and 8.1 mm). The central ring electrode contains mostly true threshold electrons along with a background of "hot" electrons, whereas the outer ring electrode collects only hot electrons. By subtracting the latter from the former, true threshold photoelectron photoion coincidence spectra are obtained. The major advantages of this approach are the high electron energy resolution with the use of high direct current extraction fields, and the complete suppression of energetic electrons.

Sztáray, Bálint; Baer, Tomas

2003-08-01

286

Effect of solenoidal magnetic field on drifting laser plasma  

SciTech Connect

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.

Takahashi, Kazumasa; Sekine, Megumi [Tokyo Institute of Technology, Yokohama 226-8502 (Japan); Okamura, Masahiro [Brookhaven National Laboratory, Upton, NY 11973 (United States) and RIKEN, Wako-shi, Saitama 351-0198 (United States); Cushing, Eric [Pennsylvania State University, University Park, PA 16802 (United States); Jandovitz, Peter [Cornell University, Ithaca, NY 14853 (United States)

2013-04-19

287

Effects of grids in drift tubes  

SciTech Connect

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.

Okamura M.; Yamauchi, H.

2012-05-20

288

DRCELL: A software package for drift chamber cell design  

SciTech Connect

Designing a drift chamber cell geometry which optimizes resolution and two track separation is not a straightforward task. This paper describes a software package which helps visualize the behavior of drifting electrons within the cell under the influence of electric and magnetic fields. Histograms of chamber pulse shapes and arrival times may be generated. In addition, a calculation of the gas gain is performed. The package presently uses drift velocity, drift angle, gain, and dE/dx parameterizations for 50:50 argon/endash/ethane but modifications may be easily made for other gas mixtures. The model is straightforward and relies on an analytical form for the electric potential of an infinite series of wires. The electric field is calculated numerically in a small region surrounding any point of interest. In the absence of a magnetic field, the drift direction of an ionization electron is the unit vector along the E field direction. When a perpendicular magnetic field is present, the drift direction is rotated by the Lorentz angle, a. 3 refs., 2 figs., 1 tab.

Baller, B.R.

1989-03-06

289

An experimental test and models of drift and dispersal processes of pallid sturgeon (Scaphirhynchus albus) free embryos in the Missouri River  

USGS Publications Warehouse

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.

Braaten, P.J.; Fuller, D.B.; Lott, R.D.; Ruggles, M.P.; Brandt, T.F.; Legare, R.G.; Holm, R.J.

2012-01-01

290

A parametric study of the drift-tearing mode using an extended-magnetohydrodynamic model  

SciTech Connect

The linear, collisional, constant-? drift-tearing mode is analyzed for different regimes of the plasma-?, ion-skin-depth parameter space with an unreduced, extended-magnetohydrodynamic model. New dispersion relations are found at moderate plasma ? and previous drift-tearing results are classified as applicable at small plasma ?.

King, J. R.; Kruger, S. E. [Tech-X Corporation, 5621 Arapahoe Ave. Suite A Boulder, Colorado 80303 (United States)

2014-10-15

291

Magnetic drift kinetic damping of the resistive wall mode in large aspect ratio tokamaks  

Microsoft Academic Search

An analytical, large aspect ratio, calculation of the drift-kinetic energy perturbation is carried out for the resistive wall mode, due to the mode resonance with the magnetic precession drifts of trapped thermal ions and electrons. Four asymptotic cases are identified and analyzed in detail. Generally, a partial stabilization of the mode is possible thanks to the kinetic correction to the

Yueqiang Liu; M. S. Chu; C. G. Gimblett; R. J. Hastie

2008-01-01

292

Drift waves in rotating plasmas  

SciTech Connect

The stability of the electron drift wave is investigated in the presence of E x B plasma rotation typical of the central cell plasma in tandem mirrors. It is shown that a rotationally-driven drift wave may occur at low azimuthal mode numbers. Conditions for rotational instabilities are derived. Quasilinear formulas are given for the anomalous transport associated with the unstable fluctuations.

Horton, W.; Liu, J.

1983-09-01

293

ATLAS Muon Drift Tube Electronics  

Microsoft Academic Search

This paper describes the electronics used for the ATLAS monitored drift tube (MDT) chambers. These chambers are the main component of the precision tracking system in the ATLAS muon spectrometer. The MDT detector system consists of 1,150 chambers containing a total of 354,000 drift tubes. It is capable of measuring the sagitta of muon tracks to an accuracy of 60

Y. Arai; B. Ball; M. Beretta; H. Boterenbrood; G. W. Brandenburg; F. Ceradini; J. W. Chapman; T. Dai; C. Ferretti; T. Fries; J. Gregory; J. Guimarães da Costa; S. Harder; E. Hazen; J. Huth; P. P. M. Jansweijer; L. E. Kirsch; A. C. König; A. Lanza; G. Mikenberg; J. Oliver; C. Posch; R. Richter; W. Riegler; E. Spiriti; F. E. Taylor; J. C. Vermeulen; B. Wadsworth; T. A. M. Wijnen

2008-01-01

294

Relativistic electron drift shell splitting  

Microsoft Academic Search

A survey of equatorial outer radiation belt relativistic electron pitch angle distributions measured on the Polar satellite shows anisotropies that are consistent with the effects of drift shell splitting. Simulations based on the observed radial intensity gradients and on drift shell calculations in a magnetospheric field model show that for low geomagnetic activity levels, the measured average anisotropies are similar

R. S. Selesnick; J. B. Blake

2002-01-01

295

Progress in semiconductor drift detectors  

SciTech Connect

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.

Rehak, P.; Walton, J.; Gatti, E.; Longoni, A.; Sanpietro, M.; Kemmer, J.; Dietl, H.; Holl, P.; Klanner, R.; Lutz, G.

1985-01-01

296

Bouchaud walks with variable drift  

E-print Network

In this paper we study a sequence of Bouchaud trap models on $\\mathbb{Z}$ with drift. We analyze the possible scaling limits for a sequence of walks, where we make the drift decay to 0 as we rescale the walks. Depending on the speed of the decay of the drift we obtain three different scaling limits. If the drift decays slowly as we rescale the walks we obtain the inverse of an \\alpha$-stable subordinator as scaling limit. If the drift decays quickly as we rescale the walks, we obtain the F.I.N. diffusion as scaling limit. There is a critical speed of decay separating these two main regimes, where a new process appears as scaling limit. This critical speed is related to the index $\\alpha$ of the inhomogeneity of the environment.

Parra, Manuel Cabezas

2010-01-01

297

Theory of semicollisional drift-interchange modes in cylindrical plasmas  

SciTech Connect

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.

Hahm, T.S.; Chen, L.

1985-01-01

298

High Performance Ion Mobility Spectrometry Using Hourglass Electrodynamic Funnel And Internal Ion Funnel  

DOEpatents

A method and apparatus enabling increased sensitivity in ion mobility spectrometry/mass spectrometry instruments which substantially reduces or eliminates the loss of ions in ion mobility spectrometer drift tubes utilizing a device for transmitting ions from an ion source which allows the transmission of ions without significant delay to an hourglass electrodynamic ion funnel at the entrance to the drift tube and/or an internal ion funnel at the exit of the drift tube. An hourglass electrodynamic funnel is formed of at least an entry element, a center element, and an exit element, wherein the aperture of the center element is smaller than the aperture of the entry element and the aperture of the exit elements. Ions generated in a relatively high pressure region by an ion source at the exterior of the hourglass electrodynamic funnel are transmitted to a relatively low pressure region at the entrance of the hourglass funnel through a conductance limiting orifice. Alternating and direct electrical potentials are applied to the elements of the hourglass electrodynamic funnel thereby drawing ions into and through the hourglass electrodynamic funnel thereby introducing relatively large quantities of ions into the drift tube while maintaining the gas pressure and composition at the interior of the drift tube as distinct from those at the entrance of the electrodynamic funnel and allowing a positive gas pressure to be maintained within the drift tube, if desired. An internal ion funnel is provided within the drift tube and is positioned at the exit of said drift tube. The advantage of the internal ion funnel is that ions that are dispersed away from the exit aperture within the drift tube, such as those that are typically lost in conventional drift tubes to any subsequent analysis or measurement, are instead directed through the exit of the drift tube, vastly increasing the amount of ions exiting the drift tube.

Smith, Richard D. (Richland, WA); Tang, Keqi (Richland, WA); Shvartsburg, Alexandre A. (Richland, WA)

2005-11-22

299

Electrodeless drift chambers with 50-cm drift distance  

SciTech Connect

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.

Ayres, D.S.; Price, L.E.

1982-08-01

300

DRIFT-INDUCED PERPENDICULAR TRANSPORT OF SOLAR ENERGETIC PARTICLES  

SciTech Connect

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.

Marsh, M. S.; Dalla, S.; Kelly, J.; Laitinen, T., E-mail: mike.s.marsh@gmail.com [Jeremiah Horrocks Institute, University of Central Lancashire, Preston, PR1 2HE (United Kingdom)

2013-09-01

301

ON PLASMA ROTATION AND DRIFTING SUBPULSES IN PULSARS: USING ALIGNED PULSAR B0826-34 AS A VOLTMETER  

SciTech Connect

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.

Van Leeuwen, J. [Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo (Netherlands); Timokhin, A. N., E-mail: leeuwen@astron.nl, E-mail: andrey.timokhin@nasa.gov [Astrophysics Science Division, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2012-06-20

302

The production of ion conics by oblique double layers. [of auroral arcs  

NASA Technical Reports Server (NTRS)

Magnetized test ions are subjected to acceleration through a numerically simulated oblique double layer in order to determine whether they emerge with velocity vectors aligned with or oblique to the ambient magnetic field. A criterion for oblique alignment, depending on the double-layer parameters and on the external magnetization, is obtained. When it is applied to observed and theoretical auroral double layers, this criterion predicts that accelerated heavy ions will be substantially less magnetic field aligned than will accelerated hydrogen ions, thus suggesting auroral double layers as a source of high-energy ion conics. Test particle simulations are also used to investigate the perpendicular heating of ions at low altitudes by the electric fields associated with moving auroral arcs. The rapid motion of small-scale structures in the arcs is suggested as a source of low-energy conical ion distributions, and the slow drifts of the entire arc forms are inferred to heat ionospheric ions.

Borovsky, J. E.

1984-01-01

303

A statistical analysis of systematic errors in temperature and ram velocity estimates from satellite-borne retarding potential analyzers  

SciTech Connect

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.

Klenzing, J. H.; Earle, G. D.; Heelis, R. A.; Coley, W. R. [William B. Hanson Center for Space Sciences, University of Texas at Dallas, 800 W. Campbell Rd. WT15, Richardson, Texas 75080 (United States)

2009-05-15

304

Gyrokinetic theory of electrostatic lower-hybrid drift instabilities in a current sheet with guide field  

SciTech Connect

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)].

Tummel, K., E-mail: tummel08@gmail.com [Department of Physics and Astronomy, University of California at Irvine, Irvine, California 92697 (United States); Chen, L. [Institute for Fusion Theory and Simulation and Department of Physics, ZheJiang University, Hang Zhou, ZheJiang 310058 (China) [Institute for Fusion Theory and Simulation and Department of Physics, ZheJiang University, Hang Zhou, ZheJiang 310058 (China); Department of Physics and Astronomy, University of California at Irvine, Irvine, California 92697 (United States); Wang, Z.; Wang, X. Y.; Lin, Y. [Department of Physics, Auburn University, Auburn, Alabama 36849 (United States)] [Department of Physics, Auburn University, Auburn, Alabama 36849 (United States)

2014-05-15

305

Drifting Oscillations in Axion Monodromy  

E-print Network

We study the pattern of oscillations in the primordial power spectrum in axion monodromy inflation, accounting for drifts in the oscillation period that can be important for comparing to cosmological data. In these models the potential energy has a monomial form over a super-Planckian field range, with superimposed modulations whose size is model-dependent. The amplitude and frequency of the modulations are set by the expectation values of moduli fields. We show that during the course of inflation, the diminishing energy density can induce slow adjustments of the moduli, changing the modulations. We provide templates capturing the effects of drifting moduli, as well as drifts arising in effective field theory models based on softly broken discrete shift symmetries, and we estimate the precision required to detect a drifting period. A non-drifting template suffices over a wide range of parameters, but for the highest frequencies of interest, or for sufficiently strong drift, it is necessary to include parameters characterizing the change in frequency over the e-folds visible in the CMB. We use these templates to perform a preliminary search for drifting oscillations in a part of the parameter space in the Planck nominal mission data.

Raphael Flauger; Liam McAllister; Eva Silverstein; Alexander Westphal

2014-12-04

306

Quantum diffusion with drift and the Einstein relation. I  

SciTech Connect

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.

De Roeck, Wojciech, E-mail: wojciech.deroeck@fys.kuleuven.be [Institute for Theoretical Physics, K.U. Leuven, 3001 Leuven (Belgium); Fröhlich, Jürg, E-mail: juerg.froehlich@itp.phys.ethz.ch [Institute for Theoretical Physics, ETH Zürich, 8093 Zürich (Switzerland); Schnelli, Kevin, E-mail: skevin@math.harvard.edu [Department of Mathematics, Harvard University, Cambridge, Massachusetts 02138 (United States)

2014-07-15

307

SPIV measurements around the DELFT 372 catamaran in steady drift  

NASA Astrophysics Data System (ADS)

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.

Falchi, M.; Felli, M.; Grizzi, S.; Aloisio, G.; Broglia, R.; Stern, F.

2014-11-01

308

Hall thruster plasma fluctuations identified as the E×B electron drift instability: Modeling and fitting on experimental data  

SciTech Connect

Microturbulence has been implicated in anomalous transport at the exit of the Hall thruster, and recent simulations have shown the presence of an azimuthal wave which is believed to contribute to the electron axial mobility. In this paper, the 3D dispersion relation of this E×B electron drift instability is numerically solved. The mode is found to resemble an ion acoustic mode for low values of the magnetic field, as long as a non-vanishing component of the wave vector along the magnetic field is considered, and as long as the drift velocity is small compared to the electron thermal velocity. In these conditions, an analytical model of the dispersion relation for the instability is obtained and is shown to adequately describe the mode obtained numerically. This model is then fitted on the experimental dispersion relation obtained from the plasma of a Hall thruster by the collective light scattering diagnostic. The observed frequency-wave vector dependences are found to be similar to the dispersion relation of linear theory, and the fit provides a non-invasive measurement of the electron temperature and density.

Cavalier, J.; Lemoine, N.; Bonhomme, G. [IJL, Université de Lorraine, CNRS (UMR 7198), BP 70239, 54506 Vandoeuvre-lès-Nancy (France)] [IJL, Université de Lorraine, CNRS (UMR 7198), BP 70239, 54506 Vandoeuvre-lès-Nancy (France); Tsikata, S. [ICARE, CNRS (UPR 3021), 1C av. de la Recherche Scientifique, 45071 Orléans (France)] [ICARE, CNRS (UPR 3021), 1C av. de la Recherche Scientifique, 45071 Orléans (France); Honoré, C.; Grésillon, D. [LPP, CNRS (UMR 7648), École Polytechnique, 91128 Palaiseau (France)] [LPP, CNRS (UMR 7648), École Polytechnique, 91128 Palaiseau (France)

2013-08-15

309

Production of Magnetic Turbulence by Cosmic Rays Drifting Upstream of Supernova Remnant Shocks  

NASA Technical Reports Server (NTRS)

I will present results of our recent two- and three-dimensional Particle-In-Cell simulations of magnetic-turbulence production by cosmic-ray ions drifting upstream of supernova remnant shocks. These studies' aim is twofold: test recent predictions of strong amplification in short wavelength, non-resonant wave modes, and study the subsequent evolution of the magnetic turbulence, including its backreaction on cosmic-ray trajectories. We confirm that the drifting cosmic rays give rise to a turbulent magnetic field, but show that an oblique filamentary mode grows more rapidly than the non-resonant parallel modes found in analytical theory. The field perturbations grow more slowly than estimated using a quasi-linear analytical approach for the parallel plane-wave mode, and saturate in amplitude at deltaB/B approximately equal to 1. The backreaction of the magnetic turbulence on the particles leads to an alignment of the bulk-flow velocities of the cosmic rays and the background medium. This is an essential characteristic of cosmic ray-modified shocks: the upstream flow speed is continuously changed by the cosmic rays. The reduction of relative drift between cosmic rays and background medium accounts for the saturation of the instability at only moderate magnetic-field amplitudes. It is possible that the prolonged magnetic field growth observed in recent MHD simulations results from a cosmic-ray current assumed to be constant and thus immune to the backreaction from the turbulent field. We speculate that the parallel plane-wave mode found in analytical treatments very quickly leads co filamentation, which we observe in our PIC modeling and is also apparent in the MHD simulations.

Stroman, Thomas; Niemiec, Jacek; Pohl, Martin; Nishikawa, Ken-ichi

2008-01-01

310

THE 15 LAYER SILICON DRIFT DETECTOR TRACKER IN EXPERIMENT 896.  

SciTech Connect

Large linear silicon drift detectors have been developed and are in production for use in several experiments. Recently 15 detectors were used as a tracking device in BNL-AGS heavy ion experiment (E896). The detectors were successfully operated in a 6.2 T magnetic field. The behavior of the detectors, such as drift uniformity, resolution, and charge collection efficiency are presented. The effect of the environment on the detector performance is discussed. Some results from the experimental run are presented. The detectors performed well in an experimental environment. This is the first tracking application of these detectors.

PANDY,S.U.

1998-11-08

311

Asymmetric particle fluxes from drifting ionization zones in sputtering magnetrons  

NASA Astrophysics Data System (ADS)

Electron and ion fluxes from direct current and high-power impulse magnetron sputtering (dcMS and HiPIMS) plasmas were measured in the plane of the target surface. Biased collector probes and a particle energy and mass analyzer showed asymmetric emission of electrons and of singly and doubly charged ions. For both HiPIMS and dcMS discharges, higher fluxes of all types of particles were observed in the direction of the electrons' E × B drift. These results are put in the context with ionization zones that drift over the magnetron's racetrack. The measured currents of time-resolving collector probes suggest that a large fraction of the ion flux originates from drifting ionization zones, while energy-resolving mass spectrometry indicates that a large fraction of the ion energy is due to acceleration by an electric field. This supports the recently proposed hypothesis that each ionization zone is associated with a negative-positive-negative space charge structure, thereby producing an electric field that accelerates ions from the location where they were formed.

Panjan, Matjaž; Franz, Robert; Anders, André

2014-04-01

312

Self?convection of floating heat sources: A model for continental drift  

Microsoft Academic Search

Two models of floating heat sources are studied. In the first model the motion of two line heat sources constrained to float at an arbitrary depth in a viscous fluid is determined in the limit of small convection velocities. It is found that the sources drift apart and at great separation attain a constant velocity proportional to the square root

L. N. Howard; W. V. R. Malkus; J. A. Whitehead

1970-01-01

313

Effect of drift waves on plasma blob dynamics.  

PubMed

Most of the work to date on plasma blobs found in the edge region of magnetic confinement devices is limited to 2D theory and simulations which ignore the variation of blob parameters along the magnetic field line. However, if the 2D convective rate of blobs is on the order of the growth rate of unstable drift waves, then drift wave turbulence can drastically alter the dynamics of blobs from that predicted by 2D theory. The density gradients in the drift plane that characterize the blob are mostly depleted during the nonlinear stage of drift waves resulting in a much more diffuse blob with a greatly reduced radial velocity. Sheath connected plasma blobs driven by effective gravity forces are considered in this Letter and it is found that the effects of resistive drift waves occur at earlier stages in the 2D motion for smaller blobs and in systems with a smaller effective gravity force. These conclusions are supported numerically by a direct comparison of 2D and 3D seeded blob simulations. PMID:23003271

Angus, Justin R; Umansky, Maxim V; Krasheninnikov, Sergei I

2012-05-25

314

High-Performance Ion Mobility Spectrometry Using Hourglass Electrodynamic Funnel And Internal Ion Funnel  

DOEpatents

A method and apparatus enabling increased sensitivity in ion mobility spectrometry/mass spectrometry instruments which substantially reduces or eliminates the loss of ions in ion mobility spectrometer drift tubes utilizing an hourglass electrodynamic ion funnel at the entrance to the drift tube and/or an internal ion funnel at the exit of the drift tube. An hourglass electrodynamic funnel is formed of at least an entry element, a center element, and an exit element, wherein the aperture of the center element is smaller than the aperture of the entry element and the aperture of the exit elements. Ions generated in a relatively high pressure region by an ion source at the exterior of the hourglass electrodynamic funnel are transmitted to a relatively low pressure region at the entrance of the hourglass funnel through a conductance limiting orifice. Alternating and direct electrical potentials are applied to the elements of the hourglass electrodynamic funnel thereby drawing ions into and through the hourglass electrodynamic funnel thereby introducing relatively large quantities of ions into the drift tube while maintaining the gas pressure and composition at the interior of the drift tube as distinct from those at the entrance of the electrodynamic funnel and allowing a positive gas pressure to be maintained within the drift tube, if desired. An internal ion funnel is provided within the drift tube and is positioned at the exit of said drift tube. The advantage of the internal ion funnel is that ions that are dispersed away from the exit aperture within the drift tube, such as those that are typically lost in conventional drift tubes to any subsequent analysis or measurement, are instead directed through the exit of the drift tube, vastly increasing the amount of ions exiting the drift tube.

Smith, Richard D. (Richland, WA); Tang, Keqi (Richland, WA); Shvartsburg, Alexandre A. (Richland, WA)

2004-11-16

315

Apparatus and method for laser velocity interferometry  

DOEpatents

An apparatus and method for laser velocity interferometry employing a fixed interferometer cavity and delay element. The invention permits rapid construction of interferometers that may be operated by those non-skilled in the art, that have high image quality with no drift or loss of contrast, and that have long-term stability even without shock isolation of the cavity.

Stanton, Philip L. (Bernalillo County, NM); Sweatt, William C. (Albuquerque, NM); Crump, Jr., O. B. (Albuquerque, NM); Bonzon, Lloyd L. (Albuquerque, NM)

1993-09-14

316

Linear electronic field time-of-flight ion mass spectrometers  

DOEpatents

Time-of-flight mass spectrometer comprising a first drift region and a second drift region enclosed within an evacuation chamber; a means of introducing an analyte of interest into the first drift region; a pulsed ionization source which produces molecular ions from said analyte of interest; a first foil positioned between the first drift region and the second drift region, which dissociates said molecular ions into constituent atomic ions and emits secondary electrons; an electrode which produces secondary electrons upon contact with a constituent atomic ion in second drift region; a stop detector comprising a first ion detection region and a second ion detection region; and a timing means connected to the pulsed ionization source, to the first ion detection region, and to the second ion detection region.

Funsten, Herbert O. (Los Alamos, NM)

2010-08-24

317

The Drifting Star  

NASA Astrophysics Data System (ADS)

By studying in great detail the 'ringing' of a planet-harbouring star, a team of astronomers using ESO's 3.6-m telescope have shown that it must have drifted away from the metal-rich Hyades cluster. This discovery has implications for theories of star and planet formation, and for the dynamics of our Milky Way. ESO PR Photo 09a/08 ESO PR Photo 09a/08 Iota Horologii The yellow-orange star Iota Horologii, located 56 light-years away towards the southern Horologium ("The Clock") constellation, belongs to the so-called "Hyades stream", a large number of stars that move in the same direction. Previously, astronomers using an ESO telescope had shown that the star harbours a planet, more than 2 times as large as Jupiter and orbiting in 320 days (ESO 12/99). But until now, all studies were unable to pinpoint the exact characteristics of the star, and hence to understand its origin. A team of astronomers, led by Sylvie Vauclair from the University of Toulouse, France, therefore decided to use the technique of 'asteroseismology' to unlock the star's secrets. "In the same way as geologists monitor how seismic waves generated by earthquakes propagate through the Earth and learn about the inner structure of our planet, it is possible to study sound waves running through a star, which forms a sort of large, spherical bell," says Vauclair. The 'ringing' from this giant musical instrument provides astronomers with plenty of information about the physical conditions in the star's interior. And to 'listen to the music', the astronomers used one of the best instruments available. The observations were conducted in November 2006 during 8 consecutive nights with the state-of-the-art HARPS spectrograph mounted on the ESO 3.6-m telescope at La Silla. Up to 25 'notes' could be identified in the unique dataset, most of them corresponding to waves having a period of about 6.5 minutes. These observations allowed the astronomers to obtain a very precise portrait of Iota Horologii: its temperature is 6150 K, its mass is 1.25 times that of the Sun, and its age is 625 million years. Moreover, the star is found to be more metal-rich than the Sun by about 50%. ESO PR Photo 09b/08 ESO PR Photo 09b/08 Constellations "These results show the power of asteroseismology when using a very precise instrument such as HARPS," says Vauclair. "It also shows that Iota Horologii has the same metal abundance and age as the Hyades cluster and this cannot be a coincidence." The Hyades is an ensemble of stars that is seen with the unaided eye in the Northern constellation Taurus ("The Bull"). This open cluster, located 151 light-years away, contains stars that were formed together 625 million years ago. The star Iota Horologii must have thus formed together with the stars of the Hyades cluster but must have slowly drifted away, being presently more than 130 light-years away from its original birthplace. This is an important result to understand how stars move on the galactic highways of the Milky Way. This also means that the amount of metals present in the star is due to the original cloud from which it formed and not because it engulfed planetary material. "The chicken and egg question of whether the star got planets because it is metal-rich, or whether it is metal-rich because it made planets that were swallowed up is at least answered in one case," says Vauclair. More information The astronomers' study is being published as a Letter to the Editor in Astronomy and Astrophysics ("The exoplanet-host star iota Horologii: an evaporated member of the primordial Hyades cluster", by S. Vauclair et al.). The team is composed of Sylvie Vauclair, Marion Laymand, Gérard Vauclair, Alain Hui Bon Hoa, and Stéphane Charpinet (LATT, Toulouse, France), François Bouchy (IAP, Paris, France), and Michaël Bazot (University of Porto, Portugal).

2008-04-01

318

Non-gyrotropic proton and alpha-particle velocity distributions in the solar wind: TAUS observations and stability analysis  

NASA Technical Reports Server (NTRS)

Ion velocity distribution functions have been measured with high time resolution by the TAUS plasma instrument on the PHOBOS mission to Mars in 1989. The unambiguous separation of protons and alpha-particles by TAUS enabled us to study the nonthermal features of their distributions separately and to analyze the stability of the distributions against excitation of waves in the cyclotron-frequency domain. Typical nonthermal features include temperature anisotropies, with T(sub perpendicular) larger than T(sub parallel), and ion beam populations drifting along the local magnetic field direction. Also, distinctly non-gyrotropic alpha-particle velocity distributions were sometimes found. Non-gyrotropy strongly changes the wave dispersion and gives rise to new growing modes, related to the coupling of the standard wave modes existing in gyrotropic plasma. It is found that for the measured non-gyrotropic ion distributions the right-hand polarized wave can also be excited by a temperature anistropy instead of the usual beam drift.

Astudillo, H. F.; Marsch, E.; Livi, S.; Rosenbauer, H.

1995-01-01

319

On the dependence of the phase velocity of equatorial irregularities on the polarization electric field and theoretical implications  

SciTech Connect

We have studied the mean Doppler shift of equatorial irregularities in the E region, using data from a coherent radar situated in Ethiopia between 1976 and 1980. We found that even though the primary two-stream (or type I) waves are drifting at a speed close to the expected ion acoustic speed, there is a small but nonnegligible increase in the phase velocity with increasing electron drift in the electrojet. We attribute this increase to a heating of the electron gas by the large-amplitude, low-frequency waves that are present in the region when conditions are favorable to the production of large-scale gradient drift instabilities. On the other hand, for the single day when the production of large-scale gradient drift instabilities was inhibited, the behavior of the irregularities was quite different. Namely, the Doppler shift of 10-m waves (type O waves) was usually below the linear threshold value while the spectra remained narrow and type I-like rather than type II-like. On the other hand, the Doppler shift followed a dependence similar to that expected from type II waves. We have tentatively attributed this type O behavior to weak mode coupling, following similar inferences from recent Condor observations made near the top of the electrojet.

St.-Maurice, J.; Hanuise, C.; Kudeki, E.

1986-12-01

320

Direct and indirect drift assessment means. Part 4: a comparative study.  

PubMed

Three contrasting drift risk assessment means were evaluated when predicting absolute losses of sedimenting pesticide drift from field crop sprayers namely PDPA laser measurements, wind tunnel measurements (both indirect drift risk assessment means) and field drift experiments (direct drift risk assessment means). In total, 90 PDPA laser measurements, 45 wind tunnel experiments and 61 field drift experiments were performed with 10 different spray nozzles at a pressure of 3.0 bar. The effect of nozzle size (ISO 02, 03 04 and 06) and nozzle type (standard flat fan, low-drift flat fan, air inclusion) on the amount of near-field sedimenting spray drift was studied. The reference spray application was defined as a Hardi ISO F 110 03 standard flat fan nozzle at a pressure of 3.0 bar with a nozzle or boom height of 0.50 m and a driving speed of 8 km.h(-1) for the field measurements; conditions that were always used for the comparative assessment of the different investigated nozzle-pressure combinations. A comparison is made between the results obtained with the indirect drift assessment means and the direct drift assessment method to evaluate the potential of these three different drift assessment means. Droplet size as well as droplet velocity characteristics are related with DRPt (field experiments) and DPRP (wind tunnel experiments). Because of the strong intercorrelation between droplet size and velocity characteristics for the nozzle-pressure combinations investigated in this study, simple first-order linear regressions with one of the droplet characteristics as a predictor variable, were the best choice to predict DRPt and DPRP. Results showed that with the indirect risk assessment means (wind tunnel and PDPA laser measurement), driftability experiments can be made with different spraying systems under directly comparable and repeatable conditions and both methods are suited to permit relative studies of drift risk. Moreover, based on these indirect drift measurements and a statistical drift prediction equation for the reference spraying, it is possible to come to a realistic estimate of field drift data at a driving speed of 8 km.h(-1) and a boom height of 0.50 m. PMID:19226827

Nuyttens, D; Baetens, K; De Schampheleire, M; Sonck, B

2008-01-01

321

Modeling cross-field drifts and current with the B2 code for the CIT divertor  

SciTech Connect

We have modified the B2 edge-plasma code to include the effects of classical fluid drifts across the magnetic field lines and plasma currents. This report presents preliminary results of these effects for the CIT parameter regime. The basic plasma model described by Braams involves solving the continuity equation, the parallel momentum balance equation, and separate energy balance equations for the ions and the electrons. If multiple ion species are present, they are all assumed to have a common temperature, but their densities and parallel velocities are solved for using additional continuity and parallel momentum balance equations for each species. Momentum and heat transport parallel to the magnetic field, B, are given by the classical collisional theory. On the other hand, transport perpendicular to B is represented by anomalous diffusion coefficients which are adjusted to agree with experimental measurements. These transport coefficients are generally taken to be constant in radius and poloidal angle, although this is not necessary. The goal of our work has been to include both the classical cross-field drift terms and the effects of parallel currents in the equations used in the B2 code. The motivation for including the cross-field terms comes from simple model calculations which indicate that the classical flows can contribute an important asymmetry which may help explain the transition from L-mode to H-mode confinement. Radial electric fields which arise near the separatrix cause E {times} B poloidal rotation which may also be related to the L-to-H mode transition through its effect on edge turbulence. Including the parallel currents is done to provide a tool for understanding the biased divertor experiments on DIII-D at General Atomics. Such biasing may provide an effective means of controlling the asymmetry of the power flow to different divertor plates.

Rognlien, T.D.; Milovich, J.L.; Rensink, M.E.

1990-10-12

322

STATUS OF THE NEUTRALIZED DRIFT COMPRESSION EXPERIMENT (NDCX-II)  

SciTech Connect

The Neutralized Drift Compression Experiment (NDCX-II) is an 11 M$ induction accelerator project currently in construction at Lawrence Berkeley National Laboratory for warm dense matter (WDM) experiments investigating the interaction of ion beams with matter at elevated temperature and pressure. The machine consists of a lithium injector, induction accelerator cells, diagnostic cells, a neutralized drift compression line, a final focus solenoid, and a target chamber. The induction cells and some of the pulsed power systems have been reused from the decommissioned Advanced Test Accelerator at Lawrence Livermore National Laboratory after refurbishment and modification. The machine relies on a sequence of acceleration waveforms to longitudinally compress the initial ion pulse from 600 ns to less than 1 ns in {approx} 12 m. Radial confinement of the beam is achieved with 2.5 T pulsed solenoids. In the initial hardware configuration, 50 nC of Li{sup +} will be accelerated to 1.25 MeV and allowed to drift-compress to a peak current of {approx}40 A. The project started in the summer of 2009. Construction of the accelerator will be completed in the fall of 2011 and will provide a worldwide unique opportunity for ion-driven warm dense matter experiments as well as research related to novel beam manipulations for heavy ion fusion drivers.

Waldron, W.L.; Kwan, J.W.

2011-04-21

323

Effects of particle drift on cosmic-ray transport. I. General properties, application to solar modulation  

Microsoft Academic Search

Although gradient and curvature drifts are explicitly contained in the general equations of cosmic-ray transport, they have been almost universally neglected in applications of these equations. We evaluate the drifts explicitly for the Parker spiral magnetic field and show that, for particles with rigidities greater than approx.0.3 GV in the solar wind, they are larger than the solar-wind velocity over

J. R. Jokipii; E. H. Levy; W. B. Hubbard

1977-01-01

324

Investigations on density and temperature asymmetries due to drift motions in the boundary layer of TEXTOR-94  

NASA Astrophysics Data System (ADS)

Electron densities and temperatures in the plasma edge have been measured by means of the helium beam diagnostic. Furthermore, the charge exchange signal driven by the thermal helium beam atoms has been used to measure the poloidal velocities of C 6+ ions. Asymmetries in the radial profiles of the edge parameters have been found. For further analysis of the physical mechanisms, calculations have been performed with the 2D boundary layer code TECXY. Experimental and modeled results are compared. The influence of the line averaged electron density and the heating power on the electron density and temperature ratios between low field side (LFS) and high field side (HFS) inside the scrape off layer (SOL) is shown. Not only drift motions but also other effects such as recycling at the limiters have an important influence on the spatial structure of the plasma parameters in the SOL.

Lehnen, M.; Brix, M.; Gerhauser, H.; Schweer, B.; Zagórski, R.

2001-03-01

325

Propagation of cylindrical lower hybrid drift solitary wave in an inhomogeneous plasma  

SciTech Connect

The nonlinear cylindrical lower hybrid drift solitary wave in an inhomogeneous, magnetized plasma with the combined effects of electron density inhomogeneity and electron temperature inhomogeneity is investigated in a two-fluid model. The amplitude and width of the solitary wave are found to decrease as the electronic density inhomogeneity increases. When the electron temperature inhomogeneity grows, the amplitude of the soliton decays and the width never changes. It is noted that the decrease of diamagnetic drift velocity will strengthen the cylindrical lower hybrid drift solitary wave height and width.

Liu Haifeng; Wang Shiqing; Fazhan Yang [Southwestern Institute of Physics, Chengdu 610041 (China); Engineering and Technical College of Chengdu University of Technology, Leshan 614000 (China); Li Kehua; Wang Zhanhe; Zhang Weibing; Wang Zhilong; Qiangxiang; Kaihuang; Yaoliu; Silili; Lanchang [Engineering and Technical College of Chengdu University of Technology, Leshan 614000 (China)

2013-04-15

326

Relative drifts and temperature anisotropies of protons and $\\alpha$ particles in the expanding solar wind -- 2.5D hybrid simulations  

E-print Network

We perform 2.5D hybrid simulations to investigate the origin and evolution of relative drift speeds between protons and $\\alpha$ particles in the collisionless turbulent low-$\\beta$ solar wind plasma. 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. The energy source is given by an initial broad-band spectrum of parallel propagating Alfv\\'en-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. This paper for the first time considers the combined effect of self-consistently initialized dispersive turbulent Alfv\\'enic spectra with differentially streaming protons and $\\alpha$ particles in the expanding solar wind outflows withi...

Maneva, Y G; Viñas, A

2014-01-01

327

The Great Continental Drift Mystery  

NSDL National Science Digital Library

This unit introduces students to the development of the theory of continental drift. They will examine the early work of Alfred Wegener and Alexander DuToit, investigate lines of evidence that resulted in the development of the theory, and learn about the final lines of evidence that resulted in the theory's acceptance. There is a set of activities in which the students construct a map of Pangea using Wegener's clues, familiarize themselves with some important geographic locations, and investigate how fossil distribution can be used to enhance the study of continental drift. Study questions and a bibliography are included.

328

Particle Acceleration in Plasmoid Ejections Derived from Radio Drifting Pulsating Structures  

NASA Astrophysics Data System (ADS)

We report observations of slowly drifting pulsating structures (DPSs) in the 0.8-4.5 GHz frequency range of the RT4 and RT5 radio spectrographs at Ond?ejov Observatory, between 2002 and 2012. We found 106 events of DPSs, which we classified into four cases: (I) single events with a constant frequency drift (12 events), (II) multiple events occurring in the same flare with constant frequency drifts (11 events), (III) single or multiple events with increasing or decreasing frequency drift rates (52 events), and (IV) complex events containing multiple events occurring at the same time in a different frequency range (31 events). Many DPSs are associated with hard X-ray (HXR) bursts (15-25 keV) and soft X-ray (SXR) gradient peaks, as they typically occurred at the beginning of HXR peaks. This indicates that DPS events are related to the processes of fast energy release and particle acceleration. Furthermore, interpreting DPSs as signatures of plasmoids, we measured their ejection velocity, their width, and their height from the DPS spectra, from which we also estimated the reconnection rate and the plasma beta. In this interpretation, constant frequency drift indicates a constant velocity of a plasmoid, and an increasing/decreasing frequency drift indicates a deceleration/acceleration of a plasmoid ejection. The reconnection rate shows a good positive correlation with the plasmoid velocity. Finally we confirmed that some DPS events show plasmoid counterparts in Solar Dynamics Observatory/Atmospheric Imaging Assembly images.

Nishizuka, N.; Karlický, M.; Janvier, M.; Bárta, M.

2015-02-01

329

Deconvolution of Velocity Vistributions from Hall Thruster LIF Spectra  

Microsoft Academic Search

Laser-induced fluorescence (LIF) has seen a recent upswing in popularity as a non-intrusive plume diagnostic. The standard method of reducing LIF spectra fits the data to a simulated spectrum, which convolves the hyperfine and isotopic line structure of the absorption transition with a drifting Maxwellian velocity distribution. The bulk velocity and temperature returned by this method are thus based on

T. B. Smith Williams Jr.; A. D. Gallimore; R. P. Drake

1999-01-01

330

Magnetohydrodynamic Slow Mode with Drifting He++: Implications for Coronal Seismology and the Solar Wind  

NASA Astrophysics Data System (ADS)

The MHD slow mode wave has application to coronal seismology, MHD turbulence, and the solar wind where it can be produced by parametric instabilities. We consider analytically how a drifting ion species (e.g. He++) affects the linear slow mode wave in a mainly electron-proton plasma, with potential consequences for the aforementioned applications. Our main conclusions are as follows. 1. For wavevectors highly oblique to the magnetic field, we find solutions that are characterized by very small perturbations of total pressure. Thus, our results may help to distinguish the MHD slow mode from kinetic Alfvén waves and non-propagating pressure-balanced structures, which can also have very small total pressure perturbations. 2. For small ion concentrations, there are solutions that are similar to the usual slow mode in an electron-proton plasma, and solutions that are dominated by the drifting ions, but for small drifts the wave modes cannot be simply characterized. 3. Even with zero ion drift, the standard dispersion relation for the highly oblique slow mode cannot be used with the Alfvén speed computed using the summed proton and ion densities, and with the sound speed computed from the summed pressures and densities of all species. 4. The ions can drive a non-resonant instability under certain circumstances. For low plasma beta, the threshold drift can be less than that required to destabilize electromagnetic modes, but damping from the Landau resonance can eliminate this instability altogether, unless Te /Tp Gt 1.

Hollweg, Joseph V.; Verscharen, Daniel; Chandran, Benjamin D. G.

2014-06-01

331

Diagnostic Measurements and Modeling of Arcjet and Ion Engine Flowfields  

NASA Astrophysics Data System (ADS)

The flowfield of a commercial hydrazine arcjet has been probed by angle and velocity resolved mass spectrometer measurements of N, N_2, H and H_2, and exit plane, position and velocity selective laser induced fluorescence measurements of H and NH. This data has been compared with direct simulation Monte Carlo calculations, offering a comprehensive description of the chemistry and physics of arcjet operation. The unexpectedly high ratio of N/N2 in the plume identifies a major efficiency-loss mechanism, and suggests approaches to thruster improvement. High resolution energy and angle resolved mass spectrometer measurements of charged species in ion engine flowfields coupled with Langmuir probe measurements, and exit plane laser induced fluorescence measurements of xenon and molybdenum density have provided a data base for understanding the life limiting erosion processes of grids. These results quantify the roles of ion temperature in the ``field-free" drift region of the thruster and charge transfer on overall grid lifetime.

Cohen, R. B.; Pollard, J. E.; Crofton, M. W.; Deboer, P. T. E.; Moore, T. A.; Brady, B. B.; Nelson, D. A.; Boyd, I.

1999-11-01

332

Helium, hydrogen, and oxygen velocities observed on ISEE-3  

NASA Technical Reports Server (NTRS)

The velocities of hydrogen, helium, and oxygen ions over a full range of solar wind conditions were recorded by the ion composition instrument and Los Alamos National Laboratory plasma instrument aboard the International Sun Earth Explorer. Interspecie velocity differences were observed frequently. For solar wind velocities between 300 and 400 km s(-1) the helium velocity exceeded the hydrogen velocity by 5 km s(-1) the average difference was 14 km s(-1), however no evidence was found for a nonzero average velocity difference between helium and oxygen ions even at the higher velocities. Velocity differences were examined in a number of streams and across a number of interplanetary shocks. Generally helium hydrogen velocity differences are bounded by the Alfven speed. Velocity differences show abrupt changes across interplanetary discontinuities, presumably tangential. The electrostatic potential change across a shock produces differences between the velocities of ions having different charges.

Ogilvie, K. W.; Coplan, M. A.; Zwicki, R. D.

1982-01-01

333

Peculiarities of collisionless drift instabilities in poloidal magnetic configurations  

SciTech Connect

Results of the numerical analysis of collisionless drift instabilities as applied to magnetic configurations with a purely poloidal magnetic field are presented. Instabilities caused by the gradients of the ion and electron temperatures and plasma density are considered within a wide range of wavenumbers. An electromagnetic model taking into account the finite plasma pressure and magnetic field curvature is formulated for configurations with a nonuniform magnetic field.

Khvesyuk, V. I.; Chirkov, A. Yu. [Bauman Moscow State Technical University (Russian Federation)

2010-12-15

334

Commissioning Results of the Upgraded Neutralized Drift Compression Experiment  

SciTech Connect

Recent changes to the NDCX beamline offer the promise of higher charge compressed bunches (>15nC), with correspondingly large intensities (>500kW/cm2), delivered to the target plane for ion-beam driven warm dense matter experiments. We report on commissioning results of the upgraded NDCX beamline that includes a new induction bunching module with approximately twice the volt-seconds and greater tuning flexibility, combined with a longer neutralized drift compression channel.

Lidia, S.M.; Roy, P.K.; Seidl, P.A.; Waldron, W.L.; Gilson, E.P.

2009-04-30

335

Terminal Velocity  

NSDL National Science Digital Library

This lab is an inquiry activity in that students have not been exposed to the idea of terminal velocity, though they are using skills that they already have to analyze the balloon's motion. The lab is both a review of graphing and translating distance ver

Horton, Michael

2009-05-30

336

The relation between invertebrate drift and two primary controls, discharge and benthic densities, in a large regulated river  

USGS Publications Warehouse

1. Invertebrate drift is a fundamental process in streams and rivers. Studies from laboratory experiments and small streams have identified numerous extrinsic (e.g. discharge, light intensity, water quality) and intrinsic factors (invertebrate life stage, benthic density, behaviour) that govern invertebrate drift concentrations (# m?3), but the factors that govern invertebrate drift in larger rivers remain poorly understood. For example, while large increases or decreases in discharge can lead to large increases in invertebrate drift, the role of smaller, incremental changes in discharge is poorly described. In addition, while we might expect invertebrate drift concentrations to be proportional to benthic densities (# m?2), the benthic–drift relation has not been rigorously evaluated. 2. Here, we develop a framework for modelling invertebrate drift that is derived from sediment transport studies. We use this framework to guide the analysis of high-resolution data sets of benthic density and drift concentration for four important invertebrate taxa from the Colorado River downstream of Glen Canyon Dam (mean daily discharge 325 m3 s?1) that were collected over 18 months and include multiple observations within days. Ramping of regulated flows on this river segment provides an experimental treatment that is repeated daily and allowed us to describe the functional relations between invertebrate drift and two primary controls, discharge and benthic densities. 3. Twofold daily variation in discharge resulted in a >10-fold increase in drift concentrations of benthic invertebrates associated with pools and detritus (i.e. Gammarus lacustris and Potamopyrgus antipodarum). In contrast, drift concentrations of sessile blackfly larvae (Simuliium arcticum), which are associated with high-velocity cobble microhabitats, decreased by over 80% as discharge doubled. Drift concentrations of Chironomidae increased proportional to discharge. 4. Drift of all four taxa was positively related to benthic density. Drift concentrations of Gammarus, Potamopyrgus and Chironomidae were proportional to benthic density. Drift concentrations of Simulium were positively related to benthic density, but the benthic–drift relation was less than proportional (i.e. a doubling of benthic density only led to a 40% increase in drift concentrations). 5. Our study demonstrates that invertebrate drift concentrations in the Colorado River are jointly controlled by discharge and benthic densities, but these controls operate at different timescales. Twofold daily variation in discharge associated with hydropeaking was the primary control on within-day variation in invertebrate drift concentrations. In contrast, benthic density, which varied 10- to 1000-fold among sampling dates, depending on the taxa, was the primary control on invertebrate drift concentrations over longer timescales (weeks to months).

Kennedy, Theodore A.; Yackulic, Charles B.; Cross, Wyatt F.; Grams, Paul E.; Yard, Michael D.; Copp, Adam J.

2014-01-01

337

Primordial Ooze and Continental Drift  

NSDL National Science Digital Library

In this lesson, students will learn that continental plates drift and this affects the layers of the earth. Following a directed reading and discussion, they will perform an experiment in which they use chocolate frosting and graham crackers to simulate tectonic plates sliding about on the mantle.

338

Some remarks on continental drift  

Microsoft Academic Search

Summary The continental drift may be explained by an expanding Earth only. In fact, there is a differences in the rate of heat flow between continents and oceans. Principially, there is a possibility of deriving the value of ancient radii by palaeomagnetic and age measurements.

L. Egyed

1960-01-01

339

GENETIC DRIFT IN A CLINE  

Microsoft Academic Search

A model is developed of genetic drift in a cline maintained by spatially varying natural selection and local dispersal of individuals. The model is analyzed by an approximation scheme which is valid for weak selection and small migration rates. The results, which are based on numerical iterations of the approximate equations, are that the cline is less steep than predicted

MONTGOMERY SLATKIN

1975-01-01

340

Forecast of iceberg ensemble drift  

SciTech Connect

The objectives of the study are to gain a better understanding of the characteristics of iceberg motion and the factors controlling iceberg drift, and to develop an iceberg ensemble drift forecast system to be operated by the Canadian Atmospheric Environment Service. An extensive review of field and theoretical studies on iceberg behaviour, and the factors controlling iceberg motion has been carried out. Long term and short term behaviour of icebergs are critically examined. A quantitative assessment of the effects of the factors controlling iceberg motion is presented. The study indicated that wind and currents are the primary driving forces. Coriolis Force and ocean surface slope also have significant effects. As for waves, only the higher waves have a significant effect. Iceberg drift is also affected by iceberg size characteristics. Based on the findings of the study a comprehensive computerized forecast system to predict the drift of iceberg ensembles off Canada's east coast has been designed. The expected accuracy of the forecast system is discussed and recommendations are made for future improvements to the system.

El-Tahan, M.S.; El-Tahan, H.W.; Venkatesh, S.

1983-05-01

341

Rotating field mass and velocity analyzer  

NASA Technical Reports Server (NTRS)

A rotating field mass and velocity analyzer having a cell with four walls, time dependent RF potentials that are applied to each wall, and a detector. The time dependent RF potentials create an RF field in the cell which effectively rotates within the cell. An ion beam is accelerated into the cell and the rotating RF field disperses the incident ion beam according to the mass-to-charge (m/e) ratio and velocity distribution present in the ion beam. The ions of the beam either collide with the ion detector or deflect away from the ion detector, depending on the m/e, RF amplitude, and RF frequency. The detector counts the incident ions to determine the m/e and velocity distribution in the ion beam.

Smith, Steven Joel (Inventor); Chutjian, Ara (Inventor)

1998-01-01

342

Fast non-explosive gases for drift chambers  

SciTech Connect

Typical gases which are stock at Fermilab are Ar:C/sub 2/H/sub 6/(50:50) and Ar:CO/sub 2/ (80:20). Argon:Ethane has the virtue of high gas gain and a saturated drift velocity. In fact, parametrizing the drift velocity as a function of electric field we find v/sub d/(E) = v/sub o/(1/minus/e/sup -E/E/o) with v/sub o/ approx. = 5.4 cm/..mu..sec and E/sub o/ = 160 V/cm. However, safety considerations make this gas somewhat inconvenient. The addition of alcohol as quencher also raises the saturation field to, for example, E/sub o/ approx. = 500 V/cm for 1.5% added alcohol. This gas also tends to break up in a high-beam flux environment and leave carbon deposits. The addition of alcohol to avoid such aging often takes a unit cell out of saturation over its entire volume. Finally, for collider applications it is useful to exclude free protons from the gas in order to reduce the sensitivity to the sea of slow neutrons which are present in the collider environment. In contrast, Ar:CO/sub 2/ (80:20) is a gas with more moderate gas gain. The drift velocity at high field is v/sub d/(E > 1.5 kV/cm) approx. = 5.8 cm/..mu..sec. For most field configurations this gas does not saturate, causing a long tail in the drift time distrubtion due to low field regions in the unit cell. The virtues of this gas mixture are that it is cheap, not flammable, and stable under high-beam flux. However as the Collider Upgrade progresses, we wish to find a gas which is faster than 5.0 cm/..mu..sec since the time separation between collisions will at some point be less than drift time of 1..mu..sec for drift distance of 5 cm. 3 refs., 5 figs.

Green, D.; Haggerty, H.; Oshima, N.; Yamada, R.

1988-05-01

343

Experimental study of particle formation by ion-ion recombination  

NASA Astrophysics Data System (ADS)

Particle formation by ion-ion recombination has been studied using an ion-ion recombination drift tube (IIR-DT). IIR-DT uses two DC corona ionizers to produce positive and negative ions at the ends of the drift tube. The ions of different polarity move in opposite directions along the electric field in the drift tube. We observed significant particle formation using ions generated in purified air containing H2O, SO2, and NH3. Particle formation was suppressed when no drift field was applied. We also observed few particles when we used a single discharge (positive or negative only). These results clearly show that particle formation observed in the IIR-DT was caused by nucleation by ion-ion recombination. Positive and negative ion species produced by corona ionizers were investigated using an atmospheric pressure ionization mass spectrometer. The ions involved in the particle formation were suggested to include H3O+(H2O)n and NH4+(H2O)n for positive ions and sulfur-based ions such as SO5-, SO5-NO2, and HSO4- for negative ions.

Nagato, Kenkichi; Nakauchi, Masataka

2014-10-01

344

Experimental study of particle formation by ion-ion recombination.  

PubMed

Particle formation by ion-ion recombination has been studied using an ion-ion recombination drift tube (IIR-DT). IIR-DT uses two DC corona ionizers to produce positive and negative ions at the ends of the drift tube. The ions of different polarity move in opposite directions along the electric field in the drift tube. We observed significant particle formation using ions generated in purified air containing H2O, SO2, and NH3. Particle formation was suppressed when no drift field was applied. We also observed few particles when we used a single discharge (positive or negative only). These results clearly show that particle formation observed in the IIR-DT was caused by nucleation by ion-ion recombination. Positive and negative ion species produced by corona ionizers were investigated using an atmospheric pressure ionization mass spectrometer. The ions involved in the particle formation were suggested to include H3O(+)(H2O)n and NH4(+)(H2O)n for positive ions and sulfur-based ions such as SO5(-), SO5(-)NO2, and HSO4(-) for negative ions. PMID:25362301

Nagato, Kenkichi; Nakauchi, Masataka

2014-10-28

345

The collisional drift mode in a partially ionized plasma. [in the F region  

NASA Technical Reports Server (NTRS)

The structure of the drift instability was examined in several density regimes. Let sub e be the total electron mean free path, k sub z the wave-vector component along the magnetic field, and the ratio of perpendicular ion diffusion to parallel electron streaming rates. At low densities (k sub z lambda 1) the drift mode is isothermal and should be treated kineticly. In the finite heat conduction regime square root of m/M k sub z Lambda sub 1) the drift instability threshold is reduced at low densities and increased at high densities as compared to the isothermal threshold. Finally, in the energy transfer limit (k sub z kambda sub e square root of m/M) the drift instability behaves adiabatically in a fully ionized plasma and isothermally in a partially ionized plasma for an ion-neutral to Coulomb collision frequency ratio.

Hudson, M. K.; Kennel, C. F.

1974-01-01

346

Ultraviolet laser calibration of drift chambers  

E-print Network

We demonstrate the use of a focused ultraviolet laser as a track calibration source in drift chambers, and specifically in a small time projection chamber (TPC). Drift chambers such as TPCs reconstruct the trajectories of ...

Elliott, Grant (Grant Andrew)

2006-01-01

347

Evolution: drift will tear us apart.  

PubMed

That the widely scattered geographical distribution of some animals could be due to continental drift is a neat idea. Now, cave animals provide evidence for extreme long-term persistence on continents drifting apart. PMID:23137684

Maderspacher, Florian

2012-11-01

348

Performance of drift tubes under high radiation  

E-print Network

In this thesis, the aging and the rejuvenation of an ATLAS proportional drift tube are described. Firstly, the Diethorn model of gain is tested using pressure and sense-wire voltage measurements. The drift tube was then ...

Shi, Yue, S.B. Massachusetts Institute of Technology

2005-01-01

349

First Principles Based Reactive Atomistic Simulations to Understand the Effects of Molecular Hyper Velocity Impact on Cassini's Ion and Neutral Mass Spectrometer  

NASA Astrophysics Data System (ADS)

We have used the recently developed electron force field (eFF) and ReaxFF reactive force field to simulate the hypervelocity impacts experienced by the Cassini ion and neutral mass spectrometer during the Enceladus and Titian encounters.

Jaramillo-Botero, A.; Cheng, M. J.; Cvicek, V.; Beegle, L. W.; Hodyss, R.; Goddard, W. A.

2011-03-01

350

Electron and ion inertia effects on current-driven collisional dust acoustic, dust ion acoustic, and ion acoustic instabilities  

E-print Network

Electron and ion inertia effects on current-driven collisional dust acoustic, dust ion acoustic, and ion acoustic instabilities Robert L. Merlino and Nicola D'Angelo Department of Physics and Astronomy online 20 April 2005 Ion acoustic waves can be excited by electrons drifting relative to the ions

Merlino, Robert L.

351

Incoherent scatter ion line enhancements and auroral arc-induced Kelvin-Helmholtz turbulence  

NASA Astrophysics Data System (ADS)

We present two cases of incoherent-scatter ion line enhancements in conjunction with auroral arcs drifting through the radar beam. The up- and downshifted ion line shoulders as well as the spectral region between them are enhanced equally and simultaneously. The power enhancements are one order of magnitude above the thermal level and are concentrated in less than 15 km wide altitude ranges at the ionospheric F region peak. The auroral arc passages are preceded by significantly enhanced ion temperatures in the E region, assumed to be caused by transient electric fields associated with velocity shears. We use a Hall MHD model of velocity shears perpendicular to the geomagnetic field and show that a Kelvin-Helmholtz instability will grow for the two presented cases.

Ekeberg, J.; Stasiewicz, K.; Wannberg, G.; Sergienko, T.; Eliasson, L.

2015-01-01

352

Multi-water-bag models of ion temperature gradient instability in cylindrical geometry  

SciTech Connect

Ion temperature gradient instabilities play a major role in the understanding of anomalous transport in core fusion plasmas. In the considered cylindrical geometry, ion dynamics is described using a drift-kinetic multi-water-bag model for the parallel velocity dependency of the ion distribution function. In a first stage, global linear stability analysis is performed. From the obtained normal modes, parametric dependencies of the main spectral characteristics of the instability are then examined. Comparison of the multi-water-bag results with a reference continuous Maxwellian case allows us to evaluate the effects of discrete parallel velocity sampling induced by the Multi-Water-Bag model. Differences between the global model and local models considered in previous works are discussed. Using results from linear, quasilinear, and nonlinear numerical simulations, an analysis of the first stage saturation dynamics of the instability is proposed, where the divergence between the three models is examined.

Coulette, David [Institut Jean Lamour UMR CNRS 7198 Département Physique de la Matière et des Matériaux, Université de Lorraine, Faculté des Sciences et Technologie, Campus Victor Grignard BP 70239, 54506 Vandoeuvre-lès-Nancy Cedex (France)] [Institut Jean Lamour UMR CNRS 7198 Département Physique de la Matière et des Matériaux, Université de Lorraine, Faculté des Sciences et Technologie, Campus Victor Grignard BP 70239, 54506 Vandoeuvre-lès-Nancy Cedex (France); Besse, Nicolas [Institut Jean Lamour UMR CNRS 7198 Département Physique de la Matière et des Matériaux and Institut Elie Cartan UMR CNRS 7502 INRIA Calvi Team, Université de Lorraine, Faculté des Sciences et Technologie, Campus Victor Grignard BP 70239, 54506 Vandoeuvre-lès-Nancy Cedex (France)] [Institut Jean Lamour UMR CNRS 7198 Département Physique de la Matière et des Matériaux and Institut Elie Cartan UMR CNRS 7502 INRIA Calvi Team, Université de Lorraine, Faculté des Sciences et Technologie, Campus Victor Grignard BP 70239, 54506 Vandoeuvre-lès-Nancy Cedex (France)

2013-05-15

353

New advances in the partial-reflection-drifts experiment using microprocessors  

NASA Technical Reports Server (NTRS)

Improvements to the partial reflection drifts experiment are completed. The results of the improvements include real time processing and simultaneous measurements of the D region with coherent scatter. Preliminary results indicate a positive correlation between drift velocities calculated by both methods during a two day interval. The possibility now exists for extended observations between partial reflection and coherent scatter. In addition, preliminary measurements could be performed between partial reflection and meteor radar to complete a comparison of methods used to determine velocities in the D region.

Ruggerio, R. L.; Bowhill, S. A.

1982-01-01

354

An ion mobility mass spectrometer for investigating photoisomerization and photodissociation of molecular ions.  

PubMed

An ion mobility mass spectrometry apparatus for investigating the photoisomerization and photodissociation of electrosprayed molecular ions in the gas phase is described. The device consists of a drift tube mobility spectrometer, with access for a laser beam that intercepts the drifting ion packet either coaxially or transversely, followed by a quadrupole mass filter. An ion gate halfway along the drift region allows the instrument to be used as a tandem ion mobility spectrometer, enabling mobility selection of ions prior to irradiation, with the photoisomer ions being separated over the second half of the drift tube. The utility of the device is illustrated with photoisomerization and photodissociation action spectra of carbocyanine molecular cations. The mobility resolution of the device for singly charged ions is typically 80 and it has a mass range of 100-440 Da, with the lower limit determined by the drive frequency for the ion funnels, and the upper limit by the quadrupole mass filter. PMID:25554274

Adamson, B D; Coughlan, N J A; Markworth, P B; Continetti, R E; Bieske, E J

2014-12-01

355

An ion mobility mass spectrometer for investigating photoisomerization and photodissociation of molecular ions  

NASA Astrophysics Data System (ADS)

An ion mobility mass spectrometry apparatus for investigating the photoisomerization and photodissociation of electrosprayed molecular ions in the gas phase is described. The device consists of a drift tube mobility spectrometer, with access for a laser beam that intercepts the drifting ion packet either coaxially or transversely, followed by a quadrupole mass filter. An ion gate halfway along the drift region allows the instrument to be used as a tandem ion mobility spectrometer, enabling mobility selection of ions prior to irradiation, with the photoisomer ions being separated over the second half of the drift tube. The utility of the device is illustrated with photoisomerization and photodissociation action spectra of carbocyanine molecular cations. The mobility resolution of the device for singly charged ions is typically 80 and it has a mass range of 100-440 Da, with the lower limit determined by the drive frequency for the ion funnels, and the upper limit by the quadrupole mass filter.

Adamson, B. D.; Coughlan, N. J. A.; Markworth, P. B.; Continetti, R. E.; Bieske, E. J.

2014-12-01

356

Response of macrofauna to drifting tidal sediments  

NASA Astrophysics Data System (ADS)

The effect of hydrodynamically-mobilized sediment on abundance and vertical distribution of macrobenthic fauna was studied in Königshafen, a sheltered tidal bay at the northern end of the Island of Sylt (North Sea). Sediment drift tended to increase from high towards low tide level, while abundance of nearly all species decreased (with the polychaete Spio filicornis as a notable exception). To test whether this decrease could be attributed to water currents affecting sediment stability, experimental flumes with funnels at both ends were set up to enhance sediment mobility by increasing tidal current velocities. Abundance and vertical distribution of fauna inside and outside the flumes were compared. Responses of individual species depended on their vertical position in the sediment, and resembled those observed along the gradient of sediment drift between high and low tide levels. Mainly juveniles of Pygospio elegans, Scoloplos armiger, Hydrobia ulvae and Macoma balthica, and the small polychaete Microphthalmus sczelkowii were washed out of the sediment. No effect of increased erosion inside the flume was found on the numbers of Capitella capitata and the oligochaetes Tubificoides benedii and T. pseudogaster. These oligochaetes probably migrated downwards with increasing erosion in the flumes. Numbers decreased in the upper cm and tended to increase below. A storm had a similar effect on oligochaete vertical distribution, while under conditions of permanently high sediment mobility near low tide level, these species were rare or absent. It is concluded that even under sheltered conditions, differential degrees of sediment mobility may have effects on the zonation of the tidal flat macrofauna.

Zühlke, R.; Reise, K.

1994-06-01

357

Spray drift mitigation with spray mix 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...

358

Improved sliced velocity map imaging apparatus optimized for H photofragments  

NASA Astrophysics Data System (ADS)

Time-sliced velocity map imaging (SVMI), a high-resolution method for measuring kinetic energy distributions of products in scattering and photodissociation reactions, is challenging to implement for atomic hydrogen products. We describe an ion optics design aimed at achieving SVMI of H fragments in a broad range of kinetic energies (KE), from a fraction of an electronvolt to a few electronvolts. In order to enable consistently thin slicing for any imaged KE range, an additional electrostatic lens is introduced in the drift region for radial magnification control without affecting temporal stretching of the ion cloud. Time slices of ˜5 ns out of a cloud stretched to ?50 ns are used. An accelerator region with variable dimensions (using multiple electrodes) is employed for better optimization of radial and temporal space focusing characteristics at each magnification level. The implemented system was successfully tested by recording images of H fragments from the photodissociation of HBr, H2S, and the CH2OH radical, with kinetic energies ranging from <0.4 eV to >3 eV. It demonstrated KE resolution ?1%-2%, similar to that obtained in traditional velocity map imaging followed by reconstruction, and to KE resolution achieved previously in SVMI of heavier products. We expect it to perform just as well up to at least 6 eV of kinetic energy. The tests showed that numerical simulations of the electric fields and ion trajectories in the system, used for optimization of the design and operating parameters, provide an accurate and reliable description of all aspects of system performance. This offers the advantage of selecting the best operating conditions in each measurement without the need for additional calibration experiments.

Ryazanov, Mikhail; Reisler, Hanna

2013-04-01

359

Kinetic effects on a tokamak pedestal ion flow, ion heat transport and bootstrap current  

NASA Astrophysics Data System (ADS)

We consider the effects of a finite radial electric field on ion orbits in a subsonic pedestal. Using a procedure that makes a clear distinction between a transit average and a flux surface average we are able to solve the kinetic equation to retain the modifications due to finite {{\\vec{{\\bit E}}}}\\times {{\\vec{{\\bit B}}}} drift orbit departures from flux surfaces. Our approach properly determines the velocity space localized, as well as the nonlocal, portion of the ion distribution function in the banana and plateau regimes in the small aspect ratio limit. The rapid variation of the poloidal ion flow coefficient and the electrostatic potential in the total energy modify previous banana regime evaluations of the ion flow, the bootstrap current, and the radial ion heat flux in a subsonic pedestal. In the plateau regime, the rapid variation of the poloidal flow coefficient alters earlier results for the ion flow and bootstrap current, while leaving the ion heat flux unchanged since the rapid poloidal variation of the total energy was properly retained.

Catto, Peter J.; Parra, Felix I.; Kagan, Grigory; Parker, Jeffrey B.; Pusztai, Istvan; Landreman, Matt

2013-04-01

360

The Holifield Heavy Ion Research Facility  

SciTech Connect

Development of the Holifield facility has continued with resulting improvements in the number of ion species provided, ion energy for tandem-only operations, and utilization efficiency. The Holifield Heavy Ion Research Facility (HHIRF) is located at the Oak Ridge National Laboratory and operated as a national user facility for research in heavy ion science. The facility operates two accelerators: an NEC pelletron tandem accelerator designed to operate at terminal potentials up to 25 MV and the Oak Ridge Isochronous Cyclotron (ORIC) which has been modified to serve as an energy booster for beams from the tandem accelerator. The principal experimental devices of the facility include a broad range spectrograph (ME/q/sup 2/ = 225) equipped with a vertical drift chamber detector system, a 4..pi.. spin spectrometer equipped with 72 NaI detectors (Ge detectors and BGO compton-suppression units can be used in place of the NaI detectors), a time-of-flight spectrometer, a 1.6-m scattering chamber, a heavy-ion/light-ion detector (HILI) which will be used for studying inverse reactions, a split-pole spectrograph, and a velocity filter. In this report, we will discuss our recent development activities, operational experience, and future development plans.

Jones, C.M.; Alton, G.D.; Ball, J.B.; Biggerstaff, J.A.; Dowling, D.T.; Erb, K.A.; Haynes, D.L.; Hoglund, D.E.; Hudson, E.D.; Juras, R.C.

1987-01-01

361

Diagnostics for ion beam driven high energy density physics experiments.  

PubMed

Intense beams of heavy ions are capable of heating volumetric samples of matter to high energy density. Experiments are performed on the resulting warm dense matter (WDM) at the NDCX-I ion beam accelerator. The 0.3 MeV, 30 mA K(+) beam from NDCX-I heats foil targets by combined longitudinal and transverse neutralized drift compression of the ion beam. Both the compressed and uncompressed parts of the NDCX-I beam heat targets. The exotic state of matter (WDM) in these experiments requires specialized diagnostic techniques. We have developed a target chamber and fielded target diagnostics including a fast multichannel optical pyrometer, optical streak camera, laser Doppler-shift interferometer (Velocity Interferometer System for Any Reflector), beam transmission diagnostics, and high-speed gated cameras. We also present plans and opportunities for diagnostic development and a new target chamber for NDCX-II. PMID:21033977

Bieniosek, F M; Henestroza, E; Lidia, S; Ni, P A

2010-10-01

362

A 3-D simulation of drifting snow in the turbulent boundary layer  

NASA Astrophysics Data System (ADS)

The drifting snow is one of the most important factors that affect the global ice mass balance and hydrological balance. Current models of drifting snow are usually one- or two-dimensional, focusing on the macroscopic quantities of drifting snow under temporal average flow. In this paper, we take the coupling effects between wind and snow particles into account and present a 3-D model of drifting snow with mixed grain size in the turbulent boundary layer. The Large Eddy Simulation (LES) method is used for simulating the turbulent boundary layer of the wind field and the 3-D trajectory of every motion snow particle is calculated through Lagrangian Particle Tracking method. The results indicated that the drifting snow in the turbulent boundary layer has apparent 3-D structure and snow streamers, which lead to an intermittent transport of the snow particles and spatial inhomogeneity, and the motion trajectories of snow particles, especially the small snow particles, are obviously affected by the turbulent fluctuation. The macro statistics of drifting snow indicates that the spanwise velocity of snow particles increases with height and is one order smaller than that of streamwise velocity. Furthermore, the diameter distribution of snow particles in the air along the height shows a stratification structure.

Huang, N.; Wang, Z.

2015-01-01

363

MPS II drift chamber system  

SciTech Connect

The MPS II detectors are narrow drift space chambers designed for high position resolution in a magnetic field and in a very high particle flux environment. Central to this implementation was the development of 3 multi-channel custom IC's and one multi-channel hybrid. The system is deadtimeless and requires no corrections on an anode-to-anode basis. Operational experience and relevance to ISABELLE detectors is discussed.

Platner, E.D.

1982-01-01

364

MODEL SIMULATIONS OF CONTINUOUS ION INTERJECTION INTO EBIS TRAP WITH SLANTED ELECTROSTATIC MIRROR.  

SciTech Connect

The efficiency of trapping ions in an EBIS is of primary importance for many applications requiring operations with externally produced ions: RIA breeders, ion sources, traps. At the present time, the most popular method of ion injection is pulsed injection, when short bunches of ions get trapped in a longitudinal trap while traversing the trap region. Continuous trapping is a challenge for EBIS devices because mechanisms which reduce the longitudinal ion energy per charge in a trap (cooling with residual gas, energy exchange with other ions, ionization) are not very effective, and accumulation of ions is slow. A possible approach to increase trapping efficiency is to slant the mirror at the end of the trap which is opposite to the injection end. A slanted mirror will convert longitudinal motion of ions into transverse motion, and, by reducing their longitudinal velocity, prevent these ions from escaping the trap on their way out. The trade off for the increased trapping efficiency this way is an increase in the initial transverse energy of the accumulated ions. The slanted mirror can be realized if the ends of two adjacent electrodes- drift tubes - which act as an electrostatic mirror, are machined to produce a slanted gap, rather than an upright one. Applying different voltages to these electrodes will produce a slanted mirror. The results are presented of 2D and 3D computer simulations of ion injection into a simplified model of EBIS with slanted mirror.

PIKIN,A.; KPONOU, A.; ALESSI, J.G.; BEEBE, E.N.; PRELEC, K.; RAPARIA, D.

2007-08-26

365

Isomer-separated photodissociation of large sized silicon and carbon cluster ions: Drift tube experiment combined with a tandem reflectron mass spectrometer for Si{24/+}- Si{27/+} and C{32/+}-C{38/+}  

NASA Astrophysics Data System (ADS)

Isomer-resolved multiphoton dissociations (PDs) with 4.66-eV laser photons were applied to carbon and silicon cluster cations, Cn+ (n = 32, 34, 36, and 38) and Sim+ (m = 24-27), in order to investigate correlations between the isomer structures and dissociation reactions. Cyclic and fullerene structures of Cn+ and prolate and spherical isomers of Sim+, which are the coexisting isomers in these size ranges, were separated by ion mobility spectrometry, followed by photolysis using a tandem reflectron mass spectrometer. Photofragment ion distributions were revealed to depend on the parent isomer structures. Dissociation mechanisms were discussed from the fragment ion distributions. ISSPIC 16 - 16th International Symposium on Small Particles and Inorganic Clusters, edited by Kristiaan Temst, Margriet J. Van Bael, Ewald Janssens, H.-G. Boyen and Françoise Remacle.

Moriyama, Ryoichi; Ohtaki, Tomohiro; Hosoya, Jun; Koyasu, Kiichirou; Misaizu, Fuminori

2013-01-01

366

Effects of particle drift on cosmic ray transport. II - Analytical solution to the modulation problem with no latitudinal diffusion  

NASA Technical Reports Server (NTRS)

An analytical solution to a model of the modulation of galactic cosmic rays in the presence of particle drifts is presented and discussed. The solution assumes an energy-independent radial diffusion coefficient proportional to distance and no latitudinal diffusion, and includes energy-independent particle drift velocities similar to those expected in a Parker spiral magnetic field with an equatorial current sheet. The solutions clearly demonstrate the large effects of drifts on the modulated cosmic-ray intensity. For values of the radial diffusion coefficient and particle drift velocity which are plausible for 1-GV-rigidity protons, the logarithmic radial gradient in the inner solar system is reduced by more than a factor of 5 over the value calculated in the absence of drifts. It is found that even for much smaller values of particle drift velocity and radial diffusion coefficient, such as might be expected for protons with energies of the order of 10 MeV, the effects of the drifts can be substantial.

Isenberg, P. A.; Jokipii, J. R.

1978-01-01

367

Statistical Analysis of Microgravity Two-Phase Slug Flow via the Drift Flux Model  

E-print Network

. The result was a statistically consistent microgravity slug flow data base consisting of 220 data points from 8 different experiments and the associated values for the concentration parameter, Co, and drift velocity, u_(gj). A key component for this model...

Larsen, Benjamin A

2014-05-01

368

Drift-flux analysis of two-phase flow in microgravity  

E-print Network

to calculate the distribution parameter, C?, and the drift-velocity, V[gj], of the two-phase mixture. The C?and V[gj] found for each flow regime were compared with other microgravity and a one-g upflow data. The C? for the slug flow regime was greater than...

Braisted, Jonathan David

2004-01-01

369

Ion transport in stellarators  

SciTech Connect

Stellarator ion transport in the low-collisionality regime with a radial electric field is calculated by a systematic expansion of the drift-Boltzmann equation. The shape of the helical well is taken into account in this calculation. It is found that the barely trapped ions with three to four times the thermal energy give the dominant contribution to the diffusion. Expressions for the ion particle and energy fluxes are derived.

Ho, D.D.M.; Kulsrud, R.M.

1985-09-01

370

Comprehensive study of drift from mechanical draft cooling towers. Final report  

SciTech Connect

Drift from mechanical draft cooling towers was studied to establish a data base for use in drift deposition model validation. This objective was met by the simultaneous measurement of cooling tower source emission parameters, meteorological variables and drift deposition patterns during seven of eight test runs. Results from six of these test runs are presented and discussed. Source characterization measurements were made of cooling tower emission parameters such as updraft velocity and temperature profiles, liquid and mineral mass drift emission rates, and drift droplet size distributions. The meteorological measurements included wet- and dry-bulb temperature and wind speed and direction at various heights to provide information on the vertical structure of temperature, moisture and mass transport. Surface deposition measurements included both droplet and bulk mineral mass deposition rates. Substantial variation in drift emissions were noticed. Large day-to-day variations for a given cell and large cell-to-cell variations were observed. The problem of deriving a total droplet emission spectrum and rate from one or two towers is complicated and the modeler must decide on the amount of detail he needs to satisfactorily predict downwind deposition patterns. Meteorological conditions during the drift study were characterized by relatively high winds, warm temperatures and moderate humidities. The relatively high winds increased the uncertainty in the measured deposition patterns. In spite of the large (factor of 2 or 3) uncertainty in the measured deposition rates, preliminary calculations of drift deposition rates are in agreement with each other for test run 1. Although the present study did not meet all the requirements for complete validation of various drift models, it has contributed a unique set of data for that purpose.

Laulainen, N.S.; Webb, R.O.; Wilber, K.R.; Ulanski, S.L.

1979-09-01

371

Modulation of drift-wave envelopes in a nonuniform quantum magnetoplasma  

NASA Astrophysics Data System (ADS)

We study the amplitude modulation of low-frequency, long-wavelength electrostatic drift-wave envelopes in a nonuniform quantum magnetoplasma consisting of cold ions and degenerate electrons. The effects of tunneling associated with the quantum Bohm potential and the Fermi pressure for nonrelativistic degenerate electrons, as well as the equilibrium density and magnetic field inhomogeneities are taken into account. Starting from a set of quantum magnetohydrodynamic equations, we derive a nonlinear Schrödinger equation (NLSE) that governs the dynamics of the modulated quantum drift-wave packets. The NLSE is used to study the modulational instability (MI) of a Stoke's wave train to a small plane wave perturbation. It is shown that the quantum tunneling effect as well as the scale length of inhomogeneity plays crucial roles for the MI of the drift-wave packets. Thus, the latter can propagate in the form of bright and dark envelope solitons or as drift-wave rogons in degenerate dense magnetoplasmas.

Misra, A. P.

2014-04-01

372

An Implicit "Drift-Lorentz" Mover for Plasma and Beam Simulations  

SciTech Connect

In order to efficiently perform particle simulations in systems with widely varying magnetization, we developed a drift-Lorentz mover, which interpolates between full particle dynamics and drift kinetics in such a way as to preserve a physically correct gyroradius and particle drifts for both large and small ratios of the timestep to the cyclotron period. In order to extend applicability of the mover to systems with plasma frequency exceeding the cyclotron frequency such as one may have with fully neutralized drift compression of a heavy-ion beam we have developed an implicit version of the mover. A first step in this direction, in which the polarization charge was added to the field solver, was described previously. Here we describe a fully implicit algorithm (which is analogous to the direct-implicit method for conventional particle-in-cell simulation), summarize a stability analysis of it, and describe several tests of the resultant code.

Cohen, R H; Friedman, A; Grote, D P; Vay, J

2009-02-12

373

AN IMPLICIT"DRIFT-LORENTZ" PARTICLE MOVER FOR PLASMA AND BEAM SIMULATIONS  

SciTech Connect

In order to efficiently perform particle simulations in systems with widely varying magnetization, we developed a drift-Lorentz mover, which interpolates between full particle dynamics and drift kinetics in such a way as to preserve a physically correct gyroradius and particle drifts for both large and small ratios of the timestep to the cyclotron period. In order to extend applicability of the mover to systems with plasma frequency exceeding the cyclotron frequency such as one may have with fully neutralized drift compression of a heavy-ion beam we have developed an implicit version of the mover. A first step in this direction, in which the polarization charge was added to the field solver, was described previously. Here we describe a fully implicit algorithm (which is analogous to the direct-implicit method for conventionalparticle-in-cell simulation), summarize a stability analysis of it, and describe several tests of the resultant code.

Friedman, A.; Grote, D.P.; Vay, J.-L; Cohen, R.H.

2008-07-15

374

Modulation of drift-wave envelopes in a nonuniform quantum magnetoplasma  

SciTech Connect

We study the amplitude modulation of low-frequency, long-wavelength electrostatic drift-wave envelopes in a nonuniform quantum magnetoplasma consisting of cold ions and degenerate electrons. The effects of tunneling associated with the quantum Bohm potential and the Fermi pressure for nonrelativistic degenerate electrons, as well as the equilibrium density and magnetic field inhomogeneities are taken into account. Starting from a set of quantum magnetohydrodynamic equations, we derive a nonlinear Schrödinger equation (NLSE) that governs the dynamics of the modulated quantum drift-wave packets. The NLSE is used to study the modulational instability (MI) of a Stoke's wave train to a small plane wave perturbation. It is shown that the quantum tunneling effect as well as the scale length of inhomogeneity plays crucial roles for the MI of the drift-wave packets. Thus, the latter can propagate in the form of bright and dark envelope solitons or as drift-wave rogons in degenerate dense magnetoplasmas.

Misra, A. P., E-mail: apmisra@visva-bharati.ac.in, E-mail: apmisra@gmail.com [Department of Mathematics, Siksha Bhavana, Visva-Bharati University, Santiniketan-731 235, West Bengal (India)

2014-04-15

375

Drift chamber tracking with neural networks  

SciTech Connect

We discuss drift chamber tracking with a commercial log VLSI neural network chip. Voltages proportional to the drift times in a 4-layer drift chamber were presented to the Intel ETANN chip. The network was trained to provide the intercept and slope of straight tracks traversing the chamber. The outputs were recorded and later compared off line to conventional track fits. Two types of network architectures were studied. Applications of neural network tracking to high energy physics detector triggers is discussed.

Lindsey, C.S.; Denby, B.; Haggerty, H.

1992-10-01

376

4, 107128, 2007 Sea-ice-drift  

E-print Network

OSD 4, 107­128, 2007 Sea-ice-drift dynamics and pack fracture A. Chmel et al. Title Page Abstract aspects of the sea-ice-drift dynamics and pack fracture A. Chmel 1 , V. N. Smirnov 2 , and L. V. Panov 2 1 to: A. Chmel (chmel@mail.ioffe.ru) 107 #12;OSD 4, 107­128, 2007 Sea-ice-drift dynamics and pack

Paris-Sud XI, Université de

377

WORLD SURFACE CURRENTS FROM SHIP'S DRIFT OBSERVATIONS  

SciTech Connect

Over 4 million observations of ship's drift are on file at the U.S. National Oceanographic Data Centre, in Washington, D. C., representing a vast amount of information on ocean surface currents. The observed drift speeds are dependent on the frequency of occurence of the particular current speeds and the frequency of observation. By comparing frequency of observation with the drift speeds observed it is possible to confirm known current patterns and detect singularities in surface currents.

Duncan, C.P.; Schladow, S.G.

1980-11-01

378

Discovery of multiple, ionization-created CS2 anions and a new mode of operation for drift chambers.  

PubMed

This paper focuses on the surprising discovery of multiple species of ionization-created CS2 anions in gas mixtures containing electronegative CS2 and O2, identified by their slightly different drift velocities. Data are presented to understand the formation mechanism and identity of these new anions. Regardless of the micro-physics, however, this discovery offers a new, trigger-less mode of operation for the drift chambers. A demonstration of trigger-less operation is presented. PMID:24517755

Snowden-Ifft, Daniel P

2014-01-01

379

Magnetic conjugate point observations of kilometer and hundred meter-scale irregularities and zonal drifts  

NASA Astrophysics Data System (ADS)

The Conjugate Point Equatorial Experiment (COPEX) campaign was held from October 1st to December 10th, 2002, over 4 sites in the Brazilian territory: Campo Grande (20.5o S, 54.7o W, -22.3o dip angle), Alta Floresta (9.7oS, 56.0o W, -3.38o dip angle), Cachimbo (9.5oS, 54.8oW, -4.25o dip angle) and Boa Vista (2.8o N, 60.7o W, -22.0o dip angle). Many ionospheric sounding instruments including GPS receivers, VHF receivers, all-sky imagers, digital ionosondes, and VHF radar were installed at the COPEX stations. In this work we will focus on the GPS (1.575 GHz) and VHF (240 MHz) receivers’ data. These 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 due to vertical drifts and the geometrical factors. The amplitude scintillations and the zonal velocities measured by these two methods are compared. The results reveal the coexistence of kilometer (VHF) and hundred-meter scale (L-band) irregularities into the underlying depletion structure. However, the VHF scintillations are more intense and tend to cease latter than the GPS L-band scintillations. Over the conjugate site of Campo Grande the average zonal velocity at VHF was consistently larger than the estimated GPS velocities, whereas over Boa Vista they are comparable. The hundred meter scale structures causing L-band scintillations seem to be drifting with comparable velocities over both the conjugate points, whereas the kilometer scale structures appear to be drifting over Campo Grande with larger velocities until about local midnight. Complementary data of ionospheric parameters scaled from collocated digital ionosondes and results published in previous COPEX reports are used in the analysis.

de Paula, E. R.; Muella, M. T.; Sobral, J. H.; Groves, K. M.; Beach, T. L.; Batista, I. S.; Abdu, M. A.

2009-12-01

380

Linking River Morphology to Larval Drift of an Endangered Sturgeon  

NASA Astrophysics Data System (ADS)

Computational models developed to calculate longitudinal advection and dispersion of contaminants in rivers have potential application in predicting larval drift. A critical component of this family of models is the longitudinal dispersion coefficient which parameterizes the processes that retain and distribute a contaminant along the river. Here we evaluate the potential for longitudinal dispersion coefficients to characterize larval drift of the endangered pallid sturgeon (Scaphirhynchus albus) in various segments of the free-flowing Missouri River ranging from Missouri to Montana. We randomly selected transects of acoustic Doppler current profiler (ADCP) flow velocity data from reach-scale datasets that were collected in the Missouri River from 2002-2008 under comparable discharge conditions. We used previously developed equations (Kim and others, 2007) to calculate a one-dimensional longitudinal dispersion coefficient for each ADCP transect. We compared the statistical distributions of these coefficients for 2 to 6 reaches chosen from each of six geomorphic segments of the Missouri. Distributional patterns indicate that dispersion coefficients relate to observed variation in hydrology and geomorphology of the channel at the segment scale. Although one-dimensional dispersion analysis demonstrates potential as a tool for estimating pallid sturgeon larval drift and habitat suitability in unchannelized portions of the Missouri River, the large spatial variation in calculated dispersion coefficients resulting from river-training structures (wing dikes) in the Lower Missouri complicates selection of appropriate values. Recent data indicating that pallid sturgeon larvae occur in greater concentration in the thalweg indicate that the majority of larvae may bypass these structures and their associated retentive eddies. A two-dimensional space-averaged dispersion calculation and analysis may more accurately characterize the potential drift times and distances of larval transport. In addition, comparison of transport predicted using ADCP-calculated dispersion coefficients with larval drift data from a side channel near Culbertson, Montana (Braaten et al., 2008), and a dye-trace study on the mainstem channel in Montana (U.S. Army Corps of Engineers, unpub. data, 2004) will help evaluate the usefulness of ADCP-calculated dispersion coefficients in predicting larval drift in mainstem segments.

Bazzetta, L.; Jacobson, R. B.; Braaten, P. J.; Elliott, C. M.; Reuter, J. M.

2009-12-01

381

Drift-Wave Instabilities and Transport in Non - Tokamak Geometry  

NASA Astrophysics Data System (ADS)

Motivated by experimental scaling laws that suggest an improvement in the confinement time of fusion plasmas in tokamaks with elongated cross section, we search theoretically for favorable dependence on elongation for drift-wave instabilities, which may be responsible for anomalous transport in tokamaks. First, using thermodynamic methods, we derive upper bounds on thermal diffusivities for drift-wave instabilities in tokamaks but find no elongation dependence to lowest order. Also, compared with experimentally inferred ion thermal diffusivities from the DIIID tokamak, the thermodynamic bounds are as much as 100 times bigger in the plasma core. Second, utilizing a simulation code to calculate linear growth rates, we obtain mixing-length estimates of ion thermal diffusivities for a specific drift wave, the ion-temperature-gradient (ITG) mode, which becomes unstable only if the temperature gradient exceeds a finite threshold value (whereas the thermodynamic constraints allow instability for any value). We find that the simulation growth rates and the diffusivities estimated from them do decrease for increasing elongation, due to finite Larmor radius effects (which do not explicitly appear in the thermodynamic constraints). Compared with the experimentally inferred diffusivities, the simulation diffusivities are similar near the edge but are 10 times bigger in the core. However, a small adjustment in the temperature profile, within experimental and theoretical uncertainties, would produce good agreement everywhere. Therefore, we suggest that for the DIIID experiments studied, the plasma is actually very close to the ITG instability threshold in the core and farther away from threshold near the edge, but not far enough to induce the full thermodynamic level of diffusivities. This conjecture is supported by model transport calculations that reproduce the experimental diffusivity profile fairly well.

Hua, Daniel Duc

382

Effect of drift control adjuvants on glyphosate spray drift and weed control  

Technology Transfer Automated Retrieval System (TEKTRAN)

Glyphosate drift on to off-target sensitive soybean may cause injury and reduce the yield. To solve this problem field experiment was conducted to determine the effect of drift control adjuvants (DCA) on downwind glyphosate drift and weed control in non-glyphosate-resistant soybean. The results show...

383

The Genetic Drift Inventory: A Tool for Measuring What Advanced Undergraduates Have Mastered about Genetic Drift  

ERIC Educational Resources Information Center

Understanding genetic drift is crucial for a comprehensive understanding of biology, yet it is difficult to learn because it combines the conceptual challenges of both evolution and randomness. To help assess strategies for teaching genetic drift, we have developed and evaluated the Genetic Drift Inventory (GeDI), a concept inventory that measures…

Price, Rebecca M.; Andrews, Tessa C.; McElhinny, Teresa L.; Mead, Louise S.; Abraham, Joel K.; Thanukos, Anna; Perez, Kathryn E.

2014-01-01

384

Electromagnetic ion cyclotron waves observed near the oxygen cyclotron frequency by ISEE 1 and 2  

NASA Technical Reports Server (NTRS)

The first results of observations of ion cyclotron waves by the elliptically orbiting ISEE 1 and 2 pair of spacecraft are reported. The most intense waves (8 nT) were observed in the outer plasmasphere where convection drift velocities were largest and the Alfven velocity was a minimum. Wave polarization is predominantly left-handed with propagation almost parallel to the ambient magnetic field, and the spectral slot and polarization reversal predicted by cold plasma propagation theory are identified in the wave data. Computations of the experimental wave spectra during the passage through the plasmapause show that the spectral slots relate to the local plasma parameters, possibly suggesting an ion cyclotron wave growth source near the spacecraft. A regular wave packet structure seen over the first 30 min of the event is attributed to the modulation of this energy source by the Pc 5 waves seen at the same time.

Fraser, B. J.; Samson, J. C.; Hu, Y. D.; Mcpherron, R. L.; Russell, C. T.

1992-01-01

385

Drift tube soft-landing for the production and characterization of materials: Applied to Cu clusters  

SciTech Connect

We have recently developed a soft-landing (SL) instrument that is capable of depositing ions onto substrates for preparative and developmental research of new materials using a laser ablation source. This instrument was designed with a custom drift tube and a split-ring ion optic for the isolation of selected ions. The drift tube allows for the separation and thermalization of ions formed after laser ablation through collisions with an inert bath gas. These collisions allow the ions to be landed at energies below 1 eV onto substrates. The split-ring ion optic is capable of directing ions toward the detector or a landing substrate for selected components. Experiments will be shown ablating Cu using an Nd:YAG (1064 and 532 nm) for cluster formation and landing onto a muscovite (mica) surface. The laser ablation of Cu in 8 Torr of He gas gives a spectrum that contains multiple peaks corresponding to Cu{sub n}, Cu{sub n}O{sub m} clusters, and their corresponding isomers. Atomic force microscopy and drift tube measurements were performed to characterize the performance characteristics of the instrument.

Davila, Stephen J.; Birdwell, David O.; Verbeck, Guido F. [Department of Chemistry, University of North Texas, Denton, Texas 76201 (United States)

2010-03-15

386

Test Results of the Phenix Drift Chamber Prototype.  

NASA Astrophysics Data System (ADS)

The central arms of the PHENIX detector are composed of several elements whose design is driven by features of heavy ion collisions at RHIC: charged particle multiplicity up to 1500 per rapidity unit and a transverse momentum spectrum of soft particles peaking at 200-300 MeV/c. Low mass, multiple focusing drift chambers (DC) which satisfy these requirements were designed and fabricated by PNPI (St.Petersburg, Russia). Each drift chamber of two PHENIX central arms is an arch-shaped titanium frame with inner radius 2 m and outer radius 2.5 m . The length of the DC along the direction of colliding beams is about 4 m and covers 90^circ in azimuthal angle. The design has the following features: modular structure for wiring X- , U- and V- planes; (2) each anode wire is cut in the middle thus decreasing the pulse rate ; (3) electrostatic configuration of drift cell minimizes left-right ambiguity and provides a short avalanche time-length; and (4) the design of the front end electronics allows 1.5 mm track separation for each registration channel. Test results of the DC full scale prototype (11.25^circ in azimuthal angle) are presented and shown to satisfy most calculations and expectations for the final DC design.

Pantuev, Vladislav

1997-04-01

387

arXiv:0802.2185v2[astro-ph]13May2008 Production of Magnetic Turbulence by Cosmic Rays Drifting  

E-print Network

arXiv:0802.2185v2[astro-ph]13May2008 Production of Magnetic Turbulence by Cosmic Rays Drifting-In-Cell simulations of magnetic-turbulence production by isotropic cosmic-ray ions drifting upstream of supernova on cosmic ray trajectories. We observe that an oblique filamentary mode grows more rapidly than the non

388

Abstraction of Seepage into Drifts  

SciTech Connect

The abstraction model used for seepage into emplacement drifts in recent TSPA simulations has been presented. This model contributes to the calculation of the quantity of water that might contact waste if it is emplaced at Yucca Mountain. Other important components of that calculation not discussed here include models for climate, infiltration, unsaturated-zone flow, and thermohydrology; drip-shield and waste-package degradation; and flow around and through the drip shield and waste package. The seepage abstraction model is stochastic because predictions of seepage are necessarily quite uncertain. The model provides uncertainty distributions for seepage fraction fraction of waste-package locations flow rate as functions of percolation flux. In addition, effects of intermediate-scale flow with seepage and seep channeling are included by means of a flow-focusing factor, which is also represented by an uncertainty distribution.

WILSON,MICHAEL L.; HO,CLIFFORD K.

2000-10-16

389

Single wire drift chamber design  

SciTech Connect

This report summarizes the design and prototype tests of single wire drift chambers to be used in Fermilab test beam lines. The goal is to build simple, reliable detectors which require a minimum of electronics. Spatial resolution should match the 300 ..mu..m rms resolution of the 1 mm proportional chambers that they will replace. The detectors will be used in beams with particle rates up to 20 KHz. Single track efficiency should be at least 99%. The first application will be in the MT beamline, which has been designed for calibration of CDF detectors. A set of four x-y modules will be used to track and measure the momentum of beam particles.

Krider, J.

1987-03-30

390

The Theory of Continental Drift  

NSDL National Science Digital Library

This is a brief review of the Theory of Continental Drift and the evidence that led Alfred Wegener to state the theory. It describes evidence of matching but misplaced rocks, uncovered fossils in places they should not have been, and discovered evidence of astounding climatological changes. In addition, fossil remains of a prehistoric reptile known as the Mesosaurus had been uncovered on both sides of the South Atlantic and plant fossils indicated that tropical forests once existed only a few hundred miles from the North Pole. It also cites glacial and stratigraphic evidence. The site discusses objections to the theory and states that at the time of his death in 1930, Wegener's theory seemed well on its way to obscurity.

2007-07-13

391

The Theory of Continental Drift  

NSDL National Science Digital Library

This is a brief review of the Theory of Continental Drift and the evidence that led Alfred Wegener to state the theory. It describes evidence of matching but misplaced rocks, uncovered fossils in places they should not have been, and discovered evidence of astounding climatological changes. In addition, fossil remains of a prehistoric reptile known as the Mesosaurus had been uncovered on both sides of the South Atlantic and plant fossils indicated that tropical forests once existed only a few hundred miles from the North Pole. It also cites glacial and stratigraphic evidence. The site discusses objections to the theory and states that at the time of his death in 1930, Wegener's theory seemed well on its way to obscurity.

392

Biology Undergraduates' Misconceptions about Genetic Drift  

ERIC Educational Resources Information Center

This study explores biology undergraduates' misconceptions about genetic drift. We use qualitative and quantitative methods to describe students' definitions, identify common misconceptions, and examine differences before and after instruction on genetic drift. We identify and describe five overarching categories that include 16 distinct…

Andrews, T. M.; Price, R. M.; Mead, L. S.; McElhinny, T. L.; Thanukos, A.; Perez, K. E.; Herreid, C. F.; Terry, D. R.; Lemons, P. P.

2012-01-01

393

Genetic Drift of HIV Populations in Culture  

Microsoft Academic Search

Populations of Human Immunodeficiency Virus type 1 (HIV-1) undergo a surprisingly large amount of genetic drift in infected patients despite very large population sizes, which are predicted to be mostly deterministic. Several models have been proposed to explain this phenomenon, but all of them implicitly assume that the process of virus replication itself does not contribute to genetic drift. We

Yegor Voronin; Sarah Holte; Julie Overbaugh; Michael Emerman

2009-01-01

394

antigen drift) NO. 500, FEBRUARY 2005 1  

E-print Network

­ -- 14 1. 2. ­antigen drift) 1 3) 4 6) NO. 500, FEBRUARY 2005 1 #12;7) 2.1 (endoparasitoid (2000) Antigenic drift of viruses within a host: A finite site model with de- mographic stochasticity, J. Mol. Evol., 51, 245­ 255 6) Boots M, Hudson P J, Sasaki A (2004) Large shifts in pathogen virulence

Sasaki, Akira

395

Banana drift transport in tokamaks with ripple  

SciTech Connect

Ripple transport in tokamaks is discussed for the banana drift collisionality regime, which lies below the ripple plateau regime treated earlier. The physical mechanisms that dominate banana drift transport are found to differ from those considered in previous work on this regime, and the resulting transport coefficients can consequently differ by several orders of magnitude.

Linsker, R.; Boozer, A.H.

1981-04-01

396

Ion-acoustic double layers in the presence of plasma source  

SciTech Connect

Steady-state plasma turbulence and formation of negative potential spikes and double layers in the presence of ion acoustic instabilities have been studied by means of one-dimensional particle simulations in which velocities of a small fraction of electrons are replaced by the initial drifting Maxwellian at a constant rate. A steady state is found where negative potential spikes appear randomly in space and time giving rise to an anomalous resistivity much greater than previously found. Comparisons of the simulation results with laboratory and space plasmas are discussed.

Okuda, H.; Ashour-Abdalla, M.

1981-11-01

397

FIELD INVESTIGATION OF THE DRIFT SHADOW  

SciTech Connect

A drift shadow is an area immediately beneath an underground void that, in theory, will be relatively drier than the surrounding rock mass. Numerical and analytical models of water flow through unsaturated rock predict the existence of a drift shadow, but field tests confirming the existence of the drift shadow have yet to be performed. Proving the existence of drift shadows and understanding their hydrologic and transport characteristics could provide a better understanding of how contaminants move in the subsurface if released from waste emplacement drifts such as the proposed nuclear waste repository at Yucca Mountain, Nevada. We describe the field program that will be used to investigate the existence of a drift shadow--and the corresponding hydrological process at the Hazel-Atlas silica-sand mine located at the Black Diamond Mines Regional Preserve in Antioch, California. The location and configuration of this mine makes it an excellent site to observe and measure drift shadow characteristics. The mine is located in a porous sandstone unit of the Domengine formation, an approximately 230 meter thick series of interbedded Eocene-age shales, coals, and massive-bedded sandstones. The mining method used at the mine required the development of two parallel drifts, one above the other, driven along the strike of the mined sandstone stratum. This configuration provides the opportunity to introduce water into the rock mass in the upper drift and to observe and measure its flow around the underlying drift. The passive and active hydrologic tests to be performed are described. In the passive method, cores will be obtained in a radial pattern around a drift and will be sectioned and analyzed for in-situ water content using a gravimetric technique, as well as analyzed for chemistry. With the active hydrologic test, water will be introduced into the upper drift of the two parallel drifts and the flow of the water will be tracked as it passes near the bottom drift. Tensiometers, electrical resistance probes, neutron probes, and ground penetrating radar may be used to monitor the change in moisture content/potential over time as water is released.

G.W. Su; T.J. Kneafsey

2006-02-01

398

Cascaded Kalman and particle filters for photogrammetry based gyroscope drift and robot attitude estimation.  

PubMed

Based on a cascaded Kalman-Particle Filtering, gyroscope drift and robot attitude estimation method is proposed in this paper. Due to noisy and erroneous measurements of MEMS gyroscope, it is combined with Photogrammetry based vision navigation scenario. Quaternions kinematics and robot angular velocity dynamics with augmented drift dynamics of gyroscope are employed as system state space model. Nonlinear attitude kinematics, drift and robot angular movement dynamics each in 3 dimensions result in a nonlinear high dimensional system. To reduce the complexity, we propose a decomposition of system to cascaded subsystems and then design separate cascaded observers. This design leads to an easier tuning and more precise debugging from the perspective of programming and such a setting is well suited for a cooperative modular system with noticeably reduced computation time. Kalman Filtering (KF) is employed for the linear and Gaussian subsystem consisting of angular velocity and drift dynamics together with gyroscope measurement. The estimated angular velocity is utilized as input of the second Particle Filtering (PF) based observer in two scenarios of stochastic and deterministic inputs. Simulation results are provided to show the efficiency of the proposed method. Moreover, the experimental results based on data from a 3D MEMS IMU and a 3D camera system are used to demonstrate the efficiency of the method. PMID:24342270

Sadaghzadeh N, Nargess; Poshtan, Javad; Wagner, Achim; Nordheimer, Eugen; Badreddin, Essameddin

2014-03-01

399

Ground Control for Emplacement Drifts for LA  

SciTech Connect

The purpose of this calculation is to analyze the stability of repository emplacement drifts during the preclosure period, and to provide a final ground support method for emplacement drifts for the License Application (LA). The scope of the work includes determination of input parameter values and loads, selection of appropriate process and methods for the calculation, application of selected methods, such as empirical or analytical, to the calculation, development and execution of numerical models, and evaluation of results. Results from this calculation are limited to use for design of the emplacement drifts and the final ground support system installed in these drifts. The design of non-emplacement openings and their ground support systems is covered in the ''Ground Control for Non-Emplacement Drifts for LA'' (BSC 2004c).

Y. Sun

2004-07-09

400

A space-charge-neutralizing plasma for beam drift compression P.K. Roya,, P.A. Seidl a  

E-print Network

A space-charge-neutralizing plasma for beam drift compression P.K. Roya,Ã?, P.A. Seidl a , A. Anders online 7 April 2009 Keywords: Beam Ion Neutralization Compression Plasma Plasma probe Plasma density a b the space- charge forces of the ion beam are neutralized. Recently, a system of four cathodic arc plasma

Gilson, Erik

401

An obliquely propagating electromagnetic drift instability in the lower hybrid frequency range  

E-print Network

Plasmas, Plasma Physics Laboratory, Princeton, New Jersey, USA William Fox Department of Physics-Organization in Laboratory and Astrophysical Plasmas, Plasma Physics Laboratory, Princeton, New Jersey, USA Received 13 April in the electron frame and the forward propagating sound (slow) wave in the ion frame when the relative drifts

Ji, Hantao

402

Low frequency electrostatic waves in a magnetized plasma with heavy negative ions  

NASA Astrophysics Data System (ADS)

We have observed large amplitude, low frequency (well below any cyclotron or plasma frequencies) electrostatic waves in a magnetized Q-machine plasma containing positive potassium ions (39 amu), electrons, and heavy negative ions (350 amu). The negative ions were produced by leaking C7F14 (perfluoromethylcyclohexane) vapor into the Q-machine. C7F14 has a large attachment rate for low energy electrons (in the Q-machine, Te 0.2,eV), so that a relatively large fraction (n- / n- ne . - ne>10^3) of magnetized C7F14^- negative ions are formed at neutral pressures 10-5Torr. The waves propagate in the azimuthal direction of the cylindrical plasma column. The frequency spectrum of the waves contains narrow features at the fundamental (m=1) and several harmonics. Possible excitation mechanisms being considered are the negative ion-modified drift instability driven by the radial density gradient, and radial shear in the azimuthal (ExB) drift velocity.

Kim, Su-Hyun; Meyer, John K.; Merlino, Robert L.

2012-10-01

403

Reflection of ion acoustic solitary waves in a dusty plasma with variable charge dust  

NASA Astrophysics Data System (ADS)

An inhomogeneous plasma comprising ions, two temperature electrons and dust grains with variable charge is explored for its unperturbed state for ions' drift due to density gradient and perturbed state for the evolution of ion acoustic solitary waves and their reflection under the effect of an external magnetic field. The ion drift velocity is found to depend on the plasma parameters and magnetic field. The perturbed state of plasma supports two types of ion acoustic waves, which evolve into fast and slow compressive solitary structures under certain conditions. However, only the fast solitary wave is observed to be reflected and acquired opposite polarity to that of the incident solitary wave. The solitary waves are found to be downshifted after their reflection. The reflection coefficient acquires higher values in the case of dust grains of fixed charge in comparison with the case of fluctuating charge on the dust grains. It means the reflection becomes stronger when the charge on the dust grains does not fluctuate and remains fixed. The effect of dust grain density is to enhance the amplitude of solitary waves but to weaken their reflection. The amplitudes of both the incident and reflected solitons remain higher for the case of fluctuating charge on the dust grains in comparison with the case of fixed charge. The effective temperature of the plasma is also found to alter the solitary structures significantly in the case of dust grains having fluctuating charge.

Tomar, Renu; Malik, Hitendra K.; Dahiya, Raj P.

2014-05-01

404

40 CFR 158.1100 - Spray drift data requirements table.  

Code of Federal Regulations, 2014 CFR

... 2014-07-01 false Spray drift data requirements table. 158.1100 Section...AGENCY (CONTINUED) PESTICIDE PROGRAMS DATA REQUIREMENTS FOR PESTICIDES Spray Drift § 158.1100 Spray drift data requirements table. (a)...

2014-07-01

405

Electric currents through ion tracks in silicon devices  

Microsoft Academic Search

A modified form of Ohm's law, describing electric currents through ion tracks, is presented as a tool for future theoretical modeling efforts related to charge collection from ion tracks in silicon devices. The equation is rigorously derived from the drift\\/diffusion equations and accounts for all currents (electron and hole, drift, and diffusion). While only one quantitative result is given, a

Larry D. Edmonds

1998-01-01

406

The molecular velocity of sound. [aqueous solutions  

NASA Technical Reports Server (NTRS)

The molecular velocity of sound was calculated according to Rao's formula and the temperature and concentration dependences of this value were studied in aqueous solutions of alkali and alkaline-earth halides. Study of relative association brought to light characteristic effects of ions. The variation of the relative association can be explained by a breaking of hydrogen bonds by ions and thermal agitation.

Auslaender, D.; Onitiu, L.

1974-01-01

407

Field Investigation of the Drift Shadow  

NASA Astrophysics Data System (ADS)

A drift shadow is an area immediately beneath an underground void that, in theory, will be relatively drier than the surrounding rock mass. Numerical and analytical models of water flow through unsaturated rock predict the existence of a drift shadow, but field tests confirming its existence have yet to be performed. Proving the existence of drift shadows and understanding their hydrologic and transport characteristics could provide a better understanding of how contaminants move in the subsurface if released from waste emplacement drifts such as the proposed nuclear waste repository at Yucca Mountain, Nevada. We describe the field program that will be used to investigate the existence of a drift shadow and the corresponding hydrological process at the Hazel-Atlas silica-sand mine located at the Black Diamond Mines Regional Preserve in Antioch, California. The location and configuration of this mine makes it an excellent site to observe and measure drift shadow characteristics. The mine is located in a porous sandstone unit of the Domengine Formation, an approximately 230 meter thick series of interbedded Eocene-age shales, coals, and massive-bedded sandstones. The mining method used at the mine required the development of two parallel drifts, one above the other, driven along the strike of the mined sandstone stratum. This configuration provides the opportunity to introduce water into the rock mass in the upper drift and to observe and measure its flow around the underlying drift. The passive and active hydrologic tests to be performed are described. In the passive method, cores will be obtained in a radial pattern around a drift and will be sectioned and analyzed for in-situ water content and chemical constituents. With the active hydrologic test, water will be introduced into the upper drift of the two parallel drifts and the flow of the water will be tracked as it passes near the bottom drift. Tensiometers, electrical resistance probes, neutron probes, and ground penetrating radar may be used to monitor the change in moisture content and potential over time as water is released.

Su, G. W.; Kneafsey, T. J.; Ghezzehei, T. A.; Marshall, B. D.; Cook, P. J.

2005-12-01

408

Creating unstable velocity-space distributions with barium injections  

NASA Technical Reports Server (NTRS)

Ion velocity-space distributions resulting from barium injections from orbiting spacecraft and shaped charges are discussed. Active experiments confirm that anomalous ionization processes may operate, but photoionization accounts for the production of the bulk of the barium ions. Pitch-angle diffusion and/or velocity-space diffusion may occur, but observations of barium ions moving upwards against gravity suggests that the ions retain a significant enough fraction of their initial perpendicular velocity to provide a mirror force. The barium ion plasmas should have a range of Alfven Mach numbers and plasma betas. Because the initial conditions can be predicted these active experiments should permit testing plasma instability hypotheses.

Pongratz, M. B.

1983-01-01

409

Reducing Spray Drift from Glyphosate and Growth Regulator  

E-print Network

also deposit illegal residues on eatable crops, especially organic grown crops or processed crops not reach its target. Particle Drift Particle drift occurs with all pesticide applications, regardless

Jiang, Wen

410

Seepage into drifts with mechanical degradation  

SciTech Connect

Seepage into drifts in unsaturated tuff is an important issue for the long-term performance of the potential nuclear waste repository at Yucca Mountain, Nevada. Drifts in which waste packages will potentially be emplaced are subject to degradation in the form of rockfall from the drift ceiling induced by stress relief, seismic, or thermal effects. The objective of this study is to calculate seepage rates for various drift-degradation scenarios and for different values of percolation flux for the Topopah Spring middle nonlithophysal (Tptpmn) and the Topopah Spring lower lithophysal (Tptpll) units. Seepage calculations are conducted by (1) defining a heterogeneous permeability model on the drift scale that is consistent with field data, (2) selecting calibrated parameters associated with the Tptpmn and Tptpll units, and (3) simulating seepage on detailed degraded-drift profiles, which were obtained from a separate rock mechanics engineering analysis. The simulation results indicate (1) that the seepage threshold (i.e., the percolation flux at which seepage first occurs) is not significantly changed by drift degradation, and (2) the degradation-induced increase in seepage above the threshold is influenced more by the shape of the cavity created by rockfall than the rockfall volume.

Li, Guomin; Tsang, Chin-Fu

2002-09-01

411

Ion-beam generated ion acoustic solitons in beam plasma system with non-isothermal electrons  

Microsoft Academic Search

Reductive perturbation method has been employed to obtain a modified KdV equation and to show the excitation of ion acoustic solitons in an ion beam-plasma system consisting of bulk of cold ions, beam ions, and nonisothermal and resonant electrons (both trapped and free electrons). The effect of ion beam velocity, beam ion density, and plasma ion to beam ion mass

P. S. Abrol; S. G. Tagare

1980-01-01

412

Bridge coupled drift tube linacs  

NASA Astrophysics Data System (ADS)

Modern linac designs for treating radioactive waste achieve high proton currents through funneling at low energy, typically around 20 MeV. The resulting switch to a high-frequency accelerating structure poses severe performance and fabrication difficulties below 100 MeV. Above 100 MeV, proven coupled-cavity linacs (CCLs) are available. However, at 20 MeV one must choose between a high-frequency drift-tube linac (DTL) or a coupled-cavity linac with very short cells. Potential radiation damage from the CW beam, excessive RF power losses, multipactoring, and fabricability all enter into this decision. At Los Alamos, we have developed designs for a bridge-coupled DTL (BCDTL) that, like a CCL, uses lattice focusing elements and bridge couplers, but that unlike a CCL, accelerates the beam in simple, short, large aperture DTL modules with no internal quadrupole focusing. Thus, the BCDTL consumes less power than the CCL linac without degrading beam performance and is simpler and cheaper to fabricate in the 20 to 100 MeV range.

Liska, D.; Smith, P.; Carlisle, L.; Larkin, T.

1993-06-01

413

Drift and proportional tracking chambers  

SciTech Connect

Many techniques have been exploited in constructing tracking chambers, particle detectors which measure the trajectories and momenta of charged particles. The particular features of high-energy interactions - charged particle multiplicities, angular correlations and complex vertex topologies, to name a few - and the experimental environment of the accelerator - event rates, background rates, and so on - accent the importance of certain detector characteristics. In high energy e/sup +/e/sup -/, anti pp and pp interactions the final states are dominated by closely collimated jets of high multiplicity, requiring good track-pair resolution in the tracking chamber. High energy particles deflect very little in limited magnetic field volumes, necessitating good spatial resolution for accurate momentum measurements. The colliding beam technique generally requires a device easily adapted to full solid-angle coverage, and the high event rates expected in some of these machines put a premium on good time resolution. Finally, the production and subsequent decays of the tau, charmed and beautiful mesons will provide multiple vertex topologies. To reconstruct these vertices reliably will require considerable improvements in spatial resolution and track-pair resolution. This lecture considers the proportional counter and its descendant, the drift chamber, as tracking chambers. Its goal is to review the physics of this device in order to understand its performance limitations and promises.

Jaros, J.A.

1980-11-01

414

Drift Time Measurement in the ATLAS Liquid Argon Electromagnetic Calorimeter using Cosmic Muons  

NASA Astrophysics Data System (ADS)

The ionization signals in the liquid argon of the ATLAS electromagnetic calorimeter are studied in detail using cosmic muons. In particular, the drift time of the ionization electrons is measured and used to assess the intrinsic uniformity of the calorimeter gaps and estimate its impact on the constant term of the energy resolution. The drift times of electrons in the cells of the second layer of the calorimeter are uniform at the level of 1.3% in the barrel and 2.8% in the endcaps. This leads to an estimated contribution to the constant term of (0.29^{+0.05}_{-0.04})% in the barrel and (0.54^{+0.06}_{-0.04})% in the endcaps. The same data are used to measure the drift velocity of ionization electrons in liquid argon, which is found to be 4.61±0.07 mm/?s at 88.5 K and 1 kV/mm.

Aad, G.; Abbott, B.; Abdallah, J.; Abdelalim, A. A.; Abdesselam, A.; Abdinov, O.; Abi, B.; Abolins, M.; Abramowicz, H.; Abreu, H.; Acharya, B. S.; Adams, D. L.; Addy, T. N.; Adelman, J.; Adorisio, C.; Adragna, P.; Adye, T.; Aefsky, S.; Aguilar-Saavedra, J. A.; Aharrouche, M.; Ahlen, S. P.; Ahles, F.; Ahmad, A.; Ahmed, H.; Ahsan, M.; Aielli, G.; Akdogan, T.; Åkesson, T. P. A.; Akimoto, G.; Akimov, A. V.; Aktas, A.; Alam, M. S.; Alam, M. A.; Albert, J.; Albrand, S.; Aleksa, M.; Aleksandrov, I. N.; Alessandria, F.; Alexa, C.; Alexander, G.; Alexandre, G.; Alexopoulos, T.; Alhroob, M.; Aliev, M.; Alimonti, G.; Alison, J.; Aliyev, M.; Allport, P. P.; Allwood-Spiers, S. E.; Almond, J.; Aloisio, A.; Alon, R.; Alonso, A.; Alviggi, M. G.; Amako, K.; Amelung, C.; Ammosov, V. V.; Amorim, A.; Amorós, G.; Amram, N.; Anastopoulos, C.; Andeen, T.; Anders, C. F.; Anderson, K. J.; Andreazza, A.; Andrei, V.; Anduaga, X. S.; Angerami, A.; Anghinolfi, F.; Anjos, N.; Antonaki, A.; Antonelli, M.; Antonelli, S.; Antos, J.; Antunovic, B.; Anulli, F.; Aoun, S.; Arabidze, G.; Aracena, I.; Arai, Y.; Arce, A. T. H.; Archambault, J. P.; Arfaoui, S.; Arguin, J.-F.; Argyropoulos, T.; Arik, E.; Arik, M.; Armbruster, A. J.; Arnaez, O.; Arnault, C.; Artamonov, A.; Arutinov, D.; Asai, M.; Asai, S.; Asfandiyarov, R.; Ask, S.; Åsman, B.; Asner, D.; Asquith, L.; Assamagan, K.; Astbury, A.; Astvatsatourov, A.; Atoian, G.; Auerbach, B.; Auge, E.; Augsten, K.; Aurousseau, M.; Austin, N.; Avolio, G.; Avramidou, R.; Axen, D.; Ay, C.; Azuelos, G.; Azuma, Y.; Baak, M. A.; Bacci, C.; Bach, A.; Bachacou, H.; Bachas, K.; Backes, M.; Badescu, E.; Bagnaia, P.; Bai, Y.; Bailey, D. C.; Bain, T.; Baines, J. T.; Baker, O. K.; Baker, M. D.; Baker, S.; Baltasar Dos Santos Pedrosa, F.; Banas, E.; Banerjee, P.; Banerjee, S.; Banfi, D.; Bangert, A.; Bansal, V.; Baranov, S. P.; Baranov, S.; Barashkou, A.; Barber, T.; Barberio, E. L.; Barberis, D.; Barbero, M.; Bardin, D. Y.; Barillari, T.; Barisonzi, M.; Barklow, T.; Barlow, N.; Barnett, B. M.; Barnett, R. M.; Baron, S.; Baroncelli, A.; Barr, A. J.; Barreiro, F.; Barreiro Guimarães da Costa, J.; Barrillon, P.; Barros, N.; Bartoldus, R.; Bartsch, D.; Bastos, J.; Bates, R. L.; Batkova, L.; Batley, J. R.; Battaglia, A.; Battistin, M.; Bauer, F.; Bawa, H. S.; Bazalova, M.; Beare, B.; Beau, T.; Beauchemin, P. H.; Beccherle, R.; Becerici, N.; Bechtle, P.; Beck, G. A.; Beck, H. P.; Beckingham, M.; Becks, K. H.; Bedajanek, I.; Beddall, A. J.; Beddall, A.; Bednár, P.; Bednyakov, V. A.; Bee, C.; Begel, M.; Behar Harpaz, S.; Behera, P. K.; Beimforde, M.; Belanger-Champagne, C.; Bell, P. J.; Bell, W. H.; Bella, G.; Bellagamba, L.; Bellina, F.; Bellomo, M.; Belloni, A.; Belotskiy, K.; Beltramello, O.; Ami, S. Ben; Benary, O.; Benchekroun, D.; Bendel, M.; Benedict, B. H.; Benekos, N.; Benhammou, Y.; Benincasa, G. P.; Benjamin, D. P.; Benoit, M.; Bensinger, J. R.; Benslama, K.; Bentvelsen, S.; Beretta, M.; Berge, D.; Bergeaas Kuutmann, E.; Berger, N.; Berghaus, F.; Berglund, E.; Beringer, J.; Bernardet, K.; Bernat, P.; Bernhard, R.; Bernius, C.; Berry, T.; Bertin, A.; Besana, M. I.; Besson, N.; Bethke, S.; Bianchi, R. M.; Bianco, M.; Biebel, O.; Biesiada, J.; Biglietti, M.; Bilokon, H.; Bindi, M.; Binet, S.; Bingul, A.; Bini, C.; Biscarat, C.; Bitenc, U.; Black, K. M.; Blair, R. E.; Blanchard, J.-B.; Blanchot, G.; Blocker, C.; Blocki, J.; Blondel, A.; Blum, W.; Blumenschein, U.; Bobbink, G. J.; Bocci, A.; Boehler, M.; Boek, J.; Boelaert, N.; Böser, S.; Bogaerts, J. A.; Bogouch, A.; Bohm, C.; Bohm, J.; Boisvert, V.; Bold, T.; Boldea, V.; Boldyrev, A.; Bondarenko, V. G.; Bondioli, M.; Boonekamp, M.; Bordoni, S.; Borer, C.; Borisov, A.; Borissov, G.; Borjanovic, I.; Borroni, S.; Bos, K.; Boscherini, D.; Bosman, M.; Bosteels, M.; Boterenbrood, H.; Bouchami, J.; Boudreau, J.; Bouhova-Thacker, E. V.; Boulahouache, C.; Bourdarios, C.; Boyd, J.; Boyko, I. R.; Bozovic-Jelisavcic, I.; Bracinik, J.; Braem, A.; Branchini, P.; Brandenburg, G. W.; Brandt, A.; Brandt, G.; Brandt, O.; Bratzler, U.; Brau, B.; Brau, J. E.; Braun, H. M.; Brelier, B.; Bremer, J.; Brenner, R.; Bressler, S.; Breton, D.; Britton, D.; Brochu, F. M.; Brock, I.; Brock, R.; Brodbeck, T. J.; Brodet, E.; Broggi, F.; Bromberg, C.; Brooijmans, G.; Brooks, W. K.; Brown, G.; Brubaker, E.; Bruckman de Renstrom, P. A.; Bruncko, D.; Bruneliere, R.; Brunet, S.; Bruni, A.; Bruni, G.; Bruschi, M.; Buanes, T.; Bucci, F.; Buchanan, J.; Buchholz, P.; Buckley, A. G.; Budagov, I. A.; Budick, B.; Büscher, V.; Bugge, L.; Bulekov, O.; Bunse, M.; Buran, T.; Burckhart, H.; Burdin, S.; Burgess, T.; Burke, S.; Busato, E.; Bussey, P.; Buszello, C. P.; Butin, F.; Butler, B.; Butler, J. M.; Buttar, C. M.; Butterworth, J. M.; Byatt, T.; Caballero, J.; Cabrera Urbán, S.; Caforio, D.

2010-12-01

415

Enhanced reliability of drift-diffusion approximation for electrons in fluid models for nonthermal plasmas  

SciTech Connect

Common fluid models used for the description of electron transport in nonthermal discharge plasmas are subject to substantial restrictions if the electron energy transport significantly influences the discharge behaviour. A drift-diffusion approach is presented which is based on a multiterm approximation of the electron velocity distribution function and overcomes some of these restrictions. It is validated using a benchmark model and applied for the analysis of argon discharge plasmas at low and atmospheric pressure. The results are compared to those of common drift-diffusion models as well as to experimental data. It is pointed out that fluid models are able to describe nonlocal phenomena caused by electron energy transport, if the energy transport is consistently described. Numerical difficulties that frequently occur when the conventional drift-diffusion model is consistently applied are avoided by the proposed method.

Becker, M. M.; Loffhagen, D. [Leibniz Institute for Plasma Science and Technology, Felix-Hausdorff-Str. 2, 17489 Greifswald (Germany)

2013-01-15

416

The Fallacy of Drifting Snow  

Microsoft Academic Search

A common parametrization over snow-covered surfaces that are undergoing saltation is that the aerodynamic roughness length for wind speed (z 0) scales as {alpha u_ast^2\\/g}, where u * is the friction velocity, g is the acceleration of gravity, and alpha is an empirical constant. Data analyses seem to support this scaling: many published plots of z 0 measured over snow

Edgar L. Andreas

2011-01-01

417

Correlation ion mobility spectroscopy  

DOEpatents

Correlation ion mobility spectrometry (CIMS) uses gating modulation and correlation signal processing to improve IMS instrument performance. Closely spaced ion peaks can be resolved by adding discriminating codes to the gate and matched filtering for the received ion current signal, thereby improving sensitivity and resolution of an ion mobility spectrometer. CIMS can be used to improve the signal-to-noise ratio even for transient chemical samples. CIMS is especially advantageous for small geometry IMS drift tubes that can otherwise have poor resolution due to their small size.

Pfeifer, Kent B. (Los Lunas, NM); Rohde, Steven B. (Corrales, NM)

2008-08-26

418

Experimental investigation of the nonlinear evolution of an impurity-driven drift wave  

SciTech Connect

An impurity-driven drift wave is observed to be destabilized by the reversed density gradient of a singly-ionized heavy-impurity-ion population in a Q-machine plasma. The evolution of the instability is investigated as it progresses from the initial linear exponential growth phase, into a nonlinear saturated state, whereupon strong radially outward anomalous diffusion is observed. The relationship between the anomalous diffusion coefficient and the wave amplitude is in agreement with estimates obtained from the nonlinear drift-wave turbulence theory of Dupree.

Allen, G.R.; Yamada, M.; Rewoldt, G.; Tang, W.M.

1982-04-01

419

Nonlinear electrostatic drift Kelvin-Helmholtz instability  

NASA Technical Reports Server (NTRS)

Nonlinear analysis of electrostatic drift Kelvin-Helmholtz instability is performed. It is shown that the analysis leads to the propagation of the weakly nonlinear dispersive waves, and the nonlinear behavior is governed by the nonlinear Burger's equation.

Sharma, Avadhesh C.; Srivastava, Krishna M.

1993-01-01

420

Mgmnt. of wastes-Drifting Stn., Weddell  

NSF Publications Database

... Systems for Management of Liquid and Gaseous Wastes from the Drifting Station in the Weddell Sea) To ... and shower wastewater treatment; o human waste (urine and faeces) treatment; o diesel power ...

421

Strange Attractors in Drift Wave Turbulence  

SciTech Connect

A multi-grid part-in-cell algorithm for a shearless slab drift wave model with kinetic electrons is presented. The algorithm, which is based on an exact separation of adiabatic and nonadiabatic electron responses, is used to investigate the presence of strange attractors in drift wave turbulence. Although the simulation model has a large number of degrees of freedom, it is found that the strange attractor is low-dimensional and that it is strongly affected by dissipative (collisional) effects.

J.L.V. Lewandowski

2003-04-25

422

Early time evolution of negative ion clouds and electron density depletions produced during electron attachment chemical release experiments  

NASA Technical Reports Server (NTRS)

Two-dimensional electrostatic particle-in-cell simulations are used to study the early time evolution of electron depletions and negative ion clouds produced during electron attachment chemical releases in the ionosphere. The simulation model considers the evolution in the plane perpendicular to the magnetic field and a three-species plasma that contains electrons, positive ions, and also heavy negative ions that result as a by-product of the electron attachment reaction. The early time evolution (less than the negative ion cyclotron period) of the system shows that a negative charge surplus initially develops outside of the depletion boundary as the heavy negative ions move across the boundary. The electrons are initially restricted from moving into the depletion due to the magnetic field. An inhomogenous electric field develops across the boundary layer due to this charge separation. A highly sheared electron flow velocity develops in the depletion boundary due to E x B and Delta-N x B drifts that result from electron density gradients and this inhomogenous electric field. Structure eventually develops in the depletion boundary layer due to low-frequency electrostatic waves that have growth times shorter than the negative ion cyclotron period. It is proposed that these waves are most likely produced by the electron-ion hybrid instability that results from sufficiently large shears in the electron flow velocity.

Scales, W. A.; Bernhardt, P. A.; Ganguli, G.

1994-01-01

423

Assessing the drift of seasonal forecasts  

NASA Astrophysics Data System (ADS)

The systematic drift (bias dependence on the forecast lead-time) present in state-of-the-art coupled general circulation models is an inherent feature of global seasonal forecasts. Usually, anomalies (relative to the model climatology) obtained from an ensemble of hindcasts are used to correct this drift. However, this procedure has not been systematically explored across different forecasting systems so far. Moreover, costly approaches for seasonal impacts forecasting, such as dynamical downscaling, would benefit from drift removal strategies involving smaller ensemble sizes. The