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Sample records for anomalous rf field

  1. Revisiting the Anomalous rf Field Penetration into a Warm Plasma

    SciTech Connect

    Igor D. Kaganovich; Oleg V. Polomarov; Constantine E. Theodosiou

    2005-06-24

    Radio-frequency [rf] waves do not penetrate into a plasma and are damped within it. The electric field of the wave and plasma current are concentrated near the plasma boundary in a skin layer. Electrons can transport the plasma current away from the skin layer due to their thermal motion. As a result, the width of the skin layer increases when electron temperature effects are taken into account. This phenomenon is called anomalous skin effect. The anomalous penetration of the rf electric field occurs not only for transversely propagating to the plasma boundary wave (inductively coupled plasmas) but also for the wave propagating along the plasma boundary (capacitively coupled plasmas). Such anomalous penetration of the rf field modifies the structure of the capacitive sheath. Recent advances in the nonlinear, non-local theory of the capacitive sheath are reported. It is shown that separating the electric field profile into exponential and non-exponential parts yields an efficient qualitative and quantitative description of the anomalous skin effect in both inductively and capacitively coupled plasma.

  2. Effect of anomalous electron cross-field transport on electron energy distribution function in a DC-RF magnetized plasma discharge

    NASA Astrophysics Data System (ADS)

    Raitses, Yevgeny; Donnelly, Vincent; Kaganovich, Igor; Godyak, Valery

    2013-09-01

    The application of the magnetic field in a low pressure plasma can cause a spatial separation of cold and hot electron groups. This so-called magnetic filter effect is not well understood and is the subject of our studies. In this work, we investigate electron energy distribution function in a DC-RF plasma discharge with crossed electric and magnetic field operating at sub-mtorr pressure range of xenon gas. Experimental studies showed that the increase of the magnetic field leads to a more uniform profile of the electron temperature across the magnetic field. This surprising result indicates the importance of anomalous electron transport that causes mixing of hot and cold electrons. High-speed imaging and probe measurements revealed a coherent structure rotating in E cross B direction with frequency of a few kHz. Similar to spoke oscillations reported for Hall thrusters, this rotating structure conducts the largest fraction of the cross-field current. This work was supported by the US DOE under Contract DE-AC02-09CH11466.

  3. Effect of anomalous electron cross-field transport on electron energy distribution function in a DC-RF magnetized plasma discharge

    NASA Astrophysics Data System (ADS)

    Raitses, Yevgeny; Donnelly, Vincent M.; Kaganovich, Igor D.; Godyak, Valery

    2013-10-01

    The application of the magnetic field in a low pressure plasma can cause a spatial separation of cold and hot electron groups. This so-called magnetic filter effect is not well understood and is the subject of our studies. In this work, we investigate electron energy distribution function in a DC-RF plasma discharge with crossed electric and magnetic field operating at sub-mtorr pressure range of xenon gas. Experimental studies showed that the increase of the magnetic field leads to a more uniform profile of the electron temperature across the magnetic field. This surprising result indicates the importance of anomalous electron transport that causes mixing of hot and cold electrons. High-speed imaging and probe measurements revealed a coherent structure rotating in E cross B direction with frequency of a few kHz. Similar to spoke oscillations reported for Hall thrusters, this rotating structure conducts the largest fraction of the cross-field current. This work was supported by DOE contract DE-AC02-09CH11466.

  4. Unbalanced field RF electron gun

    DOEpatents

    Hofler, Alicia

    2013-11-12

    A design for an RF electron gun having a gun cavity utilizing an unbalanced electric field arrangement. Essentially, the electric field in the first (partial) cell has higher field strength than the electric field in the second (full) cell of the electron gun. The accompanying method discloses the use of the unbalanced field arrangement in the operation of an RF electron gun in order to accelerate an electron beam.

  5. Anomalous rf magnetoresistance in copper at 4/degree/K

    SciTech Connect

    Halama, H.J.; Prodell, A.G.; Rogers, J.T.; De Panfilis, S.; Melissinos, A.C.; Moskowitz, B.E.; Semertzidis, Y.K.; Wuensch, W.U.; Fowler, W.B.; Nezrick, F.A.

    1988-03-01

    We have measured the effect of a magnetic field on the surface resistance of polycrystalline Cu at f = 1.2 GHz and at 4.4/degree/K; under these conditions the surface resistance is well into the anomalous skin effect regime but has not reached its limiting value. We find that the transverse and longitudinal magnetoresistance are an order of magnitude smaller than the DC magnetoresistance and depend quadratically on the field. At low fields we observe a decrease in surface resistance with increasing field which can be interpreted as a size effect of the TF surface current. 17 refs., 4 figs., 1 tab.

  6. RF Field Visualization of RF Ablation at the Larmor Frequency

    PubMed Central

    Stang, Pascal; Kerr, Adam; Pauly, John; Scott, Greig

    2012-01-01

    Radiofrequency ablation is an effective minimally invasive treatment for tumors. One primary source of difficulty is monitoring and controlling the ablation region. Currently, RF ablation is performed at 460 kHz, for which MRI could play a role given its capability for temperature monitoring and tumor visualization. If instead the ablation were to be performed at the MRI Larmor frequency, then the MR capability for B1 field mapping could be used to directly visualize the RF fields created by the ablation currents. Visualizing the RF fields may enable better control of the ablation currents, enabling better control of lesion shape and size and improving repeatability. We demonstrate the feasibility of performing RF ablations at 64 MHz and show preliminary results from imaging the RF fields from the ablation. The post-ablation RF fields show an increase in current density in the ablated region, consistent with an increase in conductivity of the ablated tissue. PMID:21775256

  7. Exploration of Anomalous Gravity Effects by rf-Pumped Magnetized High-T(c) Superconducting Oxides

    NASA Technical Reports Server (NTRS)

    Robertson, Tony; Litchford, Ron; Peters, Randall; Thompson, Byran; Rodgers, Stephen L. (Technical Monitor)

    2001-01-01

    A number of anomalous gravitational effects have been reported in the scientific literature during recent years, but there has been no independent confirmation with regard to any of these claims. Therefore, the NASA Marshall Space Flight Center, in response to the propulsion challenges specified by NASA's Breakthrough Propulsion Physics (BPP) program, proposed to explore the possibility of observing anomalous gravitation behavior through the manipulation of Josephson junction effects in magnetized high-Tc superconducting oxides. The technical goal was to critically test this revolutionary physical claim and provide a rigorous, independent, empirical confirmation (or refutation) of anomalous effects related to the manipulation of gravity by radio frequency (rf)-pumped magnetized type-2 superconductors. Because the current empirical evidence for gravity modification is anecdotal, our objective was to design, construct, and meticulously implement a discriminating experiment, which would put these observations on a more firm footing within the scientific community. Our approach is unique in that we advocate the construction of an extremely sensitive torsion balance with which to measure gravity modification effects by rf-pumped type-2 superconductor test masses. This paper reviews the anecdotal evidence for anomalous gravity effects, describes the design and development of a simplified torsion balance experiment for empirically investigating these claims, and presents the results of preliminary experiments.

  8. Calculation of rf fields in axisymmetric cavities

    SciTech Connect

    Iwashita, Y.

    1985-01-01

    A new code, PISCES, has been developed for calculating a complete set of rf electromagnetic modes in an axisymmetric cavity. The finite-element method is used with up to third-order shape functions. Although two components are enough to express these modes, three components are used as unknown variables to take advantage of the symmetry of the element matrix. The unknowns are taken to be either the electric field components or the magnetic field components. The zero-divergence condition will be satisfied by the shape function within each element.

  9. RF Head Coil Design with Improved RF Magnetic Near-Fields Uniformity for Magnetic Resonance Imaging (MRI) Systems

    PubMed Central

    Sohn, Sung-Min; DelaBarre, Lance; Gopinath, Anand; Vaughan, John Thomas

    2015-01-01

    Higher magnetic field strength in magnetic resonance imaging (MRI) systems offers higher signal-to-noise ratio (SNR), contrast, and spatial resolution in MR images. However, the wavelength in ultra-high fields (7 tesla and beyond) becomes shorter than the human body at the Larmor frequency with increasing static magnetic field (B0) of MRI system. At short wavelengths, interference effect appears resulting in non- uniformity of the RF magnetic near-field (B1) over the subject and MR images may have spatially anomalous contrast. The B1 near-field generated by the transverse electromagnetic (TEM) RF coil’s microstrip line element has a maximum near the center of its length and falls off towards both ends. In this study, a double trapezoidal shaped microstrip transmission line element is proposed to obtain uniform B1 field distribution by gradual impedance variation. Two multi-channel RF head coils with uniform and trapezoidal shape elements were built and tested with a phantom at 7T MRI scanner for comparison. The simulation and experimental results show stronger and more uniform B1+ near-field with the trapezoidal shape. PMID:25892746

  10. Evidence for Water Ie on the Moon: Results for Anomalous Polar Craters from the LRO Mini-RF Imaging Radar

    NASA Technical Reports Server (NTRS)

    Spudis, P.D.; Bussey, D. B. J.; Baloga, S. M.; Cahill, J. T. S.; Glaze, L. S.; Patterson, G. W.; Raney, R. K.; Thompson, T. W.; Thomson, B. J.; Ustinov, E. A.

    2013-01-01

    The Mini-RF radar instrument on the Lunar Reconnaissance Orbiter spacecraft mapped both lunar poles in two different RF wavelengths (complete mapping at 12.6 cm S-band and partial mapping at 4.2 cm X-band) in two look directions, removing much of the ambiguity of previous Earth- and spacecraft-based radar mapping of the Moon's polar regions. The poles are typical highland terrain, showing expected values of radar cross section (albedo) and circular polarization ratio (CPR). Most fresh craters display high values of CPR in and outside the crater rim; the pattern of these CPR distributions is consistent with high levels of wavelength-scale surface roughness associated with the presence of block fields, impact melt flows, and fallback breccia. A different class of polar crater exhibits high CPR only in their interiors, interiors that are both permanently dark and very cold (less than 100 K). Application of scattering models developed previously suggests that these anomalously high-CPR deposits exhibit behavior consistent with the presence of water ice. If this interpretation is correct, then both poles may contain several hundred million tons of water in the form of relatively "clean" ice, all within the upper couple of meters of the lunar surface. The existence of significant water ice deposits enables both long-term human habitation of the Moon and the creation of a permanent cislunar space transportation system based upon the harvest and use of lunar propellant.

  11. Evidence for water ice on the moon: Results for anomalous polar craters from the LRO Mini-RF imaging radar

    NASA Astrophysics Data System (ADS)

    Spudis, P. D.; Bussey, D. B. J.; Baloga, S. M.; Cahill, J. T. S.; Glaze, L. S.; Patterson, G. W.; Raney, R. K.; Thompson, T. W.; Thomson, B. J.; Ustinov, E. A.

    2013-10-01

    The Mini-RF radar instrument on the Lunar Reconnaissance Orbiter spacecraft mapped both lunar poles in two different RF wavelengths (complete mapping at 12.6 cm S-band and partial mapping at 4.2 cm X-band) in two look directions, removing much of the ambiguity of previous Earth- and spacecraft-based radar mapping of the Moon's polar regions. The poles are typical highland terrain, showing expected values of radar cross section (albedo) and circular polarization ratio (CPR). Most fresh craters display high values of CPR in and outside the crater rim; the pattern of these CPR distributions is consistent with high levels of wavelength-scale surface roughness associated with the presence of block fields, impact melt flows, and fallback breccia. A different class of polar crater exhibits high CPR only in their interiors, interiors that are both permanently dark and very cold (less than 100 K). Application of scattering models developed previously suggests that these anomalously high-CPR deposits exhibit behavior consistent with the presence of water ice. If this interpretation is correct, then both poles may contain several hundred million tons of water in the form of relatively "clean" ice, all within the upper couple of meters of the lunar surface. The existence of significant water ice deposits enables both long-term human habitation of the Moon and the creation of a permanent cislunar space transportation system based upon the harvest and use of lunar propellant.

  12. Evidence for Water Ice on the Moon: Results for Anomalous Polar Craters from the LRO Mini-RF Imaging Radar

    NASA Technical Reports Server (NTRS)

    Spudis, P. D.; Bussey, D. B. J.; Baloga, S. M.; Cahill, J. T. S.; Glaze, L. S.; Patterson, G. W.; Raney, R. K.; Thompson, T. W.; Thomson, B. J.; Ustinov, E. A.

    2013-01-01

    The Mini-RF radar instrument on the Lunar Reconnaissance Orbiter spacecraft mapped both lunar poles in two different RF wavelengths (complete mapping at 12.6 cm S-band and partial mapping at 4.2 cm X-band) in two look directions, removing much of the ambiguity of previous Earth- and spacecraft-based radar mapping of the Moon's polar regions. The poles are typical highland terrain, showing expected values of radar cross section (albedo) and circular polarization ratio (CPR). Most fresh craters display high values of CPR in and outside the crater rim; the pattern of these CPR distributions is consistent with high levels of wavelength-scale surface roughness associated with the presence of block fields, impact melt flows, and fallback breccia. A different class of polar crater exhibits high CPR only in their interiors, interiors that are both permanently dark and very cold (less than 100 K). Application of scattering models developed previously suggests that these anomalously high-CPR deposits exhibit behavior consistent with the presence of water ice. If this interpretation is correct, then both poles may contain several hundred million tons of water in the form of relatively "clean" ice, all within the upper couple of meters of the lunar surface. The existence of significant water ice deposits enables both long-term human habitation of the Moon and the creation of a permanent cislunar space transportation system based upon the harvest and use of lunar propellant.

  13. Observation of anomalous field penetration in collisional, cylindrical ICP discharges

    NASA Astrophysics Data System (ADS)

    Evans, John D.; Chen, Francis F.; Arnush, Donald

    2000-10-01

    Measurements of the radial penetration of RF-generated B-fields are performed in a large diameter cylindrical ICP. A loop antenna surrounds a dome-shaped Pyrex top that sits on top of a magnetic bucket. Rtop=15cm height of top, Rbucket 18cm, bucket height 30cm, N 1011cm-3, Te 3eV, Prf < 1.4kW, Frf = 2-27.12MHz, Po 1-100mT. Field penetration (``skin") depths Lsd are measured in the outer plasma region (r > R/2) that are consistent with collisional skin depth theory. However, in the interior region (r < R/2), non-monotonic radial profiles and interference phenomena that resemble standing wave behavior (e.g. nodes) are observed, where no propagating waves are predicted to occur. Similar phenomena have been observed by other groups [1], but for chambers sizes such that R Lsd. Such observations were explained as manifestations of the anomalous skin effect (ASE), the electromagnetic analog of Debye shielding. However, these phenomena are more apparent as Po (and collisionality) is increased, in apparent contradiction to the predictions of ASE theory. Results of a detailed experimental investigation of interference phenomena under conditions that fall outside of the ASE regime will be presented, as well as a simple physical picture that resolves this apparent paradox. [1]. B. Joye and H. Schneider, Helv. Phys. Acta 51, 804 (1978).

  14. Wave associated anomalous drag during magnetic field reconnection

    SciTech Connect

    Mozer, F. S.; Wilber, M.; Drake, J. F.

    2011-10-15

    The anomalous drag, D, due to large amplitude plasma waves is used for the first time, in place of {eta}*j, to estimate dissipation at the sub-solar magnetopause and to determine the extent to which this drag accounts for the reconnection electric field. This anomalous drag is determined by measuring correlations of the fluctuations in the electric field and plasma density. Large amplitude electric fields occurred more than 60% of the time in the more than 100 sub-solar, low latitude magnetopause crossings of the THEMIS satellite. They occurred mainly near the magnetospheric separatrix in the form of electrostatic lower hybrid and whistler waves. The anomalous drag at the separatrix was generally <10% of the average reconnection electric field, and it was <1% of the field in the current sheet. Thus, anomalous drag due to waves is not a significant driver of reconnection or of the required dissipation at the sub-solar magnetopause.

  15. Anomalous Thrust Production from an RF Test Device Measured on a Low-Thrust Torsion Pendulum

    NASA Technical Reports Server (NTRS)

    Brady, David A.; White, Harold G.; March, Paul; Lawrence, James T.; Davies, Frank J.

    2014-01-01

    This paper describes the test campaigns designed to investigate and demonstrate viability of using classical magnetoplasmadynamics to obtain a propulsive momentum transfer via the quantum vacuum virtual plasma. This paper will not address the physics of the quantum vacuum plasma thruster (QVPT), but instead will describe the recent test campaign. In addition, it contains a brief description of the supporting radio frequency (RF) field analysis, lessons learned, and potential applications of the technology to space exploration missions. During the first (Cannae) portion of the campaign, approximately 40 micronewtons of thrust were observed in an RF resonant cavity test article excited at approximately 935 megahertz and 28 watts. During the subsequent (tapered cavity) portion of the campaign, approximately 91 micronewtons of thrust were observed in an RF resonant cavity test article excited at approximately 1933 megahertz and 17 watts. Testing was performed on a low-thrust torsion pendulum that is capable of detecting force at a single-digit micronewton level. Test campaign results indicate that the RF resonant cavity thruster design, which is unique as an electric propulsion device, is producing a force that is not attributable to any classical electromagnetic phenomenon and therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma.

  16. Anomalous scaling of a scalar field advected by turbulence

    SciTech Connect

    Kraichnan, R.H.

    1995-12-31

    Recent work leading to deduction of anomalous scaling exponents for the inertial range of an advected passive field from the equations of motion is reviewed. Implications for other turbulence problems are discussed.

  17. Reduction of RF penetration effects in high field imaging.

    PubMed

    Foo, T K; Hayes, C E; Kang, Y W

    1992-02-01

    A method of correcting for the RF inhomogeneity in the body by dielectric loading of the coil-to-shield space in an RF resonator (coil and shield assembly) is described. The presence of the RF coil and RF shield have significant effects on RF homogeneity. Based on theoretical calculations, a method for adjusting the RF homogeneity by manipulating the axial propagation constant, kappa z, is proposed. This is accomplished by loading the coil-to-shield space with dielectric material of suitable relative permittivity so as to increase kappa z and decrease the radial propagation constant, kappa rho. In this manner, the radial wavelength (lambda rho = 2 pi/kappa rho) can be increased relative to the body dimensions, and the field amplitude variations in the axial plane minimized. Theoretical calculations indicate that a value of between 30 and 40 for the relative permittivity of the dielectric material in the coil-to-shield space would reduce the RF field inhomogeneity from +/- 15% to about +/- 3% over a central 30-cm-diameter region of a homogeneous 40-cm-diameter body at both 64 and 170 MHz. The theoretical model was verified in laboratory measurements of the [formula; see text] field generated in a test coil at 170 MHz which was scaled to correspond to a body at 64 MHz. However, the improved RF field homogeneity would be accompanied by increased RF power requirements and reduced coil sensitivity. PMID:1549043

  18. High field rf superconductivity: to pulse or not to pulse

    SciTech Connect

    Campisi, I.E.

    1984-10-01

    Experimental data on the behavior of superconductors under the application of rf fields of amplitude comparable to their critical fields are sporadic and not always consistent. In many cases the field level at which breakdown in superconducting rf cavities should be expected has not been clearly established. Tests conducted with very short (approx. 1 ..mu..s) rf pulses indicate that in this mode of operation fields close to the critical values can be consistently reached in superconducting cavities without breakdown. The advantages and disadvantages of the pulsed method are discussed compared to those of the more standard continuous wave (cw) systems. 60 references.

  19. Technique for Predicting the RF Field Strength Inside an Enclosure

    NASA Technical Reports Server (NTRS)

    Hallett, M.; Reddell, J.

    1998-01-01

    This Memorandum presents a simple analytical technique for predicting the RF electric field strength inside an enclosed volume in which radio frequency radiation occurs. The technique was developed to predict the radio frequency (RF) field strength within a launch vehicle's fairing from payloads launched with their telemetry transmitters radiating and to the impact of the radiation on the vehicle and payload. The RF field strength is shown to be a function of the surface materials and surface areas. The method accounts for RF energy losses within exposed surfaces, through RF windows, and within multiple layers of dielectric materials which may cover the surfaces. This Memorandum includes the rigorous derivation of all equations and presents examples and data to support the validity of the technique.

  20. Anomalous cross field electron transport in a Hall effect thruster

    SciTech Connect

    Boniface, C.; Garrigues, L.; Hagelaar, G. J. M.; Boeuf, J. P.; Gawron, D.; Mazouffre, S.

    2006-10-16

    The origin of anomalous electron transport across the magnetic field in the channel of a Hall effect thruster has been the subject of controversy, and the relative importance of electron-wall collisions and plasma turbulence on anomalous transport is not clear. From comparisons between Fabry-Perot measurements and hybrid model calculations of the ion velocity profile in a 5 kW Hall effect thruster, we deduce that one and the same mechanism is responsible for anomalous electron transport inside and outside the Hall effect thruster channel. This suggests that the previous assumption that Bohm anomalous conductivity is dominant outside the thruster channel whereas electron-wall conductivity prevails inside the channel is not valid.

  1. TRAK_RF - Electromagnetic Field and Charged Particle Simulations in RF Devices

    NASA Astrophysics Data System (ADS)

    Humphries, Stanley; Rees, Daniel

    1997-05-01

    An integrated software system has been developed to model electromagnetic fields and charged particle orbits in high-power RF devices. The primary application is simulation of electron multipactoring in linac vacuum windows for Accelerator Production of Tritium(G. Lawrence, et.al., Conventional and Superconducting RF Linac Design for the APT Project, in Proc. 1996 Int'l. Linear Acc. Conf. (Geneva, 1996), to be published.). The finite-element frequency-domain field solver can determine resonant fields such as cutoff and propagating modes of waveguides and TE(mnp) and TM(mnp) modes of cylindrical structures. In contrast to codes like Superfish, TRAK_RF makes direct determinations of power dissipation and phase shifts resulting ffrom lossy materials and walls. Furthermore, the program can handle scattering solutions, simulating free-space conditions with resistive termination boundary layers. TRAK_RF has advanced particle tracking capabilities to investigate a variety of innovative window designs. The program can simutaneously apply three numerical solutions for electrostatic, magnetostatic and electromagnetic fields on independent conformal triangular meshes. The finite-element method allows an unambiguous determination of particle collisions with material surfaces. It is possible to define up to 32 material types with energy-dependent secondary emission coefficients. TRAK_RF has a versatile automatic mesh generator with an interactive drafting utility for boundary input. Other applications include cavity design, radar and communications, microwave systems, and beam optics in RF accelerators.

  2. Anomalous variations of lithosphere magnetic field before several earthquakes

    NASA Astrophysics Data System (ADS)

    Ni, Z.; Chen, B.

    2015-12-01

    Based on the geomagnetic vector data measured each year since 2011 at more than 500 sites with a mean spatial interval of ~70km.we observed anomalous variations of lithospheric magnetic field before and after over 15 earthquakes having magnitude > 5. We find that the field in near proximity (about 50km) to the epicenter of large earthquakes shows high spatial and temporal gradients before the earthquake. Due to the low frequency of repeat measurements it is unclear when these variations occurred and how do them evolve. We point out anomalous magnetic filed using some circles with radius of 50km usually in June of each year, and then we would check whether quake will locat in our circles during one year after that time (June to next June). Now we caught 10 earthquakes of 15 main shocks having magnitude > 5, most of them located at less than10km away from our circles and some of them were in our circles. Most results show that the variations of lithosphere magnetic filed at the epicenter are different with surrending backgroud usually. When we figure out horizontal variations (vector) of lithosphere magnetic field and epicenter during one year after each June, we found half of them show that the earthquakes will locat at "the inlands in a flowing river", that means earthquakes may occur at "quiet"regions while the backgroud show character as"flow" as liquid. When we compared with GPS results, it appears that these variations of lithospere magnetic field may also correlate with displacement of earth's surface. However we do not compared with GPS results for each earthquake, we are not clear whether these anomalous variations of lithospere magnetic field may also correlate with anomalous displacement of earth's surface. Future work will include developing an automated method for identifying this type of anomalous field behavior and trying to short repeat measurement period to 6 month to try to find when these variations occur.

  3. Effective field theory: A modern approach to anomalous couplings

    SciTech Connect

    Degrande, Céline; Centre for Particle Physics and Phenomenology , Université Catholique de Louvain, Chemin du Cyclotron 2, B-1348 Louvain-la-Neuve ; Greiner, Nicolas; Max-Planck-Institut für Physik, Föhringer Ring 6, 80805 München ; Kilian, Wolfgang; University of Siegen, Fachbereich Physik, D-57068 Siegen ; Mattelaer, Olivier; Mebane, Harrison; Stelzer, Tim; Willenbrock, Scott; Zhang, Cen; Centre for Particle Physics and Phenomenology , Université Catholique de Louvain, Chemin du Cyclotron 2, B-1348 Louvain-la-Neuve

    2013-08-15

    We advocate an effective field theory approach to anomalous couplings. The effective field theory approach is the natural way to extend the standard model such that the gauge symmetries are respected. It is general enough to capture any physics beyond the standard model, yet also provides guidance as to the most likely place to see the effects of new physics. The effective field theory approach also clarifies that one need not be concerned with the violation of unitarity in scattering processes at high energy. We apply these ideas to pair production of electroweak vector bosons. -- Highlights: •We discuss the advantages of effective field theories compared to anomalous couplings. •We show that one need not be concerned with unitarity violation at high energy. •We discuss the application of effective field theory to weak boson physics.

  4. Vacuum field energy and spontaneous emission in anomalously dispersive cavities

    SciTech Connect

    Bradshaw, Douglas H.; Di Rosa, Michael D.

    2011-05-15

    Anomalously dispersive cavities, particularly white-light cavities, may have larger bandwidth to finesse ratios than their normally dispersive counterparts. Partly for this reason, they have been proposed for use in laser interferometer gravitational-wave observatory (LIGO)-like gravity-wave detectors and in ring-laser gyroscopes. In this paper we analyze the quantum noise associated with anomalously dispersive cavity modes. The vacuum field energy associated with a particular cavity mode is proportional to the cavity-averaged group velocity of that mode. For anomalously dispersive cavities with group index values between 1 and 0, this means that the total vacuum field energy associated with a particular cavity mode must exceed ({h_bar}/2{pi}){omega}/2. For white-light cavities in particular, the group index approaches zero and the vacuum field energy of a particular spatial mode may be significantly enhanced. We predict enhanced spontaneous emission rates into anomalously dispersive cavity modes and broadened laser linewidths when the linewidth of intracavity emitters is broader than the cavity linewidth.

  5. Anomalous Fano Profiles in External Fields

    NASA Astrophysics Data System (ADS)

    Zielinski, Alejandro; Majety, Vinay Pramod; Nagele, Stefan; Pazourek, Renate; Burgdörfer, Joachim; Scrinzi, Armin

    2015-12-01

    We show that the external control of Fano resonances in general leads to complex Fano q parameters. Fano line shapes of photoelectron and transient absorption spectra in the presence of an infrared control field are investigated. Computed transient absorption spectra are compared with a model proposed for a recent experiment [C. Ott et al., Science 340, 716 (2013)]. Control mechanisms for photoelectron spectra are exposed: control pulses applied during excitation modify the line shapes by momentum boosts of the continuum electrons. Pulses arriving after excitation generate interference fringes due to infrared two-photon transitions.

  6. Anomalous Fano Profiles in External Fields.

    PubMed

    Zielinski, Alejandro; Majety, Vinay Pramod; Nagele, Stefan; Pazourek, Renate; Burgdörfer, Joachim; Scrinzi, Armin

    2015-12-11

    We show that the external control of Fano resonances in general leads to complex Fano q parameters. Fano line shapes of photoelectron and transient absorption spectra in the presence of an infrared control field are investigated. Computed transient absorption spectra are compared with a model proposed for a recent experiment [C. Ott et al., Science 340, 716 (2013)]. Control mechanisms for photoelectron spectra are exposed: control pulses applied during excitation modify the line shapes by momentum boosts of the continuum electrons. Pulses arriving after excitation generate interference fringes due to infrared two-photon transitions. PMID:26705629

  7. A double-frequency rf gun for field emission

    NASA Astrophysics Data System (ADS)

    Li, Xiangkun; Li, Ming; Dan, Lijun; He, Tianhui; Liu, Yu; Xu, Zhou; Tang, Chuanxiang

    2015-05-01

    Cold cathodes have attracted a lot of attention in the field of accelerators in recent years. While the development of suitable cold cathodes is in progress, attempts have been made to combine the cold cathode with a rf structure. Due to the strong dependence on the electric field, field emissions peak at the wave crest, which is not the best injection phase, during a rf cycle. To make the injection phase adjustable, a flexible double-frequency rf gun is designed. The addition of a 3rd-harmonic field to the fundamental one in the half cell will move the wave crest toward a better injection phase and make the initial bunch length shorter. The full cell is resonant at the fundamental frequency. Since only the half cell is resonant at two frequencies, the gun can be easily tuned. Simulations show that the time-dependent rf effects on the transverse and longitudinal phase spaces of the electron bunch can be reduced by choosing proper rf parameters and the space charge effects can be compensated for by using an external solenoid field. Therefore, the gun is able to provide low emittance, low energy spread and short electron bunches with high average current.

  8. Anomalous resistivity and the evolution of magnetic field topology

    NASA Technical Reports Server (NTRS)

    Parker, E. N.

    1993-01-01

    This paper explores the topological restructuring of a force-free magnetic field caused by the hypothetical sudden onset of a localized region of strong anomalous resistivity. It is shown that the topological complexity increases, with the primitive planar force-free field with straight field lines developing field lines that wrap half a turn around each other, evidently providing a surface of tangential discontinuity in the wraparound region. It is suggested that the topological restructuring contributes to the complexity of the geomagnetic substorm, the aurora, and perhaps some of the flare activity on the sun, or other star, and the Galactic halo.

  9. RF breakdown of 805 MHz cavities in strong magnetic fields

    SciTech Connect

    Bowring, D.; Stratakis, D.; Kochemirovskiy, A.; Leonova, M.; Moretti, A.; Palmer, M.; Peterson, D.; Yonehara, K.; Freemire, B.; Lane, P.; Torun, Y.; Haase, A.

    2015-05-03

    Ionization cooling of intense muon beams requires the operation of high-gradient, normal-conducting RF structures in the presence of strong magnetic fields. We have measured the breakdown rate in several RF cavities operating at several frequencies. Cavities operating within solenoidal magnetic fields B > 0.25 T show an increased RF breakdown rate at lower gradients compared with similar operation when B = 0 T. Ultimately, this breakdown behavior limits the maximum safe operating gradient of the cavity. Beyond ionization cooling, this issue affects the design of photoinjectors and klystrons, among other applications. We have built an 805 MHz pillbox-type RF cavity to serve as an experimental testbed for this phenomenon. This cavity is designed to study the problem of RF breakdown in strong magnetic fields using various cavity materials and surface treatments, and with precise control over sources of systematic error. We present results from tests in which the cavity was run with all copper surfaces in a variety of magnetic fields.

  10. Transient anomalous charge production in strong-field QCD

    NASA Astrophysics Data System (ADS)

    Tanji, Naoto; Mueller, Niklas; Berges, Jürgen

    2016-04-01

    We investigate axial charge production in two-color QCD out of equilibrium. We compute the real-time evolution starting with spatially homogeneous strong gauge fields, while the fermions are in vacuum. The idealized class of initial conditions is motivated by glasma flux tubes in the context of heavy-ion collisions. We focus on axial charge production at early times, where important aspects of the anomalous dynamics can be derived analytically. This is compared to real-time lattice simulations. Quark production at early times leading to anomalous charge generation is investigated using Wilson fermions. Our results indicate that coherent gauge fields can transiently produce significant amounts of axial charge density, while part of the induced charges persist to be present even well beyond characteristic decoherence times. The comparisons to analytic results provide stringent tests of real-time representations of the axial anomaly on the lattice.

  11. Flute stabilization due to ponderomotive force created by an rf field with a variable gradient

    SciTech Connect

    Yasaka, Y.; Itatani, R.

    1986-06-30

    An rf-stabilization experiment was performed in the axisymmetric single-mirror device HIEI by controlling the radial-gradient scale length of the rf field with the aid of an azimuthally phased antenna array. The flute stability depends sensitively on the scale length of the perpendicular rf electric field, which shows that rf stabilization is caused by the ponderomotive force for ions.

  12. Identification of anomalous motion of thunderstorms using daily rainfall fields

    NASA Astrophysics Data System (ADS)

    del Moral, Anna; Llasat, Maria Carmen; Rigo, Tomeu

    2016-04-01

    Adverse weather phenomena in Catalonia (NE of the Iberian Peninsula) is commonly associated to heavy rains, large hail, strong winds, and/or tornados, all of them caused by thunderstorms. In most of the cases with adverse weather, thunderstorms vary sharply their trajectories in a concrete moment, changing completely the motion directions that have previously followed. Furthermore, it is possible that a breaking into several cells may be produced, or, in the opposite, it can be observed a joining of different thunderstorms into a bigger system. In order to identify the main features of the developing process of thunderstorms and the anomalous motions that these may follow in some cases, this contribution presents a classification of the events using daily rainfall fields, with the purpose of distinguishing quickly anomalous motion of thunderstorms. The methodology implemented allows classifying the daily rainfall fields in three categories by applying some thresholds related with the daily precipitation accumulated values and their extension: days with "no rain", days with "potentially convective" rain and days with "non-potentially convective" rain. Finally, for those "potentially convective" daily rainfall charts, it also allows a geometrical identification and classification of all the convective structures into "ellipse" and "non-ellipse", obtaining then the structures with "normal" or "anomalous" motion pattern, respectively. The work is focused on the period 2008-2015, and presents some characteristics of the rainfall behaviour in terms of the seasonal distribution of convective rainfall or the geographic variability. It shows that convective structures are mainly found during late spring and summer, even though they can be recorded in any time of the year. Consequently, the maximum number of convective structures with anomalous motion is recorded between July and November. Furthermore, the contribution shows the role of the orography of Catalonia in the

  13. Inhomogeneous electric field effects in a linear RF quadruple trap

    NASA Technical Reports Server (NTRS)

    Melborne, R. K.

    1990-01-01

    The exact potential corresponding to confining fields inside a linear rf quadrupole particle trap of finite length is presented. The analytic expressions for the trapping potential is derived by introducing a linear trap employing a relatively simple cylindrical geometry and solving Laplace's equation for the trap electrodes. The finite length of linear traps results in field distortion near the trap ends. An exact analytic determination of the fields is useful because the profile of the trapped ion cloud is highly dependent on the fields confining it. It is shown that near the ends of the trap, the effective potential arising from the rf fields acts to propel particles out of the trap, and further, that the addition of a dc bias generates an inhomogeneous in the trap that influences the particles both perpendicularly to and along the trap's long axis.

  14. Resonance properties of the biological objects in the RF field

    NASA Astrophysics Data System (ADS)

    Cocherova, E.; Kupec, P.; Stofanik, V.

    2011-12-01

    Irradiation of people with electromagnetic fields emitted from miscellaneous devices working in the radio-frequency (RF) range may have influence, for example may affect brain processes. The question of health impact of RF electromagnetic fields on population is still not closed. This article is devoted to an investigation of resonance phenomena of RF field absorption in the models of whole human body and body parts (a head) of different size and shape. The values of specific absorption rate (SAR) are evaluated for models of the different shapes: spherical, cylindrical, realistic shape and for different size of the model, that represents the case of new-born, child and adult person. In the RF frequency region, absorption depends nonlinearly on frequency. Under certain conditions (E-polarization), absorption reaches maximum at frequency, that is called "resonance frequency". The whole body absorption and the resonance frequency depends on many further parameters, that are not comprehensively clarified. The simulation results showed the dependence of the whole-body average SAR and resonance frequency on the body dimensions, as well as the influence of the body shape.

  15. Dynamo and anomalous transport in the reversed field pinch

    SciTech Connect

    Prager, S.C.

    1998-08-01

    The reversed field pinch is an effective tool to study the macroscopic consequences of magnetic fluctuations, such as the dynamo effect and anomalous transport. Several explanations exist for the dynamo (the self-generation of plasma current)--the MHD dynamo, the kinetic dynamo, and the diamagnetic dynamo. There is some experimental evidence for each, particularly from measurements of ion velocity and electron pressure fluctuations. Magnetic fluctuations are known to produce energy and particle flux in the RFP core. Current profile control is able to decrease fluctuation-induced transport by a factor of five. Improved confinement regimes are also obtained at deep reversal and, possibly, with flow shear.

  16. Rf Gun with High-Current Density Field Emission Cathode

    SciTech Connect

    Jay L. Hirshfield

    2005-12-19

    High current-density field emission from an array of carbon nanotubes, with field-emission-transistor control, and with secondary electron channel multiplication in a ceramic facing structure, have been combined in a cold cathode for rf guns and diode guns. Electrodynamic and space-charge flow simulations were conducted to specify the cathode configuration and range of emission current density from the field emission cold cathode. Design of this cathode has been made for installation and testing in an existing S-band 2-1/2 cell rf gun. With emission control and modulation, and with current density in the range of 0.1-1 kA/cm2, this cathode could provide performance and long-life not enjoyed by other currently-available cathodes

  17. Anomalous Capacitive Sheath with Deep Radio Frequency Electric Field Penetration

    SciTech Connect

    Igor D. Kaganovich

    2002-01-18

    A novel nonlinear effect of anomalously deep penetration of an external radio-frequency electric field into a plasma is described. A self-consistent kinetic treatment reveals a transition region between the sheath and the plasma. Because of the electron velocity modulation in the sheath, bunches in the energetic electron density are formed in the transition region adjusted to the sheath. The width of the region is of order V(subscript T)/omega, where V(subscript T) is the electron thermal velocity, and w is frequency of the electric field. The presence of the electric field in the transition region results in a cooling of the energetic electrons and an additional heating of the cold electrons in comparison with the case when the transition region is neglected.

  18. Anomalous Thrust Production from an RF Test Device Measured on a Low-Thrust Torsion Pendulum

    NASA Technical Reports Server (NTRS)

    Brady, David; White, Harold G.; March, Paul; Lawrence, James T.; Davies, Frank J.

    2014-01-01

    This paper describes the eight-day August 2013 test campaign designed to investigate and demonstrate viability of using classical magnetoplasmadynamics to obtain a propulsive momentum transfer via the quantum vacuum virtual plasma. This paper will not address the physics of the quantum vacuum plasma thruster, but instead will describe the test integration, test operations, and the results obtained from the test campaign. Approximately 30-50 micro-Newtons of thrust were recorded from an electric propulsion test article consisting primarily of a radio frequency (RF) resonant cavity excited at approximately 935 megahertz. Testing was performed on a low-thrust torsion pendulum that is capable of detecting force at a single-digit micronewton level, within a stainless steel vacuum chamber with the door closed but at ambient atmospheric pressure. Several different test configurations were used, including two different test articles as well as a reversal of the test article orientation. In addition, the test article was replaced by an RF load to verify that the force was not being generated by effects not associated with the test article. The two test articles were designed by Cannae LLC of Doylestown, Pennsylvania. The torsion pendulum was designed, built, and operated by Eagleworks Laboratories at the NASA Johnson Space Center of Houston, Texas. Approximately six days of test integration were required, followed by two days of test operations, during which, technical issues were discovered and resolved. Integration of the two test articles and their supporting equipment was performed in an iterative fashion between the test bench and the vacuum chamber. In other words, the test article was tested on the bench, then moved to the chamber, then moved back as needed to resolve issues. Manual frequency control was required throughout the test. Thrust was observed on both test articles, even though one of the test articles was designed with the expectation that it would not

  19. Iterative Methods to Solve Linear RF Fields in Hot Plasma

    NASA Astrophysics Data System (ADS)

    Spencer, Joseph; Svidzinski, Vladimir; Evstatiev, Evstati; Galkin, Sergei; Kim, Jin-Soo

    2014-10-01

    Most magnetic plasma confinement devices use radio frequency (RF) waves for current drive and/or heating. Numerical modeling of RF fields is an important part of performance analysis of such devices and a predictive tool aiding design and development of future devices. Prior attempts at this modeling have mostly used direct solvers to solve the formulated linear equations. Full wave modeling of RF fields in hot plasma with 3D nonuniformities is mostly prohibited, with memory demands of a direct solver placing a significant limitation on spatial resolution. Iterative methods can significantly increase spatial resolution. We explore the feasibility of using iterative methods in 3D full wave modeling. The linear wave equation is formulated using two approaches: for cold plasmas the local cold plasma dielectric tensor is used (resolving resonances by particle collisions), while for hot plasmas the conductivity kernel (which includes a nonlocal dielectric response) is calculated by integrating along test particle orbits. The wave equation is discretized using a finite difference approach. The initial guess is important in iterative methods, and we examine different initial guesses including the solution to the cold plasma wave equation. Work is supported by the U.S. DOE SBIR program.

  20. Precise quantization of anomalous Hall effect near zero magnetic field

    SciTech Connect

    Bestwick, A. J.; Fox, E. J.; Kou, Xufeng; Pan, Lei; Wang, Kang L.; Goldhaber-Gordon, D.

    2015-05-04

    In this study, we report a nearly ideal quantum anomalous Hall effect in a three-dimensional topological insulator thin film with ferromagnetic doping. Near zero applied magnetic field we measure exact quantization in the Hall resistance to within a part per 10,000 and a longitudinal resistivity under 1 Ω per square, with chiral edge transport explicitly confirmed by nonlocal measurements. Deviations from this behavior are found to be caused by thermally activated carriers, as indicated by an Arrhenius law temperature dependence. Using the deviations as a thermometer, we demonstrate an unexpected magnetocaloric effect and use it to reach near-perfect quantization by cooling the sample below the dilution refrigerator base temperature in a process approximating adiabatic demagnetization refrigeration.

  1. Anomalous transport in fracture networks: field scale experiments and modelling

    NASA Astrophysics Data System (ADS)

    Kang, P. K.; Le Borgne, T.; Bour, O.; Dentz, M.; Juanes, R.

    2012-12-01

    Anomalous transport is widely observed in different settings and scales of transport through porous and fractured geologic media. A common signature of anomalous transport is the late-time power law tailing in breakthrough curves (BTCs) during tracer tests. Various conceptual models of anomalous transport have been proposed, including multirate mass transfer, continuous time random walk, and stream tube models. Since different conceptual models can produce equally good fits to a single BTC, tracer test interpretation has been plagued with ambiguity. Here, we propose to resolve such ambiguity by analyzing BTCs obtained from both convergent and push-pull flow configurations at two different fracture planes. We conducted field tracer tests in a fractured granite formation close to Ploemeur, France. We observe that BTC tailing depends on the flow configuration and the injection fracture. Specifically the tailing disappears under push-pull geometry, and when we injected at a fracture with high flux (Figure 1). This indicates that for this fractured granite, BTC tailing is controlled by heterogeneous advection and not by matrix diffusion. To explain the change in tailing behavior for different flow configurations, we employ a simple lattice network model with heterogeneous conductivity distribution. The model assigns random conductivities to the fractures and solves the Darcy equation for an incompressible fluid, enforcing mass conservation at fracture intersections. The mass conservation constraint yields a correlated random flow through the fracture system. We investigate whether BTC tailing can be explained by the spatial distribution of preferential flow paths and stagnation zones, which is controlled by the conductivity variance and correlation length. By combining the results from the field tests and numerical modeling, we show that the reversibility of spreading is a key mechanism that needs to be captured. We also demonstrate the dominant role of the injection

  2. Pushing the Limits: RF Field Control at High Loaded Q

    SciTech Connect

    M. Liepe; S.A. Belomestnykh; J. Dobbins; R.P.K. Kaplan; C.R. Strohman; B.K. Stuhl; C. Hovater; T. Plawski

    2005-05-16

    The superconducting cavities in an Energy-Recovery-Linac will be operated with a high loaded Q of several 10{sup 7}, possible up to 10{sup 8}. Not only has no prior control system ever stabilized the RF field in a linac cavity with such high loaded Q, but also highest field stability in amplitude and phase is required at this high loaded Q. Because of a resulting bandwidth of the cavity of only a few Hz, this presents a significant challenge: the field in the cavity extremely sensitive to any perturbation of the cavity resonance frequency due to microphonics and Lorentz force detuning. To prove that the RF field in a high loaded Q cavity can be stabilized, and that Cornell's newly developed digital control system is able to achieve this, the system was connected to a high loaded Q cavity at the JLab IR-FEL. Excellent cw field stability--about 10{sup -4} rms in relative amplitude and 0.02 deg rms in phase--was achieved at a loaded Q of 2.1 x 10{sup 7} and 1.2 x 10{sup 8}, setting a new record in high loaded Q operation of a linac cavity. Piezo tuner based cavity frequency control proved to be very effective in keeping the cavity on resonance and allowed reliable to ramp up to high gradients in less than 1 second.

  3. Gauge invariant approach to low-spin anomalous conformal currents and shadow fields

    SciTech Connect

    Metsaev, R. R.

    2011-05-15

    Conformal low-spin anomalous currents and shadow fields in flat space-time of dimensions greater than or equal to four are studied. The gauge invariant formulation for such currents and shadow fields is developed. Gauge symmetries are realized by involving Stueckelberg and auxiliary fields. The gauge invariant differential constraints for anomalous currents and shadow fields and the realization of global conformal symmetries are obtained. Gauge invariant two-point vertices for anomalous shadow fields are also obtained. In the Stueckelberg gauge frame, these gauge invariant vertices become the standard two-point vertices of conformal field theory. Light-cone gauge two-point vertices of the anomalous shadow fields are derived. The AdS/CFT correspondence for anomalous currents and shadow fields and the respective normalizable and non-normalizable solutions of massive low-spin anti-de Sitter fields is studied. The bulk fields are considered in a modified de Donder gauge that leads to decoupled equations of motion. We demonstrate that leftover on-shell gauge symmetries of bulk massive fields correspond to gauge symmetries of boundary anomalous currents and shadow fields, while the modified (Lorentz) de Donder gauge conditions for bulk massive fields correspond to differential constraints for boundary anomalous currents and shadow fields.

  4. Transverse low-field RF coils in MRI.

    PubMed

    Claasen-Vujcić, T; Borsboom, H M; Gaykema, H J; Mehlkopf, T

    1996-07-01

    Imaging at low fields imposes a number of nonstandard requirements on the RF coil. At low fields, coil losses are dominant over patient losses. This means that even more stress is put on the quality factor Q. Furthermore, the low frequency also implies a high inductance L and/or a high capacitance C product. Just increasing the capacitance C results in a difficult optimal matching to the preamplifier as well as increased costs and higher complexity of the resonator construction. Coils with a high quality factor Q and a high inductance are thus required at low fields. Birdcage coils possess a number of advantages over saddle and solenoidal coils. However, the currently used birdcages have inherently low inductances limited by the size of the coil. The problem can be solved by a novel design in which the strip configuration for inductors is abandoned and the inductors are realized as a certain number of turns. The Q factor can be further improved by using Litz wire. Three novel transverse RF coils with high inductances are presented and compared with each other as well as to the standard coils. Both linear and quadrature modes are discussed. PMID:8795029

  5. Concurrent recording of RF pulses and gradient fields - comprehensive field monitoring for MRI.

    PubMed

    Brunner, David O; Dietrich, Benjamin E; Çavuşoğlu, Mustafa; Wilm, Bertram J; Schmid, Thomas; Gross, Simon; Barmet, Christoph; Pruessmann, Klaas P

    2016-09-01

    Reconstruction of MRI data is based on exact knowledge of all magnetic field dynamics, since the interplay of RF and gradient pulses generates the signal, defines the contrast and forms the basis of resolution in spatial and spectral dimensions. Deviations caused by various sources, such as system imperfections, delays, eddy currents, drifts or externally induced fields, can therefore critically limit the accuracy of MRI examinations. This is true especially at ultra-high fields, because many error terms scale with the main field strength, and higher available SNR renders even smaller errors relevant. Higher baseline field also often requires higher acquisition bandwidths and faster signal encoding, increasing hardware demands and the severity of many types of hardware imperfection. To address field imperfections comprehensively, in this work we propose to expand the concept of magnetic field monitoring to also encompass the recording of RF fields. In this way, all dynamic magnetic fields relevant for spin evolution are covered, including low- to audio-frequency magnetic fields as produced by main magnets, gradients and shim systems, as well as RF pulses generated with single- and multiple-channel transmission systems. The proposed approach permits field measurements concurrently with actual MRI procedures on a strict common time base. The combined measurement is achieved with an array of miniaturized field probes that measure low- to audio-frequency fields via (19) F NMR and simultaneously pick up RF pulses in the MRI system's (1) H transmit band. Field recordings can form the basis of system calibration, retrospective correction of imaging data or closed-loop feedback correction, all of which hold potential to render MRI more robust and relax hardware requirements. The proposed approach is demonstrated for a range of imaging methods performed on a 7 T human MRI system, including accelerated multiple-channel RF pulses. Copyright © 2015 John Wiley & Sons, Ltd

  6. Dependence of the microwave surface resistance of superconducting niobium on the magnitude of the rf field

    SciTech Connect

    Romanenko, A.; Grassellino, A.

    2013-06-24

    Utilizing difference in temperature dependencies we decoupled Bardeen-Cooper-Schrieffer (BCS) and residual components of the microwave surface resistance of superconducting niobium at all rf fields up to B{sub rf}{approx}115 mT. We reveal that the residual resistance decreases with field at B{sub rf} Less-Than-Or-Equivalent-To 40 mT and strongly increases in chemically treated niobium at B{sub rf}>80 mT. We find that BCS surface resistance is weakly dependent on field in the clean limit, whereas a strong and peculiar field dependence emerges after 120 Degree-Sign C vacuum baking.

  7. Spin resonance strength of a localized rf magnetic field

    NASA Astrophysics Data System (ADS)

    Lee, S. Y.

    2006-07-01

    Spin-resonance strength produced by a localized rf field has been a focus of recent publications [V. S. Morozov , Phys. Rev. ST Accel. Beams 7, 024002 (2004).PRABFM1098-440210.1103/PhysRevSTAB.7.024002; M. A. Leonova (to be published).; T. Roser, in Handbook of Accelerator Physics and Engineering, edited by A. W. Chao and M. Tigner (World Scientific, Singapore, 1999), p. 151.; M. Bai, W. W. MacKay, and T. Roser, Phys. Rev. ST Accel. Beams 8, 099001 (2005).PRABFM1098-440210.1103/PhysRevSTAB.8.099001; V. S. Morozov , Phys. Rev. ST Accel. Beams 8, 099002 (2005).PRABFM1098-440210.1103/PhysRevSTAB.8.099002]. This paper discusses the debated factor of 2, and provides a formula to calculate the component enhanced by the induced betatron motion.

  8. A method to localize RF B₁ field in high-field magnetic resonance imaging systems.

    PubMed

    Yoo, Hyoungsuk; Gopinath, Anand; Vaughan, J Thomas

    2012-12-01

    In high-field magnetic resonance imaging (MRI) systems, B₀ fields of 7 and 9.4 T, the RF field shows greater inhomogeneity compared to clinical MRI systems with B₀ fields of 1.5 and 3.0 T. In multichannel RF coils, the magnitude and phase of the input to each coil element can be controlled independently to reduce the nonuniformity of the RF field. The convex optimization technique has been used to obtain the optimum excitation parameters with iterative solutions for homogeneity in a selected region of interest. The pseudoinverse method has also been used to find a solution. The simulation results for 9.4- and 7-T MRI systems are discussed in detail for the head model. Variation of the simulation results in a 9.4-T system with the number of RF coil elements for different positions of the regions of interest in a spherical phantom are also discussed. Experimental results were obtained in a phantom in the 9.4-T system and are compared to the simulation results and the specific absorption rate has been evaluated. PMID:22929360

  9. Advanced electric field computation for RF sheaths prediction with TOPICA

    NASA Astrophysics Data System (ADS)

    Milanesio, Daniele; Maggiora, Riccardo

    2012-10-01

    The design of an Ion Cyclotron (IC) launcher is not only driven by its coupling properties, but also by its capability of maintaining low parallel electric fields in front of it, in order to provide good power transfer to plasma and to reduce the impurities production. However, due to the impossibility to verify the antenna performances before the starting of the operations, advanced numerical simulation tools are the only alternative to carry out a proper antenna design. With this in mind, it should be clear that the adoption of a code, such as TOPICA [1], able to precisely take into account a realistic antenna geometry and an accurate plasma description, is extremely important to achieve these goals. Because of the recently introduced features that allow to compute the electric field distribution everywhere inside the antenna enclosure and in the plasma column, the TOPICA code appears to be the only alternative to understand which elements may have a not negligible impact on the antenna design and then to suggest further optimizations in order to mitigate RF potentials. The present work documents the evaluation of the electric field map from actual antennas, like the Tore Supra Q5 and the JET A2 launchers, and the foreseen ITER IC antenna. [4pt] [1] D. Milanesio et al., Nucl. Fusion 49, 115019 (2009).

  10. Electromagnetic fields and anomalous transports in heavy-ion collisions-a pedagogical review.

    PubMed

    Huang, Xu-Guang

    2016-07-01

    The hot and dense matter generated in heavy-ion collisions may contain domains which are not invariant under P and CP transformations. Moreover, heavy-ion collisions can generate extremely strong magnetic fields as well as electric fields. The interplay between the electromagnetic field and triangle anomaly leads to a number of macroscopic quantum phenomena in these P- and CP-odd domains known as anomalous transports. The purpose of this article is to give a pedagogical review of various properties of the electromagnetic fields, the anomalous transport phenomena, and their experimental signatures in heavy-ion collisions. PMID:27275776

  11. Electromagnetic fields and anomalous transports in heavy-ion collisions—a pedagogical review

    NASA Astrophysics Data System (ADS)

    Huang, Xu-Guang

    2016-07-01

    The hot and dense matter generated in heavy-ion collisions may contain domains which are not invariant under P and CP transformations. Moreover, heavy-ion collisions can generate extremely strong magnetic fields as well as electric fields. The interplay between the electromagnetic field and triangle anomaly leads to a number of macroscopic quantum phenomena in these P- and CP-odd domains known as anomalous transports. The purpose of this article is to give a pedagogical review of various properties of the electromagnetic fields, the anomalous transport phenomena, and their experimental signatures in heavy-ion collisions.

  12. Pressurized H_{2} rf Cavities in Ionizing Beams and Magnetic Fields

    SciTech Connect

    Chung, M.; et al.

    2013-10-01

    A major technological challenge in building a muon cooling channel is operating RF cavities in multi-tesla external magnetic fields. We report the first experimental characterization of a high pressure gas-filled 805 MHz RF cavity for use with intense ionizing beams and strong external magnetic fields. RF power consumption by beam-induced plasma was investigated with hydrogen and deuterium gases with pressures between 20 and 100 atm and peak RF gradients between 5 and 50 MV/m. The energy absorption per ion pair-RF cycle ranges from 10−18 to 10−16 J. The low pressure case agrees well with an analytical model based on electron and ion mobilities. Varying concentrations of oxygen gas were investigated to remove free electrons from the cavity and reduce the RF power consumption. Measurements of the electron attachment time to oxygen and rate of ion-ion recombination were also made. Additionally, we demonstrate the operation of the gas-filled RF cavity in a solenoidal field of up to 3 T, finding no major magnetic field dependence. These results indicate that a high pressure gas-filled cavity is potentially a viable technology for muon ionization cooling.

  13. Anomalous scaling of the magnetic field in the helical Kazantsev-Kraichnan model.

    PubMed

    Jurčišinová, E; Jurčišin, M

    2015-06-01

    The field-theoretic renormalization group and the operator product expansion are used to investigate the influence of spatial parity violation of the conductive turbulent environment on the anomalous scaling behavior of correlation functions of a weak magnetic field in the framework of the Kazantsev-Kraichnan rapid change model. Two-loop expressions for the critical dimensions of the leading composite operators, which drive the anomalous scaling of the two-point single-time correlation functions of the magnetic field in the presence of large-scale anisotropy, are found to be functions of the helicity parameter. It is shown that the presence of helicity in the system leads to a significantly stronger manifestation of anomalous scaling than in the nonhelical case. At the same time, it is also shown that helicity does not destroy the standard hierarchy of the anisotropic anomalous exponents in the framework of which the leading contribution to anomalous scaling is given by the isotropic shell. PMID:26172794

  14. A New First-Principles Calculation of Field-Dependent RF Surface Impedance of BCS Superconductor

    SciTech Connect

    Xiao, Binping; Reece, Charles E.

    2014-02-01

    There is a need to understand the intrinsic limit of radiofrequency (RF) surface impedance that determines the performance of superconducting RF cavities in particle accelerators. Here we present a field-dependent derivation of Mattis-Bardeen theory of the RF surface impedance of BCS superconductors based on the shifted density of states resulting from coherently moving Cooper pairs. Our theoretical prediction of the effective BCS RF surface resistance (Rs) of niobium as a function of peak surface magnetic field amplitude agrees well with recently reported record low loss resonant cavity measurements from JLab and FNAL with carefully, yet differently, prepared niobium material. The surprising reduction in resistance with increasing field is explained to be an intrinsic effect.

  15. Anomalous cross-B field transport and spokes in HiPIMS plasma

    NASA Astrophysics Data System (ADS)

    Hecimovic, A.

    2016-05-01

    Localized light emission patterns observed during on time of a high power impulse magnetron sputtering (HiPIMS) discharge on a planar magnetron, known as spokes or ionization zones, have been identified as a potential source of anomalous cross-B field diffusion. In this paper experimental evidence is presented that anomalous diffusion is triggered by the appearance of spokes. The Hall parameter {ω\\text{ce}}{τ\\text{c}} , product of the electron cyclotron frequency and the classical collision time, reduces from Bohm diffusion values (∼ 16 and higher) down to the value of 3 as spokes appear, indicating anomalous cross-B field transport. A combination of intensified charge coupled device imaging and electric probe measurements reveals that the ions from the spokes are instantaneously diffusing away from the target. The ion diffusion coefficients calculated from a sideways image of the spoke are six times higher than Bohm diffusion coefficients, which is consistent with the reduction of the Hall parameter.

  16. Ambipolar radial electric field generated by anomalous transport induced by magnetic perturbations

    NASA Astrophysics Data System (ADS)

    Chen, Dunqiang; Zhu, Siqiang; Zhang, Debing; Wang, Shaojie

    2016-05-01

    The anomalous particle transport induced by magnetic perturbations in a tokamak is investigated. The correlation between the radial position and the kinetic energy of electrons, Dr K=-e ErDr r , is predicted theoretically and is verified by simulations in the presence of a mean radial electric field. This correlation leads to a radial particle flux produced by the radial electric field. The ambipolar radial electric field can thus be predicted by using the ambipolarity condition Γri=Γre .

  17. Field-effect modulation of anomalous Hall effect in diluted ferromagnetic topological insulator epitaxial films

    NASA Astrophysics Data System (ADS)

    Chang, CuiZu; Liu, MinHao; Zhang, ZuoCheng; Wang, YaYu; He, Ke; Xue, QiKun

    2016-03-01

    High quality chromium (Cr) doped three-dimensional topological insulator (TI) Sb2Te3 films are grown via molecular beam epitaxy on heat-treated insulating SrTiO3 (111) substrates. We report that the Dirac surface states are insensitive to Cr doping, and a perfect robust long-range ferromagnetic order is unveiled in epitaxial Sb2- x Cr x Te3 films. The anomalous Hall effect is modulated by applying a bottom gate, contrary to the ferromagnetism in conventional diluted magnetic semiconductors (DMSs), here the coercivity field is not significantly changed with decreasing carrier density. Carrier-independent ferromagnetism heralds Sb2- x Cr x Te3 films as the base candidate TI material to realize the quantum anomalous Hall (QAH) effect. These results also indicate the potential of controlling anomalous Hall voltage in future TI-based magneto-electronics and spintronics.

  18. Characterization of rf-SSET in both in-plane and perpendicular magnetic fields

    NASA Astrophysics Data System (ADS)

    Tang, Chunyang; Yang, Zhen; Yuan, Mingyun; Rimberg, A. J.; Savage, D. E.; Eriksson, M. A.; Rimberg Team; Eriksson Collaboration

    2013-03-01

    Previous success in coupling an aluminum radio-frequency superconducting single electron transistor (rf-SSET) to quantum dots (QDs) has demonstrated use of the rf-SSET as an ultra-sensitive and fast charge sensor. Since a magnetic field is usually necessary for quantum dot qubit manipulation, it is important to understand the effect of magnetic fields, either in-plane or perpendicular, on the performance of any charge sensor near the QDs. Here we report characterization of rf-SSETs in both in-plane and perpendicular magnetic fields. The rf-SSET works well in an in-plane fields up to 1 Tesla at a temperature of 30 mK. At 0.3K, in a perpendicular field generated by a stripline located 700 nm away, the rf-SSET charge sensitivity even shows improvement for up to 2.1 mA current through the stripline (corresponding roughly to a field of 6 Gauss). This work was supported by NSA, LPS and ARO

  19. Experimental investigation of heating phenomena in linac mechanical interfaces due to RF field penetration

    SciTech Connect

    Fazio, M.V.; Reid, D.W.; Potter, J.M.

    1981-01-01

    In a high duty-factor, high-current, drift-tube linear accelerator, a critical interface exists between the drift-tube stem and the tank wall. This interface must provide vacuum integrity and RF continuity, while simultaneously allowing alignment flexibility. Because of past difficulties with RF heating of vacuum bellows and RF joints encountered by others, a paucity of available information, and the high reliability requirement for the Fusion Materials Irradiation Test (FMIT) accelerator, a program was initiated to study the problem. Because RF heating is the common failure mode, an attempt was made to find a correlation between the drift-tube-stem/linac-tank interface geometry and RF field penetration from the tank into the interface region. Experiments were performed at 80 MHz on an RF structure designed to simulate the conditions to which a drift-tube stem and vacuum bellows are exposed in a drift-tube linac. Additional testing was performed on a 367-MHz model of the FMIT prototype drift-tube linac. Experimental results, and a method to predict excessive RF heating, is presented. An experimentally tested solution to the problem is discussed.

  20. A dynamo explanation for Mercury's anomalous magnetic field

    NASA Astrophysics Data System (ADS)

    Cao, Hao; Aurnou, Jonathan M.; Wicht, Johannes; Dietrich, Wieland; Soderlund, Krista M.; Russell, Christopher T.

    2014-06-01

    Recent MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) measurements have shown that Mercury's magnetic field is axial-dominant, yet strongly asymmetric with respect to the equator: the field strength in the Northern Hemisphere is approximately 3 times stronger than that in the Southern Hemisphere. Here we show that convective dynamo models driven by volumetric buoyancy with north-south symmetric thermal boundaries are capable of generating quasi-steady north-south asymmetric magnetic fields similar to Mercury's. This symmetry breaking is promoted and stabilized when the core-mantle boundary heat flux is higher at the equator than at high latitudes. The equatorially asymmetric magnetic field generation in our dynamo models corresponds to equatorially asymmetric kinetic helicity, which results from mutual excitation of two different modes of columnar convection. Our dynamo model can be tested by future assessment of Mercury's magnetic field from MESSENGER and BepiColombo as well as through investigations on Mercury's lower mantle temperature heterogeneity and buoyancy forcing in Mercury's core.

  1. Simulation of RF Cavity Dark Current in Presence of Helical Magnetic Field

    SciTech Connect

    Romanov, Gennady; Kashikhin, Vladimir; /Unlisted

    2010-09-01

    In order to produce muon beam of high enough quality to be used for a Muon Collider, its large phase space must be cooled several orders of magnitude. This task can be accomplished by ionization cooling. Ionization cooling consists of passing a high-emittance muon beam alternately through regions of low Z material, such as liquid hydrogen, and very high accelerating RF cavities within a multi-Tesla solenoidal focusing channel. But first high power tests of RF cavity with beryllium windows in solenoidal magnetic field showed a dramatic drop in accelerating gradient due to RF breakdowns. It has been concluded that external magnetic fields parallel to RF electric field significantly modifies the performance of RF cavities. However, magnetic field in Helical Cooling Channel has a strong dipole component in addition to solenoidal one. The dipole component essentially changes electron motion in a cavity compare to pure solenoidal case, making dark current less focused at field emission sites. The simulation of dark current dynamic in HCC performed with CST Studio Suit is presented in this paper.

  2. Simulation of RF Cavity Dark Current In Presence of Helical Magnetic Field

    SciTech Connect

    Romanov, Gennady; Kashikhin, Vladimir; /Fermilab

    2012-05-01

    In order to produce muon beam of high enough quality to be used for a Muon Collider, its large phase space must be cooled several orders of magnitude. This task can be accomplished by ionization cooling. Ionization cooling consists of passing a high-emittance muon beam alternately through regions of low Z material, such as liquid hydrogen, and very high accelerating RF cavities within a multi-Tesla solenoidal focusing channel. But first high power tests of RF cavity with beryllium windows in solenoidal magnetic field showed a dramatic drop in accelerating gradient due to RF breakdowns. It has been concluded that external magnetic fields parallel to RF electric field significantly modifies the performance of RF cavities. However, magnetic field in Helical Cooling Channel has a strong dipole component in addition to solenoidal one. The dipole component essentially changes electron motion in a cavity compare to pure solenoidal case, making dark current less focused at field emission sites. The simulation of dark current dynamic in HCC performed with CST Studio Suit is presented in this paper.

  3. Computational Investigation of Helical Traveling Wave Tube Transverse RF Field Forces

    NASA Technical Reports Server (NTRS)

    Kory, Carol L.; Dayton, James A.

    1998-01-01

    In a previous study using a fully three-dimensional (3D) helical slow-wave circuit cold- test model it was found, contrary to classical helical circuit analyses, that transverse FF electric fields have significant amplitudes compared with the longitudinal component. The RF fields obtained using this helical cold-test model have been scaled to correspond to those of an actual TWT. At the output of the tube, RF field forces reach 61%, 26% and 132% for radial, azimuthal and longitudinal components, respectively, compared to radial space charge forces indicating the importance of considering them in the design of electron beam focusing.

  4. Field-aligned currents, plasma waves, and anomalous resistivity in the disturbed polar cusp.

    NASA Technical Reports Server (NTRS)

    Fredricks, R. W.; Scarf, F. L.; Russell, C. T.

    1973-01-01

    During the magnetic storm of November 1, 1968, the Ogo 5 spacecraft encountered the polar cusp region at low magnetic latitudes. We show that the region just outside the last closed field lines contained a warm magnetosheath plasma, magnetic field perturbations interpretable as field-aligned current layers, and electrostatic waves possibly due to plasma instabilities driven by these currents. Estimates of anomalous resistivity extrapolated along the field lines due to these electrostatic waves lead to estimates of field-aligned potential drops between Ogo 5 and the ionosphere on the order of 2 kV.

  5. DESIGN CONSIDERATIONS FOR LOW FIELD SHORT PHOTO-INJECTED RF ELECTRON GUN WITH HIGH CHARGE ELECTRON BUNCH.

    SciTech Connect

    CHANG,X.; BEN-ZVI,I.; KEWISCH,J.

    2004-06-21

    The RF field and space charge effect in a low field RF gun is given. The cell lengths are modified to have maximum accelerating efficiency. The modification introduces an extra RF field slice emittance. The phase space evolution of the following emittance compensation system is presented taking into account the chromatic effect. The emittance compensation mechanics for RF field and chromatic effect induced emittance is similar to that of compensating the space charge induced emittance. But the requirements are different to have best compensation for them. The beam waist is far in front of linac entrance to have best compensation for the RF field and chromatic effect induced emittance. For low field RF gun with high charge electron bunch this compensation is more important.

  6. Anomalously Strong Vertical Magnetic Fields from Distant Lightning

    NASA Astrophysics Data System (ADS)

    Silber, I.; Price, C. G.; Galanti, E.; Shuval, A.

    2014-12-01

    At distances of thousands of kilometers from lightning the vertical component of the magnetic field in the Very Low Frequencies (VLF - 3-30 kHz) and Extremely Low Frequencies (ELF - 3-3000 Hz) is expected to be very weak and several orders of magnitude lower than the horizontal magnetic components. However, measurements in Israel show a relatively strong vertical magnetic component in both the ELF and VLF bands, at the same order of magnitude as the horizontal components. Our measurements suggest that the real Earth-ionosphere waveguide might often be very different from the theoretical waveguide used in model calculations.

  7. Anomalous transport theory for the reversed field pinch

    SciTech Connect

    Terry, P.W.; Hegna, C.C; Sovinec, C.R.

    1996-09-01

    Physically motivated transport models with predictive capabilities and significance beyond the reversed field pinch (RFP) are presented. It is shown that the ambipolar constrained electron heat loss observed in MST can be quantitatively modeled by taking account of the clumping in parallel streaming electrons and the resultant self-consistent interaction with collective modes; that the discrete dynamo process is a relaxation oscillation whose dependence on the tearing instability and profile relaxation physics leads to amplitude and period scaling predictions consistent with experiment; that the Lundquist number scaling in relaxed plasmas driven by magnetic turbulence has a weak S{sup {minus}1/4} scaling; and that radial E{times}B shear flow can lead to large reductions in the edge particle flux with little change in the heat flux, as observed in the RFP and tokamak. 24 refs.

  8. Multipole and field uniformity tailoring of a 750 MHz rf dipole

    SciTech Connect

    Delayen, Jean R.; Castillo, Alejandro

    2014-12-01

    In recent years great interest has been shown in developing rf structures for beam separation, correction of geometrical degradation on luminosity, and diagnostic applications in both lepton and hadron machines. The rf dipole being a very promising one among all of them. The rf dipole has been tested and proven to have attractive properties that include high shunt impedance, low and balance surface fields, absence of lower order modes and far-spaced higher order modes that simplify their damping scheme. As well as to be a compact and versatile design in a considerable range of frequencies, its fairly simple geometry dependency is suitable both for fabrication and surface treatment. The rf dipole geometry can also be optimized for lowering multipacting risk and multipole tailoring to meet machine specific field uniformity tolerances. In the present work a survey of field uniformities, and multipole contents for a set of 750 MHz rf dipole designs is presented as both a qualitative and quantitative analysis of the inherent flexibility of the structure and its limitations.

  9. RF-SABRE: A Way to Continuous Spin Hyperpolarization at High Magnetic Fields.

    PubMed

    Pravdivtsev, Andrey N; Yurkovskaya, Alexandra V; Vieth, Hans-Martin; Ivanov, Konstantin L

    2015-10-29

    A new technique is developed that allows one to carry out the signal amplification by reversible exchange (SABRE) experiments at high magnetic field. SABRE is a hyperpolarization method, which utilizes transfer of spin order from para-hydrogen to the spins of a substrate in transient iridium complexes. Previously, it has been thought that such a transfer of spin order is only efficient at low magnetic fields, notably, at level anti-crossing (LAC) regions. Here it is demonstrated that LAC conditions can also be fulfilled at high fields under the action of a RF field. The high-field RF-SABRE experiment can be implemented using commercially available nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) machines and does not require technically demanding field-cycling. The achievable NMR enhancements are around 100 for several substrates as compared to their NMR signals at thermal equilibrium conditions at 4.7 T. The frequency dependence of RF-SABRE is comprised of well pronounced peaks and dips, whose position and amplitude are conditioned solely by the magnetic resonance parameters such as chemical shifts and scalar coupling of the spin system involved in the polarization transfer and by the amplitude of the RF field. Thus, the proposed method can serve as a new sensitive tool for probing transient complexes. Simulations of the dependence of magnetization transfer (i.e., NMR signal amplifications) on the frequency and amplitude of the RF field are in good agreement with the developed theoretical approach. Furthermore, the method enables continuous re-hyperpolarization of the SABRE substrate over a long period of time, giving a straightforward way to repetitive NMR experiments. PMID:25970807

  10. RF Power and Magnetic Field Modulation Experiments with Simple Mirror Geometry in the Central Cell of Hanbit Device

    SciTech Connect

    Lee, S.G.; Bak, J.G.; Jhang, H.G.; Kim, S.S.

    2005-01-15

    The radio frequency (RF) stabilization effects to investigate the characteristics of the interchange instability by RF power and magnetic field modulation experiments were performed near {omega}/{omega}{sub i} {approx} = 1 and with low beta ({approx} 0.1%) plasmas in the central cell of the Hanbit mirror device. Temporal behaviors of the interchange mode were measured and analyzed when the interchange mode was triggered by sudden changes of the RF power and magnetic field intensity.

  11. RF Field Distributions in a Slotted-Type Lisitano Coil

    NASA Astrophysics Data System (ADS)

    Suetsugu, Yusuke; Kawai, Yoshinobu

    1984-08-01

    The field distributions in a slotted-type Lisitano coil are analyzed using a simple antenna model, and the microwave power is theoretically found to be supplied near the center of the coil. Field intensities in the Lisitano coil measured with a calibrated loop antenna are compared with the theoretical values, and results supporting the analysis are obtained. The field distributions in a vacuum chamber were also measured.

  12. ALTERATIONS IN CALCIUM ION ACTIVITY BY ELF AND RF ELECTROMAGNETIC FIELDS

    EPA Science Inventory



    Alterations in calcium ion activity by ELF and RF electromagnetic fields

    Introduction

    Calcium ions play many important roles in biological systems. For example, calcium ion activity can be used as an indicator of second-messenger signal-transduction processe...

  13. Exposure of workers to intense RF electric fields that leak from plastic sealers.

    PubMed

    Bini, M; Checcucci, A; Ignesti, A; Millanta, L; Olmi, R; Rubino, N; Vanni, R

    1986-01-01

    This paper presents the results of an environmental investigation in a plastic-ware industry using RF sealers. Environmental measurements have demonstrated the presence of strong electric fields the intensity of which: reaches significant levels from the health-protection point of view only in proximity to the applicators; often exceeds the maximal levels allowed by all standards (including the most permissive) for short duration exposures, especially in the region of the hands. Results of a cross-sectional study on the health of 63 female workers are related to the observed RF exposure. A statistically significant correlation was found to exist between RF exposure and some minor health effects--eye irritation, upper limb paresthesias, and vitreous body disorganization. PMID:3635629

  14. Final Technical Report- Back-gate Field Emission-based Cathode RF Electron Gun

    SciTech Connect

    McGuire, Gary; Martin, Allen; Noonan, John

    2010-10-30

    The objective was to complete the design of an electron gun which utilizes a radio frequency (RF) power source to apply a voltage to a field emission (FE) cathode, a so called cold cathode, in order to produce an electron beam. The concept of the RF electron gun was originally conceived at Argonne National Laboratory but never reduced to practice. The research allowed the completion of the design based upon the integration of the FE electron source. Compared to other electron guns, the RF gun is very compact, less than one third the size of other comparable guns, and produces a high energy (to several MeV), high quality, high power electron beam with a long focal length with high repetition rates. The resultant electron gun may be used in welding, materials processing, analytical equipment and waste treatment.

  15. Confinement improvement with rf poloidal current drive in the reversed-field pinch

    SciTech Connect

    Hokin, S.; Sarff, J.; Sovinec, C.; Uchimoto, E.

    1994-03-08

    External control of the current profile in a reversed-field pinch (RFP), by means such as rf poloidal current drive, may have beneficial effects well beyond the direct reduction of Ohmic input power due to auxiliary heating. Reduction of magnetic turbulence associated with the dynamo, which drives poloidal current in a conventional RFP, may allow operation at lower density and higher electron temperature, for which rf current drive becomes efficient and the RFP operates in a more favorable regime on the n{tau} vs T diagram. Projected parameters for RFX at 2 MA axe studied as a concrete example. If rf current drive allows RFX to operate with {beta} = 10% (plasma energy/magnetic energy) at low density (3 {times} 10{sup 19} m{sup {minus}3}) with classical resistivity (i.e. without dynamo-enhanced power input), 40 ms energy confinement times and 3 keV temperatures will result, matching the performance of tokamaks of similar size.

  16. Anomalous attenuation of ultrasound in ferrofluids under the influence of a magnetic field

    NASA Technical Reports Server (NTRS)

    Isler, W. E.; Chung, D. Y.

    1978-01-01

    Ultrasonic wave propagation has been studied in a water-base ferrofluid by pulse-echo methods. A commercial box-car integrator was used to measure the change in attenuation due to an external magnetic field applied at various angles relative to the ultrasonic propagation vector. Anomalous results were obtained when the attenuation was plotted as a function of the magnetic field strength. As the field increased, the attenuation reached a maximum and then decreased to a flat minimum before it approached saturation at a field of 2 KG. This variation of attenuation with magnetic field cannot be explained from the simple picture derivable from the work of McTague on the viscosity of ferrofluids. In no case was the viscosity seen to decrease with field, nor was the oscillatory behavior observed. The results of this study were compared with the theory developed by Parsons.

  17. Open Cavity Solutions to the rf in Magnetic Field Problem

    NASA Astrophysics Data System (ADS)

    Palmer, Robert B.; Berg, J. Scott; Fernow, Richard C.; Gallardo, Juan C.; Kirk, Harold G.

    2008-02-01

    It has been observed [1] that breakdown in an 805 MHz pill-box cavity occurs at much lower gradients as an external axial magnetic field is increased. This effect was not observed with on open iris cavity. It is proposed that this effect depends on the relative angles of the magnetic and maximum electric fields: parallel in the pill-box case; at an angle in the open iris case. If so, using an open iris structure with solenoid coils in the irises should perform even better. A lattice, using this principle, is presented, for use in 6D cooling for a Muon Collider. Experimental layouts to test this principle are proposed.

  18. OPEN CAVITY SOLUTIONS TO THE RF IN MAGNETIC FIELD PROBLEM.

    SciTech Connect

    PALMER,R.B.; BERG, J.S.; FERNOW, R.C.; GALLARDO, J.C.; KIRK, H.G.

    2007-08-06

    It has been observed [1] that breakdown in an 805 MHz pill-box cavity occurs at much lower gradients as an external axial magnetic field is increased. This effect was not observed with on open iris cavity. It is proposed that this effect depends on the relative angles of the magnetic and maximum electric fields: parallel in the pill-box case; at an angle in the open iris case. If so, using an open iris structure with solenoid coils in the irises should perform even better. A lattice, using this principle, is presented, for use in 6D cooling for a Muon Collider. Experimental layouts to test this principle are proposed.

  19. Measurement and control of field in RF GUN at FLASH

    NASA Astrophysics Data System (ADS)

    Brandt, A.; Hoffmann, M.; Koprek, W.; Pucyk, P.; Simrock, S.; Pozniak, K. T.; Romaniuk, R. S.

    2008-01-01

    The paper describes the hardware and software architecture of a control and measurement system for electromagnetic field stabilization inside the radio frequency electron gun, in FLASH experiment. A complete measurement path has been presented, including I and Q detectors and FPGA based, low latency digital controller. Algorithms used to stabilize the electromagnetic field have been presented as well as the software environment used to provide remote access to the control device. An input signal calibration procedure has been described as a crucial element of measurement process.

  20. Generalization of susceptibility of RF systems through far-field pattern superposition

    NASA Astrophysics Data System (ADS)

    Verdin, B.; Debroux, P.

    2015-05-01

    The purpose of this paper is to perform an analysis of RF (Radio Frequency) communication systems in a large electromagnetic environment to identify its susceptibility to jamming systems. We propose a new method that incorporates the use of reciprocity and superposition of the far-field radiation pattern of the RF system and the far-field radiation pattern of the jammer system. By using this method we can find the susceptibility pattern of RF systems with respect to the elevation and azimuth angles. A scenario was modeled with HFSS (High Frequency Structural Simulator) where the radiation pattern of the jammer was simulated as a cylindrical horn antenna. The RF jamming entry point used was a half-wave dipole inside a cavity with apertures that approximates a land-mobile vehicle, the dipole approximates a leaky coax cable. Because of the limitation of the simulation method, electrically large electromagnetic environments cannot be quickly simulated using HFSS's finite element method (FEM). Therefore, the combination of the transmit antenna radiation pattern (horn) superimposed onto the receive antenna pattern (dipole) was performed in MATLAB. A 2D or 3D susceptibility pattern is obtained with respect to the azimuth and elevation angles. In addition, by incorporating the jamming equation into this algorithm, the received jamming power as a function of distance at the RF receiver Pr(Φr, θr) can be calculated. The received power depends on antenna properties, propagation factor and system losses. Test cases include: a cavity with four apertures, a cavity above an infinite ground plane, and a land-mobile vehicle approximation. By using the proposed algorithm a susceptibility analysis of RF systems in electromagnetic environments can be performed.

  1. Effects of rf magnetic field and wave reflection on multipactor discharge on a dielectric

    SciTech Connect

    Sazontov, A. G.; Nevchaev, V. E.

    2010-03-15

    This paper analyzes the effects of the rf magnetic field and partial reflection of the circularly polarized electromagnetic wave on multipactor discharge on a dielectric. A statistical theory (taking into account the velocity spread of injected electrons) is constructed to evaluate the multipactor induced breakdown and saturation level. It is concluded that the spread of initial velocities considerably changes the condition for multipactor initiation in comparison with the dynamic approach. This effect is especially strong for the case of relatively low rf electric field amplitude (when the transit time essentially exceeds the rf period) and leads to the oscillation suppression of effective electron yield and to an increase in the threshold of multipactor growth. It is established that the rf magnetic field eliminates the upper boundary of the susceptibility diagram, while the low boundary almost remains unchanged. It is also found that the presence of partial reflection causes degradation of the saturation level (in comparison with the nonreflecting case) and results in decreasing of the characteristic time required to achieve the steady state.

  2. Evaluation of the dielectric constant for RF shimming at high field MRI

    NASA Astrophysics Data System (ADS)

    Jayatilake, Mohan; Storrs, Judd; Chu, Wen-Jang; Lee, Jing-Huei

    2010-10-01

    Optimal image quality for Magnetic Resonance Imaging (MRI) at high fields requires a homogeneous RF (B1) field; however, the dielectric properties of the human brain result in B1 field inhomogeneities and signal loss at the periphery of the head. These result from constructive and destructive RF interactions of complex wave behaviour, which become worse with increasing magnetic field strength. Placement of a shim object with high-dielectric constant adjacent to the body has been proposed as a method for reducing B1 inhomogeneity by altering wave propagation within the volume of interest. Selecting the appropriate permittivity and quantity of material for the shim is essential. Whereas previous work has determined the dielectric properties of the shim empirically, this work introduces an improved theoretical framework for determining the requisite dielectric constant of the passive shim material directly by increasing the axial or minimizing the radial propagation constant.

  3. Theoretical analysis of the electromagnetic field inside an anomalous-dispersion microresonator under synthetical pump

    NASA Astrophysics Data System (ADS)

    Xin, Xu; Xiaohong, Hu; Ye, Feng; Yuanshan, Liu; Wei, Zhang; Zhi, Yang; Wei, Zhao; Yishan, Wang

    2016-03-01

    We study the spatiotemporal evolution of the electromagnetic field inside a microresonator showing an anomalous dispersion at the pump wavelength by using the normalized Lugiato-Lefever equation. Unlike the traditional single continuous wave (CW) pumping, an additional pump source consisting of periodical pulse train with variable repetition rate is adopted. The influences of the microresonator properties and the pump parameters on the field evolution and the electromagnetic field profile are analyzed. The simulation results indicate that, in the anomalous dispersion regime, both increases of the input pulse amplitude and the repetition frequency can result in the field profiles consisting of multiple peaks. A series of equidistant pulses can also be obtained by increasing the CW pump power. In addition, we find that a large physical detuning between the pump laser carrier and the cavity resonance frequency also causes the splitting of the inside field. Project supported by the National Major Scientific Instrumentation Development Program of China (Grant No. 2011YQ120022), CAS/SAFEA International Partnership Program for Creative Research Teams, China, and the National Natural Science Foundation of China (Grant No. 61275164).

  4. Simulation of RF-fields in a fusion device

    SciTech Connect

    De Witte, Dieter; Bogaert, Ignace; De Zutter, Daniel; Van Oost, Guido; Van Eester, Dirk

    2009-11-26

    In this paper the problem of scattering off a fusion plasma is approached from the point of view of integral equations. Using the volume equivalence principle an integral equation is derived which describes the electromagnetic fields in a plasma. The equation is discretized with MoM using conforming basis functions. This reduces the problem to solving a dense matrix equation. This can be done iteratively. Each iteration can be sped up using FFTs.

  5. Model for B1 Imaging in MRI Using the Rotating RF Field

    PubMed Central

    Weber, Ewald; Crozier, Stuart

    2014-01-01

    Conventionally, magnetic resonance imaging (MRI) is performed by pulsing gradient coils, which invariably leads to strong acoustic noise, patient safety concerns due to induced currents, and costly power/space requirements. This modeling study investigates a new silent, gradient coil-free MR imaging method, in which a radiofrequency (RF) coil and its nonuniform field (B 1 +) are mechanically rotated about the patient. The advantage of the rotating B 1 + field is that, for the first time, it provides a large number of degrees of freedom to aid a successful B 1 + image encoding process. The mathematical modeling was performed using flip angle modulation as part of a finite-difference-based Bloch equation solver. Preliminary results suggest that representative MR images with intensity deviations of <5% from the original image can be obtained using rotating RF field approach. This method may open up new avenues towards anatomical and functional imaging in medicine. PMID:24963336

  6. On the Importance of Symmetrizing RF Coupler Fields for Low Emittance Beams

    SciTech Connect

    Li, Zenghai; Zhou, Feng; Vlieks, Arnold; Adolphsen, Chris; /SLAC

    2011-06-23

    The input power of accelerator structure is normally fed through a coupling slot(s) on the outer wall of the accelerator structure via magnetic coupling. While providing perfect matching, the coupling slots may produce non-axial-symmetric fields in the coupler cell that can induce emittance growth as the beam is accelerated in such a field. This effect is especially important for low emittance beams at low energies such as in the injector accelerators for light sources. In this paper, we present studies of multipole fields of different rf coupler designs and their effect on beam emittance for an X-band photocathode gun being jointly designed with LLNL, and X-band accelerator structures. We will present symmetrized rf coupler designs for these components to preserve the beam emittance.

  7. Simulations of Field-Emission Electron Beams from CNT Cathodes in RF Photoinjectors

    SciTech Connect

    Mihalcea, Daniel; Faillace, Luigi; Panuganti, Harsha; Thangaraj, Jayakar C.T.; Piot, Philippe

    2015-06-01

    Average field emission currents of up to 700 mA were produced by Carbon Nano Tube (CNT) cathodes in a 1.3 GHz RF gun at Fermilab High Brightness Electron Source Lab. (HBESL). The CNT cathodes were manufactured at Xintek and tested under DC conditions at RadiaBeam. The electron beam intensity as well as the other beam properties are directly related to the time-dependent electric field at the cathode and the geometry of the RF gun. This report focuses on simulations of the electron beam generated through field-emission and the results are compared with experimental measurements. These simulations were performed with the time-dependent Particle In Cell (PIC) code WARP.

  8. Study of microparticles' anomalous diffusion in active bath using speckle light fields (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Pince, Ercag; Sabareesh, Sabareesh K. P.; Volpe, Giorgio; Gigan, Sylvain; Volpe, Giovanni S.

    2015-08-01

    Particles undergoing a stochastic motion within a disordered medium is a ubiquitous physical and biological phenomenon. Examples can be given from organelles as molecular machines of cells performing physical tasks in a populated cytoplasm to human mobility in patchy environment at larger scales. Our recent results showed that it is possible to use the disordered landscape generated by speckle light fields to perform advanced manipulation tasks at the microscale. Here, we use speckle light fields to study the anomalous diffusion of micron size silica particles (5 μm) in the presence of active microswimmers. The microswimmers we used in the experiments are motile bacteria, Escherichia coli (E.coli). They constitute an active background constantly agitating passive silica particles within complex optical potentials. The speckle fields are generated by mode mixing inside a multimode optical fiber where a small amount of incident laser power (maximum power = 12 μW/μm2) is needed to obtain an effective random landscape pattern for the purpose of optical manipulation. We experimentally show how complex potentials contribute to the anomalous diffusion of silica particles undergoing collisions with swimming bacteria. We observed an enhanced diffusion of particles interacting with the active bath of E.coli inside speckle light fields: this effect can be tuned and controlled by varying the intensity and the statistical properties of the speckle pattern. Potentially, these results could be of interest for many technological applications, such as the manipulation of microparticles inside optically disordered media of biological interests.

  9. Magnetic field effects in RF magnetron sputtering of CdS/CdTe solar cells

    SciTech Connect

    Compaan, A.D.; Shao, M.; Tabory, C.N.; Feng, Z.; Fischer, A.; Shen, F.; Narayanswami, C.; Bohn, R.G.

    1996-01-01

    We have studied effects of magnetic field strength and configuration on rf planar magnetron sputtering of CdS and CdTe. This study was carried out with one sputter gun having an unbalanced magnetic field and a second gun having an approximately balanced magnetic field. The unbalanced field gun produces significantly higher ion and electron bombardment of the film during growth and slightly higher electron kinetic energies. Films produced with the unbalanced gun show much stronger photoluminescence and cell performance is much better when the CdTe is deposited with the unbalanced gun. {copyright} {ital 1996 American Institute of Physics.}

  10. Period Clustering of the Anomalous X-Ray Pulsars and Magnetic Field Decay in Magnetars.

    PubMed

    Colpi; Geppert; Page

    2000-01-20

    We confront theoretical models for the rotational, magnetic, and thermal evolution of an ultramagnetized neutron star, or magnetar, with available data on the anomalous X-ray pulsars (AXPs). We argue that, if the AXPs are interpreted as magnetars, their clustering of spin periods between 6 and 12 s (observed at present in this class of objects), their period derivatives, their thermal X-ray luminosities, and the association of two of them with young supernova remnants can only be understood globally if the magnetic field in magnetars decays significantly on a timescale of the order of 104 yr. PMID:10615029

  11. Global Constraints on Anomalous Triple Gauge Couplings in the Effective Field Theory Approach

    NASA Astrophysics Data System (ADS)

    Falkowski, Adam; González-Alonso, Martín; Greljo, Admir; Marzocca, David

    2016-01-01

    We present a combined analysis of LHC Higgs data (signal strengths) together with LEP-2 W W production measurements. To characterize possible deviations from the standard model (SM) predictions, we employ the framework of an effective field theory (EFT) where the SM is extended by higher-dimensional operators suppressed by the mass scale of new physics Λ . The analysis is performed consistently at the order Λ-2 in the EFT expansion keeping all the relevant operators. While the two data sets suffer from flat directions, together they impose stringent model-independent constraints on the anomalous triple gauge couplings.

  12. Global Constraints on Anomalous Triple Gauge Couplings in the Effective Field Theory Approach.

    PubMed

    Falkowski, Adam; González-Alonso, Martín; Greljo, Admir; Marzocca, David

    2016-01-01

    We present a combined analysis of LHC Higgs data (signal strengths) together with LEP-2 WW production measurements. To characterize possible deviations from the standard model (SM) predictions, we employ the framework of an effective field theory (EFT) where the SM is extended by higher-dimensional operators suppressed by the mass scale of new physics Λ. The analysis is performed consistently at the order Λ(-2) in the EFT expansion keeping all the relevant operators. While the two data sets suffer from flat directions, together they impose stringent model-independent constraints on the anomalous triple gauge couplings. PMID:26799011

  13. Fringe field NMR diffusometry of anomalous self-diffusion in molecular sieves

    NASA Astrophysics Data System (ADS)

    Ylihautala, Mika; Jokisaari, Jukka; Fischer, Elmar; Kimmich, Rainer

    1998-06-01

    Superconducting magnet fringe field NMR diffusometry is applied to an adsorbate-molecular sieve system in order to obtain intracrystalline self-diffusion of adsorbed molecules. Effects of self-diffusion, exchange, relaxation, and dipolar correlation are discussed. The proper equations for one- and two-dimensional anomalous self-diffusion with and without macroscopic order are derived. The method is applied to investigate methane self-diffusion in the molecular sieve silicoaluminophosphate, type 11 (SAPO-11). It is concluded that the nature of the methane displacements in the sieve channels is single-file self-diffusion.

  14. Reducing Near-Field RF Levels and Noise Temperature on a 34-m Beam-Waveguide Antenna by Strut Shaping

    NASA Astrophysics Data System (ADS)

    Khayatian, B.; Hoppe, D. J.; Britcliffe, M. J.; Gama, E.

    2013-02-01

    Strut shaping of NASA's Deep Space Network (DSN) 34-m beam-waveguide (BWG) antenna has been implemented to reduce near-field RF exposure while improving the antenna noise temperature. Strut shaping was achieved by introducing an RF shield that does not compromise the structural integrity of the existing structure. Reduction in the RF near-field exposure will compensate for the planned transmit power increase of the antenna from 20 kW to 80 kW while satisfying safety requirements for RF exposure. Antenna noise temperature was also improved by as much as 1.5 K for the low elevation angles and 0.5 K in other areas. Both reductions of RF near-field exposure and antenna noise temperature were verified through measurements and agree very well with calculated results.

  15. Strut Shaping of 34m Beam Waveguide Antenna for Reductions in Near-Field RF and Noise Temeperature

    NASA Technical Reports Server (NTRS)

    Khayatian, Behrouz; Hoppe, Daniel J.; Britcliffe, Michael J.; Gama, Eric

    2012-01-01

    Struts shaping of the NASA's Deep Space Network (DSN) 34m Beam Waveguide (BWG) antenna has been implemented to reduce near-field RF exposure while improving the antenna noise temperature. Strut shaping was achieved by introducing an RF shield that does not compromise the structural integrity of the existing structure. Reduction in the RF near-field exposure will compensate for the planned transmit power increase of the antenna from 20 kW to 80 kW while satisfying safety requirements for RF exposure. Antenna noise temperature was also improved by as much as 1.5 K for the low elevation angles and 0.5 K in other areas. Both reductions of RF near-field exposure and antenna noise temperature were verified through measurements and agree very well with calculated results.

  16. Use of Exotic Coordinate Systems in the Design of RF Resonators for High-Field MRI

    NASA Astrophysics Data System (ADS)

    Butterworth, Edward

    2008-10-01

    High field human MRI (11.7 Tesla is FDC approved for human research) renders standard RF coil design inadequate because the resonant wavelength in human soft tissue (about 8 cm at 500 MHz) is significantly smaller than the physical size of the human body. I propose optimizing the design of such RF coils using coordinate systems appropriate to human body parts, as has been done with ellipticalootnotetextCrozier et al, Concepts Magn Reson 1997; 9:195-210. and Cassinian ovalootnotetextDe Zanche et al, Magn Reson Med 2005; 53:201-211. cross sections. I have computed analytically the magnetic fields produced by a device of toroidal cross section using a cascade of conformal transformations.ootnotetextButterworth & Gore, J Magn Reson 2005; 175:114-123. Building upon these efforts, I will use the eleven coordinate systems of Moon & Spencer,ootnotetextMoon & Spencer, Field Theory Handbook, Berlin: Springer-Verlag; 1971. along with other possible coordinate systems and conformal transformations, to identify a small number of configurations that have the highest probability of being useful as RF coil designs for ultrahigh-field MRI.

  17. RF interference suppression in a cardiac synchronization system operating in a high magnetic field NMR imaging system

    SciTech Connect

    Damji, A.A.; Snyder, R.E.; Ellinger, D.C.; Witkowski, F.X.; Allen, P.S.

    1988-11-01

    An electrocardiographic (ECG) unit suitable for cardiac-synchronized nuclear magnetic resonance imaging in high magnetic fields is presented. The unit includes lossy transmission lines as ECG leads in order to suppress radio frequency (RF) interference in the electrocardiogram. The unit's immunity to RF interference is demonstrated.

  18. Tumor Selective Hyperthermia Induced by Short-Wave Capacitively-Coupled RF Electric-Fields

    PubMed Central

    Raoof, Mustafa; Cisneros, Brandon T.; Corr, Stuart J.; Palalon, Flavio; Curley, Steven A.; Koshkina, Nadezhda V.

    2013-01-01

    There is a renewed interest in developing high-intensity short wave capacitively-coupled radiofrequency (RF) electric-fields for nanoparticle-mediated tumor-targeted hyperthermia. However, the direct thermal effects of such high-intensity electric-fields (13.56 MHZ, 600 W) on normal and tumor tissues are not completely understood. In this study, we investigate the heating behavior and dielectric properties of normal mouse tissues and orthotopically-implanted human hepatocellular and pancreatic carcinoma xenografts. We note tumor-selective hyperthermia (relative to normal mouse tissues) in implanted xenografts that can be explained on the basis of differential dielectric properties. Furthermore, we demonstrate that repeated RF exposure of tumor-bearing mice can result in significant anti-tumor effects compared to control groups without detectable harm to normal mouse tissues. PMID:23861912

  19. CeRu2Al10: Anomalous Magnetic Ordering and Its Field Stability

    NASA Astrophysics Data System (ADS)

    Strydom, A. M.

    2010-04-01

    The intermetallic compound CeRu2Al10 orders in a new crystal structure type that is cage-like on account of its peculiar atomic arrangement and large interatomic distances—especially concerning the environment of the rare-earth element Ce. In previous work we showed that anomalous thermal, electronic, and magnetic properties of this compound coalesce into a phase transition at T *=27 K, which is exceptionally high for a cerium intermetallic compound. T * has been characterized through various temperature-dependent properties which suggest a multi-parameter nature of the ordering at T *. Here we report on continued investigations into this compound and focus in particular on the response to applied magnetic fields. Whereas transport properties in the ordered region are receptive to magnetic fields, the transition itself turns out to be more robust and is insensitive to static fields up to 14 T.

  20. A PARAMETRIC STUDY OF BCS RF SURFACE IMPEDANCE WITH MAGNETIC FIELD USING THE XIAO CODE

    SciTech Connect

    Reece, Charles E.; Xiao, Binping

    2013-09-01

    A recent new analysis of field-dependent BCS rf surface impedance based on moving Cooper pairs has been presented.[1] Using this analysis coded in Mathematica TM, survey calculations have been completed which examine the sensitivities of this surface impedance to variation of the BCS material parameters and temperature. The results present a refined description of the "best theoretical" performance available to potential applications with corresponding materials.

  1. International policy and advisory response regarding children's exposure to radio frequency electromagnetic fields (RF-EMF).

    PubMed

    Redmayne, Mary

    2016-01-01

    Radiofrequency electromagnetic field (RF-EMF) exposure regulations/guidelines generally only consider acute effects, and not chronic, low exposures. Concerns for children's exposure are warranted due to the amazingly rapid uptake of many wireless devices by increasingly younger children. This review of policy and advice regarding children's RF-EMF exposure draws material from a wide variety of sources focusing on the current situation. This is not a systematic review, but aims to provide a representative cross-section of policy and advisory responses within set boundaries. There are a wide variety of approaches which I have categorized and tabulated ranging from ICNIRP/IEEE guidelines and "no extra precautions needed" to precautionary or scientific much lower maxima and extensive advice to minimize RF-EMF exposure, ban advertising/sale to children, and add exposure information to packaging. Precautionary standards use what I term an exclusion principle. The wide range of policy approaches can be confusing for parents/carers of children. Some consensus among advisory organizations would be helpful acknowledging that, despite extensive research, the highly complex nature of both RF-EMF and the human body, and frequent technological updates, means simple assurance of long-term safety cannot be guaranteed. Therefore, minimum exposure of children to RF-EMF is recommended. This does not indicate need for alarm, but mirrors routine health-and-safety precautions. Simple steps are suggested. ICNIRP guidelines need to urgently publish how the head, torso, and limbs' exposure limits were calculated and what safety margin was applied since this exposure, especially to the abdomen, is now dominant in many children. PMID:26091083

  2. Anomalous degradation of low-field mobility in short-channel metal-oxide-semiconductor field-effect transistors

    NASA Astrophysics Data System (ADS)

    Natori, Kenji; Iwai, Hiroshi; Kakushima, Kuniyuki

    2015-12-01

    The anomalous degradation of the low-field mobility observed in short-channel metal-oxide-semiconductor field-effect transistors is analyzed by collating various reported data in experiments and simulations. It is inferred that the degradation is not caused by the channel scattering of the carriers. The origin is proposed to be the backscattering of channel carriers on injection into the drain. The expression of the low-field mobility, including the backscattering effect, is derived. The inverse of the low-field mobility is a linear function of the inverse of channel length, the expression of which reproduces that empirically derived by Bidal's group. By fitting the expression to simulated as well as experimental data, we can estimate the value of parameters related to the channel scattering and also to the backscattering from the drain. We find that these values are in reasonable magnitude.

  3. Anomalous resistivity at the field null of the FRC: a quasi-linear expression based upon flute-type modes

    SciTech Connect

    Gerwin, R.

    1983-10-01

    In the Field-Reversed Theta Pinch (FRC) experiment, the poloidal flux is observed to be lost at a rate several times greater than classical resistivity would allow. Thus, there must be anomalous resistivity at the field null. Assuming that an electromagnetic microinstability of the flute mode type is responsible for this, we derived a general expression for the anomalous resistivity at the field null based upon a quasi-linear model of the microturbulence. This general expression does not depend upon the details of the ion-species model, for example, whether the ions are fluid or kinetic.

  4. Anomalous diffusion across the magnetic field-plasma boundary - The Porcupine artificial plasma jet

    NASA Astrophysics Data System (ADS)

    Mishin, E. V.; Kapitanov, V. Ia.; Treumann, R. A.

    1986-09-01

    Very fast magnetic field diffusion into the beam is required for observation of the nearly undisturbed penetration of the Porcupine's dense, fast and heavy ion beam into the magnetized ionospheric plasma after termination of the short adiabatic phase. The diffusion is presently attributed to a transverse electron drift current-driven electrostatic instability that is excited by the diamagnetic current flowing in the boundary layer between the injected beam and the ambient field. The anomalous collision frequencies turn out to be of the order of the local lower hybrid frequency in the dense Xe plasma. Since only a very small fraction of beam energy is dissipated in the diffusion process, no significant deceleration of the ion beam is observable.

  5. Brownian motion in a speckle light field: tunable anomalous diffusion and selective optical manipulation.

    PubMed

    Volpe, Giorgio; Volpe, Giovanni; Gigan, Sylvain

    2014-01-01

    The motion of particles in random potentials occurs in several natural phenomena ranging from the mobility of organelles within a biological cell to the diffusion of stars within a galaxy. A Brownian particle moving in the random optical potential associated to a speckle pattern, i.e., a complex interference pattern generated by the scattering of coherent light by a random medium, provides an ideal model system to study such phenomena. Here, we derive a theory for the motion of a Brownian particle in a speckle field and, in particular, we identify its universal characteristic timescale. Based on this theoretical insight, we show how speckle light fields can be used to control the anomalous diffusion of a Brownian particle and to perform some basic optical manipulation tasks such as guiding and sorting. Our results might broaden the perspectives of optical manipulation for real-life applications. PMID:24496461

  6. On the anomalous mass defect of strange stars in the Field Correlator Method

    NASA Astrophysics Data System (ADS)

    Pereira, F. I. M.

    2016-09-01

    We investigate general aspects of the mass defects of strange stars in the context of the Field Correlator Method, without magnetic field. The main parameters of the model that enter the corresponding nonperturbative equation of state of the quark gluon plasma are the gluon condensate G2 and the large distance static Q Q bar potential V1. We calculate mass defects of stellar configurations in the central density range 11 < log ⁡ρc < 18. In general, the mass defects are strongly dependent on the model parameters. For a large range of values of G2 and V1, we obtain anomalous mass defects with magnitudes around 1053 erg, of the same order of the observed energies of gamma-ray bursts and neutrino emissions in SN1987A, and of the theoretically predicted energies of the quark-novae explosions.

  7. Zero-field Dissipationless Chiral Edge Current in Quantum Anomalous Hall State

    NASA Astrophysics Data System (ADS)

    Chang, Cui-Zu; Zhao, Weiwei; Kim, Duk Y.; Wei, Peng; Jain, J. K.; Liu, Chaoxing; Chan, Moses H. W.; Moodera, Jagadeesh S.

    The quantum anomalous Hall (QAH) state is predicted to possess, at zero magnetic field, chiral edge channels that conduct spin polarized current without dissipation, and thus holds great promise for future high-performance information processing. In this talk, we will discuss our transport experiments that probe the QAH state with gate bias and temperature dependences, by local and nonlocal magnetoresistance measurements. This allows us to unambiguously distinguish the dissipationless edge transport from transport via other dissipative channels in the QAH system. Our experiments confirm a fundamental feature of the QAH state, namely the dissipationless transport by edge channels in zero applied fields, which will be crucial for future chiral interconnected electric and spintronic applications. This research is supported by the NSF Grants (DMR-1420620, Penn State MRSEC; in MIT by DMR-1207469 and the STC Center for Integrated Quantum Materials under NSF Grant DMR-1231319) and by ONR Grant N00014-13-1-0301.

  8. Brownian Motion in a Speckle Light Field: Tunable Anomalous Diffusion and Selective Optical Manipulation

    NASA Astrophysics Data System (ADS)

    Volpe, Giorgio; Volpe, Giovanni; Gigan, Sylvain

    2014-02-01

    The motion of particles in random potentials occurs in several natural phenomena ranging from the mobility of organelles within a biological cell to the diffusion of stars within a galaxy. A Brownian particle moving in the random optical potential associated to a speckle pattern, i.e., a complex interference pattern generated by the scattering of coherent light by a random medium, provides an ideal model system to study such phenomena. Here, we derive a theory for the motion of a Brownian particle in a speckle field and, in particular, we identify its universal characteristic timescale. Based on this theoretical insight, we show how speckle light fields can be used to control the anomalous diffusion of a Brownian particle and to perform some basic optical manipulation tasks such as guiding and sorting. Our results might broaden the perspectives of optical manipulation for real-life applications.

  9. Micro-instabilities and anomalous transport effects in collisionless guide field reconnection

    NASA Astrophysics Data System (ADS)

    Munoz Sepulveda, Patricio Alejandro; Büchner, Jörg; Kilian, Patrick

    2016-07-01

    It is often the case that magnetic reconnection takes place in collisionless plasmas with a current aligned guide magnetic field, such as in the Solar corona. The general characteristics of this process have been exhaustively analyzed with theory and numerical simulations, under different approximations, since some time ago. However, some consequences and properties of the secondary instabilities arising spontaneously -other than tearing instability-, and their dependence on the guide field strength, have not been completely understood yet. For this sake, we use the results of fully kinetic 2D PIC numerical simulations of guide field reconnection. By using a mean field approach for the Generalized Ohm's law that explains the balance of the reconnected electric field, we find that some of the cross-streaming and gradient driven instabilities -in the guide field case- produce an additional anomalous transport term. The latter can be interpreted as a result of the enhanced correlated electromagnetic fluctuations, leading to a slow down of the current carriers and kinetic scale turbulence. We characterize these processes on dependence on the guide field strength, and explore the causal relation with the source of free energy driving the mentioned instabilities. Finally, we show the main consequences that a fully 3D approach have on all those phenomena in contrast to the reduced 2D description.

  10. A high-charge and short-pulse RF photocathode gun for wake-field acceleration

    NASA Astrophysics Data System (ADS)

    Gai, W.; Li, X.; Conde, M.; Power, J.; Schoessow, P.

    1998-02-01

    In this paper we present a design report on 1-1/2 cell, L-Band RF photocathode gun which is capable of generating and accelerating electron beams with peak currents >10 kA. We address several critical issues of high-current RF photoinjectors such as longitudinal space charge effect, and transverse emittance growth. Unlike conventional short electron pulse generation, this design does not require magnetic pulse compression. Based on numerical simulations using SUPERFISH and PARMELA, this design will produce 100 nC beam at 18 MeV with r.m.s. bunch length 1.25 mm and normalized transverse emittance 108 mm mrad. Applications of this source beam for wake-field acceleration are also discussed.

  11. RF skin-depth measurement of UIrGe in high magnetic fields

    SciTech Connect

    Nasreen, Farzana; Altarawneh, Moaz M; Harrison, Neil; Kothapalli, Karunakar; Nakotte, Heinz; Bruck, Ekkehard

    2010-01-01

    UIrGe crystallizes in the orthorhombic TiNiSi structure and it orders anti ferromagnetically at low temperatures. Previous magnetoresistance and magnetization studies had revealed multiple metamagnetic transitions between {approx}12 T and {approx}19T. Our present studies show that RF skin depth measurement offers an alternative magnetotransport probe. A proximity detector oscillator (PDO) is used to perform the contact less RF skin-depth measurements of UIrGe in pulsed magnetic fields up to 47 T in temperature range 0.57-12 K. The frequency and amplitude shifts reflect the changes in both the real and imaginary components of the conductivity. Our results confirm that the measured frequency shifts can be related to the magnetoresistance effects.

  12. Investigation of Fully Three-Dimensional Helical RF Field Effects on TWT Beam/Circuit Interaction

    NASA Technical Reports Server (NTRS)

    Kory, Carol L.

    2000-01-01

    A fully three-dimensional (3D), time-dependent, helical traveling wave-tube (TWT) interaction model has been developed using the electromagnetic particle-in-cell (PIC) code MAFIA. The model includes a short section of helical slow-wave circuit with excitation fed by RF input/output couplers, and electron beam contained by periodic permanent magnet (PPM) focusing. All components of the model are simulated in three dimensions allowing the effects of the fully 3D helical fields on RF circuit/beam interaction to be investigated for the first time. The development of the interaction model is presented, and predicted TWT performance using 2.5D and 3D models is compared to investigate the effect of conventional approximations used in TWT analyses.

  13. Electric field induced quantum anomalous Hall effect in two-dimensional antiferromagnetic triphenyl-lead lattice

    NASA Astrophysics Data System (ADS)

    Kim, Hyun-Jung; Li, Chaokai; Feng, Ji; Zhang, Zhenyu; Cho, Jun-Hyung

    The tuning of topological states is of significant fundamental and practical importance in contemporary condensed matter physics, for which the extension to two-dimensional (2D) organometallic systems is particularly attractive. Using first-principles calculations, we find that a 2D hexagonal triphenyl-lead lattice composed of only main group elements is susceptible to a magnetic instability, characterized by a antiferromagnetic (AFM) insulating state with a renormalized valley gaps with gap difference of 24 meV due to the spin and valley coupling. This AFM state will be subject to a anomalous valley Hall effect under the action of Berry curvature-induced spin and valley currents via, for example, injection of circularly polarized light. Furthermore, such a AFM band insulator can be tuned into a topologically nontrivial quantum anomalous Hall state with a Chern number of one by the application of an out-of-plane electric field. These findings further enrich our understanding of 2D hexagonal organometallic lattices for potential applications in spintronics and valleytronics.

  14. A Theory for the RF Surface Field for Various Metals at the Destructive Breakdown Limit

    SciTech Connect

    Wilson, Perry B.

    2006-11-27

    By destructive breakdown we mean a breakdown event that results in surface melting over a macroscopic area in a high E-field region of an accelerator structure. A plasma forms over the molten area, bombarding the surface with an intense ion current ({approx}108 A/cm2), equivalent to a pressure of about a thousand Atmospheres. This pressure in turn causes molten copper to migrate away from the iris tip, resulting in measurable changes in the iris shape. The breakdown process can be roughly divided into four stages: (1) the formation of ''plasma spots'' at field emission sites, each spot leaving a crater-like footprint; (2) crater clustering, and the formation of areas with hundreds of overlapping craters; (3) surface melting in the region of a crater cluster; (4) the process after surface melting that leads to destructive breakdown. The physics underlying each of these stages is developed, and a comparison is made between the theory and experimental evidence whenever possible. The key to preventing breakdown lies in stage (3). A single plasma spot emits a current of several amperes, a portion of which returns to impact the surrounding area with a power density on the order 107 Watt/cm2. This power density is not quite adequate to melt the surrounding surface on a time scale short compared to the rf pulse length. In a crater field, however, the impact areas from multiple plasma spots overlap to provide sufficient power density for surface melting over an area on the order of 0.1 mm2 or more. The key to preventing breakdown is to choose an iris tip material that requires the highest power density (proportional to the square of the rf surface field) for surface melting, taking into account the penetration depth of the impacting electrons. The rf surface field required for surface melting (relative to copper) has been calculated for a large number elementary metals, plus stainless-steel and carbon.

  15. RF heating due to conductive wires during MRI depends on the phase distribution of the transmit field.

    PubMed

    Yeung, Christopher J; Susil, Robert C; Atalar, Ergin

    2002-12-01

    In many studies concerning wire heating during MR imaging, a "resonant wire length" that maximizes RF heating is determined. This may lead to the nonintuitive conclusion that adding more wire, so as to avoid this resonant length, will actually improve heating safety. Through a theoretical analysis using the method of moments, we show that this behavior depends on the phase distribution of the RF transmit field. If the RF transmit field has linear phase, with slope equal to the real part of the wavenumber in the tissue, long wires always heat more than short wires. In order to characterize the intrinsic safety of a device without reference to a specific body coil design, this maximum-tip heating phase distribution must be considered. Finally, adjusting the phase distribution of the electric field generated by an RF transmit coil may lead to an "implant-friendly" coil design. PMID:12465125

  16. Hypersensitivity to RF fields emitted from CDMA cellular phones: a provocation study.

    PubMed

    Nam, Ki Chang; Lee, Ju Hyung; Noh, Hyung Wook; Cha, Eun Jong; Kim, Nam Hyun; Kim, Deok Won

    2009-12-01

    With the number of cellular phone users rapidly increasing, there is a considerable amount of public concern regarding the effects that electromagnetic fields (EMFs) from cellular phones have on health. People with self-attributed electromagnetic hypersensitivity (EHS) complain of subjective symptoms such as headaches, insomnia, and memory loss, and attribute these symptoms to radio frequency (RF) radiation from cellular phones and/or base stations. However, EHS is difficult to diagnose because it relies on a person's subjective judgment. Various provocation studies have been conducted on EHS caused by Global System for Mobile Communications (GSM) phones in which heart rate and blood pressure or subjective symptoms were investigated. However, there have been few sham-controlled provocation studies on EHS with Code Division Multiple Access (CDMA) phones where physiological parameters, subjective symptoms, and perception of RF radiation for EHS and non-EHS groups were simultaneously investigated. In this study, two volunteer groups of 18 self-reported EHS and 19 non-EHS persons were tested for both sham and real RF exposure from CDMA cellular phones with a 300 mW maximum exposure that lasted half an hour. We investigated not only the physiological parameters such as heart rate, respiration rate, and heart rate variability (HRV), but also various subjective symptoms and the perception of EMF. In conclusion, RF exposure did not have any effects on physiological parameters or subjective symptoms in either group. As for EMF perception, there was no evidence that the EHS group better perceived EMF than the non-EHS group. PMID:19551766

  17. Precise Quantization of the Anomalous Hall Effect near Zero Magnetic Field.

    PubMed

    Bestwick, A J; Fox, E J; Kou, Xufeng; Pan, Lei; Wang, Kang L; Goldhaber-Gordon, D

    2015-05-01

    We report a nearly ideal quantum anomalous Hall effect in a three-dimensional topological insulator thin film with ferromagnetic doping. Near zero applied magnetic field we measure exact quantization in the Hall resistance to within a part per 10 000 and a longitudinal resistivity under 1  Ω per square, with chiral edge transport explicitly confirmed by nonlocal measurements. Deviations from this behavior are found to be caused by thermally activated carriers, as indicated by an Arrhenius law temperature dependence. Using the deviations as a thermometer, we demonstrate an unexpected magnetocaloric effect and use it to reach near-perfect quantization by cooling the sample below the dilution refrigerator base temperature in a process approximating adiabatic demagnetization refrigeration. PMID:26001016

  18. Measurement of RF electric field in high- β plasma using a Pockels detector in magnetosphere plasma confinement device RT-1

    NASA Astrophysics Data System (ADS)

    Mushiake, Toshiki; Nishiura, M.; Yoshida, Z.; Yano, Y.; Kawazura, Y.; Saitoh, H.; Yamasaki, M.; Kashyap, A.; Takahashi, N.; Nakatsuka, M.; Fukuyama, Atsushi

    2015-11-01

    The magnetosphere plasma confinement device RT-1 generates a dipole magnetic field that can confine high- β plasma by using a levitated superconducting coil. So far it is reported that high temperature electrons (up to 50keV) exist and that the local electron βe value exceeds more than 100%. However, the ion β value βi remains low in the present high- β state. To realize a high-βi state, we have started Ion Cyclotron Heating (ICH) experiments. For efficient ICH in a dipole topology, it is important to measure RF electric fields and characterize the propagation of RF waves in plasmas. On this viewpoint, we started direct measurement of local RF electric fields in RT-1 with a Pockels sensor system. A non-linear optical crystal in the Pockels sensor produces birefringence in an ambient electric field. The refractive index change of the birefringence is proportional to the applied electric field strength, which can be used to measure local electric fields. RF electric field distribution radiated from an ICH antenna was measured inside RT-1 in air, and was compared with numerical results calculated by TASK code. Results on the measurement of electric field distribution in high- β plasma and evaluation of the absorbed RF power into ions will be reported. Supported by JSPS KAKENHI Grant Numbers 23224014.

  19. Simulation of ITER full-field ICWC scenario in JET: RF physics aspects

    NASA Astrophysics Data System (ADS)

    Lyssoivan, A.; Douai, D.; Koch, R.; Ongena, J.; Philipps, V.; Schüller, F. C.; Van Eester, D.; Wauters, T.; Blackman, T.; Bobkov, V.; Brezinsek, S.; de la Cal, E.; Durodié, F.; Gauthier, E.; Gerbaud, T.; Graham, M.; Jachmich, S.; Joffrin, E.; Kreter, A.; Kyrytsya, V.; Lerche, E.; Lomas, P.; Louche, F.; Maslov, M.; Mayoral, M.-L.; Moiseenko, V.; Monakhov, I.; Pankratov, I.; Paul, M. K.; Pitts, R. A.; Plyusnin, V.; Sergienko, G.; Shimada, M.; Vdovin, V. L.; contributors, JET-EFDA

    2012-07-01

    ITER as a superconducting fusion machine needs efficient wall conditioning techniques for application in the presence of the permanent high toroidal magnetic field for (i) reducing the in-vessel impurity content, (ii) controlling the surface hydrogen isotopic ratio and (iii) mitigating the in-vessel long-term tritium inventory build-up. Encouraging results recently obtained with ion-cyclotron wall conditioning (ICWC) in the present-day tokamaks and stellarators have raised ICWC to the status of one of the most promising techniques available to ITER for routine inter-pulse and overnight conditioning with the ITER main ICRF heating system in the presence of the permanent high toroidal magnetic field. This paper is dedicated to a milestone experiment in ICWC research: the first simulation of ICWC operation in an equivalent ITER full-field scenario and the assessment of the wall conditioning effect on the carbon wall in the largest present-day tokamak JET. In addition, we address in this paper the following topics: (i) an analysis of the radio frequency (RF) physics of ICWC discharges, (ii) the optimization of the operation of ICRF antennas for plasma startup and (iii) an outlook for the performance of ICWC in ITER using the ICRF heating system. Important operational aspects of the conventional ICRF heating system in JET (the so-called A2 antenna system) for use in the ICWC mode are highlighted: (i) the ability of the antenna to ignite the cleaning discharge safely and reliably in different gases, (ii) the capacity of the antennas to couple a large fraction of the RF generator power (>50%) to low-density (≈1016-1018 m-3) plasmas and (iii) the ICRF absorption schemes aimed at improved RF plasma homogeneity and enhanced conditioning effect. Successful optimization of the JET-ICWC discharge parameters (BT = 3.3 T, f = 25 MHz) resulted in a reliable operation of the JET A2 antennas and a high conditioning efficiency in a scenario imitating closely ITER full-field

  20. A simplified HTc rf SQUID to analyze the human cardiac magnetic field

    SciTech Connect

    Zhang, Chen E-mail: tfk616@sina.com E-mail: zizhaogan@pku.edu.cn; Tang, Fakuan E-mail: tfk616@sina.com E-mail: zizhaogan@pku.edu.cn; Ma, Ping E-mail: tfk616@sina.com E-mail: zizhaogan@pku.edu.cn; Gan, Zizhao E-mail: tfk616@sina.com E-mail: zizhaogan@pku.edu.cn

    2014-12-15

    We have developed a four-channel high temperature radio-frequency superconducting quantum interference device (HT{sub c} rf SQUID) in a simple magnetically shielded room (MSR) that can be used to analyze the cardiac magnetic field. It is more robust and compact than existing systems. To achieve the high-quality magnetocardiographic signal, we explored new adaptive software gradiometry technology constructed by the first-order axial gradiometer with a baseline of 80mm, which can adjust its performance timely with the surrounding conditions. The magnetic field sensitivity of each channel was less than 100fT/√Hz in the white noise region. Especially, in the analysis of MCG signal data, we proposed the total transient mapping (TTM) technique to visualize current density map (CDM), then we focused to observe the time-varying behavior of excitation propagation and estimated the underlying currents at T wave. According to the clear 3D imaging, isomagnetic field and CDM, the position and distribution of a current source in the heart can be visualized. It is believed that our four-channel HT{sub c} rf SQUID magnetometer based on biomagnetic system is available to detect MCG signals with sufficient signal-to-noise (SNR) ratio. In addition, the CDM showed the macroscopic current activation pattern, in a way, it has established strong underpinnings for researching the cardiac microscopic movement mechanism and opening the way for its use in clinical diagnosis.

  1. A simplified HTc rf SQUID to analyze the human cardiac magnetic field

    NASA Astrophysics Data System (ADS)

    Zhang, Chen; Tang, Fakuan; Ma, Ping; Gan, Zizhao

    2014-12-01

    We have developed a four-channel high temperature radio-frequency superconducting quantum interference device (HTc rf SQUID) in a simple magnetically shielded room (MSR) that can be used to analyze the cardiac magnetic field. It is more robust and compact than existing systems. To achieve the high-quality magnetocardiographic signal, we explored new adaptive software gradiometry technology constructed by the first-order axial gradiometer with a baseline of 80mm, which can adjust its performance timely with the surrounding conditions. The magnetic field sensitivity of each channel was less than 100fT/√Hz in the white noise region. Especially, in the analysis of MCG signal data, we proposed the total transient mapping (TTM) technique to visualize current density map (CDM), then we focused to observe the time-varying behavior of excitation propagation and estimated the underlying currents at T wave. According to the clear 3D imaging, isomagnetic field and CDM, the position and distribution of a current source in the heart can be visualized. It is believed that our four-channel HTc rf SQUID magnetometer based on biomagnetic system is available to detect MCG signals with sufficient signal-to-noise (SNR) ratio. In addition, the CDM showed the macroscopic current activation pattern, in a way, it has established strong underpinnings for researching the cardiac microscopic movement mechanism and opening the way for its use in clinical diagnosis.

  2. Strut Shaping of 34m Beam Waveguide Antenna for Reductions in Near-Field RF and Noise Temperature

    NASA Technical Reports Server (NTRS)

    Khayatian, Behrouz; Hoppe, Daniel J.; Britcliffe, Michael J.; Gama, Eric

    2012-01-01

    Strut shaping of NASA's Deep Space Network (DSN) 34m Beam Waveguide (BWG) antenna has been implemented to reduce near-field RF exposure while improving the antenna noise temperature. Strut shaping was achieved by introducing an RF shield that does not compromise the structural integrity of the existing antenna. Reduction in the RF near-field level will compensate for the planned transmit power increase of the antenna from 20 kW to 80 kW while satisfying safety requirements for RF exposure. Measured antenna noise temperature was also improved by as much as 1.5 K for the low elevation angles and 0.5 K in other areas.

  3. Experimental Demonstration of Anomalous Field Enhancement in All-Dielectric Transition Magnetic Metamaterials

    NASA Astrophysics Data System (ADS)

    Sun, Jingbo; Liu, Xiaoming; Zhou, Ji; Kudyshev, Zhaxylyk; Litchinitser, Natalia M.

    2015-11-01

    Anomalous field enhancement accompanied by resonant absorption phenomenon was originally discussed in the context of plasma physics and in applications related to radio-communications between the ground and spacecraft returning to Earth. Indeed, there is a critical period of time when all communications are lost due to the reflection/absorption of electromagnetic waves by the sheath of plasma created by a high speed vehicle re-entering the atmosphere. While detailed experimental studies of these phenomena in space are challenging, the emergence of electromagnetic metamaterials enables researchers exceptional flexibility to study them in the laboratory environment. Here, we experimentally demonstrated the strong localized field enhancement of magnetic field for an electromagnetic wave propagating in Mie-resonance-based inhomogeneous metamaterials with magnetic permeability gradually changing from positive to negative values. Although these experiments were performed in the microwave frequency range, the proposed all-dielectric approach to transition metamaterials can be extended to terahertz, infrared, and visible frequencies. We anticipate that these results, besides most basic science aspects, hold the potential for numerous applications, including low-intensity nonlinear transformation optics, topological photonics, and the broader area of surface and interface science.

  4. Experimental Demonstration of Anomalous Field Enhancement in All-Dielectric Transition Magnetic Metamaterials

    PubMed Central

    Sun, Jingbo; Liu, Xiaoming; Zhou, Ji; Kudyshev, Zhaxylyk; Litchinitser, Natalia M.

    2015-01-01

    Anomalous field enhancement accompanied by resonant absorption phenomenon was originally discussed in the context of plasma physics and in applications related to radio-communications between the ground and spacecraft returning to Earth. Indeed, there is a critical period of time when all communications are lost due to the reflection/absorption of electromagnetic waves by the sheath of plasma created by a high speed vehicle re-entering the atmosphere. While detailed experimental studies of these phenomena in space are challenging, the emergence of electromagnetic metamaterials enables researchers exceptional flexibility to study them in the laboratory environment. Here, we experimentally demonstrated the strong localized field enhancement of magnetic field for an electromagnetic wave propagating in Mie-resonance-based inhomogeneous metamaterials with magnetic permeability gradually changing from positive to negative values. Although these experiments were performed in the microwave frequency range, the proposed all-dielectric approach to transition metamaterials can be extended to terahertz, infrared, and visible frequencies. We anticipate that these results, besides most basic science aspects, hold the potential for numerous applications, including low-intensity nonlinear transformation optics, topological photonics, and the broader area of surface and interface science. PMID:26531855

  5. Spin-Down Mechanisms in Neutron Stars with ``Anomalous'' Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Rogers, Adam; Safi-Harb, Samar

    2015-08-01

    Energy losses from isolated neutron stars are attributed to a number of factors, the most common assumption being the emission of electromagnetic radiation from a rotating point-like magnetic dipole in vacuum. This energy loss mechanism predicts a braking index n = 3, which is not observed in highly magnetized neutron stars. Despite this fact, the assumptions of a dipole field and rapid early rotation are often assumed a priori. This typically causes a discrepancy in the characteristic age of these objects and the age of their associated Supernova Remnants (SNRs). In this work we consider neutron stars with ``anomalous'' magnetic fields - namely magnetars, high-B radio pulsars, and the Central Compact Objects (proposed to be `anti-magnetars’) that are securely associated with SNRs. Without making any assumptions about the initial spin periods of these objects and by constraining the SNR ages to match their associated pulsar ages, we compare the predictions of distinct energy loss mechanisms, such as field decay and the emission of relativistic winds using all observed data on the braking indices. This study has important implications on the proposed emission models for these exotic objects and helps in resolving the PSR-SNR age discrepancy.

  6. Experimental Demonstration of Anomalous Field Enhancement in All-Dielectric Transition Magnetic Metamaterials.

    PubMed

    Sun, Jingbo; Liu, Xiaoming; Zhou, Ji; Kudyshev, Zhaxylyk; Litchinitser, Natalia M

    2015-01-01

    Anomalous field enhancement accompanied by resonant absorption phenomenon was originally discussed in the context of plasma physics and in applications related to radio-communications between the ground and spacecraft returning to Earth. Indeed, there is a critical period of time when all communications are lost due to the reflection/absorption of electromagnetic waves by the sheath of plasma created by a high speed vehicle re-entering the atmosphere. While detailed experimental studies of these phenomena in space are challenging, the emergence of electromagnetic metamaterials enables researchers exceptional flexibility to study them in the laboratory environment. Here, we experimentally demonstrated the strong localized field enhancement of magnetic field for an electromagnetic wave propagating in Mie-resonance-based inhomogeneous metamaterials with magnetic permeability gradually changing from positive to negative values. Although these experiments were performed in the microwave frequency range, the proposed all-dielectric approach to transition metamaterials can be extended to terahertz, infrared, and visible frequencies. We anticipate that these results, besides most basic science aspects, hold the potential for numerous applications, including low-intensity nonlinear transformation optics, topological photonics, and the broader area of surface and interface science. PMID:26531855

  7. Development of the Shielding Materials Having the Highly Orientation Characteristics in the RF Magnetic Field

    NASA Astrophysics Data System (ADS)

    Nishikubo, Tokoh; Itoh, Mineo

    The conventional electromagnetic shielding technique is all but impossible to fundamental solution of the problems in the information and communication fields, such as virtual image for radar. Namely, it is necessary to receive a required electromagnetic wave as the information signal, and to shield a needless electromagnetic wave as the noise. the present research has developed the carbon, copper, ferrite, and BPSCCO plates, as the typical shielding material, having the orientation characteristics in the RF (radio frequency) magnetic field. To exhibit the orientation characteristics in the plane wave, it has formed the slit on the surface of typical shielding materials; termed the slit plate. For example, the value of RF magnetic shielding degree SDHP of slit carbon plate for holding the slit perpendicularly to the ground increased with frequency in the region from 1 MHz (7 dB) to 3 GHz (70 dB). And, the value of SDHH when holding the slit horizontally is indicated an average value of approximately 10 dB in this frequency region. That is, the difference values, SDHP-SDHH, indicated the orientation characteristics. Experimental results revealed several characteristics of the slit plates that include the influences of orientation characteristics on the slit length, slit width, and slit number. In the present paper, it was succeeded to improved the difference average value of approximately 35 dB for SDHP-SDHH, by the sandwich of slit ferrite plate over a slit carbon plate, in the civilian communication frequency region from 1 MHz to 3 GHz. In addition, important criteria are discussed for the design of an effective RF magnetic shielding plate having orientation characteristics.

  8. Vacuum effects in magnetic field with with account for fermion anomalous magnetic moment and axial-vector interaction

    NASA Astrophysics Data System (ADS)

    Bubnov, Andrey; Gubina, Nadezda; Zhukovsky, Vladimir

    2016-05-01

    We study vacuum polarization effects in the model of Dirac fermions with additional interaction of an anomalous magnetic moment with an external magnetic field and fermion interaction with an axial-vector condensate. The proper time method is used to calculate the one-loop vacuum corrections with consideration for different configurations of the characteristic parameters of these interactions.

  9. Effect of low-frequency ambient magnetic fields on the control unit and RF head of a commercial SQUID magnetometer

    NASA Technical Reports Server (NTRS)

    Marcus, C. M.

    1984-01-01

    The control unit and RF head of the SHE model 330XRFSQUID system are shown to be sensitive to ambient ac magnetic fields below 1 HZ, which cause the appearance of false signals corresponding to a magnetometer signal of 0.000001 phi(0) per gauss of field applied. The control unit shows a sensitivity that is linear with frequency, suggesting that the signal is generated by Faraday induction. In contrast, the RF head response is independent of frequency and shows a strong second-harmonic coversion. This response may be due to the magnetic field sensitivity of the ferrite core inductor in the tuned amplifier of the RF head. These signals induced by ambient fields are a potential source of error in Stanford's Relativity Gyroscope experiment, which uses SQUID's on board a rolling satellite as part of the gyroscope readout system. The extent of the magnetic field sensitivity in these components necessitates the use of additional magnetic shielding aboard the satellite.

  10. Heavy ions acceleration in RF wells of 2-frequency electromagnetic field and in the inverted FEL

    SciTech Connect

    Dzergach, A.I.; Kabanov, V.S.; Nikulin, M.G.; Vinogradov, S.V.

    1995-03-01

    Last results of the study of heavy ions acceleration by electrons trapped in moving 2-frequency 3-D RF wells are described. A linearized theoretical model of ions acceleration in a polarized spheroidal plasmoid is proposed. The equilibrium state of this plasmoid is described by the modified microcanonical distribution of the Courant-Snyder invariant ({open_quotes}quasienergy{close_quotes} of electrons). Some new results of computational simulation of the acceleration process are given. The method of computation takes into account the given cylindrical field E{sub 011}({var_phi},r,z) and the self fields of electrons and ions. The results of the computation at relatively short time intervals confirm the idea and estimated parameters of acceleration. The heavy ion accelerator using this principle may be constructed with the use of compact cm band iris-loaded and biperiodical waveguides with double-sided 2-frequency RF feeding. It can accelerate heavy ions with a charge number Z{sub i} from small initial energies {approximately} 50 keV/a.u. with the rate {approximately} Z{sub i} {center_dot} 10 MeV/m. Semirelativistic ions may be accelerated with similar rate also in the inverted FEL.

  11. Magnetization reversal of a single cobalt cluster using a RF field pulse

    NASA Astrophysics Data System (ADS)

    Tamion, A.; Raufast, C.; Bonet, E.; Dupuis, V.; Fournier, T.; Crozes, T.; Bernstein, E.; Wernsdorfer, W.

    2010-05-01

    Technological improvements require the understanding of dynamical magnetization reversal processes at the nanosecond time scales. In this paper, we present the first magnetization reversal measurements performed on a single cobalt cluster (counting only a thousand of spins), using the micro-superconducting quantum interference device (SQUID) technique by applying a constant magnetic field combined with a radio-frequency (RF) field pulse. First of all, we present the different technical steps necessary to detect the magnetic reversals at low temperature ( T=35 mK) of a well-defined nanoparticle prepared by low energy clusters beam deposition (LECBD). We previously showed that the three-dimensional (3D)-switching Stoner-Wohlfarth astroid represents the magnetic anisotropy of the nanoparticle. Then, an improved device coupled with a gold stripe line, allow us to reverse such macrospin, using a RF pulse. A qualitative understanding of the magnetization reversal by non-linear resonance has been obtained with the Landau-Lifschitz-Gilbert (LLG) equation.

  12. Effects of Anomalous Electron Cross-Field Transport in a Low Temperature Magnetized Plasma

    NASA Astrophysics Data System (ADS)

    Raitses, Yevgeny

    2014-10-01

    The application of the magnetic field in a low pressure plasma can cause a spatial separation of low and high energy electrons. This so-called magnetic filter effect is used for many plasma applications, including ion and neutral beam sources, plasma processing of semiconductors and nanomaterials, and plasma thrusters. In spite of successful practical applications, the magnetic filter effect is not well understood. In this work, we explore this effect by characterizing the electron and ion energy distribution functions in a plasma column with crossed electric and magnetic fields. Experimental results revealed a strong dependence of spatial variations of plasma properties on the gas pressure. For xenon and argon gases, below ~ 1 mtorr, the increase of the magnetic field leads to a more uniform profile of the electron temperature. This surprising result is due to anomalously high electron cross-field transport that causes mixing of hot and cold electrons. High-speed imaging and probe measurements revealed a coherent structure rotating in E cross B direction with frequency of a few kHz. Theory and simulations describing this rotating structure has been developed and points to ionization and electrostatic instabilities as their possible cause. Similar to spoke oscillations reported for Hall thrusters, this rotating structure conducts the large fraction of the cross-field current. The use of segmented electrodes with an electrical feedback control is shown to mitigate these oscillations. Finally, a new feature of the spoke phenomenon that has been discovered, namely a sensitive dependence of the rotating oscillations on the gas pressure, can be important for many applications. This work was supported by DOE Contract DE-AC02-09CH11466.

  13. A Theory for the RF Surface Field for Various Metals at the Destructive Breakdown Limit

    SciTech Connect

    Wilson, Perry B.; /SLAC

    2007-03-06

    By destructive breakdown we mean a breakdown event that results in surface melting over a macroscopic area in a high E-field region of an accelerator structure. A plasma forms over the molten area, bombarding the surface with an intense ion current ({approx} 10{sup 8} A/cm{sup 2}), equivalent to a pressure of about a thousand Atmospheres. This pressure in turn causes molten copper to migrate away from the iris tip, resulting in measurable changes in the iris shape. The breakdown process can be roughly divided into four stages: (1) the formation of ''plasma spots'' at field emission sites, each spot leaving a crater-like footprint; (2) crater clustering, and the formation of areas with hundreds of overlapping craters; (3) surface melting in the region of a crater cluster; (4) the process after surface melting that leads to destructive breakdown. The physics underlying each of these stages is developed, and a comparison is made between the theory and experimental evidence whenever possible. The key to preventing breakdown lies in stage (3). A single plasma spot emits a current of several amperes, a portion of which returns to impact the surrounding area with a power density on the order 10{sup 7} Watt/cm{sup 2}. This power density is not quite adequate to melt the surrounding surface on a time scale short compared to the rf pulse length. In a crater field, however, the impact areas from multiple plasma spots overlap to provide sufficient power density for surface melting over an area on the order of 0.1 mm{sup 2} or more. The key to preventing breakdown is to choose an iris tip material that requires the highest power density (proportional to the square of the rf surface field) for surface melting, taking into account the penetration depth of the impacting electrons. The rf surface field required for surface melting (relative to copper) has been calculated for a large number elementary metals, plus stainless-steel and carbon.

  14. ADX: a high field, high power density, advanced divertor and RF tokamak

    NASA Astrophysics Data System (ADS)

    LaBombard, B.; Marmar, E.; Irby, J.; Terry, J. L.; Vieira, R.; Wallace, G.; Whyte, D. G.; Wolfe, S.; Wukitch, S.; Baek, S.; Beck, W.; Bonoli, P.; Brunner, D.; Doody, J.; Ellis, R.; Ernst, D.; Fiore, C.; Freidberg, J. P.; Golfinopoulos, T.; Granetz, R.; Greenwald, M.; Hartwig, Z. S.; Hubbard, A.; Hughes, J. W.; Hutchinson, I. H.; Kessel, C.; Kotschenreuther, M.; Leccacorvi, R.; Lin, Y.; Lipschultz, B.; Mahajan, S.; Minervini, J.; Mumgaard, R.; Nygren, R.; Parker, R.; Poli, F.; Porkolab, M.; Reinke, M. L.; Rice, J.; Rognlien, T.; Rowan, W.; Shiraiwa, S.; Terry, D.; Theiler, C.; Titus, P.; Umansky, M.; Valanju, P.; Walk, J.; White, A.; Wilson, J. R.; Wright, G.; Zweben, S. J.

    2015-05-01

    The MIT Plasma Science and Fusion Center and collaborators are proposing a high-performance Advanced Divertor and RF tokamak eXperiment (ADX)—a tokamak specifically designed to address critical gaps in the world fusion research programme on the pathway to next-step devices: fusion nuclear science facility (FNSF), fusion pilot plant (FPP) and/or demonstration power plant (DEMO). This high-field (⩾6.5 T, 1.5 MA), high power density facility (P/S ˜ 1.5 MW m-2) will test innovative divertor ideas, including an ‘X-point target divertor’ concept, at the required performance parameters—reactor-level boundary plasma pressures, magnetic field strengths and parallel heat flux densities entering into the divertor region—while simultaneously producing high-performance core plasma conditions that are prototypical of a reactor: equilibrated and strongly coupled electrons and ions, regimes with low or no torque, and no fuelling from external heating and current drive systems. Equally important, the experimental platform will test innovative concepts for lower hybrid current drive and ion cyclotron range of frequency actuators with the unprecedented ability to deploy launch structures both on the low-magnetic-field side and the high-magnetic-field side—the latter being a location where energetic plasma-material interactions can be controlled and favourable RF wave physics leads to efficient current drive, current profile control, heating and flow drive. This triple combination—advanced divertors, advanced RF actuators, reactor-prototypical core plasma conditions—will enable ADX to explore enhanced core confinement physics, such as made possible by reversed central shear, using only the types of external drive systems that are considered viable for a fusion power plant. Such an integrated demonstration of high-performance core-divertor operation with steady-state sustainment would pave the way towards an attractive pilot plant, as envisioned in the ARC concept

  15. Rod-filter-field optimization of the J-PARC RF-driven H- ion source

    NASA Astrophysics Data System (ADS)

    Ueno, A.; Ohkoshi, K.; Ikegami, K.; Takagi, A.; Yamazaki, S.; Oguri, H.

    2015-04-01

    In order to satisfy the Japan Proton Accelerator Research Complex (J-PARC) second-stage requirements of an H- ion beam of 60mA within normalized emittances of 1.5πmm•mrad both horizontally and vertically, a flat top beam duty factor of 1.25% (500μs×25Hz) and a life-time of longer than 1month, the J-PARC cesiated RF-driven H- ion source was developed by using an internal-antenna developed at the Spallation Neutron Source (SNS). Although rod-filter-field (RFF) is indispensable and one of the most beam performance dominative parameters for the RF-driven H- ion source with the internal-antenna, the procedure to optimize it is not established. In order to optimize the RFF and establish the procedure, the beam performances of the J-PARC source with various types of rod-filter-magnets (RFMs) were measured. By changing RFM's gap length and gap number inside of the region projecting the antenna inner-diameter along the beam axis, the dependence of the H- ion beam intensity on the net 2MHz-RF power was optimized. Furthermore, the fine-tuning of RFM's cross-section (magnetmotive force) was indispensable for easy operation with the temperature (TPE) of the plasma electrode (PE) lower than 70°C, which minimizes the transverse emittances. The 5% reduction of RFM's cross-section decreased the time-constant to recover the cesium effects after an slightly excessive cesiation on the PE from several 10 minutes to several minutes for TPE around 60°C.

  16. Frequency shifts in NIST Cs primary frequency standards due to transverse rf field gradients

    NASA Astrophysics Data System (ADS)

    Ashby, Neil; Barlow, Stephan; Heavner, Thomas; Jefferts, Steven

    2015-03-01

    A single-particle Green's function (propagator) is introduced to study the deflection of laser-cooled cesium atoms in an atomic fountain due to microwave magnetic field gradients in the Ramsey TE011 cavity. The deflection results in a state-dependent loss of atoms at apertures in the physics package, resulting in a frequency bias. A model accounting only for motion in one dimension transverse to the symmetry axis of the fountain is discussed in detail and then generalized to two transverse dimensions. Results for fractional frequency shifts due to transverse field gradients are computed for NIST-F1 and NIST-F2 cesium fountains. The shifts are found to be negligible except in cases of higher rf power applied to the cavities.

  17. A numerical study of field plate configurations in RF SOI LDMOS transistors

    NASA Astrophysics Data System (ADS)

    Cortés, I.; Roig, J.; Flores, D.; Urresti, J.; Hidalgo, S.; Rebollo, J.

    2006-02-01

    The effect of the source field plate architecture on the static and dynamic electrical performances of SOI LDMOS transistors for RF applications is analysed in this paper. Three architectures are envisaged: source field plate SFP, extended gate field plate and independently biased field plate. Moreover, two different drift diffusion profiles are considered: shallow SDD and deep doped DDD diffusion. The resultant drift region is analytically modelled and the impact of geometrical and technological parameters on the transconductance value is determined by means of numerical simulation techniques. Finally, the dependence of the LDMOS capacitances on the field plate configuration is also studied. Simulation results show the trade-off between reliability and transconductance in each field plate configuration. In spite of the power efficiency improvement, the field plate biasing can significantly degrade the SOI LDMOS performances due to hot-carrier and self-heating effects. On the contrary, the SFP configuration leads to an enhanced reliability at the cost of the on-state resistance increase. The SFP structure with deep doped drift (DDD) diffusion provides the best performances in terms of cut-off frequency and self-heating degradation.

  18. Effect of External Magnetic Fields on the Operation of RF Cavities

    SciTech Connect

    Stratakis, D.; Berg, J.; Gallardo, J.C.; Palmer, R. B.

    2010-12-01

    Recent experiments have shown severe surface damage and a reduction of the maximum accelerating gradient for an rf cavity that is operating under external magnetic fields. This implies that serious problems may occur in lattices where rf cavities and external magnetic fields coexist, such as those of the proposed neutrino factory and muon collider. Although existing data suggest that this magnetic field dependent breakdown is associated with the emission of electrons from locally enhanced field regions on the cavity surface, the mechanism that drives this effect is not yet well understood. Here, we show that such field emitted electrons are accelerated by the cavity and focused by the magnetic field to the other side of the cavity where they heat its surface. We show that if the magnetic field is strong, significant surface deformation can occur that eventually could limit the accelerating gradient of the cavity. Results of our model are compared to the existing experimental data from an 805 MHz cavity. The geometry of the pillbox cavity in our case is more complicated, and the analysis depends on the electron energies, focused dimensions, and angle of impact, but damage may reasonably be expected with similar cyclical heating above 40 C. However, it is not yet known what the mechanism is for such surface damage to cause a cavity to breakdown. One possibility is that if electrons are focused on a location with a high surface gradient, then the local damage will generate new asperities with higher FN enhancement factors, thus initiating breakdown. While our preliminary analysis offers some quantification on the effects of the magnetic fields on the cavity's operation, other theoretical issues were not addressed. For instance, emission from secondary electrons was disregarded, the asperity was placed on axis, the magnetic field was assumed as uniform, the thermal-diffusion calculation ignored the shape of the rise time, and adopted an approximate calculation. On the

  19. Anomalous diffusion of field lines and charged particles in Arnold-Beltrami-Childress force-free magnetic fields

    NASA Astrophysics Data System (ADS)

    Ram, Abhay K.; Dasgupta, Brahmananda; Krishnamurthy, V.; Mitra, Dhrubaditya

    2014-07-01

    The cosmic magnetic fields in regions of low plasma pressure and large currents, such as in interstellar space and gaseous nebulae, are force-free in the sense that the Lorentz force vanishes. The three-dimensional Arnold-Beltrami-Childress (ABC) field is an example of a force-free, helical magnetic field. In fluid dynamics, ABC flows are steady state solutions of the Euler equation. The ABC magnetic field lines exhibit a complex and varied structure that is a mix of regular and chaotic trajectories in phase space. The characteristic features of field line trajectories are illustrated through the phase space distribution of finite-distance and asymptotic-distance Lyapunov exponents. In regions of chaotic trajectories, an ensemble-averaged variance of the distance between field lines reveals anomalous diffusion—in fact, superdiffusion—of the field lines. The motion of charged particles in the force-free ABC magnetic fields is different from the flow of passive scalars in ABC flows. The particles do not necessarily follow the field lines and display a variety of dynamical behavior depending on their energy, and their initial pitch-angle. There is an overlap, in space, of the regions in which the field lines and the particle orbits are chaotic. The time evolution of an ensemble of particles, in such regions, can be divided into three categories. For short times, the motion of the particles is essentially ballistic; the ensemble-averaged, mean square displacement is approximately proportional to t2, where t is the time of evolution. The intermediate time region is defined by a decay of the velocity autocorrelation function—this being a measure of the time after which the collective dynamics is independent of the initial conditions. For longer times, the particles undergo superdiffusion—the mean square displacement is proportional to tα, where α > 1, and is weakly dependent on the energy of the particles. These super-diffusive characteristics, both of magnetic

  20. Anomalous diffusion of field lines and charged particles in Arnold-Beltrami-Childress force-free magnetic fields

    SciTech Connect

    Ram, Abhay K.; Dasgupta, Brahmananda; Krishnamurthy, V.; Mitra, Dhrubaditya

    2014-07-15

    The cosmic magnetic fields in regions of low plasma pressure and large currents, such as in interstellar space and gaseous nebulae, are force-free in the sense that the Lorentz force vanishes. The three-dimensional Arnold-Beltrami-Childress (ABC) field is an example of a force-free, helical magnetic field. In fluid dynamics, ABC flows are steady state solutions of the Euler equation. The ABC magnetic field lines exhibit a complex and varied structure that is a mix of regular and chaotic trajectories in phase space. The characteristic features of field line trajectories are illustrated through the phase space distribution of finite-distance and asymptotic-distance Lyapunov exponents. In regions of chaotic trajectories, an ensemble-averaged variance of the distance between field lines reveals anomalous diffusion—in fact, superdiffusion—of the field lines. The motion of charged particles in the force-free ABC magnetic fields is different from the flow of passive scalars in ABC flows. The particles do not necessarily follow the field lines and display a variety of dynamical behavior depending on their energy, and their initial pitch-angle. There is an overlap, in space, of the regions in which the field lines and the particle orbits are chaotic. The time evolution of an ensemble of particles, in such regions, can be divided into three categories. For short times, the motion of the particles is essentially ballistic; the ensemble-averaged, mean square displacement is approximately proportional to t{sup 2}, where t is the time of evolution. The intermediate time region is defined by a decay of the velocity autocorrelation function—this being a measure of the time after which the collective dynamics is independent of the initial conditions. For longer times, the particles undergo superdiffusion—the mean square displacement is proportional to t{sup α}, where α > 1, and is weakly dependent on the energy of the particles. These super-diffusive characteristics

  1. Reduction of the higher-order field distribution in a photocathode rf gun for the X-ray free electron laser

    NASA Astrophysics Data System (ADS)

    Hong, Juho; Parc, Yong Woon; Ko, In Soo

    2014-12-01

    The mechanism of the higher-order rf field elimination in the photocathode rf gun used for the X-ray free electron laser (XFEL) machine is discovered. The analysis and the measurement results of the rf field in several models of the rf gun with several holes at the cavity wall are presented. The contribution of the holes to the asymmetrical distribution of the rf field along the azimuthal angle is measured with several model cavities. Using a comparison between the experimental results and the numerically-obtained rf field distribution, we can reveal that the origin of the quadrupole component growing at the cavity with two holes and of the octapole component growing at the cavity with four holes is the superposition of the rf fields in the cavity. Two kinds of model cavities with several holes at the cavity wall have been fabricated, and the rf field distributions of the model cavities have been measured to compare with the theoretical analysis and the numerically-obtained rf field. From the analyses, we decided to adopt an rf gun that has dual feeds and two pumping holes for the Pohang Accelerator Laboratory (PAL-XFEL) project.

  2. Full Wave Parallel Code for Modeling RF Fields in Hot Plasmas

    NASA Astrophysics Data System (ADS)

    Spencer, Joseph; Svidzinski, Vladimir; Evstatiev, Evstati; Galkin, Sergei; Kim, Jin-Soo

    2015-11-01

    FAR-TECH, Inc. is developing a suite of full wave RF codes in hot plasmas. It is based on a formulation in configuration space with grid adaptation capability. The conductivity kernel (which includes a nonlocal dielectric response) is calculated by integrating the linearized Vlasov equation along unperturbed test particle orbits. For Tokamak applications a 2-D version of the code is being developed. Progress of this work will be reported. This suite of codes has the following advantages over existing spectral codes: 1) It utilizes the localized nature of plasma dielectric response to the RF field and calculates this response numerically without approximations. 2) It uses an adaptive grid to better resolve resonances in plasma and antenna structures. 3) It uses an efficient sparse matrix solver to solve the formulated linear equations. The linear wave equation is formulated using two approaches: for cold plasmas the local cold plasma dielectric tensor is used (resolving resonances by particle collisions), while for hot plasmas the conductivity kernel is calculated. Work is supported by the U.S. DOE SBIR program.

  3. Effect of temperature on capacitive RF MEMS switch performance—a coupled-field analysis

    NASA Astrophysics Data System (ADS)

    Zhu, Yong; Espinosa, Horacio D.

    2004-08-01

    Three-dimensional multiphysics finite element analysis (FEA) was performed to investigate the reliability of RF MEMS switches at various operational temperatures. The investigated MEMS capacitive switch consists of a freestanding metal membrane actuated by a bottom electrode coated by a dielectric film. Coupled-field simulations between thermal, structural and electrostatic domains were performed. The simulations show that temperature significantly changes both the membrane stress state and out-of-plane geometry. In particular, the membrane buckles when temperature increase, from room temperature, takes place. The buckling temperature, i.e. the upper bound to the operational temperature, is a function of manufacturing residual stress state, membrane initial out-of-plane profile and a mismatch in materials coefficient of thermal expansion. The analysis also shows that temperature reduction, from room temperature to -40 °C, causes an increase in pull-in voltage to values that could compromise the switch reliability as a result of charge build-up in the dielectric layer. Our analyses illustrate that by proper designing of the membrane out-of-plane profile, it is possible to keep the pull-in voltage, at all operational temperatures, within allowable values. This design feature of RF MEMS switches offers an effective way to achieve reliable pull-in voltages in applications where large temperature variations are expected such as in satellites and airplane condition monitoring based on wireless communication.

  4. Achievement of high atomic hydrogen densities in cylindrical rf plasmas with magnetic field

    NASA Astrophysics Data System (ADS)

    Fantz, Ursel; Briefi, Stefan

    2014-10-01

    Cylindrical rf plasmas in hydrogen with and without an axial magnetic field of up to 120 G are investigated in the pressure range of 0.3 to 10 Pa. The atomic hydrogen density is determined with optical emission spectroscopy, analyzing the Balmer lines and the molecular radiation (Fulcher band). The results obtained by using different coil geometries (4 to 6 turn windings and Nagoya type antenna) as well as different diameters (10 cm and 25 cm) of a quartz, aluminum oxide or aluminum nitride cylinder are compared. RF powers of up to 600 W at a frequency of 13.56 MHz are available for the 10 cm configuration, whereas up to 70 kW power at 1 MHz are used for the 25 cm cylinder. Density ratios of atoms to molecules of up to 0.3 are achieved in both configurations, whereby the achievement in the high power setup is limited by neutral depletion. The influence of the wall material on the atomic densities, and thus the recombination coefficient, will be pointed out.

  5. Anomalous D'yakonov-Perel' spin relaxation in semiconductor quantum wells under a strong magnetic field in the Voigt configuration

    NASA Astrophysics Data System (ADS)

    Zhou, Y.; Yu, T.; Wu, M. W.

    2013-06-01

    We report an anomalous scaling of the D’yakonov-Perel’ spin relaxation with the momentum relaxation in semiconductor quantum wells under a strong magnetic field in the Voigt configuration. We focus on the case in which the external magnetic field is perpendicular to the spin-orbit-coupling-induced effective magnetic field and its magnitude is much larger than the latter one. It is found that the longitudinal spin relaxation time is proportional to the momentum relaxation time even in the strong-scattering limit, indicating that the D’yakonov-Perel’ spin relaxation demonstrates Elliott-Yafet-like behavior. Moreover, the transverse spin relaxation time is proportional (inversely proportional) to the momentum relaxation time in the strong- (weak-) scattering limit, both in the opposite trends against the well-established conventional D’yakonov-Perel’ spin relaxation behaviors. We further demonstrate that all the above anomalous scaling relations come from the unique form of the effective inhomogeneous broadening.

  6. Experimental Measurements of the Dynamic Electric Field Topology Associated with Magnetized RF Sheaths

    NASA Astrophysics Data System (ADS)

    Martin, Elijah; Caughman, J. B. O.; Shannon, S. C.; Isler, R. C.; Klepper, C. C.

    2011-10-01

    The dynamic Stark effect is a phenomenon in which photon(s) associated with an oscillating electric field are absorbed or emitted with the photon associated with an electronic transition. This multiphoton process leads to the formation of satellites in the spectrum at integer multiples of the frequency associated with the dynamic electric field. Utilizing the dynamic Stark effect the electric field parameters can be determined from the time-averaged and phase resolved emission spectra. Currently two methods are available to calculate the emission spectrum associated with an atomic system in the presence of a dynamic electric field: the quasi-static method and the Floquet method. The methodology and applicability of the quasi-static and Floquet methods will be discussed. The RF sheath electric field parameters are determined, utilizing a generalized dynamic Stark effect model and a novel line shape analysis package, from the time-averaged and phase resolved optical emission spectra. Results will be presented for working gases of hydrogen and helium. ORNL is managed by UT-Battelle, LLC, for the U.S. Dept of Energy under contract DE-AC-05-00OR22725.

  7. SPIRAL field mapping on NSTX for comparison to divertor RF heat deposition

    NASA Astrophysics Data System (ADS)

    Hosea, J. C.; Perkins, R.; Jaworski, M. A.; Kramer, G. J.; Ahn, J.-W.; Bertelli, N.; Gerhardt, S.; Gray, T. K.; LeBlanc, B. P.; Maingi, R.; Phillips, C. K.; Roquemore, L.; Ryan, P. M.; Sabbagh, S.; Taylor, G.; Tritz, K.; Wilson, J. R.; NSTX Team

    2014-02-01

    Field-aligned losses of HHFW power in the SOL of NSTX have been studied with IR cameras and probes, but the interpretation of the data depends somewhat on the magnetic equilibrium reconstruction. Both EFIT02 and LRDFIT04 magnetic equilibria have been used with the SPIRAL code to provide field mappings in the scrape off layer (SOL) on NSTX from the midplane SOL in front of the HHFW antenna to the divertor regions, where the heat deposition spirals are measured. The field-line mapping spiral produced at the divertor plate with LRDFIT04 matches the HHFW-produced heat deposition best, in general. An independent method for comparing the field-line strike patterns on the outer divertor for the two equilibria is provided by measuring Langmuir probe characteristics in the vicinity of the outer vessel strike radius (OVSR) and observing the effect on floating potential, saturation current, and zero-probe-voltage current (IV=0) with the crossing of the OVSR over the probe. Interestingly, these comparisons also reveal that LRDFIT04 gives the more accurate location of the predicted OVSR, and confirm that the RF power flow in the SOL is essentially along the magnetic field lines. Also, the probe characteristics and IV=0 data indicate that current flows under the OVSR in the divertor tiles in most cases studied.

  8. Exploiting adiabatically switched RF-field for manipulating spin hyperpolarization induced by parahydrogen

    SciTech Connect

    Kiryutin, Alexey S.; Yurkovskaya, Alexandra V.; Lukzen, Nikita N.; Ivanov, Konstantin L.; Vieth, Hans-Martin

    2015-12-21

    A method for precise manipulation of non-thermal nuclear spin polarization by switching a RF-field is presented. The method harnesses adiabatic correlation of spin states in the rotating frame. A detailed theory behind the technique is outlined; examples of two-spin and three-spin systems prepared in a non-equilibrium state by Para-Hydrogen Induced Polarization (PHIP) are considered. We demonstrate that the method is suitable for converting the initial multiplet polarization of spins into net polarization: compensation of positive and negative lines in nuclear magnetic resonance spectra, which is detrimental when the spectral resolution is low, is avoided. Such a conversion is performed for real two-spin and three-spin systems polarized by means of PHIP. Potential applications of the presented technique are discussed for manipulating PHIP and its recent modification termed signal amplification by reversible exchange as well as for preparing and observing long-lived spin states.

  9. Functional neuroimaging of inner fields-of-view with 2D-selective RF excitations.

    PubMed

    Finsterbusch, Jürgen

    2013-09-01

    Echo-planar imaging is widely used in functional neuroimaging but suffers from its pronounced sensitivity to field inhomogeneities that cause geometric distortions and image blurring which both limit the effective in-plane resolution achievable. In this work, it is shown how inner-field-of-view techniques based on 2D-selective RF excitations (2DRF) can be applied to reduce the field-of-view in the phase-encoding direction without aliasing and increase the in-plane resolution accordingly. Free-induction-decay (FID) EPI and echo-train-shifted (T2*-weighted) and standard (T2-weighted) spin-echo (SE) EPI with in-plane resolutions of up to 0.5×1.0mm(2) (slice thickness 5mm) were acquired at 3T. Unwanted signal contributions of 2DRF side excitations were shifted out of the object (FID-EPI) or of the refocusing plane by tilting the excitation plane (SE-EPI). Brain activation in healthy volunteers was investigated with checkerboard and finger-tapping block-design paradigms. Brain activation could be detected with all sequences and contrasts, most reliably with FID-EPI due to its higher signal amplitude and the longer 2DRF excitation that are more sensitive to magnetic field inhomogeneities. In conclusion, inner-FOV EPI based on 2DRF excitations could help to improve the spatial resolution of fMRI of focal target regions, e.g., for applications in the spinal cord. PMID:23602726

  10. Beam collimation and energy spectrum compression of laser-accelerated proton beams using solenoid field and RF cavity

    NASA Astrophysics Data System (ADS)

    Teng, J.; Gu, Y. Q.; Zhu, B.; Hong, W.; Zhao, Z. Q.; Zhou, W. M.; Cao, L. F.

    2013-11-01

    This paper presents a new method of laser produced proton beam collimation and spectrum compression using a combination of a solenoid field and a RF cavity. The solenoid collects laser-driven protons efficiently within an angle that is smaller than 12 degrees because it is mounted few millimeters from the target, and collimates protons with energies around 2.3 MeV. The collimated proton beam then passes through a RF cavity to allow compression of the spectrum. Particle-in-cell (PIC) simulations demonstrate the proton beam transport in the solenoid and RF electric fields. Excellent energy compression and collection efficiency of protons are presented. This method for proton beam optimization is suitable for high repetition-rate laser acceleration proton beams, which could be used as an injector for a conventional proton accelerator.

  11. Extremely Large Magnetoresistance at Low Magnetic Field by Coupling the Nonlinear Transport Effect and the Anomalous Hall Effect.

    PubMed

    Luo, Zhaochu; Xiong, Chengyue; Zhang, Xu; Guo, Zhen-Gang; Cai, Jianwang; Zhang, Xiaozhong

    2016-04-01

    The anomalous Hall effect of a magnetic material is coupled to the nonlinear transport effect of a semiconductor material in a simple structure to achieve a large geometric magnetoresistance (MR) based on a diode-assisted mechanism. An extremely large MR (>10(4) %) at low magnetic fields (1 mT) is observed at room temperature. This MR device shows potential for use as a logic gate for the four basic Boolean logic operations. PMID:26857904

  12. Spin-orbit coupling and perpendicular Zeeman field for fermionic cold atoms: Observation of the intrinsic anomalous Hall effect

    SciTech Connect

    Zhang Chuanwei

    2010-08-15

    We propose a scheme for generating Rashba spin-orbit coupling and a perpendicular Zeeman field simultaneously for cold fermionic atoms in a harmonic trap through the coupling between atoms and laser fields. The realization of Rashba spin-orbit coupling and a perpendicular Zeeman field provides opportunities for exploring many topological phenomena using cold fermionic atoms. We focus on the intrinsic anomalous Hall effect and show that it may be observed through the response of atomic density to a rotation of the harmonic trap.

  13. Note on anomalous Higgs-boson couplings in effective field theory

    NASA Astrophysics Data System (ADS)

    Buchalla, G.; Catà, O.; Celis, A.; Krause, C.

    2015-11-01

    We propose a parametrization of anomalous Higgs-boson couplings that is both systematic and practical. It is based on the electroweak chiral Lagrangian, including a light Higgs boson, as the effective field theory (EFT) at the electroweak scale v. This is the appropriate framework for the case of sizeable deviations in the Higgs couplings of order 10% from the Standard Model, considered to be parametrically larger than new-physics effects in the sector of electroweak gauge interactions. The role of power counting in identifying the relevant parameters is emphasized. The three relevant scales, v, the scale of new Higgs dynamics f, and the cut-off Λ = 4 πf, admit expansions in ξ =v2 /f2 and f2 /Λ2. The former corresponds to an organization of operators by their canonical dimension, the latter by their loop order or chiral dimension. In full generality the EFT is thus organized as a double expansion. However, as long as ξ ≫ 1 / 16π2 the EFT systematics is closer to the chiral counting. The leading effects in the consistent approximation provided by the EFT, relevant for the presently most important processes of Higgs production and decay, are given by a few (typically six) couplings. These parameters allow us to describe the properties of the Higgs boson in a general and systematic way, and with a precision adequate for the measurements to be performed at the LHC. The framework can be systematically extended to include loop corrections and higher-order terms in the EFT.

  14. High field side launch of RF waves: A new approach to reactor actuators

    NASA Astrophysics Data System (ADS)

    Wallace, G. M.; Baek, S. G.; Bonoli, P. T.; Faust, I. C.; LaBombard, B. L.; Lin, Y.; Mumgaard, R. T.; Parker, R. R.; Shiraiwa, S.; Vieira, R.; Whyte, D. G.; Wukitch, S. J.

    2015-12-01

    Launching radio frequency (RF) waves from the high field side (HFS) of a tokamak offers significant advantages over low field side (LFS) launch with respect to both wave physics and plasma material interactions (PMI). For lower hybrid (LH) waves, the higher magnetic field opens the window between wave accessibility (n∥≡c k∥/ω >√{1 -ωpi 2/ω2+ωpe 2/ωce 2 }+ωp e/|ωc e| ) and the condition for strong electron Landau damping (n∥˜√{30 /Te } with Te in keV), allowing LH waves from the HFS to penetrate into the core of a burning plasma, while waves launched from the LFS are restricted to the periphery of the plasma. The lower n∥ of waves absorbed at higher Te yields a higher current drive efficiency as well. In the ion cyclotron range of frequencies (ICRF), HFS launch allows for direct access to the mode conversion layer where mode converted waves absorb strongly on thermal electrons and ions, thus avoiding the generation of energetic minority ion tails. The absence of turbulent heat and particle fluxes on the HFS, particularly in double null configuration, makes it the ideal location to minimize PMI damage to the antenna structure. The quiescent SOL also eliminates the need to couple LH waves across a long distance to the separatrix, as the antenna can be located close to plasma without risking damage to the structure. Improved impurity screening on the HFS will help eliminate the long-standing issues of high Z impurity accumulation with ICRF. Looking toward a fusion reactor, the HFS is the only possible location for a plasma-facing RF antenna that will survive long-term. By integrating the antenna into the blanket module it is possible to improve the tritium breeding ratio compared with an antenna occupying an equatorial port plug. Blanket modules will require remote handling of numerous cooling pipes and electrical connections, and the addition of transmission lines will not substantially increase the level of complexity. The obvious engineering

  15. Electric Field Measurements of the Capacitively Coupled Magnetized RF Sheath Utilizing Passive Optical Emission Spectroscopy

    NASA Astrophysics Data System (ADS)

    Martin, Elijah Henry

    A major challenge facing magnetic confinement fusion is the implementation of reliable plasma heating systems. Ion cyclotron resonance heating (ICRH) is a key technique utilized to achieve the ion temperatures necessary for desirable fusion reaction rates. ICRH systems are designed to couple energy into the core plasma ions through a resonant interaction with an electromagnetic wave in the radio frequency range. The interaction of the wave with the scrape off layer plasma establishes an electric field which terminates directly on the plasma facing surfaces and is referred to as the near-field. In order to bridge the gap between the theoretical and actual performance of ICRF antennas, experimental measurement of this electric field is highly desired. However, due to the large amount of power launched by ICRF antennas only non-local measurements have thus far been obtained. The research presented in this dissertation is centered on the development of a non-perturbative diagnostic to locally measure the near-field with high spatial and temporal resolution. The main objective of the research presented in this dissertation is to develop and validate a spectroscopic diagnostic capable of measuring local time periodic electric fields. The development phase of the diagnostic consisted of atomic physics formulation and was carried out in two steps. The first involved the calculation of the electronic structure of the one and two-electron atom utilizing the hydrogenic wave function. The second involved the calculation of the spectral line profile based on the electric dipole connection operator. The validate phase of the diagnostic consisted of implementation of the atomic physics to measure the electric field topology associated with the capacitively coupled magnetized RF sheath using passive OES. The experimental measurements are then compared to a simple one-dimensional analytical model providing the validation of the developed atomic physics.

  16. POWER DENSITY, FIELD INTENSITY, AND CARRIER FREQUENCY DETERMINANTS OF RF-ENERGY-INDUCED CALCIUM-ION EFFLUX FROM BRAIN TISSUE

    EPA Science Inventory

    To explain a carrier frequency dependence reported for radiofrequency (RF)-induced calcium-ion efflux from brain tissue, a chick-brain hemisphere bathed in buffer solution is modeled as a sphere within the uniform field of the incident electromagnetic wave. Calculations on a sphe...

  17. A Coupled Field Multiphysics Modeling Approach to Investigate RF MEMS Switch Failure Modes under Various Operational Conditions

    PubMed Central

    Sadek, Khaled; Lueke, Jonathan; Moussa, Walied

    2009-01-01

    In this paper, the reliability of capacitive shunt RF MEMS switches have been investigated using three dimensional (3D) coupled multiphysics finite element (FE) analysis. The coupled field analysis involved three consecutive multiphysics interactions. The first interaction is characterized as a two-way sequential electromagnetic (EM)-thermal field coupling. The second interaction represented a one-way sequential thermal-structural field coupling. The third interaction portrayed a two-way sequential structural-electrostatic field coupling. An automated substructuring algorithm was utilized to reduce the computational cost of the complicated coupled multiphysics FE analysis. The results of the substructured FE model with coupled field analysis is shown to be in good agreement with the outcome of previously published experimental and numerical studies. The current numerical results indicate that the pull-in voltage and the buckling temperature of the RF switch are functions of the microfabrication residual stress state, the switch operational frequency and the surrounding packaging temperature. Furthermore, the current results point out that by introducing proper mechanical approaches such as corrugated switches and through-holes in the switch membrane, it is possible to achieve reliable pull-in voltages, at various operating temperatures. The performed analysis also shows that by controlling the mean and gradient residual stresses, generated during microfabrication, in conjunction with the proposed mechanical approaches, the power handling capability of RF MEMS switches can be increased, at a wide range of operational frequencies. These design features of RF MEMS switches are of particular importance in applications where a high RF power (frequencies above 10 GHz) and large temperature variations are expected, such as in satellites and airplane condition monitoring. PMID:22408490

  18. A Coupled Field Multiphysics Modeling Approach to Investigate RF MEMS Switch Failure Modes under Various Operational Conditions.

    PubMed

    Sadek, Khaled; Lueke, Jonathan; Moussa, Walied

    2009-01-01

    In this paper, the reliability of capacitive shunt RF MEMS switches have been investigated using three dimensional (3D) coupled multiphysics finite element (FE) analysis. The coupled field analysis involved three consecutive multiphysics interactions. The first interaction is characterized as a two-way sequential electromagnetic (EM)-thermal field coupling. The second interaction represented a one-way sequential thermal-structural field coupling. The third interaction portrayed a two-way sequential structural-electrostatic field coupling. An automated substructuring algorithm was utilized to reduce the computational cost of the complicated coupled multiphysics FE analysis. The results of the substructured FE model with coupled field analysis is shown to be in good agreement with the outcome of previously published experimental and numerical studies. The current numerical results indicate that the pull-in voltage and the buckling temperature of the RF switch are functions of the microfabrication residual stress state, the switch operational frequency and the surrounding packaging temperature. Furthermore, the current results point out that by introducing proper mechanical approaches such as corrugated switches and through-holes in the switch membrane, it is possible to achieve reliable pull-in voltages, at various operating temperatures. The performed analysis also shows that by controlling the mean and gradient residual stresses, generated during microfabrication, in conjunction with the proposed mechanical approaches, the power handling capability of RF MEMS switches can be increased, at a wide range of operational frequencies. These design features of RF MEMS switches are of particular importance in applications where a high RF power (frequencies above 10 GHz) and large temperature variations are expected, such as in satellites and airplane condition monitoring. PMID:22408490

  19. A monopole/loop dual-tuned RF coil for ultrahigh field MRI.

    PubMed

    Yan, Xinqiang; Xue, Rong; Zhang, Xiaoliang

    2014-08-01

    Proton and heteronuclear MRI/MRS using dual-tuned (DT) coils could provide both anatomical and metabolic images without repositioning the subject. However, it is technologically challenging to attain sufficiently electromagnetic (EM) decoupling between the heteronuclear channel and proton channel, and keep the imaging areas and profiles of two nuclear channels highly matched. In this study, a hybrid monopole/loop technique was proposed for DT coil design and this technique was validated by implementing and testing a DT (1)H/(23)Na coil for MR imaging at 7T. The RF fields of the monopole ((1)H channel) and regular L/C loop ((23)Na channel) were orthogonal and intrinsically EM decoupled. Bench measurement results demonstrated the isolation between the two nuclear channels was better than -28 dB at both nuclear frequencies. Compared with the conventional DT coil using trap circuits, the monopole/loop DT coil had higher MR sensitivity for sodium imaging. The experimental results indicated that the monopole/loop technique might be a simple and efficient design for multinuclear imaging at ultrahigh fields. Additionally, the proposed DT coils based on the monopole/loop technique can be used as building blocks in designing multichannel DT coil arrays. PMID:25202657

  20. A monopole/loop dual-tuned RF coil for ultrahigh field MRI

    PubMed Central

    Yan, Xinqiang

    2014-01-01

    Proton and heteronuclear MRI/MRS using dual-tuned (DT) coils could provide both anatomical and metabolic images without repositioning the subject. However, it is technologically challenging to attain sufficiently electromagnetic (EM) decoupling between the heteronuclear channel and proton channel, and keep the imaging areas and profiles of two nuclear channels highly matched. In this study, a hybrid monopole/loop technique was proposed for DT coil design and this technique was validated by implementing and testing a DT 1H/23Na coil for MR imaging at 7T. The RF fields of the monopole (1H channel) and regular L/C loop (23Na channel) were orthogonal and intrinsically EM decoupled. Bench measurement results demonstrated the isolation between the two nuclear channels was better than -28 dB at both nuclear frequencies. Compared with the conventional DT coil using trap circuits, the monopole/loop DT coil had higher MR sensitivity for sodium imaging. The experimental results indicated that the monopole/loop technique might be a simple and efficient design for multinuclear imaging at ultrahigh fields. Additionally, the proposed DT coils based on the monopole/loop technique can be used as building blocks in designing multichannel DT coil arrays. PMID:25202657

  1. Large reduction of the depinning field for a transverse domain wall under application of rf and dc currents

    NASA Astrophysics Data System (ADS)

    Metaxas, P. J.; Anane, A.; Cros, V.; Grollier, J.; Deranlot, C.; Petroff, F.; Fert, A.; Ulysse, C.; Faini, G.

    2010-03-01

    A new generation of proposed spintronic devices are based on domain wall (DW) motion (DW-MRAM, DW logic, racetrack memory...). However, reliable depinning of domain walls remains elusive, especially in zero field. Here, we have studied the combined effect of rf and dc currents on the depinning of transverse walls in the soft NiFe layer of a 100 nm wide Co/Cu/NiFe spin valve wire. Using the GMR effect, we ensure that the domain wall is always prepared at the same intrinsic defect and then measure the depinning field for different applied dc and rf currents. Notably, for a narrow range of rf frequencies at around 3GHz, we evidence a strong reduction in the depinning field (from ˜80 Oe to ˜30 Oe). Our results are suggestive of a very efficient resonant depinning effect in our spin valve wire which depends not only on the rf power but also on the polarity and amplitude of the accompanying dc current.

  2. Using a modified 3D-printer for mapping the magnetic field of RF coils designed for fetal and neonatal imaging

    NASA Astrophysics Data System (ADS)

    Vavoulas, Alexander; Vaiopoulos, Nicholas; Hedström, Erik; Xanthis, Christos G.; Sandalidis, Harilaos G.; Aletras, Anthony H.

    2016-08-01

    An experimental setup for characterizing the magnetic field of MRI RF coils was proposed and tested. The setup consisted of a specially configured 3D-printer, a network analyzer and a mid-performance desktop PC. The setup was tested on a single loop RF coil, part of a phased array for fetal imaging. Then, the setup was used for determining the magnetic field characteristics of a high-pass birdcage coil used for neonatal MR imaging with a vertical static field. The scattering parameter S21, converted into power ratio, was used for mapping the B1 magnetic field. The experimental measurements from the loop coil were close to the theoretical results (R = 0.924). A high degree of homogeneity was measured for the neonatal birdcage RF coil. The development of MR RF coils is time consuming and resource intensive. The proposed experimental setup provides an alternative method for magnetic field characterization of RF coils used in MRI.

  3. Using a modified 3D-printer for mapping the magnetic field of RF coils designed for fetal and neonatal imaging.

    PubMed

    Vavoulas, Alexander; Vaiopoulos, Nicholas; Hedström, Erik; Xanthis, Christos G; Sandalidis, Harilaos G; Aletras, Anthony H

    2016-08-01

    An experimental setup for characterizing the magnetic field of MRI RF coils was proposed and tested. The setup consisted of a specially configured 3D-printer, a network analyzer and a mid-performance desktop PC. The setup was tested on a single loop RF coil, part of a phased array for fetal imaging. Then, the setup was used for determining the magnetic field characteristics of a high-pass birdcage coil used for neonatal MR imaging with a vertical static field. The scattering parameter S21, converted into power ratio, was used for mapping the B1 magnetic field. The experimental measurements from the loop coil were close to the theoretical results (R=0.924). A high degree of homogeneity was measured for the neonatal birdcage RF coil. The development of MR RF coils is time consuming and resource intensive. The proposed experimental setup provides an alternative method for magnetic field characterization of RF coils used in MRI. PMID:27310429

  4. Transmit Array Spatial Encoding (TRASE) using broadband WURST pulses for RF spatial encoding in inhomogeneous B0 fields.

    PubMed

    Stockmann, Jason P; Cooley, Clarissa Z; Guerin, Bastien; Rosen, Matthew S; Wald, Lawrence L

    2016-07-01

    Transmit Array Spatial Encoding (TRASE) is a promising new MR encoding method that uses transmit RF (B1(+)) phase gradients over the field-of-view to perform Fourier spatial encoding. Acquisitions use a spin echo train in which the transmit coil phase ramp is modulated to jump from one k-space point to the next. This work extends the capability of TRASE by using swept radiofrequency (RF) pulses and a quadratic phase removal method to enable TRASE where it is arguably most needed: portable imaging systems with inhomogeneous B0 fields. The approach is particularly well-suited for portable MR scanners where (a) inhomogeneous B0 fields are a byproduct of lightweight magnet design, (b) heavy, high power-consumption gradient coil systems are a limitation to siting the system in non-conventional locations and (c) synergy with the use of spin echo trains is required to overcome intra-voxel dephasing (short T2(∗)) in the inhomogeneous field. TRASE does not use a modulation of the B0 field to encode, but it does suffer from secondary effects of the inhomogeneous field. Severe artifacts arise in TRASE images due to off-resonance effects when the RF pulse does not cover the full bandwidth of spin resonances in the imaging FOV. Thus, for highly inhomogeneous B0 fields, the peak RF power needed for high-bandwidth refocusing hard pulses becomes very expensive, in addition to requiring RF coils that can withstand thousands of volts. In this work, we use swept WURST RF pulse echo trains to achieve TRASE imaging in a highly inhomogeneous magnetic field (ΔB0/B0∼0.33% over the sample). By accurately exciting and refocusing the full bandwidth of spins, the WURST pulses eliminate artifacts caused by the limited bandwidth of the hard pulses used in previous realizations of TRASE imaging. We introduce a correction scheme to remove the unwanted quadratic phase modulation caused by the swept pulses. Also, a phase alternation scheme is employed to mitigate artifacts caused by mixture of

  5. Transmit Array Spatial Encoding (TRASE) using broadband WURST pulses for RF spatial encoding in inhomogeneous B0 fields

    NASA Astrophysics Data System (ADS)

    Stockmann, Jason P.; Cooley, Clarissa Z.; Guerin, Bastien; Rosen, Matthew S.; Wald, Lawrence L.

    2016-07-01

    Transmit Array Spatial Encoding (TRASE) is a promising new MR encoding method that uses transmit RF (B1+) phase gradients over the field-of-view to perform Fourier spatial encoding. Acquisitions use a spin echo train in which the transmit coil phase ramp is modulated to jump from one k-space point to the next. This work extends the capability of TRASE by using swept radiofrequency (RF) pulses and a quadratic phase removal method to enable TRASE where it is arguably most needed: portable imaging systems with inhomogeneous B0 fields. The approach is particularly well-suited for portable MR scanners where (a) inhomogeneous B0 fields are a byproduct of lightweight magnet design, (b) heavy, high power-consumption gradient coil systems are a limitation to siting the system in non-conventional locations and (c) synergy with the use of spin echo trains is required to overcome intra-voxel dephasing (short T2∗) in the inhomogeneous field. TRASE does not use a modulation of the B0 field to encode, but it does suffer from secondary effects of the inhomogeneous field. Severe artifacts arise in TRASE images due to off-resonance effects when the RF pulse does not cover the full bandwidth of spin resonances in the imaging FOV. Thus, for highly inhomogeneous B0 fields, the peak RF power needed for high-bandwidth refocusing hard pulses becomes very expensive, in addition to requiring RF coils that can withstand thousands of volts. In this work, we use swept WURST RF pulse echo trains to achieve TRASE imaging in a highly inhomogeneous magnetic field (ΔB0/B0 ∼ 0.33% over the sample). By accurately exciting and refocusing the full bandwidth of spins, the WURST pulses eliminate artifacts caused by the limited bandwidth of the hard pulses used in previous realizations of TRASE imaging. We introduce a correction scheme to remove the unwanted quadratic phase modulation caused by the swept pulses. Also, a phase alternation scheme is employed to mitigate artifacts caused by mixture of

  6. Six loop analytical calculation of the field anomalous dimension and the critical exponent η in O(n)-symmetric φ4 model

    NASA Astrophysics Data System (ADS)

    Batkovich, D. V.; Chetyrkin, K. G.; Kompaniets, M. V.

    2016-05-01

    We report on a completely analytical calculation of the field anomalous dimension γφ and the critical exponent η for the O (n)-symmetric φ4 model at the record six loop level. We successfully compare our result for γφ with n = 1 with the predictions based on the method of the Borel resummation combined with a conformal mapping (Kazakov et al., 1979 [40]). Predictions for seven loop contribution to the field anomalous dimensions are given.

  7. Dust particles under the influence of crossed electric and magnetic fields in the sheath of an rf discharge

    SciTech Connect

    Puttscher, M. Melzer, A.

    2014-12-15

    Experimental studies on the interaction of micron-sized dust particles in plasmas with external magnetic fields are presented. The particles are levitated in the sheath region of an rf discharge by gravity and electric field force under the presence of a horizontal magnetic field of up to 50 mT. It is observed that the dust particles are pushed either in the E{sup →}×B{sup →}- or in the opposite direction depending on magnetic field strength, particle properties, and discharge conditions. This transport behavior is described by a competition between horizontal ambipolar electric field force and ion and neutral drag.

  8. Anomalously High Geothermal Gradients in the Buckman Well Field, Santa Fe County, New Mexico

    NASA Astrophysics Data System (ADS)

    Pollack, A.; Munda, R.; Farrell, T. F.; Kelley, S. A.; Frost, J.; Jiracek, G. R.

    2013-12-01

    Temperature as a function of depth was measured in ten wells in the Santa Fe, NM area as part of the Summer of Applied Geophysics Experience (SAGE) program. Eight of the wells are within 5.5 km of the city's Buckman municipal well field and two wells are at La Tierra, 16.5 km to the SE. Geothermal gradients increase from east to west towards the Buckman area, from 20°C/km at La Tierra to 76°C/km at Buckman. Within the Buckman well field, two wells on its eastern side were determined to have temperature gradients of 32°C/km and 42°C/km. Only 300 m west, the geothermal gradient sharply increases, and measured gradients reach 76 °C/km (well number SF4A), 62°C/km (SF4B), and 68°C/km (SF3A) in three shallow (<100 m) monitoring drill holes. Both local and regional causes may explain the geothermal anomaly. The short spatial wavelength of the horizontal gradient increase argues for a localized source. The unusually high gradients in three of the wells may be associated with fault-controlled, effective shallow-source, warm water upflow or with lateral flow in a shallow aquifer. On the regional level, the east to west increase in temperature gradients can be explained by deep circulating groundwater flow in the Espanola Basin and upwelling near the Rio Grande. Another possible explanation comes from gravity data gathered by SAGE over several years that shows a local NW-striking structural high in the area that could force localized convective upflow. Regional aeromag maps indicate magnetic lows exactly underneath the anomalous wells. These may be interpreted as buried volcanic plugs beneath the Buckman well field, acting as conduits for upwelling warmer waters. They may also indicate hydrothermally altered rock beneath the surface. A more nontraditional cause of the sharp thermal anomaly is also possible. The geothermal gradient anomaly coincides with the dramatic discovery by InSAR in 1993-2000 of localized ground subsidence due to excessive water well pumping

  9. Nonlocal and local magnetization dynamics excited by an RF magnetic field in magnetic multilayers

    NASA Astrophysics Data System (ADS)

    Moriyama, Takahiro

    A microwave study in spintronic devices has been actively pursued in the past several years due to the fertile physics and potential applications. On one hand, a passive use of microwave can be very helpful to analyze and understand the magnetization dynamics in spintronic devices. Examples include ferromagnetic resonance (FMR) measurements, and various microwave spectrum analyses in ferromagnetic materials. The most important chrematistic parameter for the phenomenological analysis on the magnetization dynamics is, so called, the Gilbert damping constant. In this work, a relatively new measurement technique, a flip-chip FMR measurement, to conduct the ferromagnetic resonance measurements has been developed. The measurement technique is equally comparable to a conventional FMR measurement. The Gilbert damping constants were extracted for single ferromagnetic layer, spin vale structures, and magnetic tunnel junctions (MTJs). On the other hand, an active use of microwave yields a great potential for interesting phenomena which give new functionalities into spintronic devices. For instance, a spin wave excitation by an rf field can be used to reduce the switching field of a ferromagnet, i.e. microwave assisted magnetization reversal, which could be a potential application in advanced recording media. More interestingly, a precessing magnetization driven by an rf field can generate a pure spin current into a neighboring layer, i.e. spin pumping effect, which is one of the candidates for generating a pure spin current. A ferromagnetic tunnel junction (MTJ) is one of the important devices in spintronics, which is also the key device to investigate the local and nonlocal magnetization dynamics in this work. Therefore, it is also important to develop high quality MTJs. My work starts from the development of MTJ with AlOx and MgO tunnel barriers where it was found it is crucial to find the proper condition for forming a few nanometers thick tunnel barrier. After obtaining

  10. Noninvasive quantitative mapping of conductivity and dielectric distributions using RF wave propagation effects in high-field MRI

    NASA Astrophysics Data System (ADS)

    Wen, Han

    2003-06-01

    In this paper I show with phantom and animal experiments a non-invasive and quantitative method for measuring the conductivity and dielectric distributions based on high field magnetic resonance imaging. High field MRI is accompanied by significant RF wave propagation effects. They are observed as phase and magnitude variations of the image that cannot be removed by optimizing the static field homogeneity, or by improving the RF coils. These variations reflect the RF field distribution in the sample, and in fact obey a modified Helmholtz equation. By mapping both the phase and magnitude of the field with MRI techniques, both the conductivity and the dielectric constant are determined non-invasively. In phantom experiments at 1.5 tesla, conductivity values were measured at 4 mm resolution to 0.5 S/m accuracy. At 4.7 tesla, the accuracy was improved to 0.2 S/m, and the dielectric constant was measured to an accuracy of 5 (relative to vacuum) for 2cm regions.

  11. RF excitation using time interleaved acquisition of modes (TIAMO) to address B1 inhomogeneity in high-field MRI.

    PubMed

    Orzada, Stephan; Maderwald, Stefan; Poser, Benedikt Andreas; Bitz, Andreas K; Quick, Harald H; Ladd, Mark E

    2010-08-01

    As the field strength and, therefore, the operational frequency in MRI is increased, the wavelength approaches the size of the human head/body, resulting in wave effects, which cause signal decreases and dropouts. Several multichannel approaches have been proposed to try to tackle these problems, including RF shimming, where each element in an array is driven by its own amplifier and modulated with a certain (constant) amplitude and phase relative to the other elements, and Transmit SENSE, where spatially tailored RF pulses are used. In this article, a relatively inexpensive and easy to use imaging scheme for 7 Tesla imaging is proposed to mitigate signal voids due to B(1)(+) field inhomogeneity. Two time-interleaved images are acquired using a different excitation mode for each. By forming virtual receive elements, both images are reconstructed together using GRAPPA to achieve a more homogeneous image, with only small SNR and SAR penalty in head and body imaging at 7 Tesla. PMID:20574991

  12. Anomalous thermal hysteresis in the high-field magnetic moments of magnetic nanoparticles embedded in multi-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Zhao, Guo-Meng; Wang, Jun; Ren, Yang; Beeli, Pieder

    2012-02-01

    We report high-temperature (300-1120 K) magnetic properties of Fe and Fe3O4 nanoparticles embedded in multi-walled carbon nanotubes. We unambiguously show that the magnetic moments of Fe and Fe3O4 nanoparticles are seemingly enhanced by a factor of about 3 compared with what they would be expected to have for free (unembedded) magnetic nanoparticles. What is more intriguing is that the enhanced moments were completely lost when the sample was heated up to 1120 K and the lost moments at 1120 K were completely recovered through several thermal cycles below 1020 K. The anomalous thermal hysteresis of the high-field magnetic moments is unlikely to be explained by existing physical models except for the high-field paramagnetic Meissner effect due to the existence of ultrahigh temperature superconductivity in the multi-walled carbon nanotubes.

  13. Investigation of analog/RF performance of staggered heterojunctions based nanowire tunneling field-effect transistors

    NASA Astrophysics Data System (ADS)

    Chakraborty, Avik; Sarkar, Angsuman

    2015-04-01

    In this paper, the analog/RF performance of an III-V semiconductor based staggered hetero-tunnel-junction (HETJ) n-type nanowire (NW) tunneling FET (n-TFET) is investigated, for the first time. The device performance figure-of-merits governing the analog/RF performance such as transconductance (gm), transconductance-to-drive current ratio (gm/IDS), output resistance (Rout), intrinsic gain and unity-gain cutoff frequency (fT) have been studied. The analog/RF performance parameters is compared between HETJ NW TFET and a homojunction (HJ) NW n-type TFET of similar dimensions. In addition to enhanced ION and subthreshold swing, a significant improvement in the analog/RF performance parameters obtained by the HETJ n-TFET over HJ counterpart for use in analog/mixed signal System-on-Chip (SoC) applications is reported. Moreover, the analog/RF performance parameters of a III-V based staggered HETJ NW TFET is also compared with a heterojunction (HETJ) NW n-type MOSFET having same material as HETJ n-TFET and equal dimension in order to provide a systematic comparison between HETJ-TFET and HETJ-MOSFET for use in analog/mixed-signal applications. The results reveal that HETJ n-TFET provides higher Rout and hence, a higher intrinsic gain, an improved gm/IDS ratio, and reasonable fT at lower values of gate-overdrive voltage as compared to the HETJ NW n-MOSFET.

  14. Computational electromagnetic analysis in a human head model with EEG electrodes and leads exposed to RF-field sources at 915 MHz and 1748 MHz.

    PubMed

    Angelone, Leonardo M; Bit-Babik, Giorgi; Chou, Chung-Kwang

    2010-07-01

    An electromagnetic analysis of a human head with EEG electrodes and leads exposed to RF-field sources was performed by means of Finite-Difference Time-Domain simulations on a 1-mm(3) MRI-based human head model. RF-field source models included a half-wave dipole, a patch antenna, and a realistic CAD-based mobile phone at 915 MHz and 1748 MHz. EEG electrodes/leads models included two configurations of EEG leads, both a standard 10-20 montage with 19 electrodes and a 32-electrode cap, and metallic and high resistive leads. Whole-head and peak 10-g average SAR showed less than 20% changes with and without leads. Peak 1-g and 10-g average SARs were below the ICNIRP and IEEE guideline limits. Conversely, a comprehensive volumetric assessment of changes in the RF field with and without metallic EEG leads showed an increase of two orders of magnitude in single-voxel power absorption in the epidermis and a 40-fold increase in the brain during exposure to the 915 MHz mobile phone. Results varied with the geometry and conductivity of EEG electrodes/leads. This enhancement confirms the validity of the question whether any observed effects in studies involving EEG recordings during RF-field exposure are directly related to the RF fields generated by the source or indirectly to the RF-field-induced currents due to the presence of conductive EEG leads. PMID:20681803

  15. Anomalous metamagnetic-like transition in a FeRh/Fe3Pt interface occurring at T ≈ 120 K in the field-cooled-cooling curves for low magnetic fields

    NASA Astrophysics Data System (ADS)

    Salem-Sugui, S.; Alvarenga, A. D.; Noce, R. D.; Guimarães, R. B.; Mejia, C. Salazar; Salim, H.; Gandra, F. G.

    2012-09-01

    We report on the magnetic properties of a special configuration of a FeRh thin film. An anomalous behavior on the magnetisation vs. temperature was observed when low magnetic fields are applied in the plane of a thin layer of FeRh deposited on ordered Fe3Pt. The anomalous effect resembles a metamagnetic transition and occur only in the field-cooled-cooling magnetisation curve at temperatures near 120 K in samples without any heat treatment.

  16. Multipacting analysis and electromagnetic field computation by the boundary integral equation method in RF cavities and waveguides

    NASA Astrophysics Data System (ADS)

    Yla-Oijala, Pasi

    Electron multipacting is a serious problem in many rf components operating in vacuum. Multipacting can cause remarkable power losses and heating of the walls. This phenomenon starts if certain resonant conditions for electron trajectories are fulfilled and if the impacted surface has a secondary yield larger than one. In this work new computational methods have been developed which combine the standard trajectory calculations with advanced searching and analyzing methods for multipacting resonances. These methods have been applied to the analysis of electron multipacting in TESLA superconducting cavities and input power couplers with ceramic windows. TESLA is an international linear collider research and development project. Since even small errors in the rf field may destroy the trajectory calculation of a relativistic electron, the electromagnetic fields must be known accurately, especially close to the surfaces. The electromagnetic field computation is carried out by the boundary integral equation method. Due to the singularities of the integral equations, the numerical computations become rather involved, especially when computing the fields near the boundaries. Therefore, in this work special integration techniques and algorithms have been developed. In the axisymmetric geometries the numerical efficiency of various boundary integral equations has been studied.

  17. Self-induced steady-state magnetic field in the negative ion sources with localized rf power deposition

    NASA Astrophysics Data System (ADS)

    Shivarova, A.; Todorov, D.; Lishev, St.

    2016-02-01

    The study is in the scope of a recent activity on modeling of SPIDER (Source for Production of Ions of Deuterium Extracted from RF plasma) which is under development regarding the neutral beam injection heating system of ITER. The regime of non-ambipolarity in the source, established before, is completed here by introducing in the model the steady state magnetic field, self-induced in the discharge due to the dc current flowing in it. Strong changes in the discharge structure are reported.

  18. Self-induced steady-state magnetic field in the negative ion sources with localized rf power deposition.

    PubMed

    Shivarova, A; Todorov, D; Lishev, St

    2016-02-01

    The study is in the scope of a recent activity on modeling of SPIDER (Source for Production of Ions of Deuterium Extracted from RF plasma) which is under development regarding the neutral beam injection heating system of ITER. The regime of non-ambipolarity in the source, established before, is completed here by introducing in the model the steady state magnetic field, self-induced in the discharge due to the dc current flowing in it. Strong changes in the discharge structure are reported. PMID:26932036

  19. Anomalous Spectral Shift of Near- and Far-Field Plasmonic Resonances in Nanogaps

    PubMed Central

    2016-01-01

    The near-field and far-field spectral response of plasmonic systems are often assumed to be identical, due to the lack of methods that can directly compare and correlate both responses under similar environmental conditions. We develop a widely tunable optical technique to probe the near-field resonances within individual plasmonic nanostructures that can be directly compared to the corresponding far-field response. In tightly coupled nanoparticle-on-mirror constructs with nanometer-sized gaps we find >40 meV blue-shifts of the near-field compared to the dark-field scattering peak, which agrees with full electromagnetic simulations. Using a transformation optics approach, we show such shifts arise from the different spectral interference between different gap modes in the near- and far-field. The control and tuning of near-field and far-field responses demonstrated here is of paramount importance in the design of optical nanostructures for field-enhanced spectroscopy, as well as to control near-field activity monitored through the far-field of nano-optical devices. PMID:27077075

  20. Infrared thermography analysis of thermal diffusion induced by RF magnetic field on agar phantoms loaded with magnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Bante-Guerra, Jose; Macías, J. D.; Caballero-Aguilar, L.; Vales-Pinzón, C.; Alvarado-Gil, J. J.

    2013-02-01

    Recently, several treatments for fighting malignant tumors have been designed. However these procedures have well known inconveniences, depending on their applicability, tumor size and side effects, among others. Magnetic hyperthermia is a safe, non-invasive method for cancer therapy. This treatment is applied via elevation of target tissue temperature by dissipation of heat from Magnetic Nanoparticles (MNPs), previously located within the tumor. The induction of heat causes cell death and therefore the removal of the tumor. In this work the thermal diffusion in phantoms of agar loaded with magnetic nanoparticles (MNPs) is studied using the infrared thermography technique, which is widely used in biology/medicine (e.g. skin temperature mapping). Agar is one of the materials used to simulate different types of body tissues, these samples are known as "phantoms". Agar is of natural origin, low cost and high degree of biocompatibility. In this work the agar gel was embedded with MNPs by coprecipitation and placed in an alternating magnetic field radiation. As a consequence, the energy from the radiation source is dissipated as heat and then transferred from the MNP to the gel, increasing its temperature. For the temperature analysis, the samples of agar gel were stimulated by RF magnetic field generated by coils. Heating was measured with infrared thermography using a Thermovision A20M infrared camera. Thermographic images allowed obtaining the dependence of thermal diffusion in the phantom as a function of the magnitude of the applied RF magnetic field and the load of magnetic particles.

  1. Measurements and Modeling of the RF Fields from an Interdigital Line Antenna for Lower Hybrid Experiments in MST

    NASA Astrophysics Data System (ADS)

    Caughman, J. B. O.; Carter, M. D.; Rasmussen, D. A.; Ryan, P. M.; Thomas, M. A.; Goetz, J. A.

    2003-10-01

    A system for launching lower hybrid slow waves at 800 MHz has been developed on MST, and the antenna used to launch the lower hybrid waves is being analyzed. The antenna is an enclosed interdigital line using λ/4 resonators with an opening in the cavity through which the wave is coupled to the plasma. The RF fields are measured as a function of distance away from the antenna in 3 dimensions using electric and magnetic field probes. The power deposition is being measured with a heat deposition technique where a simple mirror, contoured to the shape of the antenna, is used to act as a load under moderate power from the antenna ( 100 W). The power deposition in the thin metallic coating of the mirror is imaged with an infrared camera. The RF fields in vacuum are being modeled using Microwave Studio^TM. Plasma effects on power absorption and coupling are modeled using the RANT/GLOSI codes. Details of the measurement technique and comparison between the measurements and the modeling results will be presented.

  2. An investigation into the effectiveness of ELF protective clothing when exposed to RF fields between 65 MHz and 3 GHz.

    PubMed

    Findlay, R P; Dimbylow, P J

    2012-05-01

    Protective garments are worn by electric power workers to shield the body against electromagnetic fields. This paper uses the finite-difference time-domain method to calculate SAR in the heterogeneous human voxel model NORMAN, clad in a protective suit and exposed to radio-frequency (RF) electromagnetic fields between 65 MHz and 3 GHz. The representation of the suit was produced for this work by the modelling and voxelization of a surface-rendered object, based on the dimensions of the male voxel phantom. The calculations showed that the peak-localized SAR in the head was higher than that calculated for a model without a protective suit for a number of exposure situations. These localized SAR values could be up to three times the values of those calculated for a model without a protective suit for a particular frequency. It is thought that the SAR hotspots in the head are caused by resonances in a cavity, which in this case is the conductive hood of the suit. This work shows that the increase in the peak-localized SAR in the head due to wearing the suit meant that, in certain situations, the ICNIRP and IEEE reference levels were no longer conservative. Therefore, it is important that power line workers exposed to RF fields wear the correct high-frequency protective suits with conducting visors. PMID:22510683

  3. An investigation into the effectiveness of ELF protective clothing when exposed to RF fields between 65 MHz and 3 GHz

    NASA Astrophysics Data System (ADS)

    Findlay, R. P.; Dimbylow, P. J.

    2012-05-01

    Protective garments are worn by electric power workers to shield the body against electromagnetic fields. This paper uses the finite-difference time-domain method to calculate SAR in the heterogeneous human voxel model NORMAN, clad in a protective suit and exposed to radio-frequency (RF) electromagnetic fields between 65 MHz and 3 GHz. The representation of the suit was produced for this work by the modelling and voxelization of a surface-rendered object, based on the dimensions of the male voxel phantom. The calculations showed that the peak-localized SAR in the head was higher than that calculated for a model without a protective suit for a number of exposure situations. These localized SAR values could be up to three times the values of those calculated for a model without a protective suit for a particular frequency. It is thought that the SAR hotspots in the head are caused by resonances in a cavity, which in this case is the conductive hood of the suit. This work shows that the increase in the peak-localized SAR in the head due to wearing the suit meant that, in certain situations, the ICNIRP and IEEE reference levels were no longer conservative. Therefore, it is important that power line workers exposed to RF fields wear the correct high-frequency protective suits with conducting visors.

  4. Anomalous arsenic contents in Lower Pennsylvanian Coals, Warrior field, northwestern Alabama, USA: Evidence for fluid flow during Alleghanian thrusting

    SciTech Connect

    Hatch, J.R.; Goldhaber, M.B.; Pashin, J.C.; Offield, T.W.; Finkelman, R.B.

    1998-12-31

    This paper summarizes initial results from a study of the geology and geochemistry of anomalous arsenic (As) contents in bituminous coals from the Lower Pennsylvanian Pottsville Formation, Warrior field, northwestern Alabama. Since 1977, the US Geological Survey has chemically analyzed 913 core and mine samples of coal and shaley coal from the Warrior field. These analyses document arsenic contents in coal of up to 1500 ppm (whole-coal, remnant-moisture basis) which are some of the highest contents reported for all United States coals. Warrior field coals also have elevated contents of copper (Cu), molybdenum (Mo), and antimony (Sb). For the approximately 13,000 samples of United States coals analyzed by the US Geological Survey, mean arsenic content is about 24 ppm. Nearly 80% of the 103 arsenic analyses greater than three standard deviations above this mean are from Alabama. A figure illustrates the distribution of arsenic contents in Warrior field coals and compares this distribution with the substantially lower arsenic contents in Paleocene coals from the Powder River basin, Wyoming and Montana, and Middle Pennsylvanian coals from the Illinois basin, Illinois, Indiana and western Kentucky.

  5. Anomalous hysteresis as evidence for a magnetic-field-induced chiral superconducting state in LiFeAs

    NASA Astrophysics Data System (ADS)

    Li, G.; Urbano, R. R.; Goswami, P.; Tarantini, C.; Lv, B.; Kuhns, P.; Reyes, A. P.; Chu, C. W.; Balicas, L.

    2013-01-01

    Magnetometry measurements in high-quality LiFeAs single crystals reveal a change in the sign of the magnetic hysteresis in the vicinity of the upper critical field Hc2, from a clear diamagnetic response dominated by the pinning of vortices to a considerably smaller net hysteretic response of opposite sign, which disappears at Hc2. If the diamagnetic response at high fields results from pinned vortices and associated screening supercurrents, this sign change must result from currents circulating in the opposite sense, which give rise to a small field-dependent magnetic moment below Hc2. This behavior seems to be extremely sensitive to the sample quality or stoichiometry, as we have observed it only in a few fresh crystals, which also display the de Haas van Alphen effect. We provide arguments against the surface superconductivity, the flux compression, and the random π junction scenarios, which have been previously put forward to explain a paramagnetic Meissner effect, below the lower critical field Hc1. The observed anomalous hysteresis at high fields will be compatible with the existence of chiral gap wave functions, which possess a field-dependent magnetic moment. Within a Landau-Ginzburg framework, we demonstrate how a (dx2-y2+idxy) or a (px+ipy) chiral superconducting component can be stabilized in the mixed state of s± superconductor, due to the combined effects of the magnetic field and the presence of competing pairing channels. The realization of a particular chiral pairing depends on the microscopic details of the strengths of the competing pairing channels.

  6. Superconducting surface impedance under radiofrequency field

    DOE PAGESBeta

    Xiao, Binping P.; Reece, Charles E.; Kelley, Michael J.

    2013-04-26

    Based on BCS theory with moving Cooper pairs, the electron states distribution at 0K and the probability of electron occupation with finite temperature have been derived and applied to anomalous skin effect theory to obtain the surface impedance of a superconductor under radiofrequency (RF) field. We present the numerical results for Nb and compare these with representative RF field-dependent effective surface resistance measurements from a 1.5 GHz resonant structure.

  7. The ANL experiment for a wake field accelerator using an rf structure

    SciTech Connect

    Ruggiero, A.G.; Schoessow, P.; Simpson, J.

    1986-08-27

    Experiments are planned at ANL to study a new accelerating concept that has been developed during the last few years named the WAKEATRON. This requires a very special, simple configuration of the beams and of the rf structure involved. The basic concepts are explained. Like most proposed experimental work, this too was initiated by a considerable amount of computational work, both analytical and numerical, on which we would like to report. We will then describe details of the planned experiments we will carry out at ANL to check some of our predictions for this concept. These experiments concentrate on beam and cavity geometry applicable to the Wakeatron.

  8. Anomalous Increase in Nematic-Isotropic Transition Temperature in Dimer Molecules Induced by a Magnetic Field

    NASA Astrophysics Data System (ADS)

    Salili, S. M.; Tamba, M. G.; Sprunt, S. N.; Welch, C.; Mehl, G. H.; Jákli, A.; Gleeson, J. T.

    2016-05-01

    We have determined the nematic-isotropic transition temperature as a function of an applied magnetic field in three different thermotropic liquid crystalline dimers. These molecules are comprised of two rigid calamitic moieties joined end to end by flexible spacers with odd numbers of methylene groups. They show an unprecedented magnetic field enhancement of nematic order in that the transition temperature is increased by up to 15 K when subjected to a 22 T magnetic field. The increase is conjectured to be caused by a magnetic-field-induced decrease of the average bend angle in the aliphatic spacers connecting the rigid mesogenic units of the dimers.

  9. Efficiency enhancement of anomalous-Doppler electron cyclotron masers with tapered magnetic field

    SciTech Connect

    Xie, Chao-Ran; Hou, Zhi-Ling; Kong, Ling-Bao E-mail: pkliu@pku.edu.cn; Beijing Key Laboratory of Harmful Chemicals Analysis and School of Science, Beijing University of Chemical Technology, Beijing 100029 ; Liu, Pu-Kun E-mail: pkliu@pku.edu.cn; Du, Chao-Hai; Jin, Hai-Bo

    2014-02-15

    The efficiency of slow-wave electron cyclotron masers (ECM) is usually low, thus limiting the practical applications. Here, a method of tapered magnetic field is introduced for the efficiency enhancement of the slow-wave ECM. The numerical calculations show that the tapered magnetic-field method can enhance the efficiency of slow-wave ECM significantly. The effect of beam electron velocity spread on the efficiency has also been studied. Although the velocity spread reduces the efficiency, a great enhancement of efficiency can still be obtained by the tapered magnetic field method.

  10. Field and photo-emission in a short-pulse, high-charge Cesium telluride RF photoinjector

    NASA Astrophysics Data System (ADS)

    Wisniewski, Eric E.

    A new high-charge RF gun is now operating at the Argonne Wakefield Accelerator (AWA) facility at Argonne National Laboratory (ANL). The 1.5 cell 1.3 GHz gun uses a Cesium telluride photocathode driven with a 248 nm laser to provide short-pulse, high charge electron beams for the new 75 MeV drive beamline. The high-gradient RF gun (peak field on the cathode > 80MV/m) is a key piece of the facility upgrade. The large Cs2Te photocathode (diameter > 30 mm) was fabricated in-house. The photo-injector will be used to generate high-charge, short pulse, single bunches (Q > 100 nC) and bunch-trains (Q > 1000 nC) for wakefield experiments, typically involving dielectric-loaded accelerating structures. Details of the photocathode fabrication process and the results of associated diagnostic measurements are presented, including QE measurements and work function measurements performed with a Kelvin probe. Fieldemitted dark current from the Cs2Te cathode was measured during RF conditioning and characterized. Fowler-Nordheim plots of the data are presented and compared to similar measurements made using a copper cathode in the initial phase of conditioning. The results for cesium telluride exhibited non-linear regions within the Fowler-Nordheim plots similar to previous experimental results for other p-type semiconductors. Results of quantum efficiency (QE) studies are presented with the cathode operating in both single and bunch-train modes. QE uniformity and lifetime studies are presented. During commissioning, the cesium telluride photocathode produced bunch-charge of 100 nC, breaking the previous record. No evidence of bunch-train position-dependence of QE was found when generating four-bunch trains with total charge up to 200 nC.

  11. Rod-filter-field optimization of the J-PARC RF-driven H{sup −} ion source

    SciTech Connect

    Ueno, A. Ohkoshi, K.; Ikegami, K.; Takagi, A.; Yamazaki, S.; Oguri, H.

    2015-04-08

    In order to satisfy the Japan Proton Accelerator Research Complex (J-PARC) second-stage requirements of an H{sup −} ion beam of 60mA within normalized emittances of 1.5πmm•mrad both horizontally and vertically, a flat top beam duty factor of 1.25% (500μs×25Hz) and a life-time of longer than 1month, the J-PARC cesiated RF-driven H{sup −} ion source was developed by using an internal-antenna developed at the Spallation Neutron Source (SNS). Although rod-filter-field (RFF) is indispensable and one of the most beam performance dominative parameters for the RF-driven H{sup −} ion source with the internal-antenna, the procedure to optimize it is not established. In order to optimize the RFF and establish the procedure, the beam performances of the J-PARC source with various types of rod-filter-magnets (RFMs) were measured. By changing RFM’s gap length and gap number inside of the region projecting the antenna inner-diameter along the beam axis, the dependence of the H{sup −} ion beam intensity on the net 2MHz-RF power was optimized. Furthermore, the fine-tuning of RFM’s cross-section (magnetmotive force) was indispensable for easy operation with the temperature (T{sub PE}) of the plasma electrode (PE) lower than 70°C, which minimizes the transverse emittances. The 5% reduction of RFM’s cross-section decreased the time-constant to recover the cesium effects after an slightly excessive cesiation on the PE from several 10 minutes to several minutes for T{sub PE} around 60°C.

  12. A 0.5 GHz to 20.0 GHz RF generator instrument-on-a-card using MMIC and field programmable gate arrays

    NASA Astrophysics Data System (ADS)

    Lepine, Robert A.; Martuscello, Anthony R.

    An instrument-on-a-card (IAC) has been developed which uses monolithic microwave integrated circuit technology and field programmable gate arrays to provide a +20-dBm RF stimulus capability over the frequency range of 0.5 to 20.0 GHz. It is capable of being tuned in 0.15-Hz steps, in 200 microsec per step. The entire frequency range can be swept in less than 1 s. Pulse and arbitrary amplitude modulation capabilities are provided along with RF frequency agility. Within the IAC, enhanced electromagnetic interference (EMI) performance is achieved by isolating the RF circuitry from the rest of the VXI circuitry. This is accomplished, in the three-slot-wide C-size VXI module, by means of an RF-tight, shielded compartment.

  13. Anomalous self-generated electrostatic fields in nanosecond laser-plasma interaction

    SciTech Connect

    Lancia, L.; Antici, P.; Grech, M.; Weber, S.; Marques, J.-R.; Romagnani, L.; Bourgeois, N.; Audebert, P.; Fuchs, J.; Nakatsutsumi, M.; Bellue, A.; Feugeas, J.-L.; Nicolaie, Ph.; Tikhonchuk, V. T.; Grismayer, T.; Lin, T.; Nkonga, B.; Kodama, R.

    2011-03-15

    Electrostatic (E) fields associated with the interaction of a well-controlled, high-power, nanosecond laser pulse with an underdense plasma are diagnosed by proton radiography. Using a current three-dimensional wave propagation code equipped with nonlinear and nonlocal hydrodynamics, we can model the measured E-fields that are driven by the laser ponderomotive force in the region where the laser undergoes filamentation. However, strong fields of up to 110 MV/m measured in the first millimeter of propagation cannot be reproduced in the simulations. This could point to the presence of unexpected strong thermal electron pressure gradients possibly linked to ion acoustic turbulence, thus emphasizing the need for the development of full kinetic collisional simulations in order to properly model laser-plasma interaction in these strongly nonlinear conditions.

  14. Anomalous Cross-Field Current and Fluctuating Equilibrium of Magnetized Plasmas

    SciTech Connect

    Rypdal, K.; Garcia, O.E.; Paulsen, J.

    1997-09-01

    It is shown by simple physical arguments and fluid simulations that electrostatic flute-mode fluctuations can sustain a substantial cross-field current in addition to mass and energy transport. The simulations show that this current determines essential features of the fluctuating plasma equilibrium, and explain qualitatively the experimental equilibria and the coherent flute-mode structures observed in a simple magnetized torus. {copyright} {ital 1997} {ital The American Physical Society}

  15. Measured performance of the GTA rf systems

    SciTech Connect

    Denney, P.M.; Jachim, S.P.

    1993-06-01

    This paper describes the performance of the RF systems on the Ground Test Accelerator (GTA). The RF system architecture is briefly described. Among the RF performance results presented are RF field flatness and stability, amplitude and phase control resolution, and control system bandwidth and stability. The rejection by the RF systems of beam-induced disturbances, such as transients and noise, are analyzed. The observed responses are also compared to computer-based simulations of the RF systems for validation.

  16. Measured performance of the GTA rf systems

    SciTech Connect

    Denney, P.M.; Jachim, S.P.

    1993-01-01

    This paper describes the performance of the RF systems on the Ground Test Accelerator (GTA). The RF system architecture is briefly described. Among the RF performance results presented are RF field flatness and stability, amplitude and phase control resolution, and control system bandwidth and stability. The rejection by the RF systems of beam-induced disturbances, such as transients and noise, are analyzed. The observed responses are also compared to computer-based simulations of the RF systems for validation.

  17. Anomalously strong vertical magnetic fields from distant ELF/VLF sources

    NASA Astrophysics Data System (ADS)

    Silber, Israel; Price, Colin; Galanti, Eli; Shuval, Abraham

    2015-07-01

    There are many sources of very low frequency (VLF—3-30 kHz) and extremely low frequency (ELF—3-3000 Hz) radiation in the Earth-ionosphere waveguide (e.g., lightning and ELF/VLF communication transmitters). At distances of thousands of kilometers from these sources, the vertical component of the ELF/VLF AC magnetic fields is expected to be very weak and several orders of magnitude lower than the horizontal magnetic components. However, measurements in Israel show a relatively strong vertical magnetic component in both the ELF and VLF bands, at the same order of magnitude as the horizontal components. Our measurements suggest that the real Earth-ionosphere waveguide might often be very different from the theoretical waveguide used in model calculations. In addition, our results imply that using only the horizontal components for direction finding or the absolute magnetic field strength may result in errors, since often a significant fraction of the magnetic field energy hides in the vertical component.

  18. Development of gas cluster ion beam surface treatments for reducing field emission and breakdown in RF cavities

    SciTech Connect

    Swenson, D R; Degenkolb, E; Wu, A T; Insepov, Z

    2006-11-01

    Sub-micron-scale surface roughness and contamination cause field emission that can lead to high voltage breakdown of electrodes, and these are limiting factors in the development of high gradient RF technology. We are studying various Gas Cluster Ion Beam (GCIB) treatments to smooth, clean, etch and/or chemically alter electrode surfaces to allow higher fields and accelerating gradients, and to reduce the time and cost of conditioning high voltage electrodes. For this paper, we have processed Nb, Stainless Steel, and Ti electrode materials using beams of Ar, O2, or NF3 +O2 clusters with accelerating potentials up to 35 kV. Using a Scanning Field Emission Microscope (SFEM), we have repeatedly seen a dramatic reduction in the number of field emission sites on Nb coupons treated with GCIB. Smoothing effects on Stainless steel and Ti substrates have been evaluated using AFM imaging and show that 200-nm wide polishing scratch marks are greatly attenuated. A 150-mm diameter GCIB treated stainless steel electrode has now shown virtually no DC field emission current at gradients over 20 MV/m.

  19. Development of Gas Cluster Ion Beam Surface Treatments for Reducing Field Emission and Breakdown in RF cavities

    SciTech Connect

    Swenson, D. R.; Degenkolb, E.; Wu, A. T.; Insepov, Z.

    2006-11-27

    Sub-micron-scale surface roughness and contamination cause field emission that can lead to high voltage breakdown of electrodes, and these are limiting factors in the development of high gradient RF technology. We are studying various Gas Cluster Ion Beam (GCIB) treatments to smooth, clean, etch and/or chemically alter electrode surfaces to allow higher fields and accelerating gradients, and to reduce the time and cost of conditioning high voltage electrodes. For this paper, we have processed Nb, Stainless Steel, and Ti electrode materials using beams of Ar, O2, or NF3 +O2 clusters with accelerating potentials up to 35 kV. Using a Scanning Field Emission Microscope (SFEM), we have repeatedly seen a dramatic reduction in the number of field emission sites on Nb coupons treated with GCIB. Smoothing effects on Stainless steel and Ti substrates have been evaluated using AFM imaging and show that 200-nm wide polishing scratch marks are greatly attenuated. A 150-mm diameter GCIB treated stainless steel electrode has now shown virtually no DC field emission current at gradients over 20 MV/m.

  20. RF Performance of Diamond Metel-Semiconductor Field-Effect Transistor at Elevated Temperatures and Analysis of its Equivalent Circuit

    NASA Astrophysics Data System (ADS)

    Ye, Haitao; Kasu, Makoto; Ueda, Kenji; Yamauchi, Yoshiharu; Maeda, Narihiko; Sasaki, Satoshi; Makimoto, Toshiki

    2006-04-01

    Temperature dependent DC and RF characteristics of p-type diamond metal-semiconductor field-effect transistors (MESFETs) on hydrogen-terminated surfaces are investigated. The device is thermally stable up to 100 °C, because it does not deteriorate at all at higher temperatures. Temperature coefficients of transconductance (gm), drain conductance (gds), gate-source capacitance (Cgs), gate-drain capacitance (Cgd), cut-off frequency ( fT), and maximum drain current (Ids) were obtained from small-signal equivalent circuit analysis. The cut-off frequency ( fT) is almost totally independent of temperature. Intrinsic gm, gds, and Cgs decrease with increasing temperature. Cgd is almost totally independent of temperature. The threshold voltage shifts to the negative side with increasing temperature. We propose a band model of an Al-gate contact/H-terminated diamond to explain the temperature dependence of these components.

  1. A modified capacitance model of RF MEMS shunt switch incorporating fringing field effects of perforated beam

    NASA Astrophysics Data System (ADS)

    Guha, Koushik; Kumar, Mithlesh; Agarwal, Saurabh; Baishya, Srimanta

    2015-12-01

    This paper deals with the approach to accurately model the capacitance of non-uniform meander based RF MEMS shunt switch with perforated structure. Here the general analytical model of capacitance is proposed for both up state and down state condition of the switch. The model also accounts for fringing capacitance due to beam thickness and etched holes on the beam. Calculated results are validated with the simulated results of full 3D FEM solver Coventorware in both the conditions of the switch. Variation of Up-state and Down-state capacitances with different dielectric thicknesses and voltages are plotted and error of analytical value is estimated and analyzed. Three benchmark models of parallel plate capacitance are modified for MEMS switch operation and their results are compared with the proposed model. Percentage contribution of fringing capacitance in up-state and down-state is approx. 25% and 2%, respectively, of the total capacitance. The model shows good accuracy with the mean error of -4.45% in up-state and -5.78% in down-state condition for a wide range of parameter variations and -2.13% for ligament efficiency of μ = 0.3.

  2. Coupling Factor Determination in the Control of Unintentionally Generated RF Fields

    NASA Technical Reports Server (NTRS)

    McCollum, Matthew B.; Clark, Tony L.

    1999-01-01

    Radiated emissions and susceptibility requirements imposed in bands where intentional RF reception or transmission does not occur is problematical. It is often desired to compare radiated emissions with radiated susceptibility performance to assess system level compatibility. For reasons purely theoretical and because of practical measurement limitations, this not realistic. McCollum and Clark proposed a limit and test method that provided a direct comparison of radiated emissions and radiated susceptibility performance in those cases where only unintentional emissions and reception are of interest (non-tunable electronics). This test method, referred to as bulk current emissions (BCE) testing, and its associated limit is a complementary test method to bulk current injection testing and radiated susceptibility testing. Previous work utilized victim and culprit circuits with low common-mode loop impedance. Forward work identified in this publication was to determine how different loop impedance on culprit and victim circuits affected cable-to-cable coupling and the corresponding BCE test limit. Cable coupling factors for victim and culprit circuits with different loop impedance are investigated.

  3. Weakened magnetic braking as the origin of anomalously rapid rotation in old field stars.

    PubMed

    van Saders, Jennifer L; Ceillier, Tugdual; Metcalfe, Travis S; Aguirre, Victor Silva; Pinsonneault, Marc H; García, Rafael A; Mathur, Savita; Davies, Guy R

    2016-01-14

    A knowledge of stellar ages is crucial for our understanding of many astrophysical phenomena, and yet ages can be difficult to determine. As they become older, stars lose mass and angular momentum, resulting in an observed slowdown in surface rotation. The technique of 'gyrochronology' uses the rotation period of a star to calculate its age. However, stars of known age must be used for calibration, and, until recently, the approach was untested for old stars (older than 1 gigayear, Gyr). Rotation periods are now known for stars in an open cluster of intermediate age (NGC 6819; 2.5 Gyr old), and for old field stars whose ages have been determined with asteroseismology. The data for the cluster agree with previous period-age relations, but these relations fail to describe the asteroseismic sample. Here we report stellar evolutionary modelling, and confirm the presence of unexpectedly rapid rotation in stars that are more evolved than the Sun. We demonstrate that models that incorporate dramatically weakened magnetic braking for old stars can--unlike existing models--reproduce both the asteroseismic and the cluster data. Our findings might suggest a fundamental change in the nature of ageing stellar dynamos, with the Sun being close to the critical transition to much weaker magnetized winds. This weakened braking limits the diagnostic power of gyrochronology for those stars that are more than halfway through their main-sequence lifetimes. PMID:26727162

  4. SnTe field effect transistors and the anomalous electrical response of structural phase transition

    SciTech Connect

    Li, Haitao Zhu, Hao; Yuan, Hui; Li, Qiliang; You, Lin; Kopanski, Joseph J.; Richter, Curt A.; Zhao, Erhai

    2014-07-07

    SnTe is a conventional thermoelectric material and has been newly found to be a topological crystalline insulator. In this work, back-gate SnTe field-effect transistors have been fabricated and fully characterized. The devices exhibit n-type transistor behaviors with excellent current-voltage characteristics and large on/off ratio (>10{sup 6}). The device threshold voltage, conductance, mobility, and subthreshold swing have been studied and compared at different temperatures. It is found that the subthreshold swings as a function of temperature have an apparent response to the SnTe phase transition between cubic and rhombohedral structures at 110 K. The abnormal and rapid increase in subthreshold swing around the phase transition temperature may be due to the soft phonon/structure change which causes the large increase in SnTe dielectric constant. Such an interesting and remarkable electrical response to phase transition at different temperatures makes the small SnTe transistor attractive for various electronic devices.

  5. Weakened magnetic braking as the origin of anomalously rapid rotation in old field stars

    NASA Astrophysics Data System (ADS)

    van Saders, Jennifer L.; Ceillier, Tugdual; Metcalfe, Travis S.; Silva Aguirre, Victor; Pinsonneault, Marc H.; García, Rafael A.; Mathur, Savita; Davies, Guy R.

    2016-01-01

    A knowledge of stellar ages is crucial for our understanding of many astrophysical phenomena, and yet ages can be difficult to determine. As they become older, stars lose mass and angular momentum, resulting in an observed slowdown in surface rotation. The technique of ‘gyrochronology’ uses the rotation period of a star to calculate its age. However, stars of known age must be used for calibration, and, until recently, the approach was untested for old stars (older than 1 gigayear, Gyr). Rotation periods are now known for stars in an open cluster of intermediate age (NGC 6819; 2.5 Gyr old), and for old field stars whose ages have been determined with asteroseismology. The data for the cluster agree with previous period-age relations, but these relations fail to describe the asteroseismic sample. Here we report stellar evolutionary modelling, and confirm the presence of unexpectedly rapid rotation in stars that are more evolved than the Sun. We demonstrate that models that incorporate dramatically weakened magnetic braking for old stars can—unlike existing models—reproduce both the asteroseismic and the cluster data. Our findings might suggest a fundamental change in the nature of ageing stellar dynamos, with the Sun being close to the critical transition to much weaker magnetized winds. This weakened braking limits the diagnostic power of gyrochronology for those stars that are more than halfway through their main-sequence lifetimes.

  6. B0 mapping with multi-channel RF coils at high field.

    PubMed

    Robinson, Simon; Jovicich, Jorge

    2011-10-01

    Mapping the static magnetic field via the phase evolution over gradient echo scans acquired at two or more echo times is an established method. A number of possibilities exist, however, for combining phase data from multi-channel coils, denoising and thresholding field maps for high field applications. Three methods for combining phase images when no body/volume coil is available are tested: (i) Hermitian product, (ii) phase-matching over channels, and (iii) a new approach based on calculating separate field maps for each channel. The separate channel method is shown to yield field maps with higher signal-to-noise ratio than the Hermitian product and phase-matching methods and fewer unwrapping errors at low signal-to-noise ratio. Separate channel combination also allows unreliable voxels to be identified via the standard deviation over channels, which is found to be the most effective means of denoising field maps. Tests were performed using multichannel coils with between 8 and 32 channels at 3 T, 4 T, and 7 T. For application in the correction of distortions in echo-planar images, a formulation is proposed for reducing the local gradient of field maps to eliminate signal pile-up or swapping artifacts. Field maps calculated using these techniques, implemented in a freely available MATLAB toolbox, provide the basis for an effective correction for echo-planar imaging distortions at high fields. PMID:21608027

  7. Exploration of the origin of anomalous dependence for near-threshold harmonics in {{\\rm{H}}}_{2}^{+} on the ellipticity of driving laser fields

    NASA Astrophysics Data System (ADS)

    Nasiri Avanaki, K.; Telnov, Dmitry A.; Chu, Shih-I.

    2016-06-01

    The anomalous dependence of near-threshold harmonics in the {{{H}}}2+ molecular ion on the ellipticity of the driving near-infrared laser field is studied theoretically based on accurate solution of the time-dependent Schrödinger equation in prolate spheroidal coordinates with the help of the generalized pseudospectral method. For these harmonics, the maximum radiation energy corresponds to a non-zero ellipticity of the driving field. Our analysis reveals that the origin of the phenomenon lies in the near-resonant excitation of π-symmetry molecular orbitals. The excited states responsible for the anomalous ellipticity dependence of different near-threshold harmonics are identified. The effect is confirmed at the equilibrium internuclear separation R = 2 a.u. as well as for stretched molecules at R = 3 a.u.

  8. RF-PECVD synthesis of carbon nanowalls and their field emission properties

    NASA Astrophysics Data System (ADS)

    Cui, Linfan; Chen, Jiangtao; Yang, Bingjun; Sun, Dongfei; Jiao, Tifeng

    2015-12-01

    Carbon nanowalls (CNWs) were successfully fabricated on various substrates by radio frequency plasma-enhanced chemical vapor deposition using gas mixtures of acetylene, argon and hydrogen without aid of any catalyst or substrate pretreatment. The influence of synthesis parameters on the field emission behaviors of CNWs was investigated in depth. The results showed that the morphology and microstructure of CNWs could be adjusted by growth parameters (temperature, pressure and gas flow rate), and CNWs with sharp edges displayed good field emission properties. Especially, the sample prepared under the pressure of 300 Pa and the temperature of 650 °C with H2 flow rate of 120 sccm exhibited the best field emission performance (the turn-on and threshold fields were 4.7 and 6.0 V/μm, respectively). In addition, the field emission characteristics of CNWs after stability test had no obvious deterioration; however, the morphology and microstructure of CNWs changed.

  9. A target field design of open multi-purpose RF coil for musculoskeletal MR imaging at 3T.

    PubMed

    Gao, Fei; Zhang, Rui; Zhou, Diange; Wang, Xiaoying; Huang, Kefu; Zhang, Jue

    2016-10-01

    Musculoskeletal MR imaging under multi-angle situations plays an increasingly important role in assessing joint and muscle tissues system. However, there are still limitations due to the closed structures of most conventional RF coils. In this study, a time-harmonic target-field method was employed to design open multi-purpose coil (OMC) for multi-angle musculoskeletal MR imaging. The phantom imaging results suggested that the proposed OMC could achieve homogeneously distributed magnetic field and high signal-to-noise ratio (SNR) of 239.04±0.83 in the region of interest (ROI). The maximum temperature in the heating hazard test was 16°C lower than the standard regulation, which indicated the security of the designed OMC. Furthermore, to demonstrate the effectiveness of the proposed OMC for musculoskeletal MR imaging, especially for multi-angle imaging, a healthy volunteer was examined for MR imaging of elbow, ankle and knee using OMC. The in vivo imaging results showed that the proposed OMC is effective for MR imaging of musculoskeletal tissues at different body parts, with satisfied B1 field homogeneity and SNR. Moreover, the open structure of the OMC could provide a large joint movement region. The proposed open multi-purpose coil is feasible for musculoskeletal MR imaging, and potentially, it is more suitable for the evaluation of musculoskeletal tissues under multi-angle conditions. PMID:27114344

  10. Consideration of the effects of intense tissue heating on the RF electromagnetic fields during MRI: simulations for MRgFUS in the hip

    NASA Astrophysics Data System (ADS)

    Xuegang Xin, Sherman; Gu, Shiyong; Carluccio, Giuseppe; Collins, Christopher M.

    2015-01-01

    Due to the strong dependence of tissue electrical properties on temperature, it is important to consider the potential effects of intense tissue heating on the RF electromagnetic fields during MRI, as can occur in MR-guided focused ultrasound surgery. In principle, changes of the RF electromagnetic fields could affect both efficacy of RF pulses, and the MRI-induced RF heating (SAR) pattern. In this study, the equilibrium temperature distribution in a whole-body model with 2 mm resolution before and during intense tissue heating up to 60 °C at the target region was calculated. Temperature-dependent electric properties of tissues were assigned to the model to establish a temperature-dependent electromagnetic whole-body model in a 3T MRI system. The results showed maximum changes in conductivity, permittivity, ≤ft|\\mathbf{B}1+\\right|, and SAR of about 25%, 6%, 2%, and 20%, respectively. Though the B1 field and SAR distributions are both temperature-dependent, the potential harm to patients due to higher SARs is expected to be minimal and the effects on the B1 field distribution should have minimal effect on images from basic MRI sequences.

  11. Consideration of the effects of intense tissue heating on the RF electromagnetic fields during MRI: simulations for MRgFUS in the hip.

    PubMed

    Xin, Sherman Xuegang; Gu, Shiyong; Carluccio, Giuseppe; Collins, Christopher M

    2015-01-01

    Due to the strong dependence of tissue electrical properties on temperature, it is important to consider the potential effects of intense tissue heating on the RF electromagnetic fields during MRI, as can occur in MR-guided focused ultrasound surgery. In principle, changes of the RF electromagnetic fields could affect both efficacy of RF pulses, and the MRI-induced RF heating (SAR) pattern. In this study, the equilibrium temperature distribution in a whole-body model with 2 mm resolution before and during intense tissue heating up to 60 °C at the target region was calculated. Temperature-dependent electric properties of tissues were assigned to the model to establish a temperature-dependent electromagnetic whole-body model in a 3T MRI system. The results showed maximum changes in conductivity, permittivity, [absolute value]B(1)(+)[absolute value] and SAR of about 25%, 6%, 2%, and 20%, respectively. Though the B1 field and SAR distributions are both temperature-dependent, the potential harm to patients due to higher SARs is expected to be minimal and the effects on the B1 field distribution should have minimal effect on images from basic MRI sequences. PMID:25503104

  12. Wake field of electron beam accelerated in a RF-gun of free electron laser ``ELSA''

    NASA Astrophysics Data System (ADS)

    Salah, Wa'el; Dolique, J.-M.

    1999-07-01

    Wake field effects driven by a coasting relativistic charged particle beam have been studied for various cavity geometries. In the particular case of a cylindrical "pill-box" cavity, an analytical expression of the ( E, B)( x, t) map has been obtained as a development on the complete base cavity normal modes. We extend this method to the case of an accelerated beam, which leaves the downstream face of the cavity with a thermal velocity, and becomes relativistic in a few cm. This situation is very different from the classical wake of an ultrarelativistic beam for two reasons: (a) in the case of an ultrarelativistic beam, the field directly generated by beam particles in their wake can be neglected, and the so-called wake field is the electromagnetic linear reponse of the cavity to the exciting signal which is the beam. For a transrelativistic beam, the direct field must be taken into account and added to cavity reponse, which is no longer linear, except for low-intensity beam; (b) causality prevents any beam's field influence at a distance from the emissive cathode greater than ct.

  13. A toy model of fractal glioma development under RF electric field treatment.

    PubMed

    Iomin, A

    2012-06-01

    A toy model for glioma treatment by a radio frequency electric field is suggested. This low-intensity, intermediate-frequency alternating electric field is known as the tumor-treating field (TTF). In the framework of this model the efficiency of this TTF is estimated, and the interplay between the TTF and the migration-proliferation dichotomy of cancer cells is considered. The model is based on a modification of a comb model for cancer cells, where the migration-proliferation dichotomy becomes naturally apparent. Considering glioma cancer as a fractal dielectric composite of cancer cells and normal tissue cells, a new effective mechanism of glioma treatment is suggested in the form of a giant enhancement of the TTF. This leads to the irreversible electroporation that may be an effective non-invasive method of treating brain cancer. PMID:22661268

  14. Characterization of personal RF electromagnetic field exposure and actual absorption for the general public.

    PubMed

    Joseph, W; Vermeeren, G; Verloock, L; Heredia, Mauricio Masache; Martens, Luc

    2008-09-01

    In this paper, personal electromagnetic field exposure of the general public due to 12 different radiofrequency sources is characterized. Twenty-eight different realistic exposure scenarios based upon time, environment, activity, and location have been defined and a relevant number of measurements were performed with a personal exposure meter. Indoor exposure in office environments can be higher than outdoor exposure: 95th percentiles of field values due to WiFi ranged from 0.36 to 0.58 V m(-1), and for DECT values of 0.33 V m(-1) were measured. The downlink signals of GSM and DCS caused the highest outdoor exposures up to 0.52 V m(-1). The highest total field exposure occurred for mobile scenarios (inside a train or bus) from uplink signals of GSM and DCS (e.g., mobile phones) due to changing environmental conditions, handovers, and higher required transmitted signals from mobile phones due to penetration through windows while moving. A method to relate the exposure to the actual whole-body absorption in the human body is proposed. An application is shown where the actual absorption in a human body model due to a GSM downlink signal is determined. Fiftieth, 95th, and 99 th percentiles of the whole-body specific absorption rate (SAR) due to this GSM signal of 0.58 microW kg(-1), 2.08 microW kg(-1), and 5.01 microW kg(-1) are obtained for a 95th percentile of 0.26 V m(-1). A practical usable function is proposed for the relation between the whole-body SAR and the electric fields. The methodology of this paper enables epidemiological studies to make an analysis in combination with both electric field and actual whole-body SAR values and to compare exposure with basic restrictions. PMID:18695413

  15. A Theory for the Comparative RF Surface Fields at Destructive Breakdown for Various Metels

    SciTech Connect

    Wilson, Perry; /SLAC

    2006-03-20

    By destructive breakdown we mean a breakdown event that results in surface melting over large areas on the iris tip region of an accelerator structure. The melting is the result of the formation of macroscopic areas of plasma in contact with the surface. The plasma bombards the surface with an intense ion current ({approx}10{sup 8} A/cm{sup 2}), which is equivalent to a pressure on the order of a thousand Atmospheres. A radial gradient in the pressure produces a ponderomotive force that causes molten copper to migrate away from the iris tip, resulting in a measurable change in the iris shape. This distortion in the iris shape in turn produces an error in the cell-to-cell phase shift of the accelerating wave with a consequent loss in synchronism with the electron beam and a reduction in the effective accelerating gradient. Assuming a long lifetime is desired for the structure, such breakdowns must be avoided or at least limited in number. The accelerating gradient at which these breakdowns begin to occur imposes, therefore, an absolute limit on an operationally attainable gradient. The destructive breakdown limit (DBL) on the accelerating gradient depends on a number of factors, such as the geometry of the irises and coupler, the accuracy of the cell-to-cell tuning (''field flatness''), and the properties of the metal used in the high E-field regions of the structure. In this note we consider only the question of the dependence of the DBL on the metal used in the high surface field areas of the structure. There are also various types of non-destructive breakdowns (NDB's) that occur during the ''processing'' period that, after the initial application of high power, is necessary to bring the gradient up to the desired operating level. During this period, as the input power and gradient are gradually increased, thousands of such NDB's occur. These breakdowns produce a collapse in the fields in the structure as energy stored in the fields is absorbed at the breakdown

  16. Photo-Induced Anomalous Deformation of Poly(N-Isopropylacrylamide) Gel Hybridized with an Inorganic Nanosheet Liquid Crystal Aligned by Electric Field.

    PubMed

    Inadomi, Takumi; Ikeda, Shogo; Okumura, Yasushi; Kikuchi, Hirotsugu; Miyamoto, Nobuyoshi

    2014-09-16

    Poly-(N-isopropylacrylamide) (PNIPA) hydrogel films doped with uniaxially aligned liquid crystalline (LC) nanosheets adsorbed with a dye are synthesized and its anomalous photothermal deformation is demonstrated. The alignment of the nanosheet LC at the cm-scale is easily achieved by the application of an in-plane or out-of-plane AC electric field during photo-polymerization. A photoresponsive pattern is printable onto the gel with μm-scale resolution by adsorption of the dye through a pattern-holed silicone rubber. When the gel is irradiated with light, only the colored part is photothermally deformed. Interestingly, the photo-irradiated gel shows temporal expansion along one direction followed by anisotropic shrinkage, which is an anomalous behavior for a conventional PNIPA gel. PMID:25228493

  17. Microparticles in a Collisional Rf Plasma Sheath under Hypergravity Conditions as Probes for the Electric Field Strength and the Particle Charge

    SciTech Connect

    Beckers, J.; Stoffels, W. W.; Dijk, J. van; Kroesen, G. M. W.; Ockenga, T.; Wolter, M.; Kersten, H.

    2011-03-18

    We used microparticles under hypergravity conditions, induced by a centrifuge, in order to measure nonintrusively and spatially resolved the electric field strength as well as the particle charge in the collisional rf plasma sheath. The measured electric field strengths demonstrate good agreement with the literature, while the particle charge shows decreasing values towards the electrode. We demonstrate that it is indeed possible to measure these important quantities without changing or disturbing the plasma.

  18. Kinetic theory of spin-polarized systems in electric and magnetic fields with spin-orbit coupling. I. Kinetic equation and anomalous Hall and spin-Hall effects

    NASA Astrophysics Data System (ADS)

    Morawetz, K.

    2015-12-01

    The coupled kinetic equation for density and spin Wigner functions is derived including spin-orbit coupling, electric and magnetic fields, and self-consistent Hartree mean fields suited for SU(2) transport. The interactions are assumed to be with scalar and magnetic impurities as well as scalar and spin-flip potentials among the particles. The spin-orbit interaction is used in a form suitable for solid state physics with Rashba or Dresselhaus coupling, graphene, extrinsic spin-orbit coupling, and effective nuclear matter coupling. The deficiencies of the two-fluid model are worked out consisting of the appearance of an effective in-medium spin precession. The stationary solution of all these systems shows a band splitting controlled by an effective medium-dependent Zeeman field. The self-consistent precession direction is discussed and a cancellation of linear spin-orbit coupling at zero temperature is reported. The precession of spin around this effective direction caused by spin-orbit coupling leads to anomalous charge and spin currents in an electric field. Anomalous Hall conductivity is shown to consist of the known results obtained from the Kubo formula or Berry phases and a symmetric part interpreted as an inverse Hall effect. Analogously the spin-Hall and inverse spin-Hall effects of spin currents are discussed which are present even without magnetic fields showing a spin accumulation triggered by currents. The analytical dynamical expressions for zero temperature are derived and discussed in dependence on the magnetic field and effective magnetizations. The anomalous Hall and spin-Hall effect changes sign at higher than a critical frequency dependent on the relaxation time.

  19. Radio Frequency (RF) Trap for Confinement of Antimatter Plasmas Using Rotating Wall Electric Fields

    NASA Technical Reports Server (NTRS)

    Sims, William Herbert, III; Pearson, J. Boise

    2004-01-01

    Perturbations associated with a rotating wall electric field enable the confinement of ions for periods approaching weeks. This steady state confinement is a result of a radio frequency manipulation of the ions. Using state-of-the-art techniques it is shown that radio frequency energy can produce useable manipulation of the ion cloud (matter or antimatter) for use in containment experiments. The current research focuses on the improvement of confinement systems capable of containing and transporting antimatter.

  20. Increase of Efficiency of Gyrotron by Optimizing Conditions of RF-field Emission

    SciTech Connect

    Kuklin, V. M.; Lapshin, V. I.; Puzyrkov, S. Yu

    2006-01-15

    Dependence of efficiency and output power on parameter which is equal to ratio of total emission power to accumulated energy is considered in simplified model of gyrotron. It is shown that this parameter changes with changing of emission conditions at the generator output, which leads to the change of field distribution inside of gyrotron as well. Behavior of efficiency and output power is introduced in the vicinity of their maximal values.

  1. INTERCOMPARISON OF PERFORMANCE OF RF COIL GEOMETRIES FOR HIGH FIELD MOUSE CARDIAC MRI

    PubMed Central

    Constantinides, Christakis; Angeli, S.; Gkagkarellis, S.; Cofer, G.

    2012-01-01

    Multi-turn spiral surface coils are constructed in flat and cylindrical arrangements and used for high field (7.1 T) mouse cardiac MRI. Their electrical and imaging performances, based on experimental measurements, simulations, and MRI experiments in free space, and under phantom, and animal loading conditions, are compared with a commercially available birdcage coil. Results show that the four-turn cylindrical spiral coil exhibits improved relative SNR (rSNR) performance to the flat coil counterpart, and compares fairly well with a commercially available birdcage coil. Phantom experiments indicate a 50% improvement in the SNR for penetration depths ≤ 6.1 mm from the coil surface compared to the birdcage coil, and an increased penetration depth at the half-maximum field response of 8 mm in the 4-spiral cylindrical coil case, in contrast to 2.9 mm in the flat 4-turn spiral case. Quantitative comparison of the performance of the two spiral coil geometries in anterior, lateral, inferior, and septal regions of the murine heart yield maximum mean percentage rSNR increases of the order of 27–167% in vivo post-mortem (cylindrical compared to flat coil). The commercially available birdcage outperforms the cylindrical spiral coil in rSNR by a factor of 3–5 times. The comprehensive approach and methodology adopted to accurately design, simulate, implement, and test radiofrequency coils of any geometry and type, under any loading conditions, can be generalized for any application of high field mouse cardiac MRI. PMID:23204945

  2. RF potentials analysis using TOPICA

    NASA Astrophysics Data System (ADS)

    Milanesio, Daniele; Sorba, Marco; Maggiora, Riccardo

    2008-11-01

    Radio-frequency (RF) heating is fully dependent on edge plasma conditions and particularly on the acceleration of charged particles which can damage the antennas and surroundings. Rectified RF field induces drifts on ions that can hit the first wall, causing hot spots, sputtering, impurities, fuel dilution and, eventually, disruption. These phenomena mainly depend on the antenna geometry and materials, on the plasma density profile at the edge and on the connection patterns. The heat flux attributed to accelerated ions is somehow proportional to the RF potential in front of the antenna. Because of this, the understanding of the RF potential generation in front of the antenna is crucial for every high RF power systems, in order to predict the deleterious particle flux and therefore mitigate its effect by means of a proper design. The TOPICA code, an innovative tool realized for the analysis and design of ICRH and LH antennas, has been upgraded to evaluate the RF potential in front of the antenna. The solution of the Maxwell's equations in plasma combined with the RF field map at the plasma edge (standard outputs of TOPICA calculation) allow for the computation of the RF fields also in the plasma region. A new TOPICA module has been developed to account for a rigorous procedure to obtain the RF potentials and RF potential mitigation techniques through antenna geometrical modifications have been studied and will be presented.

  3. Overcoming high-field RF problems with non-magnetic Cartesian feedback transceivers.

    PubMed

    Hoult, D I; Foreman, D; Kolansky, G; Kripiakevich, D

    2008-03-01

    In extending human MR to field strengths approaching 10 T, the wavelength of electromagnetic radiation at the proton Larmor frequency becomes less than human body size and conventional radio-frequency coil circumference. Consequently, radio-frequency magnetic fields are better generated by an array of small coils than by one large coil. In this article, the primary problem of array coil interactions during transmission is examined, and a standard proposed whereby secondary induced currents should be less than 1% of the primary coil current. The use of cancellation methods and of power amplifiers with high output impedance to reduce interactions is examined in the light of this standard and found wanting. Non-magnetic Cartesian feedback transceivers functioning at the magnet entrance are then proposed as a solution that both reduces instrumentation cost and increases the bandwidth over which the standard may be met. The compromises inherent in instrument design are detailed and examples given of the innovative circuitry used. It is shown experimentally that when connected to interacting coils, two Cartesian feedback instruments function stably in accord with theory and such that the proposed standard is typically attained over a bandwidth of 22 kHz during transmission (much greater during signal reception)-enough for all current MR protocols. PMID:18026763

  4. Wireless hippocampal neural recording via a multiple input RF receiver to construct place-specific firing fields.

    PubMed

    Lee, Seung Bae; Manns, Joseph R; Ghovanloo, Maysam

    2012-01-01

    This paper reports scientifically meaningful in vivo experiments using a 32-channel wireless neural recording system (WINeR). The WINeR system is divided into transmitter (Tx) and receiver (Rx) parts. On the Tx side, we had WINeR-6, a system-on-a-chip (SoC) that operated based on time division multiplexing (TDM) of pulse width modulated (PWM) samples. The chip was fabricated in a 0.5-µm CMOS process, occupying 4.9 × 3.3 mm(2) and consuming 15 mW from ±1.5V supplies. The Rx used two antennas with separate pathways to down-convert the RF signal from a large area. A time-to-digital converter (TDC) in an FPGA converted the PWM pulses into digitized samples. In order to further increase the wireless coverage area and eliminate blind spots within a large experimental arena, two receivers were synchronized. The WINeR system was used to record epileptic activities from a rat that was injected with tetanus toxin (TT) in the dorsal hippocampus. In a different in vivo experiment, place-specific firing fields of place cells, which are parts of the hippocampal-dependent memory, were mapped from a series of behavioral experiments from a rat running in a circular track. Results from the same animal were compared against a commercial hard-wired recording system to evaluate the quality of the wireless recordings. PMID:23366004

  5. Anomalous Arms

    NASA Technical Reports Server (NTRS)

    2007-01-01

    In this composite image of spiral galaxy M106 (NGC 4258), optical data from the Digitized Sky Survey is shown as yellow, radio data from the Very Large Array appears as purple, X-ray data from Chandra is coded blue, and infrared data from the Spitzer Space Telescope appears red. Two anomalous arms, which aren't visible at optical wavelengths, appear as purple and blue emission.

  6. Mini-RF PSR Observations: Water Ice or Rocks?

    NASA Astrophysics Data System (ADS)

    Fa, W.; Cai, Y.

    2016-05-01

    The enhanced CPRs in the interior of anomalous craters in Mini-RF images are most probably caused by meter-scale rocks, suggesting that ice deposits, if present, are not the only physical agent causing the enhanced CPR.

  7. Research on heating, instabilities, turbulence and RF emission from electric field dominated plasmas

    NASA Astrophysics Data System (ADS)

    Roth, J. R.; Alexeff, Igor

    1989-07-01

    This contract has supported four research programs: (1) a program of research on plasma turbulence; (2) a program of research on plasma heating by collisional magnetic pumping; (3) a research program on the Orbitron submillimeter maser; and (4) the initial phase of a program on plasma cloaking of military targets for protection against radar and directed microwave energy weapons. Progress in these areas is documented in the text of this final report and in the twenty archival publications included in the appendices to this report. In addition to the above four research areas, work was continued on plasma diagnostic development, and the development of new state-of-the-art data analysis and reduction methods, including software development for online reduction of Langmuir probe, capacitive probe, and other diagnostic information. Also being developed is the capability to analyze electrostatic potential fluctuations by the methods of nonlinear dynamics. An important part of the research program was the training of graduate and undergraduate research assistants in state-of-the-art methods in the fields of high temperature plasma physics, plasma diagnostics, communications, and related areas.

  8. RF Sheath Models

    NASA Astrophysics Data System (ADS)

    D'Ippolito, D. A.; Myra, J. R.

    2007-11-01

    RF sheath formation on the antennas and walls in ICRF-heated experiments can reduce the heating efficiency, limit the coupled power, and cause damage to plasma-facing structures. The sheaths are driven by a slow wave component of the rf field due to a mismatch between the magnetic field and the boundary (antenna or wall). Quantitative modeling of the highly nonlinear sheaths may now be feasible for the first time in massively-parallel-processing (MPP) codes developed in the RF SciDAC project. Recently, a new approach to sheath modeling was proposed,ootnotetextD.A. D'Ippolito and J.R. Myra, Phys. Plasmas 13, 102508 (2006). in which the sheath physics is incorporated into the RF wave computation by using a modified boundary condition (BC) on the RF fields in both wave propagation and antenna codes. Here, we illustrate the use of the sheath BC for near-field sheaths by a model calculation that includes electromagnetic effects and a simple antenna coupling model. Properties of the model (such as the role of sheath-plasma waves) and implications for antenna codes such as TOPICAootnotetextV. Lancellotti et al., Nucl. Fusion 46, S476 (2006). will be discussed.

  9. AC/RF Superconductivity

    SciTech Connect

    Ciovati, Gianluigi

    2015-02-01

    This contribution provides a brief introduction to AC/RF superconductivity, with an emphasis on application to accelerators. The topics covered include the surface impedance of normal conductors and superconductors, the residual resistance, the field dependence of the surface resistance, and the superheating field.

  10. Anomalous field-induced magnetoresistance behavior in Pr0.5Sr0.5MnO3 at low temperatures

    NASA Astrophysics Data System (ADS)

    Kumar, Dhirendra; Shahee, Aga; Rawat, Rajeev; Lalla, N. P.

    2012-06-01

    Low-temperature (LT) XRD and magnetoresistance (MR) have been studied in the single phase polycrystalline Pr0.5Sr0.5MnO3 with space-group I4/mcm. The resistance-vs-temperature (R-T) variation at zero-field show a broad paramagnetic to ferromagnetic metallic (FMM) transition at Tc ˜ 240K and it further undergoes FMM to antiferromagnetic insulating (AFMI) transition at TN ˜ 90K with a broad hysteresis indicates a disorder broadened first order phase transition (FOPT). The zero-field cooled (ZFC) MR at 5K shows an open loop with virgin curve lying outside the envelope curve. This anomalous behavior vanishes with increasing temperature. This has been attributed to field-induced transformation of AFMI to FMM phase, which remains arrested down to zero magnetic field at 5K.

  11. Auxiliary coil controls temperature of RF induction heater

    NASA Technical Reports Server (NTRS)

    1966-01-01

    Auxiliary coil controls the temperature of an RF induction furnace that is powered by a relatively unstable RF generator. Manual or servoed adjustments of the relative position of the auxiliary coil, which is placed in close proximity to the RF coil, changes the looseness of the RF coil and hence the corresponding heating effect of its RF field.

  12. Dependence of beam emittance on plasma electrode temperature and rf-power, and filter-field tuning with center-gapped rod-filter magnets in J-PARC rf-driven H- ion source

    NASA Astrophysics Data System (ADS)

    Ueno, A.; Koizumi, I.; Ohkoshi, K.; Ikegami, K.; Takagi, A.; Yamazaki, S.; Oguri, H.

    2014-02-01

    The prototype rf-driven H- ion-source with a nickel plated oxygen-free-copper (OFC) plasma chamber, which satisfies the Japan Proton Accelerator Research Complex (J-PARC) 2nd stage requirements of a H- ion beam current of 60 mA within normalized emittances of 1.5 π mm mrad both horizontally and vertically, a flat top beam duty factor of 1.25% (500 μs × 25 Hz) and a life-time of more than 50 days, was reported at the 3rd international symposium on negative ions, beams, and sources (NIBS2012). The experimental results of the J-PARC ion source with a plasma chamber made of stainless-steel, instead of nickel plated OFC used in the prototype source, are presented in this paper. By comparing these two sources, the following two important results were acquired. One was that the about 20% lower emittance was produced by the rather low plasma electrode (PE) temperature (TPE) of about 120 °C compared with the typically used TPE of about 200 °C to maximize the beam current for the plasma with the abundant cesium (Cs). The other was that by using the rod-filter magnets with a gap at each center and tuning the gap-lengths, the filter-field was optimized and the rf-power necessary to produce the J-PARC required H- ion beam current was reduced typically 18%. The lower rf-power also decreases the emittances.

  13. Dependence of beam emittance on plasma electrode temperature and rf-power, and filter-field tuning with center-gapped rod-filter magnets in J-PARC rf-driven H{sup −} ion source

    SciTech Connect

    Ueno, A. Koizumi, I.; Ohkoshi, K.; Ikegami, K.; Takagi, A.; Yamazaki, S.; Oguri, H.

    2014-02-15

    The prototype rf-driven H{sup −} ion-source with a nickel plated oxygen-free-copper (OFC) plasma chamber, which satisfies the Japan Proton Accelerator Research Complex (J-PARC) 2nd stage requirements of a H{sup −} ion beam current of 60 mA within normalized emittances of 1.5 π mm mrad both horizontally and vertically, a flat top beam duty factor of 1.25% (500 μs × 25 Hz) and a life-time of more than 50 days, was reported at the 3rd international symposium on negative ions, beams, and sources (NIBS2012). The experimental results of the J-PARC ion source with a plasma chamber made of stainless-steel, instead of nickel plated OFC used in the prototype source, are presented in this paper. By comparing these two sources, the following two important results were acquired. One was that the about 20% lower emittance was produced by the rather low plasma electrode (PE) temperature (T{sub PE}) of about 120 °C compared with the typically used T{sub PE} of about 200 °C to maximize the beam current for the plasma with the abundant cesium (Cs). The other was that by using the rod-filter magnets with a gap at each center and tuning the gap-lengths, the filter-field was optimized and the rf-power necessary to produce the J-PARC required H{sup −} ion beam current was reduced typically 18%. The lower rf-power also decreases the emittances.

  14. Theory and simulation of high-brightness electron beam production from laser-irradiated photocathodes in the presence of dc and rf electric fields

    SciTech Connect

    Jones, M.E.; Peter, W.

    1986-01-01

    To take advantage of properties of laser-controlled photodiodes to produce electron beams, a new set of diode design criteria are needed. An analytical and numerical study of the geometrical and temporal factors that affect the design of high-brightness electron beams is presented. This study extends our previous work on this concept to include the effects of laser pulse shape, and emittance effects in the presence of rf fields. In general, the diode will not be space-charge limited. Therefore, the conventional Pierce electrode shapes are not appropriate. Furthermore, the finite temporal profile of the electron beams introduces a time-dependent space charge into the design problem. The approach taken here to minimize the emittance growth from the temporal profile of the space charge is to operate at low perveance. To obtain high currents, large electric fields are required. We exploit the fact that the electron emission is controlled by the laser and is independent of the voltage on the diode. The diode can then be driven by an rf field. In principle, operating at higher frequency allows higher breakdown limits, so the perveance can be made very small. However, operating at too high an rf frequency introduces other detrimental effects.

  15. Spatial and temporal RF electromagnetic field exposure of children and adults in indoor micro environments in Belgium and Greece.

    PubMed

    Vermeeren, Günter; Markakis, Ioannis; Goeminne, Francis; Samaras, Theodoros; Martens, Luc; Joseph, Wout

    2013-11-01

    Personal radio frequency electromagnetic field (RF-EMF) exposure, or exposimetry, is gaining importance in the bioelectromagnetics community but only limited data on personal exposure is available in indoor areas, namely schools, crèches, homes, and offices. Most studies are focused on adult exposure, whereas indoor microenvironments, where children are exposed, are usually not considered. A method to assess spatial and temporal indoor exposure of children and adults is proposed without involving the subjects themselves. Moreover, maximal possible daily exposure is estimated by combining instantaneous spatial and temporal exposure. In Belgium and Greece, the exposure is measured at 153 positions spread over 55 indoor microenvironments with spectral equipment. In addition, personal exposimeters (measuring EMFs of people during their daily activities) captured the temporal exposure variations during several days up to one week at 98 positions. The data were analyzed using the robust regression on order statistics (ROS) method to account for data below the detection limit. All instantaneous and maximal exposures satisfied international exposure limits and were of the same order of magnitude in Greece and Belgium. Mobile telecommunications and radio broadcasting (FM) were most present. In Belgium, digital cordless phone (DECT) exposure was present for at least 75% in the indoor microenvironments except for schools. Temporal variations of the exposure were mainly due to variations of mobile telecommunication signals. The exposure was higher during daytime than at night due to the increased voice and data traffic on the networks. Total exposure varied the most in Belgian crèches (39.3%) and Greek homes (58.2%). PMID:23872299

  16. Micro-emitter heating by rf current

    NASA Astrophysics Data System (ADS)

    Volkov, V.; Petrov, V. M.

    2016-05-01

    One factor limiting the accelerating gradients in radiofrequency (rf) cavities are field emission currents emitted by micro-emitters. The value of emitter heating power plays a key role in theories of an rf cavity processing allowing to enhance the accelerating gradient. In this paper, the emitter heating by rf current is studied. This heating mechanism associates with a large heating power (by several orders of magnitude higher than the power of field emission current) and demonstrates explicit dependence on the frequency of the electromagnetic rf field (scales with the square of the rf field frequency).

  17. Electron's anomalous magnetic-moment effects on electron-hydrogen elastic collisions in the presence of a circularly polarized laser field

    SciTech Connect

    Elhandi, S.; Taj, S.; Attaourti, Y.; Manaut, B.; Oufni, L.

    2010-04-15

    The effect of the electron's anomalous magnetic moment on the relativistic electronic dressing for the process of electron-hydrogen atom elastic collisions is investigated. We consider a laser field with circular polarization and various electric field strengths. The Dirac-Volkov states taking into account this anomaly are used to describe the process in the first order of perturbation theory. The correlation between the terms coming from this anomaly and the electric field strength gives rise to the strong dependence of the spinor part of the differential cross section (DCS) with respect to these terms. A detailed study has been devoted to the nonrelativistic regime as well as the moderate relativistic regime. Some aspects of this dependence as well as the dynamical behavior of the DCS in the relativistic regime have been addressed.

  18. RF plugging of mirror plasma

    SciTech Connect

    Kotelnikov, I.A.; Kuzmin, S.G.

    1996-12-01

    Discovery of superconducting materials that operate at high temperatures revives interest in the use of rf field for plasma confinement. This paper discusses feasibility of a scheme where resonant rf cavities are attached to the mirror ends of an open system for plasma confinement. 9 refs., 9 figs.

  19. Multi-harmonic RF test stand for RF breakdown studies

    SciTech Connect

    Jiang, Y.; Shchelkunov, S.; Yakovlev, V. P.; Solyak, N.; Kuzikov, S. V.; Hirshfield, J. L.

    2012-12-21

    A multi-harmonic RF test stand is under construction at Yale Beam Physics Laboratory. It includes a frequency multiplier which can generate high power harmonics efficiently that are phase locked to the fundamental drive frequency. In a bi-modal asymmetric cavity powered by this RF source, the cavity may experience reduced exposure time to peak fields and sweeping of peak fields across their surfaces, and strong asymmetry between surfaces that may experience cathode-and anode-like fields; these phenomena are to be assessed for their influence on RF breakdown probabilities.

  20. Effects of Hot Carriers on DC and RF Performances of Deep Submicron p-Channel Metal-Oxide-Semiconductor Field-Effect Transistors with Various Oxide Layer Thicknesses

    NASA Astrophysics Data System (ADS)

    Tang, Mao-Chyuan; Fang, Yean-Kuen; Liao, Wen-Shiang; Chen, David C.; Yeh, Chune-Sin; Chien, Shan-Chieh

    2008-04-01

    In this work, the effects of hot carriers on the DC and RF performances of 45 nm p-channel metal-oxide-semiconductor field-effect transistors (PMOSFETs) with various oxide layer thicknesses were investigated in detail by RF automatic measurements. It was found that a PMOSFET with a thinner oxide layer suffers more serious damage from hot carriers than that with a thicker oxide layer. Also, the greatest degradation occurs at the bias condition when gate stress voltage Vgstr is equal to drain stress voltage Vdstr, and it was found that the degradation of the cutoff frequency fT is dependent on transconductance gm only. This is different from conventional long-channel devices, in which the greatest degradation takes place at Vgstr = Vdstr/2 and when fT is dependent on both gm and the total gate capacitance Cgg (=Cgs+Cgd).

  1. Non-uniformity correction of human brain imaging at high field by RF field mapping of B1+ and B1-

    NASA Astrophysics Data System (ADS)

    Watanabe, Hidehiro; Takaya, Nobuhiro; Mitsumori, Fumiyuki

    2011-10-01

    A new method of non-uniform image correction is proposed. Image non-uniformity is originated from the spatial distribution of RF transmission and reception fields, represented as B1+ and B1-, respectively. In our method, B1+ mapping was performed invivo by a phase method. In B1- mapping, images with multiple TEs were acquired with a multi-echo adiabatic spin echo (MASE) sequence which enables homogeneous excitation. By T2 fitting of these images an M0 map ( M0MASE) was obtained, in which signal intensity was expressed as the product of B1- and M0(1-e). The ratio of this M0MASE map to the B1+ map showed a similar spatial pattern in different human brains. These ratios of M0MASE to B1+ in 24 subjects were averaged and then fitted with a spatially polynomial function to obtain a ratio map of B1-/B1+(α). Uniform image was achieved in spin echo (SE), MASE and inversion recovery turboFLASH (IRTF) images using measured B1+ and calculated B1- by αB1+. Water fractions in gray and white matters obtained from the M0 images corrected by this method were in good agreement with previously reported values. From these experimental results, the proposed method of non-uniformity correction is validated at 4.7 T imaging.

  2. Nd2Sn2O7 : An all-in-all-out pyrochlore magnet with no divergence-free field and anomalously slow paramagnetic spin dynamics

    NASA Astrophysics Data System (ADS)

    Bertin, A.; Dalmas de Réotier, P.; Fâk, B.; Marin, C.; Yaouanc, A.; Forget, A.; Sheptyakov, D.; Frick, B.; Ritter, C.; Amato, A.; Baines, C.; King, P. J. C.

    2015-10-01

    We report measurements performed on a polycrystalline sample of the pyrochlore compound Nd2Sn2O7 . It undergoes a second order magnetic phase transition at Tc≈0.91 K to a noncoplanar all-in-all-out magnetic structure of the Nd3 + magnetic moments. The thermal behavior of the low temperature specific heat fingerprints excitations with linear dispersion in a three-dimensional lattice. The temperature independent spin-lattice relaxation rate measured below Tc and the anomalously slow paramagnetic spin dynamics detected up to ≈30 Tc are suggested to be due to magnetic short-range correlations in unidimensional spin clusters, i.e., spin loops. The observation of a spontaneous field in muon spin relaxation measurements is associated with the absence of a divergence-free field for the ground state of an all-in-all-out pyrochlore magnet as predicted recently.

  3. DC characteristics and analog/RF performance of novel polarity control GaAs-Ge based tunnel field effect transistor

    NASA Astrophysics Data System (ADS)

    Nigam, Kaushal; Kondekar, Pravin; Sharma, Dheeraj

    2016-04-01

    In this paper, for the first time, DC characteristics and analog/RF performance of polarity control GaAs-Ge hetero TFET (GaAs-Ge H-TFET) structure have been analysed, using electrically doped dynamically configurable concept. For this, we have considered a hetero structure with two distinctive gates (Control gate and Polarity gate). Polarity gate induces p+ region at the source side and n+ region at the drain side, instead of relying on the abrupt doping profile at the junctions. Therefore, the fabrication process of the proposed device avoids ion-implantation, photo masking and complicated thermal budget. Hence, it shows high immunity against process variations, doping control issues and random dopant fluctuations (RDF). In order to optimize the device performance, interfacing of III-V groups materials with IV group semiconductor is done for hetero-junction. The introduction of hetero-junction and band gap engineering offer higher ION/IOFF ratio (5.1 × 1012), steep sub-threshold slope (18 mV/decade) and significantly change in analog/RF performance. The analog/RF figures of merit are analysed in term of transconductance (gm), output conductance (gds), gate to source capacitance (Cgs), gate to drain capacitance (Cgd), cutoff frequency (fT) and gain bandwidth (GBW) product. The proposed work would be beneficial for low power high frequency applications. The simulation results presented in this paper were carried out by using 2-D ATLAS.

  4. A Conceptual Model to Link Anomalously High Temperature Gradients in the Cerros del Rio Volcanic Field to Regional Flow in the Espanola Basin, New Mexico

    NASA Astrophysics Data System (ADS)

    Fillingham, E. J.; Keller, S. N.; McCullough, K. R.; Watters, J.; Weitering, B.; Wilce, A. M.; Folsom, M.; Kelley, S.; Pellerin, L.

    2015-12-01

    Temperature-depth well data along with electromagnetic (EM) data were collected by students of the Summer of Applied Geophysics Experience (SAGE) 2015 field season in the Espanola Basin, New Mexico. The data from this year, in addition to data acquired since 2013, were used to construct a conceptual east-west cross-section of the Espanola Basin and the adjacent highlands in order to evaluate the regional flow system. Vertical geothermal gradients from several monitoring wells were measured using a thermistor. Anomalously warm geothermal gradients were mapped in the Cerros del Rio volcanic field in the basin just east of the Rio Grande. Temperature gradients are up to 70℃/km, while the background geothermal gradients in the Rio Grande rift zone generally show 28℃-35℃/km. This anomaly extends to the Buckman well field, which supplies water to the city of Santa Fe. Overpumping of this well field has led to subsidence in the past. However, discharge temperature plots indicate that the temperature gradients of the Buckman field may be rebounding as pumping is reduced. Audiomagnetotelluric (AMT) and transient electromagnetic (TEM) data were acquired in the vicinity of three monitoring wells. TEM and AMT methods complement each other with the former having depths of investigation of less than ten to hundreds of meters and AMT having depths of investigation comparable to the wells deeper than 500m. These datasets were used collectively to image the subsurface stratigraphy and, more specifically, the hydrogeology related to shallow aquifers. The EM data collected at these wells showed a trend indicating a shallow aquifer with a shallower resistive layer of approximately 100 ohm-m at 70-100 meters depth. Beneath this resistive layer we resolved a more conductive, clay-rich layer of 10 ohm-m. These resistivity profiles compliment the electrical logs provided by Jet West, which indicate shallower sandstone interbedded with silt on top of more silt-dominant layers. Our

  5. Anomalous diffusion in the evolution of soccer championship scores: Real data, mean-field analysis, and an agent-based model

    NASA Astrophysics Data System (ADS)

    da Silva, Roberto; Vainstein, Mendeli H.; Gonçalves, Sebastián; Paula, Felipe S. F.

    2013-08-01

    Statistics of soccer tournament scores based on the double round robin system of several countries are studied. Exploring the dynamics of team scoring during tournament seasons from recent years we find evidences of superdiffusion. A mean-field analysis results in a drift velocity equal to that of real data but in a different diffusion coefficient. Along with the analysis of real data we present the results of simulations of soccer tournaments obtained by an agent-based model which successfully describes the final scoring distribution [da Silva , Comput. Phys. Commun.CPHCBZ0010-465510.1016/j.cpc.2012.10.030 184, 661 (2013)]. Such model yields random walks of scores over time with the same anomalous diffusion as observed in real data.

  6. RF transformer

    DOEpatents

    Smith, James L.; Helenberg, Harold W.; Kilsdonk, Dennis J.

    1979-01-01

    There is provided an improved RF transformer having a single-turn secondary of cylindrical shape and a coiled encapsulated primary contained within the secondary. The coil is tapered so that the narrowest separation between the primary and the secondary is at one end of the coil. The encapsulated primary is removable from the secondary so that a variety of different capacity primaries can be utilized with one secondary.

  7. Photovoltaic properties of ferroelectric BaTiO3 thin films RF sputter deposited on silicon

    NASA Technical Reports Server (NTRS)

    Dharmadhikari, V. S.; Grannemann, W. W.

    1982-01-01

    Ferroelectric thin films of BaTiO3 have been successfully deposited on n-type silicon substrates at temperatures above 500 C by RF sputtering in an O2/Ar atmosphere. Analysis by X-ray diffraction patterns show that films deposited at room temperature are amorphous. At temperatures above 500 C, crystalline BaTiO3 films with a tetragonal structure are obtained. The polarization-electric field (P-E) hysteresis loops and a broad peak in the dielectric constant versus temperature curve at Curie point indicate that the RF sputtered BaTiO3 films are ferroelectric. An anomalous photovoltaic effect is observed in these thin films which is related to the remanent polarization of the material. The results on open-circuit and short-circuit measurements provide an important basis for a better understanding of the role of photovoltaic field, photovoltaic current, and the pyroelectric properties in photoferroelectric domain switching.

  8. Investigation of the B1 field distribution and RF power deposition in a birdcage coil as functions of the number of coil legs at 4.7 T, 7.0 T, and 11.7 T

    NASA Astrophysics Data System (ADS)

    Seo, Jeung-Hoon; Han, Sang-Doc; Kim, Kyoung-Nam

    2015-06-01

    The proper design of birdcage (BC) coils plays a very important role in the acquisition of highresolution magnetic resonance imaging (MRI) of small animals such as rodents. In this context, we investigate multiple-leg (8-, 16-, 32-, 64-, and 128-leg) BC coils operating at ultra-high fields (UHF) of 7.0 T and 11.7 T and a high-field (HF) of 4.7 T for rodent magnetic resonance imaging (MRI). Primarily, Our study comparatively examines the parameters of the radiofrequency (RF) transmission (|B1 +|)-field, the magnetic flux (|B1|)-field, and RF power deposition (RF-PD) as functions of the number of BC-coil legs via finite-difference time-domain (FDTD) calculations under realistic loading conditions with a biological phantom. In particular, the specific ratio |E/B1 +| is defined for predicting RF-PD values in different coil structures. Our results indicate that the optimal number of legs of the BC coil can be chosen for different resonance frequencies of 200 MHz, 300 MHz, and 500 MHz and that this choice can be lead to superior |B1 +|-field intensity and |B1|-field homogeneity and decreased RF-PD. We believe that our approach to determining the optimal number of legs for a BC coil can contribute to rodent MR imaging.

  9. High-field actively detuneable transverse electromagnetic (TEM) coil with low-bias voltage for high-power RF transmission.

    PubMed

    Avdievich, Nikolai I; Bradshaw, Ken; Kuznetsov, Andrey M; Hetherington, Hoby P

    2007-06-01

    The design and construction of a 4T (170 MHz) transverse electromagnetic (TEM) actively detuneable quadrature head coil is described. Conventional schemes for active detuning require high negative bias voltages (>300 V) to prevent leakage of RF pulses with amplitudes of 1-2 kW. To extend the power handling capacity and avoid the use of high DC bias voltages, we developed an alternate method of detuning the volume coil. In this method the PIN diodes in the detuning circuits are shorted when the RF volume coil is tuned, and negatively biased with -12 V when the coil is detuned. To preserve the high Q(U)/Q(L) ratio of the TEM coil, we modified the method of Nabetani and Watkins (Proceedings of the 13th Annual Meeting of ISMRM, Kyoto, Japan, 2004, abstract 1574) by utilizing a high-impedance (approximately 200 Omega), lumped-element, quarter-wavelength transformer. A Q(U) of 500 was achieved for the detuneable TEM, such that incorporation of the detuning network had minimal effect (<1 dB) on the performance of the coil in vivo. PMID:17534919

  10. Lossless anomalous dispersion and an inversionless gain doublet via dressed interacting ground states

    SciTech Connect

    Weatherall, James Owen; Search, Christopher P.

    2010-02-15

    Transparent media exhibiting anomalous dispersion have been of considerable interest since Wang, Kuzmich, and Dogariu [Nature 406, 277 (2000)] first observed light propagate with superluminal and negative group velocities without absorption. Here, we propose an atomic model exhibiting these properties, based on a generalization of amplification without inversion in a five-level dressed interacting ground-state system. The system consists of a {Lambda} atom prepared as in standard electromagnetically induced transparency (EIT), with two additional metastable ground states coupled to the {Lambda} atom ground states by two rf-microwave fields. We consider two configurations by which population is incoherently pumped into the ground states of the atom. Under appropriate circumstances, we predict a pair of new gain lines with tunable width, separation, and height. Between these lines, absorption vanishes but dispersion is large and anomalous. The system described here is a significant improvement over other proposals in the anomalous dispersion literature in that it permits additional coherent control over the spectral properties of the anomalous region, including a possible 10{sup 4}-fold increase over the group delay observed by Wang, Kuzmich, and Dogariu.

  11. Rheumatoid factor (RF)

    MedlinePlus

    Rheumatoid factor (RF) is a blood test that measures the amount of the RF antibody in the blood. ... these conditions still have a "normal" or low RF. Normal value ranges may vary slightly among different ...

  12. Anomalous Shocks on the Measured Near-Field Pressure Signatures of Low-Boom Wind-Tunnel Models

    NASA Technical Reports Server (NTRS)

    Mack, Robert J.

    2006-01-01

    Unexpected shocks on wind-tunnel-measured pressure signatures prompted questions about design methods, pressure signature measurement techniques, and the quality of measurements in the flow fields near lifting models. Some of these unexpected shocks were the result of component integration methods. Others were attributed to the three-dimension nature of the flow around a lifting model, to inaccuracies in the prediction of the area-ruled lift, or to wing-tip stall effects. This report discusses the low-boom model wind-tunnel data where these unexpected shocks were initially observed, the physics of the lifting wing/body model's flow field, the wind-tunnel data used to evaluate the applicability of methods for calculating equivalent areas due to lift, the performance of lift prediction codes, and tip stall effects so that the cause of these shocks could be determined.

  13. Observation of anomalously long relaxation phenomena in Pb 3BiS x thin films under pulsed magnetic field

    NASA Astrophysics Data System (ADS)

    Iguchi, I.; Yasuda, T.

    1998-04-01

    We report the observation of very long relaxation time under pulsed magnetic fields of 0.15-1.3 kG for the Pb3BiS x thin films ( x=2.0-3.0) biased at a certain current at liquid helium temperatures below 4.2 K. Both the superconducting ( x=2.0, 2.5, 2.7) and nonsuperconducting ( x=3.0) films exhibit the novel phenomena. They develop with reducing bath temperature below 4.2 K. The response time to a pulsed magnetic field ranges from a few seconds to a few tens of seconds much greater than those expected from the conventional microscopic lifetimes in the solid. The observed pulse shape is quite asymmetric, and the rise time is longer than the fall time. It strongly depends on the amplitude of magnetic field, but it weakly depends on the sulfur concentration x. The discussion is given in connection with the possible formation of quasilocal states of charge carriers separated from the band states by a barrier.

  14. An Analysis of the Temperature and Field Dependence of the RF Surface Resistance of Nitrogen-Doped Niobium SRF Cavities with Respect to Existing Theoretical Models

    SciTech Connect

    Reece, Charles E.; Palczewski, Ari D.; Xiao, Binping

    2015-09-01

    Recent progress with the reduction of rf surface resistance (Rs) of niobium SRF cavities via the use of high temperature surface doping by nitrogen has opened a new regime for energy efficient accelerator applications. For particular doping conditions one observes dramatic decreases in Rs with increasing surface magnetic fields. The observed variations as a function of temperature may be analyzed in the context of recent theoretical treatments in hopes of gaining insight into the underlying beneficial mechanism of the nitrogen treatment. Systematic data sets of Q0 vs. Eacc vs. temperature acquired during the high Q0 R&D work of the past year will be compared with theoretical model predictions..

  15. Optical/Near-infrared Polarization Survey of Sh 2-29: Magnetic Fields, Dense Cloud Fragmentations, and Anomalous Dust Grain Sizes

    NASA Astrophysics Data System (ADS)

    Santos, Fábio P.; Franco, Gabriel A. P.; Roman-Lopes, Alexandre; Reis, Wilson; Román-Zúñiga, Carlos G.

    2014-03-01

    Sh 2-29 is a conspicuous star-forming region marked by the presence of massive embedded stars as well as several notable interstellar structures. In this research, our goals were to determine the role of magnetic fields and to study the size distribution of interstellar dust particles within this turbulent environment. We have used a set of optical and near-infrared polarimetric data obtained at OPD/LNA (Brazil) and CTIO (Chile), correlated with extinction maps, Two Micron All Sky Survey data, and images from the Digitized Sky Survey and Spitzer. The region's most striking feature is a swept out interstellar cavity whose polarimetric maps indicate that magnetic field lines were dragged outward, piling up along its borders. This led to a higher magnetic strength value (≈400 μG) and an abrupt increase in polarization degree, probably due to an enhancement in alignment efficiency. Furthermore, dense cloud fragmentations with peak AV between 20 and 37 mag were probably triggered by its expansion. The presence of 24 μm point-like sources indicates possible newborn stars inside this dense environment. A statistical analysis of the angular dispersion function revealed areas where field lines are aligned in a well-ordered pattern, seemingly due to compression effects from the H II region expansion. Finally, Serkowski function fits were used to study the ratio of the total-to-selective extinction, revealing a dual population of anomalous grain particle sizes. This trend suggests that both effects of coagulation and fragmentation of interstellar grains are present in the region. Based on observations collected at the National Optical Astronomy Observatory (CTIO, Chile) and Observatório do Pico dos Dias, operated by Laboratório Nacional de Astrofísica (LNA/MCT, Brazil).

  16. Optical/near-infrared polarization survey of Sh 2-29: Magnetic fields, dense cloud fragmentations, and anomalous dust grain sizes

    SciTech Connect

    Santos, Fábio P.; Franco, Gabriel A. P.; Reis, Wilson; Roman-Lopes, Alexandre; Román-Zúñiga, Carlos G. E-mail: franco@fisica.ufmg.br E-mail: roman@dfuls.cl

    2014-03-01

    Sh 2-29 is a conspicuous star-forming region marked by the presence of massive embedded stars as well as several notable interstellar structures. In this research, our goals were to determine the role of magnetic fields and to study the size distribution of interstellar dust particles within this turbulent environment. We have used a set of optical and near-infrared polarimetric data obtained at OPD/LNA (Brazil) and CTIO (Chile), correlated with extinction maps, Two Micron All Sky Survey data, and images from the Digitized Sky Survey and Spitzer. The region's most striking feature is a swept out interstellar cavity whose polarimetric maps indicate that magnetic field lines were dragged outward, piling up along its borders. This led to a higher magnetic strength value (≈400 μG) and an abrupt increase in polarization degree, probably due to an enhancement in alignment efficiency. Furthermore, dense cloud fragmentations with peak A{sub V} between 20 and 37 mag were probably triggered by its expansion. The presence of 24 μm point-like sources indicates possible newborn stars inside this dense environment. A statistical analysis of the angular dispersion function revealed areas where field lines are aligned in a well-ordered pattern, seemingly due to compression effects from the H II region expansion. Finally, Serkowski function fits were used to study the ratio of the total-to-selective extinction, revealing a dual population of anomalous grain particle sizes. This trend suggests that both effects of coagulation and fragmentation of interstellar grains are present in the region.

  17. Anomalous behaviour of critical fields near a superconducting quantum critical point in BaFe2(As1-xPx)2

    NASA Astrophysics Data System (ADS)

    Putzke, C.; Carrington, A.; Walmsley, P.; Malone, L.; Fletcher, J. D.; See, P.; Vignolles, D.; Proust, C.; Badoux, S.; Kasahara, S.; Mazukami, Y.; Shibauchi, T.; Matsuda, Y.

    2014-03-01

    BaFe2(As1-xPx)2 presents one of the cleanest and clearest systems in which to study the influence of quantum critical fluctuations on high temperature superconductivity. In this material a sharp maximum in the magnetic penetration depth has been found at the quantum critical point (QCP x = 0 . 3) where Tc is maximal1. Specific heat and de Haas-van Alphen effect measurements2 show that this peak is driven by a corresponding increase in the quasiparticle effective mass. Based on these previous results a simple one-band theory would suggest that at the QCP we should expect a large increase in Hc 2 and a corresponding dip in Hc 1 . Actual measurements of these critical fields, which we present here, shows quite different behavior which we suggest is caused by an anomalous enhancement in the vortex core energy close to the QCP. 1 K.Hashimoto et.al., Science 336, 1554 (2012) 2 P.Walmsley, C.Putzke et.al., Phys. Rev. Lett. 110, 257002 (2013) This work was supported by the Engineering and Physical Sciences Research Council, EuroMagNET II, and KAKENHI from JSPS.

  18. Insights about the Origin of Anomalous Transport through Fractured Media: Modeling and Observations from a Field Test in Fractured Granite

    NASA Astrophysics Data System (ADS)

    Kang, P. K.; Le Borgne, T.; Bour, O.; Klepikova, M.; Lavenant, N.; Dentz, M.; Juanes, R.

    2011-12-01

    For the studies of surface soil moisture, radar observations offer high spatial resolution through aperture synthesis. The spatial resolution may be tens of meters from airborne platform to a few kilometers for global mapping from spaceborne platforms such as the L-band Soil Moisture Active Passive (SMAP) mission. A suite of sophisticated radar scattering forward models 'data-cubes' were developed for 17 land cover classes that simulate the radar response to soil moisture, surface roughness, and diverse vegetation. The inversion of the forward models to estimate soil moisture becomes a well-constrained problem through time-series analysis and parameterization of vegetation structure through an empirical allometric relationship. The retrieval approach has been developed for application using SMAP radar observations. This paper studies the applicability of the approach to radar observations over various spatial scales. The high-resolution airborne L-band radar data were collected by the Uninhabited Aerial Vehicle Synthetic Aperture Radar during the SMAP Validation Experiment 2012 conducted near Winnipeg, Canada in 2012 over agriculture fields. During the six-week campaign period, there were three major drying cycles of surface soil moisture that occurred while the agricultural vegetation grew from bare condition to full canopy. The volumetric soil moisture and radar backscattering generally showed a positive relationship when the vegetation effect was not strong, such as over pasture fields, or when the vegetation effect did not change substantially over time, such as for wheat fields. However, the significant temporal changes in corn and soybean canopies from bare to full growth result in a reverse of this relationship over these fields. The data-cube retrieval approach was able to systematically correct for the effect of the changing vegetation. Errors in soil moisture retrieval ranged from 0.037 to 0.086 cm3/cm3, when evaluated over all the available fields. In

  19. Design and Evaluation of a Hybrid Radiofrequency Applicator for Magnetic Resonance Imaging and RF Induced Hyperthermia: Electromagnetic Field Simulations up to 14.0 Tesla and Proof-of-Concept at 7.0 Tesla

    PubMed Central

    Winter, Lukas; Özerdem, Celal; Hoffmann, Werner; Santoro, Davide; Müller, Alexander; Waiczies, Helmar; Seemann, Reiner; Graessl, Andreas; Wust, Peter; Niendorf, Thoralf

    2013-01-01

    This work demonstrates the feasibility of a hybrid radiofrequency (RF) applicator that supports magnetic resonance (MR) imaging and MR controlled targeted RF heating at ultrahigh magnetic fields (B0≥7.0T). For this purpose a virtual and an experimental configuration of an 8-channel transmit/receive (TX/RX) hybrid RF applicator was designed. For TX/RX bow tie antenna electric dipoles were employed. Electromagnetic field simulations (EMF) were performed to study RF heating versus RF wavelength (frequency range: 64 MHz (1.5T) to 600 MHz (14.0T)). The experimental version of the applicator was implemented at B0 = 7.0T. The applicators feasibility for targeted RF heating was evaluated in EMF simulations and in phantom studies. Temperature co-simulations were conducted in phantoms and in a human voxel model. Our results demonstrate that higher frequencies afford a reduction in the size of specific absorption rate (SAR) hotspots. At 7T (298 MHz) the hybrid applicator yielded a 50% iso-contour SAR (iso-SAR-50%) hotspot with a diameter of 43 mm. At 600 MHz an iso-SAR-50% hotspot of 26 mm in diameter was observed. RF power deposition per RF input power was found to increase with B0 which makes targeted RF heating more efficient at higher frequencies. The applicator was capable of generating deep-seated temperature hotspots in phantoms. The feasibility of 2D steering of a SAR/temperature hotspot to a target location was demonstrated by the induction of a focal temperature increase (ΔT = 8.1 K) in an off-center region of the phantom. Temperature simulations in the human brain performed at 298 MHz showed a maximum temperature increase to 48.6C for a deep-seated hotspot in the brain with a size of (19×23×32)mm3 iso-temperature-90%. The hybrid applicator provided imaging capabilities that facilitate high spatial resolution brain MRI. To conclude, this study outlines the technical underpinnings and demonstrates the basic feasibility of an 8-channel hybrid TX

  20. Design and evaluation of a hybrid radiofrequency applicator for magnetic resonance imaging and RF induced hyperthermia: electromagnetic field simulations up to 14.0 Tesla and proof-of-concept at 7.0 Tesla.

    PubMed

    Winter, Lukas; Özerdem, Celal; Hoffmann, Werner; Santoro, Davide; Müller, Alexander; Waiczies, Helmar; Seemann, Reiner; Graessl, Andreas; Wust, Peter; Niendorf, Thoralf

    2013-01-01

    This work demonstrates the feasibility of a hybrid radiofrequency (RF) applicator that supports magnetic resonance (MR) imaging and MR controlled targeted RF heating at ultrahigh magnetic fields (B0≥7.0T). For this purpose a virtual and an experimental configuration of an 8-channel transmit/receive (TX/RX) hybrid RF applicator was designed. For TX/RX bow tie antenna electric dipoles were employed. Electromagnetic field simulations (EMF) were performed to study RF heating versus RF wavelength (frequency range: 64 MHz (1.5T) to 600 MHz (14.0T)). The experimental version of the applicator was implemented at B0 = 7.0T. The applicators feasibility for targeted RF heating was evaluated in EMF simulations and in phantom studies. Temperature co-simulations were conducted in phantoms and in a human voxel model. Our results demonstrate that higher frequencies afford a reduction in the size of specific absorption rate (SAR) hotspots. At 7T (298 MHz) the hybrid applicator yielded a 50% iso-contour SAR (iso-SAR-50%) hotspot with a diameter of 43 mm. At 600 MHz an iso-SAR-50% hotspot of 26 mm in diameter was observed. RF power deposition per RF input power was found to increase with B0 which makes targeted RF heating more efficient at higher frequencies. The applicator was capable of generating deep-seated temperature hotspots in phantoms. The feasibility of 2D steering of a SAR/temperature hotspot to a target location was demonstrated by the induction of a focal temperature increase (ΔT = 8.1 K) in an off-center region of the phantom. Temperature simulations in the human brain performed at 298 MHz showed a maximum temperature increase to 48.6C for a deep-seated hotspot in the brain with a size of (19×23×32)mm(3) iso-temperature-90%. The hybrid applicator provided imaging capabilities that facilitate high spatial resolution brain MRI. To conclude, this study outlines the technical underpinnings and demonstrates the basic feasibility of an 8-channel hybrid TX

  1. Theoretical approach of the photoinjector exit aperture influence on the wake field driven by an electron beam accelerated in an RF gun of free-electron laser ``ELSA''

    NASA Astrophysics Data System (ADS)

    Salah, Wa'el; Dolique, J.-M.

    2000-06-01

    The wake field generated in the cylindrical cavity of an RF photoinjector, by a strongly accelerated electron beam, has been analytically calculated (Salah, Dolique, Nucl. Instr. and Meth. A 437 (1999) 27) under the assumption that the perturbation of the field map by the exit hole is negligible as long as the ratio: exit hole radius/cavity radius is lower than approximately 1/3. Shown experimentally in the different context of a long accelerating structure formed by a sequence of bored pill-box cavity (Figuera et al., Phys. Rev. Lett. 60 (1988) 2144; Kim et al., J. Appl. Phys. 68 (1990) 4942), this often-quoted result must be checked for the wake field map excited in a photo injector cavity. Further, in the latter case, the empirical rule in question can be broken more easily because, due to causality, the cavity radius to be considered is not the physical radius but that of the part of the anode wall around the exit hole reached by the beam electromagnetic influence. We present an analytical treatment of the wake field driven in a photoinjector by the accelerated electron beam which takes this hole effect into account, whatever the hole radius may be.

  2. Anomalous effect in a hydrogenic impurity in a spherical quantum dot under the influence of parallel electric and magnetic fields

    NASA Astrophysics Data System (ADS)

    Ho, Y. K.; Lin, Y. C.; Sahoo, S.

    2004-03-01

    We will present calculations for the energy levels and the resonance widths of the quasi-bound states of a confined hydrogenic impurity in an isolate quantum dot subjected to external electric and magnetic fields in parallel directions. A method of complex absorbing potential [1] is used in our present investigation. Resonance positions and widths are reported for a wide range of dot sizes to demonstrate that Stark resonances in a confined hydrogen atom leads to a new phenomenon as a consequence of the quantum confinement of the atom, contrary to the Stark effect on a free atom. * This work was supported by the National Science Council of ROC. [1] S. Sahoo and Y. K. Ho, Chin. J. Phys. 38, 127 (2000); J. Phys. B 33, 2195 (2000); J. Phys. B 33, 5151 (2000); Phys. Rev. A 65, 015403 (2001);

  3. Exposure to GSM RF Fields Does Not Affect Calcium Homeostasis in Human Endothelial Cells, Rat Pheocromocytoma Cells or Rat Hippocampal Neurons

    PubMed Central

    O'Connor, Rodney P.; Madison, Steve D.; Leveque, Philippe; Roderick, H. Llewelyn; Bootman, Martin D.

    2010-01-01

    exposure on Ca2+ signals. Our data indicate that 900 MHz GSM fields do not affect either basal Ca2+ homeostasis or provoked Ca2+ signals. Even at the highest field strengths applied, which exceed typical phone exposure levels, we did not observe any changes in cellular Ca2+ signals. We conclude that under the conditions employed in our experiments, and using a highly-sensitive assay, we could not detect any consequence of RF exposure. PMID:20676401

  4. Exposure to GSM RF fields does not affect calcium homeostasis in human endothelial cells, rat pheocromocytoma cells or rat hippocampal neurons.

    PubMed

    O'Connor, Rodney P; Madison, Steve D; Leveque, Philippe; Roderick, H Llewelyn; Bootman, Martin D

    2010-01-01

    exposure on Ca2+ signals. Our data indicate that 900 MHz GSM fields do not affect either basal Ca2+ homeostasis or provoked Ca2+ signals. Even at the highest field strengths applied, which exceed typical phone exposure levels, we did not observe any changes in cellular Ca2+ signals. We conclude that under the conditions employed in our experiments, and using a highly-sensitive assay, we could not detect any consequence of RF exposure. PMID:20676401

  5. Spectrum of anomalous magnetohydrodynamics

    NASA Astrophysics Data System (ADS)

    Giovannini, Massimo

    2016-05-01

    The equations of anomalous magnetohydrodynamics describe an Abelian plasma where conduction and chiral currents are simultaneously present and constrained by the second law of thermodynamics. At high frequencies the magnetic currents play the leading role, and the spectrum is dominated by two-fluid effects. The system behaves instead as a single fluid in the low-frequency regime where the vortical currents induce potentially large hypermagnetic fields. After deriving the physical solutions of the generalized Appleton-Hartree equation, the corresponding dispersion relations are scrutinized and compared with the results valid for cold plasmas. Hypermagnetic knots and fluid vortices can be concurrently present at very low frequencies and suggest a qualitatively different dynamics of the hydromagnetic nonlinearities.

  6. Association of Exposure to Radio-Frequency Electromagnetic Field Radiation (RF-EMFR) Generated by Mobile Phone Base Stations with Glycated Hemoglobin (HbA1c) and Risk of Type 2 Diabetes Mellitus

    PubMed Central

    Meo, Sultan Ayoub; Alsubaie, Yazeed; Almubarak, Zaid; Almutawa, Hisham; AlQasem, Yazeed; Muhammed Hasanato, Rana

    2015-01-01

    Installation of mobile phone base stations in residential areas has initiated public debate about possible adverse effects on human health. This study aimed to determine the association of exposure to radio frequency electromagnetic field radiation (RF-EMFR) generated by mobile phone base stations with glycated hemoglobin (HbA1c) and occurrence of type 2 diabetes mellitus. For this study, two different elementary schools (school-1 and school-2) were selected. We recruited 159 students in total; 96 male students from school-1, with age range 12–16 years, and 63 male students with age range 12–17 years from school-2. Mobile phone base stations with towers existed about 200 m away from the school buildings. RF-EMFR was measured inside both schools. In school-1, RF-EMFR was 9.601 nW/cm2 at frequency of 925 MHz, and students had been exposed to RF-EMFR for a duration of 6 h daily, five days in a week. In school-2, RF-EMFR was 1.909 nW/cm2 at frequency of 925 MHz and students had been exposed for 6 h daily, five days in a week. 5–6 mL blood was collected from all the students and HbA1c was measured by using a Dimension Xpand Plus Integrated Chemistry System, Siemens. The mean HbA1c for the students who were exposed to high RF-EMFR was significantly higher (5.44 ± 0.22) than the mean HbA1c for the students who were exposed to low RF-EMFR (5.32 ± 0.34) (p = 0.007). Moreover, students who were exposed to high RF-EMFR generated by MPBS had a significantly higher risk of type 2 diabetes mellitus (p = 0.016) relative to their counterparts who were exposed to low RF-EMFR. It is concluded that exposure to high RF-EMFR generated by MPBS is associated with elevated levels of HbA1c and risk of type 2 diabetes mellitus. PMID:26580639

  7. Association of Exposure to Radio-Frequency Electromagnetic Field Radiation (RF-EMFR) Generated by Mobile Phone Base Stations with Glycated Hemoglobin (HbA1c) and Risk of Type 2 Diabetes Mellitus.

    PubMed

    Meo, Sultan Ayoub; Alsubaie, Yazeed; Almubarak, Zaid; Almutawa, Hisham; AlQasem, Yazeed; Hasanato, Rana Muhammed

    2015-11-01

    Installation of mobile phone base stations in residential areas has initiated public debate about possible adverse effects on human health. This study aimed to determine the association of exposure to radio frequency electromagnetic field radiation (RF-EMFR) generated by mobile phone base stations with glycated hemoglobin (HbA1c) and occurrence of type 2 diabetes mellitus. For this study, two different elementary schools (school-1 and school-2) were selected. We recruited 159 students in total; 96 male students from school-1, with age range 12-16 years, and 63 male students with age range 12-17 years from school-2. Mobile phone base stations with towers existed about 200 m away from the school buildings. RF-EMFR was measured inside both schools. In school-1, RF-EMFR was 9.601 nW/cm² at frequency of 925 MHz, and students had been exposed to RF-EMFR for a duration of 6 h daily, five days in a week. In school-2, RF-EMFR was 1.909 nW/cm² at frequency of 925 MHz and students had been exposed for 6 h daily, five days in a week. 5-6 mL blood was collected from all the students and HbA1c was measured by using a Dimension Xpand Plus Integrated Chemistry System, Siemens. The mean HbA1c for the students who were exposed to high RF-EMFR was significantly higher (5.44 ± 0.22) than the mean HbA1c for the students who were exposed to low RF-EMFR (5.32 ± 0.34) (p = 0.007). Moreover, students who were exposed to high RF-EMFR generated by MPBS had a significantly higher risk of type 2 diabetes mellitus (p = 0.016) relative to their counterparts who were exposed to low RF-EMFR. It is concluded that exposure to high RF-EMFR generated by MPBS is associated with elevated levels of HbA1c and risk of type 2 diabetes mellitus. PMID:26580639

  8. Direct, spectroscopic measurement of electric fields in a plasma-RF antenna interaction region in Tore Supra

    SciTech Connect

    Klepper, C Christopher; Hillis, Donald Lee; Isler, Ralph C; Hillairet, J.; Martin, E. H.; Colas, L.; Ekedahl, A.; Goniche, M.; Lotte, Ph.; Colledani, G.; Martin, V.; Panayotis, Stephanie; Pegourie, B.; Harris, Jeffrey H

    2013-01-01

    Balmer-series spectral line profiles of deuterium emission near a lower-hybrid (3.7 GHz) wave, high power (1-4 MW) launcher were measured with high-spectral resolution in the Tore Supra tokamak and fitted to an atomic physics model which includes both Zeeman and dynamic Stark effects. The magnetic field is static and the electric field is assumed to be monochromatic at 3.7 GHz. The determined strength and direction of the high-frequency electric field is found to be in good agreement with the results of a simulation that computes the propagation of these lower hybrid waves into the plasma in the region around the launch antenna and specifically in the region of estimated peak emission contributing to the measurement. This agreement indicates feasibility for the use of dynamic Stark effect spectroscopy to study interaction at the plasma antenna interactions in a fusion plasma environment. (C) 2013 Elsevier B. V. All rights reserved.

  9. Plasma rotation and rf heating in DIII-D

    SciTech Connect

    deGrassie, J.S.; Baker, D.R.; Burrell, K.H.

    1999-05-01

    In a variety of discharge conditions on DIII-D it is observed that rf electron heating reduces the toroidal rotation speed and core ion temperature. The rf heating can be with either fast wave or electron cyclotron heating and this effect is insensitive to the details of the launched toroidal wavenumber spectrum. To date all target discharges have rotation first established with co-directed neutral beam injection. A possible cause is enhanced ion momentum and thermal diffusivity due to electron heating effectively creating greater anomalous viscosity. Another is that a counter directed toroidal force is applied to the bulk plasma via rf driven radial current.

  10. Classification of personal exposure to radio frequency electromagnetic fields (RF-EMF) for epidemiological research: Evaluation of different exposure assessment methods.

    PubMed

    Frei, Patrizia; Mohler, Evelyn; Bürgi, Alfred; Fröhlich, Jürg; Neubauer, Georg; Braun-Fahrländer, Charlotte; Röösli, Martin

    2010-10-01

    The use of personal exposure meters (exposimeters) has been recommended for measuring personal exposure to radio frequency electromagnetic fields (RF-EMF) from environmental far-field sources in everyday life. However, it is unclear to what extent exposimeter readings are affected by measurements taken when personal mobile and cordless phones are used. In addition, the use of exposimeters in large epidemiological studies is limited due to high costs and large effort for study participants. In the current analysis we aimed to investigate the impact of personal phone use on exposimeter readings and to evaluate different exposure assessment methods potentially useful in epidemiological studies. We collected personal exposimeter measurements during one week and diary data from 166 study participants. Moreover, we collected spot measurements in the participants' bedrooms and data on self-estimated exposure, assessed residential exposure to fixed site transmitters by calculating the geo-coded distance and mean RF-EMF from a geospatial propagation model, and developed an exposure prediction model based on the propagation model and exposure relevant behavior. The mean personal exposure was 0.13 mW/m(2), when measurements during personal phone calls were excluded and 0.15 mW/m(2), when such measurements were included. The Spearman correlation with personal exposure (without personal phone calls) was 0.42 (95%-CI: 0.29 to 0.55) for the spot measurements, -0.03 (95%-CI: -0.18 to 0.12) for the geo-coded distance, 0.28 (95%-CI: 0.14 to 0.42) for the geospatial propagation model, 0.50 (95%-CI: 0.37 to 0.61) for the full exposure prediction model and 0.06 (95%-CI: -0.10 to 0.21) for self-estimated exposure. In conclusion, personal exposure measured with exposimeters correlated best with the full exposure prediction model and spot measurements. Self-estimated exposure and geo-coded distance turned out to be poor surrogates for personal exposure. PMID:20538340

  11. RF Field Enhancement with High Dielectric Constant (HDC) Pads in a Receive Array Coil at 3.0 T

    PubMed Central

    Yang, Qing X.; Luo, Wei; Rupprecht, Sebastian; Herse, Zachary; Sica, Christopher; Wang, Jianli; Cao, Zhipeng; Vesek, Jeffrey; Lanagan, Michael T.; Carluccio, Giuseppe; Ryu, Yeun-Chul; Collins, Christopher M.

    2012-01-01

    Purpose To investigate the use of a new high-dielectric constant (HDC) material for improving SNR and transmission efficiency for clinical MRI applications at 3T with cervical spine imaging. Materials and Methods Human subjects were imaged using a commercial cervical spine receive array coil on a clinical system with and without pads containing Barium Titanate beads in deuterium water placed around the neck. Numerical electromagnetic field simulations of the same configuration were also performed. Results Experimental and simulated maps of transmit and receive fields showed greater efficiency for imaging the cervical spine when the pads were present. Experimental measurements showed a significant improvement in SNR with the pads present and an average input power reduction of 46%. Conclusion Use of HDC material can enhance SNR and transmission efficiency for clinical imaging of the cervical spine at 3.0 T. PMID:23293090

  12. Recycler barrier RF buckets

    SciTech Connect

    Bhat, C.M.; /Fermilab

    2011-03-01

    The Recycler Ring at Fermilab uses a barrier rf systems for all of its rf manipulations. In this paper, I will give an overview of historical perspective on barrier rf system, the longitudinal beam dynamics issues, aspects of rf linearization to produce long flat bunches and methods used for emittance measurements of the beam in the RR barrier rf buckets. Current rf manipulation schemes used for antiproton beam stacking and longitudinal momentum mining of the RR beam for the Tevatron collider operation are explained along with their importance in spectacular success of the Tevatron luminosity performance.

  13. Improvements in RF Shimming in High Field MRI Using High Permittivity Materials With Low Order Pre-Fractal Geometries.

    PubMed

    Schmidt, Rita; Webb, Andrew

    2016-08-01

    Ultra-high field MRI is an area of great interest for clinical research and basic science due to the increased signal-to-noise, spatial resolution and magnetic-susceptibility-based contrast. However, the fact that the electromagnetic wavelength in tissue is comparable to the relevant body dimensions means that the uniformity of the excitation field is much poorer than at lower field strengths. In addition to techniques such as transmit arrays, one simple but effective method to counteract this effect is to use high permittivity "pads". Very high permittivities enable thinner, flexible pads to be used, but the limiting factor is wavelength effects within the pads themselves, which can lead to image artifacts. So far, all studies have used simple continuous rectangular/circular pad geometries. In this work we investigate how the wavelength effects can be partially mitigated utilizing shaped pad with holes. Several arrangements have been simulated, including low order pre-fractal geometries, which maintain the overall coverage of the pad, but can provide better image homogeneity in the region of interest or higher sensitivity depending on the setup. Experimental data in the form of in vivo human images at 7T were acquired to validate the simulation results. PMID:26890643

  14. The Quantum Anomalous Hall Effect: Theory and Experiment

    NASA Astrophysics Data System (ADS)

    Liu, Chao-Xing; Zhang, Shou-Cheng; Qi, Xiao-Liang

    2016-03-01

    The quantum anomalous Hall effect is defined as a quantized Hall effect realized in a system without an external magnetic field. The quantum anomalous Hall effect is a novel manifestation of topological structure in many-electron systems and may have potential applications in future electronic devices. In recent years, the quantum anomalous Hall effect was proposed theoretically and realized experimentally. In this review article, we provide a systematic overview of the theoretical and experimental developments in this field.

  15. RF hyperthermia using conductive nanoparticles

    NASA Astrophysics Data System (ADS)

    Gach, H. Michael; Balachandrasekaran, Arvind; Nair, Tejas

    2010-02-01

    Specific absorption rate (SAR) heating using radiofrequency (RF) waves is affected by the RF frequency and amplitude, and the conductivity of the tissue. Recently, conductive nanoparticles were demonstrated to induce hyperthermia in vitro and in vivo upon irradiation with an external 13.56 MHz RF field. The addition of conductive nanoparticles was assumed to increase the tissue conductivity and SAR. However, no quantitative studies have been performed that characterize the conductivities of biocompatible colloids or tissues containing nanoparticles, and relate the conductivity to SAR. The complex permittivities were measured for colloids containing single-wall carbon nanotubes (SWCNTs) in normal saline with 0.32% w/v Pluronic F108 nonionic surfactant. The carbon concentrations of the colloids ranged from 0 to 88 mM. The permittivities were measured using a dielectric probe and RF network analyzer for RF frequencies from 200 MHz to 3 GHz. The nonionic surfactant was added to the colloids to minimize flocculation of the nanotubes during the RF heating experiments. The results were compared with prior measurements of colloids containing 0.02% Pluronic F108. The dielectric and conductivity of the 0.02% Pluronic colloids rose linearly with carbon concentration but the 0.32% Pluronic colloids varied from linearity. Based on the permittivity results, selected colloid samples were placed inside a Bruker 7T/20 magnetic resonance (MR) imaging (MRI) system and irradiated at 300 MHz using a high duty cycle RF pulse sequence. The temperature changes were measured directly using fiber-optic thermometers and indirectly using MR thermometry and spectroscopy. Temperature changes were consistent with the colloid conductivities.

  16. Ion bombardment in RF photoguns

    SciTech Connect

    Pozdeyev,E.; Kayran, D.; Litvinenko, V. N.

    2009-05-04

    A linac-ring eRHIC design requires a high-intensity CW source of polarized electrons. An SRF gun is viable option that can deliver the required beam. Numerical simulations presented elsewhere have shown that ion bombardment can occur in an RF gun, possibly limiting lifetime of a NEA GaAs cathode. In this paper, we analytically solve the equations of motion of ions in an RF gun using the ponderomotive potential of the Rf field. We apply the method to the BNL 1/2-cell SRF photogun and demonstrate that a significant portion of ions produced in the gun can reach the cathode if no special precautions are taken. Also, the paper discusses possible mitigation techniques that can reduce the rate of ion bombardment.

  17. Intrauterine effects of electromagnetic fields--(low frequency, mid-frequency RF, and microwave): review of epidemiologic studies.

    PubMed

    Robert, E

    1999-04-01

    Electromagnetic radiations are named according to frequency or to wavelength (which is inversely proportional to frequency) and create electromagnetic fields (EMFs). Frequencies widely vary according to sources: high-voltage power lines, electrically heated beds, MRI, VDTs, microwave ovens, satellite, and radio/TV transmissions or cellular phone transmitters/receivers. Public concern has increased about the potential health effects of EMFs. There are arguments in favour of EMFs being biologically active, but no mechanism has been identified that explains the link between EMFs and bioeffects. Human data reviewed concern the potential reproductive effects (mainly spontaneous abortions, low birthweight and congenital malformations) of exposure to sources of EMFs: maternal residence, electrically heated beds, occupational exposure (mainly video display terminals), and medical exposures. The available epidemiologic studies all have limitations that prevent to draw clearcut conclusions on the effects of EMFs on human reproduction. EMFs are ubiquitous and unavoidable exposures. The matter of possible effects cannot be considered closed, but until our understanding of the biologic important parameters of EMFs exposures is stronger,design of new studies will be difficult and small epidemiologic studies are unlikely to provide definitive answers and should not be given high priority. No conclusion can be drawn for radiofrequencies and microwaves because of lack of data. There is no convincing evidence today that EMFs of the sort pregnant women or potential fathers meet in occupational or daily life exposures does any harm to the human reproductive process. PMID:10331531

  18. The charmonium dissociation in an ''anomalous wind''

    DOE PAGESBeta

    Sadofyev, Andrey V.; Yin, Yi

    2016-01-11

    We study the charmonium dissociation in a strongly coupled chiral plasma in the presence of magnetic field and axial charge imbalance. This type of plasma carries "anomalous flow" induced by the chiral anomaly and exhibits novel transport phenomena such as chiral magnetic effect. We found that the "anomalous flow" would modify the charmonium color screening length by using the gauge/gravity correspondence. We derive an analytical expression quantifying the "anomalous flow" experienced by a charmonium for a large class of chiral plasma with a gravity dual. We elaborate on the similarity and it qualitative difference between anomalous effects on the charmoniummore » color screening length which are model-dependent and those on the heavy quark drag force which are fixed by the second law of thermodynamics. As a result, we speculate on the possible charmonium dissociation induced by the chiral anomaly in heavy ion collisions.« less

  19. Tunneling Anomalous and Spin Hall Effects.

    PubMed

    Matos-Abiague, A; Fabian, J

    2015-07-31

    We predict, theoretically, the existence of the anomalous Hall effect when a tunneling current flows through a tunnel junction in which only one of the electrodes is magnetic. The interfacial spin-orbit coupling present in the barrier region induces a spin-dependent momentum filtering in the directions perpendicular to the tunneling current, resulting in a skew tunneling even in the absence of impurities. This produces an anomalous Hall conductance and spin Hall currents in the nonmagnetic electrode when a bias voltage is applied across the tunneling heterojunction. If the barrier is composed of a noncentrosymmetric material, the anomalous Hall conductance and spin Hall currents become anisotropic with respect to both the magnetization and crystallographic directions, allowing us to separate this interfacial phenomenon from the bulk anomalous and spin Hall contributions. The proposed effect should be useful for proving and quantifying the interfacial spin-orbit fields in metallic and metal-semiconductor systems. PMID:26274432

  20. The charmonium dissociation in an "anomalous wind"

    NASA Astrophysics Data System (ADS)

    Sadofyev, Andrey V.; Yin, Yi

    2016-01-01

    We study the charmonium dissociation in a strongly coupled chiral plasma in the presence of magnetic field and axial charge imbalance. This type of plasma carries "anomalous flow" induced by the chiral anomaly and exhibits novel transport phenomena such as chiral magnetic effect. We found that the "anomalous flow" would modify the charmonium color screening length by using the gauge/gravity correspondence. We derive an analytical expression quantifying the "anomalous flow" experienced by a charmonium for a large class of chiral plasma with a gravity dual. We elaborate on the similarity and qualitative difference between anomalous effects on the charmonium color screening length which are model-dependent and those on the heavy quark drag force which are fixed by the second law of thermodynamics. We speculate on the possible charmonium dissociation induced by the chiral anomaly in heavy ion collisions.

  1. On Anomalous Quark Triangles

    NASA Astrophysics Data System (ADS)

    Vainshtein, Arkady

    2011-04-01

    Anomalous quark triangles with one axial and two vector currents are studied in special kinematics when one of the vector currents carries a soft momentum. According to the Adler-Bardeen theorem the anomalous longitudinal part of the triangle is not renormalized in the chiral limit. We show that perturbative corrections the transversal part of the triangle is also absent. This nonrenormalization, in difference with the longitudinal part, holds on only perturbatively.

  2. RF power generation for future linear colliders

    SciTech Connect

    Fowkes, W.R.; Allen, M.A.; Callin, R.S.; Caryotakis, G.; Eppley, K.R.; Fant, K.S.; Farkas, Z.D.; Feinstein, J.; Ko, K.; Koontz, R.F.; Kroll, N.; Lavine, T.L.; Lee, T.G.; Miller, R.H.; Pearson, C.; Spalek, G.; Vlieks, A.E.; Wilson, P.B.

    1990-06-01

    The next linear collider will require 200 MW of rf power per meter of linac structure at relatively high frequency to produce an accelerating gradient of about 100 MV/m. The higher frequencies result in a higher breakdown threshold in the accelerating structure hence permit higher accelerating gradients per meter of linac. The lower frequencies have the advantage that high peak power rf sources can be realized. 11.42 GHz appears to be a good compromise and the effort at the Stanford Linear Accelerator Center (SLAC) is being concentrated on rf sources operating at this frequency. The filling time of the accelerating structure for each rf feed is expected to be about 80 ns. Under serious consideration at SLAC is a conventional klystron followed by a multistage rf pulse compression system, and the Crossed-Field Amplifier. These are discussed in this paper.

  3. Magnetoplasmonic RF mixing and nonlinear frequency generation

    NASA Astrophysics Data System (ADS)

    Firby, C. J.; Elezzabi, A. Y.

    2016-07-01

    We present the design of a magnetoplasmonic Mach-Zehnder interferometer (MZI) modulator facilitating radio-frequency (RF) mixing and nonlinear frequency generation. This is achieved by forming the MZI arms from long-range dielectric-loaded plasmonic waveguides containing bismuth-substituted yttrium iron garnet (Bi:YIG). The magnetization of the Bi:YIG can be driven in the nonlinear regime by RF magnetic fields produced around adjacent transmission lines. Correspondingly, the nonlinear temporal dynamics of the transverse magnetization component are mapped onto the nonreciprocal phase shift in the MZI arms, and onto the output optical intensity signal. We show that this tunable mechanism can generate harmonics, frequency splitting, and frequency down-conversion with a single RF excitation, as well as RF mixing when driven by two RF signals. This magnetoplasmonic component can reduce the number of electrical sources required to generate distinct optical modulation frequencies and is anticipated to satisfy important applications in integrated optics.

  4. Electric-field manipulation of coercivity in FePt/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructures investigated by anomalous Hall effect measurement

    NASA Astrophysics Data System (ADS)

    Liu, Mingfeng; Hao, Liang; Jin, Tianli; Cao, Jiangwei; Bai, Jianmin; Wu, Dongping; Wang, Ying; Wei, Fulin

    2015-06-01

    The effect of electric field (E-field) on the magnetism of FePt thin films in FePt/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) heterostructures was investigated by anomalous Hall effect measurement. For FePt films of different thicknesses, the coercivity vs E-field curves show a typical butterfly-like loop behavior. Further results indicate that the coercivity variation is composed of the volatile symmetrical butterfly-like loop and nonvolatile hysteresis loop-like parts, which originate from the volatile and nonvolatile strains induced by the E-field in the PMN-PT(001) substrate, respectively. No significant difference has been observed after inserting a 2 nm W interlayer, suggesting that the charge-mediated coercivity variation is negligible in FePt/PMN-PT heterostructures.

  5. Anomalous is ubiquitous

    SciTech Connect

    Eliazar, Iddo; Klafter, Joseph

    2011-09-15

    Brownian motion is widely considered the quintessential model of diffusion processes-the most elemental random transport processes in Science and Engineering. Yet so, examples of diffusion processes displaying highly non-Brownian statistics-commonly termed 'Anomalous Diffusion' processes-are omnipresent both in the natural sciences and in engineered systems. The scientific interest in Anomalous Diffusion and its applications is growing exponentially in the recent years. In this Paper we review the key statistics of Anomalous Diffusion processes: sub-diffusion and super-diffusion, long-range dependence and the Joseph effect, Levy statistics and the Noah effect, and 1/f noise. We further present a theoretical model-generalizing the Einstein-Smoluchowski diffusion model-which provides a unified explanation for the prevalence of Anomalous Diffusion statistics. Our model shows that what is commonly perceived as 'anomalous' is in effect ubiquitous. - Highlights: > The article provides an overview of Anomalous Diffusion (AD) statistics. > The Einstein-Smoluchowski diffusion model is extended and generalized. > The generalized model universally generates AD statistics. > A unified 'universal macroscopic explanation' for AD statistics is established. > AD statistics are shown to be fundamentally connected to robustness.

  6. RF study and 3-D simulations of a side-coupling thermionic RF-gun

    NASA Astrophysics Data System (ADS)

    Rimjaem, S.; Kusoljariyakul, K.; Thongbai, C.

    2014-02-01

    A thermionic RF-gun for generating ultra-short electron bunches was optimized, developed and used as a source at a linac-based THz radiation research laboratory of the Plasma and Beam Physics Research Facility, Chiang Mai University, Thailand. The RF-gun is a π/2-mode standing wave structure, which consists of two S-band accelerating cells and a side-coupling cavity. The 2856 MHz RF wave is supplied from an S-band klystron to the gun through the waveguide input-port at the cylindrical wall of the second cell. A fraction of the RF power is coupled from the second cell to the first one via a side-coupling cavity. Both the waveguide input-port and the side-coupling cavity lead to an asymmetric geometry of the gun. RF properties and electromagnetic field distributions inside the RF-gun were studied and numerically simulated by using computer codes SUPERFISH 7.19 and CST Microwave Studio 2012©. RF characterizations and tunings of the RF-gun were performed to ensure the reliability of the gun operation. The results from 3D simulations and measurements are compared and discussed in this paper. The influence of asymmetric field distributions inside the RF-gun on the electron beam properties was investigated via 3D beam dynamics simulations. A change in the coupling-plane of the side-coupling cavity is suggested to improve the gun performance.

  7. Effects of anomalous transport on lower hybrid electron heating

    SciTech Connect

    McCoy, M.G.; Harvey, R.W.

    1981-02-01

    The transport of electron energy out of tokamaks is known to be far greater than that calculated using classical and neoclassical theory. However, low levels of non-axisymmetric magnetic field turbulence can couple the fast transport of electrons parallel to the magnetic field lines to radial transport, thus providing a plausible explanation for observed energy confinement. These models further predict that the electron loss rate is proportional to v/sub parallel bars/. This has subsequently been found to be consistent with data for runaway electrons in PLT, at energies up to 1 MeV. Recently it has been pointed out by Chan, Chiu and Ohkawa that anomalous transport processes should be taken into account in attempting to determine steady state electron distribution functions for cases involving RF electron tail heating, particularly in view of the v/sub parallel bars/ dependence of the loss rate. In this work these physical processes are modeled through a 2-D nonlinear program which describes the evolution of the electron distribution function in velocity magnitude; (v) and plasma radius (r), and which studies the efficiency of tail electron heating.

  8. Beam dynamics enhancement due to accelerating field symmetrization in the BNL/SLAC/UCLA 1.6 cell S-band photocathode RF gun

    SciTech Connect

    Palmer, D.T.; Miller, R.H.; Wang, X.J.; Ben-Zvi, I.

    1997-07-01

    A 1.6 cell photocathode S-Band gun developed by the BNL/SLAC/UCLA collaboration is now in operation at the Brookhaven Accelerator Test Facility (ATF). One of the main features of this RF gun is the symmetrization of the RF coupling iris with an identical vacuum pumping port located in the full cell. The effects of the asymmetry caused by the RF coupling iris were experimentally investigated by positioning a metallic plunger at the back wall of the vacuum port iris. The higher order modes produced were studied using electron beamlets with 8-fold symmetry. The 8-fold beamlets were produced by masking the laser beam. These experimental results indicate that the integrated electrical center and the geometrical center of the gun are within 175 {micro}m. Which is within the laser alignment tolerance of 250 {micro}m.

  9. Rf Feedback free electron laser

    DOEpatents

    Brau, Charles A.; Swenson, Donald A.; Boyd, Jr., Thomas J.

    1981-01-01

    A free electron laser system and electron beam system for a free electron laser which use rf feedback to enhance efficiency. Rf energy is extracted from an electron beam by decelerating cavities and returned to accelerating cavities using rf returns such as rf waveguides, rf feedthroughs, etc. This rf energy is added to rf klystron energy to lower the required input energy and thereby enhance energy efficiency of the system.

  10. Rf feedback free electron laser

    DOEpatents

    Brau, C.A.; Swenson, D.A.; Boyd, T.J. Jr.

    1979-11-02

    A free electron laser system and electron beam system for a free electron laser are provided which use rf feedback to enhance efficiency. Rf energy is extracted from an electron beam by decelerating cavities and returned to accelerating cavities using rf returns such as rf waveguides, rf feedthroughs, etc. This rf energy is added to rf klystron energy to lower the required input energy and thereby enhance energy efficiency of the system.

  11. High gradient RF breakdown studies

    NASA Astrophysics Data System (ADS)

    Laurent, Lisa Leanne

    Higher accelerating gradients are required by future demands for TeV electron linear colliders. With higher energy comes the challenge of handling stronger electromagnetic fields in the accelerator structures and in the microwave sources that supply the power. A limit on the maximum field gradient is imposed by rf electrical breakdown. Investigating methods to achieve higher gradients and to better understand the mechanisms involved in the rf breakdown process has been the focal point of this study. A systematic series of rf breakdown experiments have been conducted at Stanford Linear Accelerator Center utilizing a transmission cavity operating in the TM020 mode. A procedure was developed to examine the high gradient section of the cavity in an electron microscope. The results have revealed that breakdown asymmetry exists between opposing high gradient surfaces. During breakdown, a plasma formation is detected localized near the surface with no visible evidence of an arc traversing the gap. These findings support the theory that high frequency rf breakdown is a single surface phenomenon. Other results from this study have shown that breakdown can occur at relatively low voltages when surface irregularities exist and along grain boundaries. A series of steps have been developed through this study that have significantly reduced the number of breakdowns that occur along grain boundaries. Testing under various vacuum conditions (10-11--10 -5 Torr) have revealed that while the breakdown threshold remained the same, the field emitted current density increased by almost two orders of magnitude. This suggests that the total field emitted current density is not the critical parameter in the initiation of high frequency vacuum breakdown. In the course of this study, microparticles were carefully tracked before and after rf processing. The outcome of this research suggests that expensive cleanroom facilities may not offer any advantage over practicing good cleaning and

  12. On the reliable determination of the magnetic field for first flux-line penetration in technical niobium material

    SciTech Connect

    Ganapati Rao Myneni

    2007-09-05

    We present a way to reliably determine the field for first penetration H$_P$ in various kinds of bulk samples of niobium material used in the technical applications like fabrication of superconducting RF-cavities. Special attention is given to the role of flux line pinning in the determination of H$_P$. It is observed that the pinning properties and H$_P$ can change (or can be altered) significantly with the chemical treatment of bulk niobium. A correlation is proposed between H$_P$ of the niobium materials and the anomalous high-field Q-drop observed in the superconducting RF-cavities fabricated using such niobium material.

  13. Field induced domain switching as the origin of anomalous lattice strain along non-polar direction in rhombohedral BiScO{sub 3}-PbTiO{sub 3} close to the morphotropic phase boundary

    SciTech Connect

    Lalitha, K. V.; Ranjan, Rajeev; Fancher, Chris M.; Jones, Jacob L.

    2015-08-03

    The lattice strain and domain switching behavior of xBiScO{sub 3}–(1-x)PbTiO{sub 3} (x = 0.40) was investigated as a function of cyclic field and grain orientation by in situ X-ray diffraction during application of electric fields. The electric field induced 200 lattice strain was measured to be five times larger than the 111 lattice strain in pseudorhombohedral xBiScO{sub 3}–(1-x)PbTiO{sub 3} (x = 0.40). It is shown that the anomalous 200 lattice strain is not an intrinsic phenomenon, but arises primarily due to stress associated with the reorientation of the 111 domains in dense polycrystalline ceramic.

  14. Drag suppression in anomalous chiral media

    NASA Astrophysics Data System (ADS)

    Sadofyev, Andrey V.; Yin, Yi

    2016-06-01

    We study a heavy impurity moving longitudinal with the direction of an external magnetic field in an anomalous chiral medium. Such system would carry a nondissipative current of chiral magnetic effect associated with the anomaly. We show, by generalizing Landau's criterion for superfluidity, that the "anomalous component" which gives rise to the anomalous transport will not contribute to the drag experienced by an impurity. We argue on a very general basis that those systems with a strong magnetic field would exhibit an interesting transport phenomenon—the motion of the heavy impurity is frictionless, in analogy to the case of a superfluid. We demonstrate and confirm our general results with two complementary examples: weakly coupled chiral fermion gases and strongly interacting chiral liquids.

  15. Experimental realization of quantized anomalous Hall effect

    NASA Astrophysics Data System (ADS)

    Xue, Qi-Kun

    2014-03-01

    Anomalous Hall effect was discovered by Edwin Hall in 1880. In this talk, we report the experimental observation of the quantized version of AHE, the quantum anomalous Hall effect (QAHE) in thin films of Cr-doped (Bi,Sb)2Te3 magnetic topological insulator. At zero magnetic field, the gate-tuned anomalous Hall resistance exhibits a quantized value of h /e2 accompanied by a significant drop of the longitudinal resistance. The longitudinal resistance vanishes under a strong magnetic field whereas the Hall resistance remains at the quantized value. The realization of QAHE paves a way for developing low-power-consumption electronics. Implications on observing Majorana fermions and other exotic phenomena in magnetic topological insulators will also be discussed. The work was collaborated with Ke He, Yayu Wang, Xucun Ma, Xi Chen, Li Lv, Dai Xi, Zhong Fang and Shoucheng Zhang.

  16. Electric field and radio frequency measurements for rocket engine health monitoring applications

    NASA Technical Reports Server (NTRS)

    Valenti, Elizabeth L.

    1992-01-01

    Electric-field (EF) and radio-frequency (RF) emissions generated in the exhaust plumes of the diagnostic testbed facility thruster (DTFT) and the SSME are examined briefly for potential applications to plume diagnostics and engine health monitoring. Hypothetically, anomalous engine conditions could produce measurable changes in any characteristic EF and RF spectral signatures identifiable with a 'healthly' plumes. Tests to determine the presence of EF and RF emissions in the DTFT and SSME exhaust plumes were conducted. EF and RF emissions were detected using state-of-the-art sensors. Analysis of limited data sets show some apparent consistencies in spectral signatures. Significant emissions increases were detected during controlled tests using dopants injected into the DTFT.

  17. Electric field and radio frequency measurements for rocket engine health monitoring applications

    NASA Astrophysics Data System (ADS)

    Valenti, Elizabeth L.

    1992-10-01

    Electric-field (EF) and radio-frequency (RF) emissions generated in the exhaust plumes of the diagnostic testbed facility thruster (DTFT) and the SSME are examined briefly for potential applications to plume diagnostics and engine health monitoring. Hypothetically, anomalous engine conditions could produce measurable changes in any characteristic EF and RF spectral signatures identifiable with a 'healthly' plumes. Tests to determine the presence of EF and RF emissions in the DTFT and SSME exhaust plumes were conducted. EF and RF emissions were detected using state-of-the-art sensors. Analysis of limited data sets show some apparent consistencies in spectral signatures. Significant emissions increases were detected during controlled tests using dopants injected into the DTFT.

  18. Characteristics of anomalous skin effect and evolution of power absorption regions in a cylindrical radio frequency inductively coupled plasma

    SciTech Connect

    Ding, Z. F.; Sun, B.; Huo, W. G.

    2015-06-15

    In a low-pressure radio-frequency (13.56 MHz), inductively coupled argon plasma generated by a normal cylindrical rf coil, electric field, current density, and absorbed power density is calculated from magnetic field measured with a phase-resolved magnetic probe. The anomalous skin effect (ASE) for the cylindrical rf coil is compared to those previously reported for the planar and re-entrant cylindrical rf coils. Physical reasons for our observed characteristics of ASE are presented. With the increasing discharge power, the size and the number of negative and positive power absorption regions evolve into several distinct patterns. For the low discharge power (at 156.9 W), there is one area of positive and one area of negative power absorption in the radial direction. For the medium discharge power (279 W–683.5 W), there are two areas of negative and two areas of positive power absorption. For the even higher discharge power (above 803.5 W), the number of areas is the same as that of the medium discharge power, but the size of the inner positive and negative power absorption areas is approximately doubled and halved, respectively, while the outer positive and negative power absorption areas slightly shrinks. The evolution of positive and negative power absorption regions is explained as a result of electron thermal diffusion and the energy conversion between rf current and electric field. The spatial decays of electric field and current density are also elucidated by linking them with the positive and negative power absorption pattern.

  19. RF-sheath assessment of ICRF Faraday Screens

    SciTech Connect

    Colas, L.

    2007-09-28

    The line-integrated parallel RF electric field {delta}V{sub RF} is studied on 'long field lines' radially in front of an ICRF antenna closed by a Faraday screen (FS). Several issues are addressed analytically and numerically. To what extent is a FS necessary to shield {delta}V{sub RF} in presence of magnetized plasma, depending on strap phasing? How efficient is it as a function of FS misalignment on tilted magnetic field? Can a FS attenuate {delta}V{sub RF} produced on antenna frame?.

  20. Measurements of the rf surface resistance of high- Tc superconductors

    SciTech Connect

    Delayen, J.R.; Bohn, C.L.; Roche, C.T.

    1990-01-01

    An experimental program is being conducted to assess the applicability of high-{Tc} superconductors for use in high power rf and microwave devices. The program involves the measurement of the rf surface resistance of high-{Tc} samples at frequencies between 0.15 and 40 GHz and rf surface magnetic fields as high as 640 gauss. Polycrystalline samples were found to have surface resistances which increase monotonically with rf-field amplitude, saturating at high field at a few percent of the normal-state surface resistance just above {Tc}. 13 refs., 2 figs., 1 tab.

  1. Anomalous law of cooling

    SciTech Connect

    Lapas, Luciano C.; Ferreira, Rogelma M. S.; Rubí, J. Miguel; Oliveira, Fernando A.

    2015-03-14

    We analyze the temperature relaxation phenomena of systems in contact with a thermal reservoir that undergoes a non-Markovian diffusion process. From a generalized Langevin equation, we show that the temperature is governed by a law of cooling of the Newton’s law type in which the relaxation time depends on the velocity autocorrelation and is then characterized by the memory function. The analysis of the temperature decay reveals the existence of an anomalous cooling in which the temperature may oscillate. Despite this anomalous behavior, we show that the variation of entropy remains always positive in accordance with the second law of thermodynamics.

  2. Anomalous law of cooling.

    PubMed

    Lapas, Luciano C; Ferreira, Rogelma M S; Rubí, J Miguel; Oliveira, Fernando A

    2015-03-14

    We analyze the temperature relaxation phenomena of systems in contact with a thermal reservoir that undergoes a non-Markovian diffusion process. From a generalized Langevin equation, we show that the temperature is governed by a law of cooling of the Newton's law type in which the relaxation time depends on the velocity autocorrelation and is then characterized by the memory function. The analysis of the temperature decay reveals the existence of an anomalous cooling in which the temperature may oscillate. Despite this anomalous behavior, we show that the variation of entropy remains always positive in accordance with the second law of thermodynamics. PMID:25770525

  3. Anomalous law of cooling

    NASA Astrophysics Data System (ADS)

    Lapas, Luciano C.; Ferreira, Rogelma M. S.; Rubí, J. Miguel; Oliveira, Fernando A.

    2015-03-01

    We analyze the temperature relaxation phenomena of systems in contact with a thermal reservoir that undergoes a non-Markovian diffusion process. From a generalized Langevin equation, we show that the temperature is governed by a law of cooling of the Newton's law type in which the relaxation time depends on the velocity autocorrelation and is then characterized by the memory function. The analysis of the temperature decay reveals the existence of an anomalous cooling in which the temperature may oscillate. Despite this anomalous behavior, we show that the variation of entropy remains always positive in accordance with the second law of thermodynamics.

  4. Anomalous gauge boson interactions

    SciTech Connect

    Aihara, H.; Barklow, T.; Baur, U. |

    1995-03-01

    We discuss the direct measurement of the trilinear vector boson couplings in present and future collider experiments. The major goals of such experiments will be the confirmation of the Standard Model (SM) predictions and the search for signals of new physics. We review our current theoretical understanding of anomalous trilinear gauge-boson self interactions. If the energy scale of the new physics is {approximately} 1 TeV, these low energy anomalous couplings are expected to be no larger than {Omicron}(10{sup {minus}2}). Constraints from high precision measurements at LEP and low energy charged and neutral current processes are critically reviewed.

  5. Anomalous Diffraction in Cold Magnetized Plasma

    NASA Astrophysics Data System (ADS)

    Abelson, Z.; Gad, R.; Bar-Ad, S.; Fisher, A.

    2015-10-01

    Cold magnetized plasma possesses an anisotropic permittivity tensor with a unique dispersion relation that for adequate electron density and magnetic field results in anomalous diffraction of a right-hand circularly polarized beam. In this work, we demonstrate experimentally anomalous diffraction of a microwave beam in plasma. Additionally, decreasing the electron density enables observation of the transition of the material from a hyperbolic to a standard material. Manipulation of the control parameters will enable plasma to serve as a reconfigurable metamaterial-like medium.

  6. Anomalous Diffraction in Cold Magnetized Plasma.

    PubMed

    Abelson, Z; Gad, R; Bar-Ad, S; Fisher, A

    2015-10-01

    Cold magnetized plasma possesses an anisotropic permittivity tensor with a unique dispersion relation that for adequate electron density and magnetic field results in anomalous diffraction of a right-hand circularly polarized beam. In this work, we demonstrate experimentally anomalous diffraction of a microwave beam in plasma. Additionally, decreasing the electron density enables observation of the transition of the material from a hyperbolic to a standard material. Manipulation of the control parameters will enable plasma to serve as a reconfigurable metamaterial-like medium. PMID:26551813

  7. The RF Design of an HOM Polarized RF Gun for the ILC

    SciTech Connect

    Wang, J.W.; Clendenin, J.E.; Colby, E.R.; Miller, R.A.; Lewellen, J.W.; /Argonne

    2006-11-15

    The ILC requires a polarized electron beam. While a highly polarized beam can be produced by a GaAs-type cathode in a DC gun of the type currently in use at SLAC, JLAB and elsewhere, the ILC injector system can be simplified and made more efficient if a GaAs-type cathode can be combined with a low emittance RF gun. Since this type of cathode is known to be extremely sensitive to vacuum contamination including back bombardment by electrons and ions, any successful polarized RF gun must have a significantly improved operating vacuum compared to existing RF guns. We present a new RF design for an L-Band normal conducting (NC) RF gun for the ILC polarized electron source. This design incorporates a higher order mode (HOM) structure, whose chief virtue in this application is an improved conductance for vacuum pumping on the cathode. Computer simulation models have been used to optimize the RF parameters with two principal goals: first to minimize the required RF power; second to reduce the peak surface field relative to the field at the cathode in order to suppress field emitted electron bombardment. The beam properties have been simulated initially using PARMELA. Vacuum and other practical issues for implementing this design are discussed.

  8. Pulsed rf superconductivity program at SLAC

    SciTech Connect

    Campisi, I.E.; Farkas, Z.D.

    1984-08-01

    Recent tests performed at SLAC on superconducting TM/sub 010/ caavities using short rf pulses (less than or equal to 2.5 ..mu..s) have established that at the cavity surface magnetic fields can be reached in the vicinity of the theoretical critical fields without an appreciable increase in average losses. Tests on niobium and lead cavities are reported. The pulse method seems to be best suited to study peak field properties of superconductors in the microwave band, without the limitations imposed by defects. The short pulses also seem to be more effective in decreasing the causes of field emission by rf processing. Applications of the pulsed rf superconductivity to high-gradient linear accelerators are also possible.

  9. Anomalous Growth of Aging Populations

    NASA Astrophysics Data System (ADS)

    Grebenkov, Denis S.

    2016-04-01

    We consider a discrete-time population dynamics with age-dependent structure. At every time step, one of the alive individuals from the population is chosen randomly and removed with probability q_k depending on its age, whereas a new individual of age 1 is born with probability r. The model can also describe a single queue in which the service order is random while the service efficiency depends on a customer's "age" in the queue. We propose a mean field approximation to investigate the long-time asymptotic behavior of the mean population size. The age dependence is shown to lead to anomalous power-law growth of the population at the critical regime. The scaling exponent is determined by the asymptotic behavior of the probabilities q_k at large k. The mean field approximation is validated by Monte Carlo simulations.

  10. Single frequency RF powered ECG telemetry system

    NASA Technical Reports Server (NTRS)

    Ko, W. H.; Hynecek, J.; Homa, J.

    1979-01-01

    It has been demonstrated that a radio frequency magnetic field can be used to power implanted electronic circuitry for short range telemetry to replace batteries. A substantial reduction in implanted volume can be achieved by using only one RF tank circuit for receiving the RF power and transmitting the telemetered information. A single channel telemetry system of this type, using time sharing techniques, was developed and employed to transmit the ECG signal from Rhesus monkeys in primate chairs. The signal from the implant is received during the period when the RF powering radiation is interrupted. The ECG signal is carried by 20-microsec pulse position modulated pulses, referred to the trailing edge of the RF powering pulse. Satisfactory results have been obtained with this single frequency system. The concept and the design presented may be useful for short-range long-term implant telemetry systems.

  11. Phase stable RF transport system

    DOEpatents

    Curtin, Michael T.; Natter, Eckard F.; Denney, Peter M.

    1992-01-01

    An RF transport system delivers a phase-stable RF signal to a load, such as an RF cavity of a charged particle accelerator. A circuit generates a calibration signal at an odd multiple frequency of the RF signal where the calibration signal is superimposed with the RF signal on a common cable that connects the RF signal with the load. Signal isolating diplexers are located at both the RF signal source end and load end of the common cable to enable the calibration to be inserted and extracted from the cable signals without any affect on the RF signal. Any phase shift in the calibration signal during traverse of the common cable is then functionally related to the phase shift in the RF signal. The calibration phase shift is used to control a phase shifter for the RF signal to maintain a stable RF signal at the load.

  12. RF Processing Experience with the GTF Prototype RF Gun

    SciTech Connect

    Schmerge, J.F.

    2010-11-24

    The SSRL Gun Test Facility (GTF) was built to develop a high brightness electron injector for the LCLS and has been operational since 1996. A total of five different metal cathodes (4 Cu and 1 Mg) have been installed on the GTF gun. The rf processing history with the different cathodes will be presented including peak field achieved at the cathode. The LCLS gun is intended to operate at 120 MV/m and fields up to 140 MV/m have been achieved in the GTF gun. After installing a new cathode the number of rf pulses required to reach 120 MV/m is approximately 5-10 million. Total emitted dark current and Fowler Nordheim plots are also shown over the life of the cathode. The GTF photo-injector gun is an S-band standing-wave structure, with two resonant cavities and an intervening thick washer (Figure 1). The flat, back wall of the first cavity is a copper plate that serves as photocathode when illuminated with ultraviolet light from a pulsed, high-power laser. RF power enters the gun through an iris on the outer wall of the second cavity, and is coupled to the first through the axial opening of the washer. The first cavity is often referred to as a half cell, because its full-cell length has been truncated by the cathode plate and the second cavity is called the full cell. The gun is designed to operate in a {pi} mode, with the peak field on axis in each cell approximately equal. The maximum in the half cell occurs at the cathode, and in the full cell near the center of the cavity. The field profile and tuning procedures are discussed in a separate tech note [1].

  13. Effect of low temperature baking on the RF properties of niobium superconducting cavities for particle accelerators

    SciTech Connect

    Gianluigi Ciovati

    2004-03-01

    Radio-frequency superconducting (SRF) cavities are widely used to accelerate a charged particle beam in particle accelerators. The performance of SRF cavities made of bulk niobium has significantly improved over the last ten years and is approaching the theoretical limit for niobium. Nevertheless, RF tests of niobium cavities are still showing some ''anomalous'' losses that require a better understanding in order to reliably obtain better performance. These losses are characterized by a marked dependence of the surface resistance on the surface electromagnetic field and can be detected by measuring the quality factor of the resonator as a function of the peak surface field. A low temperature (100 C-150 C) ''in situ'' bake under ultra-high vacuum has been successfully applied as final preparation of niobium RF cavities by several laboratories over the last few years. The benefits reported consist mainly of an improvement of the cavity quality factor at low field and a recovery from ''anomalous'' losses (so-called ''Q-drop'') without field emission at higher field. A series of experiments with a CEBAF single-cell cavity have been carried out at Jefferson Lab to carefully investigate the effect of baking at progressively higher temperatures for a fixed time on all the relevant material parameters. Measurements of the cavity quality factor in the temperature range 1.37 K-280 K and resonant frequency shift between 6 K-9.3 K provide information about the surface resistance, energy gap, penetration depth and mean free path. The experimental data have been analyzed with the complete BCS theory of superconductivity. The hydrogen content of small niobium samples inserted in the cavity during its surface preparation was analyzed with Nuclear Reaction Analysis (NRA). The single-cell cavity has been tested at three different temperatures before and after baking to gain some insight on thermal conductivity and Kapitza resistance and the data are compared with different models

  14. Colored models for anomalous nuclei

    SciTech Connect

    Watson, P.J.S.; Saly, R.; Romo, W.J.; Sundaresan, M.K.; Campbell, B.; Elias, V.

    1983-04-01

    There seems to be good experimental evidence that anomalous nuclei are produced in heavy-ion collisions; they are anomalous in that they have an abnormally short mean free path, for example, in nuclear emulsions. Here we consider the possibility that anomalous nuclei are combinations of a colored anomalous particle fragment (based on theories with spontaneous breakdown of color symmetry) with ordinary nucleons. Phenomenological implications of various possible models in which the anomalous particle fragment is considered to be a colored particle with the color symmetry SU(3)/sub c/ explicitly broken are given.

  15. Fractional order analysis of Sephadex gel structures: NMR measurements reflecting anomalous diffusion

    NASA Astrophysics Data System (ADS)

    Magin, Richard L.; Akpa, Belinda S.; Neuberger, Thomas; Webb, Andrew G.

    2011-12-01

    We report the appearance of anomalous water diffusion in hydrophilic Sephadex gels observed using pulse field gradient (PFG) nuclear magnetic resonance (NMR). The NMR diffusion data was collected using a Varian 14.1 Tesla imaging system with a home-built RF saddle coil. A fractional order analysis of the data was used to characterize heterogeneity in the gels for the dynamics of water diffusion in this restricted environment. Several recent studies of anomalous diffusion have used the stretched exponential function to model the decay of the NMR signal, i.e., exp[-( bD) α], where D is the apparent diffusion constant, b is determined the experimental conditions (gradient pulse separation, durations and strength), and α is a measure of structural complexity. In this work, we consider a different case where the spatial Laplacian in the Bloch-Torrey equation is generalized to a fractional order model of diffusivity via a complexity parameter, β, a space constant, μ, and a diffusion coefficient, D. This treatment reverts to the classical result for the integer order case. The fractional order decay model was fit to the diffusion-weighted signal attenuation for a range of b-values (0 < b < 4000 s mm -2). Throughout this range of b values, the parameters β, μ and D, were found to correlate with the porosity and tortuosity of the gel structure.

  16. Electric field-assisted metal insulator transition in vanadium dioxide (VO2) thin films: optical switching behavior and anomalous far-infrared emissivity variation

    NASA Astrophysics Data System (ADS)

    Crunteanu, Aurelian; Fabert, Marc; Cornette, Julie; Colas, Maggy; Orlianges, Jean-Christophe; Bessaudou, Annie; Cosset, Françoise

    2014-03-01

    We present the vanadium dioxide (VO2) thin films deposition using e-beam evaporation of a vanadium target under oxygen atmosphere on different substrates (sapphire, Si, SiO2/Si…) and we focus on their electrical and optical properties variations as the material undergoes a metal-insulator transition under thermal and electrical stimuli. The phase transition induces extremely abrupt changes in the electronic and optical properties of the material: the electrical resistivity increases up to 5 orders of magnitude while the optical properties (transmission, reflection, refractive index) are drastically modified. We present the integration of these films in simple planar optical devices and we demonstrate electrical-activated optical modulators for visible-infrared signals with high discrimination between the two states. We will highlight a peculiar behavior of the VO2 material in the infrared and far infrared regions (2- 20 μm), namely its anomalous emissivity change under thermal- end electrical activation (negative differential emittance phenomenon) with potential applications in active coatings for thermal regulation, optical limiting or camouflage coatings.

  17. X-Band RF Gun Development

    SciTech Connect

    Vlieks, Arnold; Dolgashev, Valery; Tantawi, Sami; Anderson, Scott; Hartemann, Fred; Marsh, Roark; /LLNL, Livermore

    2012-06-22

    In support of the MEGa-ray program at LLNL and the High Gradient research program at SLAC, a new X-band multi-cell RF gun is being developed. This gun, similar to earlier guns developed at SLAC for Compton X-ray source program, will be a standing wave structure made of 5.5 cells operating in the pi mode with copper cathode. This gun was designed following criteria used to build SLAC X-band high gradient accelerating structures. It is anticipated that this gun will operate with surface electric fields on the cathode of 200 MeV/m with low breakdown rate. RF will be coupled into the structure through a final cell with symmetric duel feeds and with a shape optimized to minimize quadrupole field components. In addition, geometry changes to the original gun, operated with Compton X-ray source, will include a wider RF mode separation, reduced surface electric and magnetic fields.

  18. BN / Graphene / BN RF Transistors

    NASA Astrophysics Data System (ADS)

    Wang, Han; Taychatanapat, Thiti; Hsu, Allen; Jarillo-Herrero, Pablo; Palacios, Tomas

    2011-03-01

    In this work we demonstrate the first BN/graphene/BN transistor for high frequency RF applications. This sandwich structure allows a significant improvement in the mobility of graphene, which reaches more than 18,000 cm2 /Vs at room temperature. Graphene field effect transistors (GFETs) have been fabricated with LDS = 800 nm and LG = 300 nm. The minimum conduction point of these devices is very close to zero, a result of the negligible substrate doping to the graphene. A current density in excess of 1 A/mm and DC transconductance above 200 mS/mm are achieved for both electron and hole conductions. RF characterization is performed for the first time on this device structure and initial results show a current-gain cut-off frequency fT = 10 GHz. These experimental results have been combined with simulations of the small-signal model to study the scaling potential of these GFETs for high frequency applications. The impact of the access resistances (Rs , Rd) , the capacitances (Cgs , Cgd , Cds) , and the transconductance (g m) on the frequency performance of the GFETs has also been studied. Finally, the fabricated devices have been compared to GFETs fabricated with Si O2 substrate and Al 2 O3 gate dielectrics. The improved performance obtained by the BN/graphene/BN structure is very promising to enable the next generation of high frequency RF electronics.

  19. Rf power sources

    SciTech Connect

    Allen, M.A.

    1988-05-01

    This paper covers RF power sources for accelerator applications. The approach has been with particular customers in mind. These customers are high energy physicists who use accelerators as experimental tools in the study of the nucleus of the atom, and synchrotron light sources derived from electron or positron storage rings. This paper is confined to electron-positron linear accelerators since the RF sources have always defined what is possible to achieve with these accelerators. 11 refs., 13 figs.

  20. Microbunching and RF Compression

    SciTech Connect

    Venturini, M.; Migliorati, M.; Ronsivalle, C.; Ferrario, M.; Vaccarezza, C.

    2010-05-23

    Velocity bunching (or RF compression) represents a promising technique complementary to magnetic compression to achieve the high peak current required in the linac drivers for FELs. Here we report on recent progress aimed at characterizing the RF compression from the point of view of the microbunching instability. We emphasize the development of a linear theory for the gain function of the instability and its validation against macroparticle simulations that represents a useful tool in the evaluation of the compression schemes for FEL sources.

  1. Status of Nb-Pb superconducting RF-gun cavities

    SciTech Connect

    J. Sekutowicz; J. Iversen; D. Klinke; D. Kostin; W. Möller; A. Muhs; P. Kneisel; J. Smedley; T. Rao; P. Strzyżewski; Z. Li; K. Ko; L. Xiao; R. Lefferts; A. Lipski; M. Ferrario

    2007-06-01

    We report on the progress in the status of an electron RF-gun made of two superconductors: niobium and lead. The presented design combines the advantages of the RF performance of bulk niobium superconducting cavities and the reasonably high quantum efficiency of lead. Measured values of quantum efficiency for lead at 2K and the RF-performance of three half-cell niobium cavities with the lead spot exposed to high electric fields are reported in this contribution.

  2. Nonlocal Anomalous Hall Effect

    NASA Astrophysics Data System (ADS)

    Zhang, Steven S.-L.; Vignale, Giovanni

    2016-04-01

    The anomalous Hall (AH) effect is deemed to be a unique transport property of ferromagnetic metals, caused by the concerted action of spin polarization and spin-orbit coupling. Nevertheless, recent experiments have shown that the effect also occurs in a nonmagnetic metal (Pt) in contact with a magnetic insulator [yttrium iron garnet (YIG)], even when precautions are taken to ensure that there is no induced magnetization in the metal. We propose a theory of this effect based on the combined action of spin-dependent scattering from the magnetic interface and the spin-Hall effect in the bulk of the metal. At variance with previous theories, we predict the effect to be of first order in the spin-orbit coupling, just as the conventional anomalous Hall effect—the only difference being the spatial separation of the spin-orbit interaction and the magnetization. For this reason we name this effect the nonlocal anomalous Hall effect and predict that its sign will be determined by the sign of the spin-Hall angle in the metal. The AH conductivity that we calculate from our theory is in order of magnitude agreement with the measured values in Pt /YIG structures.

  3. Electroweak baryogenesis with anomalous Higgs couplings

    NASA Astrophysics Data System (ADS)

    Kobakhidze, Archil; Wu, Lei; Yue, Jason

    2016-04-01

    We investigate feasibility of efficient baryogenesis at the electroweak scale within the effective field theory framework based on a non-linear realisation of the electroweak gauge symmetry. In this framework the LHC Higgs boson is described by a singlet scalar field, which, therefore, admits new interactions. Assuming that Higgs couplings with the eletroweak gauge bosons are as in the Standard Model, we demonstrate that the Higgs cubic coupling and the CP-violating Higgs-top quark anomalous couplings alone may drive the a strongly first-order phase transition. The distinguished feature of this transition is that the anomalous Higgs vacuum expectation value is generally non-zero in both phases. We identify a range of anomalous couplings, consistent with current experimental data, where sphaleron rates are sufficiently fast in the `symmetric' phase and are suppressed in the `broken' phase and demonstrate that the desired baryon asymmetry can indeed be generated in this framework. This range of the Higgs anomalous couplings can be further constrained from the LHC Run 2 data and be probed at high luminosity LHC and beyond.

  4. Hydrogen-filled RF Cavities for Muon Beam Cooling

    SciTech Connect

    CHARLES, Ankenbrandt

    2009-04-17

    Ionization cooling requires low-Z energy absorbers immersed in a strong magnetic field and high-gradient, large-aperture RF cavities to be able to cool a muon beam as quickly as the short muon lifetime requires. RF cavities that operate in vacuum are vulnerable to dark-current- generated breakdown, which is exacerbated by strong magnetic fields, and they require extra safety windows that degrade cooling, to separate RF regions from hydrogen energy absorbers. RF cavities pressurized with dense hydrogen gas will be developed that use the same gas volume to provide the energy absorber and the RF acceleration needed for ionization cooling. The breakdown suppression by the dense gas will allow the cavities to operate in strong magnetic fields. Measurements of the operation of such a cavity will be made as functions of external magnetic field and charged particle beam intensity and compared with models to understand the characteristics of this technology and to develop mitigating strategies if necessary.

  5. RF heating of nanoclusters for cancer therapy

    NASA Astrophysics Data System (ADS)

    Letfullin, Renat R.; Letfullin, Alla R.; George, Thomas F.

    2015-03-01

    Nanodrugs selectively delivered to a tumor site can be activated by radiation for drug release, or nanoparticles (NPs) can be used as a drug themselves by producing biological damage in cancer cells through thermal, mechanical ablations or charged particle emission. Radio-frequency (RF) waves have an excellent ability to penetrate into the human body without causing healthy tissue damage, which provides a great opportunity to activate/heat NPs delivered inside the body as a contrast agent for diagnosis and treatment purposes. However the heating of NPs in the RF range of the spectrum is controversial in the research community because of the low power load of RF waves and low absorption of NPs in the RF range. To resolve these weaknesses in the RF activation of NPs and dramatically increase absorption of contrast agents in tumor, we suggest aggregating the nanoclusters inside or on the surface of the cancer cells. We simulate space distribution of temperature changes inside and outside metal and dielectric nanopraticles/nanoclusters, determine the number of nanoparticles needed to form a cluster, and estimate the thermal damage area produced in surrounding medium by nanopraticles/nanoclusters heated in the RF field.

  6. Investigation of Microscopic Materials Limitations of Superconducting RF Cavities

    SciTech Connect

    Anlage, Steven

    2014-07-23

    The high-field performance of SRF cavities is often limited by breakdown events below the intrinsic limiting surface fields of Nb, and there is abundant evidence that these breakdown events are localized in space inside the cavity. Also, there is a lack of detailed understanding of the causal links between surface treatments and ultimate RF performance at low temperatures. An understanding of these links would provide a clear roadmap for improvement of SRF cavity performance, and establish a cause-and-effect ‘RF materials science’ of Nb. We propose two specific microscopic approaches to addressing these issues. First is a spatially-resolved local microwave-microscope probe that operates at SRF frequencies and temperatures to discover the microscopic origins of breakdown, and produce quantitative measurements of RF critical fields of coatings and films. Second, RF Laser Scanning Microscopy (LSM) has allowed visualization of RF current flow and sources of nonlinear RF response in superconducting devices with micro-meter spatial resolution. The LSM will be used in conjunction with surface preparation and characterization techniques to create definitive links between physical and chemical processing steps and ultimate cryogenic microwave performance. We propose to develop RF laser scanning microscopy of small-sample Nb pieces to establish surface-processing / RF performance relations through measurement of RF current distributions on micron-length scales and low temperatures.

  7. Control electronics of the PEP RF system

    SciTech Connect

    Pellegrin, J.L.; Schwarz, H.

    1981-01-01

    The operation of the major components used for controlling the phase and field level of the PEP RF cavities is described. The control electronics of one RF station is composed of several control loops: each cavity has a tuners' servo loop which maintains the frequency constant and also keeps the fields of each cavity balanced; the total gap voltage developed by a pair of cavities is regulated by a gap voltage controller; finally, the phase variation along the amplification chain, the klystron and the cavities are compensated by a phase lock loop. The design criteria of each loop are set forth and the circuit implementation and test results are presented.

  8. RF Curves for Extraction from the Accumulator

    SciTech Connect

    McGinnis, Dav; /Fermilab

    2002-03-10

    Since the start of Run IIa, the RF curves for the extraction process from the Accumulator have been based on an algorithm described in Pbar Note 636. There are a number of problems with this procedure that result in a dilution of the longitudinal phase space of the extracted beam. The procedure consists of a number of steps in which the frequency curve during each process is a linear time ramp. For a constant bend field, the synchronous phase angle is given as: {Lambda} = sin({phi}{sub s}) = -h/{eta} (1/f{sub rf}){sup 2}df{sub rf}/dt/qV/pc where h is the harmonic number of the RF. Equation (1) shows that if the frequency curve consists of a number of linear time ramps with different slopes, there will be discontinuities in the synchronous phase. These discontinuities in the synchronous phase will lead to dipole oscillations of the beam in the RF bucket. The discontinuities observed for the present RF curves are about 10 degrees. In the procedure outlined in Pbar Note 636, the RF bucket is formed on the high energy edge of the rectangular momentum distribution. As the RF bucket is pulled away from the core, it is also programmed to increase in area. If the distribution is not perfectly rectangular, or if the bucket is not formed at the edge of the distribution, the growing bucket will gather up more particles at the edges of the bucket resulting in a substantial increase of longitudinal emittance. Finally, it is fairly difficult to prepare a rectangular momentum distribution and keep it rectangular for extended periods of time. Once the rectangular distribution is prepared, the core momentum cooling must be turned off. If there is a delay in the extraction process, the sharp edges of the rectangular distribution will soon diffuse. With the momentum cooling disabled, the longitudinal emittance of the core will grow resulting in larger longitudinal emittances for the extracted beam.

  9. Anomalous lattice expansion in yttria stabilized zirconia under simultaneous applied electric and thermal fields: A time-resolved in situ energy dispersive x-ray diffractometry study with an ultrahigh energy synchrotron probe

    SciTech Connect

    Akdogan, E. K.; Savkl Latin-Small-Letter-Dotless-I y Latin-Small-Letter-Dotless-I ld Latin-Small-Letter-Dotless-I z, I.; Bicer, H.; Paxton, W.; Toksoy, F.; Tsakalakos, T.; Zhong, Z.

    2013-06-21

    Nonisothermal densification in 8% yttria doped zirconia (8YSZ) particulate matter of 250 nm median particle size was studied under 215 V/cm dc electric field and 9 Degree-Sign C/min heating rate, using time-resolved in-situ high temperature energy dispersive x-ray diffractometry with a polychromatic 200 keV synchrotron probe. Densification occurred in the 876-905 Degree-Sign C range, which resulted in 97% of the theoretical density. No local melting at particle-particle contacts was observed in scanning electron micrographs, implying densification was due to solid state mass transport processes. The maximum current draw at 905 Degree-Sign C was 3 A, corresponding to instantaneous absorbed power density of 570 W/cm{sup 3}. Densification of 8YSZ was accompanied by anomalous elastic volume expansions of the unit cell by 0.45% and 2.80% at 847 Degree-Sign C and 905 Degree-Sign C, respectively. The anomalous expansion at 905 Degree-Sign C at which maximum densification was observed is characterized by three stages: (I) linear stage, (II) anomalous stage, and (III) anelastic recovery stage. The densification in stage I (184 s) and II (15 s) was completed in 199 s, while anelastic relaxation in stage III lasted 130 s. The residual strains ({epsilon}) at room temperature, as computed from tetragonal (112) and (211) reflections, are {epsilon}{sub (112)} = 0.05% and {epsilon}{sub (211)} = 0.13%, respectively. Time dependence of (211) and (112) peak widths ({beta}) show a decrease with both exhibiting a singularity at 905 Degree-Sign C. An anisotropy in (112) and (211) peak widths of {l_brace} {beta}{sub (112)}/{beta}{sub (211)}{r_brace} = (3:1) magnitude was observed. No phase transformation occurred at 905 Degree-Sign C as verified from diffraction spectra on both sides of the singularity, i.e., the unit cell symmetry remains tetragonal. We attribute the reduction in densification temperature and time to ultrafast ambipolar diffusion of species arising from the

  10. Anomalous temperature relaxation and particle transport in a strongly non-unifrom, fully in ionized Plasma in a stromg mangnetic field

    NASA Astrophysics Data System (ADS)

    Øien, Alf H.

    1995-02-01

    In classical kinetic and transport theory for a fully ionized plasma in a magnetic field, collision integrals from a uniform theory without fields are used. When the magnetic field is so strong that electrons may gyrate during electron—electron and electron—ion interactions, the form of the collision integrals will be modified. Another modification will stem from strong non-uniformities transverse to the magnetic field B. Using collision terms that explicitly incorporate these effects, we derive in particular the temperature relaxation between electrons and ions and the particle transport transverse to the magnetic field. In both cases collisions between gyrating electrons, which move along the magnetic field, and non-gyrating ions, which move in arbitrary directions at a distance transverse to B from the electrons larger than the electron Larmor radius but smaller than the Debye length, give rise to enhancement factors in the corresponding classical expressions of order In (mion/mel).

  11. Reducing the Heat Load on the LCLS 120 Hz RF Gun with RF Pulse Shaping

    SciTech Connect

    Schmerge, J.

    2005-01-31

    The LCLS injector must operate at 120 Hz repetition frequency but to date the maximum operating frequency of an S-band rf gun has been 50 Hz. The high fields desired for the LCLS gun operation limit the repetition frequency due to thermal expansion causing rf detuning and field redistribution. One method of addressing the thermal loading problem is too reduce the power lost on the cavity walls by properly shaping the rf pulse incident on the gun. The idea is to reach the steady state field value in the gun faster than the time constant of the gun would allow when using a flat incident rf pulse. By increasing the incident power by about a factor of three and then decreasing the incident power when the field reaches the desired value in the gun, the field build up time can be decreased by more than a factor of three. Using this technique the heat load is also decreased by more than a factor of three. In addition the rf coupling coefficient can be increased from the typical critically coupled designs to an overcoupled design which also helps reduce the field build up time. Increasing the coupling coefficient from 1 to 2 reduces the heat load by another 25% and still limits the reflected power and coupling hole size to manageable levels.

  12. FLASH Beam-Off RF Measurements and Analyses

    SciTech Connect

    Pei, Shilun; Adolphsen, Chris; Carwardine, John; /Argonne

    2009-03-31

    The FLASH L-band (1.3 GHz) superconducting accelerator facility at DESY has a Low Level RF (LLRF) system that is similar to that envisioned for ILC. This system has extensive monitoring capability and was used to gather performance data relevant to ILC. In particular, waveform data were recorded with beam off for three, 8-cavity cryomodules to evaluate the input rf stability, perturbations to the SC cavity frequencies and the rf overhead required to achieve constant gradient during the 800-s pulses. In this paper, we discuss the measurements and data analysis procedures and present key findings on the pulse-to-pulse input rf and cavity field stability.

  13. EM modeling of RF drive in DTL tank 4

    SciTech Connect

    Kurennoy, Sergey S.

    2012-06-19

    A 3-D MicroWave Studio model for the RF drive in the LANSCE DTL tank 4 has been built. Both eigensolver and time-domain modeling are used to evaluate maximal fields in the drive module and RF coupling. The LANSCE DTL tank 4 has recently been experiencing RF problems, which may or may not be related to its replaced RF coupler. This situation stimulated a request by Dan Rees to provide EM modeling of the RF drive in the DTL tank 4 (T4). Jim O'Hara provided a CAD model that was imported into the CST Microwave Studio (MWS) and after some modifications became a part of a simplified MWS model of the T4 RF drive. This technical note describes the model and presents simulation results.

  14. RF BREAKDOWN STUDIES USING PRESSURIZED CAVITIES

    SciTech Connect

    Johnson, Rolland

    2014-09-21

    Many present and future particle accelerators are limited by the maximum electric gradient and peak surface fields that can be realized in RF cavities. Despite considerable effort, a comprehensive theory of RF breakdown has not been achieved and mitigation techniques to improve practical maximum accelerating gradients have had only limited success. Part of the problem is that RF breakdown in an evacuated cavity involves a complex mixture of effects, which include the geometry, metallurgy, and surface preparation of the accelerating structures and the make-up and pressure of the residual gas in which plasmas form. Studies showed that high gradients can be achieved quickly in 805 MHz RF cavities pressurized with dense hydrogen gas, as needed for muon cooling channels, without the need for long conditioning times, even in the presence of strong external magnetic fields. This positive result was expected because the dense gas can practically eliminate dark currents and multipacting. In this project we used this high pressure technique to suppress effects of residual vacuum and geometry that are found in evacuated cavities in order to isolate and study the role of the metallic surfaces in RF cavity breakdown as a function of magnetic field, frequency, and surface preparation. One of the interesting and useful outcomes of this project was the unanticipated collaborations with LANL and Fermilab that led to new insights as to the operation of evacuated normal-conducting RF cavities in high external magnetic fields. Other accomplishments included: (1) RF breakdown experiments to test the effects of SF6 dopant in H2 and He gases with Sn, Al, and Cu electrodes were carried out in an 805 MHz cavity and compared to calculations and computer simulations. The heavy corrosion caused by the SF6 components led to the suggestion that a small admixture of oxygen, instead of SF6, to the hydrogen would allow the same advantages without the corrosion in a practical muon beam line. (2) A

  15. Low-level RF control for the AFEL

    SciTech Connect

    Ziomek, C.; Kinross-Wright, J.; Plato, J.

    1994-09-01

    A limiting factor in the performance of the Los Alamos Advanced Free Electron Laser (AFEL) is the stability of the RF accelerating field. A high-performance low-level RF control system has been implemented that uses analog feedback and digital feed forward to regulate the RF field. This low-level RF control system has achieved long-term amplitude and phase stabilities better than {+-}0.25% and {+-}0.33{degree} respectively. In order to improve the RF field stability further, a detailed system analysis and design is proceeding. Subsystem measurements are being used to model the system performance, predict the performance-limiting components, and determine possible improvements. Results to-date, modeling analyses, and suggested future improvements are presented.

  16. Proposal for high pressure RF cavity test in the MTA

    SciTech Connect

    Yonehara, K.; /Fermilab

    2010-09-01

    In order to demonstrate the feasibility of high pressure hydrogen gas filled RF (HPRF) cavities for muon ionization cooling, an HPRF cavity must be tested with a high intensity charged beam. When an HPRF cavity is irradiated with an intense beam each incident particle generates about 1000 electrons and ions per cubic centimeter in a high pressure cavity via ionization. These ionization electrons are influenced by the RF field and the RF quality factor goes down. This Q factor reduction will be a problem with a multi bunch beam, e.g., a muon beam for a muon collider consists of a 12 to 20 bunch train beam with 5 ns timing gap. Thus, the RF field must recover in few nano seconds. We propose to use a 400 MeV proton beam in the MTA and measure a beam loading effect in the HPRF cavity and study the recovery mechanism of the RF field.

  17. Cold Test Measurements on the GTF Prototype RF Gun

    SciTech Connect

    Gierman, S.M.

    2010-12-03

    The SSRL Gun Test Facility (GTF) was built to develop a high brightness electron injector for the LCLS and has been operational since 1996. Based on longitudinal phase space measurements showing a correlated energy spread the gun was removed and re-characterized in 2002. The low power RF measurements performed on the gun are described below. Perturbative bead measurements were performed to determine the field ratio in the two-cell gun, and network analyzer measurements were made to characterize the mode structure. A second probe was installed to monitor the RF field in the first cell, and a diagnostic was developed to monitor the high-power field ratio. Calibration of the RF probes, a model for analyzing RF measurements, and Superfish simulations of bead and RF measurements are described.

  18. Limitation of linear colliders from transverse rf deflections

    SciTech Connect

    Seeman, J.T.

    1987-01-01

    Offaxis beam trajectories in a linear collider produce transverse wakefield and chromatic effects which cause emittance enlargement. One cause for non-centered trajectories in the accelerating structures is radial rf fields which produce transverse deflections. Static deflections can be compensated by static dipole magnetic fields. However, fluctuations of the rf fields cause variations in the deflections which must be managed or limited. Given the level of fluctuation of the phase and amplitude of an rf system, a limit on the allowable rf deflection can be calculated. Parameters, such as the beam emittance, lattice design, rf wavelength and the initial and final beam energies, influence the tolerances. Two tolerances are calculated: (1) one assumes that the wakefields are completely controlled, and that chromatic effects are the only enlarging mechanism (optimistic), and (2) the other assumes the limit is due to transverse wakefields without the aid of Landau damping (pessimistic).

  19. Beta function and anomalous dimensions

    SciTech Connect

    Pica, Claudio; Sannino, Francesco

    2011-06-01

    We demonstrate that it is possible to determine the coefficients of an all-orders beta-function linear in the anomalous dimensions using as data the 2-loop coefficients together with the first one of the anomalous dimensions which are universal. The beta function allows us to determine the anomalous dimension of the fermion masses at the infrared fixed point, and the resulting values compare well with the lattice determinations.

  20. RF Design of the LCLS Gun

    SciTech Connect

    Limborg-Deprey, C

    2010-12-13

    Final dimensions for the LCLS RF gun are described. This gun, referred to as the LCLS gun, is a modified version of the UCLA/BNL/SLAC 1.6 cell S-Band RF gun [1], referred to as the prototype gun. The changes include a larger mode separation (15 MHz for the LCLS gun vs. 3.5 MHz for the prototype gun), a larger radius at the iris between the 2 cells, a reduced surface field on the curvature of the iris between the two cells, Z power coupling, increased cooling channels for operation at 120 Hz, dual rf feed, deformation tuning of the full cell, and field probes in both cells. Temporal shaping of the klystron pulse, to reduce the average power dissipated in the gun, has also been adopted. By increasing the mode separation, the amplitude of the 0-mode electric field on the cathode decreases from 10% of the peak on axis field for the prototype gun to less than 3% for the LCLS gun for the steady state fields. Beam performance is improved as shown by the PARMELA simulations. The gun should be designed to accept a future load lock system. Modifications follow the recommendations of our RF review committee [2]. Files and reference documents are compiled in Section IV.

  1. RF Cavity Characterization with VORPAL

    SciTech Connect

    C. Nieter, C. Roark, P. Stoltz, C.D. Zhou, F. Marhauser

    2011-03-01

    When designing a radio frequency (RF) accelerating cavity structure various figures of merit are considered before coming to a final cavity design. These figures of merit include specific field and geometry based quantities such as the ratio of the shunt impedance to the quality factor (R/Q) or the normalized peak fields in the cavity. Other important measures of cavity performance include the peak surface fields as well as possible multipacting resonances in the cavity. High fidelity simulations of these structures can provide a good estimate of these important quantities before any cavity prototypes are built. We will present VORPAL simulations of a simple pillbox structure where these quantities can be calculated analytically and compare them to the results from the VORPAL simulations. We will then use VORPAL to calculate these figures of merit and potential multipacting resonances for two cavity designs under development at Jefferson National Lab for Project X.

  2. Barrier RF stacking

    SciTech Connect

    Chou, W.; Wildman, D.; Zheng, H.; Takagi, A.; /KEK, Tsukuba

    2004-12-01

    A novel wideband RF system, nicknamed the barrier RF, has been designed, fabricated and installed in the Fermilab Main Injector. The cavity is made of seven Finemet cores, and the modulator made of two bipolar high-voltage fast solid-state switches. The system can deliver {+-}7 kV square pulses at 90 kHz. The main application is to stack two proton batches injected from the Booster and squeeze them into the size of one so that the bunch intensity can be doubled. High intensity beams have been successfully stacked and accelerated to 120 GeV with small losses. The problem of large longitudinal emittance growth is the focus of the present study. An upgraded system with two barrier RF cavities for continuous stacking is under construction. This work is part of the US-Japan collaborative agreement.

  3. Barrier RF Stacking

    SciTech Connect

    Chou, W.; Wildman, D.; Zheng, H.; Takagi, A.

    2005-06-08

    A novel wideband RF system, nicknamed the barrier RF, has been designed, fabricated and installed in the Fermilab Main Injector. The cavity is made of seven Finemet cores, and the modulator made of two bipolar high-voltage fast solid-state switches. The system can deliver {+-}7 kV square pulses at 90 kHz. The main application is to stack two proton batches injected from the Booster and squeeze them into the size of one so that the bunch intensity can be doubled. High intensity beams have been successfully stacked and accelerated to 120 GeV with small losses. The problem of large longitudinal emittance growth is the focus of the present study. An upgraded system with two barrier RF cavities for continuous stacking is under construction. This work is part of the US-Japan collaborative agreement.

  4. Barrier RF Stacking

    NASA Astrophysics Data System (ADS)

    Chou, W.; Wildman, D.; Zheng, H.; Takagi, A.

    2005-06-01

    A novel wideband RF system, nicknamed the barrier RF, has been designed, fabricated and installed in the Fermilab Main Injector. The cavity is made of seven Finemet cores, and the modulator made of two bipolar high-voltage fast solid-state switches. The system can deliver ±7 kV square pulses at 90 kHz. The main application is to stack two proton batches injected from the Booster and squeeze them into the size of one so that the bunch intensity can be doubled. High intensity beams have been successfully stacked and accelerated to 120 GeV with small losses. The problem of large longitudinal emittance growth is the focus of the present study. An upgraded system with two barrier RF cavities for continuous stacking is under construction. This work is part of the US-Japan collaborative agreement.

  5. RF Gun Optimization Study

    SciTech Connect

    A. S. Hofler; P. Evtushenko; M. Krasilnikov

    2007-08-01

    Injector gun design is an iterative process where the designer optimizes a few nonlinearly interdependent beam parameters to achieve the required beam quality for a particle accelerator. Few tools exist to automate the optimization process and thoroughly explore the parameter space. The challenging beam requirements of new accelerator applications such as light sources and electron cooling devices drive the development of RF and SRF photo injectors. RF and SRF gun design is further complicated because the bunches are space charge dominated and require additional emittance compensation. A genetic algorithm has been successfully used to optimize DC photo injector designs for Cornell* and Jefferson Lab**, and we propose studying how the genetic algorithm techniques can be applied to the design of RF and SRF gun injectors. In this paper, we report on the initial phase of the study where we model and optimize gun designs that have been benchmarked with beam measurements and simulation.

  6. Anomalous subdiffusion with multispecies linear reaction dynamics.

    PubMed

    Langlands, T A M; Henry, B I; Wearne, S L

    2008-02-01

    We have introduced a set of coupled fractional reaction-diffusion equations to model a multispecies system undergoing anomalous subdiffusion with linear reaction dynamics. The model equations are derived from a mesoscopic continuous time random walk formulation of anomalously diffusing species with linear mean field reaction kinetics. The effect of reactions is manifest in reaction modified spatiotemporal diffusion operators as well as in additive mean field reaction terms. One consequence of the nonseparability of reaction and subdiffusion terms is that the governing evolution equation for the concentration of one particular species may include both reactive and diffusive contributions from other species. The general solution is derived for the multispecies system and some particular special cases involving both irreversible and reversible reaction dynamics are analyzed in detail. We have carried out Monte Carlo simulations corresponding to these special cases and we find excellent agreement with theory. PMID:18351991

  7. Flashing anomalous color contrast.

    PubMed

    Pinna, Baingio; Spillmann, Lothar; Werner, John S

    2004-01-01

    A new visual phenomenon that we call flashing anomalous color contrast is described. This phenomenon arises from the interaction between a gray central disk and a chromatic annulus surrounded by black radial lines. In an array of such figures, the central gray disk no longer appears gray, but assumes a color complementary to that of the surrounding annulus. The induced color appears: (1) vivid and saturated; (2) self-luminous, not a surface property; (3) flashing with eye or stimulus movement; (4) floating out of its confines; and (5) stronger in extrafoveal than in foveal vision. The strength of the effect depends on the number, length, width, and luminance contrast of the radial lines. The results suggest that the chromatic ring bounding the inner tips of the black radial lines induces simultaneous color contrast, whereas the radial lines elicit, in conjunction with the gray disk and the ring, the flashing, vividness, and high saturation of the effect. The stimulus properties inducing the illusion suggest that flashing anomalous color contrast may be based on asynchronous interactions among multiple visual pathways. PMID:15518215

  8. Fickian dispersion is anomalous

    SciTech Connect

    Cushman, John H.; O’Malley, Dan

    2015-06-22

    The thesis put forward here is that the occurrence of Fickian dispersion in geophysical settings is a rare event and consequently should be labeled as anomalous. What people classically call anomalous is really the norm. In a Lagrangian setting, a process with mean square displacement which is proportional to time is generally labeled as Fickian dispersion. With a number of counter examples we show why this definition is fraught with difficulty. In a related discussion, we show an infinite second moment does not necessarily imply the process is super dispersive. By employing a rigorous mathematical definition of Fickian dispersion we illustrate why it is so hard to find a Fickian process. We go on to employ a number of renormalization group approaches to classify non-Fickian dispersive behavior. Scaling laws for the probability density function for a dispersive process, the distribution for the first passage times, the mean first passage time, and the finite-size Lyapunov exponent are presented for fixed points of both deterministic and stochastic renormalization group operators. The fixed points of the renormalization group operators are p-self-similar processes. A generalized renormalization group operator is introduced whose fixed points form a set of generalized self-similar processes. Finally, power-law clocks are introduced to examine multi-scaling behavior. Several examples of these ideas are presented and discussed.

  9. Fickian dispersion is anomalous

    DOE PAGESBeta

    Cushman, John H.; O’Malley, Dan

    2015-06-22

    The thesis put forward here is that the occurrence of Fickian dispersion in geophysical settings is a rare event and consequently should be labeled as anomalous. What people classically call anomalous is really the norm. In a Lagrangian setting, a process with mean square displacement which is proportional to time is generally labeled as Fickian dispersion. With a number of counter examples we show why this definition is fraught with difficulty. In a related discussion, we show an infinite second moment does not necessarily imply the process is super dispersive. By employing a rigorous mathematical definition of Fickian dispersion wemore » illustrate why it is so hard to find a Fickian process. We go on to employ a number of renormalization group approaches to classify non-Fickian dispersive behavior. Scaling laws for the probability density function for a dispersive process, the distribution for the first passage times, the mean first passage time, and the finite-size Lyapunov exponent are presented for fixed points of both deterministic and stochastic renormalization group operators. The fixed points of the renormalization group operators are p-self-similar processes. A generalized renormalization group operator is introduced whose fixed points form a set of generalized self-similar processes. Finally, power-law clocks are introduced to examine multi-scaling behavior. Several examples of these ideas are presented and discussed.« less

  10. Barrier RF stacking

    SciTech Connect

    Weiren Chou and Akira Takagi

    2003-02-24

    This paper introduces a new method for stacking beams in the longitudinal phase space. It uses RF barriers to confine and compress beams in an accelerator, provided that the machine momentum acceptance is a few times larger than the momentum spread of the injected beam. This is the case for the Fermilab Main Injector. A barrier RF system employing Finemet cores and high-voltage solid-state switches is under construction. The goal is to double the number of protons per cycle on the production target for Run2 and NuMI experiments.

  11. Rf2a and rf2b transcription factors

    DOEpatents

    Beachy, Roger N.; Petruccelli, Silvana; Dai, Shunhong

    2007-10-02

    A method of activating the rice tungro bacilliform virus (RTBV) promoter in vivo is disclosed. The RTBV promoter is activated by exposure to at least one protein selected from the group consisting of Rf2a and Rf2b.

  12. Probing anomalous gauge boson couplings at LEP

    SciTech Connect

    Dawson, S.; Valencia, G.

    1994-12-31

    We bound anomalous gauge boson couplings using LEP data for the Z {yields} {bar {integral}}{integral} partial widths. We use an effective field theory formalism to compute the one-loop corrections resulting from non-standard model three and four gauge boson vertices. We find that measurements at LEP constrain the three gauge boson couplings at a level comparable to that obtainable at LEPII.

  13. Anomalously large electro-optic Pockels effect at the air-water interface with an electric field applied parallel to the interface

    NASA Astrophysics Data System (ADS)

    Suzuki, Yuto; Osawa, Kengo; Yukita, Shunpei; Kobayashi, Takayoshi; Tokunaga, Eiji

    2016-05-01

    The optical Pockels effect was observed at the air-water interface by electromodulation spectroscopy. When an AC electric field of frequency f was applied parallel to a water surface between Pt electrodes, the field induced a change in the transmitted light intensity synchronized at 1f proportional to the field strength. The 1f signals dominated over 2f signals by one order of magnitude and the signal disappeared when the electrodes were completely immersed under the water surface, strongly suggesting that the observed phenomena were due to the Pockels effect at the air-water interface. The Pockels coefficient was estimated to be | r | = 1.4 × 105 pm/V, which is much larger than that at the solid-water interface. However, this is unusual because the parallel electric field does not induce the break in inversion symmetry required for the appearance of the Pockels effect. The electrowetting effect was experimentally ruled out as a mechanism for the Pockels effect, and this made the existence of a field perpendicular to the surface, although extremely weak, the most likely explanation.

  14. RF Voltage Measurements on ICRF Antennas

    NASA Astrophysics Data System (ADS)

    Bell, G. L.; Goulding, R. H.; Hoffman, D. J.; Wilgen, J. B.; Zhang, H. M.; Ryan, P. M.; Syed, G. M. S.; Kaye, A. S.

    1996-11-01

    Particle and heat flux on the plasma facing surfaces of high-power RF antennas used in fusion devices can result in damage to the antenna structures. High impedance capacitive probe measurements of the RF voltages on Faraday shields of several loop antennas indicate that voltages as high as 30% of the drive voltage can exist for 0/0 phasing (D.J. Hoffman, et al., AIP Conf. Proc. 355), 368 (Palm Spgs., CA, 1995).. These voltages can contribute to increased energy deposition on the antenna owing to increased RF sheath voltages. We report on continued efforts to understand the source and to control these RF voltages. E and B field distributions have been measured on the mock-up of the JET A2 antenna using standard B-dot probes and novel E-field probes positioned with a new automated scanning system. These data are compared with calculated fields from 3-D antenna models. The measurements demonstrate the dependency of the surface E-fields on the phasing of the strap currents and show the charge accumulation at the antenna top and bottom predicted by the models.

  15. Recent developments in superconducting cavity RF control

    NASA Astrophysics Data System (ADS)

    Simrock, Stefan

    2005-02-01

    Presently a large number of superconducting accelerators under construction or proposed impose stringent requirements on the rf control of the accelerating fields, operability, and reliability. The accelerator application range from linear colliders, UV-FELs and X-FELs, ERL based light sources, high power proton accelerators to heavy ion accelerators. Examples are TESLA and NLC, the European XFEL and Lux, the Cornell ERL based light source, the high power ERL based IR-FEL at JLAB, the neutron spallation source SNS, the heavy ion accelerator RIA, and the energy upgrade of the CEBAF accelerator at JLAB. The requirements on the rf systems range from low to high current, medium to high gradient, and relativistic to non-relativistics beam. With the technology in analog and digital electronics developing rapidly, the technology for rf feedback system is changing more and more from analog or hybrid systems towards fully digital systems. Todays DSPs and FPGAs can process sophisticated feedback algorithms on a time scale of some 100 ns to a few us with ADCs and DACs with about 100 MHz bandwidth at 14 bit and latencies less than 100 ns available to inter-face to the field detectors and field control actuators. Also fast analog multiplier technology allows for field detection and actuators for rf control with high linearity, measurement and control bandwidth while maintaining low noise levels.

  16. Hic Sunt Leones: Anomalous Scaling In Rainfall

    NASA Astrophysics Data System (ADS)

    Ferraris, L.; Gabellani, S.; Provenzale, A.; Rebora, N.

    In recent years the spatio-temporal intermittency of precipitation fields has often been quantified in terms of scaling and/or multifractal behaviour. In this work we anal- yse the spatial scaling properties of precipitation intensity fields measured during the GATE radar experiment, and compare the results with those obtained from surrogate data generated by nonlinearly filtered, linear stochastic processes and from random shuffling of the original data. The results of the study suggest a spurious nature of the spatial multifractal behaviour of the GATE fields and indicate that claims of multifrac- tality and anomalous scaling in rainfall may have to be reconsidered.

  17. The origin of anomalous muonium in semiconductors

    NASA Astrophysics Data System (ADS)

    Eshchenko, D. G.; Storchak, V. G.; Brewer, J. H.; Morris, G. D.; Clarker-Gayther, M. A.; Cottrell, S. P.; Cox, S. F. J.; Lord, J. S.

    2000-08-01

    The origin of muonium defect centers in semi-insulating GaAs has been studied using newly developed μSR techniques employing alternating electric fields. This technique prevents the accumulation of near-surface charges which may screen the external field. The screening effect was tested at ISIS by the measurements of the current induced by muon beam. Suppression of anomalous muonium signal with electric field suggests that muonium formation proceeds via transport of excess electrons from the ionization track to the muons.

  18. A Design and Performance Analysis Tool for Superconducting RF Systems

    NASA Astrophysics Data System (ADS)

    Schilcher, Th.; Simrock, S. N.; Merminga, L.; Wang, D. X.

    1997-05-01

    Superconducting rf systems are usually operated with continuous rf power or with rf pulse lengths exceeding 1 ms to maximize the overall plug power efficiency. Typical examples are CEBAF at Jefferson Lab and the TESLA Test Facility at DESY. The long pulses allow for effective application of feedback to stabilize the accelerating field in presence of microphonics, Lorentz force detuning, and fluctuations of the beam current. In this paper we describe a set of tools to be used with MATLAB and SIMULINK, which allow to analyse the quality of field regulation for a given design. The tools include models for the cavities, the rf power source, the beam, sources of field perturbations, and the rf feedback system. The rf control relevant electrical and mechanical characteristics of the cavity are described in form of time-varying state space models. The power source is modeled as a current generator and includes saturation characteristics and noise. An arbitrary time structure can be imposed on the beam current to reflect a macro-pulse stucture and bunch charge fluctuations. For rf feedback several schemes can be selected: Traditional amplitude and phase control as well as I/Q control. The choices for the feedback controller include analog or digital approaches and various choices of frequency response. Feedforward can be added to further supress repetitive errors. The results of a performance analysis of the CEBAF and the TESLA Linac rf system using these tools are presented.

  19. A design and performance analysis tool for superconducting RF systems

    SciTech Connect

    T. Schilcher; S.N. Simrock; L. Merminga; D.X. Wang

    1997-05-01

    Superconducting rf systems are usually operated with continuous rf power or with rf pulse lengths exceeding 1 ms to maximize the overall wall plug power efficiency. Typical examples are CEBAF at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) and the TESLA Test Facility at DESY. The long pulses allow for effective application of feedback to stabilize the accelerating field in presence of microphonics, Lorentz force detuning, and fluctuations of the beam current. In this paper the authors describe a set of tools to be used with MATLAB and SIMULINK, which allow to analyze the quality of field regulation for a given design. The tools include models for the cavities, the rf power source, the beam, sources of field perturbations, and the rf feedback system. The rf control relevant electrical and mechanical characteristics of the cavity are described in form of time-varying state space models. The power source is modeled as a current generator and includes saturation characteristics and noise.An arbitrary time structure can be imposed on the beam current to reflect a macro-pulse structure and bunch charge fluctuations. For rf feedback several schemes can be selected: Traditional amplitude and phase control as well as I/Q control. The choices for the feedback controller include analog or digital approaches and various choices of frequency response. Feed forward can be added to further suppress repetitive errors. The results of a performance analysis of the CEBAF and the TESLA Linac rf system using these tools are presented.

  20. Designing focusing solenoids for superconducting RF accelerators

    SciTech Connect

    Davis, G.; Kashikhin, V.V.; Page, T.; Terechkine, I.; Tompkins, J.; Wokas, T.; /Fermilab

    2006-08-01

    The design of a focusing solenoid for use in a superconducting RF linac requires resolving a range of problems with conflicting requirements. Providing the required focusing strength contradicts the goal of minimizing the stray field on the surfaces of adjacent superconducting RF cavities. The requirement of a compact solenoid, able to fit into a gap between cavities, contradicts the need of mechanical support necessary to restrain electromagnetic forces that can result in coil motion and subsequent quenching. In this report we will attempt to address these and other issues arising during the development of focusing solenoids. Some relevant test data will also be presented.

  1. Performance of the Brookhaven photocathode rf gun

    SciTech Connect

    Batchelor, K.; Ben-Zvi, I.; Fernow, R.C.; Fischer, J.; Fisher, A.S.; Gallardo, J.; Ingold, G.; Kirk, H.G.; Leung, K.P.; Malone, R.; Pogorelsky, I.; Srinivasan-Rao, T.; Rogers, J.; Tsang, T.; Sheehan, J.; Ulc, S.; Woodle, M.; Xie, J.; Zhang, R.S.; Lin, L.Y.; McDonald, K.T.; Russell, D.P.; Hung, C.M.; Wang, X.J.

    1991-12-31

    The Brookhaven Accelerator Test Facility (ATF) uses a photocathode rf gun to provide a high-brightness electron beam intended for FEL and laser-acceleration experiments. The rf gun consists of 1{1/2} cells driven at 2856 MHz in {pi}-mode with a maximum cathode field of 100 MV/m. To achieve long lifetimes, the photocathode development concentrates on robust metals such as copper, yttrium and samarium. We illuminate these cathodes with a 10-ps, frequency-quadrupled Nd:YAG laser. We describe the initial operation of the gun, including measurements of transverse and longitudinal emittance, quantum efficiencies, and peak current. The results are compared to models.

  2. Performance of the Brookhaven photocathode rf gun

    SciTech Connect

    Batchelor, K.; Ben-Zvi, I.; Fernow, R.C.; Fischer, J.; Fisher, A.S.; Gallardo, J.; Ingold, G.; Kirk, H.G.; Leung, K.P.; Malone, R.; Pogorelsky, I.; Srinivasan-Rao, T.; Rogers, J.; Tsang, T.; Sheehan, J.; Ulc, S.; Woodle, M.; Xie, J.; Zhang, R.S. ); Lin, L.Y. . Dept. of Applied Physics); McDonald, K.T.; Russell, D.P. (Pr

    1991-01-01

    The Brookhaven Accelerator Test Facility (ATF) uses a photocathode rf gun to provide a high-brightness electron beam intended for FEL and laser-acceleration experiments. The rf gun consists of 1{1/2} cells driven at 2856 MHz in {pi}-mode with a maximum cathode field of 100 MV/m. To achieve long lifetimes, the photocathode development concentrates on robust metals such as copper, yttrium and samarium. We illuminate these cathodes with a 10-ps, frequency-quadrupled Nd:YAG laser. We describe the initial operation of the gun, including measurements of transverse and longitudinal emittance, quantum efficiencies, and peak current. The results are compared to models.

  3. Anomalous diffusion in quantum Brownian motion with colored noise

    SciTech Connect

    Ford, G. W.; O'Connell, R. F.

    2006-03-15

    Anomalous diffusion is discussed in the context of quantum Brownian motion with colored noise. It is shown that earlier results follow simply and directly from the fluctuation-dissipation theorem. The limits on the long-time dependence of anomalous diffusion are shown to be a consequence of the second law of thermodynamics. The special case of an electron interacting with the radiation field is discussed in detail. We apply our results to wave-packet spreading.

  4. Origin of the Anomalous Color of Egyptian and Han Blue Historical Pigments: Going beyond the Complex Approximation in Ligand Field Theory

    ERIC Educational Resources Information Center

    García-Fernandez, Pablo; Moreno, Miguel; Aramburu, José Antonio

    2016-01-01

    The complex approximation is widely used in the framework of the Ligand Field Theory for explaining the optical properties of crystalline coordination compounds. Here, we show that there are essential features of these systems that cannot be understood with the usual approximation that only considers an isolated complex at the correct equilibrium…

  5. Anomalous reflections from the ionosphere

    NASA Astrophysics Data System (ADS)

    Givishvili, G. V.; Leshchenko, L. N.

    2013-09-01

    The existence of anomalous ionospheric reflections was shown on the basis of vertical soundings at the Moskow station. They are observed at heights of 100-200 km. These anomalous reflections are not related to the main Ne( h) ionospheric profile. Morphological characteristics of such reflections are presented: the daily, seasonal, and cyclic dependences of their appearance.

  6. Anomalous electrodynamic explosions in liquids

    SciTech Connect

    Aspden, H.

    1986-06-01

    The recently reported Graneau experiments on electrodynamic explosions in liquids, which reveal anomalous longitudinal electrodynamic forces of the order of 10/sup 4/ times greater than expected, verify the need for a term in the law of electrodynamics that corresponds to the ion/electron mass ratio. This confirms an earlier theoretical interpretation of the anomalous cathode reaction forces found in the vacuum arc.

  7. Space Shuttle and Space Station Radio Frequency (RF) Exposure Analysis

    NASA Technical Reports Server (NTRS)

    Hwu, Shian U.; Loh, Yin-Chung; Sham, Catherine C.; Kroll, Quin D.

    2005-01-01

    This paper outlines the modeling techniques and important parameters to define a rigorous but practical procedure that can verify the compliance of RF exposure to the NASA standards for astronauts and electronic equipment. The electromagnetic modeling techniques are applied to analyze RF exposure in Space Shuttle and Space Station environments with reasonable computing time and resources. The modeling techniques are capable of taking into account the field interactions with Space Shuttle and Space Station structures. The obtained results illustrate the multipath effects due to the presence of the space vehicle structures. It's necessary to include the field interactions with the space vehicle in the analysis for an accurate assessment of the RF exposure. Based on the obtained results, the RF keep out zones are identified for appropriate operational scenarios, flight rules and necessary RF transmitter constraints to ensure a safe operating environment and mission success.

  8. A Dual-Moded Cavity for RF Breakdown Studies

    SciTech Connect

    Nantista, Christopher; Adolphsen, Chris; Wang, Faya; /SLAC

    2010-08-25

    The phenomenon of rf breakdown presents a technological limitation in the application of high-gradient particle acceleration in normal conducting rf structures. Attempts to understand the onset of this phenomenon and to study its limits with different materials, cell shapes, and pulse widths has been driven in recent years by linear collider development. One question of interest is the role magnetic field plays relative to electric field. A design is presented for a single, nonaccelerating, rf cavity resonant in two modes, which, driven independently, allow the rf magnetic field to be increased on the region of highest electric field without affecting the latter. The design allows for the potential reuse of the cavity with different samples in the high-field region. High power data is not yet available.

  9. The TESLA RF System

    NASA Astrophysics Data System (ADS)

    Choroba, S.

    2003-12-01

    The TESLA project proposed by the TESLA collaboration in 2001 is a 500 to 800GeV e+/e- linear collider with integrated free electron laser facility. The accelerator is based on superconducting cavity technology. Approximately 20000 superconducting cavities operated at 1.3GHz with a gradient of 23.4MV/m or 35MV/m will be required to achieve the energy of 500GeV or 800GeV respectively. For 500GeV ˜600 RF stations each generating 10MW of RF power at 1.3GHz at a pulse duration of 1.37ms and a repetition rate of 5 or 10Hz are required. The original TESLA design was modified in 2002 and now includes a dedicated 20GeV electron accelerator in a separate tunnel for free electron laser application. The TESLA XFEL will provide XFEL radiation of unprecedented peak brilliance and full transverse coherence in the wavelength range of 0.1 to 6.4nm at a pulse duration of 100fs. The technology of both accelerators, the TESLA linear collider and the XFEL, will be identical, however the number of superconducting cavities and RF stations for the XFEL will be reduced to 936 and 26 respectively. This paper describes the layout of the entire RF system of the TESLA linear collider and the TESLA XFEL and gives an overview of its various subsystems and components.

  10. Improved RF Isolation Amplifier

    NASA Technical Reports Server (NTRS)

    Stevens, G. L.; Macconnell, J.

    1985-01-01

    Circuit has high reverse isolation and wide bandwidth. Wideband isolation amplifier has low intermodulation distortion and high reverse isolation. Circuit does not require selected or matched components or directional coupling device. Circuit used in applications requiring high reverse isolation such as receiver intermediate-frequency (IF) strips and frequency distribution systems. Also applicable in RF and video signaling.

  11. Prospects for Advanced RF Theory and Modeling

    SciTech Connect

    Batchelor, D.B.

    1999-04-12

    This paper represents an attempt to express in print the contents of a rather philosophical review talk. The charge for the talk was not to summarize the present status of the field and what we can do, but to assess what we will need to do in the future and where the gaps are in fulfilling these needs. The objective was to be complete, covering all aspects of theory and modeling in all frequency regimes, although in the end the talk mainly focussed on the ion cyclotron range of frequencies (ICRF). In choosing which areas to develop, it is important to keep in mind who the customers for RF modeling are likely to be and what sorts of tasks they will need for RF to do. This occupies the first part of the paper. Then we examine each of the elements of a complete RF theory and try to identify the kinds of advances needed.

  12. RF-Based Accelerators for HEDP Research

    SciTech Connect

    Staples, John W.; Sessler, Andrew; Keller, Roderich; Ostroumov,Petr; Chou, Weiren

    2005-05-09

    Accelerator-driven High-Energy Density Physics (HEDP) experiments require typically 1 nanosecond, 1 microcoulomb pulses of mass 20 ions accelerated to several MeV to produce eV-level excitations in thin targets, the warm dense matter regime. Traditionally the province of induction linacs, RF-based acceleration may be a viable alternative with recent breakthroughs in accelerating structures and high-field compact superconducting solenoids. A reference design for an RF-based accelerator for HEDP research is presented using 15 T solenoids and multiple-gap RF structures configured with multiple parallel beams combined at the target. The beam is ballistically compressed with an induction linac core providing the necessary energy sweep and injected into a plasma-neutralized drift compression channel resulting in a 1 mm radius beam spot 1 nanosecond long at a thin foil or low-density target.

  13. Active high-power RF switch and pulse compression system

    DOEpatents

    Tantawi, Sami G.; Ruth, Ronald D.; Zolotorev, Max

    1998-01-01

    A high-power RF switching device employs a semiconductor wafer positioned in the third port of a three-port RF device. A controllable source of directed energy, such as a suitable laser or electron beam, is aimed at the semiconductor material. When the source is turned on, the energy incident on the wafer induces an electron-hole plasma layer on the wafer, changing the wafer's dielectric constant, turning the third port into a termination for incident RF signals, and. causing all incident RF signals to be reflected from the surface of the wafer. The propagation constant of RF signals through port 3, therefore, can be changed by controlling the beam. By making the RF coupling to the third port as small as necessary, one can reduce the peak electric field on the unexcited silicon surface for any level of input power from port 1, thereby reducing risk of damaging the wafer by RF with high peak power. The switch is useful to the construction of an improved pulse compression system to boost the peak power of microwave tubes driving linear accelerators. In this application, the high-power RF switch is placed at the coupling iris between the charging waveguide and the resonant storage line of a pulse compression system. This optically controlled high power RF pulse compression system can handle hundreds of Megawatts of power at X-band.

  14. Detection of anomalous events

    DOEpatents

    Ferragut, Erik M.; Laska, Jason A.; Bridges, Robert A.

    2016-06-07

    A system is described for receiving a stream of events and scoring the events based on anomalousness and maliciousness (or other classification). The system can include a plurality of anomaly detectors that together implement an algorithm to identify low-probability events and detect atypical traffic patterns. The anomaly detector provides for comparability of disparate sources of data (e.g., network flow data and firewall logs.) Additionally, the anomaly detector allows for regulatability, meaning that the algorithm can be user configurable to adjust a number of false alerts. The anomaly detector can be used for a variety of probability density functions, including normal Gaussian distributions, irregular distributions, as well as functions associated with continuous or discrete variables.

  15. Anomalous gauge boson couplings

    SciTech Connect

    Barklow, T.; Rizzo, T.; Baur, U.

    1997-01-13

    The measurement of anomalous gauge boson self couplings is reviewed for a variety of present and planned accelerators. Sensitivities are compared for these accelerators using models based on the effective Lagrangian approach. The sensitivities described here are for measurement of {open_quotes}generic{close_quotes} parameters {kappa}{sub V}, {lambda}{sub V}, etc., defined in the text. Pre-LHC measurements will not probe these coupling parameters to precision better than O(10{sup -1}). The LHC should be sensitive to better than O(10{sup -2}), while a future NLC should achieve sensitivity of O(10{sup -3}) to O(10{sup -4}) for center of mass energies ranging from 0.5 to 1.5 TeV.

  16. Photocathodes for RF photoinjectors

    NASA Astrophysics Data System (ADS)

    Michelato, P.

    1997-02-01

    Over the past ten years photocathodes have been extensively used as high-brightness electron sources in RF guns. In this paper, I present a general review of the alkali-based high quantum efficiency (QE) photoemitters (e.g. Cs 3Sb, K 2CsSb and Cs 2Te), together with a comparative analysis of the different preparation procedures and the results obtained, both in the preparation chambers and in RF guns. The need to increase the photocathode reliability has provided the impetus to get an R&D activity to go over the alchemy of photocathode preparation procedure. In this paper, I will discuss the results so far obtained in different laboratories, both by using traditional investigation strategy (e.g. QE and RF behavior) and by means of surface science techniques as Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS). Alkali antimonides have been used at first in the RF gun due to the high QE response to the green light of the Nd:YLF second-harmonic radiation. Measurements have confirmed the high reactivity of the alkali antimonide photocathodes to the residual gases: this fact makes their use in RF guns not practical, mainly for short lifetimes. Further investigations have shown that the choice of the substratum preparation procedure and chemical composition plays a fundamental role in the photocathode performance, both from the point of view of the QE and the operative lifetime and ruggedness to gas exposition. Cesium telluride (Cs 2Te) prepared on a molybdenum substratum seems to be, nowadays, the best compromise, in terms of preparation procedure reliability and ruggedness, that now the characteristics and drawbacks of this material are well understood (e.g. the need of an UV laser source). Future possible developments will be discussed. In particular, the measurement and the control of the thermal emittance and the time response could be an important task.

  17. A self-adaptive feedforward rf control system for linacs

    NASA Astrophysics Data System (ADS)

    Zhang, Renshan; Ben-Zvi, Ilan; Xie, Jialin

    1993-01-01

    The design and performance of a self-adaptive feedforward rf control system are reported. The system was built for the linac of the Accelerator Test Facility (ATF) at Brookhaven National Laboratory. Variables of time along the linac macropulse, such as field or phase are discretized and represented as vectors. Upon turn-on or after a large change in the operating-point, the control system acquires the response of the system to test signal vectors and generates a linearized system response matrix. During operation an error vector is generated by comparing the linac variable vectors and a target vector. The error vector is multiplied by the inverse of the system's matrix to generate a correction vector is added to an operating point vector. This control system can be used to control a klystron to produce flat rf amplitude and phase pulses, to control a rf cavity to reduce the rf field fluctuation, and to compensate the energy spread among bunches in a rf linac. Beam loading effects can be corrected and a programmed ramp can be produced. The performance of the control system has been evaluated on the control of a klystron's output as well as an rf cavity. Both amplitude and phase have been regulated simultaneously. In initial tests, the rf output from a klystron has been regulated to an amplitude fluctuation of less than ±0.3% and phase variation of less than ±0.6°. The rf field of the ATF's photo-cathode microwave gun cavity has been regulated to ±0.5% in amplitude and simultaneously to ±1° in phase. Regulating just the rf field amplitude in the rf gun cavity, we have achieved amplitude fluctuation of less than ±0.2%.

  18. Superconducting cavities and modulated RF

    SciTech Connect

    Farkas, Z.D.

    1981-02-01

    If a cavity has an infinite Q/sub o/, 81.5% of the energy contained in a pulse incident upon the cavity is transferred into the cavity by the end of the pulse if the cavity Q/sub e/ is chosen so that the cavity time constant is 0.796 pulse width (T/sub a/). As Q/sug o/ decreases, the energy in the cavity at the end of the pulse decreases very slowly as long as T/sub a/ is much less than the unloaded cavity time constant, T/sub co/. SC cavities with very high Q/sub o/ enable one to obtain very high gradients with a low power cw source. At high gradients, however, one often does not attain the high Q/sub o/ predicted by theory. Therefore, if one is inteerested in attaining maximum energy in the cavity, as is the case for RF processing and diagnostics, for a given available source energy there is no point in keeping the power on for longer than 0.1 T/sub co/ because the energy expended after 0.1 T/sub co/ is wasted. Therefore, to attain high fields at moderate Q/sub o/, pulsed operation is indicated. This note derives the fields and energy stored and dissipated in the cavity when Q/sub e/ is optimized for a given T/sub a/. It shows how to use this data to measure Q/sub o/ of an SC cavity as a function of field level, how to process the cavity with high RF fields, how to operate SC cavities in the pulsed mode to obtain higher efficiencies and gradients. Experimental results are also reported.

  19. Experimental Study of RF Pulsed Heating

    SciTech Connect

    Laurent, Lisa; Tantawi, Sami; Dolgashev, Valery; Nantista, Christopher; Higashi, Yasuo; Aicheler, Markus; Heikkinen, Samuli; Wuensch, Walter; /CERN

    2011-11-04

    Cyclic thermal stresses produced by rf pulsed heating can be the limiting factor on the attainable reliable gradients for room temperature linear accelerators. This is especially true for structures that have complicated features for wakefield damping. These limits could be pushed higher by using special types of copper, copper alloys, or other conducting metals in constructing partial or complete accelerator structures. Here we present an experimental study aimed at determining the potential of these materials for tolerating cyclic thermal fatigue due to rf magnetic fields. A special cavity that has no electric field on the surface was employed in these studies. The cavity shape concentrates the magnetic field on one flat surface where the test material is placed. The materials tested in this study have included oxygen free electronic grade copper, copper zirconium, copper chromium, hot isostatically pressed copper, single crystal copper, electroplated copper, Glidcop(reg. sign), copper silver, and silver plated copper. The samples were exposed to different machining and heat treatment processes prior to rf processing. Each sample was tested to a peak pulsed heating temperature of approximately 110 C and remained at this temperature for approximately 10 x 10{sup 6} rf pulses. In general, the results showed the possibility of pushing the gradient limits due to pulsed heating fatigue by the use of copper zirconium and copper chromium alloys.

  20. Reduction of RF sheaths potentials by compensation or suppression of parallel RF currents on ICRF antennae

    NASA Astrophysics Data System (ADS)

    Mendes, A.; Colas, L.; Vulliez, K.; Argouarch, A.; Milanesio, D.

    2009-11-01

    Radio Frequency (RF) sheaths are suspected to limit the performance of present-day Ion Cyclotron Range of Frequencies (ICRF) antennae over long pulses and should be minimized in future Fusion devices. Within the simplest models, RF sheath effects are quantified by the integral VRF = ∫E//ṡdl where the parallel RF field E// is linked with the slow wave. On "long open field lines" with large toroidal extension on both sides of the antenna it was shown that VRF is excited by parallel RF currents j// flowing on the antenna structure. We thus propose two ways to reduce |VRF| by acting on j// on the antenna front face. The first method, more adapted for protruding antennae, consists in avoiding the j// circulation on the antenna structure, by slotting the antenna frame on its horizontal edges and by cutting partially the Faraday screen rods. The second method, well suited for recessed antennae, consists in compensating j// of opposite signs along long flux tubes, with parallelepiped antennae aligned with tilted flux tubes. The different concepts are assessed numerically on a 2-strap Tore Supra antenna phased [0, π] using near RF fields from the antenna code TOPICA. Simulations stress the need to suppress all current paths for j// to reduce substantially |VRF| over the whole antenna height.

  1. Alternative RF coupling configurations for H- ion sources

    NASA Astrophysics Data System (ADS)

    Briefi, S.; Gutmann, P.; Fantz, U.

    2015-04-01

    RF heated sources for negative hydrogen ions both for fusion and accelerators require very high RF powers in order to achieve the required H- current what poses high demands on the RF generators and the RF circuit. Therefore it is highly desirable to improve the RF efficiency of the sources. This could be achieved by applying different RF coupling concepts than the currently used inductive coupling via a helical antenna, namely Helicon coupling or coupling via a planar ICP antenna enhanced with ferrites. In order to investigate the feasibility of these concepts, two small laboratory experiments have been set up. The PlanICE experiment, where the enhanced inductive coupling is going to be investigated, is currently under assembly. At the CHARLIE experiment systematic measurements concerning Helicon coupling in hydrogen and deuterium are carried out. The investigations show that a prominent feature of Helicon discharges occurs: the so-called low-field peak. This is a local improvement of the coupling efficiency at a magnetic field strength of a few mT which results in an increased electron density and dissociation degree. The full Helicon mode has not been achieved yet due to the limited available RF power and magnetic field strength but it might be sufficient for the application of the coupling concept to ion sources to operate the discharge in the low-field-peak region.

  2. Barrier rf systems in synchrotrons

    SciTech Connect

    Chandra M. Bhat

    2004-06-28

    Recently, many interesting applications of the barrier RF system in hadron synchrotrons have been realized. A remarkable example of this is the development of longitudinal momentum mining and implementation at the Fermilab Recycler for extraction of low emittance pbars for the Tevatron shots. At Fermilab, we have barrier RF systems in four different rings. In the case of Recycler Ring, all of the rf manipulations are carried out using a barrier RF system. Here, the author reviews various uses of barrier rf systems in particle accelerators including some new schemes for producing intense proton beam and possible new applications.

  3. RF current drive and plasma fluctuations

    NASA Astrophysics Data System (ADS)

    Peysson, Yves; Decker, Joan; Morini, L.; Coda, S.

    2011-12-01

    The role played by electron density fluctuations near the plasma edge on rf current drive in tokamaks is assessed quantitatively. For this purpose, a general framework for incorporating density fluctuations in existing modelling tools has been developed. It is valid when rf power absorption takes place far from the fluctuating region of the plasma. The ray-tracing formalism is modified in order to take into account time-dependent perturbations of the density, while the Fokker-Planck solver remains unchanged. The evolution of the electron distribution function in time and space under the competing effects of collisions and quasilinear diffusion by rf waves is determined consistently with the time scale of fluctuations described as a statistical process. Using the ray-tracing code C3PO and the 3D linearized relativistic bounce-averaged Fokker-Planck solver LUKE, the effect of electron density fluctuations on the current driven by the lower hybrid (LH) and the electron cyclotron (EC) waves is estimated quantitatively. A thin fluctuating layer characterized by electron drift wave turbulence at the plasma edge is considered. The effect of fluctuations on the LH wave propagation is equivalent to a random scattering process with a broadening of the poloidal mode spectrum proportional to the level of the perturbation. However, in the multipass regime, the LH current density profile remains sensitive to the ray chaotic behaviour, which is not averaged by fluctuations. The effect of large amplitude fluctuations on the EC driven current is found to be similar to an anomalous radial transport of the fast electrons. The resulting lower current drive efficiency and broader current profile are in better agreement with experimental observations. Finally, applied to the ITER ELMy H-mode regime, the model predicts a significant broadening of the EC driven current density profile with the fluctuation level, which can make the stabilization of neoclassical tearing mode potentially

  4. RF-dressed Rydberg atoms in hollow-core fibres

    NASA Astrophysics Data System (ADS)

    Veit, C.; Epple, G.; Kübler, H.; Euser, T. G.; Russell, P. St. J.; Löw, R.

    2016-07-01

    The giant electro-optical response of Rydberg atoms manifests itself in the emergence of sidebands in the Rydberg excitation spectrum if the atom is exposed to a radio-frequency (RF) electric field. Here we report on the study of RF-dressed Rydberg atoms inside hollow-core photonic crystal fibres, a system that enables the use of low modulation voltages and offers the prospect of miniaturised vapour-based electro-optical devices. Narrow spectroscopic features caused by the RF field are observed for modulation frequencies up to 500 MHz.

  5. Application of anomalous diffusion in production of negative ions

    NASA Astrophysics Data System (ADS)

    Jimbo, Kouichi

    1984-11-01

    The production of negative hydrogen ions is investigated in the reflex-type negative ion sources. When anomalous diffusion in the positive column was found by Hoh and Lehnert [Phys. Fluids 3, 600 (1960)], it was pointed out that the large particle loss produced by anomalous diffusion is compensated for by the larger particle production inside the plasma. In the present experiments anomalous diffusion was artificially encouraged by changing the radial electric field inside the reflex discharge. Apparent encouragement of negative ion current by the increase of the density fluctuation amplitude is observed. Twice as much negative ion current was obtained with the artificial encouragement as without. On the other hand, the larger extracted negative ion current was observed with a lower electron temperature, which is calculated from the anomalous diffusion coefficient derived from a simple nonlinear theory. This result is consistent with Wadehra's calculated results [Appl. Phys. Lett. 35, 917 (1979)].

  6. Application of anomalous diffusion in production of negative ions

    SciTech Connect

    Jimbo, K.

    1984-11-01

    The production of negative hydrogen ions is investigated in the reflex-type negative ion sources. When anomalous diffusion in the positive column was found by Hoh and Lehnert (Phys. Fluids 3, 600 (1960)), it was pointed out that the large particle loss produced by anomalous diffusion is compensated for by the larger particle production inside the plasma. In the present experiments anomalous diffusion was artificially encouraged by changing the radial electric field inside the reflex discharge. Apparent encouragement of negative ion current by the increase of the density fluctuation amplitude is observed. Twice as much negative ion current was obtained with the artificial encouragement as without. On the other hand, the larger extracted negative ion current was observed with a lower electron temperature, which is calculated from the anomalous diffusion coefficient derived from a simple nonlinear theory. This result is consistent with Wadehra's calculated results (Appl. Phys. Lett. 35, 917 (1979)).

  7. More modular invariant anomalous U(1) breaking

    SciTech Connect

    Gaillard, Mary K.; Giedt, Joel

    2002-06-27

    We consider the case of several scalar fields, charged under a number of U(1) factors, acquiring vacuum expectation values due to anomalous U(1). We demonstrate how to make redefinitions at the superfield level in order to account for tree-level exchange of vector supermultiplets in the effective supergravity theory of the light fields in the supersymmetric vacuum phase. Our approach builds up on previous results that we obtained in a more elementary case. We find that the modular weights of light fields are typically shifted from their original values, allowing an interpretation in terms of the preservation of modular invariance in the effective theory. We address various subtleties in defining unitary gauge that are associated with the noncanonical Kahler potential of modular invariant supergravity, the vacuum degeneracy, and the role of the dilaton field. We discuss the effective superpotential for the light fields and note how proton decay operators may be obtained when the heavy fields are integrated out of the theory at the tree-level. We also address how our formalism may be extended to describe the generalized Green-Schwarz mechanism for multiple anomalous U(1)'s that occur in four-dimensional Type I and Type IIB string constructions.

  8. Algebraic isomorphism in two-dimensional anomalous gauge theories

    SciTech Connect

    Carvalhaes, C.G.; Natividade, C.P.

    1997-08-01

    The operator solution of the anomalous chiral Schwinger model is discussed on the basis of the general principles of Wightman field theory. Some basic structural properties of the model are analyzed taking a careful control on the Hilbert space associated with the Wightman functions. The isomorphism between gauge noninvariant and gauge invariant descriptions of the anomalous theory is established in terms of the corresponding field algebras. We show that (i) the {Theta}-vacuum representation and (ii) the suggested equivalence of vector Schwinger model and chiral Schwinger model cannot be established in terms of the intrinsic field algebra. {copyright} 1997 Academic Press, Inc.

  9. Racetrack microtron rf system

    SciTech Connect

    Tallerico, P.J.; Keffeler, D.R.

    1985-01-01

    The rf system for the National Bureau of Standards (NBS)/Los Alamos cw racetrack microtron is described. The low-power portion consists of five 75-W amplifers that drive two input ports in each of two chopper deflection cavities and one port in the prebuncher cavity. A single 500-kW klystron drives four separate 2380-MHz cavity sections: the two main accelerator sections, a capture section, and a preaccelerator section. The phases and amplitudes in all cavities are controlled by electronic or electromechanical controls. The 1-MW klystron power supply and crowbar system were purchased as a unit; several modifications are described that improve power-supply performance. The entire rf system has been tested and shipped to the NBS, and the chopper-buncher system has been operated with beam at the NBS. 5 refs., 2 figs.

  10. Anomalous Hall effect

    NASA Astrophysics Data System (ADS)

    Nagaosa, Naoto; Sinova, Jairo; Onoda, Shigeki; MacDonald, A. H.; Ong, N. P.

    2010-04-01

    The anomalous Hall effect (AHE) occurs in solids with broken time-reversal symmetry, typically in a ferromagnetic phase, as a consequence of spin-orbit coupling. Experimental and theoretical studies of the AHE are reviewed, focusing on recent developments that have provided a more complete framework for understanding this subtle phenomenon and have, in many instances, replaced controversy by clarity. Synergy between experimental and theoretical works, both playing a crucial role, has been at the heart of these advances. On the theoretical front, the adoption of the Berry-phase concepts has established a link between the AHE and the topological nature of the Hall currents. On the experimental front, new experimental studies of the AHE in transition metals, transition-metal oxides, spinels, pyrochlores, and metallic dilute magnetic semiconductors have established systematic trends. These two developments, in concert with first-principles electronic structure calculations, strongly favor the dominance of an intrinsic Berry-phase-related AHE mechanism in metallic ferromagnets with moderate conductivity. The intrinsic AHE can be expressed in terms of the Berry-phase curvatures and it is therefore an intrinsic quantum-mechanical property of a perfect crystal. An extrinsic mechanism, skew scattering from disorder, tends to dominate the AHE in highly conductive ferromagnets. The full modern semiclassical treatment of the AHE is reviewed which incorporates an anomalous contribution to wave-packet group velocity due to momentum-space Berry curvatures and correctly combines the roles of intrinsic and extrinsic (skew-scattering and side-jump) scattering-related mechanisms. In addition, more rigorous quantum-mechanical treatments based on the Kubo and Keldysh formalisms are reviewed, taking into account multiband effects, and demonstrate the equivalence of all three linear response theories in the metallic regime. Building on results from recent experiment and theory, a

  11. RF Processing of the Couplers for the SNS Superconducting Cavities

    SciTech Connect

    Y.Kang; I.E. Campisi; D. Stout; A. Vassioutchenko; M. Stirbet; M. Drury; T. Powers

    2005-07-10

    All eighty-one fundamental power couplers for the 805 MHz superconducting cavities of the SNS linac have been RF conditioned and installed in the cryomodules successfully. The couplers were RF processed at JLAB or at the SNS in ORNL: more than forty couplers have been RF conditioned in the SNS RF Test Facility (RFTF) after the first forty couplers were conditioned at JLAB. The couplers were conditioned up to 650 kW forward power at 8% duty cycle in traveling and standing waves. They were installed on the cavities in the cryomodules and then assembled with the airside waveguide transitions. The couplers have been high power RF tested with satisfactory accelerating field gradients in the cooled cavities.

  12. Anomalous - viscosity current drive

    DOEpatents

    Stix, Thomas H.; Ono, Masayuki

    1988-01-01

    An apparatus and method for maintaining a steady-state current in a toroidal magnetically confined plasma. An electric current is generated in an edge region at or near the outermost good magnetic surface of the toroidal plasma. The edge current is generated in a direction parallel to the flow of current in the main plasma and such that its current density is greater than the average density of the main plasma current. The current flow in the edge region is maintained in a direction parallel to the main current for a period of one or two of its characteristic decay times. Current from the edge region will penetrate radially into the plasma and augment the main plasma current through the mechanism of anomalous viscosity. In another aspect of the invention, current flow driven between a cathode and an anode is used to establish a start-up plasma current. The plasma-current channel is magnetically detached from the electrodes, leaving a plasma magnetically insulated from contact with any material obstructions including the cathode and anode.

  13. Anomalous discrete symmetry

    SciTech Connect

    Huang, Z. )

    1992-12-01

    We examine an interesting scenario to solve the domain-wall problem recently suggested by Preskill, Trivedi, Wilczek, and Wise. The effective potential is calculated in the presence of the QCD axial anomaly. It is shown that some discrete symmetries such as {ital CP} and {ital Z}{sub 2} can be anomalous due to a so-called {ital K} term induced by instantons. We point out that the {ital Z}{sub 2} domain-wall problem in the two-doublet standard model can be resolved by two types of solutions: the {ital CP}-conserving one and the {ital CP}-breaking one. In the first case, there exist two {ital Z}{sub 2}-related local minima whose energy splitting is provided by the instanton effect. In the second case, there is only one unique vacuum so that the domain walls do not form at all. The consequences of this new source of {ital CP} violation are discussed and shown to be well within the experimental limits in weak interactions.

  14. RF system considerations for large high-duty-factor linacs

    SciTech Connect

    Lynch, M.T.; Ziomek, C.D.; Tallerico, P.J.; Regan, A.H.; Eaton, L.; Lawrence, G.

    1994-09-01

    RF systems are often a major cost item for linacs, but this is especially true for large high-duty-factor linacs (up to and including CW) such as the Accelerator for Production of Tritium (APT) or the Accelerator for Transmutation of nuclear Waste (ATW). In addition, the high energy and high average beam current of these machines (approximately 1 GeV, 100--200 mA) leads to a need for excellent control of the accelerating fields in order to minimize the possibility of beam loss in the accelerator and the resulting activation. This paper will address the key considerations and limitations in the design of the RF system. These considerations impact the design of both the high power RF components and the RF controls. As might be expected, the two concerns sometimes lead to conflicting design requirements. For example minimum RF operating costs lead to a desire for operation near saturation of the high power RF generators in order to maximize the operating efficiency. Optimal control of the RF fields leads to a desire for maximum overdrive capability in those same generators in order to respond quickly to disturbances of the accelerator fields.

  15. RF packaging for space applications

    NASA Astrophysics Data System (ADS)

    Drevon, C.; Monfraix, P.; Paillard, M.; Schaffauser, C.; Vendier, O.

    2002-12-01

    Alcatel Space has been working in the field of RF hybrids for a long time. This paper presents the evolution of microwave packaging, up to 40 GHz, towards more and more miniaturisation. RF packaging presents challenging trade-offs between electrical performances and manufacturability, the higher the frequency; the more these two parameters are intertwined. An important step in the field of miniaturisation was the use, beginning of 90's, of MMICs based on GaAs - Gallium Arsenide - and micropackages, following by the introduction of mixed LF/MMwave MCM. Now a good choice could be made between those MCMs and advanced micropackages. The next evolution is the use of flip-chip interconnection to minimise the length of RF connections. In term of bonding reliability, the results give values over more than five times the limits from the standards, even after 500 thermal cycles. The association of power flip-chip which high thermal conductive substrates like Aluminum Nitride - could give at least 40% reduction in the Rth for an amplifier with MMIC mounted flip-chip with emitter bumps. The glob-top technology is not yet used for higher frequencies (i.e. some or some tens of GHz). However, the results presented in this paper show that glob-top are compatible with GaAs MMICs working up to 12 GHz. With some specific design rules, the right encapsulant and the associated processes, there are little degradations of the electrical performances of a Low Level Amplifier working at 10.7 - 12.7 GHz. This has been also checked after thermal cycles.Another emergent technology with MEMS - MicroElectroMechanical Systems - could be used soon for space application, especially for very small switches with low losses. This will be made only if they could be encapsulated with an adapted packaging and if the reliability is full demonstrated following space criteria. Now, those different technologies could be associated with other miniaturization new concepts adapted to the microwave needs, such

  16. ANALYZING SURFACE ROUGHNESS DEPENDENCE OF LINEAR RF LOSSES

    SciTech Connect

    Reece, Charles E.; Kelley, Michael J.; Xu, Chen

    2012-09-01

    Topographic structure on Superconductivity Radio Frequency (SRF) surfaces can contribute additional cavity RF losses describable in terms of surface RF reflectivity and absorption indices of wave scattering theory. At isotropic homogeneous extent, Power Spectrum Density (PSD) of roughness is introduced and quantifies the random surface topographic structure. PSD obtained from different surface treatments of niobium, such Buffered Chemical Polishing (BCP), Electropolishing (EP), Nano-Mechanical Polishing (NMP) and Barrel Centrifugal Polishing (CBP) are compared. A perturbation model is utilized to calculate the additional rough surface RF losses based on PSD statistical analysis. This model will not consider that superconductor becomes normal conducting at fields higher than transition field. One can calculate the RF power dissipation ratio between rough surface and ideal smooth surface within this field range from linear loss mechanisms.

  17. Recent Progress of RF Cavity Study at Mucool Test Area

    SciTech Connect

    Yonehara, Katsuya; /Fermilab

    2011-12-02

    Summar of presentation is: (1) MTA is a multi task working space to investigate RF cavities for R&D of muon beam cooling channel - (a) Intense 400 MeV H{sup -} beam, (b) Handle hydrogen (flammable) gas, (c) 5 Tesla SC solenoid magnet, (d) He cryogenic/recycling system; (2) Pillbox cavity has been refurbished to search better RF material - Beryllium button test will be happened soon; (3) E x B effect has been tested in a box cavity - Under study (result seems not to be desirable); (4) 201 MHz RF cavity with SRF cavity treatment has been tested at low magnetic field - (a) Observed some B field effect on maximum field gradient and (b) Further study is needed (large bore SC magnet will be delivered end of 2011); and (5) HPRF cavity beam test has started - (a) No RF breakdown observed and (b) Design a new HPRF cavity to investigate more plasma loading effect.

  18. High-power RF testing of a 352-MHZ fast-ferrite RF cavity tuner at the Advanced Photon Source.

    SciTech Connect

    Horan, D.; Cherbak, E.; Accelerator Systems Division

    2006-01-01

    A 352-MHz fast-ferrite rf cavity tuner, manufactured by Advanced Ferrite Technology, was high-power tested on a single-cell copper rf cavity at the Advanced Photon Source. These tests measured the fast-ferrite tuner performance in terms of power handling capability, tuning bandwidth, tuning speed, stability, and rf losses. The test system comprises a single-cell copper rf cavity fitted with two identical coupling loops, one for input rf power and the other for coupling the fast-ferrite tuner to the cavity fields. The fast-ferrite tuner rf circuit consists of a cavity coupling loop, a 6-1/8-inch EIA coaxial line system with directional couplers, and an adjustable 360{sup o} mechanical phase shifter in series with the fast-ferrite tuner. A bipolar DC bias supply, controlled by a low-level rf cavity tuning loop consisting of an rf phase detector and a PID amplifier, is used to provide a variable bias current to the tuner ferrite material to maintain the test cavity at resonance. Losses in the fast-ferrite tuner are calculated from cooling water calorimetry. Test data will be presented.

  19. Petrology of Anomalous Eucrites

    NASA Technical Reports Server (NTRS)

    Mittlefehldt, D. W.; Peng, Z. X.; Ross, D. K.

    2015-01-01

    Most mafic achondrites can be broadly categorized as being "eucritic", that is, they are composed of a ferroan low-Ca clinopyroxene, high-Ca plagioclase and a silica phase. They are petrologically distinct from angritic basalts, which are composed of high-Ca, Al-Ti-rich clinopyroxene, Carich olivine, nearly pure anorthite and kirschsteinite, or from what might be called brachinitic basalts, which are composed of ferroan orthopyroxene and high-Ca clinopyroxene, intermediate-Ca plagioclase and ferroan olivine. Because of their similar mineralogy and composition, eucrite-like mafic achondrites formed on compositionally similar asteroids under similar conditions of temperature, pressure and oxygen fugacity. Some of them have distinctive isotopic compositions and petrologic characteristics that demonstrate formation on asteroids different from the parent of the HED clan (e.g., Ibitira, Northwest Africa (NWA) 011). Others show smaller oxygen isotopic distinctions but are otherwise petrologically and compositionally indistinguishable from basaltic eucrites (e.g., Pasamonte, Pecora Escarpment (PCA) 91007). The degree of uniformity in delta O-17 of eucrites and diogenites is one piece of evidence considered to favor of a magma-ocean scenario for their petrogenesis. Given that the O isotopic differences separating Pasamonte and PCA 91007 from other eucrites are small, and that there is an absence of other distinguishing characteristics, a legitimate question is: Did the HED parent asteroid fail to homogenize via a magma-ocean stage, thus explaining outliers like Pasamonte? We are initiating a program of study of anomalous eucrite-like achondrites as one part of our effort to seek a resolution of this issue. Here we present preliminary petrologic information on Asuka (A-) 881394, Elephant Moraine (EET) 87520 and EET 87542. We will have studied several more by conference time.

  20. Nonlocal anomalous Hall effect

    NASA Astrophysics Data System (ADS)

    Zhang, Shulei; Vignale, Giovanni

    Anomalous Hall effect (AHE) is a distinctive transport property of ferromagnetic metals arising from spin orbit coupling (SOC) in concert with spontaneous spin polarization. Nonetheless, recent experiments have shown that the effect also appears in a nonmagnetic metal in contact with a magnetic insulator. The main puzzle lies in the apparent absence of spin polarized electrons in the non-magnetic metal. Here, we theoretically demonstrate that the scattering of electrons from a rough metal-insulator interface is generally spin-dependent, which results in mutual conversion between spin and charge currents flowing in the plane of the layer. It is the current-carrying spin polarized electrons and the spin Hall effect in the bulk of the metal layer that conspire to generate the AH current. This novel AHE differs from the conventional one only in the spatial separation of the SOC and the magnetization, so we name it as nonlocal AHE. In contrast to other previously proposed mechanisms (e.g., spin Hall AHE and magnetic proximity effect (MPE)), the nonlocal AHE appears on the first order of spin Hall angle and does not rely on the induced moments in the metal layer, which make it experimentally detectable by contrasting the AH current directions of two layered structures such as Pt/Cu/YIG and β -Ta/Cu/YIG (with a thin inserted Cu layer to eliminate the MPE). We predict that the directions of the AH currents in these two trilayers would be opposite since the spin Hall angles of Pt and β -Ta are of opposite signs. Work supported by NSF Grants DMR-1406568.

  1. The design for the LCLS RF photoinjector

    NASA Astrophysics Data System (ADS)

    Alley, R.; Bharadwaj, V.; Clendenin, J.; Emma, P.; Fisher, A.; Frisch, J.; Kotseroglou, T.; Miller, R. H.; Palmer, D. T.; Schmerge, J.; Sheppard, J. C.; Woodley, M.; Yeremian, A. D.; Rosenzweig, J.; Meyerhofer, D. D.; Serafini, L.

    1999-06-01

    We report on the design of the RF photoinjector of the Linac Coherent Light Source. The RF photoinjector is required to produce a single 150 MeV bunch of ˜1 nC and ˜100 A peak current at a repetition rate of 120 Hz with a normalized rms transverse emittance of ˜1 π mm-mrad. The design employs a 1.6-cell S-band RF gun with an optical spot size at the cathode of a radius of ˜1 mm and a pulse duration with an rms sigma of ˜3 ps. The peak RF field at the cathode is 150 MV/m with extraction 57° ahead of the RF peak. A solenoidal field near the cathode allows the compensation of the initial emittance growth by the end of the injection linac. Spatial and temporal shaping of the laser pulse striking the cathode will reduce the compensated emittance even further. Also, to minimize the contribution of the thermal emittance from the cathode surface, while at the same time optimizing the quantum efficiency, the laser wavelength for a Cu cathode should be tunable around 260 nm. Following the injection linac the geometric emittance simply damps linearly with energy growth. PARMELA simulations show that this design will produce the desired normalized emittance, which is about a factor of two lower than has been achieved to date in other systems. In addition to low emittance, we also aim for laser amplitude stability of 1% in the UV and a timing jitter in the electron beam of 0.5 ps rms, which will lead to less than 10% beam intensity fluctuation after the electron bunch is compressed in the main linac.

  2. Methyl tunnelling sidebands in the low-field NMR spectrum of 3-pentanone: Driving A-E transitions using rf irradiation.

    PubMed

    Zhang, Bo; Horsewill, Anthony J

    2015-09-01

    Using magnetic field-cycling at cryogenic temperatures, low-field dipole-dipole driven NMR spectra have been recorded on 3-pentanone (CH3CH2C(O)CH2CH3). The spectra are characterised by tunnelling sidebands arising from the quantum dynamics of the methyl (CH3) rotors. From the sideband frequencies, the CH3 tunnelling frequency is determined to be νt=3.05±0.01MHz. The tunnelling sidebands are characterised by A-E transitions in nuclear spin-symmetry, involving simultaneous changes in tunnelling and nuclear spin states. To gain further insight, a theoretical analysis of the spin Hamiltonian matrix has been used to calculate the sideband transition probabilities. These are subsequently used in a thermodynamic model to simulate the low-field NMR spectrum which is compared with experiment. The level-crossings encountered as part of the magnetic field-cycling NMR sequence are found to play an essential role in determining the tunnelling sideband intensities. PMID:26183303

  3. Transparency and Coherence in rf SQUID Metamaterials

    NASA Astrophysics Data System (ADS)

    Anlage, Steven; Trepanier, Melissa; Zhang, Daimeng

    We have developed active metamaterials capable of quickly tuning their electrical and magnetic responses over a wide frequency range. These metamaterials are based on superconducting elements to form low loss, physically and electrically small, highly tunable structures for fundamental studies of extraordinarily nonlinear media. The meta-atoms are rf superconducting quantum interference devices (SQUIDs) that incorporate the Josephson effect. RF SQUIDs have an inductance which is strongly tunable with dc and rf magnetic fields and currents. The rf SQUID metamaterial is a richly nonlinear effective medium introducing qualitatively new macroscopic quantum phenomena into the metamaterials community, namely magnetic flux quantization and the Josephson effect. The coherent oscillation of the meta-atoms is strongly sensitive to the environment and measurement conditions, and we have developed several strategies to improve the coherence experimentally by exploiting ideas from nonlinear dynamics. The metamaterials also display a unique form of transparency whose development can be manipulated through multiple parametric dependences. We discuss these qualitatively new metamaterial phenomena. This work is supported by the NSF-GOALI and OISE Programs through Grant No. ECCS-1158644 and the Center for Nanophysics and Advanced Materials (CNAM).

  4. RF current sensor

    DOEpatents

    Moore, James A.; Sparks, Dennis O.

    1998-11-10

    An RF sensor having a novel current sensing probe and a voltage sensing probe to measure voltage and current. The current sensor is disposed in a transmission line to link all of the flux generated by the flowing current in order to obtain an accurate measurement. The voltage sensor is a flat plate which operates as a capacitive plate to sense voltage on a center conductor of the transmission line, in which the measured voltage is obtained across a resistance leg of a R-C differentiator circuit formed by the characteristic impedance of a connecting transmission line and a capacitance of the plate, which is positioned proximal to the center conductor.

  5. Tomcat-Projects_RF

    SciTech Connect

    Warrant, Marilyn M.; Garcia, Rudy J.; Zhang, Pengchu; Arms, Robert M.; Herzer, John A.; Conrad, Gregory N.; Brabson, John M.

    2004-09-15

    Tomcat-Projects_RF is a software package for analyzing sensor data obtained from a database and displaying the results with Java Servlet Pages (JSP). SQL Views into the dataset are tailored for personnel having different roles in monitoring the items in a storage facility. For example, an inspector, a host treaty compliance officer, a system engineer and software developers were the users identified that would need to access data at different levels of detail, The analysis provides a high level status of the storage facility and allows the user to go deeper into the data details if the user desires.

  6. RF modal quantity gaging

    NASA Astrophysics Data System (ADS)

    Vanleuven, K.

    1989-05-01

    The primary objective is to provide a concept of a radio frequency (RF) modal resonance technique which is being investigated as a method for gaging the quantities of subcritical cryogenic propellants in metallic tanks. Of special interest are the potential applications of the technique to microgravity propellant gaging situations. The results of concept testing using cryogenic oxygen, hydrogen, and nitrogen, as well as paraffin simulations of microgravity fluid orientations, are reported. These test results were positive and showed that the gaging concept was viable.

  7. Tomcat-Projects_RF

    Energy Science and Technology Software Center (ESTSC)

    2004-09-15

    Tomcat-Projects_RF is a software package for analyzing sensor data obtained from a database and displaying the results with Java Servlet Pages (JSP). SQL Views into the dataset are tailored for personnel having different roles in monitoring the items in a storage facility. For example, an inspector, a host treaty compliance officer, a system engineer and software developers were the users identified that would need to access data at different levels of detail, The analysis providesmore » a high level status of the storage facility and allows the user to go deeper into the data details if the user desires.« less

  8. Ion source with external RF antenna

    DOEpatents

    Leung, Ka-Ngo; Ji, Qing; Wilde, Stephen

    2005-12-13

    A radio frequency (RF) driven plasma ion source has an external RF antenna, i.e. the RF antenna is positioned outside the plasma generating chamber rather than inside. The RF antenna is typically formed of a small diameter metal tube coated with an insulator. An external RF antenna assembly is used to mount the external RF antenna to the ion source. The RF antenna tubing is wound around the external RF antenna assembly to form a coil. The external RF antenna assembly is formed of a material, e.g. quartz, which is essentially transparent to the RF waves. The external RF antenna assembly is attached to and forms a part of the plasma source chamber so that the RF waves emitted by the RF antenna enter into the inside of the plasma chamber and ionize a gas contained therein. The plasma ion source is typically a multi-cusp ion source.

  9. Anomalous Hall Effect in a Kagome Ferromagnet

    NASA Astrophysics Data System (ADS)

    Ye, Linda; Wicker, Christina; Suzuki, Takehito; Checkelsky, Joseph; Joseph Checkelsky Team

    The ferromagnetic kagome lattice is theoretically known to possess topological band structures. We have synthesized large single crystals of a kagome ferromagnet Fe3Sn2 which orders ferromagnetically well above room temperature. We have studied the electrical and magnetic properties of these crystals over a broad temperature and magnetic field range. Both the scaling relation of anomalous Hall effect and anisotropic magnetic susceptibility show that the ferromagnetism of Fe3Sn2 is unconventional. We discuss these results in the context of magnetism in kagome systems and relevance to the predicted topological properties in this class of compounds. This research is supported by DMR-1231319.

  10. Anomalous optical forces on radially anisotropic nanowires

    NASA Astrophysics Data System (ADS)

    Chen, H. L.; Gao, L.

    2015-11-01

    Full-wave electromagnetic scattering theory and Maxwell stress tensor integration techniques have been established to study the optical force on the radially anisotropic nanowires. The optical forces on the isotropic nanowires are dependent on the size of the nanowire and the wave vector in the media with the Rayleigh's law. However, the optical forces on the anisotropic nanowires have the anomalous behaviors under non-Rayleigh vanishing condition and non-Rayleigh diverging condition. Therefore, the optical forces on the anisotropic nanowires may be enhanced or reduced by tuning the anisotropic parameters. These results may promote the potential applications in the field of nanotechnology.

  11. Cathode Ion Bombardment in RF Photoguns

    SciTech Connect

    Pozdeyev,E.; Kayran, D.; Litvinenko, V.

    2008-09-01

    In this paper, we use the method of rapid oscillating field to solve the equation of ion motion in an RF gun. We apply the method to the BNL 1/2-cell SRF photogun and demonstrate that a significant portion of ions produced in the gun can reach the cathode if no special precautions are taken. Also, the paper proposes a simple mitigation recipe that can reduce the rate of ion bombardment.

  12. High gain proportional rf control stability at TESLA cavities

    NASA Astrophysics Data System (ADS)

    Vogel, Elmar

    2007-05-01

    Fast proportional rf control is used as the basis for rf field regulation in actual linear accelerator projects like the international linear collider (ILC) and the European x-ray free electron laser (XFEL) based on TESLA technology. Additional control loops improve the field regulation by treating repetitive effects and compensating the beam loading. Nevertheless, the ability for high gain operation of the fast loops is desirable for the strong suppression of nonpredictive and nonrepetitive disturbances. TESLA cavities host nine fundamental modes (FMs) where only one is used for beam acceleration. The unwanted FMs have a significant influence on the proportional rf control loop stability at high gains. Within this paper, the stability of proportional rf control loops taking the FMs and digitalization effects into account will be discussed in detail together with measures enabling a significant increase of the gain values.

  13. A Micromechanical RF Channelizer

    NASA Astrophysics Data System (ADS)

    Akgul, Mehmet

    The power consumption of a radio generally goes as the number and strength of the RF signals it must process. In particular, a radio receiver would consume much less power if the signal presented to its electronics contained only the desired signal in a tiny percent bandwidth frequency channel, rather than the typical mix of signals containing unwanted energy outside the desired channel. Unfortunately, a lack of filters capable of selecting single channel bandwidths at RF forces the front-ends of contemporary receivers to accept unwanted signals, and thus, to operate with sub-optimal efficiency. This dissertation focuses on the degree to which capacitive-gap transduced micromechanical resonators can achieve the aforementioned RF channel-selecting filters. It aims to first show theoretically that with appropriate scaling capacitive-gap transducers are strong enough to meet the needed coupling requirements; and second, to fully detail an architecture and design procedure needed to realize said filters. Finally, this dissertation provides an actual experimentally demonstrated RF channel-select filter designed using the developed procedures and confirming theoretical predictions. Specifically, this dissertation introduces four methods that make possible the design and fabrication of RF channel-select filters. The first of these introduces a small-signal equivalent circuit for parallel-plate capacitive-gap transduced micromechanical resonators that employs negative capacitance to model the dependence of resonance frequency on electrical stiffness in a way that facilitates the analysis of micromechanical circuits loaded with arbitrary electrical impedances. The new circuit model not only correctly predicts the dependence of electrical stiffness on the impedances loading the input and output electrodes of parallel-plate capacitive-gap transduced micromechanical device, but does so in a visually intuitive way that identifies current drive as most appropriate for

  14. Anomalous Nernst Effect of Perpendicularly Magnetic Anisotropy TbFeCo Thin Films

    NASA Astrophysics Data System (ADS)

    Ando, Ryo; Komine, Takashi; Hasegawa, Yasuhiro

    2016-07-01

    In this study, we investigated anomalous Nernst effect (ANE) of perpendicularly magnetized TbFeCo thin films with various Tb content, and especially studied the relation between ANE and anomalous Hall effect. As a result, the hysteresis of anomalous Nernst coefficient showed the same behavior as that of anomalous Hall resistivity, and the sign of anomalous Nernst coefficient was consistent with that of anomalous Hall voltage in any Tb content, whereas the Seebeck coefficient and the resistivity were almost constant even if the applied magnetic field was varied. Taking into account of thermoelectric coefficient tensor, it was revealed that the off-diagonal thermopower corresponding to the ANE in TbFeCo thin films is the product of Hall angle and Seebeck coefficient.

  15. Vulnerability of digitized platforms to modern rf electromagnetic weapons

    NASA Astrophysics Data System (ADS)

    Frater, Michael R.; Ryan, Michael J.

    2001-08-01

    Radio Frequency Directed Energy Weapons (RF DEW) have the potential to disrupt the operation of, or cause the failure of, a broad range of military electronic equipment. Over the past 30 years, there has been considerable effort in the development of these weapons. Recent reports suggest that a number of countries, including the USA and Russia, have fielded such weapons. This paper examines the potential performance of non-nuclear RF DEW.

  16. Modulator considerations for the SNS RF system

    SciTech Connect

    Tallerico, P.J.; Reass, W.A.

    1998-12-31

    The Spallation Neutron Source (SNS) is an intense neutron source for neutron scattering experiments. The project is in the research stage, with construction funding beginning next year. The SNS is comprised of an ion source, a 1,000 MeV, H{sup {minus}} linear accelerator, an accumulator ring, a neutron producing target, and experimental area to utilize the scattering of the neutrons. The linear accelerator is RF driven, and the peak beam current is 27 mA and the beam duty factor is 5.84%. The peak RF power required is 104 MW, and the H{sup {minus}} beam pulse length is 0.97 ms at a 60 Hz repetition rate. The RF pulses must be about 0.1 ms longer than the beam pulses, due to the Q of the accelerating cavities, and the time required to establish control of the cavity fields. The modulators for the klystrons in this accelerator are discussed in this paper. The SNS is designed to be expandable, so the beam power can be doubled or even quadrupled in the future. One of the double-power options is to double the beam pulse length and duty factor. The authors are specifying the klystrons to operate in this twice-duty-factor mode, and the modulator also should be expandable to 2 ms pulses at 60 Hz. Due to the long pulse length and low RF frequency of 805 MHz, the klystron power is specified at 2.5 MW peak, and the RF system will have 56 klystrons at 805 MHz, and three 1.25 MW peak power klystrons at 402.5 MHz for the low energy portion of the accelerator. The low frequency modulators are conventional floating-deck modulation anode control systems.

  17. An improved RF circuit for Overhauser magnetometer excitation

    NASA Astrophysics Data System (ADS)

    Zheng, Di; Zhang, Shuang; Guo, Xin; Fu, Haoyang

    2015-08-01

    Overhauser magnetometer is a high-precision device for magnetostatic field measurement, which can be used in a wide variety of purposes: UXO detection, pipeline mapping and other engineering and environmental applications. Traditional proton magnetometer adopts DC polarization, suffering from low polarization efficiency, high power consumption and low signal noise ratio (SNR). Compared with the traditional proton magnetometer, nitroxide free radicals are used for dynamic nuclear polarization (DNP) to enhance nuclear magnetic resonance (NMR). RF excitation is very important for electron resonance in nitrogen oxygen free radical solution, and it is primarily significant for the obtention of high SNR signal and high sensitive field observation. Therefore, RF excitation source plays a crucial role in the development of Overhauser magnetometer. In this paper, an improved design of a RF circuit is discussed. The new RF excitation circuit consists of two parts: Quartz crystal oscillator circuit and RF power amplifier circuit. Simulation and optimization designs for power amplifier circuit based on software ADS are presented. Finally we achieve a continuous and stable sine wave of 60MHz with 1-2.5 W output power, and the second harmonic suppression is close to -20dBc. The improved RF circuit has many merits such as small size, low-power consumption and high efficiency, and it can be applied to Overhauser magnetometer to obtain high sensitive field observation.

  18. Sensing RF signals with the optical wideband converter

    NASA Astrophysics Data System (ADS)

    Valley, George C.; Sefler, George A.; Shaw, T. J.

    2013-01-01

    The optical wideband converter (OWC) is a system for measuring properties of RF signals in the GHz band without use of high speed electronics. In the OWC the RF signal is modulated on a repetitively pulsed optical field with a large wavelength chirp, the optical field is diffracted onto a spatial light modulator (SLM) whose pixels are modulated with a pseudo-random bit sequences (PRBSs), and finally the optical field is directed to a photodiode and the resulting current integrated for each PRBS. When the number of PRBSs and measurements equals the number of SLM pixels, the RF signal can be obtained in principle by multiplying the measurement vector by the inverse of the square matrix given by the PRBSs and the properties of the optics. When the number of measurements is smaller than the number of pixels, a compressive sensing (CS) measurement can be performed, and sparse RF signals can be obtained using one of the standard CS recovery algorithms such as the penalized l1 norm (also known as basis pursuit) or one of the variants of matching pursuit. Accurate reconstruction of RF signals requires good calibration of the OWC. In this paper, we present results using the OWC for RF signals consisting of 2 sinusoids recovered using 3 techniques (matrix inversion, basis pursuit, and matching pursuit). We compare results obtained with orthogonal matching pursuit with nonlinear least squares to basis pursuit with an over-complete dictionary.

  19. NSLS-II RF SYSTEMS

    SciTech Connect

    Rose, J.; Gash, W.; Holub, B.; Kawashima, Y.; Ma, H.; Towne, N.; Yeddulla, M.

    2011-03-28

    The NSLS-II is a new third generation light source being constructed at Brookhaven Lab. The storage ring is optimized for low emittance by use of damping wigglers to reduce the emittance to below 1 nm-rad. The RF systems are designed to provide stable beam through tight RF phase and amplitude stability requirements.

  20. RF MEMS Based Reconfigurable Antennas

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.

    2004-01-01

    The presentation will first of all address the advantages of RF MEMS circuit in antenna applications and also the need for electronically reconfigurable antennas. Next, discuss some of the recent examples of RF MEMS based reconfigurable microstrip antennas. Finally, conclude the talk with a summary of MEMS antenna performance.

  1. Research on heating, instabilities, turbulence, and rf (radiofrequency) emission from electric-field dominated plasmas. Final report, 15 March 1986-14 May 1989

    SciTech Connect

    Roth, J.R.; Alexeff, I.

    1989-07-01

    This contract has supported four research programs: (1) a program of research on plasma turbulence; (2) a program of research on plasma heating by collisional magnetic pumping; (3) a research program on the Orbitron submillimeter maser; and (4) the initial phase of a program on plasma cloaking of military targets for protection against radar and directed microwave energy weapons. Progress in these areas is documented in the text of this final report and in the twenty archival publications included in the appendices to this report. In addition to the above four research areas, work is continuing on plasma diagnostic development, and the development of new state-of-the-art data analysis and reduction methods, including software development for on-line reduction of Langmuir probe, capacitive probe, and other diagnostic information. The authors are also developing the capability to analyze electrostatic-potential fluctuations by the methods of nonlinear dynamics. An important part of our research program has been the training of graduate and undergraduate research assistants in state-of-the-art methods in the fields of high-temperature plasma physics, plasma diagnostics, communications, and related areas.

  2. A novel RF resonator for human-body MRI at 3 T

    NASA Astrophysics Data System (ADS)

    Son, Hyeok-Woo; Cho, Young-Ki; Yoo, Hyoungsuk

    2014-03-01

    A square-slot-loaded (SSL) radio-frequency (RF) resonator using a microstrip transmission line (MTL) is designed for human-body magnetic resonance imaging (MRI) at 3 T MRI. The SSL RF resonator shows improved RF magnetic fields resulting in more homogenous fields near the center of the phantom than traditional RF resonators using MTL. A multichannel body coil using the SSL RF resonators is also simulated and provides improved parallel excitation performance. In addition, RF shimming for homogenization can be effectively controlled by adjusting the inputs to the eight resonators. Numerical results are obtained by using a spherical phantom and a realistic human-body model at 3 T to calculate the B {1/+} fields.

  3. Spatially selective 2D RF inner field of view (iFOV) diffusion kurtosis imaging (DKI) of the pediatric spinal cord

    PubMed Central

    Conklin, Chris J.; Middleton, Devon M.; Alizadeh, Mahdi; Finsterbusch, Jürgen; Raunig, David L.; Faro, Scott H.; Shah, Pallav; Krisa, Laura; Sinko, Rebecca; Delalic, Joan Z.; Mulcahey, M.J.; Mohamed, Feroze B.

    2016-01-01

    Magnetic resonance based diffusion imaging has been gaining more utility and clinical relevance over the past decade. Using conventional echo planar techniques, it is possible to acquire and characterize water diffusion within the central nervous system (CNS); namely in the form of Diffusion Weighted Imaging (DWI) and Diffusion Tensor Imaging (DTI). While each modality provides valuable clinical information in terms of the presence of diffusion and its directionality, both techniques are limited to assuming an ideal Gaussian distribution for water displacement with no intermolecular interactions. This assumption neglects pathological processes that are not Gaussian therefore reducing the amount of potentially clinically relevant information. Additions to the Gaussian distribution measured by the excess kurtosis, or peakedness, of the probabilistic model provide a better understanding of the underlying cellular structure. The objective of this work is to provide mathematical and experimental evidence that Diffusion Kurtosis Imaging (DKI) can offer additional information about the micromolecular environment of the pediatric spinal cord. This is accomplished by a more thorough characterization of the nature of random water displacement within the cord. A novel DKI imaging sequence based on a tilted 2D spatially selective radio frequency pulse providing reduced field of view (FOV) imaging was developed, implemented, and optimized on a 3 Tesla MRI scanner, and tested on pediatric subjects (healthy subjects: 15; patients with spinal cord injury (SCI):5). Software was developed and validated for post processing of the DKI images and estimation of the tensor parameters. The results show statistically significant differences in mean kurtosis (p < 0.01) and radial kurtosis (p < 0.01) between healthy subjects and subjects with SCI. DKI provides incremental and novel information over conventional diffusion acquisitions when coupled with higher order estimation algorithms

  4. Spatially selective 2D RF inner field of view (iFOV) diffusion kurtosis imaging (DKI) of the pediatric spinal cord.

    PubMed

    Conklin, Chris J; Middleton, Devon M; Alizadeh, Mahdi; Finsterbusch, Jürgen; Raunig, David L; Faro, Scott H; Shah, Pallav; Krisa, Laura; Sinko, Rebecca; Delalic, Joan Z; Mulcahey, M J; Mohamed, Feroze B

    2016-01-01

    Magnetic resonance based diffusion imaging has been gaining more utility and clinical relevance over the past decade. Using conventional echo planar techniques, it is possible to acquire and characterize water diffusion within the central nervous system (CNS); namely in the form of Diffusion Weighted Imaging (DWI) and Diffusion Tensor Imaging (DTI). While each modality provides valuable clinical information in terms of the presence of diffusion and its directionality, both techniques are limited to assuming an ideal Gaussian distribution for water displacement with no intermolecular interactions. This assumption neglects pathological processes that are not Gaussian therefore reducing the amount of potentially clinically relevant information. Additions to the Gaussian distribution measured by the excess kurtosis, or peakedness, of the probabilistic model provide a better understanding of the underlying cellular structure. The objective of this work is to provide mathematical and experimental evidence that Diffusion Kurtosis Imaging (DKI) can offer additional information about the micromolecular environment of the pediatric spinal cord. This is accomplished by a more thorough characterization of the nature of random water displacement within the cord. A novel DKI imaging sequence based on a tilted 2D spatially selective radio frequency pulse providing reduced field of view (FOV) imaging was developed, implemented, and optimized on a 3 Tesla MRI scanner, and tested on pediatric subjects (healthy subjects: 15; patients with spinal cord injury (SCI):5). Software was developed and validated for post processing of the DKI images and estimation of the tensor parameters. The results show statistically significant differences in mean kurtosis (p < 0.01) and radial kurtosis (p < 0.01) between healthy subjects and subjects with SCI. DKI provides incremental and novel information over conventional diffusion acquisitions when coupled with higher order estimation algorithms

  5. An Efficient RF Source for Jlab

    SciTech Connect

    Neubauer, M.; Dudas, A.; Rimmer, Robert A.; Wang, Haipeng

    2013-12-01

    We propose the development of a highly reliable high efficiency RF source for JLAB with a lower lifetime cost operating at 80% efficiency with system operating costs of about 0.7M$/year for the 6 GeV machine. The design of the RF source will be based upon two injection locked magnetrons in a novel combining architecture for amplitude modulation and a cross field amplifier (CFA) as an output tube for the 12 GeV upgrade. A cost analysis including efficiency and reliability will be performed to determine the optimum system architecture. Several different system architectures will be designed and evaluated for a dual injection locked magnetron source using novel combining techniques and possibly a CFA as the output tube. A paper design for the 1497 MHz magnetron system will be completed. The optimum system architecture with all relevant specifications will be completed so that a prototype can be built.

  6. Shielding for thermoacoustic tomography with RF excitation

    NASA Astrophysics Data System (ADS)

    Mitchell, M.; Becker, G.; Dey, P.; Generotzky, J.; Patch, S. K.

    2008-02-01

    Radiofrequency (RF) pulses used to generate thermoacoustic computerized tomography (TCT) signal couple directly into the pulser-receiver and oscilloscope, swamping true TCT signal. We use a standard RF enclosure housing both RF amplifier and object being imaged. This is similar to RF shielding of magnetic resonance imaging (MRI) suites and protects electronics outside from stray RF. Unlike MRI, TCT receivers are ultrasound transducers, which must also be shielded from RF. A transducer housing that simultaneously shields RF and permits acoustic transmission was developed specifically for TCT. We compare TCT signals measured with and without RF shielding.

  7. A Micromechanical RF Channelizer

    NASA Astrophysics Data System (ADS)

    Akgul, Mehmet

    The power consumption of a radio generally goes as the number and strength of the RF signals it must process. In particular, a radio receiver would consume much less power if the signal presented to its electronics contained only the desired signal in a tiny percent bandwidth frequency channel, rather than the typical mix of signals containing unwanted energy outside the desired channel. Unfortunately, a lack of filters capable of selecting single channel bandwidths at RF forces the front-ends of contemporary receivers to accept unwanted signals, and thus, to operate with sub-optimal efficiency. This dissertation focuses on the degree to which capacitive-gap transduced micromechanical resonators can achieve the aforementioned RF channel-selecting filters. It aims to first show theoretically that with appropriate scaling capacitive-gap transducers are strong enough to meet the needed coupling requirements; and second, to fully detail an architecture and design procedure needed to realize said filters. Finally, this dissertation provides an actual experimentally demonstrated RF channel-select filter designed using the developed procedures and confirming theoretical predictions. Specifically, this dissertation introduces four methods that make possible the design and fabrication of RF channel-select filters. The first of these introduces a small-signal equivalent circuit for parallel-plate capacitive-gap transduced micromechanical resonators that employs negative capacitance to model the dependence of resonance frequency on electrical stiffness in a way that facilitates the analysis of micromechanical circuits loaded with arbitrary electrical impedances. The new circuit model not only correctly predicts the dependence of electrical stiffness on the impedances loading the input and output electrodes of parallel-plate capacitive-gap transduced micromechanical device, but does so in a visually intuitive way that identifies current drive as most appropriate for

  8. Anomalous-viscosity current drive

    DOEpatents

    Stix, T.H.; Ono, M.

    1986-04-25

    The present invention relates to a method and apparatus for maintaining a steady-state current for magnetically confining the plasma in a toroidal magnetic confinement device using anomalous viscosity current drive. A second aspect of this invention relates to an apparatus and method for the start-up of a magnetically confined toroidal plasma.

  9. The MuCool Test Area and RF Program

    SciTech Connect

    Bross, A D; Jansson, A; Moretti, A; Yonehara, K; Huang, D; Torun, Y; Li, D; Norem, J; Palmer, R B; Stratakis, D

    2010-05-01

    The MuCool RF Program focuses on the study of normal conducting RF structures operating in high magnetic field for applications in muon ionization cooling for Neutrino Factories and Muon Colliders. This paper will give an overview of the program, which will include a description of the test facility and its capabilities, the current test program, and the status of a cavity that can be rotated in the magnetic field which allows for a more detailed study of the maximum stable operating gradient vs. magnetic field strength and angle.

  10. Hyperfine structure of high-L states in 143,145i by atomic-beam laser-rf double resonance

    NASA Astrophysics Data System (ADS)

    Childs, W. J.

    1991-07-01

    The atomic-beam laser-rf double-resonance technique has been used to study the hyperfine structure (hfs) of the metastable 7L5-11 and 7K4 states of the 4f45d6s configuration in 143,145i. Four zero-field intervals were measured in each state and the results used to assign the conventional hfs constants A and B. Comparison of the results with predictions of the Sandars-Beck model allowed evaluation of the relevant single-electron radial hfs integrals. These are compared with earlier results from the Nd i atomic ground term and with extrapolations from other rare-earth elements. The unusually large orbital-angular-momentum values (L=7 and 8 for the states studied) do not appear to have introduced any anomalous effects. Ab initio calculations are not yet feasible for the complex 4f45d6s levels studied.

  11. DESIGN OF A DC/RF PHOTOELECTRON GUN.

    SciTech Connect

    YU,D.NEWSHAM,Y.SMIRONOV,A.YU,J.SMEDLEY,J.SRINIVASAN RAU,T.LEWELLEN,J.ZHOLENTS,A.

    2003-05-12

    An integrated dc/rf photoelectron gun produces a low-emittance beam by first rapidly accelerating electrons at a high gradient during a short ({approx}1 ns), high-voltage pulse, and then injecting the electrons into an rf cavity for subsequent acceleration. Simulations show that significant improvement of the emittance appears when a high field ({approx} 0.5-1 GV/m) is applied to the cathode surface. An adjustable dc gap ({le} 1 mm) which can be integrated with an rf cavity is designed for initial testing at the Injector Test Stand at Argonne National Laboratory using an existing 70-kV pulse generator. Plans for additional experiments of an integrated dc/rf gun with a 250-kV pulse generator are being made.

  12. Tokamak Plasma Flows Induced by Local RF Forces

    NASA Astrophysics Data System (ADS)

    Chen, Jiale; Gao, Zhe

    2015-10-01

    The tokamak plasma flows induced by the local radio frequency (RF) forces in the core region are analyzed. The effective components of local RF forces are composed of the momentum absorption term and the resonant parallel momentum transport term (i.e. the parallel component of the resonant ponderomotive forces). Different momentum balance relations are employed to calculate the plasma flows depending on different assumptions of momentum transport. With the RF fields solved from RF simulation codes, the toroidal and poloidal flows by these forces under the lower hybrid current drive and the mode conversion ion cyclotron resonance heating on EAST-like plasmas are evaluated. supported by National Natural Science Foundation of China (Nos. 11405218, 11325524, 11375235 and 11261140327), in part by the National Magnetic Confinement Fusion Science Program of China (Nos. 2013GB111002, 2013GB112001 and 2013GB112010), and the Program of Fusion Reactor Physics and Digital Tokamak with the CAS “One-Three-Five” Strategic Planning

  13. Anomalous Weyl superfluid in three-dimensional ultracold fermionic gases

    NASA Astrophysics Data System (ADS)

    Huang, Beibing

    2016-08-01

    In this paper we use layer construction method to construct an experimentally feasible model to realize one type of anomalous Weyl superfluids (WS) in the context of cold fermionic gases. This exotic phase still characterizes the Weyl points in the bulk but completely different Majorana Fermi arc surface state (MFASS) on the boundaries. In contrast to conventional WS, where MFASS only connects the projection of Weyl points, new MFASS continuously stretches to the border of surface Brillouin zone. We self-consistently determine the phase diagram of model at the mean-field level to claim the achievement of anomalous WS. In addition, inversion symmetry and band inversion in this model are analyzed in detail to provide unique feature of identifying anomalous WS experimentally by momentum-resolved radio-frequency spectroscopy.

  14. RF breakdown experiments at SLAC

    SciTech Connect

    Laurent, L.; Vlieks, A.; Pearson, C.; Caryotakis, G.; Luhmann, N.C.

    1999-05-01

    RF breakdown is a critical issue in the conditioning of klystrons, accelerator sections, and rf components for the next linear collider (NLC), as well as other high gradient accelerators and high power microwave sources. SLAC is conducting a series of experiments using an X-band traveling wave ring to characterize the processes and trigger mechanisms associated with rf breakdown. The goal of the research is to identify materials, processes, and manufacturing methods that will increase the breakdown threshold and minimize the time required for conditioning. {copyright} {ital 1999 American Institute of Physics.}

  15. An RF dosimeter for independent SAR measurement in MRI scanners

    PubMed Central

    Qian, Di; El-Sharkawy, AbdEl-Monem M.; Bottomley, Paul A.; Edelstein, William A.

    2013-01-01

    Purpose: The monitoring and management of radio frequency (RF) exposure is critical for ensuring magnetic resonance imaging (MRI) safety. Commercial MRI scanners can overestimate specific absorption rates (SAR) and improperly restrict clinical MRI scans or the application of new MRI sequences, while underestimation of SAR can lead to tissue heating and thermal injury. Accurate scanner-independent RF dosimetry is essential for measuring actual exposure when SAR is critical for ensuring regulatory compliance and MRI safety, for establishing RF exposure while evaluating interventional leads and devices, and for routine MRI quality assessment by medical physicists. However, at present there are no scanner-independent SAR dosimeters. Methods: An SAR dosimeter with an RF transducer comprises two orthogonal, rectangular copper loops and a spherical MRI phantom. The transducer is placed in the magnet bore and calibrated to approximate the resistive loading of the scanner's whole-body birdcage RF coil for human subjects in Philips, GE and Siemens 3 tesla (3T) MRI scanners. The transducer loop reactances are adjusted to minimize interference with the transmit RF field (B1) at the MRI frequency. Power from the RF transducer is sampled with a high dynamic range power monitor and recorded on a computer. The deposited power is calibrated and tested on eight different MRI scanners. Whole-body absorbed power vs weight and body mass index (BMI) is measured directly on 26 subjects. Results: A single linear calibration curve sufficed for RF dosimetry at 127.8 MHz on three different Philips and three GE 3T MRI scanners. An RF dosimeter operating at 123.2 MHz on two Siemens 3T scanners required a separate transducer and a slightly different calibration curve. Measurement accuracy was ∼3%. With the torso landmarked at the xiphoid, human adult whole‑body absorbed power varied approximately linearly with patient weight and BMI. This indicates that whole-body torso SAR is on average

  16. An RF dosimeter for independent SAR measurement in MRI scanners

    SciTech Connect

    Qian, Di; Bottomley, Paul A.; El-Sharkawy, AbdEl-Monem M.; Edelstein, William A.

    2013-12-15

    Purpose: The monitoring and management of radio frequency (RF) exposure is critical for ensuring magnetic resonance imaging (MRI) safety. Commercial MRI scanners can overestimate specific absorption rates (SAR) and improperly restrict clinical MRI scans or the application of new MRI sequences, while underestimation of SAR can lead to tissue heating and thermal injury. Accurate scanner-independent RF dosimetry is essential for measuring actual exposure when SAR is critical for ensuring regulatory compliance and MRI safety, for establishing RF exposure while evaluating interventional leads and devices, and for routine MRI quality assessment by medical physicists. However, at present there are no scanner-independent SAR dosimeters. Methods: An SAR dosimeter with an RF transducer comprises two orthogonal, rectangular copper loops and a spherical MRI phantom. The transducer is placed in the magnet bore and calibrated to approximate the resistive loading of the scanner's whole-body birdcage RF coil for human subjects in Philips, GE and Siemens 3 tesla (3T) MRI scanners. The transducer loop reactances are adjusted to minimize interference with the transmit RF field (B{sub 1}) at the MRI frequency. Power from the RF transducer is sampled with a high dynamic range power monitor and recorded on a computer. The deposited power is calibrated and tested on eight different MRI scanners. Whole-body absorbed power vs weight and body mass index (BMI) is measured directly on 26 subjects. Results: A single linear calibration curve sufficed for RF dosimetry at 127.8 MHz on three different Philips and three GE 3T MRI scanners. An RF dosimeter operating at 123.2 MHz on two Siemens 3T scanners required a separate transducer and a slightly different calibration curve. Measurement accuracy was ∼3%. With the torso landmarked at the xiphoid, human adult whole‑body absorbed power varied approximately linearly with patient weight and BMI. This indicates that whole-body torso SAR is on

  17. The impact of funding through the RF President's grants for young scientists (the field--medicine) on research productivity: a quasi-experimental study and a brief systematic review.

    PubMed

    Saygitov, Ruslan T

    2014-01-01

    The impact of grants on research productivity has been investigated by a number of retrospective studies. The results of these studies vary considerably. The objective of my study was to investigate the impact of funding through the RF President's grants for young scientists on the research productivity of awarded applicants. The study compared the number of total articles and citations for awarded and rejected applicants who in 2007 took part in competitions for young candidates of science (CoS's) and doctors of science (DoS's) in the scientific field of medicine. The bibliometric analysis was conducted for the period from 2003 to 2012 (five years before and after the competition). The source of bibliometric data is the eLIBRARY.RU database. The impact of grants on the research productivity of Russian young scientists was assessed using the meta-analytical approach based on data from quasi-experimental studies conducted in other countries. The competition featured 149 CoS's and 41 DoS's, out of which 24 (16%) and 22 (54%) applicants, respectively, obtained funding. No difference in the number of total articles and citations at baseline, as well as in 2008-2012, for awarded and rejected applicants was found. The combination of data from the Russian study and other quasi-experimental studies (6 studies, 10 competitions) revealed a small treatment effect--an increase in the total number of publications over a 4-5-year period after the competition by 1.23 (95% CI 0.48-1.97). However, the relationship between the number of total publications published by applicants before and after the competition revealed that this treatment effect is an effect of the "maturation" of scientists with a high baseline publication activity--not of grant funding. PMID:24475203

  18. Design and optimization for variable rate selective excitation using an analytic RF scaling function

    NASA Astrophysics Data System (ADS)

    Gai, Neville D.; Zur, Yuval

    2007-11-01

    At higher B0 fields, specific absorption rate (SAR) deposition increases. Due to maximum SAR limitation, slice coverage decreases and/or scan time increases. Conventional selective RF pulses are played out in conjunction with a time independent field gradient. Variable rate selective excitation (VERSE) is a technique that modifies the original RF and gradient waveforms such that slice profile is unchanged. The drawback is that the slice profile for off-resonance spins is distorted. A new VERSE algorithm based on modeling the scaled waveforms as a Fermi function is introduced. It ensures that system related constraints of maximum gradient amplitude and slew rate are not exceeded. The algorithm can be used to preserve the original RF pulse duration while minimizing SAR and peak b1 or to minimize the RF pulse duration. The design is general and can be applied to any symmetrical or asymmetrical RF waveform. The algorithm is demonstrated by using it to (a) minimize the SAR of a linear phase RF pulse, (b) minimize SAR of a hyperbolic secant RF pulse, and (c) minimize the duration of a linear phase RF pulse. Images with a T1-FLAIR (T1 FLuid Attenuated Inversion Recovery) sequence using a conventional and VERSE adiabatic inversion RF pulse are presented. Comparison of images and scan parameters for different anatomies and coils shows increased scan coverage and decreased SAR with the VERSE inversion RF pulse, while image quality is preserved.

  19. RF tuning element

    NASA Technical Reports Server (NTRS)

    McGrath, William R. (Inventor); Lubecke, Victor M. (Inventor)

    1992-01-01

    A device for tuning a circuit includes a substrate, a transmission line on the substrate that includes first and second conductors coupled to a circuit to be tuned, and a movable short-circuit for varying the impedance the transmission line presents to the circuit to be tuned. The movable short-circuit includes a dielectric layer disposed atop the transmission line and a distributed shorting element in the form of a conductive member that is configured to be slid along at least a portion of the transmission line atop the dielectric layer. The conductive member is configured to span the first and second conductors of the transmission line and to define at least a first opening that spans the two conductors so that the conductive member includes first and second sections separated by the first opening. The first and second sections of the conductive member combine with the first and second conductors of the transmission line to form first and second low impedance sections of transmission line, and the opening combines with the first and second conductors of the transmission line and the dielectric layer to form a first high impedance section of transmission line intermediate the first and second low impedance sections. Each of the first low impedance section and the first high impedance section have a length along the transmission line of approximately one-quarter wavelength, thus providing a periodic variation of transmission line impedance. That enhances reflection of rf power.

  20. ANOMALOUSLY PRESSURED GAS DISTRIBUTION IN THE WIND RIVER BASIN, WYOMING

    SciTech Connect

    Dr. Ronald C. Surdam

    2003-03-31

    Anomalously pressured gas (APG) assets, typically called ''basin-center'' gas accumulations, represent either an underdeveloped or undeveloped energy resource in the Rocky Mountain Laramide Basins (RMLB). Historically, the exploitation of these gas resources has proven to be very difficult and costly. In this topical report, an improved exploration strategy is outlined in conjunction with a more detailed description of new diagnostic techniques that more efficiently detect anomalously pressured, gas-charged domains. The ability to delineate gas-charged domains occurring below a regional velocity inversion surface allows operators to significantly reduce risk in the search for APG resources. The Wind River Basin was chosen for this demonstration because of the convergence of public data availability (i.e., thousands of mud logs and DSTs and 2400 mi of 2-D seismic lines); the evolution of new diagnostic techniques; a 175 digital sonic log suite; a regional stratigraphic framework; and corporate interest. In the exploration scheme discussed in this topical report, the basinwide gas distribution is determined in the following steps: (1) A detailed velocity model is established from sonic logs, 2-D seismic lines, and, if available, 3-D seismic data. In constructing the seismic interval velocity field, automatic picking technology using continuous, statistically-derived interval velocity selection, as well as conventional graphical interactive methodologies are utilized. (2) Next, the ideal regional velocity/depth function is removed from the observed sonic or seismic velocity/depth profile. The constructed ideal regional velocity/depth function is the velocity/depth trend resulting from the progressive burial of a rock/fluid system of constant rock/fluid composition, with all other factors remaining constant. (3) The removal of the ideal regional velocity/depth function isolates the anomalously slow velocities and allows the evaluation of (a) the regional velocity

  1. Anomalous supercurrent switching in graphene under proximity effect

    NASA Astrophysics Data System (ADS)

    Levchenko, Alex; Coskun, U. C.; Brenner, M.; Hymel, T.; Vakaryuk, V.; Bezryadin, A.

    2012-02-01

    We report a study of hysteretic current-voltage characteristics in superconductor-graphene-superconductor (SGS) junctions. The stochastic nature of the phase slips is characterized by measuring the distribution of the switching currents. We find that in SGS junctions the dispersion of the switching current scales with temperature as σIT^αG with αG 1/3. This observation is in sharp contrast with the known Josephson junction behavior where σIT^αJ with αJ=2/3. We propose an explanation using a modified version of Kurkijarvi's theory for the flux stability in rf-SQUID and attribute this anomalous effect to the temperature dependence of the critical current which persists down to low temperatures.

  2. Anomalous magnetic moments in Co/Nb multilayers

    NASA Astrophysics Data System (ADS)

    Chuang, T. M.; Lee, S. F.; Huang, S. Y.; Yao, Y. D.; Cheng, W. C.; Huang, G. R.

    2002-02-01

    Response of Co/Nb multilayers to external field near the superconducting transition temperature ( TC) was studied. The average moment of Co was suppressed with decreasing Co thickness. At 10 K, for Co thickness larger than 0.5 nm, the multilayers showed hysteresis and ferromagnetism. Some samples showed anomalous field-cooled paramagnetic moments, similar to Paramagnetic Meissner Effect (PME). This is attributed not to the Co moment but to the suppressed surface TC causing PME.

  3. ADX - Advanced Divertor and RF Tokamak Experiment

    NASA Astrophysics Data System (ADS)

    Greenwald, Martin; Labombard, Brian; Bonoli, Paul; Irby, Jim; Terry, Jim; Wallace, Greg; Vieira, Rui; Whyte, Dennis; Wolfe, Steve; Wukitch, Steve; Marmar, Earl

    2015-11-01

    The Advanced Divertor and RF Tokamak Experiment (ADX) is a design concept for a compact high-field tokamak that would address boundary plasma and plasma-material interaction physics challenges whose solution is critical for the viability of magnetic fusion energy. This device would have two crucial missions. First, it would serve as a Divertor Test Tokamak, developing divertor geometries, materials and operational scenarios that could meet the stringent requirements imposed in a fusion power plant. By operating at high field, ADX would address this problem at a level of power loading and other plasma conditions that are essentially identical to those expected in a future reactor. Secondly, ADX would investigate the physics and engineering of high-field-side launch of RF waves for current drive and heating. Efficient current drive is an essential element for achieving steady-state in a practical, power producing fusion device and high-field launch offers the prospect of higher efficiency, better control of the current profile and survivability of the launching structures. ADX would carry out this research in integrated scenarios that simultaneously demonstrate the required boundary regimes consistent with efficient current drive and core performance.

  4. Anomalous Quasiparticles on the Domain Wall Between Topological Insulators and Spin Ice Compounds

    NASA Astrophysics Data System (ADS)

    Kanazawa, I.; Sasaki, T.

    We have discussed the behavior of anomalous quasiparticle with fractional electronic charge on the domain wall between topological insulators and spin ice compounds from the standpoint of the field-theoretical formula.

  5. Properties of a low-pressure inductive RF discharge I: Experiment

    SciTech Connect

    Aleksandrov, A. F.; Vavilin, K. V.; Kral'kina, E. A.; Pavlov, V. B.; Rukhadze, A. A.

    2007-09-15

    Results are presented from experimental studies of low-pressure inductive RF discharges (including those with a capacitive component) employed in plasma technology. It is shown that both the RF power absorbed in the plasma and the electron density depend nonmonotonically on the external magnetic field. Discharge disruptions occurring at critical values of the magnetic field and the spatial redistribution and hysteresis of the plasma parameters were observed when varying the magnetic field and RF generator power. The parameters of the plasma of low-pressure (0.5-5 mTorr) inductive RF discharges were investigated, and the discharge properties related to the redistribution of the RF generator power between the plasma and the discharge external circuit were revealed. The experiments were performed with both conventional unmagnetized inductive plasma sources and plasma sources with a magnetic field.

  6. Nuclear magnetic resonance apparatus having semitoroidal rf coil for use in topical NMR and NMR imaging

    DOEpatents

    Fukushima, Eiichi; Roeder, Stephen B. W.; Assink, Roger A.; Gibson, Atholl A. V.

    1986-01-01

    An improved nuclear magnetic resonance (NMR) apparatus for use in topical magnetic resonance (TMR) spectroscopy and other remote sensing NMR applications includes a semitoroidal radio-frequency (rf) coil. The semitoroidal rf coil produces an effective alternating magnetic field at a distance from the poles of the coil, so as to enable NMR measurements to be taken from selected regions inside an object, particularly including human and other living subjects. The semitoroidal rf coil is relatively insensitive to magnetic interference from metallic objects located behind the coil, thereby rendering the coil particularly suited for use in both conventional and superconducting NMR magnets. The semitoroidal NMR coil can be constructed so that it emits little or no excess rf electric field associated with the rf magnetic field, thus avoiding adverse effects due to dielectric heating of the sample or to any other interaction of the electric field with the sample.

  7. Discontinuity interaction and anomalous source models in through transmission eddy current testing

    SciTech Connect

    Mergelas, B.J.; Atherton, D.L.

    1996-01-01

    Growing interest in the detection of external, axially aligned stress corrosion cracks in ferromagnetic oil and gas transmission pipelines, has prompted a detailed investigation of discontinuity interactions in remote field eddy current (RFEC) testing. Experimental measurements and numerical modeling were undertaken to study discontinuity interactions in a single through-wall transmission geometry for ferromagnetic and nonferromagnetic pipes. Anomalous source models have been introduced in order to explain the responses of axial discontinuities to circumferential eddy currents or circumferential AC magnetic fields. In nonferromagnetic material, discontinuity responses may be modeled by two types of anomalous eddy current sources. In ferromagnetic materials, an anomalous magnetization source is useful for explaining discontinuity response.

  8. Magnetic effects in anomalous dispersion

    SciTech Connect

    Blume, M.

    1992-12-31

    Spectacular enhancements of magnetic x-ray scattering have been predicted and observed experimentally. These effects are the result of resonant phenomena closely related to anomalous dispersion, and they are strongest at near-edge resonances. The theory of these resonances will be developed with particular attention to the symmetry properties of the scatterer. While the phenomena to be discussed concern magnetic properties the transitions are electric dipole or electric quadrupole in character and represent a subset of the usual anomalous dispersion phenomena. The polarization dependence of the scattering is also considered, and the polarization dependence for magnetic effects is related to that for charge scattering and to Templeton type anisotropic polarization phenomena. It has been found that the strongest effects occur in rare-earths and in actinides for M shell edges. In addition to the scattering properties the theory is applicable to ``forward scattering`` properties such as the Faraday effect and circular dichroism.

  9. Exactly solvable relativistic model with the anomalous interaction

    NASA Astrophysics Data System (ADS)

    Ferraro, Elena; Messina, Antonino; Nikitin, A. G.

    2010-04-01

    A special class of Dirac-Pauli equations with time-like vector potentials of an external field is investigated. An exactly solvable relativistic model describing the anomalous interaction of a neutral Dirac fermion with a cylindrically symmetric external electromagnetic field is presented. The related external field is a superposition of the electric field generated by a charged infinite filament and the magnetic field generated by a straight line current. In the nonrelativistic approximation the considered model is reduced to the integrable Pron’ko-Stroganov model.

  10. A photocathode RF gun for x-ray FEL

    SciTech Connect

    Wang, X.J.; Batchelor, K.; Ben-Zvi, I.

    1995-12-31

    A 1.6 cell photocathode RF gun was developed by a BNL/SLAC/UCLA collaboration for X-ray FEL and other applications. The objective of the collaboration is to develop a cost effective and more reliable photocathode RF gun based on the operational experience of the original BNL gun. The new photocathode RF gun is cable of producing 1 mm-mrad normalized rms emittance photocurrent with a peak current of 100 A. The half-cell length of the new RF gun was lengthened to reduce the peak field on the cavity surface, the side-coupled scheme for cavity and waveguide coupling was replaced by a symmetrized coupling to the full-cell. The cavity aperture was increased to improve the coupling between two cells and for flat beam application. The experimental results of cold testing the RF gun will be presented. We will also present an injector design based on the new photocathode RF gun and emittance compensation technique.

  11. RF Breakdown in Normal Conducting Single-Cell Structures

    SciTech Connect

    Dolgashev, V.A.; Nantista, C.D.; Tantawi, S.G.; Higashi, Y.; Higo, T.; /KEK, Tsukuba

    2006-02-22

    Operating accelerating gradient in normal conducting accelerating structures is often limited by rf breakdown. The limit depends on multiple parameters, including input rf power, rf circuit, cavity shape and material. Experimental and theoretical study of the effects of these parameters on the breakdown limit in full scale structures is difficult and costly. We use 11.4 GHz single-cell traveling wave and standing wave accelerating structures for experiments and modeling of rf breakdown behavior. These test structures are designed so that the electromagnetic fields in one cell mimic the fields in prototype multicell structures for the X-band linear collider. Fields elsewhere in the test structures are significantly lower than that of the single cell. The setup uses matched mode converters that launch the circular TM{sub 01} mode into short test structures. The test structures are connected to the mode launchers with vacuum rf flanges. This setup allows economic testing of different cell geometries, cell materials and preparation techniques with short turn-around time. Simple 2D geometry of the test structures simplifies modeling of the breakdown currents and their thermal effects.

  12. 805 MHz and 201 MHz RF cavity development for MUCOOL

    SciTech Connect

    DLi@lbl.gov

    2002-10-10

    A muon cooling channel calls for very high acceleratinggradient RF structures to restore the energy lost by muons in theabsorbers. The RF structures have to be operated in a strong magneticfield and thus the use of superconducting RF cavities is excluded. Toachieve a high shunt impedance while maintaining a large enough apertureto accommodate a large transverse emittance muon beam, the cavity designadopted is a pillbox-like geometry with thin Be foils to terminate theelectromagnetic field at the cavity iris. The possibility of using gridsof thin-walled metallic tubes for the termination is also being explored.Many of the RF-related issues for muon cooling channels are being studiedboth theoretically and experimentally using an 805 MHz cavity that has apillbox-like geometry with thin Be windows to terminate the cavityaperture. The design and performance of this cavity are reported here.High-power RF tests of the 805 MHz cavity are in progress at Lab G inFermilab. The cavity has exceeded its design gradient of 30 MV/m,reaching 34 MV/m without external magnetic field. No surface damage wasobserved at this gradient. The cavity is currently under conditioning atLab G with an external magnetic field of 2.5 T. We also present here a201 MHz cavity design for muoncooling channels. The proposed cavitydesign is also suitable for use in a proof-of-principle Muon IonizationCooling Experiment (MICE).

  13. A toroidal trap for cold {}^{87}{Rb} atoms using an rf-dressed quadrupole trap

    NASA Astrophysics Data System (ADS)

    Chakraborty, A.; Mishra, S. R.; Ram, S. P.; Tiwari, S. K.; Rawat, H. S.

    2016-04-01

    We demonstrate the trapping of cold {}87{Rb} atoms in a toroidal geometry using a radio frequency (rf) dressed quadrupole magnetic trap formed by superposing a strong rf-field on a quadrupole trap. This rf-dressed quadrupole trap has the minimum potential away from the quadrupole trap centre on a circular path which facilitates trapping in toroidal geometry. In these experiments, the laser cooled atoms were first trapped in a quadrupole trap, then cooled evaporatively using a weak rf-field, and finally trapped in an rf-dressed quadrupole trap. The radius of the toroid could be varied by varying the frequency of the dressing rf-field. It has also been demonstrated that a single rf source and an antenna can be used for the rf-evaporative cooling as well as for the rf-dressing of atoms. The atoms trapped in the toroidal trap may have applications in the realization of an atom gyroscope as well as in studying the quantum gases in low dimensions.

  14. Proposed RF Breakdown Studies at the AWA

    SciTech Connect

    Antipov, S.; Conde, M.; Gai, W.; Power, J.G.; Spentzouris, L.; Yusof, Z.; Dolgashev, V.; /SLAC

    2007-03-21

    A study of breakdown mechanism has been initiated at the Argonne Wakefield Accelerator (AWA). Breakdown may include several factors such as local field enhancement, explosive electron emission, Ohmic heating, tensile stress produced by electric field, and others. The AWA is building a dedicated facility to test various models for breakdown mechanisms and to determine the roles of different factors in the breakdown. We plan to trigger breakdown events with a high-powered laser at various wavelengths (IR to UV) to determine the role of explosive electron emission in the breakdown process. Another experimental idea follows from the recent work on a Schottky-enabled photoemission in an RF photoinjector [1] that allows us to determine in situ the field enhancement factor on a cathode surface. Monitoring the field enhancement factor before and after the breakdown can shed some light on a number of observations such as the crater formation process.

  15. Realizing Tunable Inverse and Normal Doppler Shifts in Reconfigurable RF Metamaterials

    NASA Astrophysics Data System (ADS)

    Ran, Jia; Zhang, Yewen; Chen, Xiaodong; Fang, Kai; Zhao, Junfei; Sun, Yong; Chen, Hong

    2015-06-01

    The Doppler effect has well-established applications in astronomy, medicine, radar and metrology. Recently, a number of experimental demonstrations of the inverse Doppler effect have begun to appear. However, the inverse Doppler effect has never been observed on an electronically reconfigurable system with an external electromagnetic wave source at radio frequencies (RF) in experiment. Here we demonstrate an experimental observation of the inverse Doppler shift on an electronically reconfigurable RF metamaterial structure, which can exhibit anomalous dispersion, normal dispersion or a stop band, depending on an applied bias voltage. Either inverse or normal Doppler shift is realized by injecting an external RF signal into the electronically reconfigurable metamaterial, on which an electronically controllable moving reflective boundary is formed. The effective velocity of this boundary and the resulting frequency shift can be tuned over a wide range by a digital switching circuit. This work is expected to open up possibilities in applying the inverse Doppler effect in wireless communications, radar and satellite navigation.

  16. A discrete time random walk model for anomalous diffusion

    NASA Astrophysics Data System (ADS)

    Angstmann, C. N.; Donnelly, I. C.; Henry, B. I.; Nichols, J. A.

    2015-07-01

    The continuous time random walk, introduced in the physics literature by Montroll and Weiss, has been widely used to model anomalous diffusion in external force fields. One of the features of this model is that the governing equations for the evolution of the probability density function, in the diffusion limit, can generally be simplified using fractional calculus. This has in turn led to intensive research efforts over the past decade to develop robust numerical methods for the governing equations, represented as fractional partial differential equations. Here we introduce a discrete time random walk that can also be used to model anomalous diffusion in an external force field. The governing evolution equations for the probability density function share the continuous time random walk diffusion limit. Thus the discrete time random walk provides a novel numerical method for solving anomalous diffusion equations in the diffusion limit, including the fractional Fokker-Planck equation. This method has the clear advantage that the discretisation of the diffusion limit equation, which is necessary for numerical analysis, is itself a well defined physical process. Some examples using the discrete time random walk to provide numerical solutions of the probability density function for anomalous subdiffusion, including forcing, are provided.

  17. Modular open RF architecture: extending VICTORY to RF systems

    NASA Astrophysics Data System (ADS)

    Melber, Adam; Dirner, Jason; Johnson, Michael

    2015-05-01

    Radio frequency products spanning multiple functions have become increasingly critical to the warfighter. Military use of the electromagnetic spectrum now includes communications, electronic warfare (EW), intelligence, and mission command systems. Due to the urgent needs of counterinsurgency operations, various quick reaction capabilities (QRCs) have been fielded to enhance warfighter capability. Although these QRCs were highly successfully in their respective missions, they were designed independently resulting in significant challenges when integrated on a common platform. This paper discusses how the Modular Open RF Architecture (MORA) addresses these challenges by defining an open architecture for multifunction missions that decomposes monolithic radio systems into high-level components with welldefined functions and interfaces. The functional decomposition maximizes hardware sharing while minimizing added complexity and cost due to modularization. MORA achieves significant size, weight and power (SWaP) savings by allowing hardware such as power amplifiers and antennas to be shared across systems. By separating signal conditioning from the processing that implements the actual radio application, MORA exposes previously inaccessible architecture points, providing system integrators with the flexibility to insert third-party capabilities to address technical challenges and emerging requirements. MORA leverages the Vehicular Integration for Command, Control, Communication, Computers, Intelligence, Surveillance, and Reconnaissance (C4ISR)/EW Interoperability (VICTORY) framework. This paper concludes by discussing how MORA, VICTORY and other standards such as OpenVPX are being leveraged by the U.S. Army Research, Development, and Engineering Command (RDECOM) Communications Electronics Research, Development, and Engineering Center (CERDEC) to define a converged architecture enabling rapid technology insertion, interoperability and reduced SWaP.

  18. Rf power sources for linear colliders

    SciTech Connect

    Allen, M.A.; Callin, R.S.; Caryotakis, G.; Deruyter, H.; Eppley, K.R.; Fant, K.S.; Farkas, Z.D.; Fowkes, W.R.; Hoag, H.A.; Feinstein, J.; Ko, K.; Koontz, R.F.; Kroll, N.M.; Lavine, T.L.; Lee, T.G.; Loew, G.A.; Miller, R.H.; Nelson, E.M.; Ruth, R.D.; Vlieks, A.E.; Wang, J.W.; Wilson, P.B. ); Boyd, J.K.; Houk, T.; Ryne, R.D.; Westenskow, G.A.; Yu, S.S. (Lawrence Live

    1990-06-01

    The next generation of linear colliders requires peak power sources of over 200 MW per meter at frequencies above 10 GHz at pulse widths of less than 100 nsec. Several power sources are under active development, including a conventional klystron with rf pulse compression, a relativistic klystron (RK) and a crossed-field amplifier. Power from one of these has energized a 0.5 meter two- section High Gradient Accelerator (HGA) and accelerated a beam at over 80 MeV meter. Results of tests with these experimental devices are presented here.

  19. Computer control of rf at SLAC

    SciTech Connect

    Schwarz, H.D.

    1985-03-01

    The Stanford Linear Accelerator is presently upgraded for the SLAC Linear Collider project. The energy is to be increased from approximately 31 GeV to 50 GeV. Two electron beams and one positron beam are to be accelerated with high demands on the quality of the beams. The beam specifications are shown. To meet these specifications, all parameters influencing the beams have to be under tight control and continuous surveillance. This task is accomplished by a new computer system implemented at SLAC which has, among many other functions, control over rf accelerating fields. 13 refs., 8 figs., 2 tabs.

  20. Design and test results of the Low Energy Demonstration Accelerator (LEDA) RF systems

    SciTech Connect

    Rees, D.; Bradley, J. III; Cummings, K.; Lynch, M.; Regan, A.; Rohlev, T.; Roybal, W.; Wang, Y.M.

    1998-12-01

    The Low Energy Demonstration Accelerator (LEDA) being constructed at Los Alamos will serve as the prototype for the low energy section of the Accelerator Production of Tritium (APT) accelerator. The APT accelerator requires over 200 RF systems each with a continuous wave output power of 1 MW. The reliability and availability of these RF systems is critical to the successful operation of the APT plant and prototypes of these systems are being developed and demonstrated on LEDA. The RF system design for LEDA includes three, 1.2 MW, 350 MHz continuous wave (CW), RF systems driving a radio frequency quadrupole (RFQ) and one, 1.0 MW, CW, RF system driving a coupled-cavity drift tube linac (CCDTL). This paper presents the design and test results for these RF systems including the klystrons, cathode power supply, circulators, RF vacuum windows, accelerator field and resonance control system, and RF transmission components. The three RF systems driving the RFQ use the accelerating structure as a power combiner, and this places some unique requirements on the RF system. These requirements and corresponding operational implications will be discussed.

  1. Workgroup Report: Base Stations and Wireless Networks—Radiofrequency (RF) Exposures and Health Consequences

    PubMed Central

    Valberg, Peter A.; van Deventer, T. Emilie; Repacholi, Michael H.

    2007-01-01

    Radiofrequency (RF) waves have long been used for different types of information exchange via the airwaves—wireless Morse code, radio, television, and wireless telephony (i.e., construction and operation of telephones or telephonic systems). Increasingly larger numbers of people rely on mobile telephone technology, and health concerns about the associated RF exposure have been raised, particularly because the mobile phone handset operates in close proximity to the human body, and also because large numbers of base station antennas are required to provide widespread availability of service to large populations. The World Health Organization convened an expert workshop to discuss the current state of cellular-telephone health issues, and this article brings together several of the key points that were addressed. The possibility of RF health effects has been investigated in epidemiology studies of cellular telephone users and workers in RF occupations, in experiments with animals exposed to cell-phone RF, and via biophysical consideration of cell-phone RF electric-field intensity and the effect of RF modulation schemes. As summarized here, these separate avenues of scientific investigation provide little support for adverse health effects arising from RF exposure at levels below current international standards. Moreover, radio and television broadcast waves have exposed populations to RF for > 50 years with little evidence of deleterious health consequences. Despite unavoidable uncertainty, current scientific data are consistent with the conclusion that public exposures to permissible RF levels from mobile telephony and base stations are not likely to adversely affect human health. PMID:17431492

  2. Anomalous Flavor U(1)_X for Everything

    SciTech Connect

    Dreiner, Herbi K.; Murayama, Hitoshi; Thormeier, Marc

    2003-12-01

    We present an ambitious model of flavor, based on an anomalous U(1)_X gauge symmetry with one flavon, only two right-handed neutrinos and only two mass scales: M_{grav} and m_{3/2}. In particular, there are no new scales introduced for right-handed neutrino masses. The X-charges of the matter fields are such that R-parity is conserved exactly, higher-dimensional operators are sufficiently suppressed to guarantee a proton lifetime in agreement with experiment, and the phenomenology is viable for quarks, charged leptons, as well as neutrinos. In our model one of the three light neutrinos automatically is massless. The price we have to pay for this very successful model are highly fractional X-charges which can likely be improved with less restrictive phenomenological ansatze for mass matrices.

  3. Anomalous magnetoresistance in magnetized topological insulator cylinders

    SciTech Connect

    Siu, Zhuo Bin; Jalil, Mansoor B. A.

    2015-05-07

    The close coupling between the spin and momentum degrees of freedom in topological insulators (TIs) presents the opportunity for the control of one to manipulate the other. The momentum can, for example, be confined on a curved surface and the spin influenced by applying a magnetic field. In this work, we study the surface states of a cylindrical TI magnetized in the x direction perpendicular to the cylindrical axis lying along the z direction. We show that a large magnetization leads to an upwards bending of the energy bands at small |k{sub z}|. The bending leads to an anomalous magnetoresistance where the transmission between two cylinders magnetized in opposite directions is higher than when the cylinders are magnetized at intermediate angles with respect to each other.

  4. Low-Level RF Control of Microphonics in Superconducting Spoke-Loaded Cavities

    SciTech Connect

    Conway, Z.A.; Kelly, M.P.; Sharamentov, S.I.; Shepard, K.W.; Davis, G.; Delayen, Jean; Doolittle, Lawrence

    2007-10-01

    This paper presents the results of cw RF frequency control and RF phase-stabilization experiments performed with a piezoelectric fast tuner mechanically coupled to a superconducting, 345 MHz, Ë = 0.5 triple-spoke-loaded cavity operating at 4.2K. The piezoelectric fast tuner damped low-frequency microphonic-noise by an order of magnitude. Two methods of RF phase-stabilization were characterized: overcoupling with negative phase feedback, and also fast mechanical tuner feedback. The Ë = 0.5 triple-spoke-loaded cavity RF field amplitude and phase errors were controlled to ±0.5% and ±30 respectively.

  5. Resonant Frequency Dependence on Outer Diameter of High Tc rf-SQUID

    NASA Astrophysics Data System (ADS)

    Ashizuka, Takuya; Sakai, Akira; Miyato, Yuji; Itozaki, Hideo

    Superconducting quantum interference devices (SQUIDs) have been applied to various magnetic sensing. An rf-SQUID can measure magnetic signals by applying external rf-magnetic field whose frequency is tuned to its resonance. Our rf-SQUID having the outer diameter of 3.5 mm needed a substrate resonator to operate it within the operation frequency range of our using FLL electronics. The designs of the rf-SQUID and the resonator were critical to the resonant frequency and the effective area. In this paper, the outer diameter dependence of the resonant frequency and the effective area were investigated by both the electromagnetic simulations and the experiments. The results showed that the rf-SQUID having the larger outer diameter has the smaller resonant frequency and the larger effective area. The rf-SQUIDs having the larger outer diameter were fabricated according to the simulation results. They could be operated within the operation frequency range even though a resonator was omitted.

  6. Investigation of Readout RF Pulse Impact on the Chemical Exchange Saturation Transfer Spectrum.

    PubMed

    Huang, Sheng-Min; Jan, Meei-Ling; Liang, Hsin-Chin; Chang, Chia-Hao; Wu, Yi-Chun; Tsai, Shang-Yueh; Wang, Fu-Nien

    2015-01-01

    Chemical exchange saturation transfer magnetic resonance imaging (CEST-MRI) is capable of both microenvironment and molecular imaging. The optimization of scanning parameters is important since the CEST effect is sensitive to factors such as saturation power and field homogeneity. The aim of this study was to determine if the CEST effect would be altered by changing the length of readout RF pulses. Both theoretical computer simulation and phantom experiments were performed to examine the influence of readout RF pulses. Our results showed that the length of readout RF pulses has unremarkable impact on the Z-spectrum and CEST effect in both computer simulation and phantom experiment. Moreover, we demonstrated that multiple refocusing RF pulses used in rapid acquisition with relaxation enhancement (RARE) sequence induced no obvious saturation transfer contrast. Therefore, readout RF pulse has negligible effect on CEST Z-spectrum and the optimization of readout RF pulse length can be disregarded in CEST imaging protocol. PMID:26455576

  7. Investigation of Readout RF Pulse Impact on the Chemical Exchange Saturation Transfer Spectrum

    PubMed Central

    Huang, Sheng-Min; Jan, Meei-Ling; Liang, Hsin-Chin; Chang, Chia-Hao; Wu, Yi-Chun; Tsai, Shang-Yueh; Wang, Fu-Nien

    2015-01-01

    Chemical exchange saturation transfer magnetic resonance imaging (CEST-MRI) is capable of both microenvironment and molecular imaging. The optimization of scanning parameters is important since the CEST effect is sensitive to factors such as saturation power and field homogeneity. The aim of this study was to determine if the CEST effect would be altered by changing the length of readout RF pulses. Both theoretical computer simulation and phantom experiments were performed to examine the influence of readout RF pulses. Our results showed that the length of readout RF pulses has unremarkable impact on the Z-spectrum and CEST effect in both computer simulation and phantom experiment. Moreover, we demonstrated that multiple refocusing RF pulses used in rapid acquisition with relaxation enhancement (RARE) sequence induced no obvious saturation transfer contrast. Therefore, readout RF pulse has negligible effect on CEST Z-spectrum and the optimization of readout RF pulse length can be disregarded in CEST imaging protocol. PMID:26455576

  8. Dependence of nuclear spin singlet lifetimes on RF spin-locking power

    NASA Astrophysics Data System (ADS)

    DeVience, Stephen J.; Walsworth, Ronald L.; Rosen, Matthew S.

    2012-05-01

    We measure the lifetime of long-lived nuclear spin singlet states as a function of the strength of the RF spin-locking field and present a simple theoretical model that agrees well with our measurements, including the low-RF-power regime. We also measure the lifetime of a long-lived coherence between singlet and triplet states that does not require a spin-locking field for preservation. Our results indicate that for many molecules, singlet states can be created using weak RF spin-locking fields: more than two orders of magnitude lower RF power than in previous studies. Our findings suggest that for many endogenous biomolecules, singlets and related states with enhanced lifetimes might be achievable in vivo with safe levels of RF power.

  9. Additive manufacturing of RF absorbers

    NASA Astrophysics Data System (ADS)

    Mills, Matthew S.

    The ability of additive manufacturing techniques to fabricate integrated electromagnetic absorbers tuned for specific radio frequency bands within structural composites allows for unique combinations of mechanical and electromagnetic properties. These composites and films can be used for RF shielding of sensitive electromagnetic components through in-plane and out-of-plane RF absorption. Structural composites are a common building block of many commercial platforms. These platforms may be placed in situations in which there is a need for embedded RF absorbing properties along with structural properties. Instead of adding radar absorbing treatments to the external surface of existing structures, which adds increased size, weight and cost; it could prove to be advantageous to integrate the microwave absorbing properties directly into the composite during the fabrication process. In this thesis, a method based on additive manufacturing techniques of composites structures with prescribed electromagnetic loss, within the frequency range 1 to 26GHz, is presented. This method utilizes screen printing and nScrypt micro dispensing to pattern a carbon based ink onto low loss substrates. The materials chosen for this study will be presented, and the fabrication technique that these materials went through to create RF absorbing structures will be described. The calibration methods used, the modeling of the RF structures, and the applications in which this technology can be utilized will also be presented.

  10. Phase modulation in RF tag

    DOEpatents

    Carrender, Curtis Lee; Gilbert, Ronald W.

    2007-02-20

    A radio frequency (RF) communication system employs phase-modulated backscatter signals for RF communication from an RF tag to an interrogator. The interrogator transmits a continuous wave interrogation signal to the RF tag, which based on an information code stored in a memory, phase-modulates the interrogation signal to produce a backscatter response signal that is transmitted back to the interrogator. A phase modulator structure in the RF tag may include a switch coupled between an antenna and a quarter-wavelength stub; and a driver coupled between the memory and a control terminal of the switch. The driver is structured to produce a modulating signal corresponding to the information code, the modulating signal alternately opening and closing the switch to respectively decrease and increase the transmission path taken by the interrogation signal and thereby modulate the phase of the response signal. Alternatively, the phase modulator may include a diode coupled between the antenna and driver. The modulating signal from the driver modulates the capacitance of the diode, which modulates the phase of the response signal reflected by the diode and antenna.

  11. FPGA-based RF interference reduction techniques for simultaneous PET–MRI

    NASA Astrophysics Data System (ADS)

    Gebhardt, P.; Wehner, J.; Weissler, B.; Botnar, R.; Marsden, P. K.; Schulz, V.

    2016-05-01

    The combination of positron emission tomography (PET) and magnetic resonance imaging (MRI) as a multi-modal imaging technique is considered very promising and powerful with regard to in vivo disease progression examination, therapy response monitoring and drug development. However, PET–MRI system design enabling simultaneous operation with unaffected intrinsic performance of both modalities is challenging. As one of the major issues, both the PET detectors and the MRI radio-frequency (RF) subsystem are exposed to electromagnetic (EM) interference, which may lead to PET and MRI signal-to-noise ratio (SNR) deteriorations. Early digitization of electronic PET signals within the MRI bore helps to preserve PET SNR, but occurs at the expense of increased amount of PET electronics inside the MRI and associated RF field emissions. This raises the likelihood of PET-related MRI interference by coupling into the MRI RF coil unwanted spurious signals considered as RF noise, as it degrades MRI SNR and results in MR image artefacts. RF shielding of PET detectors is a commonly used technique to reduce PET-related RF interferences, but can introduce eddy-current-related MRI disturbances and hinder the highest system integration. In this paper, we present RF interference reduction methods which rely on EM field coupling–decoupling principles of RF receive coils rather than suppressing emitted fields. By modifying clock frequencies and changing clock phase relations of digital circuits, the resulting RF field emission is optimised with regard to a lower field coupling into the MRI RF coil, thereby increasing the RF silence of PET detectors. Our methods are demonstrated by performing FPGA-based clock frequency and phase shifting of digital silicon photo-multipliers (dSiPMs) used in the PET modules of our MR-compatible Hyperion II D PET insert. We present simulations and magnetic-field map scans visualising the impact of altered clock phase pattern on the spatial RF field

  12. FPGA-based RF interference reduction techniques for simultaneous PET-MRI.

    PubMed

    Gebhardt, P; Wehner, J; Weissler, B; Botnar, R; Marsden, P K; Schulz, V

    2016-05-01

    The combination of positron emission tomography (PET) and magnetic resonance imaging (MRI) as a multi-modal imaging technique is considered very promising and powerful with regard to in vivo disease progression examination, therapy response monitoring and drug development. However, PET-MRI system design enabling simultaneous operation with unaffected intrinsic performance of both modalities is challenging. As one of the major issues, both the PET detectors and the MRI radio-frequency (RF) subsystem are exposed to electromagnetic (EM) interference, which may lead to PET and MRI signal-to-noise ratio (SNR) deteriorations. Early digitization of electronic PET signals within the MRI bore helps to preserve PET SNR, but occurs at the expense of increased amount of PET electronics inside the MRI and associated RF field emissions. This raises the likelihood of PET-related MRI interference by coupling into the MRI RF coil unwanted spurious signals considered as RF noise, as it degrades MRI SNR and results in MR image artefacts. RF shielding of PET detectors is a commonly used technique to reduce PET-related RF interferences, but can introduce eddy-current-related MRI disturbances and hinder the highest system integration. In this paper, we present RF interference reduction methods which rely on EM field coupling-decoupling principles of RF receive coils rather than suppressing emitted fields. By modifying clock frequencies and changing clock phase relations of digital circuits, the resulting RF field emission is optimised with regard to a lower field coupling into the MRI RF coil, thereby increasing the RF silence of PET detectors. Our methods are demonstrated by performing FPGA-based clock frequency and phase shifting of digital silicon photo-multipliers (dSiPMs) used in the PET modules of our MR-compatible Hyperion II (D) PET insert. We present simulations and magnetic-field map scans visualising the impact of altered clock phase pattern on the spatial RF field

  13. An analog RF gap voltage regulation system for the Advanced Photon Source storage ring.

    SciTech Connect

    Horan, D.

    1999-04-13

    An analog rf gap voltage regulation system has been designed and built at Argonne National Laboratory to maintain constant total storage ring rf gap voltage, independent of beam loading and cavity tuning effects. The design uses feedback control of the klystron mod-anode voltage to vary the amount of rf power fed to the storage ring cavities. The system consists of two independent feedback loops, each regulating the combined rf gap voltages of eight storage ring cavities by varying the output power of either one or two rf stations, depending on the mode of operation. It provides full operator control and permissive logic to permit feedback control of the rf system output power only if proper conditions are met. The feedback system uses envelope-detected cavity field probe outputs as the feedback signal. Two different methods of combining the individual field probe signals were used to generate a relative DC level representing one-half of the total storage ring rf voltage, an envelope-detected vector sum of the field probe rf signals, and the DC sum of individual field probe envelope detector outputs. The merits of both methods are discussed. The klystron high-voltage power supply (HVPS) units are fitted with an analog interface for external control of the mod-anode voltage level, using a four-quadrant analog multiplier to modulate the HVPS mod-anode voltage regulator set-point in response to feedback system commands.

  14. Mössbauer forward scattering on FeBO3 in the RF remagnetization regime

    NASA Astrophysics Data System (ADS)

    Sadykov, E. K.; Dzyublik, A. Ya.; Petrov, G. I.; Arinin, V. V.; Spivak, V. Yu.

    2010-10-01

    The RF Mössbauer spectra have been measured on iron borate (FeBO3) in the forward scattering scheme. A model based on the mechanism of the RF reversal of the hyperfine field reproduces all features of the observed spectra, including the appearance of satellites at the double frequency.

  15. Single echo acquisition MRI using RF encoding.

    PubMed

    Wright, Steven M; McDougall, Mary Preston

    2009-11-01

    Encoding of spatial information in magnetic resonance imaging is conventionally accomplished by using magnetic field gradients. During gradient encoding, the position in k-space is determined by a time-integral of the gradient field, resulting in a limitation in imaging speed due to either gradient power or secondary effects such as peripheral nerve stimulation. Partial encoding of spatial information through the sensitivity patterns of an array of coils, known as parallel imaging, is widely used to accelerate the imaging, and is complementary to gradient encoding. This paper describes the one-dimensional limit of parallel imaging in which all spatial localization in one dimension is performed through encoding by the radiofrequency (RF) coil. Using a one-dimensional array of long and narrow parallel elements to localize the image information in one direction, an entire image is obtained from a single line of k-space, avoiding rapid or repeated manipulation of gradients. The technique, called single echo acquisition (SEA) imaging, is described, along with the need for a phase compensation gradient pulse to counteract the phase variation contained in the RF coil pattern which would otherwise cause signal cancellation in each imaging voxel. Image reconstruction and resolution enhancement methods compatible with the speed of the technique are discussed. MR movies at frame rates of 125 frames per second are demonstrated, illustrating the ability to monitor the evolution of transverse magnetization to steady state during an MR experiment as well as demonstrating the ability to image rapid motion. Because this technique, like all RF encoding approaches, relies on the inherent spatially varying pattern of the coil and is not a time-integral, it should enable new applications for MRI that were previously inaccessible due to speed constraints, and should be of interest as an approach to extending the limits of detection in MR imaging. PMID:19441080

  16. Unexpected Enhancements and Reductions of RF Resonance Strengths

    SciTech Connect

    Leonova, M. A.; Krisch, A. D.; Morozov, V. S.; Raymond, R. S.; Sivers, D. W.; Wong, V. K.; Gebel, R.; Lehrach, A.; Lorentz, B.; Maier, R.; Prasuhn, D.; Schnase, A.; Stockhorst, H.; Hinterberger, F.; Ulbrich, K.

    2007-06-13

    We analyzed all available data on spin-flipping stored beams of protons, deuterons and electrons. We first calculated the rf-induced spin resonance strength ratio {epsilon}FS/*{epsilon}Bdl; the {epsilon}FS was obtained by fitting the measured polarization data to the modified Froissart-Stora equation, while *{epsilon}Bdl was calculated using the {integral}Bdl of the rf dipole or rf solenoid. We found that {epsilon}FS/*{epsilon}Bdl was often 7 times lower than predicted for deuterons, and 12 to 170 times higher than predicted for protons. We studied these discrepancies with vertically polarized beams of 2.1 GeV/c protons and 1.85 GeV/c deuterons stored in the COSY ring in Juelich, Germany. These studies involved flipping their polarization direction, by sweeping the frequency of a water-cooled ferrite rf dipole, of typically {integral}Bdlrms = 0.60 {+-} 0.3 T{center_dot}mm, through an rf-induced spin resonance.We studied the dependence of {epsilon}FS/*Bdl on the beam size, the momentum spread and the distance from the nearest 1st-order intrinsic spin resonance for both protons and deuterons, and on the frequency sweep range {delta}f for deuterons. We observed no measurable dependence of {epsilon}FS/*Bdl on the beam's size or momentum spread for either protons or deuterons. When we varied the vertical betatron tune {nu}y near a 1st-order intrinsic spin resonance, we observed a strong enhancement of {epsilon}FS/*{epsilon}Bdl with a hyperbolic dependence on the distance from the 1st-order intrinsic spin resonance for both protons and deuterons. This explained much of the proton discrepancy, but did not explain the deuteron's very small {epsilon}FS/*{epsilon}Bdl. All early deuteron data had small {delta}f values of 100-200 Hz; however, when {delta}f was increased from 100 to 3000 Hz, in four steps, there was no dependence of {epsilon}FS/*{epsilon}Bdl on {delta}f Thus, this anomalously small {epsilon}FS/*{epsilon}Bdl ratio may be due to some unexpected behavior of

  17. Klystron equalization for RF feedback

    SciTech Connect

    Corredoura, P.

    1993-01-01

    The next generation of colliding beam storage rings support higher luminosities by significantly increasing the number of bunches and decreasing the spacing between respective bunches. The heavy beam loading requires large RF cavity detuning which drives several lower coupled bunch modes very strongly. One technique which has proven to be very successful in reducing the coupled bunch mode driving impedance is RF feedback around the klystron-cavity combination. The gain and bandwidth of the feedback loop is limited by the group delay around the feedback loop. Existing klystrons on the world market have not been optimized for this application and contribute a large portion of the total loop group delay. This paper describes a technique to reduce klystron group delay by adding an equalizing filter to the klystron RF drive. Such a filter was built and tested on a 500 kill klystron as part of the on going PEP-II R D effort here at SLAC.

  18. Klystron equalization for RF feedback

    SciTech Connect

    Corredoura, P.

    1993-01-01

    The next generation of colliding beam storage rings support higher luminosities by significantly increasing the number of bunches and decreasing the spacing between respective bunches. The heavy beam loading requires large RF cavity detuning which drives several lower coupled bunch modes very strongly. One technique which has proven to be very successful in reducing the coupled bunch mode driving impedance is RF feedback around the klystron-cavity combination. The gain and bandwidth of the feedback loop is limited by the group delay around the feedback loop. Existing klystrons on the world market have not been optimized for this application and contribute a large portion of the total loop group delay. This paper describes a technique to reduce klystron group delay by adding an equalizing filter to the klystron RF drive. Such a filter was built and tested on a 500 kill klystron as part of the on going PEP-II R&D effort here at SLAC.

  19. Cryogenic vacuumm RF feedthrough device

    DOEpatents

    Wu, Genfa; Phillips, Harry Lawrence

    2008-12-30

    A cryogenic vacuum rf feedthrough device comprising: 1) a probe for insertion into a particle beam; 2) a coaxial cable comprising an inner conductor and an outer conductor, a dielectric/insulating layer surrounding the inner conductor, the latter being connected to the probe for the transmission of higher mode rf energy from the probe; and 3) a high thermal conductivity stub attached to the coaxial dielectric about and in thermal contact with the inner conductor which high thermal conductivity stub transmits heat generated in the vicinity of the probe efficiently and radially from the area of the probe and inner conductor all while maintaining useful rf transmission line characteristics between the inner and outer coaxial conductors.

  20. Anomalous phosphenes in ocular protontherapy

    NASA Astrophysics Data System (ADS)

    Khan, E.; Maréchal, F.; Dendale, R.; Mabit, C.; Calugaru, V.; Desjardin, L.; Narici, L.

    2010-04-01

    We have undertaken a clinical ground study of proton-induced light flashes (phosphenes). Patients treated at the Institut Curie - Centre de Protonthérapie in Orsay, France, received radiation therapy to cure ocular and skull-base cancers. Sixty percent of the patients treated for choroidal melanomas using 73 MeV protons report anomalous phosphenes. Delivering a radiation dose on the retina only is not sufficient to trigger the light flash. The present study may be the first indication of phosphenes triggered by protons of few tens of MeV.

  1. Khinchin Theorem and Anomalous Diffusion

    NASA Astrophysics Data System (ADS)

    Lapas, Luciano C.; Morgado, Rafael; Vainstein, Mendeli H.; Rubí, J. Miguel; Oliveira, Fernando A.

    2008-12-01

    A recent Letter [M. H. Lee, Phys. Rev. Lett. 98, 190601 (2007)PRLTAO0031-900710.1103/PhysRevLett.98.190601] has called attention to the fact that irreversibility is a broader concept than ergodicity, and that therefore the Khinchin theorem [A. I. Khinchin, Mathematical Foundations of Statistical Mechanics (Dover, New York, 1949)] may fail in some systems. In this Letter we show that for all ranges of normal and anomalous diffusion described by a generalized Langevin equation the Khinchin theorem holds.

  2. Geophysical Characterization and Monitoring for Anomalous Transport (Invited)

    NASA Astrophysics Data System (ADS)

    Day-Lewis, F. D.; Singha, K.

    2013-12-01

    For several decades, geophysical methods (e.g., electrical, electromagnetic, and radar) have been used to monitor transport of ionic tracers and contaminants, thus providing information about the spatial and temporal morphology and evolution of tracer or contaminant plumes. In the last five years, time-lapse geophysical methods have been applied to understand non-equilibrium between mobile and immobile (or less mobile) domains in porous media (e.g., fractures and matrix) and surface water (i.e., transient storage). Electrical methods have been used in combination with conventional sampling to investigate the exchange of solute between domains and thereby infer exchange rates and relative volumes of mobile and immobile domains. Other methods, including nuclear magnetic resonance and complex resistivity, have been used to study the distribution of pore sizes present, which in turn control anomalous transport. Here, we (1) review the underlying petrophysical/hydrologic link between anomalous transport and geophysical monitoring; (2) review the emerging body of work using geophysical methods to understand anomalous transport and summarize case studies involving field experiments at an aquifer-storage recovery site in Charleston, SC, and two Department of Energy sites in Hanford, WA and Naturita, CO; and (3) discuss potential future directions for geophysical research to further elucidate anomalous transport behavior.

  3. Detection of the Anomalous Velocity with Subpicosecond Time Resolution in Semiconductor Nanostructures

    NASA Astrophysics Data System (ADS)

    Priyadarshi, Shekhar; Pierz, Klaus; Bieler, Mark

    2015-12-01

    We report on the time-resolved detection of the anomalous velocity, constituting charge carriers moving perpendicular to an electric driving field, in undoped GaAs quantum wells. For this we optically excite the quantum wells with circularly polarized femtosecond laser pulses, thereby creating a state which breaks time-inversion symmetry. We then employ a quasi-single-cycle terahertz pulse as an electric driving field to induce the anomalous velocity. The electromagnetic radiation emitted from the anomalous velocity is studied with a subpicosecond time resolution and reveals intriguing results. We are able to distinguish between intrinsic (linked to the Berry curvature) and extrinsic (linked to scattering) contributions to the anomalous velocity both originating from the valence band and observe local energy space dependence of the anomalous velocity. Our results thus constitute a significant step towards noninvasive probing of the anomalous velocity locally in the full energy-momentum space and enable the investigation of many popular physical effects such as the anomalous Hall effect and spin Hall effect on ultrafast time scales.

  4. Detection of the Anomalous Velocity with Subpicosecond Time Resolution in Semiconductor Nanostructures.

    PubMed

    Priyadarshi, Shekhar; Pierz, Klaus; Bieler, Mark

    2015-12-18

    We report on the time-resolved detection of the anomalous velocity, constituting charge carriers moving perpendicular to an electric driving field, in undoped GaAs quantum wells. For this we optically excite the quantum wells with circularly polarized femtosecond laser pulses, thereby creating a state which breaks time-inversion symmetry. We then employ a quasi-single-cycle terahertz pulse as an electric driving field to induce the anomalous velocity. The electromagnetic radiation emitted from the anomalous velocity is studied with a subpicosecond time resolution and reveals intriguing results. We are able to distinguish between intrinsic (linked to the Berry curvature) and extrinsic (linked to scattering) contributions to the anomalous velocity both originating from the valence band and observe local energy space dependence of the anomalous velocity. Our results thus constitute a significant step towards noninvasive probing of the anomalous velocity locally in the full energy-momentum space and enable the investigation of many popular physical effects such as the anomalous Hall effect and spin Hall effect on ultrafast time scales. PMID:26722942

  5. Plasma rotation induced by RF

    SciTech Connect

    Chan, V. S.; Chiu, S. C.; Lin-Liu, Y. R. [General Atomics, P.O. Box 85608, San Diego, California 92186-5698; Omelchenko, Y. A. [General Atomics, P.O. Box 85608, San Diego, California 92186-5698

    1999-09-20

    Plasma rotation has many beneficial effects on tokamak operation including stabilization of MHD and microturbulence to improve the beta limit and confinement. Contrary to present-day tokamaks, neutral beams may not be effective in driving rotation in fusion reactors; hence the investigation of radiofrequency (RF) induced plasma rotation is of great interest and potential importance. This paper reviews the experimental results of RF induced rotation and possible physical mechanisms, suggested by theories, to explain the observations. This subject is only in the infancy of its research and many challenging issues remained to be understood and resolved. (c) 1999 American Institute of Physics.

  6. Anomalous Hall effect in localization regime

    NASA Astrophysics Data System (ADS)

    Wu, Lin; Zhu, Kai; Yue, Di; Tian, Yuan; Jin, Xiaofeng

    2016-06-01

    The anomalous Hall effect in the ultrathin film regime is investigated in Fe(001)(1-3 nm) films epitaxial on MgO(001). The logarithmic localization correction to longitudinal resistivity and anomalous Hall resistivity are observed at low temperature. We identify that the coefficient of skew scattering has a reduction from metallic to localized regime, while the contribution of side jump has inconspicuous change except for a small drop below 10 K. Furthermore, we discover that the intrinsic anomalous Hall conductivity decreases with the reduction of thickness below 2 nm. Our results provide unambiguous experimental evidence to clarify the problem of localization correction to the anomalous Hall effect.

  7. Rf cavity primer for cyclic proton accelerators

    NASA Astrophysics Data System (ADS)

    Griffin, J. E.

    1988-04-01

    The electrical and mechanical properities of particle accelerator rf cavities are described in a manner which will be useful to physics and engineering graduates entering the accelerator field. The discussion is limited to proton (or antiproton) synchrotron accelerators or storage rings operating roughly in the range of 20 to 200 MHz. The very high gradient, fixed frequency UHF or microwave devices appropriate for electron machines and the somewhat lower frequency and broader bandwidth devices required for heavy ion accelerators are discussed extensively in other papers in this series. While it is common practice to employ field calculation programs such as SUPERFISH, URMEL, or MAFIA as design aids in the development of rf cavities, we attempt here to elucidate various of the design parameters commonly dealt with in proton machines through the use of simple standing wave coaxial resonator expressions. In so doing, we treat only standing wave structures. Although low-impedance, moderately broad pass-band travelling wave accelerating systems are used in the CERN SPS, such systems are more commonly found in linacs, and they have not been used widely in large cyclic accelerators. Two appendices providing useful supporting material regarding relativistic particle dynamics and synchrotron motion in cyclic accelerators are added to supplement the text.

  8. Pressurized rf cavities in ionizing beams

    NASA Astrophysics Data System (ADS)

    Freemire, B.; Tollestrup, A. V.; Yonehara, K.; Chung, M.; Torun, Y.; Johnson, R. P.; Flanagan, G.; Hanlet, P. M.; Collura, M. G.; Jana, M. R.; Leonova, M.; Moretti, A.; Schwarz, T.

    2016-06-01

    A muon collider or Higgs factory requires significant reduction of the six dimensional emittance of the beam prior to acceleration. One method to accomplish this involves building a cooling channel using high pressure gas filled radio frequency cavities. The performance of such a cavity when subjected to an intense particle beam must be investigated before this technology can be validated. To this end, a high pressure gas filled radio frequency (rf) test cell was built and placed in a 400 MeV beam line from the Fermilab linac to study the plasma evolution and its effect on the cavity. Hydrogen, deuterium, helium and nitrogen gases were studied. Additionally, sulfur hexafluoride and dry air were used as dopants to aid in the removal of plasma electrons. Measurements were made using a variety of beam intensities, gas pressures, dopant concentrations, and cavity rf electric fields, both with and without a 3 T external solenoidal magnetic field. Energy dissipation per electron-ion pair, electron-ion recombination rates, ion-ion recombination rates, and electron attachment times to SF6 and O2 were measured.

  9. Negative ion source with external RF antenna

    DOEpatents

    Leung, Ka-Ngo; Hahto, Sami K.; Hahto, Sari T.

    2007-02-13

    A radio frequency (RF) driven plasma ion source has an external RF antenna, i.e. the RF antenna is positioned outside the plasma generating chamber rather than inside. The RF antenna is typically formed of a small diameter metal tube coated with an insulator. An external RF antenna assembly is used to mount the external RF antenna to the ion source. The RF antenna tubing is wound around the external RF antenna assembly to form a coil. The external RF antenna assembly is formed of a material, e.g. quartz, which is essentially transparent to the RF waves. The external RF antenna assembly is attached to and forms a part of the plasma source chamber so that the RF waves emitted by the RF antenna enter into the inside of the plasma chamber and ionize a gas contained therein. The plasma ion source is typically a multi-cusp ion source. A converter can be included in the ion source to produce negative ions.

  10. Anomalous Josephson effect in semiconducting nanowires as a signature of the topologically nontrivial phase

    NASA Astrophysics Data System (ADS)

    Nesterov, Konstantin N.; Houzet, Manuel; Meyer, Julia S.

    2016-05-01

    We study Josephson junctions made of semiconducting nanowires with Rashba spin-orbit coupling, where superconducting correlations are induced by the proximity effect. In the presence of a suitably directed magnetic field, the system displays the anomalous Josephson effect: a nonzero supercurrent in the absence of a phase bias between two superconductors. We show that this anomalous current can be increased significantly by tuning the nanowire into the helical regime. In particular, in a short junction, a large anomalous current is a signature for topologically nontrivial superconductivity in the nanowire.

  11. Anomalous Cases of Astronaut Helmet Detection

    NASA Technical Reports Server (NTRS)

    Dolph, Chester; Moore, Andrew J.; Schubert, Matthew; Woodell, Glenn

    2015-01-01

    An astronaut's helmet is an invariant, rigid image element that is well suited for identification and tracking using current machine vision technology. Future space exploration will benefit from the development of astronaut detection software for search and rescue missions based on EVA helmet identification. However, helmets are solid white, except for metal brackets to attach accessories such as supplementary lights. We compared the performance of a widely used machine vision pipeline on a standard-issue NASA helmet with and without affixed experimental feature-rich patterns. Performance on the patterned helmet was far more robust. We found that four different feature-rich patterns are sufficient to identify a helmet and determine orientation as it is rotated about the yaw, pitch, and roll axes. During helmet rotation the field of view changes to frames containing parts of two or more feature-rich patterns. We took reference images in these locations to fill in detection gaps. These multiple feature-rich patterns references added substantial benefit to detection, however, they generated the majority of the anomalous cases. In these few instances, our algorithm keys in on one feature-rich pattern of the multiple feature-rich pattern reference and makes an incorrect prediction of the location of the other feature-rich patterns. We describe and make recommendations on ways to mitigate anomalous cases in which detection of one or more feature-rich patterns fails. While the number of cases is only a small percentage of the tested helmet orientations, they illustrate important design considerations for future spacesuits. In addition to our four successful feature-rich patterns, we present unsuccessful patterns and discuss the cause of their poor performance from a machine vision perspective. Future helmets designed with these considerations will enable automated astronaut detection and thereby enhance mission operations and extraterrestrial search and rescue.

  12. Powder diffraction studies using anomalous dispersion

    SciTech Connect

    Cox, D.E.; Wilkinson, A.P.

    1993-05-01

    With the increasing availability and accessibility of high resolution powder diffractometers at many synchrotron radiation sources throughout the world, there is rapidly-growing interest in the exploitation of anomalous dispersion techniques for structural studies of polycrystalline materials. In conjunction with the Rietveld profile method for structure refinement, such studies are especially useful for the determination of the site distributions of two or more atoms which are near neighbors in the periodic table, or atoms which are distributed among partially occupied sites. Additionally, it is possible to (1) determine the mean-square displacements associated with different kinds of atoms distributed over a single set of sites, (2) distinguish between different oxidation states and coordination geometries of a particular atom in a compound and (3) to determine f` for a wide range of atomic species as a function of energy in the vicinity of an absorption edge. Experimental methods for making anomalous dispersion measurements are described in some detail, including data collection strategies, data analysis and correlation problems, possible systematic errors, and the accuracy of the results. Recent work in the field is reviewed, including cation site-distribution studies (e.g. doped high {Tc} superconductors, ternary alloys, FeCo{sub 2}(PO{sub 4}){sub 3}, FeNi{sub 2}BO{sub 5}), oxidation-state contrast (e.g. YBa{sub 2}Cu{sub 3}O{sub 6+x}, Eu{sub 3}O{sub 4}, GaCl{sub 2}, Fe{sub 2}PO{sub 5}), and the effect of coordination geometry (e.g. Y{sub 3}Ga{sub 5}O{sub l2}).

  13. Powder diffraction studies using anomalous dispersion

    SciTech Connect

    Cox, D.E. ); Wilkinson, A.P. . Dept. of Materials)

    1993-01-01

    With the increasing availability and accessibility of high resolution powder diffractometers at many synchrotron radiation sources throughout the world, there is rapidly-growing interest in the exploitation of anomalous dispersion techniques for structural studies of polycrystalline materials. In conjunction with the Rietveld profile method for structure refinement, such studies are especially useful for the determination of the site distributions of two or more atoms which are near neighbors in the periodic table, or atoms which are distributed among partially occupied sites. Additionally, it is possible to (1) determine the mean-square displacements associated with different kinds of atoms distributed over a single set of sites, (2) distinguish between different oxidation states and coordination geometries of a particular atom in a compound and (3) to determine f' for a wide range of atomic species as a function of energy in the vicinity of an absorption edge. Experimental methods for making anomalous dispersion measurements are described in some detail, including data collection strategies, data analysis and correlation problems, possible systematic errors, and the accuracy of the results. Recent work in the field is reviewed, including cation site-distribution studies (e.g. doped high [Tc] superconductors, ternary alloys, FeCo[sub 2](PO[sub 4])[sub 3], FeNi[sub 2]BO[sub 5]), oxidation-state contrast (e.g. YBa[sub 2]Cu[sub 3]O[sub 6+x], Eu[sub 3]O[sub 4], GaCl[sub 2], Fe[sub 2]PO[sub 5]), and the effect of coordination geometry (e.g. Y[sub 3]Ga[sub 5]O[sub l2]).

  14. Phase noise reduction and photoelectron acceleration in a high-Q RF gun

    SciTech Connect

    Landahl, E.C.; Hartemann, F.V.; Baldis, H.A. |; Le Sage, G.P.; White, W.E.; Bennett, C.V.; Heritage, J.P.; Luhmann, N.C. Jr.; Ho, C.H.

    1998-06-01

    The phase noise and jitter characteristics of the laser and RF systems of a high-gradient X-band photoinjector have been measured experimentally. The laser oscillator is a self-mode-locked titanium: sapphire system operating at the 108th subharmonic of the RF gun. The X-band signal is produced from the laser by a phase-locked dielectric resonance oscillator and amplified by a pulsed TWT and klystron. A comparison between the klystron and TWT amplifier phase noise and the fields excited in the RF gun demonstrates the filtering effect of the high-Q structure, thus indicating that the RF gun can be used as a master oscillator and could be energized by either an RF oscillator, such as a magnetron, or a compact source, such as a cross-field amplifier. In particular, the RF gun can play the role of a pulsed RF clock to synchronize the photocathode laser system; direct drive of a synchronously mode-locked AlGaAs quantum well laser has been achieved using the X-band gun RF fields. This novel, gigahertz repetition rate, laser system is being developed to replace the more conventional femtosecond Ti:Al{sub 2}O{sub 3} system. Some advantages include pumping this laser with a stabilized current source instead of a costly, low-efficiency pump laser. Finally, dark current measurements and initial photoelectron measurements are reported.

  15. ERTS-1 anomalous dark patches

    NASA Technical Reports Server (NTRS)

    Strong, A. E. (Principal Investigator)

    1973-01-01

    The author has identified the following significant results. Through combined use of imagery from ERTS-1 and NOAA-2 satellites was found that when the sun elevation exceeds 55 degrees, the ERTS-1 imagery is subject to considerable contamination by sunlight even though the actual specular point is nearly 300 nautical miles from nadir. Based on sea surface wave slope information, a wind speed of 10 knots will theoretically provide approximately 0.5 percent incident solar reflectance under observed ERTS multispectral scanner detectors. This reflectance nearly doubles under the influence of a 20 knot wind. The most pronounced effect occurs in areas of calm water where anomalous dark patches are observed. Calm water at distances from the specular point found in ERTS scenes will reflect no solar energy to the multispectral scanner, making these regions stand out as dark areas in all bands in an ocean scene otherwise comprosed by a general diffuse sunlight from rougher ocean surfaces. Anomalous dark patches in the outer parts of the glitter zones may explain the unusual appearance of some scenes.

  16. Ion extraction from a saddle antenna RF surface plasma source

    NASA Astrophysics Data System (ADS)

    Dudnikov, V.; Johnson, R. P.; Han, B.; Murray, S.; Pennisi, T.; Piller, C.; Santana, M.; Stockli, M.; Welton, R.; Breitschopf, J.; Dudnikova, G.

    2015-04-01

    Existing RF Surface Plasma Sources (SPS) for accelerators have specific efficiencies for H+ and H- ion generation around 3 to 5 mA/cm2 per kW, where about 50 kW of RF power is typically needed for 50 mA beam current production. The Saddle Antenna (SA) SPS described here was developed to improve H- ion production efficiency and SPS reliability and availability. At low RF power, the efficiency of positive ion generation in the plasma has been improved to 200 mA/cm2 per kW of RF power at 13.56 MHz. Initial cesiation of the SPS was performed by heating cesium chromate cartridges by discharge as was done in the very first versions of the SPS. A small oven to decompose cesium compounds and alloys was developed and tested. After cesiation, the current of negative ions to the collector was increased from 1 mA to 10 mA with RF power ˜1.5 kW in the plasma (6 mm diameter emission aperture) and up to 30 mA with ˜4 kW RF power in the plasma and 250 Gauss longitudinal magnetic field. The ratio of electron current to negative ion current was improved from 30 to 2. Stable generation of H- beam without intensity degradation was demonstrated in the AlN discharge chamber for a long time at high discharge power in an RF SPS with an external antenna. Continuous wave (CW) operation of the SA SPS has been tested on the small test stand. The general design of the CW SA SPS is based on the pulsed version. Some modifications were made to improve the cooling and cesiation stability. The extracted collector current can be increased significantly by optimizing the longitudinal magnetic field in the discharge chamber. CW operation with negative ion extraction was tested with RF power up to 1.8 kW from the generator (˜1.2 kW in the plasma) with production up to Ic=7 mA. Long term operation was tested with 1.2 kW from the RF generator (˜0.8 kW in the plasma) with production of Ic=5 mA, Iex ˜15 mA (Uex=8 kV, Uc=14 kV).

  17. Ion extraction from a saddle antenna RF surface plasma source

    SciTech Connect

    Dudnikov, V. Johnson, R. P.; Han, B.; Murray, S.; Pennisi, T.; Piller, C.; Santana, M.; Stockli, M.; Welton, R.; Breitschopf, J.; Dudnikova, G.

    2015-04-08

    Existing RF Surface Plasma Sources (SPS) for accelerators have specific efficiencies for H{sup +} and H{sup −} ion generation around 3 to 5 mA/cm{sup 2} per kW, where about 50 kW of RF power is typically needed for 50 mA beam current production. The Saddle Antenna (SA) SPS described here was developed to improve H{sup −} ion production efficiency and SPS reliability and availability. At low RF power, the efficiency of positive ion generation in the plasma has been improved to 200 mA/cm{sup 2} per kW of RF power at 13.56 MHz. Initial cesiation of the SPS was performed by heating cesium chromate cartridges by discharge as was done in the very first versions of the SPS. A small oven to decompose cesium compounds and alloys was developed and tested. After cesiation, the current of negative ions to the collector was increased from 1 mA to 10 mA with RF power ∼1.5 kW in the plasma (6 mm diameter emission aperture) and up to 30 mA with ∼4 kW RF power in the plasma and 250 Gauss longitudinal magnetic field. The ratio of electron current to negative ion current was improved from 30 to 2. Stable generation of H{sup −} beam without intensity degradation was demonstrated in the AlN discharge chamber for a long time at high discharge power in an RF SPS with an external antenna. Continuous wave (CW) operation of the SA SPS has been tested on the small test stand. The general design of the CW SA SPS is based on the pulsed version. Some modifications were made to improve the cooling and cesiation stability. The extracted collector current can be increased significantly by optimizing the longitudinal magnetic field in the discharge chamber. CW operation with negative ion extraction was tested with RF power up to 1.8 kW from the generator (∼1.2 kW in the plasma) with production up to Ic=7 mA. Long term operation was tested with 1.2 kW from the RF generator (∼0.8 kW in the plasma) with production of Ic=5 mA, Iex ∼15 mA (Uex=8 kV, Uc=14 kV)

  18. Experiments with very-high-power RF pulses at SLAC

    SciTech Connect

    Hogg, H.A.; Loew, G.A.; Price, V.G.

    1983-03-01

    Experiments in which the powers of two SLAC klystrons were combined and fed into a resonant cavity pulse-compression system (SLED) are described. Pulse powers up to 65 MW into SLED were reached. The corresponding instantaneous peak power out of SLED was 390 MW. After normal initial aging, no persistent RF breakdown problems were encountered. X-radiation at the SLED cavities was generally less than 400 mR/h after aging. The theoretical relationship between x-radiation intensity and RF electric field strength is discussed.

  19. High power testing of a 17 GHz photocathode RF gun

    SciTech Connect

    Chen, S.C.; Danly, B.G.; Gonichon, J.

    1995-12-31

    The physics and technological issues involved in high gradient particle acceleration at high microwave (RF) frequencies are under study at MIT. The 17 GHz photocathode RF gun has a 1 1/2 cell ({pi} mode) room temperature cooper cavity. High power tests have been conducted at 5-10 MW levels with 100 ns pulses. A maximum surface electric field of 250 MV/m was achieved. This corresponds to an average on-axis gradient of 150 MeV/m. The gradient was also verified by a preliminary electron beam energy measurement. Even high gradients are expected in our next cavity design.

  20. Cathodic arc grown niobium films for RF superconducting cavity applications

    NASA Astrophysics Data System (ADS)

    Catani, L.; Cianchi, A.; Lorkiewicz, J.; Tazzari, S.; Langner, J.; Strzyzewski, P.; Sadowski, M.; Andreone, A.; Cifariello, G.; Di Gennaro, E.; Lamura, G.; Russo, R.

    2006-07-01

    Experimental results on the characterization of the linear and non-linear microwave properties of niobium film produced by UHV cathodic arc deposition are presented. Surface impedance Zs as a function of RF field and intermodulation distortion (IMD) measurement have been carried out by using a dielectrically loaded resonant cavity operating at 7 GHz. The experimental data show that these samples have a lower level of intrinsic non-linearities at low temperature and low circulating power in comparison with Nb samples grown by sputtering. These results make UHV cathodic arc deposition a promising technique for the improvement of RF superconducting cavities for particle accelerators.