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Sample records for field current drive

  1. Bootstrapped tokamak with oscillating field current drive

    SciTech Connect

    Weening, R.H. )

    1993-07-01

    A magnetic helicity conserving mean-field Ohm's law is used to study bootstrapped tokamaks with oscillating field current drive. The Ohm's law leads to the conclusion that the tokamak bootstrap effect can convert the largely alternating current of oscillating field current drive into a direct toroidal plasma current. This plasma current rectification is due to the intrinsically nonlinear nature of the tokamak bootstrap effect, and suggests that it may be possible to maintain the toroidal current of a tokamak reactor by supplementing the bootstrap current with oscillating field current drive. Steady-state tokamak fusion reactors operating with oscillating field current drive could provide an alternative to tokamak reactors operating with external current drive.

  2. Reversed field pinch current drive with oscillating helical fields

    SciTech Connect

    Farengo, Ricardo; Clemente, Roberto Antonio

    2006-04-15

    The use of oscillating helical magnetic fields to produce and sustain the toroidal and poloidal currents in a reversed field pinch (RFP) is investigated. A simple physical model that assumes fixed ions, massless electrons, and uniform density and resistivity is employed. Thermal effects are neglected in Ohm's law and helical coordinates are introduced to reduce the number of coupled nonlinear equations that must be advanced in time. The results show that it is possible to produce RFP-like magnetic field profiles with pinch parameters close to the experimental values. The efficiencies obtained for moderate resistivity, and the observed scaling, indicate that this could be a very attractive method for high temperature plasmas.

  3. Equilibrium evolution in oscillating-field current-drive experiments

    SciTech Connect

    McCollam, K. J.; Anderson, J. K.; Blair, A. P.; Craig, D.; Den Hartog, D. J.; Ebrahimi, F.; O'Connell, R.; Reusch, J. A.; Sarff, J. S.; Stephens, H. D.; Stone, D. R.; Brower, D. L.; Deng, B. H.; Ding, W. X.

    2010-08-15

    Oscillating-field current drive (OFCD) is a proposed method of steady-state toroidal plasma sustainment in which ac poloidal and toroidal loop voltages are applied to produce a dc plasma current. OFCD is added to standard, inductively sustained reversed-field pinch plasmas in the Madison Symmetric Torus [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)]. Equilibrium profiles and fluctuations during a single cycle are measured and analyzed for different relative phases between the two OFCD voltages and for OFCD off. For OFCD phases leading to the most added plasma current, the measured energy confinement is slightly better than that for OFCD off. By contrast, the phase of the maximum OFCD helicity-injection rate also has the maximum decay rate, which is ascribed to transport losses during discrete magnetic-fluctuation events induced by OFCD. Resistive-magnetohydrodynamic simulations of the experiments reproduce the observed phase dependence of the added current.

  4. Equilibrium evolution in oscillating-field current-drive experiments

    NASA Astrophysics Data System (ADS)

    McCollam, K. J.; Anderson, J. K.; Blair, A. P.; Craig, D.; Den Hartog, D. J.; Ebrahimi, F.; O'Connell, R.; Reusch, J. A.; Sarff, J. S.; Stephens, H. D.; Stone, D. R.; Brower, D. L.; Deng, B. H.; Ding, W. X.

    2010-08-01

    Oscillating-field current drive (OFCD) is a proposed method of steady-state toroidal plasma sustainment in which ac poloidal and toroidal loop voltages are applied to produce a dc plasma current. OFCD is added to standard, inductively sustained reversed-field pinch plasmas in the Madison Symmetric Torus [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)]. Equilibrium profiles and fluctuations during a single cycle are measured and analyzed for different relative phases between the two OFCD voltages and for OFCD off. For OFCD phases leading to the most added plasma current, the measured energy confinement is slightly better than that for OFCD off. By contrast, the phase of the maximum OFCD helicity-injection rate also has the maximum decay rate, which is ascribed to transport losses during discrete magnetic-fluctuation events induced by OFCD. Resistive-magnetohydrodynamic simulations of the experiments reproduce the observed phase dependence of the added current.

  5. Rotating magnetic quadrupole current drive for field-reversed configurations

    SciTech Connect

    Milroy, Richard D.; Guo, H.Y.

    2005-07-15

    In the translation, confinement, and sustainment experiment [A. L. Hoffman, H. Y. Guo, J. T. Slough, S. J. Tobin, L. S. Schrank, W. A. Reass, and G. A. Wurden, Fusion Sci. Technol. 41, 92 (2002)], field-reversed configurations (FRCs) are created and sustained using a rotating magnetic field (RMF). The RMF is usually in the form of a rotating dipole, which in vacuum penetrates uniformly to the axis of symmetry. However, plasma conditions in the FRC normally adjust so that the RMF only partially penetrates the plasma column. We have investigated the possibility of using a rotating quadrupole rather than a rotating dipole magnetic field. The vacuum field from a quadrupole is proportional to radius and cannot penetrate to the axis of symmetry; however, this is not a disadvantage if the current drive is confined to the outer region of the FRC. It was found that the quadrupole drive efficiency is comparable to that of a dipole, but the rotating dipole is more effective at stabilizing the n=2 rotational instability. A strong internal oscillation in B{sub {theta}} is often observed in FRCs sustained by a quadrupole field. The spectral content of the signals indicates that an internal n=1 magnetic structure forms and corotates with the electrons. Similar but much lower amplitude structures can form when a rotating dipole is employed (edge-driven mode)

  6. Oscillating-field current-drive experiments in a reversed field pinch.

    PubMed

    McCollam, K J; Blair, A P; Prager, S C; Sarff, J S

    2006-01-27

    Oscillating-field current drive (OFCD) is a steady-state magnetic helicity injection method to drive net toroidal current in a plasma by applying oscillating poloidal and toroidal loop voltages. OFCD is added to standard toroidal induction to produce about 10% of the total current in the Madison symmetric torus. The dependence of the added current on the phase between the two applied voltages is measured. Maximum current does not occur at the phase of the maximum helicity injection rate. Effects of OFCD on magnetic fluctuations and dissipated power are shown. PMID:16486717

  7. Modifications to the edge current profile with auxiliary edge current drive and improved confinement in a reversed-field pinch

    SciTech Connect

    Chapman, B.E.; Biewer, T.M.; Chattopadhyay, P.K.; Chiang, C.-S.; Craig, D.J.; Crocker, N.A.; Den Hartog, D.J.; Fiksel, G.; Fontana, P.W.; Prager, S.C.; Sarff, J.S.

    2000-09-01

    Auxiliary edge current drive is routinely applied in the Madison Symmetric Torus [R.N. Dexter, D. W. Kerst, T.W. Lovell et.al., Fusion Technol. 19, 131 (1991)] with the goal of modifying the parallel current profile to reduce current- driven magnetic fluctuations and the associated particle and energy transport. Provided by an inductive electric field, the current drive successfully reduces energy transport. First-time measurements of the modified edge current profile reveal that, relative to discharges without auxiliary current drive, the edge current density decreases. This decrease is explicable in terms of newly measured reductions in the dynamo (fluctuation-based) electric field and the electrical conductivity. Induced by the current drive, these two changes to the edge plasma play as much of a role in determining the resultant edge current profile as does the current drive itself.

  8. Modifications to the edge current profile with auxiliary edge current drive and improved confinement in a reversed-field pinch

    SciTech Connect

    Chapman, B. E.; Biewer, T. M.; Chattopadhyay, P. K.; Chiang, C.-S.; Craig, D. J.; Crocker, N. A.; Den Hartog, D. J.; Fiksel, G.; Fontana, P. W.; Prager, S. C.

    2000-09-01

    Auxiliary edge current drive is routinely applied in the Madison Symmetric Torus [R. N. Dexter, D. W. Kerst, T. W. Lovell et al., Fusion Technol. 19, 131 (1991)] with the goal of modifying the parallel current profile to reduce current-driven magnetic fluctuations and the associated particle and energy transport. Provided by an inductive electric field, the current drive successfully reduces fluctuations and transport. First-time measurements of the modified edge current profile reveal that, relative to discharges without auxiliary current drive, the edge current density decreases. This decrease is explicable in terms of newly measured reductions in the dynamo (fluctuation-based) electric field and the electrical conductivity. Induced by the current drive, these two changes to the edge plasma play as much of a role in determining the resultant edge current profile as does the current drive itself. (c) 2000 American Institute of Physics.

  9. Radial current density effects on rotating magnetic field current drive in field-reversed configurations

    SciTech Connect

    Clemente, R. A.; Gilli, M.; Farengo, R.

    2008-10-15

    Steady state solutions, suitable for field-reversed configurations (FRCs) sustained by rotating magnetic fields (RMFs) are obtained by properly including three-dimensional effects, in the limit of large FRC elongation, and the radial component of Ohm's law. The steady electrostatic potential, necessary to satisfy Ohm's law, is considered to be a surface function. The problem is analyzed at the midplane of the configuration and it is reduced to the solution of two coupled nonlinear differential equations for the real and imaginary parts of the phasor associated to the longitudinal component of the vector potential. Additional constraints are obtained by requesting that the steady radial current density and poloidal magnetic flux vanish at the plasma boundary which is set at the time-averaged separatrix. The results are presented in terms of the degree of synchronism of the electrons with the RMF and compared with those obtained when radial current effects are neglected. Three important differences are observed when compared with the case without radial current density. First, at low penetration of the RMF into the plasma there is a significant increase in the driven azimuthal current. Second, the RMF amplitude necessary to access the high synchronism regime, starting from low synchronism, is larger and the difference appears to increase as the separatrix to classical skin depth ratio increases. Third, the minimum RMF amplitude necessary to sustain almost full synchronism is reduced.

  10. 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.

  11. Fluctuation and transport reduction in a reversed field pinch by inductive poloidal current drive

    SciTech Connect

    Sarff, J.S.; Hokin, S.A.; Ji, H.; Prager, S.C.; Sovinec, C.R.

    1993-12-01

    An auxilliay poloidal inductive electric field applied to a reversed field pinch plasma reduces the current density gradient, slows the growth of m=1 tearing fluctations, suppresses their associated sawteeth, and doubles the energy confinement time. Small sawteeth occur in the improved state but with m=0 precursors. By requiring a change of toroidal flux embedding the plasma, inductive poloidal current profile drive is transient, but the improvement encourages the program of RFP transport suppression using current profile control.

  12. Principal physics of rotating magnetic-field current drive of field reversed configurations

    SciTech Connect

    Hoffman, A.L.; Guo, H.Y.; Miller, K.E.; Milroy, R.D.

    2006-01-15

    After extensive experimentation on the Translation, Confinement, and Sustainment rotating magnetic-field (RMF)-driven field reversed configuration (FRC) device [A. L. Hoffman et al., Fusion Sci. Technol. 41, 92 (2002)], the principal physics of RMF formation and sustainment of standard prolate FRCs inside a flux conserver is reasonably well understood. If the RMF magnitude B{sub {omega}} at a given frequency {omega} is high enough compared to other experimental parameters, it will drive the outer electrons of a plasma column into near synchronous rotation, allowing the RMF to penetrate into the plasma. If the resultant azimuthal current is strong enough to reverse an initial axial bias field B{sub o} a FRC will be formed. A balance between the RMF applied torque and electron-ion friction will determine the peak plasma density n{sub m}{proportional_to}B{sub {omega}}/{eta}{sup 1/2}{omega}{sup 1/2}r{sub s}, where r{sub s} is the FRC separatrix radius and {eta} is an effective weighted plasma resistivity. The plasma total temperature T{sub t} is free to be any value allowed by power balance as long as the ratio of FRC diamagnetic current, I{sup '}{sub dia}{approx_equal}2B{sub e}/{mu}{sub o}, is less than the maximum possible synchronous current, I{sup '}{sub sync}=e{omega}r{sub s}{sup 2}/2. The RMF will self-consistently penetrate a distance {delta}{sup *} governed by the ratio {zeta}=I{sup '}{sub dia}/I{sup '}{sub sync}. Since the FRC is a diamagnetic entity, its peak pressure p{sub m}=n{sub m}kT{sub t} determines its external magnetic field B{sub e}{approx_equal}(2{mu}{sub o}p{sub m}){sup 1/2}. Higher FRC currents, magnetic fields, and poloidal fluxes can thus be obtained, with the same RMF parameters, simply by raising the plasma temperature. Higher temperatures have also been noted to reduce the effective plasma resistivity, so that these higher currents can be supported with surprisingly little increase in absorbed RMF power.

  13. Lower-hybrid poloidal current drive for fluctuation reduction in a reversed field pinch

    SciTech Connect

    Uchimoto, E.; Cekic, M.; Harvey, R.W.; Litwin, C.; Prager, S.C.; Sarff, J.S.; Sovinec, C.R.

    1994-06-01

    Current drive using the lower-hybrid slow wave is shown to be a promising candidate for improving confinement properties of a reversed field pinch (RFP). Ray-tracing calculations indicate that the wave will make a few poloidal turns while spiraling radially into a target zone inside the reversal layer. The poloidal antenna wavelength of the lower hybrid wave can be chosen so that efficient parallel current drive will occur mostly in the poloidal direction in this outer region. Three-dimensional resistive magnetohydrodynamic (MHD) computation demonstrates that an additive poloidal current in this region will reduce the magnetic fluctuations and magnetic stochasticity.

  14. Balancing Current Drive and Heating in DIII-D High Noninductive Current Fraction Discharges Through Choice of the Toroidal Field

    SciTech Connect

    Ferron, J.R.; Holcomb, C T; Luce, T.C.; Politzer, P. A.; Turco, F.; DeBoo, J. C.; Doyle, E. J.; In, Y.; La Haye, R.; Murakami, Masanori; Okabayashi, M.; Park, J. M.; Petrie, T W; Petty, C C.; Reimerdes, H.

    2011-01-01

    In order to maintain stationary values of the stored energy and the plasma current in a tokamak discharge with all of the current driven noninductively, the sum of the alpha-heating power and the power required to provide externally driven current must be equal to the power required to maintain the pressure against transport losses. In a study of high noninductive current fraction discharges in the DIII-D tokamak, it is shown that in the case of present-day tokamaks with no alpha-heating, adjustment of the toroidal field strength (B(T)) is a tool to obtain this balance between the required current drive and heating powers with other easily modifiable discharge parameters (beta(N), q(95), discharge shape, n(e)) fixed at values chosen to satisfy specific constraints. With all of the external power sources providing both heating and current drive, and beta(N) and q(95) fixed, the fraction of externally driven current scales with B(T) with little change in the bootstrap current fraction, thus allowing the noninductive current fraction to be adjusted.

  15. THE ROTATING MAGNETIC FIELD OSCILLATOR SYSTEM FOR CURRENT DRIVE IN THE TRANSLATION, CONFINEMENT AND SUSTAINMENT EXPERIMENT

    SciTech Connect

    S. TOBIN; ET AL

    2000-12-01

    The experimental setup and test results for the {approximately}125 MW rotating magnetic field current drive system of the Translation, Confinement and Sustainment Experiment at the University of Washington are described. The oscillator system, constructed at Los Alamos National Laboratory, drives two tank circuits (15 kV{sub peak} potential, 8.5 kA{sub peak} maximum circulating current in each tank to date) operated 90{degree} out of phase to produce a 54 G rotating magnetic field with a frequency of 163 kHz ({omega} = 1.02{sup x} 10{sup {minus}6} s{sup {minus}1}). Programmable waveform generators control ''hot deck'' totem pole drivers that are used to control the grid of 12 Machlett 8618 magnetically beamed triode tubes. This setup allows the current to be turned on or off in less than 100 ns ({approximately}6{degree}). Both tank circuits are isolated from the current source by a 1:1 air core, transmission line transformer. Each tank circuit contains two saddle coils (combined inductance of 1.6 {micro}H) and radio frequency capacitors (580 nF). Test results are presented for three conditions: no external load, a resistive external load and a plasma load. A SPICE model of the oscillator system was created. Comparisons between this model and experimental data are given.

  16. Microturbulence studies of pulsed poloidal current drive discharges in the reversed field pinch

    NASA Astrophysics Data System (ADS)

    Carmody, D.; Pueschel, M. J.; Anderson, J. K.; Terry, P. W.

    2015-01-01

    Experimental discharges with pulsed poloidal current drive (PPCD) in the Madison Symmetric Torus reversed field pinch are investigated using a semi-analytic equilibrium model in the gyrokinetic turbulence code Gene. PPCD cases, with plasma currents of 500 kA and 200 kA, exhibit a density-gradient-driven trapped electron mode (TEM) and an ion temperature gradient mode, respectively. Relative to expectations of tokamak core plasmas, the critical gradients for the onset of these instabilities are found to be greater by roughly a factor of the aspect ratio. A significant upshift in the nonlinear TEM transport threshold, previously found for tokamaks, is confirmed in nonlinear reversed field pinch simulations and is roughly three times the threshold for linear instability. The simulated heat fluxes can be brought in agreement with measured diffusivities by introducing a small, resonant magnetic perturbation, thus modeling the residual fluctuations from tearing modes. These fluctuations significantly enhance transport.

  17. Microturbulence studies of pulsed poloidal current drive discharges in the reversed field pinch

    SciTech Connect

    Carmody, D. Pueschel, M. J.; Anderson, J. K.; Terry, P. W.

    2015-01-15

    Experimental discharges with pulsed poloidal current drive (PPCD) in the Madison Symmetric Torus reversed field pinch are investigated using a semi-analytic equilibrium model in the gyrokinetic turbulence code GENE. PPCD cases, with plasma currents of 500 kA and 200 kA, exhibit a density-gradient-driven trapped electron mode (TEM) and an ion temperature gradient mode, respectively. Relative to expectations of tokamak core plasmas, the critical gradients for the onset of these instabilities are found to be greater by roughly a factor of the aspect ratio. A significant upshift in the nonlinear TEM transport threshold, previously found for tokamaks, is confirmed in nonlinear reversed field pinch simulations and is roughly three times the threshold for linear instability. The simulated heat fluxes can be brought in agreement with measured diffusivities by introducing a small, resonant magnetic perturbation, thus modeling the residual fluctuations from tearing modes. These fluctuations significantly enhance transport.

  18. Rotating magnetic field current drive of high-temperature field reversed configurations with high {zeta} scaling

    SciTech Connect

    Guo, H. Y.; Hoffman, A. L.; Milroy, R. D.

    2007-11-15

    Greatly reduced recycling and impurity ingestion in the Translation, Confinement, and Sustainment--Upgrade (TCSU) device has allowed much higher plasma temperatures to be achieved in the field reversed configurations (FRC) under rotating magnetic field (RMF) formation and sustainment. The hotter plasmas have higher magnetic fields and much higher diamagnetic electron rotation rates so that the important ratio of average electron rotation frequency to RMF frequency, called {zeta}, approaches unity, for the first time, in TCSU. A large fraction of the RMF power is absorbed by an as yet unexplained (anomalous) mechanism directly proportional to the square of the RMF magnitude. It becomes of relatively lesser significance as the FRC current increases, and simple resistive heating begins to dominate, but the anomalous absorption is useful for initial plasma heating. Measurements of total absorbed power, and comparisons of applied RMF torque to torque on the electrons due to electron-ion friction under high-{zeta} operation, over a range of temperatures and fields, have allowed the separation of the classical Ohmic and anomalous heating to be inferred, and cross-field plasma resistivities to be calculated.

  19. SnSe2 field-effect transistors with high drive current

    NASA Astrophysics Data System (ADS)

    Su, Yang; Ebrish, Mona A.; Olson, Eric J.; Koester, Steven J.

    2013-12-01

    SnSe2 field-effect transistors fabricated using mechanical exfoliation are reported. Substrate-gated devices with source-to-drain spacing of 0.5 μm have been fabricated with drive current of 160 μA/μm at T = 300 K. The transconductance at a drain-to-source voltage of Vds = 2 V increases from 0.94 μS/μm at 300 K to 4.0 μS/μm at 4.4 K, while the field-effect mobility increases from 8.6 cm2/Vs at 300 K to 28 cm2/Vs at 77 K. The conductance at Vds = 50 mV shows an activation energy of only 5.5 meV, indicating the absence of a significant Schottky barrier at the source and drain contacts.

  20. A mechanism for the dynamo terms to sustain closed-flux current, including helicity balance, by driving current which crosses the magnetic field

    SciTech Connect

    Jarboe, T. R.; Nelson, B. A.; Sutherland, D. A.

    2015-07-15

    An analysis of imposed dynamo current drive (IDCD) [T.R. Jarboe et al., Nucl. Fusion 52 083017 (2012)] reveals: (a) current drive on closed flux surfaces seems possible without relaxation, reconnection, or other flux-surface-breaking large events; (b) the scale size of the key physics may be smaller than is often computationally resolved; (c) helicity can be sustained across closed flux; and (d) IDCD current drive is parallel to the current which crosses the magnetic field to produce the current driving force. In addition to agreeing with spheromak data, IDCD agrees with selected tokamak data.

  1. Convective Power Loss Measurements in a Field Reversed Configuration with Rotating Magnetic Field Current Drive

    NASA Astrophysics Data System (ADS)

    Melnik, Paul

    The Translation, Confinement, and Sustainment Upgrade (TCSU) experiment achieves direct formation and sustainment of a field reversed configuration (FRC) plasma through rotating magnetic fields (RMF). The pre-ionized gas necessary for FRC formation is supplied by a magnetized cascade arc source that has been developed for TCSU. To ensure ideal FRC performance, the condition of the vacuum chamber prior to RMF start-up has been characterized with the use of a fast response ion gauge. A circuit capable of gating the puff valves with initial high voltage for quick response and then indefinite operational voltage was also designed. A fully translatable combination Langmuir / Mach probe was also built to measure the electron temperature, electron density, and ion velocity of the FRC. These measurements were also successfully completed in the FRC exhaust jets allowing for an accurate analysis of the FRC power loss through convection.

  2. Current drive by helicon waves

    SciTech Connect

    Paul, Manash Kumar; Bora, Dhiraj

    2009-01-01

    Helicity in the dynamo field components of helicon wave is examined during the novel study of wave induced helicity current drive. Strong poloidal asymmetry in the wave magnetic field components is observed during helicon discharges formed in a toroidal vacuum chamber of small aspect ratio. High frequency regime is chosen to increase the phase velocity of helicon waves which in turn minimizes the resonant wave-particle interactions and enhances the contribution of the nonresonant current drive mechanisms. Owing to the strong poloidal asymmetry in the wave magnetic field structures, plasma current is driven mostly by the dynamo-electric-field, which arise due to the wave helicity injection by helicon waves. Small, yet finite contribution from the suppressed wave-particle resonance cannot be ruled out in the operational regime examined. A brief discussion on the parametric dependence of plasma current along with numerical estimations of nonresonant components is presented. A close agreement between the numerical estimation and measured plasma current magnitude is obtained during the present investigation.

  3. 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.

  4. 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.

  5. Current Drive in Recombining Plasma

    SciTech Connect

    P.F. Schmit and N.J. Fisch

    2012-05-15

    The Langevin equations describing the average collisional dynamics of suprathermal particles in nonstationary plasma remarkably admit an exact analytical solution in the case of recombining plasma. The current density produced by arbitrary particle fluxes is derived including the effect of charge recombination. Since recombination has the effect of lowering the charge density of the plasma, thus reducing the charged particle collisional frequencies, the evolution of the current density can be modified substantially compared to plasma with fixed charge density. The current drive efficiency is derived and optimized for discrete and continuous pulses of current, leading to the discovery of a nonzero "residual" current density that persists indefinitely under certain conditions, a feature not present in stationary plasmas.

  6. Dynamic modeling of lower hybrid current drive

    SciTech Connect

    Ignat, D.W.; Valeo, E.J.; Jardin, S.C.

    1993-10-01

    A computational model of lower hybrid current drive in the presence of an electric field is described and some results are given. Details of geometry, plasma profiles and circuit equations are treated carefully. Two-dimensional velocity space effects are approximated in a one-dimensional Fokker-Planck treatment.

  7. Direct drive field actuator motors

    DOEpatents

    Grahn, A.R.

    1998-03-10

    A positive-drive field actuator motor is described which includes a stator carrying at least one field actuator which changes in dimension responsive to application of an energy field, and at least one drive shoe movable by the dimensional changes of the field actuator to contact and move a rotor element with respect to the stator. Various embodiments of the motor are disclosed, and the rotor element may be moved linearly or arcuately. 62 figs.

  8. Direct drive field actuator motors

    DOEpatents

    Grahn, Allen R.

    1998-01-01

    A positive-drive field actuator motor including a stator carrying at least one field actuator which changes in dimension responsive to application of an energy field, and at least one drive shoe movable by the dimensional changes of the field actuator to contact and move a rotor element with respect to the stator. Various embodiments of the motor are disclosed, and the rotor element may be moved linearly or arcuately.

  9. Driving toroidally asymmetric current through the tokamak scrape-off layer, Part II: Magnetic field structure and spectrum

    SciTech Connect

    Joseph, I

    2009-04-08

    The structure of the magnetic field perturbations due to non-axisymmetric field-aligned currents in the tokamak scrape-off layer (SOL) are analytically calculated near the X-point. Part I [I. Joseph, et al., submitted to Phys. Plasmas (2008)] demonstrated that biasing divertor target plates in a toroidally asymmetric fashion can generate an appreciable toroidally asymmetric parallel current density in the SOL along the separatrix. Here, the magnetic field perturbation caused by a SOL current channel of finite width and step-wise constant amplitude at the target plate is derived. Flux expansion amplifies the magnetic perturbation near the X-point, while phase interference causes the SOL amplitude to be reduced at large toroidal mode number. Far enough from the current channel, the magnetic field can be approximated as arising from a surface current near the separatrix with differing amplitudes in the SOL and the divertor leg. The perturbation spectrum and resonant components of this field are computed analytically asymptotically close to the separatrix in magnetic flux coordinates. The size of the stochastic layer due to the applied perturbation that would result without self-consistent plasma shielding is also estimated. If enough resonant field is generated, control of the edge pressure gradient may allow stabilization of edge localized modes.

  10. Steady State Tokamak Equilibria without Current Drive

    SciTech Connect

    Shaing, K.C.; Aydemir, A.Y.; Lin-Liu, Y.R.; Miller, R.L.

    1997-11-01

    Steady state tokamak equilibria without current drive are found. This is made possible by including the potato bootstrap current close to the magnetic axis. Tokamaks with this class of equilibria do not need seed current or current drive, and are intrinsically steady state. {copyright} {ital 1997} {ital The American Physical Society}

  11. Oscillatory nonhmic current drive for maintaining a plasma current

    DOEpatents

    Fisch, Nathaniel J.

    1986-01-01

    Apparatus and method of the invention maintain a plasma current with an oscillatory nonohmic current drive. Each cycle of operation has a generation period in which current driving energy is applied to the plasma, and a relaxation period in which current driving energy is removed. Plasma parameters, such as plasma temperature or plasma average ionic charge state, are modified during the generation period so as to oscillate plasma resistivity in synchronism with the application of current driving energy. The invention improves overall current drive efficiencies.

  12. Oscillatory nonohomic current drive for maintaining a plasma current

    DOEpatents

    Fisch, N.J.

    1984-01-01

    Apparatus and methods are described for maintaining a plasma current with an oscillatory nonohmic current drive. Each cycle of operation has a generation period in which current driving energy is applied to the plasma, and a relaxation period in which current driving energy is removed. Plasma parameters, such as plasma temperature or plasma average ionic charge state, are modified during the generation period so as to oscillate plasma resistivity in synchronism with the application of current driving energy. The invention improves overall current drive efficiencies.

  13. Fast wave current drive in DEMO

    SciTech Connect

    Lerche, E.; Van Eestera, D.; Messiaen, A.; Collaboration: EFDA-PPPT Contributors

    2014-02-12

    The ability to non-inductively drive a large fraction of the toroidal plasma current in magnetically confined plasmas is an essential requirement for steady state fusion reactors such as DEMO. Besides neutral beam injection (NBI), electron-cyclotron resonance heating (ECRH) and lower hybrid wave heating (LH), ion-cyclotron resonance heating (ICRH) is a promising candidate to drive current, in particular at the high temperatures expected in fusion plasmas. In this paper, the current drive (CD) efficiencies calculated with coupled ICRF wave / CD numerical codes for the DEMO-1 design case (R{sub 0}=9m, B{sub 0}=6.8T, a{sub p}=2.25m) [1] are presented. It will be shown that although promising CD efficiencies can be obtained in the usual ICRF frequency domain (20-100MHz) by shifting the dominant ion-cyclotron absorption layers to the high-field side, operation at higher frequencies (100-300MHz) has a stronger CD potential, provided the parasitic RF power absorption of the alpha particles can be minimized.

  14. Lower Hybrid Heating and Current Drive

    NASA Astrophysics Data System (ADS)

    Fu, Xiangrong; Horton, Wendell; Peysson, Yves; Decker, Joan

    2012-10-01

    Lower hybrid current drive (LHCD) is the most robust and efficient method of driving the tokamak current with external radio frequency waves in steady-state tokamak operation. The electron distribution functions in the LHCD experiments contain substantial parallel thermal fluxes with radial gradients that are greater than those in the current and temperature profiles. We re-examine the growth rates of the electron temperature gradient (ETG) modes in these plasmas based on an analytic model for electron distribution function with three temperatures T, T|F, and T|B. The stability and turbulent transport is also analyzed using the electron distribution functions computed with a combined ray tracing/Fokker Planck code (DELPHINE C3P/LUKE). Electron Landau damping is reduced compared to its value in a Maxwell distribution. These potential instability drives are controlled by the magnetic sheared induced electron Landau damping that becomes strong as the fluctuations propagate into regions of large parallel wavenumber away from the mode rational surfaces. The feedback of the ETG turbulence on the propagation of the penetration of RF fields that shape the electron distribution function feeding the ETG growth rate make the problem a complex dynamical system.

  15. Electron cyclotron current drive in DIII-D

    SciTech Connect

    Luce, T.C.; Lin-Liu, Y.R.; Lohr, J.M.; Petty, C.C.; Politzer, P.A.; Prater, R.; Harvey, R.W.; Giruzzi, G.; Rice, B.W.

    1999-05-01

    Clear measurements of the localized current density driven by electron cyclotron waves have been made on the DIII-D tokamak. Direct evidence of the current drive is seen on the internal magnetic field measurements by motional Stark effect spectroscopy. Comparison with theoretical calculations in the collisionless limit shows the experimental current drive exceeds the predictions by a substantial amount for currents driven near the half radius. In all cases the experimental current density profile is broader than the predicted one.

  16. Microwave heating and current drive in tokamaks

    SciTech Connect

    Cohen, B.I.; Cohen, R.H.; Kerbel, G.D.; Logan, B.G.; Matsuda, Y.; McCoy, M.G.; Nevins, W.M.; Rognlien, T.D.; Smith, G.R.; Harvey, R.W.; Kritz, A.H.; Bonoli, P.T.; Porkolab, M.

    1988-08-23

    The use of powerful microwave sources provide unique opportunities for novel and efficient heating and current-drive schemes in the electron-cyclotron and lower-hybrid ranges of frequencies. Free- electron lasers and relativistic klystrons are new sources that have a number of technical advantages over conventional, lower-intensity sources; their use can lead to improved current-drive efficiencies and better penetration into a reactor-grade plasma in specific cases. This paper reports on modeling of absorption and current drive, in intense-pulse and quasilinear regimes, and on analysis of parametric instabilities and self-focusing. 16 refs., 2 figs.

  17. RMF concept: a rotating-magnetic-field technique for driving steady plasma currents in compact toroid devices

    SciTech Connect

    McKenna, K.F.

    1980-09-01

    The generation and/or sustaining of a Compact Toroid (CT) configuration using the RMF technique is a relatively new and unknown concept. In this report the basic principles, historical development, and current theoretical understanding of this concept are reviewed. Significant experimental and theoretical results, potential problem areas, and recommendations for the direction of future work are discussed. An illustrative analysis of the application of the RMF technique to a CT reactor is presented. The results of a recent experiment, the Rotamak, in which a Spheromak-like CT plasma was produced using the RMF technique, are presented.

  18. ITER equilibrium with bootstrap currents, lower hybrid current drive and fast wave current drive

    SciTech Connect

    Ehst, D.A.

    1989-03-01

    A current drive system is proposed for the technology phase of ITER which relies on rf power and bootstrap currents. The rf/bootstrap system permits operation at high safety factor, and we consider the axial value to be q/sub a/ approx. = 1.9, which minimizes the need for seed current near the magnetic axis. Lower hybrid power (/approximately/30 MW) provides current density near the surface, ICRF (/approximately/65 MHz, /approximately/30 MW) fast waves generate current near the axis, and high frequency fast waves (/approximately/250 MHz, /approximately/74 MW) supply the remaining current density. The system is not yet optimized but appears to offer great flexibility (ion heating for ignition, current rampup, etc.) with relatively inexpensive and well developed technology. 29 refs., 16 figs., 1 tab.

  19. Electron cyclotron current drive in DIII-D

    SciTech Connect

    Luce, T. C.; Lin-Liu, Y. R.; Harvey, R. W.; Giruzzi, G.; Lohr, J. M.; Petty, C. C.; Politzer, P. A.; Prater, R.; Rice, B. W.

    1999-09-20

    Clear measurements of the localized current density driven by electron cyclotron waves have been made on the DIII-D tokamak. Direct evidence of the current drive is seen on the internal magnetic field measurements by motional Stark effect spectroscopy. Comparison with theoretical calculations in the collisionless limit shows the experimental current drive exceeds the predictions by a substantial amount for currents driven near the half radius. In all cases the experimental current density profile is broader than the predicted one. (c) 1999 American Institute of Physics.

  20. Fast wave current drive: Experimental status and reactor prospects

    SciTech Connect

    Ehst, D.A.

    1988-03-01

    The fast wave is one of the two possible wave polarizations which propagate according to the basic theory of cold plasmas. It is distinguished from the other (slow wave) branch by having an electric field vector which is mainly orthogonal to the confining magnetic field of the plasma. The plasma and fast wave qualitatively assume different behavior depending on the frequency range of the launched wave. The high frequency fast wave (HFFW), with a frequency (..omega..2..pi.. )approximately) GHz) much higher than the ion cyclotron frequency (..cap omega../sub i/), suffers electron Landau damping and drives current by supplying parallel momentum to superthermal electrons in a fashion similar to lower hybrid (slow wave) current drive. In the simple theory the HFFW should be superior to the slow wave and can propagate to very high density and temperature without impediment. Experiments, however, have not conclusively shown that HFFW current drive can be achieved at densities above the slow wave current drive limit, possibly due to conversion of the launched fast waves into slow waves by density fluctuations. Alternatively, the low frequency fast wave (LFFW), with frequencies ()approxreverse arrowlt) 100 MHz) only a few times the ion cyclotron frequency, is damped by electron Landau damping and, in a hot plasma ()approxreverse arrowgt) 10 keV), by electron transit time magnetic pumping; current drive is achieved by pushing superthermal electrons, and efficiency is prediocted to be slightly better than for lower hybrid current drive. Most significantly, the slow wave does not propagate in high density plasma when ..omega.. )approximately) ..cap omega../sub i/, so parasitic coupling to the slow wave can be avoided, and no density and temperture limitations are foreseen. Experiments with fast wve current drive invariably find current drive efficiency as good as obtained in lower hybrid experiments at comparable, low temperatures. 45 refs., 4 figs., 1 tab

  1. Heating and current drive systems for TPX

    SciTech Connect

    Swain, D.; Goranson, P.; Halle, A. von; Bernabei, S.; Greenough, N.

    1994-05-24

    The heating and current drive (H and CD) system proposed for the TPX tokamak will consist of ion cyclotron, neutral beam, and lower hybrid systems. It will have 17.5 MW of installed H and CD power initially, and can be upgraded to 45 MW. It will be used to explore advanced confinement and fully current-driven plasma regimes with pulse lengths of up to 1,000 s.

  2. Calculation of rf current drive in tokamaks

    NASA Astrophysics Data System (ADS)

    Peysson, Y.; Decker, J.

    2008-11-01

    The toroidal plasma current is a key parameter for controlling MHD stability and fusion performances in tokamaks. Among the various methods for driving current, rf waves are a flexible and powerful tool. Therefore, their role in the design and optimization of advanced scenarios is considerable. The universal ray-tracing code C3PO coupled with the fully implicit linearized 3-D bounce-averaged relativistic electron Fokker-Planck solver LUKE is an illustration of the present day effort for performing fast and realistic calculations of the rf driven plasma current. The versatility of this tool is highlighted by simulations concerning the lower hybrid and electron cyclotron waves.

  3. Neutral Beam Current Drive in Spheromak plasma and plasma stability

    NASA Astrophysics Data System (ADS)

    Pearlstein, L. D.; Jayakumar, R. J.; Hudson, B.; Hill, D. N.; Lodestro, L. L.; McLean, H. S.; Fowler, T. K.; Casper, T. A.

    2007-11-01

    A key question for the Sustained Spheromak Physics Experiment (SSPX) is understanding how spheromaks can be sustained by other current drive tools such as neutral beam current drive. Another question is whether the present relationship between current and maximum spheromak magnetic field (plasma beta) is related to Alcator-like ohmic confinement limit or is a stability limit. Using the code CORSICA, the fraction of neutral beam current drive that can be achieved has been calculated for different injection angles with a fixed equilibrium. It is seen that relaxing the equilibrium with this drive simply drives the core safety factor to low values. Other equilibria where the NBI may give aligned current drive are being explored. Free-boundary equilibria calculations are underway to see what hyper-resistivity model gives the observed sustained SSPX performance and include that in the NBI calculations. Work performed under the auspices of the US DOE by University of California Lawrence Livermore National Laboratory under contract W-7405-ENG-48.

  4. Collisional current drive in two interpenetrating plasma jets

    SciTech Connect

    Ryutov, D. D.; Kugland, N. L.; Park, H.-S.; Pollaine, S. M.; Remington, B. A.; Ross, J. S.

    2011-10-15

    The magnetic field generation in two interpenetrating, weakly collisional plasma streams produced by intense lasers is considered. The generation mechanism is very similar to the neutral beam injection current drive in toroidal fusion devices, with the differences related to the absence of the initial magnetic field, short interaction time, and different geometry. Spatial and temporal characteristics of the magnetic field produced in two counterstreaming jets are evaluated; it is shown that the magnetic field of order of 1 T can be generated for modest jet parameters. Conditions under which this mechanism dominates that of the ''Biermann battery'' are discussed. Other settings where the mechanism of the collisional current drive can be important for the generation of seed magnetic fields include astrophysics and interiors of hohlraums.

  5. Current Sensor Fault Reconstruction for PMSM Drives

    PubMed Central

    Huang, Gang; Luo, Yi-Ping; Zhang, Chang-Fan; He, Jing; Huang, Yi-Shan

    2016-01-01

    This paper deals with a current sensor fault reconstruction algorithm for the torque closed-loop drive system of an interior PMSM. First, sensor faults are equated to actuator ones by a new introduced state variable. Then, in αβ coordinates, based on the motor model with active flux linkage, a current observer is constructed with a specific sliding mode equivalent control methodology to eliminate the effects of unknown disturbances, and the phase current sensor faults are reconstructed by means of an adaptive method. Finally, an αβ axis current fault processing module is designed based on the reconstructed value. The feasibility and effectiveness of the proposed method are verified by simulation and experimental tests on the RT-LAB platform. PMID:26840317

  6. Current Sensor Fault Reconstruction for PMSM Drives.

    PubMed

    Huang, Gang; Luo, Yi-Ping; Zhang, Chang-Fan; He, Jing; Huang, Yi-Shan

    2016-01-01

    This paper deals with a current sensor fault reconstruction algorithm for the torque closed-loop drive system of an interior PMSM. First, sensor faults are equated to actuator ones by a new introduced state variable. Then, in αβ coordinates, based on the motor model with active flux linkage, a current observer is constructed with a specific sliding mode equivalent control methodology to eliminate the effects of unknown disturbances, and the phase current sensor faults are reconstructed by means of an adaptive method. Finally, an αβ axis current fault processing module is designed based on the reconstructed value. The feasibility and effectiveness of the proposed method are verified by simulation and experimental tests on the RT-LAB platform. PMID:26840317

  7. 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

  8. Direct-drive field actuator motors

    DOEpatents

    Grahn, Allen R.

    1995-01-01

    A high-torque, low speed, positive-drive field actuator motor including a stator carrying at least one field actuator which changes in dimension responsive to application of an energy field, and at least one drive shoe movable by the dimensional changes of the field actuator to contact and move a rotor element with respect to the stator. Various embodiments of the motor are disclosed, and the rotor element may be moved linearly or arcuately.

  9. Direct-drive field actuator motors

    DOEpatents

    Grahn, A.R.

    1995-07-11

    A high-torque, low speed, positive-drive field actuator motor is disclosed including a stator carrying at least one field actuator which changes in dimension responsive to application of an energy field, and at least one drive shoe movable by the dimensional changes of the field actuator to contact and move a rotor element with respect to the stator. Various embodiments of the motor are disclosed, and the rotor element may be moved linearly or arcuately. 37 figs.

  10. Current drive experiments in the Helicity Injected Torus - II

    NASA Astrophysics Data System (ADS)

    Hamp, W. T.; Redd, A. J.; Jarboe, T. R.; Nelson, B. A.; O'Neill, R. G.; Raman, R.; Sieck, P. E.; Smith, R. J.; Mueller, D.

    2006-10-01

    The HIT-II spherical torus (ST) device has demonstrated four toroidal plasma current drive configurations to form and sustain a tokamak: 1) inductive (ohmic) current drive, 2) coaxial helicity injection (CHI) current drive, 3) CHI initiated plasmas with ohmic sustainment (CHI+OH), and 4) ohmically initiated plasmas with CHI edge current drive (OH+ECD). CHI discharges with a sufficiently high ratio of injector current to toroidal field current form a closed flux core, and amplify the injector poloidal flux through magnetic reconnection. CHI+OH plasmas are more robust than unassisted ohmic discharges, with a wider operating space and more efficient use of the transformer Volt-seconds. Finally, edge CHI can enhance the plasma current of an ohmic discharge without significantly degrading the quality of the discharge. Results will be presented for each HIT-II operating regime, including empirical performance scalings, applicable parametric operating spaces, and requirements to produce these discharges. Thomson scattering measurements and EFIT simulations are used to evaluate confinement in several representative plasmas. Finally, we outline extensions to the HIT-II CHI studies that could be performed with NSTX, SUNIST, or other ST devices.

  11. Theory of current-drive in plasmas

    SciTech Connect

    Fisch, N.J.

    1986-12-01

    The continuous operation of a tokamak fusion reactor requires, among other things, a means of providing continuous toroidal current. Such operation is preferred to the conventional pulsed operation, where the plasma current is induced by a time-varying magnetic field. A variety of methods has been proposed to provide continuous current, including methods which utilize particle beams or radio frequency waves in any of several frequency regimes. Currents as large as half a mega-amp have now been produced in the laboratory by such means, and experimentation in these techniques has now involved major tokamak facilities worldwide.

  12. Electric machine and current source inverter drive system

    DOEpatents

    Hsu, John S

    2014-06-24

    A drive system includes an electric machine and a current source inverter (CSI). This integration of an electric machine and an inverter uses the machine's field excitation coil for not only flux generation in the machine but also for the CSI inductor. This integration of the two technologies, namely the U machine motor and the CSI, opens a new chapter for the component function integration instead of the traditional integration by simply placing separate machine and inverter components in the same housing. Elimination of the CSI inductor adds to the CSI volumetric reduction of the capacitors and the elimination of PMs for the motor further improve the drive system cost, weight, and volume.

  13. Numerical Modeling of HHFW Heating and Current Drive on NSTX

    NASA Astrophysics Data System (ADS)

    Phillips, C. K.; Bell, R. E.; Hosea, J. C.; Leblanc, B. P.; Taylor, G.; Valeo, E. J.; Wilson, J. R.; Berry, L. A.; Jaeger, E. F.; Ryan, P. M.; Wilgen, J. B.; Bonoli, P. T.; Wright, J. C.; Harvey, R. W.; Yuh, H. Y.

    2008-11-01

    High harmonic fast wave (HHFW) heating and current drive, at frequencies up to 15 times the fundamental deuterium cyclotron frequency, are being studied on NSTX. Recent experiments indicate that the core heating efficiency depends strongly on the antenna phasing and plasma conditions [1], and improves significantly at higher toroidal magnetic fields. Wave propagation, absorption and current drive characteristics for L-mode and H-mode NSTX discharges have been analyzed using both ray tracing and full wave models. Simulations obtained with the AORSA and TORIC full codes agree reasonably well with Motional Stark Effect measurements of the driven current, and indicate the importance of trapping effects on the driven current profile. Collisional damping effects on the wave absorption, particularly in edge regions, will be considered. [1] J. C. Hosea, et al, Phys. Plasmas 15, 056104 (2008).

  14. TOKAMAK EQUILIBRIA WITH CENTRAL CURRENT HOLES AND NEGATIVE CURRENT DRIVE

    SciTech Connect

    CHU, M.S.; PARKS, P.B.

    2002-06-01

    OAK B202 TOKAMAK EQUILIBRIA WITH CENTRAL CURRENT HOLES AND NEGATIVE CURRENT DRIVE. Several tokamak experiments have reported the development of a central region with vanishing currents (the current hole). Straightforward application of results from the work of Greene, Johnson and Weimer [Phys. Fluids, 3, 67 (1971)] on tokamak equilibrium to these plasmas leads to apparent singularities in several physical quantities including the Shafranov shift and casts doubts on the existence of this type of equilibria. In this paper, the above quoted equilibrium theory is re-examined and extended to include equilibria with a current hole. It is shown that singularities can be circumvented and that equilibria with a central current hole do satisfy the magnetohydrodynamic equilibrium condition with regular behavior for all the physical quantities and do not lead to infinitely large Shafranov shifts. Isolated equilibria with negative current in the central region could exist. But equilibria with negative currents in general do not have neighboring equilibria and thus cannot have experimental realization, i.e. no negative currents can be driven in the central region.

  15. Mode conversion heating and current drive experiments in TFTR

    SciTech Connect

    Majeski, R.; Rogers, J.H.; Batha, S.H.; Budny, R.; Fredrickson, E.; Grek, B.; Hill, K.; Hosea, J.C.; LeBlanc, B.; Levinton, F.; Murakami, M.; Phillips, C.K.; Ramsey, A.T.; Schilling, G.; Taylor, G.; Wilson, J.R.; Zarnstorff, M.C.

    1996-01-01

    The first experimental demonstration that mode conversion from the fast magnetosonic wave to an ion Bernstein wave can efficiently heat electrons and drive current with low field side antennas in a tokamak plasma is reported. Up to 130 kA of current was noninductively driven, on and off axis, and the resultant current profiles were measured in the Tokamak Fusion Test Reactor. In heating experiments, 10 keV peak electron temperatures were produced with 3.3 MW of radio-frequency heating power. {copyright} {ital 1996 The American Physical Society.}

  16. MHD simulation of RF current drive in MST

    SciTech Connect

    Hendries, E. R.; Anderson, J. K.; Forest, C. B.; Reusch, J. A.; Seltzman, A. H.; Sovinec, C. R.; Diem, S.; Harvey, R. W.

    2014-02-12

    Auxiliary heating and current drive using RF waves such as the electron Bernstein wave (EBW) promises to advance the performance of the reversed field pinch (RFP). In previous computational work [1], a hypothetical edge-localized current drive is shown to suppress the tearing activity which governs the macroscopic transport properties of the RFP. The ideal conditions for tearing stabilization include a reduced toroidal induction, and precise width and radial position of the Gaussian-shaped external current drive. In support of the EBW experiment on the Madison Symmetric Torus, an integrated modeling scheme now incorporates ray tracing and Fokker-Plank predictions of auxiliary current into single fluid MHD. Simulations at low Lundquist number (S ∼ 10{sup 4}) generally agree with the previous work; significantly more burdensome simulations at MST-like Lundquist number (S ∼ 3×10{sup 6}) show unexpected results. The effect on nonlinearly saturated current profile by a particular RF-driven external force decreases in magnitude and widens considerably as the Lundquist number increases toward experimental values. Simulations reproduce the periodic current profile relaxation events observed in experiment (sawteeth) in the absence of current profile control. Reduction of the tearing mode amplitudes is still observable; however, reduction is limited to periods between the large bursts of magnetic activity at each sawtooth. The sawtoothing pattern persists with up to 10 MW of externally applied RF power. Periods with prolonged low tearing amplitude are predicted with a combination of external current drive and a reduced toroidal loop voltage, consistent with previous conclusions. Finally, the resistivity profile is observed to have a strong effect on the optimal externally driven current profile for mode stabilization.

  17. Radiofrequency current source (RFCS) drive and decoupling technique for parallel transmit arrays using a high-power metal oxide semiconductor field-effect transistor (MOSFET).

    PubMed

    Lee, Wonje; Boskamp, Eddy; Grist, Thomas; Kurpad, Krishna

    2009-07-01

    A radiofrequency current source (RFCS) design using a high-power metal oxide semiconductor field effect transistor (MOSFET) that enables independent current control for parallel transmit applications is presented. The design of an RFCS integrated with a series tuned transmitting loop and its associated control circuitry is described. The current source is operated in a gated class AB push-pull configuration for linear operation at high efficiency. The pulsed RF current amplitude driven into the low impedance transmitting loop was found to be relatively insensitive to the various loaded loop impedances ranging from 0.4 to 10.3 ohms, confirming current mode operation. The suppression of current induced by a neighboring loop was quantified as a function of center-to-center loop distance, and was measured to be 17 dB for nonoverlapping, adjacent loops. Deterministic manipulation of the B(1) field pattern was demonstrated by the independent control of RF phase and amplitude in a head-sized two-channel volume transmit array. It was found that a high-voltage rated RF power MOSFET with a minimum load resistance, exhibits current source behavior, which aids in transmit array design. PMID:19353658

  18. Electron cyclotron current drive experiments on DIII-D

    SciTech Connect

    James, R.A. ); Giruzzi, G.; Gentile, B. de; Rodriguez, L. ); Fyaretdinov, A.; Gorelov, Yu.; Trukhin, V. ); Harvey, R.; Lohr, J.; Luce, T.C.; Matsuda, K.; Politzer, P.; Prater, R.; Snider, R. (General Atomics, San Di

    1990-05-01

    Electron Cyclotron Current Drive (ECCD) experiments on the DIII-D tokamak have been performed using 60 GHz waves launched from the high field side of the torus. Preliminary analysis indicates rf driven currents between 50 and 100 kA in discharges with total plasma currents between 200 and 500 kA. These are the first ECCD experiments with strong first pass absorption, localized deposition of the rf power, and {tau}{sub E} much longer than the slowing-down time of the rf generated current carriers. The experimentally measured profiles for T{sub e}, {eta}{sub e} and Z{sub eff} are used as input for a 1D transport code and a multiply-ray, 3D ray tracing code. Comparisons with theory and assessment of the influence of the residual electric field, using a Fokker-Planck code, are in progress. The ECH power levels were between 1 and 1.5 MW with pulse lengths of about 500 msec. ECCD experiments worldwide are motivated by issues relating to the physics and technical advantages of the use of high frequency rf waves to drive localized currents. ECCD is accomplished by preferentially heating electrons moving in one toroidal direction, reducing their collisionality and thereby producing a non-inductively driven toroidal current. 6 refs., 4 figs.

  19. An Imposed Dynamo Current Drive Experiment: Demonstration of Confinement

    NASA Astrophysics Data System (ADS)

    Jarboe, Thomas; Hansen, Chris; Hossack, Aaron; Marklin, George; Morgan, Kyle; Nelson, Brian; Sutherland, Derek; Victor, Brian

    2014-10-01

    An experiment for studying and developing the efficient sustainment of a spheromak with sufficient confinement (current-drive power heats the plasma to its stability β-limit) and in the keV temperature range is discussed. A high- β spheromak sustained by imposed dynamo current drive (IDCD) is justified because: previous transient experiments showed sufficient confinement in the keV range with no external toroidal field coil; recent results on HIT-SI show sustainment with sufficient confinement at low temperature; the potential of IDCD of solving other fusion issues; a very attractive reactor concept; and the general need for efficient current drive in magnetic fusion. The design of a 0.55 m minor radius machine with the required density control, wall loading, and neutral shielding for a 2 s pulse is presented. Peak temperatures of 1 keV and toroidal currents of 1.35 MA and 16% wall-normalized plasma beta are envisioned. The experiment is large enough to address the key issues yet small enough for rapid modification and for extended MHD modeling of startup and code validation.

  20. On Current Drive and Wave Induced Bootstrap Current in Toroidal Plasmas

    SciTech Connect

    Hellsten, T.; Johnson, T.

    2008-11-01

    A comprehensive treatment of wave-particle interactions in toroidal plasmas including collisional relaxation, applicable to heating or anomalous wave induced transport, has been obtained by using Monte Carlo operators satisfying quasi-neutrality. This approach enables a self-consistent treatment of wave-particle interactions applicable to the banana regime in the neoclassical theory. It allows an extension into a regime with large temperature and density gradients, losses and transport of particles by wave-particle interactions making the method applicable to transport barriers. It is found that at large gradients the relationship between radial electric field, parallel velocity, temperature and density gradient in the neoclassical theory is modified such that coefficient in front of the logarithmic ion temperature gradient, which in the standard neoclassical theory is small and counteracts the electric field caused by the density gradient, now changes sign and contributes to the built up of the radial electric field. The possibility to drive current by absorbing the waves on trapped particles has been studied and how the wave-particle interactions affect the bootstrap current. Two new current drive mechanisms are studied: current drive by wave induced bootstrap current and selective detrapping into passing orbits by directed waves.

  1. Penetration of lower hybrid current drive waves in tokamaks

    SciTech Connect

    Horton, W.; Goniche, M.; Peysson, Y.; Decker, J.; Ekedahl, A.; Litaudon, X.

    2013-11-15

    Lower hybrid (LH) ray propagation in toroidal plasma is shown to be controlled by combination of the azimuthal spectrum launched by the antenna, the poloidal variation of the magnetic field, and the scattering of the waves by the drift wave fluctuations. The width of the poloidal and radial radio frequency wave spectrum increases rapidly as the rays penetrate into higher density and scatter from the drift waves. The electron temperature gradient (ETG) spectrum is particularly effective in scattering the LH waves due to its comparable wavelengths and phase velocities. ETG turbulence is also driven by the radial gradient of the electron current profile giving rise to an anomalous viscosity spreading the LH driven plasma currents. The LH wave scattering is derived from a Fokker-Planck equation for the distribution of the ray trajectories with diffusivities derived from the drift wave fluctuations. The condition for chaotic diffusion for the rays is derived. The evolution of the poloidal and radial mode number spectrum of the lower hybrid waves are both on the antenna spectrum and the spectrum of the drift waves. Antennas launching higher poloidal mode number spectra drive off-axis current density profiles producing negative central shear [RS] plasmas with improved thermal confinement from ETG transport. Core plasma current drive requires antennas with low azimuthal mode spectra peaked at m = 0 azimuthal mode numbers.

  2. Review of Japanese results on heating and current drive

    NASA Astrophysics Data System (ADS)

    Watari, T.

    1992-10-01

    This article discusses Japanese contributions in the fields of plasma heating and current drive and, together with other reviews presented at this conference, will serve as a reference for future investigations. The Japanese fusion community has several tokamaks: JAERI (STA) has JT-60 and JFT-2M. TRIAM-1M (Kyushu University), WT-3 (Kyoto University), and JIPP T-2 U (National Institute for Fusion Science (NIFS)) belong to the Ministry of Education (MOE). A lot of contributions were made by these devices in heating and current drive in the various frequency ranges: electron cyclotron (EC) frequency range, lower hybrid (LH) frequency range, and ion cyclotron (IC) frequency range. This paper only deals with tokamak results: results on LHCD are described in section 1; ECH is described in section 2; results of high power ICRF heating are given in section 3; IBWH is described in section 4; and finally, FWCD is covered in section 5. Because the Matrix of different machine and different frequency range gives an intractable list of results, sampling will be made in describing the progress, i.e., JT-60 for LHCD, WT-3 for ECH/CD, JIPP T-2 U for IBWH, and JT-60 for higher harmonic ICRF heating. Special attention is given to the investigation of fast wave current drive which has some history in Japan. Results from JIPP T-2 U, JFT-2M, HT-2, and JT-60 are summarized. Aside from the tokamak, MOE has an alternative magnetic fusion program centered around CHS and HELIOTORON-E (Kyoto University). The LHD (Large Helical Device) is a machine under construction in the new site of NIFS. Gamma-10 (Tsukuba University) and HIEI (Kyoto University) are tandem mirror type open end systems. Due to the allotted space, works in this field will not be covered in this review. It should also be noted that there are a lot of contributions in theory which continued to support experiments very strongly through this decade.

  3. Requirements for neutral beam current drive in tokamaks

    SciTech Connect

    Dory, R.A.

    1988-01-01

    This paper contains viewgraphs on the use of neutral beam current drive in future tokamaks. Current profiles, slowing down distributions, beam destabilization of alfven waves and plasma parameters are some items covered in this paper. (DWL)

  4. Electron cyclotron current drive and current profile control in the DIII-D tokamak

    SciTech Connect

    Prater, R.; Luce, T.C.; Petty, C.C.

    1998-07-01

    Recent work in many tokamaks has indicated that optimization of the current profile is a key element needed to sustain modes of improved confinement and stability. Generation of localized current through application of electron cyclotron (EC) waves offers a means of accomplishing this. In addition to profile control, electron cyclotron current drive (ECCD) is useful for sustaining the bulk current in a steady state manner and for instability suppression. ECCD is particularly well suited for control of the current profile because the location of the driven current can be regulated by external means, through steering of the incident EC waves and setting the magnitude of the toroidal magnetic field. Under most conditions the location of the driven current is insensitive to the plasma parameters. Central ECCD has been studied in a number of tokamaks and found to have characteristics commensurate with theory as expressed through ray tracing and Fokker-Planck computer codes. The present experiments on DIII-D explore central current drive and are the first to test off-axis ECCD. These experiments are unique in using internal measurements of the magnetic field to determine the magnitude and profile of driven current.

  5. High frequency fast wave current drive for DEMO

    SciTech Connect

    Koch, R.; Lerche, E.; Van Eester, D.

    2011-12-23

    A steady-state tokamak reactor (SSTR) requires a high efficiency current drive system, from plug to driven mega-amps. RF systems working in the ion-cyclotron range of frequencies (ICRF) have high efficiency from plug to antenna but a limited current drive (CD) efficiency and centrally peaked CD profiles. The latter feature is not adequate for a SSTR where the current should be sufficiently broad to keep the central safety factor (possibly significantly) above 1. In addition, the fact that the fast wave (FW) is evanescent at the edge limits coupling, requiring high voltage operation, which makes the system dependent on plasma edge properties and prone to arcing, reducing its reliability. A possible way to overcome these weaknesses is to operate at higher frequency (10 times or more the cyclotron frequency). The advantages are: (1) The coupling can be much better (waves propagate in vacuum) if the parallel refractive index n{sub ||} is kept below one, (2) The FW group velocity tends to align to the magnetic field, so the power circumnavigates the magnetic axis and can drive off-axis current, (3) Due to the latter property, n{sub ||} can be upshifted along the wave propagation path, allowing low n{sub ||} launch (hence good coupling, large CD efficiency) with ultimately good electron absorption (which requires higher n{sub ||}. Note however that the n{sub ||} upshift is a self-organized feature, that electron absorption is in competition with {alpha}-particle absorption and that uncoupling of the FW from the lower hybrid resonance at the edge requires n{sub ||} slightly above one. The latter possibly counterproductive features might complicate the picture. The different aspects of this potentially attractive off-axis FWCD scheme are discussed.

  6. Electron heating and current drive by mode converted slow waves

    SciTech Connect

    Majeski, R.; Phillips, C.K.; Wilson, J.R.

    1994-08-01

    An approach to obtaining efficient single pass mode conversion at high parallel wavenumber from the fast magnetosonic wave to the slow ion Bernstein wave, in a two ion species tokamak plasma, is described. The intent is to produce localized electron heating or current drive via the mode converted slow wave. In particular, this technique can be adapted to off-axis current drive for current profile control. Modelling for the case of deuterium-tritium plasmas in TFTR is presented.

  7. Sensorless optimal sinusoidal brushless direct current for hard disk drives

    NASA Astrophysics Data System (ADS)

    Soh, C. S.; Bi, C.

    2009-04-01

    Initiated by the availability of digital signal processors and emergence of new applications, market demands for permanent magnet synchronous motors have been surging. As its back-emf is sinusoidal, the drive current should also be sinusoidal for reducing the torque ripple. However, in applications like hard disk drives, brushless direct current (BLDC) drive is adopted instead of sinusoidal drive for simplification. The adoption, however, comes at the expense of increased harmonics, losses, torque pulsations, and acoustics. In this paper, we propose a sensorless optimal sinusoidal BLDC drive. First and foremost, the derivation for an optimal sinusoidal drive is presented, and a power angle control scheme is proposed to achieve an optimal sinusoidal BLDC. The scheme maintains linear relationship between the motor speed and drive voltage. In an attempt to execute the sensorless drive, an innovative power angle measurement scheme is devised, which takes advantage of the freewheeling diodes and measures the power angle through the detection of diode voltage drops. The objectives as laid out will be presented and discussed in this paper, supported by derivations, simulations, and experimental results. The proposed scheme is straightforward, brings about the benefits of sensorless sinusoidal drive, negates the need for current sensors by utilizing the freewheeling diodes, and does not incur additional cost.

  8. Optimized calculation of the synergy conditions between electron cyclotron current drive and lower hybrid current drive on EAST

    NASA Astrophysics Data System (ADS)

    Wei, Wei; Bo-Jiang, Ding; Y, Peysson; J, Decker; Miao-Hui, Li; Xin-Jun, Zhang; Xiao-Jie, Wang; Lei, Zhang

    2016-01-01

    The optimized synergy conditions between electron cyclotron current drive (ECCD) and lower hybrid current drive (LHCD) with normal parameters of the EAST tokamak are studied by using the C3PO/LUKE code based on the understanding of the synergy mechanisms so as to obtain a higher synergistic current and provide theoretical reference for the synergistic effect in the EAST experiment. The dependences of the synergistic effect on the parameters of two waves (lower hybrid wave (LHW) and electron cyclotron wave (ECW)), including the radial position of the power deposition, the power value of the LH and EC waves, and the parallel refractive indices of the LHW (N∥) are presented and discussed. Project supported by the National Magnetic Confinement Fusion Science Program of China (Grant Nos. 2011GB102000, 2012GB103000, and 2013GB106001), the National Natural Science Foundation of China (Grant Nos. 11175206 and 11305211), the JSPS-NRF-NSFC A3 Foresight Program in the Field of Plasma Physics (Grant No. 11261140328), and the Fundamental Research Funds for the Central Universities of China (Grant No. JZ2015HGBZ0472).

  9. Co-counter asymmetry in fast wave heating and current drive

    SciTech Connect

    Jaeger, E.F.; Carter, M.D.; Berry, L.A.; Batchelor, D.B.; Forest, C.B.; Weitzner, H.

    1997-04-01

    Full wave ICRF coupling models show differences in plasma response when antenna arrays are phase to drive currents and counter to the plasma current. The source of this difference lies in the natural up- sown asymmetry of the antenna`s radiated power spectrum. This asymmetry is due to Hall terms in the wave equation, and occurs even without a poloidal magnetic field. When a poloidal field is included, the up-down asymmetry acquires a toroidal component. The result is that plasma absorption (i.e. antenna loading) is shifted or skewed toward the co-current drive direction, independent of the direction of the magnetic field. When wave are launched to drive current counter the plasma current , electron heating an current profiles are more peaked on axis, and this peaking becomes more pronounce a lower toroidal magnetic fields.

  10. Observation of Lower-Hybrid Current Drive at High Densities in the Alcator C Tokamak

    NASA Astrophysics Data System (ADS)

    Porkolab, M.; Schuss, J. J.; Lloyd, B.; Takase, Y.; Texter, S.; Bonoli, P.; Fiore, C.; Gandy, R.; Gwinn, D.; Lipschultz, B.; Marmar, E.; Pappas, D.; Parker, R.; Pribyl, P.

    1984-07-01

    A quasi-steady-state lower-hybrid current-drive operation is demonstrated in the Alcator C tokamak at densities up to n―e~=1×1014 cm-3. The current-drive efficiency is measured experimentally over a wide range of densities and magnetic fields. The radial distribution of high-energy x rays indicates that the current-carrying electrons peak near the plasma axis.

  11. Plasma heating and current drive using intense, pulsed microwaves

    SciTech Connect

    Cohen, B.I.; Cohen, R.H.; Nevins, W.M.; Rognlien, T.D.; Bonoli, P.T.; Porkolab, M.

    1988-01-01

    The use of powerful new microwave sources, e.g., free-electron lasers and relativistic gyrotrons, provide unique opportunities for novel heating and current-drive schemes in the electron-cyclotron and lower-hybrid ranges of frequencies. These high-power, pulsed sources have a number of technical advantages over conventional, low-intensity sources; and their use can lead to improved current-drive efficiencies and better penetration into a reactor-grade plasma in specific cases. The Microwave Tokamak Experiment at Lawrence Livermore National Laboratory will provide a test for some of these new heating and current-drive schemes. This paper reports theoretical progress both in modeling absorption and current drive for intense pulses and in analyzing some of the possible complications that may arise, e.g., parametric instabilities and nonlinear self-focusing. 22 refs., 9 figs., 1 tab.

  12. Fast Wave Current Drive in JET ITB-Plasma

    SciTech Connect

    Hellsten, T.; Laxaaback, M.; Bergkvist, T.; Johnson, T.; Brzozowski, J.; Rachlew, E.; Tennfors, E.; Mantsinen, M.; Matthews, G.; Tala, T.; Meo, F.; Nguyen, F.; Eriksson, L.-G.; Joffrin, E.; Noterdaeme, J.-M.; Petty, C.C.; Eester, D. van

    2005-09-26

    Fast wave current drive has been performed in JET plasmas with internal transport barriers, ITBs, and strongly reversed magnetic shear. Although the current drive efficiency of the power absorbed on the electrons is fairly high, only small effects are seen in the central current density. The main reasons are the parasitic absorption of RF power, the strongly inductive nature of the plasma and the interplay between the fast wave driven current and bootstrap current. The direct electron heating in the FWCD experiments is found to be strongly degraded compared to that with the dipole phasing.

  13. Key Aspects of EBW Heating and Current Drive in Tokamaks

    NASA Astrophysics Data System (ADS)

    Urban, Jakub; Decker, Joan; Preinhaelter, Josef; Taylor, Gary; Vahala, Linda; Vahala, George

    2010-11-01

    Electron Bernstein wave (EBW) heating and current drive is modeled by coupled mode conversion, ray-tracing (AMR) and Fokker-Planck (LUKE) codes. Deposition and current drive profiles are determined for EBW with various injection parameters under realistic spherical tokamak conditions. There parameters are varied to investigate the robustness of the applied scenarios. The importance of relativistic corrections to EBW absorption is considered. The differences between various relativistic models are explored.

  14. Decoherence suppression in a resonant driving field

    NASA Astrophysics Data System (ADS)

    Minns, R. S.; Kutteruf, M. R.; Commisso, M. A.; Jones, R. R.

    2008-04-01

    Resonant radio frequency (rf) control fields have been employed to suppress decoherence in single quantum bits (qubits) encoded in the probability amplitudes of np fine-structure states in Li Rydberg atoms. As described previously [1], static electric-field tuning of the spin and orbital angular momentum composition of the fine-structure eigenstates enables qubit storage in an approximate decoherence-free subspace in which phase errors due to small stray electric and magnetic fields are strongly suppressed. In addition, it was found that sequences of short electric field pulses could be utilized in a 'bang-bang' dynamic decoupling scheme to improve coherence times. We now show that a continuous resonant rf field can also suppress decoherence in this system. The rf-dressed fine-structure states form a more robust basis in which the energy splitting between the component qubit levels is locked to the drive frequency, and decoherence is essentially eliminated. Measurements of the operational range of rf frequency and field strength required to achieve decoherence suppression are in agreement with the predictions of a two-level model.

  15. General Linear Rf-Current Drive Calculation in Toroidal Plasma

    NASA Astrophysics Data System (ADS)

    Smirnov, A. P.; Harvey, R. W.; Prater, R.

    2009-04-01

    A new general linear calculation of RF current drive has been implemented in the GENRAY all-frequencies RF ray tracing code. This is referred to as the ADJ-QL package, and is based on the Karney, et al. [1] relativistic Green function calculator, ADJ, generalized to non-circular plasmas in toroidal geometry, and coupled with full, bounce-averaged momentum-space RF quasilinear flux [2] expressions calculated at each point along the RF ray trajectories. This approach includes momentum conservation, polarization effects and the influence of trapped electrons. It is assumed that the electron distribution function remains close to a relativistic Maxwellian function. Within the bounds of these assumptions, small banana width, toroidal geometry and low collisionality, the calculation is applicable for all-frequencies RF electron current drive including electron cyclotron, lower hybrid, fast waves and electron Bernstein waves. GENRAY ADJ-QL calculations of the relativistic momentum-conserving current drive have been applied in several cases: benchmarking of electron cyclotron current drive in ITER against other code results; and electron Bernstein and high harmonic fast wave current drive in NSTX. The impacts of momentum conservation on the current drive are also shown for these cases.

  16. Controlling Casimir force via coherent driving field

    NASA Astrophysics Data System (ADS)

    Ahmad, Rashid; Abbas, Muqaddar; Ahmad, Iftikhar; Qamar, Sajid

    2016-04-01

    A four level atom-field configuration is used to investigate the coherent control of Casimir force between two identical plates made up of chiral atomic media and separated by vacuum of width d. The electromagnetic chirality-induced negative refraction is obtained via atomic coherence. The behavior of Casimir force is investigated using Casimir-Lifshitz formula. It is noticed that Casimir force can be switched from repulsive to attractive and vice versa via coherent control of the driving field. This switching feature provides new possibilities of using the repulsive Casimir force in the development of new emerging technologies, such as, micro-electro-mechanical and nano-electro-mechanical systems, i.e., MEMS and NEMS, respectively.

  17. Analysis of current driving capability of pentacene TFTs for OLEDs

    NASA Astrophysics Data System (ADS)

    Ryu, Gi Seong; Byun, Hyun Sook; Xu, Yong Xian; Pyo, Kyung Soo; Choe, Ki Beom; Song, Chung Kun

    2005-01-01

    The flexible display and the application of Roll-To-Roll process is difficult because high temperature process of a-Si;H TFT and poly-Si TFT limited the use of plastic substrate. We proposed AMOLED using Pentacene TFT (OTFT) to fabricate flexible display. The first stage for OTFT application to OLED, we analyzed OTFT as driving device of OLED. The process performed on glass and plastic (PET) substrate that is coated ITO and PVP is used for gate insulator. The field effect mobility of the fabricated OTFT is 0.1~0.3cm2/V"sec and Ion/Ioff current ratio is 103~105. OLED is fabricated with two stories structure of TPD and Alq3, and we can observe the light at 5V by the naked eye. The wavelength of observed lights is 530nm ~550nm. We can confirm the driving of OLED due to OTFT using Test panel and observe OLED control by gate voltage of OTFT. Also, we verify designed structure and process, and make a demonstration fabricating 64 by 64 backplane based on Test panel.

  18. Magnetospheric electric fields and currents

    NASA Technical Reports Server (NTRS)

    Mauk, B. H.; Zanetti, L. J.

    1987-01-01

    The progress made in the years 1983-1986 in understanding the character and operation of magnetospheric electric fields and electric currents is discussed, with emphasis placed on the connection with the interior regions. Special attention is given to determinations of global electric-field configurations, measurements of the response of magnetospheric particle populations to the electric-field configurations, and observations of the magnetospheric currents at high altitude and during northward IMF. Global simulations of current distributions are discussed, and the sources of global electric fields and currents are examined. The topics discussed in the area of impulsive and small-scale phenomena include substorm current systems, impulsive electric fields and associated currents, and field-aligned electrodynamics. A key finding of these studies is that the electric fields and currents are interrelated and cannot be viewed as separate entities.

  19. Fast electron transport in lower-hybrid current drive

    SciTech Connect

    Kupfer, K.; Bers, A.

    1991-01-01

    We generalize the quasilinear-Fokker-Planck formulation for lower-hybrid current drive to include the wave induced radial transport of fast electrons. Toroidal ray tracing shows that the wave fields in the plasma develop a large poloidal component associated with the upshift in k1l and the filling of the "spectral gap". These fields lead to an enhanced radial E x B drift of resonant electrons. Two types of radial flows are obtained: an outward convective flow driven by the asymmetry in the poloidal wave spectrum, and a diffusive flow proportional to the width of the poloidal spectrum. Simulations of Alcator C and JT60, show that the radial convection velocity has a broad maximum of nearly 1 m/sec and is independent of the amplitude of fields. In both cases, the radial diffusion is found to be highly localized near the magnetic axis. For JT60, the peak of the diffusion profile can be quite large, nearly 1 m2/sec.

  20. A thermodynamical analysis of rf current drive with fast electrons

    NASA Astrophysics Data System (ADS)

    Bizarro, João P. S.

    2015-08-01

    The problem of rf current drive (CD) by pushing fast electrons with high-parallel-phase-velocity waves, such as lower-hybrid (LH) or electron-cyclotron (EC) waves, is revisited using the first and second laws, the former to retrieve the well-known one-dimensional (1D) steady-state CD efficiency, and the latter to calculate a lower bound for the rate of entropy production when approaching steady state. The laws of thermodynamics are written in a form that explicitly takes care of frictional dissipation and are thus applied to a population of fast electrons evolving under the influence of a dc electric field, rf waves, and collisions while in contact with a thermal, Maxwellian reservoir with a well-defined temperature. Besides the laws of macroscopic thermodynamics, there is recourse to basic elements of kinetic theory only, being assumed a residual dc electric field and a strong rf drive, capable of sustaining in the resonant region, where waves interact with electrons, a raised fast-electron tail distribution, which becomes an essentially flat plateau in the case of the 1D theory for LHCD. Within the 1D model, particularly suited for LHCD as it solely retains fast-electron dynamics in velocity space parallel to the ambient magnetic field, an H theorem for rf CD is also derived, which is written in different forms, and additional physics is recovered, such as the synergy between the dc and rf power sources, including the rf-induced hot conductivity, as well as the equation for electron-bulk heating. As much as possible 1D results are extended to 2D, to account for ECCD by also considering fast-electron velocity-space dynamics in the direction perpendicular to the magnetic field, which leads to a detailed discussion on how the definition of an rf-induced conductivity may depend on whether one works at constant rf current or power. Moreover, working out the collisional dissipated power and entropy-production rate written in terms of the fast-electron distribution, it

  1. A thermodynamical analysis of rf current drive with fast electrons

    SciTech Connect

    Bizarro, João P. S.

    2015-08-15

    The problem of rf current drive (CD) by pushing fast electrons with high-parallel-phase-velocity waves, such as lower-hybrid (LH) or electron-cyclotron (EC) waves, is revisited using the first and second laws, the former to retrieve the well-known one-dimensional (1D) steady-state CD efficiency, and the latter to calculate a lower bound for the rate of entropy production when approaching steady state. The laws of thermodynamics are written in a form that explicitly takes care of frictional dissipation and are thus applied to a population of fast electrons evolving under the influence of a dc electric field, rf waves, and collisions while in contact with a thermal, Maxwellian reservoir with a well-defined temperature. Besides the laws of macroscopic thermodynamics, there is recourse to basic elements of kinetic theory only, being assumed a residual dc electric field and a strong rf drive, capable of sustaining in the resonant region, where waves interact with electrons, a raised fast-electron tail distribution, which becomes an essentially flat plateau in the case of the 1D theory for LHCD. Within the 1D model, particularly suited for LHCD as it solely retains fast-electron dynamics in velocity space parallel to the ambient magnetic field, an H theorem for rf CD is also derived, which is written in different forms, and additional physics is recovered, such as the synergy between the dc and rf power sources, including the rf-induced hot conductivity, as well as the equation for electron-bulk heating. As much as possible 1D results are extended to 2D, to account for ECCD by also considering fast-electron velocity-space dynamics in the direction perpendicular to the magnetic field, which leads to a detailed discussion on how the definition of an rf-induced conductivity may depend on whether one works at constant rf current or power. Moreover, working out the collisional dissipated power and entropy-production rate written in terms of the fast-electron distribution, it

  2. Calculations of lower hybrid current drive in ITER

    NASA Astrophysics Data System (ADS)

    Decker, J.; Peysson, Y.; Hillairet, J.; Artaud, J.-F.; Basiuk, V.; Becoulet, A.; Ekedahl, A.; Goniche, M.; Hoang, G. T.; Imbeaux, F.; Ram, A. K.; Schneider, M.

    2011-07-01

    A detailed study of lower hybrid current drive (LHCD) in ITER is provided, focusing on the wave propagation and current drive mechanisms. A combination of ray-tracing and Fokker-Planck calculations are presented for various plasma scenarios, wave frequency and polarization. The dependence of the driven current and the location of power deposition upon the coupled wave spectrum is systematically determined, in order to set objectives for the antenna design. The respective effects of finite-power levels, magnetic trapping, and detailed antenna spectra are accounted for and quantitatively estimated. The sensitivity of LHCD to density and temperature profiles is calculated. From the simulation results, an optimum value for the parallel index of refraction is proposed as a compromise between efficiency and robustness with respect to those profile variations. The corresponding current drive efficiency is found to be similar for the two frequencies generally considered for ITER, f = 3.7 GHz and f = 5.0 GHz.

  3. Fast wave current drive in DIII-D

    SciTech Connect

    Petty, C.C.; Callis, R.W.; Chiu, S.C.; deGrassie, J.S.; Forest, C.B.; Freeman, R.L.; Gohil, P.; Harvey, R.W.; Ikezi, H.; Lin-Liu, Y.-R.

    1995-02-01

    The non-inductive current drive from fast Alfven waves launched by a directional four-element antenna was measured in the DIII-D tokamak. The fast wave frequency (60 MHz) was eight times the deuterium cyclotron frequency at the plasma center. An array of rf pickup loops at several locations around the torus was used to verify the directivity of the four-element antenna. Complete non-inductive current drive was achieved using a combination of fast wave current drive (FWCD) and electron cyclotron current drive (ECCD) in discharges for which the total plasma current was inductively ramped down from 400 to 170 kA. For discharges with steady plasma current, up to 110 kA of FWCD was inferred from an analysis of the loop voltage, with a maximum non-inductive current (FWCD, ECCD, and bootstrap) of 195 out of 310 kA. The FWCD efficiency increased linearly with central electron temperature. For low current discharges, the FWCD efficiency was degraded due to incomplete fast wave damping. The experimental FWCD was found to agree with predictions from the CURRAY ray-tracing code only when a parasitic loss of 4% per pass was included in the modeling along with multiple pass damping.

  4. Electron Cyclotron Current Drive by Radial Transport of Particles in the Continuous Current Tokamak

    NASA Astrophysics Data System (ADS)

    Park, Sanghyun

    In the Continuous Current Tokamak at the UCLA, electron cyclotron current drive (ECCD) experiments have been conducted in the absence of ohmic heating or any other power input. With X-band source of 30 kW lasting 1 mS launched from the high field side in X-mode, 240 A of plasma current has been generated at the neutral pressure corresponding to the critical density for the wave frequency. The Spitzer resistivity calculated from the L/R decay time of the current yielded an electron temperature of 100 eV. For the interest of mapping out radial profiles of wave and particle parameters, S-band sources at 2.45 GHz, 1.5 kW lasting 8 mS with duty cycle of 50% have been used for quasi-steady state current drive experiments. There are four launching structures; (1) Inside perpendicular, (2) Outside perpendicular, (3) Outside 60^circ, and (4) Outside -60^circ with respect to the toroidal magnetic field. It has been found that the four ways of microwaves give comparable results in plasma current driven. The plasma current measurements as a function of the radial location of the electron cyclotron resonance layer show a I_{rm p}~ -sin(pi r/a) where R_{res} = R_{0} + r for -a >=q r >=q O. The vertical field dependence has been shown to be I_{rm p}~ -x exp(-x^2) where x is a normalized vertical field for -inftycurrent is reversed as the applied vertical field is reversed for all four launch schemes. As a toroidal electric field is applied, the co(counter)-injection with cos^{-1}( k_0 cdot B_{t}) = +(-)60^circ give the same result in plasma current driven. The energy distribution of the current carrying electrons as determined by the biased, two-side Langmuir probe show that the current is carried by the bulk of the plasma electrons whose energy is comparable to the plasma electron temperature, and not by the high energy tail of the distribution as predicted by theories based on the Fokker-Planck equation. The vertical and toroidal field

  5. Fokker-Planck modeling of current penetration during electron cyclotron current drive

    SciTech Connect

    Merkulov, A.; Westerhof, E.; Schueller, F. C.

    2007-05-15

    The current penetration during electron cyclotron current drive (ECCD) on the resistive time scale is studied with a Fokker-Planck simulation, which includes a model for the magnetic diffusion that determines the parallel electric field evolution. The existence of the synergy between the inductive electric field and EC driven current complicates the process of the current penetration and invalidates the standard method of calculation in which Ohm's law is simply approximated by j-j{sub cd}={sigma}E. Here it is proposed to obtain at every time step a self-consistent approximation to the plasma resistivity from the Fokker-Planck code, which is then used in a concurrent calculation of the magnetic diffusion equation in order to obtain the inductive electric field at the next time step. A series of Fokker-Planck calculations including a self-consistent evolution of the inductive electric field has been performed. Both the ECCD power and the electron density have been varied, thus varying the well known nonlinearity parameter for ECCD P{sub rf}[MW/m{sup -3}]/n{sub e}{sup 2}[10{sup 19} m{sup -3}] [R. W. Harvey et al., Phys. Rev. Lett 62, 426 (1989)]. This parameter turns out also to be a good predictor of the synergetic effects. The results are then compared with the standard method of calculations of the current penetration using a transport code. At low values of the Harvey parameter, the standard method is in quantitative agreement with Fokker-Planck calculations. However, at high values of the Harvey parameter, synergy between ECCD and E{sub parallel} is found. In the case of cocurrent drive, this synergy leads to the generation of large amounts of nonthermal electrons and a concomitant increase of the electrical conductivity and current penetration time. In the case of countercurrent drive, the ECCD efficiency is suppressed by the synergy with E{sub parallel} while only a small amount of nonthermal electrons is produced.

  6. Currents and electric fields in the ionosphere due to field-aligned auroral currents

    NASA Technical Reports Server (NTRS)

    Nisbet, J. S.; Miller, M. J.; Carpenter, L. A.

    1978-01-01

    Birkeland (1908, 1913) did a detailed analysis of the upper atmospheric current system in the high-latitude region, and suggested that field-aligned currents flowing into and out of the auroral ionosphere were the driving mechanism for this current system. In the present paper, static electric field and current patterns due to the field-aligned Birkeland currents are examined, using a model in which currents approximating those reported by Iijima and Potemra (1976) are used as input to a global model of the ionospheric conductivities, in which interhemispheric coupling along field lines is included. The model reproduces the main features of the high-latitude current and voltage system and the penetration of these currents within the plasmasphere.

  7. Electron cyclotron current drive efficiency in general tokamak geometry

    SciTech Connect

    Lin-Liu, Y. R.; Chan, V. S.; Prater, R.

    2003-01-01

    Green's-function techniques are used to calculate electron cyclotron current drive (ECCD) efficiency in general tokamak geometry in the low-collisionality regime. Fully relativistic electron dynamics is employed in the theoretical formulation. The high-velocity collision model is used to model Coulomb collisions and a simplified quasi-linear rf diffusion operator describes wave-particle interactions. The approximate analytic solutions which are benchmarked with a widely used ECCD model, facilitate time-dependent simulations of tokamak operational scenarios using the non-inductive current drive of electron cyclotron waves.

  8. Numerical modeling of lower hybrid heating and current drive

    SciTech Connect

    Valeo, E.J.; Eder, D.C.

    1986-03-01

    The generation of currents in toroidal plasma by application of waves in the lower hybrid frequency range involves the interplay of several physical phenomena which include: wave propagation in toroidal geometry, absorption via wave-particle resonances, the quasilinear generation of strongly nonequilibrium electron and ion distribution functions, and the self-consistent evolution of the current density in such a nonequilibrium plasma. We describe a code, LHMOD, which we have developed to treat these aspects of current drive and heating in tokamaks. We present results obtained by applying the code to a computation of current ramp-up and to an investigation of the possible importance of minority hydrogen absorption in a deuterium plasma as the ''density limit'' to current drive is approached.

  9. Simulations of EBW current drive and power deposition in the WEGA Stellarator

    SciTech Connect

    Preinhaelter, J.; Urban, J.; Vahala, L.; Vahala, G.

    2009-11-26

    The WEGA stellarator is well suited for fundamental electron Bernstein wave (EBW) studies. Heating and current drive experiments at 2.45 GHz and 28 GHz, carried out in WEGA's low temperature, steady state overdense plasmas, were supported by intensive modelling. We employ our AMR (Antenna-Mode-conversion-Ray-tracing) code to calculate the O-X-EBW conversion efficiency with a full-wave equation solver, while the power deposition and current drive profiles using ray tracing. Several phenomena have been studied and understood. Particularly, EBW current drive was theoretically predicted and experimentally detected at 2.45 GHz. Simulations confirmed the presence of two (cold and hot) electron components and the resonant behaviour of the EBW power deposition and its dependence on the magnetic field configuration. Furthermore, the code is used to predict the 28 GHz heating and current drive performance and to simulate EBW emission spectra.

  10. 53. Drive shaft, motors, eddie currents, brakes, and differential gears ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    53. Drive shaft, motors, eddie currents, brakes, and differential gears in south machinery room (interior of both machinery rooms is identical). Facing east. - Henry Ford Bridge, Spanning Cerritos Channel, Los Angeles-Long Beach Harbor, Los Angeles, Los Angeles County, CA

  11. Flux averaged current drive efficiency of electron Bernstein waves

    NASA Astrophysics Data System (ADS)

    McGregor, D. E.; Cairns, R. A.; Lashmore Davies, C. N.; O'Brien, M. R.

    2008-01-01

    Electron Bernstein waves are of interest for heating and current drive in spherical tokamaks where the central region of the plasma is not accessible to the ordinary and extraordinary modes. In this paper we adapt an analytical theory of current drive in toroidal geometry developed by Lin-Liu et al (2003 Phys. Plasmas 10 4064) to this system. This involves taking account of the fact that the ratio of the Larmor radius to the perpendicular wavelength is not, in general, small for the Bernstein waves and also including the effects of a non-circular plasma cross section. By comparing the results with those of a full Fokker-Planck code, we demonstrate that the analytical method can yield a good approximation to the current drive efficiency in most regimes of practical interest. Since it is much less computationally demanding than using a Fokker-Planck code we suggest that it could be a useful tool for analysing experiments on Bernstein mode current drive in spherical tokamaks.

  12. Alternating-Current Motor Drive for Electric Vehicles

    NASA Technical Reports Server (NTRS)

    Krauthamer, S.; Rippel, W. E.

    1982-01-01

    New electric drive controls speed of a polyphase as motor by varying frequency of inverter output. Closed-loop current-sensing circuit automatically adjusts frequency of voltage-controlled oscillator that controls inverter frequency, to limit starting and accelerating surges. Efficient inverter and ac motor would give electric vehicles extra miles per battery charge.

  13. The Effects of Dextromethorphan on Driving Performance and the Standardized Field Sobriety Test.

    PubMed

    Perry, Paul J; Fredriksen, Kristian; Chew, Stephanie; Ip, Eric J; Lopes, Ingrid; Doroudgar, Shadi; Thomas, Kelan

    2015-09-01

    Dextromethorphan (DXM) is abused most commonly among adolescents as a recreational drug to generate a dissociative experience. The objective of the study was to assess driving with and without DXM ingestion. The effects of one-time maximum daily doses of DXM 120 mg versus a guaifenesin 400 mg dose were compared among 40 healthy subjects using a crossover design. Subjects' ability to drive was assessed by their performance in a driving simulator (STISIM® Drive driving simulator software) and by conducting a standardized field sobriety test (SFST) administered 1-h postdrug administration. The one-time dose of DXM 120 mg did not demonstrate driving impairment on the STISIM® Drive driving simulator or increase SFST failures compared to guaifenesin 400 mg. Doses greater than the currently recommended maximum daily dose of 120 mg are necessary to perturb driving behavior. PMID:26294136

  14. The current status of the psychoanalytic theory of instinctual drives. I: Drive concept, classification, and development.

    PubMed

    Compton, A

    1983-07-01

    The evolution of Freud's theory of instinctual drives, with the accompanying models of a mental apparatus, is remarkable for its tenacious adherence to addressing the fundamental problems of human psychology, here phrased as the problems of body-mind-environment relationships. The concept of instinctual drives continues to be one of the most pervasive concepts of psychoanalysis, weathering considerable attack over the last several decades, although losing some clarity in the process. I have cited and discussed as basic issues of the concept of instinctual drives: the relationship of observational data and theoretical constructs in psychology; whether our construct of drives is or should be or can be purely psychological; the problem of conceptualizing the ontogenetic origin of mind; the issues of the "force-meaning conjunction" and the problem of psychic energy in psychoanalytic constructs; and the relation of our concept of instinctual drives to the concept of instincts in general. It seems that progress with these fundamental issues might be made by utilizing models that are more homologous with present knowledge in related fields than is Freud's reflex arc model of the nervous system, in order to build a better drive construct within the framework of psychoanalysis. The classification of instinctual drives remains a problem. Clinically, aggression seems to be a factor in conflict, very much like sexuality. Despite widespread acceptance of the idea of aggression as simply parallel to sexuality in all respects, there are major discrepancies. Perhaps aggression cannot be viewed as a drive after all; perhaps our drive construct needs to be modified to accommodate aggression. Certainly, controversy in this area has interfered with the production of good clinical studies which could begin to increase our understanding of aggression and its place in the human personality. The psychoanalytic theory of drive development has probably undergone less change in the last

  15. Modeling of high harmonic fast wave current drive on EAST tokamak

    SciTech Connect

    Li, J. C.; Gong, X. Y. Li, F. Y.; Dong, J. Q.; Gao, Q. D.; Zhang, N.

    2015-10-15

    High harmonic fast waves (HHFW) are among the candidates for non-inductive current drive (CD), which is essential for long-pulse or steady-state operation of tokamaks. Current driven with HHFW in EAST tokamak plasmas is numerically studied. The HHFW CD efficiency is found to increase non-monotonically with the wave frequency, and this phenomenon is attributed to the multi-pass absorption of HHFW. The sensitivity of CD efficiency to the value of the parallel refraction index of the launched wave is confirmed. The quasilinear effects, assessed as significant in HHFW current drive with the GENRAY/CQL3D package, cause a significant increase in CD efficiency as RF power is increased, which is very different from helicon current drive. Simulations for a range of toroidal dc electric fields, in combination with a range of fast wave powers, are also presented and indicate that the presence of the DC field can also enhance the CD efficiency.

  16. Modeling of high harmonic fast wave current drive on EAST tokamak

    NASA Astrophysics Data System (ADS)

    Li, J. C.; Gong, X. Y.; Dong, J. Q.; Gao, Q. D.; Zhang, N.; Li, F. Y.

    2015-10-01

    High harmonic fast waves (HHFW) are among the candidates for non-inductive current drive (CD), which is essential for long-pulse or steady-state operation of tokamaks. Current driven with HHFW in EAST tokamak plasmas is numerically studied. The HHFW CD efficiency is found to increase non-monotonically with the wave frequency, and this phenomenon is attributed to the multi-pass absorption of HHFW. The sensitivity of CD efficiency to the value of the parallel refraction index of the launched wave is confirmed. The quasilinear effects, assessed as significant in HHFW current drive with the GENRAY/CQL3D package, cause a significant increase in CD efficiency as RF power is increased, which is very different from helicon current drive. Simulations for a range of toroidal dc electric fields, in combination with a range of fast wave powers, are also presented and indicate that the presence of the DC field can also enhance the CD efficiency.

  17. Modification of the Current Profile in DIII-D by Off-Axis Electron Cyclotron Current Drive

    SciTech Connect

    Luce, T.C.; Lin-Liu, Y.R.; Harvey, R.W.; Giruzzi, G.; Lohr, J.M.; Petty, C.C.; Politzer, P.A.; Prater, R.; Rice, B.W.

    1999-07-01

    Localized non-inductive currents due to electron cyclotron wave absorption have been measured on the DIII-D tokamak. Clear evidence of the non-inductive currents is seen on the internal magnetic field measurements by motional Stark effect spectroscopy. The magnitude and location of the non-inductive current is evaluated by comparing the total and Ohmic current profiles of discharges with and without electron cyclotron wave power. The measured current agrees with Fokker-Planck calculations near the magnetic axis, but exceeds the predicted value as the location of the current drive is moved to the half radius.

  18. Current drive at plasma densities required for thermonuclear reactors.

    PubMed

    Cesario, R; Amicucci, L; Cardinali, A; Castaldo, C; Marinucci, M; Panaccione, L; Santini, F; Tudisco, O; Apicella, M L; Calabrò, G; Cianfarani, C; Frigione, D; Galli, A; Mazzitelli, G; Mazzotta, C; Pericoli, V; Schettini, G; Tuccillo, A A

    2010-01-01

    Progress in thermonuclear fusion energy research based on deuterium plasmas magnetically confined in toroidal tokamak devices requires the development of efficient current drive methods. Previous experiments have shown that plasma current can be driven effectively by externally launched radio frequency power coupled to lower hybrid plasma waves. However, at the high plasma densities required for fusion power plants, the coupled radio frequency power does not penetrate into the plasma core, possibly because of strong wave interactions with the plasma edge. Here we show experiments performed on FTU (Frascati Tokamak Upgrade) based on theoretical predictions that nonlinear interactions diminish when the peripheral plasma electron temperature is high, allowing significant wave penetration at high density. The results show that the coupled radio frequency power can penetrate into high-density plasmas due to weaker plasma edge effects, thus extending the effective range of lower hybrid current drive towards the domain relevant for fusion reactors. PMID:20975718

  19. Current-Drive Efficiency in a Degenerate Plasma

    SciTech Connect

    S. Son and N.J. Fisch

    2005-11-01

    a degenerate plasma, the rates of electron processes are much smaller than the classical model would predict, affecting the efficiencies of current generation by external non-inductive means, such as by electromagnetic radiation or intense ion beams. For electron-based mechanisms, the current-drive efficiency is higher than the classical prediction by more than a factor of 6 in a degenerate hydrogen plasma, mainly because the electron-electron collisions do not quickly slow down fast electrons. Moreover, electrons much faster than thermal speeds are more readily excited without exciting thermal electrons. In ion-based mechanisms of current drive, the efficiency is likewise enhanced due to the degeneracy effects, since the electron stopping power on slow ion beams is significantly reduced.

  20. PHYSICS OF ELCTRON CYCLOTRON CURRENT DRIVE ON DIII-D

    SciTech Connect

    PETTY,CC; PRATER,R; LUCE,TC; ELLIS,RA; HARVEY,RW; KINSEY,JE; LAO,LL; LOHR,J; MAKOWSKI,MA

    2002-09-01

    OAK A271 PHYSICS OF ELCTRON CYCLOTRON CURRENT DRIVE ON DIII-D. Recent experiments on the DIII-D tokamak have focused on determining the effect of trapped particles on the electron cyclotron current drive (ECCD) efficiency. The measured ECCD efficiency increases as the deposition location is moved towards the inboard midplane or towards smaller minor radius for both co and counter injection. The measured ECCD efficiency also increases with increasing electron density and/or temperature. The experimental ECCD is compared to both the linear theory (Toray-GA) as well as a quasilinear Fokker-Planck model (CQL3D). The experimental ECCD is found to be in better agreement with the more complete Fokker-Planck calculation, especially for cases of high rf power density and/or loop voltage. The narrow width of the measured ECCD profile is consistent with only low levels of radial transport for the current carrying electrons.

  1. Measurement of helicon wave coupling for current drive and anticipated role for high beta KSTAR plasmas

    NASA Astrophysics Data System (ADS)

    Wang, S. J.; Kim, H. J.; Joung, M.; Jeong, J. H.; Kim, J. H.; Bae, Y. S.; Kwak, J. G.; Wi, H. H.; Kim, H.-S.

    2015-11-01

    Helicon wave current drive has been suggested for efficient off-axis current drive in high electron beta tokamak plasmas. Fast wave drives centrally peaking current in the frequency range up to several ion cyclotron harmonics in the present tokamaks, such as KSTAR. Increasing fast wave frequency up to LH resonance frequency at the plasma edge, the spiral propagation of wave at the outer region of plasma lengthens the wave path to the plasma center. Also, optical thickness increases with frequency. It is expected that these effects produce efficient off-axis power deposition depending on the electron beta and magnetic field pitch. A low power TWA for helicon wave was installed and tested in KSTAR tokamak which is aiming for the steady-state high beta plasma requiring off-axis current drive. The power coupling properties of TWA at various plasma conditions will be presented. In addition to the coupling efficiency, issues such as load sensitivity and unwanted slow wave coupling will be addressed. Also, the simulation of plasma performance with the combination of helicon wave current drive and other conventional heating and current drive power in KSTAR will be discussed. This work was supported by the Korean Ministry of Science, ICT and Future Planning and by R&D Program through the National Fusion Research Institute of Korea (NFRI) funded by the Government funds.

  2. Fivefold confinement time increase in the Madison Symmetric Torus using inductive poloidal current drive

    SciTech Connect

    Stoneking, M.R.; Lanier, N.E.; Prager, S.C.; Sarff, J.S.; Sinitsyn, D.

    1996-12-01

    Current profile control is employed in the Madison Symmetric Torus reversed field pinch to reduce the magnetic fluctuations responsible for anomalous transport. An inductive poloidal electric field pulse is applied in the sense to flatten the parallel current profile, reducing the dynamo fluctuation amplitude required to sustain the equilibrium. This technique demonstrates a substantial reduction in fluctuation amplitude (as much as 50%), and improvement in energy confinement (from 1 ms to 5 ms); a record low fluctuation (0.8%) and record high temperature (615 eV) for this device were observed simultaneously during current drive experiments. Plasma beta increases by 50% and the Ohmic input power is three times lower. Particle confinement improves and plasma impurity contamination is reduced. The results of the transient current drive experiments provide motivation for continuing development of steady-state current profile control strategies for the reversed field pinch.

  3. PHYSICS OF ELECTRON CYCLOTRON CURRENT DRIVE ON DIII-D

    SciTech Connect

    PETTY,CC; PRATER,R; LUCE,TC; ELLIS,RA; HARVEY,RW; KINSEY,JE; LAO,LL; LOHR,J; MAKOWSKI,MA

    2002-11-01

    OAK A271 PHYSICS OF ELECTRON CYCLOTRON CURRENT DRIVE ON DIII-D. Recent experiments on the DIII-D tokamak have focused on determining the effect of trapped particles on the electron cyclotron current drive (ECCD) efficiency. The measured ECCD efficiency increases as the deposition location is moved towards the inboard midplane or towards smaller minor radius for both co and counter injection. The measured ECCD efficiency also increases with increasing electron density and/or temperature. The experimental ECCD is compared to both the linear theory (Toray-GA) as well as a quasilinear Fokker-Planck model (CQL3D). The experimental ECCD is found to be in better agreement with the more complete Fokker-Planck calculation, especially for cases of high rf power density and/or loop voltage.

  4. Lower hybrid current drive favoured by electron cyclotron radiofrequency heating

    SciTech Connect

    Cesario, R.; Cardinali, A.; Castaldo, C.; Marinucci, M.; Tuccillo, A. A.; Giruzzi, G.; Napoli, F.; Schettini, G.

    2014-02-12

    The important goal of adding to the bootstrap a fraction of non-inductive plasma current, which would be controlled for obtaining and optimizing steady-state profiles, can be reached by using the Current Drive produced by Lower Hybrid waves (LHCD). FTU (Frascati Tokamak Upgrade) experiments demonstrated, indeed, that LHCD is effective at reactor-graded high plasma density, and the LH spectral broadening is reduced, operating with higher electron temperature in the outer region of plasma column (T{sub e-periphery}). This method was obtained following the guidelines of theoretical predictions indicating that the broadening of launched spectrum produced by parametric instability (PI) should be reduced, and the LHCD effect at high density consequently enabled, under higher (T{sub e-periphery}). In FTU, the temperature increase in the outer plasma region was obtained by operating with reduced particle recycling, lithized walls and deep gas fuelling by means of fast pellet. Heating plasma periphery with electron cyclotron resonant waves (ECRH) will provide a further tool for achieving steady-state operations. New FTU experimental results are presented here, demonstrating that temperature effect at the plasma periphery, affecting LH penetration, occurs in a range of plasma parameters broader than in previous work. New information is also shown on the modelling assessing frequencies and growth rates of the PI coupled modes responsible of spectral broadening. Finally, we present the design of an experiment scheduled on FTU next campaign, where ECRH power is used to slightly increase the electron temperature in the outer plasma region of a high-density discharge aiming at restoring LHCD. Consequent to model results, by operating with a toroidal magnetic field of 6.3 T, useful for locating the electron cyclotron resonant layer at the periphery of the plasma column (r/a∼0.8, f{sub 0}=144 GHz), an increase of T{sub e} in the outer plasma (from 40 eV to 80 eV at r/a∼0.8) is

  5. Current drive for stability of thermonuclear plasma reactor

    NASA Astrophysics Data System (ADS)

    Amicucci, L.; Cardinali, A.; Castaldo, C.; Cesario, R.; Galli, A.; Panaccione, L.; Paoletti, F.; Schettini, G.; Spigler, R.; Tuccillo, A.

    2016-01-01

    To produce in a thermonuclear fusion reactor based on the tokamak concept a sufficiently high fusion gain together stability necessary for operations represent a major challenge, which depends on the capability of driving non-inductive current in the hydrogen plasma. This request should be satisfied by radio-frequency (RF) power suitable for producing the lower hybrid current drive (LHCD) effect, recently demonstrated successfully occurring also at reactor-graded high plasma densities. An LHCD-based tool should be in principle capable of tailoring the plasma current density in the outer radial half of plasma column, where other methods are much less effective, in order to ensure operations in the presence of unpredictably changes of the plasma pressure profiles. In the presence of too high electron temperatures even at the periphery of the plasma column, as envisaged in DEMO reactor, the penetration of the coupled RF power into the plasma core was believed for long time problematic and, only recently, numerical modelling results based on standard plasma wave theory, have shown that this problem should be solved by using suitable parameter of the antenna power spectrum. We show here further information on the new understanding of the RF power deposition profile dependence on antenna parameters, which supports the conclusion that current can be actively driven over a broad layer of the outer radial half of plasma column, thus enabling current profile control necessary for the stability of a reactor.

  6. Overview of recent results on Heating and Current Drive in JET

    SciTech Connect

    Ongena, J.; Durodie, F.; Lerche, E.; Eester, D. van; Vrancken, M.; Baranov, Yu.; Challis, C. D.; Jacquet, Ph.; Jenkins, I.; Kiptily, V.; Kirov, K.; Mailloux, J.; Mayoral, M. L.; Monakhov, I.; Nightingale, M.; Walden, A.; Bobkov, V.; Lennholm, M.; Colas, L.; Ekedahl, A.

    2007-09-28

    Recent progress on heating and current drive on JET is reported. Topics discussed are: high power coupling of ICRF/LH at ITER relevant antenna/launcher-separatrix distances, succesfull demonstration of 3 dB couplers for ELM tolerance of the ICRF system, influence of ICRF on LH operation, rotation studies in plasma without external momentum with standard and enhanced JET toriodal field ripple, studies of different ICRF heating schemes and of NTM avoidance schemes using Ion Cyclotron Current Drive. A brief outlook on future plans for experiments at JET is given.

  7. Effects of MHD instabilities on neutral beam current drive

    SciTech Connect

    Podestà, M.; Gorelenkova, M.; Darrow, D. S.; Fredrickson, E. D.; Gerhardt, S. P.; White, R. B.

    2015-04-17

    One of the primary tools foreseen for heating, current drive (CD) and q-profile control in future fusion reactors such as ITER and a Fusion Nuclear Science Facility is the neutral beam injection (NBI). However, fast ions from NBI may also provide the drive for energetic particle-driven instabilities (e.g. Alfvénic modes (AEs)), which in turn redistribute fast ions in both space and energy, thus hampering the control capabilities and overall efficiency of NB-driven current. Based on experiments on the NSTX tokamak (M. Ono et al 2000 Nucl. Fusion 40 557), the effects of AEs and other low-frequency magneto-hydrodynamic instabilities on NB-CD efficiency are investigated. When looking at the new fast ion transport model, which accounts for particle transport in phase space as required for resonant AE perturbations, is utilized to obtain consistent simulations of NB-CD through the tokamak transport code TRANSP. It is found that instabilities do indeed reduce the NB-driven current density over most of the plasma radius by up to ~50%. Moreover, the details of the current profile evolution are sensitive to the specific model used to mimic the interaction between NB ions and instabilities. Finally, implications for fast ion transport modeling in integrated tokamak simulations are briefly discussed.

  8. Effects of MHD instabilities on neutral beam current drive

    DOE PAGESBeta

    Podestà, M.; Gorelenkova, M.; Darrow, D. S.; Fredrickson, E. D.; Gerhardt, S. P.; White, R. B.

    2015-04-17

    One of the primary tools foreseen for heating, current drive (CD) and q-profile control in future fusion reactors such as ITER and a Fusion Nuclear Science Facility is the neutral beam injection (NBI). However, fast ions from NBI may also provide the drive for energetic particle-driven instabilities (e.g. Alfvénic modes (AEs)), which in turn redistribute fast ions in both space and energy, thus hampering the control capabilities and overall efficiency of NB-driven current. Based on experiments on the NSTX tokamak (M. Ono et al 2000 Nucl. Fusion 40 557), the effects of AEs and other low-frequency magneto-hydrodynamic instabilities on NB-CDmore » efficiency are investigated. When looking at the new fast ion transport model, which accounts for particle transport in phase space as required for resonant AE perturbations, is utilized to obtain consistent simulations of NB-CD through the tokamak transport code TRANSP. It is found that instabilities do indeed reduce the NB-driven current density over most of the plasma radius by up to ~50%. Moreover, the details of the current profile evolution are sensitive to the specific model used to mimic the interaction between NB ions and instabilities. Finally, implications for fast ion transport modeling in integrated tokamak simulations are briefly discussed.« less

  9. An anomalous current drive mechanism in low collisionality plasmas

    NASA Astrophysics Data System (ADS)

    McDevitt, Chris; Tang, Xianzhu; Guo, Zehua

    2013-10-01

    Steady state tokamak operation requires non-inductive current drive, of which the neoclassical bootstrap current is the most economic option. Here we report a novel mechanism through which a bootstrap current may be driven even in a collisionless plasma. In analogy with the neoclassical mechanism, in which the collisional equilibrium established between trapped and passing electrons produces a steady state current, we show that resonant scattering of electrons by drift wave microturbulence provides an additional means of determining the equilibrium between trapped and passing electrons. The resulting collisionless equilibrium is shown to produce a mean current whose magnitude scales with the thermodynamic forces. Employing a linearized Fokker-Planck collision operator, the plasma current in the presence of both collisions and resonant electron scattering is computed as a function of collisionality. It is found that while the volume integrated electron current is only modestly affected by the turbulent fluctuations, the radial distribution of electron current is significantly modified in low collisionality plasmas. This work was supported by DOE OFES.

  10. Remote field eddy current inspection

    SciTech Connect

    Atherton, D.L.

    1995-11-01

    The Remote Field Eddy Current (RFEC) technique uses an internal probe to inspect conducting tubes nondestructively. A coaxial solenoidal exciter, energized with low frequency AC, and detector coils near the inside of the pipe wall are separated by about two pipe diameters to obtain through wall transmission and equal sensitivity to defects on the outside or inside of the pipe wall. Calculation methods are outlined and the voltage plane polar plot signal representation for defect measurement is described. Slit defect interactions in ferromagnetic and non-ferromagnetic tubes are discussed. Defect-induced anomalous fields are interpreted in terms of anomalous source eddy current and missing magnetization defect models. The use of computer animations to represent the time variations of high resolution field measurements and calculations is described.

  11. Fluid equations in the presence of electron cyclotron current drive

    SciTech Connect

    Jenkins, Thomas G.; Kruger, Scott E.

    2012-12-15

    Two-fluid equations, which include the physics imparted by an externally applied radiofrequency source near electron cyclotron resonance, are derived in their extended magnetohydrodynamic forms using the formalism of Hegna and Callen [Phys. Plasmas 16, 112501 (2009)]. The equations are compatible with the closed fluid/drift-kinetic model developed by Ramos [Phys. Plasmas 17, 082502 (2010); 18, 102506 (2011)] for fusion-relevant regimes with low collisionality and slow dynamics, and they facilitate the development of advanced computational models for electron cyclotron current drive-induced suppression of neoclassical tearing modes.

  12. Lower hybrid heating and current drive on PLT

    SciTech Connect

    Stevens, J.E.; Bernabei, S.; Bitter, M.

    1983-03-01

    800 MHz lower hybrid waves have been launched into PLT with a six waveguide coupler. Recent improvements have allowed powers up to 400 kW to be launched with good coupling (R approx. 10 to 25%). Experiments at low density (anti n/sub e/ < 7 x 10/sup 12/ cm/sup -3/, i.e., ..omega../..omega../sub LH/ > 2) have demonstrated current drive and plasma heating. Experiments at higher densities have produced hot-ion tails, but so far have shown inefficient body heating. To date, only a limited parameters space has been investigated at high power.

  13. FLANDERS FIELDS MEMORIAL IN TRAFFIC ISLAND ON EAST DRIVE. VIEW ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    FLANDERS FIELDS MEMORIAL IN TRAFFIC ISLAND ON EAST DRIVE. VIEW TO NORTHEAST. - Rock Island National Cemetery, Rock Island Arsenal, 0.25 mile north of southern tip of Rock Island, Rock Island, Rock Island County, IL

  14. Driving magnetic skyrmions with microwave fields

    NASA Astrophysics Data System (ADS)

    Wang, Weiwei; Beg, Marijan; Zhang, Bin; Kuch, Wolfgang; Fangohr, Hans

    2015-07-01

    We show theoretically by numerically solving the Landau-Lifshitz-Gilbert equation with a classical spin model on a two-dimensional system that both magnetic skyrmions and skyrmion lattices can be moved with microwave magnetic fields. The mechanism is enabled by breaking the axial symmetry of the skyrmion, for example, through application of a static in-plane external field. The net velocity of the skyrmion depends on the frequency and amplitude of the microwave fields as well as the strength of the in-plane field. The maximum velocity is found where the frequency of the microwave coincides with the resonance frequency of the breathing mode of the skyrmions.

  15. Current drive with fast waves, electron cyclotron waves, and neutral injection in the DIII-D tokamak

    SciTech Connect

    Prater, R.; Petty, C.C.; Pinsker, R.I.; Chiu, S.C.; deGrassie, J.S.; Harvey, R.W.; Ikel, H.; Lin-Liu, Y.R.; Luce, T.C. ); James, R.A. ); Porkolab, M. ); Baity, F.W.; Goulding, R.H.; Hoffmann, D.J. ); Kawash

    1992-09-01

    Current drive experiments have been performed on the DIII-D tokamak using fast waves, electron cyclotron waves, and neutral injection. Fast wave experiments were performed using a 4-strap antenna with 1 MW of power at 60 MHz. These experiments showed effective heating of electrons, with a global heating efficiency equivalent to that of neutral injection even when the single pass damping was calculated to be as small as 5%. The damping was probably due to the effect of multiple passes of the wave through the plasma. Fast wave current drive experiments were performed with a toroidally directional phasing of the antenna straps. Currents driven by fast wave current drive (FWCD) in the direction of the main plasma current of up to 100 kA were found, not including a calculated 40 kA of bootstrap current. Experiments with FWCD in the counter current direction showed little current drive. In both cases, changes in the sawtooth behavior and the internal inductance qualitatively support the measurement of FWCD. Experiments on electron cyclotron current drive have shown that 100 kA of current can be driven by 1 MW of power at 60 GHz. Calculations with a Fokker-Planck code show that electron cyclotron current drive (ECCD) can be well predicted when the effects of electron trapping and of the residual electric field are included. Experiments on driving current with neutral injection showed that effective current drive could be obtained and discharges with full current drive were demonstrated. Interestingly, all of these methods of current drive had about the same efficiency, 0.015 {times} 10{sup 20} MA/MW/m{sup 2}.

  16. Spectral Effects on Fast Wave Core Heating and Current Drive

    SciTech Connect

    C.K. Phillips, R.E. Bell, L.A. Berry, P.T. Bonoli, R.W. Harvey, J.C. Hosea, E.F. Jaeger, B.P. LeBlanc, P.M. Ryan, G. Taylor, E.J. Valeo, J.R. Wilson, J.C. Wright, H. Yuh, and the NSTX Team

    2009-05-11

    Recent results obtained with high harmonic fast wave (HHFW) heating and current drive (CD) on NSTX strongly support the hypothesis that the onset of perpendicular fast wave propagation right at or very near the launcher is a primary cause for a reduction in core heating efficiency at long wavelengths that is also observed in ICRF heating experiments in numerous tokamaks. A dramatic increase in core heating efficiency was first achieved in NSTX L-mode helium majority plasmas when the onset for perpendicular wave propagation was moved away from the antenna and nearby vessel structures. Efficient core heating in deuterium majority L mode and H mode discharges, in which the edge density is typically higher than in comparable helium majority plasmas, was then accomplished by reducing the edge density in front of the launcher with lithium conditioning and avoiding operational points prone to instabilities. These results indicate that careful tailoring of the edge density profiles in ITER should be considered to limit rf power losses to the antenna and plasma facing materials. Finally, in plasmas with reduced rf power losses in the edge regions, the first direct measurements of high harmonic fast wave current drive were obtained with the motional Stark effect (MSE) diagnostic. The location and radial dependence of HHFW CD measured by MSE are in reasonable agreement with predictions from both full wave and ray tracing simulations.

  17. Recent experimental results of KSTAR RF heating and current drive

    SciTech Connect

    Wang, S. J. Kim, J.; Jeong, J. H.; Kim, H. J.; Joung, M.; Bae, Y. S.; Kwak, J. G.

    2015-12-10

    The overview of KSTAR activities on ICRH, LHCD and ECH/CD including the last experimental results and future plan aiming for long-pulse high-beta plasma will be presented. Recently we achieved reasonable coupling of ICRF power to H-mode plasma through several efforts to increase system reliability. Power balance will be discussed on this experiment. LHCD is still struggling in the low power regime. Review of antenna spectrum for the higher coupling in H-mode plasma will be tried. ECH/CD provides 41 sec, 0.8 MW of heating power to support high-performance long-pulse discharge. Also, 170 GHz ECH system is integrated with the Plasma Control System (PCS) for the feedback controlling of NTM. Status and plan of ECH/CD will be discussed. Finally, helicon current drive is being prepared for the next stage of KSTAR operation. The hardware preparation and the calculation results of helicon current drive in KSTAR plasma will be discussed.

  18. Recent experimental results of KSTAR RF heating and current drive

    NASA Astrophysics Data System (ADS)

    Wang, S. J.; Kim, J.; Jeong, J. H.; Kim, H. J.; Joung, M.; Bae, Y. S.; Kwak, J. G.

    2015-12-01

    The overview of KSTAR activities on ICRH, LHCD and ECH/CD including the last experimental results and future plan aiming for long-pulse high-beta plasma will be presented. Recently we achieved reasonable coupling of ICRF power to H-mode plasma through several efforts to increase system reliability. Power balance will be discussed on this experiment. LHCD is still struggling in the low power regime. Review of antenna spectrum for the higher coupling in H-mode plasma will be tried. ECH/CD provides 41 sec, 0.8 MW of heating power to support high-performance long-pulse discharge. Also, 170 GHz ECH system is integrated with the Plasma Control System (PCS) for the feedback controlling of NTM. Status and plan of ECH/CD will be discussed. Finally, helicon current drive is being prepared for the next stage of KSTAR operation. The hardware preparation and the calculation results of helicon current drive in KSTAR plasma will be discussed.

  19. Technology of fast-wave current drive antennas

    SciTech Connect

    Hoffman, D.J.; Baity, F.W.; Goulding, R.H.; Haste, G.R.; Ryan, P.M.; Taylor, D.J.; Swain, D.W.; Mayberry, M.J.; Yugo, J.J.; General Atomics, San Diego, CA; Oak Ridge National Lab., TN )

    1989-01-01

    The design of fast-wave current drive (FWCD) antennas combines the usual antenna considerations (e.g., the plasma/antenna interface, disruptions, high currents and voltages, and thermal loads) with new requirements for spectral shaping and phase control. The internal configuration of the antenna array has a profound effect on the spectrum and the ability to control phasing. This paper elaborates on these considerations, as epitomized by a proof-of-principle (POP) experiment designed for the DIII-D tokamak. The extension of FWCD for machines such as the International Thermonuclear Engineering Reactor (ITER) will require combining ideas implemented in the POP experiment with reactor-relevant antenna concepts, such as the folded waveguide. 6 refs., 8 figs.

  20. Current profile modification with electron cyclotron current drive in the DIII-D tokamak

    SciTech Connect

    Luce, T.C.; Lin-Liu, Y.R.; Lohr, J.M.

    1998-11-01

    Proof-of-principle experiments on the suitability of electron cyclotron current drive (ECCD) for active current profile control are reported. Experiments with second harmonic extraordinary mode absorption at power levels near 1 MW have demonstrated ability to modify the current profile. This modification is manifested in changes in the internal inductance and the time at which sawteeth appear. Measurements of the local current density and internal loop voltage using high resolution motional Stark effect spectroscopy to half of the minor radius in discharges with localized deposition clearly demonstrate localized off-axis ECCD at the predicted location. Comparison with theory indicates the detrimental effect of trapped electrons on the current drive efficiency is less than predicted. Modification of the theory for finite collisionality is the leading candidate to explain the observations.

  1. Noninductive plasma generation and current drive in the Globus-M spherical tokamak

    SciTech Connect

    D'yachenko, V. V.; Gusev, V. K.; Larionov, M. M.; Mel'nik, A. D.; Novokhatskii, A. N.; Petrov, Yu. V.; Rozhdestvenskii, V. V.; Sakharov, N. V.; Stepanov, A. Yu.; Khitrov, S. A.; Khromov, N. A.; Chernyshev, F. V.; Shevelev, A. E.; Shcherbinin, O. N.; Bender, S. E.; Kavin, A. A.; Lobanov, K. M.

    2013-03-15

    Experimental results on the generation and maintenance of the toroidal current in the Globus-M spherical tokamak by using waves in the lower hybrid frequency range without applying an inductive vortex electric field are presented. For this purpose, the original ridge guide antennas forming a field distribution similar to that produced by multiwaveguide grills were used. The high-frequency field (900 MHz) was used for both plasma generation and current drive. The magnitude of the generated current reached 21 kA, and its direction depended on the direction of the vertical magnetic field. Analysis of the experimental results indicates that the major fraction of the current is carried by the suprathermal electron beam.

  2. Simulation Study of Current Drive Efficiency for KSTAR 5 GHz LHCD

    SciTech Connect

    Aria, A. K.; Bae, Y. S.; Yang, H. L.; Kwon, M.; Do, H. J.; Namkung, W.; Cho, M. H.; Park, H.

    2011-12-23

    Theoretical 5 GHz lower hybrid current drive (LHCD) efficiency using power spectrum given by 0-D Brambilla code and Lower Hybrid Simulation Code (LSC) have been studied for KSTAR. In LSC simulation, RF-driven current and current drive efficiency has been found to be deeply dependent on the profiles of the plasma density and temperature as well as on current profile in order to obtain hollow current profile favorable for advance tokamak operation mode and steady state operation. The peaked density and broad temperature profile control has been found to be efficient in current drive with maximum RF-driven current larger than 400 kA/MW with very high efficiency when the peak plasma density is ranged from 0.2 to 2.0x1020 m-3, and the peak electron temperature range of 2-20 keV together with toroidal field 2-3.5 T and Ip = 0.5-2 MA. The on-/off-axis current profile controllability is also investigated through parametric scan, and small negative magnetic shear is seen at the narrow region of the off-axis for very high temperature regime and for high BT and I{sub p}. In order to achieve the same for lower temperature regime Ip has to be lower and also for higher LH-power compromising with CD efficiency in this case.

  3. Electron cyclotron heating and current drive results from the DIII-D tokamak

    SciTech Connect

    Luce, T.C.; Harvey, R.; Lohr, J.; Prater, R.; Snider, R.; Stallard, B.; Stockdale, R. ); James, R.A.; deHaas, J. ); Fyaretdinov, A.; Gorelov, Yu; Trukhin, V. ); de Gentile, B.; Giruzzi, G.; Rodriguez, L. (CEA Centre d'Etudes Nucleaires de Cadarache, 13 - Saint-Paul-lez-Durance (Fra

    1990-11-01

    Auxiliary heating experiments with electron cyclotron heating have been carried out in the DIII-D tokamak. Waves at 60 GHz have been launched at power levels up to 1.4 MW from both the high-field and low-field side with the appropriate polarization for damping at the fundamental resonance (2.14 T). Confinement was studied in L-mode and H-mode plasmas for a single-null, open divertor geometry. For L-mode discharges, the energy confinement scaling agrees well with the ITER-89 power law or offset linear scaling relations. With strong off-axis heating, the electron temperature profile remains peaked, and power balance analysis indicates that the transport cannot be described by a purely diffusive model. In H-mode confinement plasmas, the magnitude and scaling of the confinement time are equal to that of plasmas heated by neutral beam injection (NBI), if the energy stored in the fast ions is removed in the NBI cases. A major issue for steady-state H-mode plasmas is control of the edge-localized mode (ELM) behavior. By moving the resonance location {plus minus}5 cm around the separatrix, the frequency of giant ELMs can be changed by a factor of three. Non-inductive current drive with electron cyclotron waves has also been investigated. Driven currents up to 70 kA have been observed, but the current drive is enhanced by the residual dc electric field. Currents aiding and opposing the Ohmic current have been measured. The magnitude of the current for co-current drive is greater than expected from modeling which includes trapped particle effects, but no electric field. Preliminary calculations including the residual dc electric field can account for the observed enhancement.

  4. Off-axis Neutral Beam Current Drive for Advanced Scenario Development in DIII-D

    SciTech Connect

    Murakami, M; Park, J; Petty, C; Luce, T; Heidbrink, W; Osborne, T; Wade, M; Austin, M; Brooks, N; Budny, R; Challis, C; DeBoo, J; deGrassie, J; Ferron, J; Gohil, P; Hobirk, J; Holcomb, C; Hollmann, E; Hong, R; Hyatt, A; Lohr, J; Lanctot, M; Makowski, M; McCune, D; Politzer, P; Prater, R; John, H S; Suzuki, T; West, W; Unterberg, E; Van Zeeland, M; Yu, J

    2008-10-13

    Modification of the two existing DIII-D neutral beam lines is proposed to allow vertical steering to provide off-axis neutral beam current drive (NBCD) as far off-axis as half the plasma radius. New calculations indicate very good current drive with good localization off-axis as long as the toroidal magnetic field, B{sub T}, and the plasma current, I{sub p}, are in the same direction (for a beam steered downward). The effects of helicity can be large: e.g., ITER off-axis NBCD can be increased by more than 20% if the B{sub T} direction is reversed. This prediction has been tested by an off-axis NBCD experiment using reduced size plasmas that are vertically shifted with the existing NBI on DIII-D. The existence of off-axis NBCD is evident in sawtooth and internal inductance behavior. By shifting the plasma upward or downward, or by changing the sign of the toroidal field, measured off-axis NBCD profiles, determined from MSE data, are consistent with predicted differences (40%-45%) arising from the NBI orientation with respect to the magnetic field lines. Modification of the DIII-D NB system will strongly support scenario development for ITER and future tokamaks as well as providing flexible scientific tools for understanding transport, energetic particles and heating and current drive.

  5. Particle pinch with fully noninductive lower hybrid current drive in Tore Supra.

    PubMed

    Hoang, G T; Bourdelle, C; Pégourié, B; Schunke, B; Artaud, J F; Bucalossi, J; Clairet, F; Fenzi-Bonizec, C; Garbet, X; Gil, C; Guirlet, R; Imbeaux, F; Lasalle, J; Loarer, T; Lowry, C; Travère, J M; Tsitrone, E

    2003-04-18

    Recently, plasmas exceeding 4 min have been obtained with lower hybrid current drive (LHCD) in Tore Supra. These LHCD plasmas extend for over 80 times the resistive current diffusion time with zero loop voltage. Under such unique conditions the neoclassical particle pinch driven by the toroidal electric field vanishes. Nevertheless, the density profile remains peaked for more than 4 min. For the first time, the existence of an inward particle pinch in steady-state plasma without toroidal electric field, much larger than the value predicted by the collisional neoclassical theory, is experimentally demonstrated. PMID:12732041

  6. Integrated Plasma Simulation of Lower Hybrid Current Drive in Tokamaks

    NASA Astrophysics Data System (ADS)

    Bonoli, P. T.; Wright, J. C.; Harvey, R. W.; Batchelor, D. B.; Berry, L. A.; Kessel, C. E.; Jardin, S. C.

    2012-03-01

    It has been shown in Alcator C-Mod that the onset time for sawteeth can be delayed significantly (up to 0.5 s) relative to ohmically heated plasmas, through the injection of off-axis LH current drive power [1]. We are simulating these experiments using the Integrated Plasma Simulator (IPS) [2], where the driven LH current density profiles are computed using a ray tracing component (GENRAY) and Fokker Planck code (CQL3D) [3] that are run in a tightly coupled time advance. The background plasma is evolved using the TSC transport code with the Porcelli sawtooth model [4]. Predictions of the driven LH current profiles will be compared with simpler ``reduced'' models for LHCD such as the LSC code which is implemented in TSC and which is also invoked within the IPS. [4pt] [1] C. E. Kessel et al, Bull. of the Am. Phys. Soc. 53, Poster PP6.00074 (2008). [0pt] [2] D. Batchelor et al, Journal of Physics: Conf. Series 125, 012039 (2008). [0pt] [3] R. W. Harvey and M. G. McCoy, Proc. of the IAEA Tech. Comm. Meeting on Simulation and Modeling of Therm. Plasmas, Montreal, Canada (1992). [0pt] [4] S. C. Jardin et al, J. Comp. Phys. 66, 481 (1986).

  7. A survey of the current experimental database for lower hybrid current-drive and heating

    SciTech Connect

    Blackfield, D.T.

    1988-02-10

    The proposed ITER design may rely heavily on Lower Hybrid waves to provide heating, current drive, MHD stabilization through current profile modification and transformer recharging. This paper presents a detailed survey of recent LH experimental results from PLT, Alcator C, ASDEX, Petula-B, FT and JT-60. Current drive and heating efficiencies are given, as well as regimes where sawteeth and m = 1 and 2 oscillations are stabilized. In addition, in ASDEX and JT-60, LH waves in combination with neutral beams, (a possible ITER scenario) experiments are examined. Finally, the current drive efficiency for ITER is obtained by extrapolating from the LHCD database. Assuming 12 MW of LH power, approximately 4.5 to 5.6 MA of current could be driven in ITER. However, the high density (/ovr /n///sub e/ = 8 /times/ 10/sup 19/ m/sup /minus/3/) and high temperature (/ovr/T///sub e/ = 21 keV) will preclude wave penetration to the center. Assuming a narrow N/sub /parallel// spectrum (1.2 /approx lt/ N/sub /parallel// /approx lt/ 2) the LH waves should be absorbed within the outer half of the plasma. 43 refs., 18 figs., 10 tabs.

  8. Lower Hybrid Current Drive Experiments in Alcator C-Mod

    SciTech Connect

    J.R. Wilson, S. Bernabei, P. Bonoli, A. Hubbard, R. Parker, A. Schmidt, G. Wallace, J. Wright, and the Alcator C-Mod Team

    2007-10-09

    A Lower Hybrid Current Drive (LHCD) system has been installed on the Alcator C-MOD tokamak at MIT. Twelve klystrons at 4.6 GHz feed a 4x22 waveguide array. This system was designed for maximum flexibility in the launched parallel wave-number spectrum. This flexibility allows tailoring of the lower hybrid deposition under a variety of plasma conditions. Power levels up to 900 kW have been injected into the tokomak. The parallel wave number has been varied over a wide range, n|| ~ 1.6–4. Driven currents have been inferred from magnetic measurements by extrapolating to zero loop voltage and by direct comparison to Fisch-Karney theory, yielding an efficiency of n20IR/P ~ 0.3. Modeling using the CQL3D code supports these efficiencies. Sawtooth oscillations vanish, accompanied with peaking of the electron temperature (Te0 rises from 2.8 to 3.8 keV). Central q is inferred to rise above unity from the collapse of the sawtooth inversion radius, indicating off-axis cd as expected. Measurements of non-thermal x-ray and electron cyclotron emission confirm the presence of a significant fast electron population that varies with phase and plasma density. The x-ray emission is observed to be radialy broader than that predicted by simple ray tracing codes. Possible explanations for this broader emission include fast electron diffusion or broader deposition than simple ray tracing predictions (perhaps due to diffractive effects).

  9. Lower hybrid counter current drive for edge current density modification in DIII-D

    SciTech Connect

    Fenstermacher, M.E.; Nevins, W.M.; Porkolab, M.; Bonoli, P.T.; Harvey, R.W.

    1993-07-01

    Each of the Advanced Tokamak operating modes in DIII-D is thought to have a distinctive current density profile. So far these modes have only been achieved transiently through experiments which ramp the plasma current and shape. Extension of these modes to steady state requires non-inductive current profile control, e.g. with lower hybrid current drive (LHCD). Calculations of LHCD have been done for DIII-D using the ACCOME and CQL3D codes, showing that counter driven current at the plasma edge can cancel some of the undesirable edge bootstrap current and potentially extend the VH-mode. Results are presented for scenarios using 2.45 GHz LH waves launched from both the midplane and off-axis ports. The sensitivity of the results to injected power, n{sub e} and T{sub e}, and launched wave spectrum is also shown.

  10. Lower-hybrid counter current drive for edge current density modification in DIII-D

    SciTech Connect

    Fenstermacher, M.E.; Nevins, W.M. ); Porkolab, M.; Bonoli, P.T. ); Harvey, R.W. )

    1994-10-15

    Each of the Advanced Tokamak operating modes in DIII-D is thought to have a distinctive current density profile. So far these modes have only been achieved transiently through experiments which ramp the plasma current and shape. Extension of these modes to steady state requires non-inductive current profile control, e.g., with lower hybrid current drive (LHCD). Calculations of LHCD have been done for DIII-D using the ACCOME and CQL3D codes, showing that counter driven current at the plasma edge can cancel some of the undesirable edge bootstrap current and potentially extend the VH-mode. Results will be presented for scenarios using 2.45 GHz LH waves launched from both the midplane and off-axis ports. The sensitivity of the results to injected power, [ital n][sub [ital e

  11. D Helicity Injection Studies on the Current Drive Experiment

    NASA Astrophysics Data System (ADS)

    Darrow, Douglass Sterling

    A tokamak-like plasma has been created and sustained in the CDX device solely by means of an electron beam. The poloidal field structure observed is that of a tokamak and the density and temperatures seen are larger than in previous types of plasmas generated in this device. A plasma current scaling consistent with the helicity balance equation is observed and about 40% of the injected helicity appears in the tokamak plasma. Rapid transport of current from the region of injection to the center produces a peaked current profile. Plasmas with beta in the neighborhood of the Troyon-Sykes limit may be generated by this technique. In high-beta plasmas, a coherent fluctuation is seen which has its largest amplitude in a region of unfavorable curvature. The mode is absent below a certain density and plasma current, corresponding to a threshold beta. When present, the mode has an m = 4 structure and it propagates in the ion diamagnetic direction. These properties identify it as a ballooning mode. A significant radial electric field alters the observed frequency and dispersion of the mode.

  12. Determination of the Electron Cyclotron Current Drive Profile

    SciTech Connect

    Luce, T.C.; Petty, C.C.; Schuster, D.I.; Makowski, M.A.

    1999-11-01

    Evaluation of the profile of non-inductive current density driven by absorption of electron cyclotron waves (ECCD) using time evolution of the poloidal flux indicated a broader profile than predicted by theory. To determine the nature of this broadening, a 1-1/2 D transport calculation of current density evolution was used to generate the signals which the DIII-D motional Stark effect (MSE) diagnostic would measure in the event that the current density evolution followed the neoclassical Ohm's law with the theoretical ECCD profile. Comparison with the measured MSE data indicates the experimental data is consistent with the ECCD profile predicted by theory. The simulations yield a lower limit on the magnitude of the ECCD which is at or above the value found in Fokker-Planck calculations of the ECCD including quasilinear and parallel electric field effects.

  13. On the efficiency of electrical submersible pumps equipped with variable frequency drives: A field study

    SciTech Connect

    Patterson, M.M.

    1996-02-01

    A field study was conducted on 18 electrical-submersible-pump- (ESP-) equipped wells operating in the Williston basin. Fifteen of these wells were run with variable frequency drives (VFD`s). The purpose of the study was to determine the efficiency and operating characteristics of ESP`s operating with VFD`s and compare them to those without. Voltage, current, power, and frequency were measured at the drive input, the drive output, and ESP input. Production data were recorded and power and efficiency were calculated at all measurement locations and compared to published data.

  14. Current ramp-up with lower hybrid current drive in EAST

    SciTech Connect

    Ding, B. J.; Li, M. H.; Li, J. G.; Kong, E. H.; Zhang, L.; Wei, W.; Li, Y. C.; Wang, M.; Xu, H. D.; Gong, X. Z.; Shen, B.; Liu, F. K.; Shan, J. F.; Fisch, N. J.; Qin, H.; Wilson, J. R.; Collaboration: EAST Team

    2012-12-15

    More economical fusion reactors might be enabled through the cyclic operation of lower hybrid current drive. The first stage of cyclic operation would be to ramp up the plasma current with lower hybrid waves alone in low-density plasma. Such a current ramp-up was carried out successfully on the EAST tokamak. The plasma current was ramped up with a time-averaged rate of 18 kA/s with lower hybrid (LH) power. The average conversion efficiency P{sub el}/P{sub LH} was about 3%. Over a transient phase, faster ramp-up was obtained. These experiments feature a separate measurement of the L/R time at the time of current ramp up.

  15. Lower hybrid current drive for edge current density modification in DIII-D: Final status report

    SciTech Connect

    Fenstermacher, M.E.; Porkolab, M.

    1993-08-04

    Application of Lower Hybrid (LH) Current Drive (CD) in the DIII-D tokamak has been studied at LLNL, off and on, for several years. The latest effort began in February 1992 in response to a letter from ASDEX indicating that the 2.45 GHz, 3 MW system there was available to be used on another device. An initial assessment of the possible uses for such a system on DIII-D was made and documented in September 1992. Multiple meetings with GA personnel and members of the LH community nationwide have occurred since that time. The work continued through the submission of the 1995 Field Work Proposals in March 1993 and was then put on hold due to budget limitations. The purpose of this document is to record the status of the work in such a way that it could fairly easily be restarted at a future date. This document will take the form of a collection of Appendices giving both background and the latest results from the FY 1993 work, connected by brief descriptive text. Section 2 will describe the final workshop on LHCD in DIII-D held at GA in February 1993. This was an open meeting with attendees from GA, LLNL, MIT and PPPL. Summary documents from the meeting and subsequent papers describing the results will be included in Appendices. Section 3 will describe the status of work on the use of low frequency (2.45 GHZ) LH power and Parametric Decay Instabilities (PDI) for the special case of high dielectric in the edge regions of the DIII-D plasma. This was one of the critical issues identified at the workshop. Other potential issues for LHCD in the DIII-D scenarios are: (1) damping of the waves on fast ions from neutral beam injection, (2) runaway electrons in the low density edge plasma, (3) the validity of the WKB approximation used in the ray-tracing models in the steep edge density gradients.

  16. Spectral effects on fast wave core heating and current drive

    SciTech Connect

    Phillips, Cynthia; Bell, R. E.; Berry, Lee; Jaeger, Erwin Frederick; Ryan, Philip Michael; Wilgen, John B

    2009-01-01

    Recent results obtained with high harmonic fast wave (HHFW) heating and current drive (CD) on NSTX strongly support the hypothesis that the onset of perpendicular fast wave propagation right at or very near the launcher is a primary cause for a reduction in core heating efficiency at long wavelengths that is also observed in ICRF heating experiments in numerous tokamaks. A dramatic increase in core heating efficiency was first achieved in NSTX L-mode helium majority plasmas when the onset for perpendicular wave propagation was moved away from the antenna and nearby vessel structures. Efficient core heating in deuterium majority L-mode and H-mode discharges, in which the edge density is typically higher than in comparable helium majority plasmas, was then accomplished by reducing the edge density in front of the launcher with lithium conditioning and avoiding operational points prone to instabilities. These results indicate that careful tailoring of the edge density profiles in ITER should be considered to limit radio frequency (rf) power losses to the antenna and plasma facing materials. Finally, in plasmas with reduced rf power losses in the edge regions, the first direct measurements of HHFW CD were obtained with the motional Stark effect (MSE) diagnostic. The location and radial dependence of HHFW CD measured by MSE are in reasonable agreement with predictions from both full wave and ray tracing simulations.

  17. EBW Current Drive and Heating for Fusion/Fission Hybrids

    NASA Astrophysics Data System (ADS)

    Urban, Jakub; Preinhaelter, Josef; Vahala, George; Vahala, Linda; Decker, Joan; Ram, Abhay

    2011-10-01

    From the RF requirements for spherical tokamak and the need to reduce antenna exposure to neutron bombardment, EBW are an important source for both heating and current drive (CD). ICRF, LH, HHFW antennas are subject to significant neutron damage (as are NBI) because of their very large size and necessary proximity to the plasma. Recently Mahajan et. al. have studied other important uses of fusion neutrons - in particular their use in the efficient breeding of fission reactor fuel as well as in the ``rapid'' destruction of nuclear waste using their Compact High Power Density Fast Neutron Source (CFNS). For overdense plasmas the standard electromagnetic O- and X- mode experience cutoffs. EBW can propagate and be absorbed in such plasmas but its characteristics are strongly dependent on the plasma parameters with important variations in the parallel wave number. If the required temperatures in CFNS are around 35 KeV, then one will may need to revisit the electrostatic approximation and incorporate relativistic effects for EBW rays.

  18. On the current drive capability of low dimensional semiconductors: 1D versus 2D

    DOE PAGESBeta

    Zhu, Y.; Appenzeller, J.

    2015-10-29

    Low-dimensional electronic systems are at the heart of many scaling approaches currently pursuit for electronic applications. Here, we present a comparative study between an array of one-dimensional (1D) channels and its two-dimensional (2D) counterpart in terms of current drive capability. Lastly, our findings from analytical expressions derived in this article reveal that under certain conditions an array of 1D channels can outperform a 2D field-effect transistor because of the added degree of freedom to adjust the threshold voltage in an array of 1D devices.

  19. Summary and viewgraphs from the Q-121 US/Japan advanced current drive concepts workshop

    SciTech Connect

    Bonoli, P.; Porkolab, M. ); Chan, V.; Pinsker, R.; Politzer, P. ); Darrow, D. . Plasma Physics Lab.); Ehst, D. ); Fukuyama, Atsushi ); Imai, Tsuyoshi; Watari, Tetsuo ); Itoh, Satoshi; Naka

    1990-03-09

    With the emphasis placed on current drive by ITER, which requires steady state operation in its engineering phase, it is important to bring theory and experiment in agreement for each of the schemes that could be used in that design. Both neutral beam and lower hybrid (LH) schemes are in excellent shape in that regard. Since the projected efficiency of all schemes is marginal it is also important to continue our search for more efficient processes. This workshop featured experimental and theoretical work in each processes. This workshop featured experimental and theoretical work in each of these areas, that is, validation of theory and the search for better ideas. There were a number of notable results to report, the most striking again (as with last year) the long pulse operation of TRIAM-1M. A low current was sustained for over 1 hour with LH waves, using new hall-effect sensors in the equilibrium field circuit to maintain position control. In JT-60, by sharpening the wave spectrum the current drive efficiency was improved to 0.34 {times} 10{sup 20}m{sup -2}A/W and 1.5 MA of current was driven entirely by the lower hybrid system. Also in that machine, using two different LH frequencies, the H-mode was entered. Finally, by using the LH system for startup they saved 2.5 resistive volt-sec of flux, which if extrapolated to ITER would save 40 volt-sec there. For the first time, and experiment on ECH current drive showed reasonable agreement with theory. Those experiments are reported here by James (LLNL) on the D3-D machine. Substantially lower ECH current drive than expected theoretically was observed on WT-3, but if differed by being in a low absorption regime. Nonetheless, excellent physics results were achieved in the WT-3 experiments, notably in having careful measurements of the parallel velocity distributions.

  20. Advances in modeling of lower hybrid current drive

    NASA Astrophysics Data System (ADS)

    Peysson, Y.; Decker, J.; Nilsson, E.; Artaud, J.-F.; Ekedahl, A.; Goniche, M.; Hillairet, J.; Ding, B.; Li, M.; Bonoli, P. T.; Shiraiwa, S.; Madi, M.

    2016-04-01

    First principle modeling of the lower hybrid (LH) current drive in tokamak plasmas is a longstanding activity, which is gradually gaining in accuracy thanks to quantitative comparisons with experimental observations. The ability to reproduce simulatenously the plasma current and the non-thermal bremsstrahlung radial profiles in the hard x-ray (HXR) photon energy range represents in this context a significant achievement. Though subject to limitations, ray tracing calculations are commonly used for describing wave propagation in conjunction with Fokker-Planck codes, as it can capture prominent features of the LH wave dynamics in a tokamak plasma-like toroidal refraction. This tool has been validated on several machines when the full absorption of the LH wave requires the transfer of a small fraction of power from the main lobes of the launched power spectrum to a tail at a higher parallel refractive index. Conversely, standard modeling based on toroidal refraction only becomes more challenging when the spectral gap is large, except if other physical mechanisms may dominate to bridge it, like parametric instabilities, as suggested for JET LH discharges (Cesario et al 2004 Phys. Rev. Lett. 92 175002), or fast fluctuations of the launched power spectrum or ‘tail’ LH model, as shown for Tore Supra (Decker et al 2014 Phys. Plasma 21 092504). The applicability of the heuristic ‘tail’ LH model is investigated for a broader range of plasma parameters as compared to the Tore Supra study and with different LH wave characteristics. Discrepancies and agreements between simulations and experiments depending upon the different models used are discussed. The existence of a ‘tail’ in the launched power spectrum significantly improves the agreement between modeling and experiments in plasma conditions for which the spectral gap is large in EAST and Alcator C-Mod tokamaks. For the Alcator C-Mod tokamak, the experimental evolution of the HXR profiles with density suggests

  1. Plasma Heating and Current Drive for Fusion Reactors

    NASA Astrophysics Data System (ADS)

    Holtkamp, Norbert

    2010-02-01

    ITER (in Latin ``the way'') is designed to demonstrate the scientific and technological feasibility of fusion energy. Fusion is the process by which two light atomic nuclei combine to form a heavier one and thus release energy. In the fusion process two isotopes of hydrogen - deuterium and tritium - fuse together to form a helium atom and a neutron. Thus fusion could provide large scale energy production without greenhouse effects; essentially limitless fuel would be available all over the world. The principal goals of ITER are to generate 500 megawatts of fusion power for periods of 300 to 500 seconds with a fusion power multiplication factor, Q, of at least 10. Q >= 10 (input power 50 MW / output power 500 MW). In a Tokamak the definition of the functionalities and requirements for the Plasma Heating and Current Drive are relevant in the determination of the overall plant efficiency, the operation cost of the plant and the plant availability. This paper summarise these functionalities and requirements in perspective of the systems under construction in ITER. It discusses the further steps necessary to meet those requirements. Approximately one half of the total heating will be provided by two Neutral Beam injection systems at with energy of 1 MeV and a beam power of 16 MW into the plasma. For ITER specific test facility is being build in order to develop and test the Neutral Beam injectors. Remote handling maintenance scheme for the NB systems, critical during the nuclear phase of the project, will be developed. In addition the paper will give an overview over the general status of ITER. )

  2. Electron-cyclotron-current-drive experiments in the DIII-D tokamak

    SciTech Connect

    James, R.A. ); Giruzzi, G.; de Gentile, B.; Rodriguez, L. ); Harvey, R.; Lohr, J.; Luce, T.C.; Matsuda, K.; Moeller, C.P.; Prater, R.; Snider, R. ); Fyakhretdinov, A.; Gorelov, Y.; Trukhin, V. ); Janz, S. )

    1992-06-15

    Electron-cyclotron-current-drive (ECCD) experiments performed in the DIII-D tokamak have produced rf-driven currents of up to 100 kA. The experimental results, which exceed predictions using linear theory, are enhanced by the presence of a residual, toroidal dc electric field. These ECCD experiments are performed with plasma conditions sufficient to result in strong localized deposition of the rf power and good confinement of the rf-generated current carriers. These improved conditions permit a test of theory under reactor relevant conditions. Theoretical predictions obtained using a Fokker-Planck code are in good agreement with the experimental results when effects due to electron trapping and the residual dc electric field are included.

  3. Low frequency RF current drive. Final report, January 1, 1988--May 31, 1997

    SciTech Connect

    Hershkowitz, N.

    1999-05-01

    This report starts with a summary of research done on the Phaedrus Tandom Mirror concept and how this research led to the design and construction of the Phaedrus-T Tokamak. Next it gives a more detailed description of the results from the last four years of research, which include the following areas: (1) first experimental demonstration of AWCD (Alfven Wave Current Drive); (2) current drive location and loop voltage response; (3) trapping and current drive efficiency; and (4) reflectometry.

  4. First results on fast wave current drive in advanced tokamak discharges in DIII-D

    SciTech Connect

    Prater, R.; Cary, W.P.; Baity, F.W.

    1995-07-01

    Initial experiments have been performed on the DIII-D tokamak on coupling, direct electron heating, and current drive by fast waves in advanced tokamak discharges. These experiments showed efficient central heating and current drive in agreement with theory in magnitude and profile. Extrapolating these results to temperature characteristic of a power plant (25 keV) gives current drive efficiency of about 0.3 MA/m{sup 2}.

  5. 60 MHz fast wave current drive experiments for DIII-D

    SciTech Connect

    Mayberry, M.J.; Chiu, S.C.; Porkolab, M.; Chan, V.; Freeman, R.; Harvey, R.; Pinsker, R.

    1989-05-01

    Non-inductive current drive is an essential element of the ITER program because it enhances high fluence nuclear testing during the technology phase of operations. By using fast waves in the ion cyclotron range of frequencies (ICRF), current drive efficiencies comparable to lower-hybrid current drive can be obtained with good penetration of wave power to the high temperature plasma core. An additional advantage of the low frequency scheme is its technological simplicity due to the present availability of efficient, multi-megawatt rf sources in the ICRF. The DIII-D facility provides an excellent opportunity to test the feasibility of the low frequency FWCD approach. By combining with high power (2 MW) ECH injection at 60 GHz, it should be possible to generate plasmas with central electron temperatures of T/sub e0/ approx. = 4 keV, and by operating at a reduced toroidal field (B = 1T) to increase the electron ..beta.., strong single-pass absorption (/eta//sub abs/ greater than or equal to 0.3) can be achieved. The availability of a wide port recess (1m toroidal by 0.5m poloidal) will enable a travelling wave spectrum to be launched with N/sub parallel/ approx. = 5--7 at 60 MHz, which should be optimum for strong electron interaction. The resulting current drive efficiency should be sufficiently high to demonstrate FWCD at the /approximately/ 0.25--0.5 MA level at moderate densities (/bar n/ approx. = 1.3 /times/ 10/sup 19/ m/sup /minus/3/) using the existing 2 MW ICRF transmitter. 7 refs., 5 figs.

  6. HHFW Heating and Current Drive Progress on NSTX

    NASA Astrophysics Data System (ADS)

    Ryan, P. M.; Jaeger, E. F.; Wilgen, J. B.; Hosea, J. C.; Wilson, J. R.; Bell, R. E.; Bernabei, S.; Leblanc, B. P.; Phillips, C. K.; Delgado-Aparicio, L.; Tritz, K.; Sabbagh, S.; Yuh, H.

    2007-11-01

    Operation of NSTX at BT(0) = 0.55 T has increased the core power deposition and heating efficiency of the 30 MHz High Harmonic Fast Waves (HHFW) compared to previous BT(0) <= 0.45 T operation, particularly when launching longer parallel wavelengths. This improvement is attributed in part to moving the onset density at which the fast waves begin to propagate into the plasma to a point further from the wall [1]. At this field strength the HHFW power deposition at k|| = 7 m-1 is comparable to that of k|| = 14 m-1, and core heating at k|| = 3 m-1 is now seen, albeit at lower efficiency. Comparisons with power deposition from full-wave models (AORSA) will be made and MSE measurements of driven current will be presented. [1] see Invited Talk by J. Hosea, this conference.

  7. Beat wave current drive experiment on the Davis Diverted Tokamak (DDT). Final report

    SciTech Connect

    Hwang, D.Q.; Horton, R.D.; Rogers, J.H. |

    1993-12-31

    The beatwave current drive experiment is summarized. The first phase of the experiment was the construction of the microwave sources and the diagnostics needed to demonstrate the beat wave effects, i.e. the measurement of the electrostatic plasma wave produced by the beating of two high intensity electromagnetic waves. In order to keep the cost of the experiments to a minimum, a low density filament plasma source (10{sup 8}) to (10{sup 10} particles cm{sup {minus}3}) was employed and the magnetic field in the toroidal plasma was produced by a dc power supply.

  8. Angular distribution of the bremsstrahlung emission during lower-hybrid current drive on PLT

    SciTech Connect

    von Goeler, S.; Stevens, J.; Bernabei, S.; Bitter, M.; Chu, T.K.; Efthimion, P.; Fisch, N.; Hooke, W.; Hill, K.; Hosea, J.

    1985-06-01

    The bremsstrahlung emission from the PLT tokamak during lower-hybrid current drive has been measured as a function of angle between the magnetic field and the emission direction. The emission is peaked strongly in the forward direction, indicating a strong anisotropy of the electron-velocity distribution. The data demonstrate the existence of a nearly flat tail of the velocity distribution, which extends out to approximately 500 keV and which is interpreted as the plateau created by Landau damping of the lower-hybrid waves.

  9. Influence of driving frequency on discharge modes in a dielectric-barrier discharge with multiple current pulses

    SciTech Connect

    Jiang, Weiman; Tang, Jie; Wang, Yishan; Zhao, Wei; Duan, Yixiang

    2013-07-15

    A one-dimensional self-consistent fluid model was employed to investigate the effect of the driving frequency on the discharge modes in atmospheric-pressure argon discharge with multiple current pulses. The discharge mode was discussed in detail not only at current peaks but also between two adjacent peaks. The simulation results show that different transitions between the Townsend and glow modes during the discharge take place with the driving frequency increased. A complicated transition from the Townsend mode, through glow, Townsend, and glow, and finally back to the Townsend one is found in the discharge with the driving frequency of 8 kHz. There is a tendency of transition from the Townsend to glow mode for the discharge both at the current peaks and troughs with the increasing frequency. The discharge in the half period can all along operate in the glow mode with the driving frequency high enough. This is resulted from the preservation of more electrons in the gas gap and acquisition of more electron energy from the swiftly varying electric field with the increase in driving frequency. Comparison of the spatial and temporal evolutions of the electron density at different driving frequencies indicates that the increment of the driving frequency allows the plasma chemistry to be enhanced. This electrical characteristic is important for the applications, such as surface treatment and biomedical sterilization.

  10. Analysis of Wave Fields induced by Offshore Pile Driving

    NASA Astrophysics Data System (ADS)

    Ruhnau, M.; Heitmann, K.; Lippert, T.; Lippert, S.; von Estorff, O.

    2015-12-01

    Impact pile driving is the common technique to install foundations for offshore wind turbines. With each hammer strike the steel pile - often exceeding 6 m in diameter and 80 m in length - radiates energy into the surrounding water and soil, until reaching its targeted penetration depth. Several European authorities introduced limitations regarding hydroacoustic emissions during the construction process to protect marine wildlife. Satisfying these regulations made the development and application of sound mitigation systems (e.g. bubble curtains or insulation screens) inevitable, which are commonly installed within the water column surrounding the pile or even the complete construction site. Last years' advances have led to a point, where the seismic energy tunneling the sound mitigation systems through the soil and radiating back towards the water column gains importance, as it confines the maximum achievable sound mitigation. From an engineering point of view, the challenge of deciding on an effective noise mitigation layout arises, which especially requires a good understanding of the soil-dependent wave field. From a geophysical point of view, the pile acts like a very unique line source, generating a characteristic wave field dominated by inclined wave fronts, diving as well as head waves. Monitoring the seismic arrivals while the pile penetration steadily increases enables to perform quasi-vertical seismic profiling. This work is based on datasets that have been collected within the frame of three comprehensive offshore measurement campaigns during pile driving and demonstrates the potential of seismic arrivals induced by pile driving for further soil characterization.

  11. Advanced Tokamak Regimes in Alcator C-Mod with Lower Hybrid Current Drive

    NASA Astrophysics Data System (ADS)

    Parker, R.; Bonoli, P.; Gwinn, D.; Hutchinson, I.; Porkolab, M.; Ramos, J.; Bernabei, S.; Hosea, J.; Wilson, R.

    1999-11-01

    Alcator C-Mod has been proposed as a test-bed for developing advanced tokamak scenarios owing to its strong shaping, relatively long pulse length capability at moderate field, e.g. t ~ L/R at B = 5T and T_eo ~ 7keV, and the availability of strong ICRF heating. We plan to exploit this capability by installing up to 4 MW RF power at 4.6 GHz for efficient off-axis current drive by lower hybrid waves. By launching LH waves with a grill whose n_xx spectrum can be dynamically controlled over the range 2 < n_xx < 3.5, the driven current profile can be modified so that, when combined with bootstrap current in high ɛβ_pol regimes, q_min > 2. Such reversed or nearly zero shear regimes have already been proposed as the basis of an advanced tokamak burning-plasma experiment-ATBX (M. Porkolab et al, IAEA-CN-69/FTP/13, IAEA,Yokohama 1998.), and could provide the basis for a demonstration power reactor. Theoretical and experimental basis for this advanced tokamak research program on C-Mod, including design of the lower hybrid coupler, its spectrum and current drive capabilities will be presented.

  12. Shadows, currents, and AdS fields

    SciTech Connect

    Metsaev, R. R.

    2008-11-15

    Conformal totally symmetric arbitrary spin currents and shadow fields in flat space-time of dimension greater than or equal to four are studied. A gauge invariant formulation for such currents and shadow fields is developed. Gauge symmetries are realized by involving the Stueckelberg fields. A realization of global conformal boost symmetries is obtained. Gauge invariant differential constraints for currents and shadow fields are obtained. AdS/CFT correspondence for currents and shadow fields and the respective normalizable and non-normalizable solutions of massless totally symmetric arbitrary spin AdS fields are 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 fields correspond to gauge symmetries of boundary currents and shadow fields, while the modified de Donder gauge conditions for bulk fields correspond to differential constraints for boundary conformal currents and shadow fields. Breaking conformal symmetries, we find interrelations between the gauge invariant formulation of the currents and shadow fields, and the gauge invariant formulation of massive fields.

  13. Relationships between the Birkeland currents, ionospheric currents, and electric fields

    NASA Technical Reports Server (NTRS)

    Bleuler, E.; Li, C. H.; Nisbet, J. S.

    1982-01-01

    Currents and electric fields in the ionosphere are calculated using a global model of the electron density including conjugate coupling along field lines. Incoherent scatter and rocket measurements of high-latitude electron densities are used to derive realistic variations of the polar conductivities as a function of magnetic activity. The Birkeland currents are specified in terms of three indices, and the relationship between these parameters and the auroral electrojets indices is examined along with the polar cap potential and the electric field at lower latitudes. A mathematical model of the currents, electric fields, and energy inputs produced by field aligned currents is developed, which is consistent with and specifiable in terms of measured geophysical indices.

  14. Driving difficulties among military veterans: clinical needs and current intervention status.

    PubMed

    Possis, Elizabeth; Bui, Thao; Gavian, Margaret; Leskela, Jennie; Linardatos, Effie; Loughlin, Jennifer; Strom, Thad

    2014-06-01

    Military personnel deployed to Iraq and Afghanistan often develop mental health difficulties, which may manifest as problematic driving behavior. Veterans may be more likely to engage in risky driving and to subsequently be involved in motor vehicle accidents and fatalities. This article reviews literature on driving difficulties among military veterans and evaluates available research on the potential pathways that underlie risky driving behavior. Current interventions for problematic driving behaviors are considered, and the necessity of modifying these interventions to address the unique difficulties encountered by military veterans is highlighted. The review concludes with a discussion of clinical implications of these findings and identification of possible avenues for future research and intervention. PMID:24902130

  15. Fast wave current drive in neutral beam heated plasmas on DIII-D

    SciTech Connect

    Petty, C.C.; Forest, C.B.; Pinsker, R.I.

    1997-04-01

    The physics of non-inductive current drive and current profile control using the fast magnetosonic wave has been demonstrated on the DIII-D tokamak. In non-sawtoothing discharges formed by neutral beam injection (NBI), the radial profile of the fast wave current drive (FWCD) was determined by the response of the loop voltage profile to co, counter, and symmetric antenna phasings, and was found to be in good agreement with theoretical models. The application of counter FWCD increased the magnetic shear reversal of the plasma and delayed the onset of sawteeth, compared to co FWCD. The partial absorption of fast waves by energetic beam ions at high harmonics of the ion cyclotron frequency was also evident from a build up of fast particle pressure near the magnetic axis and a correlated increase in the neutron rate. The anomalous fast particle pressure and neutron rate increased with increasing NBI power and peaked when a harmonic of the deuterium cyclotron frequency passed through the center of the plasma. The experimental FWCD efficiency was highest at 2 T where the interaction between the fast waves and the beam ions was weakest; as the magnetic field strength was lowered, the FWCD efficiency decreased to approximately half of the maximum theoretical value.

  16. Electron-cyclotron wave propagation, absorption and current drive in the presence of neoclassical tearing modes

    NASA Astrophysics Data System (ADS)

    Isliker, Heinz; Chatziantonaki, Ioanna; Tsironis, Christos; Vlahos, Loukas

    2012-09-01

    We analyze the propagation of electron-cyclotron waves, their absorption and current drive when neoclassical tearing modes (NTMs), in the form of magnetic islands, are present in a tokamak plasma. So far, the analysis of the wave propagation and power deposition in the presence of NTMs has been performed mainly in the frame of an axisymmetric magnetic field, ignoring any effects from the island topology. Our analysis starts from an axisymmetric magnetic equilibrium, which is perturbed such as to exhibit magnetic islands. In this geometry, we compute the wave evolution with a ray-tracing code, focusing on the effect of the island topology on the efficiency of the absorption and current drive. To increase the precision in the calculation of the power deposition, the standard analytical flux-surface labeling for the island region has been adjusted from the usual cylindrical to toroidal geometry. The propagation up to the O-point is found to be little affected by the island topology, whereas the power absorbed and the driven current are significantly enhanced, because the resonant particles are bound to the small volumes in between the flux surfaces of the island. The consequences of these effects on the NTM evolution are investigated in terms of the modified Rutherford equation.

  17. ELECTRON CYCLOTRON CURRENT DRIVE IN DIII-D: EXPERIMENT AND THEORY

    SciTech Connect

    PRATER,R; PETTY,CC; LUCE,TC; HARVEY,RW; CHOI,M; LAHAYE,RJ; LIN-LIU,Y-R; LOHR,J; MURAKAMI,M; WADE,MR; WONG,K-L

    2003-07-01

    A271 ELECTRON CYCLOTRON CURRENT DRIVE IN DIII-D: EXPERIMENT AND THEORY. Experiments on the DIII-D tokamak in which the measured off-axis electron cyclotron current drive has been compared systematically to theory over a broad range of parameters have shown that the Fokker-Planck code CQL3D provides an excellent model of the relevant current drive physics. This physics understanding has been critical in optimizing the application of ECCD to high performance discharges, supporting such applications as suppression of neoclassical tearing modes and control and sustainment of the current profile.

  18. Increased confinement and beta by inductive poloidal current drive in the RFP

    SciTech Connect

    Sarff, J.S.; Lanier, N.E.; Prager, S.C.; Stoneking, M.R.

    1996-10-01

    Progress in understanding magnetic-fluctuation-induced transport in the reversed field pinch (RFP) has led to the idea of current profile control to reduce fluctuations and transport. With the addition of inductive poloidal current drive in the Madison Symmetric Torus (MST), the magnetic fluctuation amplitude is halved, leading to a four- to five-fold increase in the energy confinement time to {tau}{sub E}{approximately}5 ms as a result of both decreased plasma resistance and increased stored thermal energy. The record low fluctuation amplitude coincides with a record high electron temperature of {approximately}600 eV (for MST), and beta {beta} = 2{mu}{sub 0}

    / B(a){sup 2} increases from 6% to 8% compared with conventional MST RFP plasmas. Other improvements include increased particle confinement and impurity reduction. 19 refs., 4 figs., 1 tab.

  19. Current drive due to localized electron cyclotron power deposition in DIII-D

    SciTech Connect

    Harvey, R. W.; Lin-Liu, Y. R.; Sauter, O.; Smirnov, A. P.; Luce, T. C.; Prater, R.

    1999-09-20

    Due to spatial localization of electron cyclotron wave injection in DIII-D, electrons heated in an off-axis region must toroidally transit the tokamak 25-50 times before re-entering the heating region. This distance is of the order of the mean free path. The effect of such RF localization is simulated with a time-dependent Fokker-Planck code which is 2D-in-velocity, 1D-in-space-along-B, and periodic in space. An effective parallel electric field arises to maintain continuity of the driven current. Somewhat suprisingly, the localized current drive efficiency remains equal to that for a uniform medium. (c) 1999 American Institute of Physics.

  20. Broadband sidebands generated by parametric instability in lower hybrid current drive experiments on EAST

    SciTech Connect

    Amicucci, L. Castaldo, C.; Cesario, R.; Giovannozzi, E.; Tuccillo, A. A.; Ding, B. J.; Li, M. H.

    2015-12-10

    Modern research on nuclear fusion energy, based on the tokamak concept, has strong need of tools for actively driving non-inductive current especially at the periphery of plasma column, where tools available so far have poor efficiency. This is essential for solving one of the most critical problems for thermonuclear reactor, consisting in how to achieve the figure of fusion gain in the context of sufficient stability. The lower hybrid current drive (LHCD) effect has the potential capability of driving current at large radii of reactor plasma with high efficiency [1]. Experiments recently carried out on EAST showed that a strong activity of LH sideband waves (from the RF probe spectra), accompanied by weak core penetration of the coupled LH power, is present when operating at relatively high plasma densities. Previous theoretical results, confirmed by experiments on FTU, showed that the LH sideband phenomenon is produced by parametric instability (PI), which are mitigated by higher plasma edge temperatures. This condition is thus useful for enabling the LH power propagation when operating with profiles having high plasma densities even at the edge. In the present work, we show new PI modeling of EAST plasmas data, obtained in condition of higher plasma edge temperature due to chamber lithisation. The obtained trend of the PI frequencies and growth rates is consistent with data of RF probe spectra, available in different regimes of lithisated and not lithisated vessel. Moreover, these spectra are interpreted as PI effect occurring at the periphery of plasma column, however in the low field side where the LH power is coupled.

  1. Broadband sidebands generated by parametric instability in lower hybrid current drive experiments on EAST

    NASA Astrophysics Data System (ADS)

    Amicucci, L.; Ding, B. J.; Castaldo, C.; Cesario, R.; Giovannozzi, E.; Li, M. H.; Tuccillo, A. A.

    2015-12-01

    Modern research on nuclear fusion energy, based on the tokamak concept, has strong need of tools for actively driving non-inductive current especially at the periphery of plasma column, where tools available so far have poor efficiency. This is essential for solving one of the most critical problems for thermonuclear reactor, consisting in how to achieve the figure of fusion gain in the context of sufficient stability. The lower hybrid current drive (LHCD) effect has the potential capability of driving current at large radii of reactor plasma with high efficiency [1]. Experiments recently carried out on EAST showed that a strong activity of LH sideband waves (from the RF probe spectra), accompanied by weak core penetration of the coupled LH power, is present when operating at relatively high plasma densities. Previous theoretical results, confirmed by experiments on FTU, showed that the LH sideband phenomenon is produced by parametric instability (PI), which are mitigated by higher plasma edge temperatures. This condition is thus useful for enabling the LH power propagation when operating with profiles having high plasma densities even at the edge. In the present work, we show new PI modeling of EAST plasmas data, obtained in condition of higher plasma edge temperature due to chamber lithisation. The obtained trend of the PI frequencies and growth rates is consistent with data of RF probe spectra, available in different regimes of lithisated and not lithisated vessel. Moreover, these spectra are interpreted as PI effect occurring at the periphery of plasma column, however in the low field side where the LH power is coupled.

  2. Temporal behavior of the plasma current distribution in the ASDEX tokamak during lower-hybrid current drive

    SciTech Connect

    McCormick, K.; Soeldner, F.X.; Eckhartt, D.; Leuterer, F.; Murmann, H.; Derfler, H.; Eberhagen, A.; Gehre, O.; Gernhardt, J.; Gierke, G.v.; and others

    1987-02-02

    Measurements of the time evolution of the current-density distribution in ASDEX show that lower-hybrid current drive leads to broader profiles, whereby q increases from qapprox. <1 to q>1 in the plasma central region. Simultaneously, the electron temperature is observed to peak, thus demonstrating that the lower-hybrid--driven current distribution is decoupled from the classical conductivity profile.

  3. Novel current drive experiments on the CDX-U, HIT, and DIII-D Tokamaks

    SciTech Connect

    Ono, M.; Forest, C.B.; Hwang, Y.S.; Armstrong, R.J.; Choe, W.; Darrow, D.S.; Greene, G.; Jones, T. . Plasma Physics Lab.); Jarboe, T.R.; Martin, A.; Nelson, B.A.; Orvis, D.; Painter, C.; Zhou, L.; Rogers, J.A. ); Schaffer, M.J.; Hyatt, A.W.; Pinsker, R.I.; Staebler, G.M.; Stambaugh, R.D.; Strait, E.J.; Greene, K.L.; Leuer, J.A.; Lohr, J.

    1992-01-01

    Two types of novel, non-inductive current drive concepts for starting-up and maintaining tokamak discharges have been developed on the CDX-U, HIT, and DIII-D Tokamaks. On CDX-U, a new, non-inductive current drive technique utilizing fully internally generated pressure driven currents has been demonstrated. The measured current density profile shows a non-hollow profile which agrees with a modeling calculation including helicity conserving non-classical current transport providing the seed current''. Another current drive concept, dc-helicity injection, has been investigated on, CDX-U, HIT and DIII-D. This method utilizes injection of magnetic helicity via low energy electron currents, maintaining the plasma current through helicity conserving relaxiation. In these experiments, non-ohmic tokamak plasmas were formed and maintained in the tens of kA range.

  4. Novel current drive experiments on the CDX-U, HIT, and DIII-D Tokamaks

    SciTech Connect

    Ono, M.; Forest, C.B.; Hwang, Y.S.; Armstrong, R.J.; Choe, W.; Darrow, D.S.; Greene, G.; Jones, T.; Jarboe, T.R.; Martin, A.; Nelson, B.A.; Orvis, D.; Painter, C.; Zhou, L.; Rogers, J.A.; Schaffer, M.J.; Hyatt, A.W.; Pinsker, R.I.; Staebler, G.M.; Stambaugh, R.D.; Strait, E.J.; Greene, K.L.; Leuer, J.A.; Lohr, J.M.

    1992-10-01

    Two types of novel, non-inductive current drive concepts for starting-up and maintaining tokamak discharges have been developed on the CDX-U, HIT, and DIII-D Tokamaks. On CDX-U, a new, non-inductive current drive technique utilizing fully internally generated pressure driven currents has been demonstrated. The measured current density profile shows a non-hollow profile which agrees with a modeling calculation including helicity conserving non-classical current transport providing the ``seed current``. Another current drive concept, dc-helicity injection, has been investigated on, CDX-U, HIT and DIII-D. This method utilizes injection of magnetic helicity via low energy electron currents, maintaining the plasma current through helicity conserving relaxiation. In these experiments, non-ohmic tokamak plasmas were formed and maintained in the tens of kA range.

  5. Lower hybrid current drive in the PLT tokamak

    SciTech Connect

    Bernabei, S.; Daughney, C.; Efthimion, P.

    1982-07-01

    Order of magnitude improvements in the level and duration of current driven by lower hybrid waves have been achieved in the PLT tokamak. Steady currents up to 175 kA have been maintained for three seconds and 400 kA for 0.3 sec by the rf power alone. The principal current carrier appears to be a high energy (approx. 100 keV) electron component, concentrated in the central 20 to 40 cm diameter core of the 80 cm PLT discharge.

  6. The underwater sound field from vibratory pile driving.

    PubMed

    Dahl, Peter H; Dall'Osto, David R; Farrell, Dara M

    2015-06-01

    Underwater noise from vibratory pile driving was observed using a vertical line array placed at range 16 m from the pile source (water depth 7.5 m), and using single hydrophones at range 417 m on one transect, and range 207 and 436 m on another transect running approximately parallel to a sloping shoreline. The dominant spectral features of the underwater noise are related to the frequency of the vibratory pile driving hammer (typically 15-35 Hz), producing spectral lines at intervals of this frequency. The mean-square pressure versus depth is subsequently studied in third-octave bands. Depth and frequency variations of this quantity observed at the vertical line array are well modeled by a field consisting of an incoherent sum of sources distributed over the water column. Adiabatic mode theory is used to propagate this field to greater ranges and model the observations made along the two depth-varying transects. The effect of shear in the seabed, although small, is also included. Bathymetric refraction on the transect parallel to the shoreline reduced mean-square pressure levels at the 436-m measurement site. PMID:26093441

  7. Plasma Heating and Current Drive by Stochastic Acceleration of Relativistic Electrons at the WEGA Stellarator

    NASA Astrophysics Data System (ADS)

    Laqua, Heinrich; Chlechowitz, Enrico; Fuchs, Vladimir; Otte, Matthias; Stange, Torsten

    2013-10-01

    Relativistic electrons with parallel energies of up to 2 MeV have been continuously (10 s) generated by a stochastic interaction with the rf-field (6-26kW) of a 2.45 GHz open waveguide antenna without any loop voltage. These ``run-away'' electrons have been detected by their synchrotron, x- and γ-ray emission and have also generated a toroidal plasma current in the kA range. They are perfectly confined in the stellarator magnetic field of 0.5 T. The particle trajectories form their own nested drift surfaces which are shrunken inward and shifted outward with respect to the magnetic flux surfaces. This geometrical effect connects the antenna region, where the electrons are accelerated, with the plasma core, where a low temperature (20eV, 0.2-5 1018m3) bulk plasma is generated. The acceleration process was modelled by a random walk diffusion model and a Fermi Ulan map Monte-Carlo simulation. Both calculations show similar results for the heating and current drive efficiencies. They also reproduce the temporal behaviour of the plasma current and the synchrotron radiation, when the RF-power is modulated and show the need for a random phase interaction between the relativistic electrons and the antenna field.

  8. Bearing currents and their relationship to PWM drives

    SciTech Connect

    Busse, D.; Erdman, J.; Kerkman, J.; Schlegel, D.; Skibinski, G.

    1997-03-01

    This paper examines ac motor shaft voltages and the resulting bearing currents when operated under pulse width modulation (PWM) voltage source inverters. The paper reviews the mechanical and electrical characteristics of the bearings and motor in relation to shaft voltages and bearing currents. A brief review of previous work is addressed, including the system model and experimental results. The theory of electric discharge machining (EDM) is presented, including component calculations of the system elements. The effect of system elements on shaft voltages and bearing currents are evaluated experimentally and the results compared to theory. A design calculation is proposed that provides the relative potential for EDM. Finally, the paper will present quantitative results on one solution to the shaft voltage and bearing current problem.

  9. Electromagnetic currents induced by color fields

    NASA Astrophysics Data System (ADS)

    Tanji, Naoto

    2015-12-01

    The quark production in classical color fields is investigated with a focus on the induction of an electromagnetic current by produced quarks. We show that the color SU(2) and the SU(3) theories lead significantly different results for the electromagnetic current. In uniform SU(2) color fields, the net electromagnetic current is not generated, while in SU(3) color fields the net current is induced depending on the color direction of background fields. Also the numerical study of the quark production in inhomogeneous color fields is done. Motivated by gauge field configurations provided by the color glass condensate framework, we introduce an ensemble of randomly distributed color electric fluxtubes. The spectrum of photons emitted from the quarks by a classical process is shown.

  10. Field-aligned currents and large scale magnetospheric electric fields

    NASA Technical Reports Server (NTRS)

    Dangelo, N.

    1980-01-01

    D'Angelo's model of polar cap electric fields (1977) was used to visualize how high-latitude field-aligned currents are driven by the solar wind generator. The region 1 and region 2 currents of Iijima and Potemra (1976) and the cusp field-aligned currents of Wilhjelm et al. (1978) and McDiarmid et al. (1978) are apparently driven by different generators, although in both cases the solar wind is their ultimate source.

  11. Transient analysis of electromagnets with emphasis on solid components, eddy currents, and driving circuitry

    NASA Astrophysics Data System (ADS)

    Batdorff, Mark A.

    Valves are commonly used in fluid power systems to control pressure and flow. The emerging field of digital hydraulics demands high-speed, low cost, on/off valves with improved performance. Electromagnets, or solenoids, are commonly used to actuate valves due to their low cost, high reliability, and moderate performance. This work develops a dynamic model for a solid steel electromagnet that can be used for design and optimization, and unveils design tradeoffs with geometry and driving circuitry that are often overlooked. This work develops an accurate, computationally efficient, nonlinear, coupled, dynamic, axisymmetric, high fidelity magnetic equivalent circuit (HFMEC) electromagnet model capable of predicting force, inductance, dynamic response, and energy consumption. The model is intended for applications where both accuracy and solution time are critical. Axisymmetric magnetic fringing and leakage permeances were derived in order to capture nonlinear magnetic field phenomena that affect force and inductance. The tradeoffs between solid-center and hollow-center electromagnets were investigated. It was shown with both simulation and measurement that a hollow-center electromagnet has a 37.7% shorter useful stroke due to increased magnetic fringing and leakage (from 4.0mm to 2.5mm). However, it was also shown that the hollow-center electromagnet has a 70% improved turn-off response (from 617ms to 362ms). A single objective optimization study was performed demonstrating that hollow-center electromagnets are advantageous and can up to 204% increased dynamic response for systems where dynamics are dominated by eddy current lag. Electromagnets experience dynamic lag when turning on and off due to inductance and eddy currents. Coil driving methods, such as peak-and-hold, are often used to minimize turn-on lag by using high initial voltages and currents. However, circuits often do not address turn-off lag, which can be significant. This work investigates the effects of

  12. Modeling of Trapped Electron Effects on Electron Cyclotron Current Drive for Recent DIII-D Experiments

    SciTech Connect

    Lin-Liu, Y.R.; Sauter, O.; Harvey, R.W.; Chan, V.S.; Luce, T.C.; Prater, R.

    1999-08-01

    Owing to its potential capability of generating localized non-inductive current, especially off-axis, Electron Cyclotron Current Drive (ECCD) is considered a leading candidate for current profile control in achieving Advanced Tokamak (AT) operation. In recent DIII-D proof-of-principle experiments [1], localized off-axis ECCD has been clearly demonstrated for first time. The measured current drive efficiency near the magnetic axis agrees well with predictions of the bounce-averaged Fokker-Planck theory [2,3]. However, the off-axis current drive efficiency was observed to exceed the theoretical results, which predict significant degradation of the current drive efficiency due to trapped electron effects. The theoretical calculations have been based on an assumption that the effective collision frequency is much smaller than the bounce frequency such that the trapped electrons are allowed to complete the banana orbit at all energies. The assumption might be justified in reactor-grade tokamak plasmas, in which the electron temperature is sufficiently high or the velocity of resonant electrons is much larger than the thermal velocity, so that the influence of collisionality on current drive efficiency can be neglected. For off-axis deposition in the present-day experiments, the effect of high density and low temperature is to reduce the current drive efficiency, but the increasing collisionality reduces the trapping of current-carrying electrons, leading to compensating increases in the current drive efficiency. In this work, we use the adjoint function formulation [4] to examine collisionality effects on the current drive efficiency.

  13. Review of the experimental papers at the IAEA conference on noninductive current drive, Culham, 1983

    SciTech Connect

    Motley, R.W.

    1983-10-01

    Three types of noninductive current drive experiments have been reported at this conference: (1) neutral beam (2) rf current drive, and (3) relativistic electron beams (REB). If we compare the effort to develop current drive to a horse race, the neutral beam horse was first out of the gates, but it quickly found greener pastures (heating) and has dropped temporarily out of the race. The lower hybrid horse now has a big lead at the first furlong (200 m), but the bulk of the race remains to be run. The fast wave and REB horses have yet to get up speed.

  14. Direct-current-like Phase Space Manipulation Using Chirped Alternating Current Fields

    SciTech Connect

    P.F. Schmit and N.J. Fisch

    2010-02-01

    Waves in plasmas can accelerate particles that are resonant with the wave. A dc electric field also accelerates particles, but without a resonance discrimination, which makes the acceleration mechanism profoundly different. Whereas wave-particle acceleration mechanisms have been widely discussed in the literature, this work discusses the direct analogy between wave acceleration and dc field acceleration in a particular parameter regime explored in previous works. Apart from the academic interest of this correspondence, there may be practical advantages in using waves to mimic dc electric fields, for example, in driving plasma current with high efficiency.

  15. Conserved currents of double field theory

    NASA Astrophysics Data System (ADS)

    Blair, Chris D. A.

    2016-04-01

    We find the conserved current associated to invariance under generalised diffeomorphisms in double field theory. This can be used to define a generalised Komar integral. We comment on its applications to solutions, in particular to the fundamental string/pp-wave. We also discuss the current in the context of Scherk-Schwarz compactifications. We calculate the current for both the original double field theory action, corresponding to the NSNS sector alone, and for the RR sector.

  16. Overview of Recent Results on Heating and Current Drive in the JET tokamak

    SciTech Connect

    Mayoral, M.-L.; Baranov, Yu.; Blackman, T.; Graham, M.; Jacquet, Ph.; Kiptily, V.; Kirov, K.; Mailloux, J.; Monakhov, I.; Nightingale, M.; Whitehurst, A.; Wooldridge, E.; Argouarch, A.; Colas, L.

    2009-11-26

    In this paper, significant results in the heating and current drive domains obtained at JET in the past few years following systems upgrade and dedicated experimental time, will be reviewed. Firstly, an overview of the new Ion Cyclotron Resonance Frequency (ICRF) heating capabilities will be presented i.e. results from the ITER-Like ICRF antenna (ILA), the use of External Conjugate-T and 3dB hybrid couplers to increase the ICRF power during ELMy H-mode. Furthermore, experiments to study the influence of the phasing of the ICRF antenna on power absorption and coupling will be described. Looking at Low Hybrid (LH) issues for ITER, the effect of the location of gas injection on the LH coupling improvement at large launcher-separatrix distances will be discussed as the possibility to operate at ITER-relevant power densities. Experiments to characterise the LH power losses in the Scrape-Off-Layer (SOL) and to determine the LH wave absorption and current drive using power modulation will be shown. Finally, plasma rotation studies in the presence of ICRF heating with standard and enhanced JET toroidal field ripple will be presented.

  17. Simulations of fast-wave current drive in pulsed and steady-state DEMO designs

    NASA Astrophysics Data System (ADS)

    Bilato, R.; Brambilla, M.; Fable, E.

    2014-11-01

    Electromagnetic waves in the ion-cyclotron (IC) range of frequencies are presently investigated as possible current drive (CD) systems in fusion reactors. Among many physical and technical issues, an accurate description of radio-frequency (RF) power absorption by fusion- born alpha particles is of special importance, since RF heating of these particles is not only detrimental for the CD efficiency, but might worsen the operative conditions by increasing their prompt losses. The capability of the full-wave TORIC code has been recently augmented to account for RF absorption by fusion-born alpha particles, calculated to all-orders in finite Larmor radius and with a realistic distribution function. Here, we present simulation with TORIC addressing the sensitivity of current drive efficiency on the design of a future reactor, in particular density and temperature profiles, magnetic field intensity, and plasma dimensions. For this purpose, we have investigated possible frequency windows for CD for two proposed versions of the DEMO reactor, namely its pulsed and its more ambitious steady-state design. The important role of the antenna for a realistic estimate of the CD efficiency is pointed out.

  18. The Plasma Physics Processes that Drive Ring Current Enhancements during Geomagnetic Storms and Substorms

    NASA Astrophysics Data System (ADS)

    Cash, Michele Diane

    Geomagnetic storms result when energetic particles of solar and ionospheric origin fill Earth's inner magnetosphere and create a strong westward current, known as the ring current. This dissertation presents results from investigating the plasma dynamics that contribute to the development of Earth's ring current from ionospheric outflow of H+ and O+ ions, and the role of ring current enhancements in the generation of geomagnetic storms and substorms. Modeling was carried via a combined multifluid and particle approach, which enables us to resolve the small-scale dynamics that are key to particle energization within the context of the global magnetosphere. The results presented in this dissertation substantially contribute to our understanding of the development and composition of the ring current during geomagnetic storms and substorms, and offer insight into the ionospheric sources regions for ring current ions, as well as the processes through which these particles are energized, injected, and trapped within the inner magnetosphere. This thesis presents results that show how small-scale particle dynamics within the current sheet, boundary layers, and reconnection regions drive the acceleration of ring current particles within the larger global context of the magnetosphere. Small-scale structures within the magnetotail are shown to be more important in determining when particles are accelerated than the time after particles are initialized in the ionosphere. It is also found that after a period of southward IMF, in which particle energization is observed, a northerly turning of the IMF is necessary in order to trap energetic particles in orbit around the Earth and form a symmetric ring current. Asymmetries in the acceleration mechanisms between ionospheric H+ and O + ions were observed with oxygen ions convecting duskward according to the cross-tail current and gaining more energy than protons, which moved earthward on reconnecting field lines and were accelerated

  19. MHD Modeling in Complex 3D Geometries: Towards Predictive Simulation of SIHI Current Drive

    NASA Astrophysics Data System (ADS)

    Hansen, Christopher James

    The HIT-SI experiment studies Steady Inductive Helicity Injection (SIHI) for the purpose of forming and sustaining a spheromak plasma. A spheromak is formed in a nearly axisymmetric flux conserver, with a bow tie cross section, by means of two semi-toroidal injectors. The plasma-facing surfaces of the device, which are made of copper for its low resistivity, are covered in an insulating coating in order to operate in a purely inductive manner. Following formation, the spheromak flux and current are increased during a quiescent period marked by a decrease in the global mode activity. A proposed mechanism, Imposed Dynamo Current Drive (IDCD), is expected to be responsible for this phase of quiescent current drive. Due to the geometric complexity of the experiment, previous numerical modeling efforts have used a simplified geometry that excludes the injector volumes from the simulated domain. The effect of helicity injection is then modeled by boundary conditions on this reduced plasma volume. The work presented here has explored and developed more complete computational models of the HIT-SI device. This work is separated into 3 distinct but complementary areas: 1) Development of a 3D MHD equilibrium code that can incorporate the non-axisymmetric injector fields present in HIT-SI and investigation of equilibria of interest during spheromak sustainment. 2) A 2D axisymmetric MHD equilibrium code that was used to explore reduced order models for mean-field evolution using equations derived from IDCD theory including coupling to 3D equilibria. 3) A 3D time-dependent non-linear MHD code that is capable of modeling the entire plasma volume including dynamics within the injectors. Although HIT-SI was the motivation for, and experiment studied in this research, the tools and methods developed are general --- allowing their application to a broad range of magnetic confinement experiments. These tools constitute a significant advance for modeling plasma dynamics in devices with

  20. Current drive with the second ECR harmonic on T-10

    SciTech Connect

    Alikaev, V.V.; Bagdasarov, A.A.; Borshegovskij, A.A.; Dremin, M.M.; Esipchuk, Y.V.; Gorelov, Y.A.; Ivanov, N.V.; Kislov, A.Y.; Kuznetsova, L.K.; Notkin, G.E.; Pavlov, Y.D.; Razumova, K.A.; Roy, I.N.; Vasin, N.L.; Vershkov, V.A. , Moscow ); Forest, C.B.; Lohr, J.; Luce, T.C.; Harvey, R.W. ); The T-10 Team

    1994-10-15

    The experiments on ECCD on the second harmonic were done. Current about 35 kA was generated. The efficiency of ECCD and its dependencies on plasma parameters were measured. Not all observed phenomena may be explained by the predictions of linear theory.

  1. Current-Produced Magnetic Field Effects on Current Collection

    NASA Technical Reports Server (NTRS)

    Khazanov, George V.; Stone, N. H.; Whitaker, Ann F. (Technical Monitor)

    2002-01-01

    Current collection by an infinitely long, conducting cylinder in a magnetized plasma, taking into account the magnetic field of the collected current, is discussed. A region of closed magnetic surfaces disconnects the cylinder from infinity. Due to this, the collected current depends on the ratio between this region and the plasma sheath region and, under some conditions, current reduction arises. The current collection along a realistic "bare wire" space tether is considered. A number of factors are taken into account, including the resistance of the wire and shielding resulting from the current-induced magnetic field produced by current flow in the tether. The plasma density, tether length and radius, the geomagnetic field strength and angle to the orbital velocity vector were all used as parameters in the study. It is shown that magnetic shielding for certain tether system configurations, when combined with particular values of the governing parameters, significantly reduces the collected current. Specifically, it is shown that an electrodynamic tether in the "thruster" mode suffers greater reduction from magnetic shielding than a tether with the same characteristics deployed in the "generator" mode. We find that, for both modes, current-induced magnetic shielding becomes more significant as plasma density and wire radius increase. The same is true for the dependence on the angle of the geomagnetic field to the orbital velocity vector and the motion-induced electric field for the generator mode For the thruster mode, the effect is larger for smaller angles. In both operating modes, the shielding is more important for smaller angles between the tether and magnetic field. In addition to the above dependencies, the effect for the thruster mode essentially depends on the tether length. In general, any parametric change that increases tether current, relative to the strength of the electric field between the tether and the ambient plasma, will increase the shielding

  2. Full-wave calculation of fast-wave current drive in tokamaks including k sub parallel variations

    SciTech Connect

    Jaeger, E.F; Batchelor, D.B.

    1991-01-01

    When fast waves propagate inward from the edge of a tokamak toward the plasma center, the k{perpendicular} spectrum produced by the antenna is not maintained but is shifted and deformed due to the presence of the finite poloidal magnetic field. This k{perpendicular} shift causes a variation in the parallel phase speed of the wave and can therefore have a strong effect on electron damping and current drive efficiency. In this paper, we include this effect in a new full-wave calculation (PICES) which represents the wave fields as a superposition of poloidal modes, thereby reducing k{perpendicular} to an algebraic operator. The wave equation is solved in general flux coordinates, including a full (non-perturbative) solution for E{perpendicular} and a reduced-order dielectric formulation to eliminate short-wavelength ion Bernstein modes. A simplified current drive model which includes particle trapping is used to estimate the effect of the k{perpendicular} shift on current drive efficiency in ITER and D3-D. Results suggest that when single-pass absorption is weak, reflected power may drive current nearly as efficiently as that absorbed on the first pass. 15 refs., 5 figs.

  3. Field and Current Amplification in the SSPX Spheromak

    SciTech Connect

    Hill, D N; Blumer, R H; Cohen, B I; Hooper, E B; McLean, H S; Moller, J; Pearlstein, L D; Ryutov, D D; Stallard, B W; Wood, R D; Woodruff, S; Holcomb, C T; Jarboe, T; Bellan, P; Romero-Talamas, C

    2002-10-08

    Results are presented from experiments relating to magnetic field generation and current amplification in the SSPX spheromak. The SSPX spheromak plasma is driven by DC coaxial helicity injection using a 2MJ capacitor bank. Peak toroidal plasma currents of up to 0.7MA and peak edge poloidal fields of 0.3T are produced; lower current discharges can be sustained up to 3.5msec. When edge magnetic fluctuations are reduced below 1% by driving the plasma near threshold, it is possible to produce plasmas with Te > 150eV, <{beta}{sub e}>-4% and core {chi}{sub e} {approx} 30m{sup 2}/s. Helicity balance for these plasmas suggests that sheath dissipation can be significant, pointing to the importance of maximizing the voltage on the coaxial injector. For most operational modes we find a stiff relationship between peak spheromak field and injector current, and little correlation with plasma temperature, which suggests that other processes than ohmic dissipation may limit field amplification. However, slowing spheromak buildup by limiting the initial current pulse increases the ratio of toroidal current to injected current and points to new operating regimes with more favorable current amplification.

  4. Driving mechanism for plunger pumps in oil field installations

    SciTech Connect

    Gazarov, R.E.; Zaslavskii, Yu.V.

    1995-07-01

    Mobile oil field pumping installations of up to 1600 kW power at a pressure up to 140 MPa are widely used in hydraulic fracturing of beds, acid treatment of the near-face zone, cementation of wells, and other flushing and pressure operations. Equipment in these installations, which include high-pressure plunger pumps of high unit capacity, are mounted on mobile bases of limited lifting capacity (KrAZ automobile chassis, T-130 tractors, etc.). Very strict demands are made on the reliability, durability, and mass/size characteristics of the pumps and on all the equipment of the mobile installations. In modern pumps, an axial load of up to 100 tons or more, which is transmitted to the crankshaft, acts on each plunger. The engine of the installation rotates the crankshaft through a multiple-speed transmission and the transmission shaft of the pump. The forces acting on the elements of the driving part of a pump with a connecting rod - crank drive and a single-reduction tooth gear are described.

  5. Isotopic effect in experiments on lower hybrid current drive in the FT-2 tokamak

    SciTech Connect

    Lashkul, S. I. Altukhov, A. B.; Gurchenko, A. D. Gusakov, E. Z.; D’yachenko, V. V.; Esipov, L. A.; Irzak, M. A. Kantor, M. Yu.; Kouprienko, D. V.; Saveliev, A. N.; Stepanov, A. Yu.; Shatalin, S. V.

    2015-12-15

    To analyze factors influencing the limiting value of the plasma density at which lower hybrid (LH) current drive terminates, the isotopic factor (the difference in the LH resonance densities in hydrogen and deuterium plasmas) was used for the first time in experiments carried out at the FT-2 tokamak. It is experimentally found that the efficiency of LH current drive in deuterium plasma is appreciably higher than that in hydrogen plasma. The significant role of the parametric decay of the LH pumping wave, which hampers the use of the LH range of RF waves for current drive at high plasma densities, is confirmed. It is demonstrated that the parameters characterizing LH current drive agree well with the earlier results obtained at large tokamaks.

  6. Heating and current drive on NSTX and HHFW experiments on CDX-U

    SciTech Connect

    Wilson, J.R.; Hosea, J.; Grisham, L.

    1998-07-01

    The NSTX (National Spherical Torus Experiment) device to be built at Princeton is a low-aspect-ratio toroidal device that has the achievement of high toroidal beta ({approximately} 45%) and noninductive operation as two of its main research goals. To achieve these goals, significant auxiliary-heating and current-drive systems are required. Present plans include ECH (electron cyclotron heating) for preionized and start-up assist, HHFW (high harmonic fast wave) for heating and current drive, and, eventually, NBI (neutral-beam injection) for heating, current drive and plasma rotation. In support of the NSTX program, experimental tests of HHFW physics have been performed on the Current Drive Experiment-Upgrade (CDX-U).

  7. Coupling of α-channeling to |k∥| upshift in lower hybrid current drive

    SciTech Connect

    Ochs, I. E.; Bertelli, N.; Fisch, N. J.

    2014-08-26

    Although lower hybrid waves have been shown to be effective in driving plasma current in present-day tokamaks, they are predicted to strongly interact with the energetic α particles born from fusion reactions in eventual tokamak reactors.

  8. A theory for LH heating and current drive experiments

    SciTech Connect

    Canobbio, E.; Croci, R.

    1985-07-01

    The relevant nonlinear partial differential equation for the amplitude E of a LH wave in a uniform plasma half-space is solved for E's which exclude solitary wave formation. The original k-spectrum of the field of a resonance cone is found to decay substantially as a result of a secular (in space) effect. This is instrumental in solving the spectral gap problem. Also, even for smooth E-profiles at the plasma boundary, there is a surface of discontinuity of grad E (wave breaking). The minimum distance of such a surface from the plasma boundary is a measure of the maximum penetration depth of a LH pump.

  9. HEATING AND CURRENT DRIVE IN NSTX WITH ELECTRON BERNSTEIN WAVES AND HIGH HARMONIC FAST WAVES

    SciTech Connect

    Ram, Abhay K

    2010-06-14

    A suitable theoretical and computational framework for studying heating and current drive by electron Bernstein waves in the National Spherical Torus Experiment has been developed. This framework can also be used to study heating and current drive by electron Bernstein waves in spherical tori and other magnetic confinement devices. It is also useful in studying the propagation and damping of electron cyclotron waves in the International Thermonuclear Experimental Reactor

  10. Control of plasma profiles and stability through localised Electron Cyclotron Current Drive

    NASA Astrophysics Data System (ADS)

    Merkulov, Oleksiy

    2006-06-01

    The work presented in this thesis addresses several topics from the physics of the magnetically confined plasma inside a tokamak. At the moment, the tokamak is the most successful concept for becoming a future thermonuclear reactor. However, there are plenty of physics and engineering problems to surpass before the prototype can become an economically and environmentally feasible device. The plasma in the tokamak experiences periodic oscillations of the central temperature and density when the safety factor, q, drops below unity on-axis. These oscillations are called the sawtooth instability and are the subject of the first part of this thesis. The sawtooth oscillations are characterised by the relatively slow rise phase, when the central temperature increases, and a following crash phase, when the central temperature drops. The energy, particles and plasma current are redistributed during the sawtooth crash. Obviously, this leads to a confinement degradation and moreover, the sawtooth instability can trigger potentially other more dangerous instabilities, such as a neoclassical tearing mode. The sawtooth period control is realised on the basis of the sawtooth trigger model, derived by Porcelli. The main idea of this model is that the sawtooth crash is triggered when the magnetic shear at the q=1 surface, s1, reaches a critical value which depends on the local plasma parameters. The magnetic shear, s, is a measure for the rate of change in the direction of the field line as a function of the position in the plasma. The sawtooth period can be changed by affecting the evolution of s1. The effects of the electron cyclotron current drive (ECCD) on the shear evolution are studied with a simple model for the poloidal field evolution. The results of the model are summarised in a form of a criterion for the amount of the non-inductive current drive required for sawtooth period control. The effects of the ECCD have been studied in the TEXTOR tokamak in order to confirm the

  11. Integrated modelling of steady-state scenarios and heating and current drive mixes for ITER

    SciTech Connect

    Murakami, Masanori; Park, Jin Myung

    2011-01-01

    Recent progress on ITER steady-state (SS) scenario modelling by the ITPA-IOS group is reviewed. Code-to-code benchmarks as the IOS group's common activities for the two SS scenarios (weak shear scenario and internal transport barrier scenario) are discussed in terms of transport, kinetic profiles, and heating and current drive (CD) sources using various transport codes. Weak magnetic shear scenarios integrate the plasma core and edge by combining a theory-based transport model (GLF23) with scaled experimental boundary profiles. The edge profiles (at normalized radius rho = 0.8-1.0) are adopted from an edge-localized mode-averaged analysis of a DIII-D ITER demonstration discharge. A fully noninductive SS scenario is achieved with fusion gain Q = 4.3, noninductive fraction f(NI) = 100%, bootstrap current fraction f(BS) = 63% and normalized beta beta(N) = 2.7 at plasma current I(p) = 8MA and toroidal field B(T) = 5.3 T using ITER day-1 heating and CD capability. Substantial uncertainties come from outside the radius of setting the boundary conditions (rho = 0.8). The present simulation assumed that beta(N)(rho) at the top of the pedestal (rho = 0.91) is about 25% above the peeling-ballooning threshold. ITER will have a challenge to achieve the boundary, considering different operating conditions (T(e)/T(i) approximate to 1 and density peaking). Overall, the experimentally scaled edge is an optimistic side of the prediction. A number of SS scenarios with different heating and CD mixes in a wide range of conditions were explored by exploiting the weak-shear steady-state solution procedure with the GLF23 transport model and the scaled experimental edge. The results are also presented in the operation space for DT neutron power versus stationary burn pulse duration with assumed poloidal flux availability at the beginning of stationary burn, indicating that the long pulse operation goal (3000s) at I(p) = 9 MA is possible. Source calculations in these simulations have been

  12. The Driving Magnetic Field and Reconnection in CME/Flare Eruptions and Coronal Jets

    NASA Technical Reports Server (NTRS)

    Moore, Ronald L.

    2010-01-01

    Signatures of reconnection in major CME (coronal mass ejection)/flare eruptions and in coronal X-ray jets are illustrated and interpreted. The signatures are magnetic field lines and their feet that brighten in flare emission. CME/flare eruptions are magnetic explosions in which: 1. The field that erupts is initially a closed arcade. 2. At eruption onset, most of the free magnetic energy to be released is not stored in field bracketing a current sheet, but in sheared field in the core of the arcade. 3. The sheared core field erupts by a process that from its start or soon after involves fast "tether-cutting" reconnection at an initially small current sheet low in the sheared core field. If the arcade has oppositely-directed field over it, the eruption process from its start or soon after also involves fast "breakout" reconnection at an initially small current sheet between the arcade and the overarching field. These aspects are shown by the small area of the bright field lines and foot-point flare ribbons in the onset of the eruption. 4. At either small current sheet, the fast reconnection progressively unleashes the erupting core field to erupt with progressively greater force. In turn, the erupting core field drives the current sheet to become progressively larger and to undergo progressively greater fast reconnection in the explosive phase of the eruption, and the flare arcade and ribbons grow to become comparable to the pre-eruption arcade in lateral extent. In coronal X-ray jets: 1. The magnetic energy released in the jet is built up by the emergence of a magnetic arcade into surrounding unipolar "open" field. 2. A simple jet is produced when a burst of reconnection occurs at the current sheet between the arcade and the open field. This produces a bright reconnection jet and a bright reconnection arcade that are both much smaller in diameter that the driving arcade. 3. A more complex jet is produced when the arcade has a sheared core field and undergoes an

  13. Current Research Activities in Drive System Technology in Support of the NASA Rotorcraft Program

    NASA Technical Reports Server (NTRS)

    Handschuh, Robert F.; Zakrajsek, James J.

    2006-01-01

    Drive system technology is a key area for improving rotorcraft performance, noise/vibration reduction, and reducing operational and manufacturing costs. An overview of current research areas that support the NASA Rotorcraft Program will be provided. Work in drive system technology is mainly focused within three research areas: advanced components, thermal behavior/emergency lubrication system operation, and diagnostics/prognostics (also known as Health and Usage Monitoring Systems (HUMS)). Current research activities in each of these activities will be presented. Also, an overview of the conceptual drive system requirements and possible arrangements for the Heavy Lift Rotorcraft program will be reviewed.

  14. Changing Chilean coastal currents could drive aquatic evolution

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2012-01-01

    For invertebrate and fish species that spend most of their lives in rich coastal waters rather than migrating freely throughout the open ocean, the formation of island populations and the associated risk of genetic diversity loss are threats to long-term population health. Many species cope through a spawning mechanism whereby larvae are released en masse into near-shore ocean currents, like pollen adrift in the wind. The larvae are viable in open waters from days to months, but only those that find their way back to shore can settle and develop. To increase their chances, different species' larvae often use particular swimming behaviors, for example, varying their depth in the water column throughout the day.

  15. Intervening to decrease the probability of alcohol-impaired driving: Impact of novel field sobriety tests.

    PubMed

    Smith, Ryan C; Robinson, Zechariah; Bazdar, Alexandra; Geller, E Scott

    2016-01-01

    The efficacy of novel field sobriety tests to predict breath alcohol content (BAC) and perceptions of driving risk was evaluated. Participants (N = 210) were passersby at two downtown locations near local bars and one on-campus location near a late-night dining facility between the hours of 10:00 p.m. and 2:00 a.m. Participants gave ratings of their perceived risk to drive at their current level of intoxication, then completed three sobriety tests (a hand-pat, tracing test, and Romberg test), and finally provided new ratings of their perceived risk to drive. After completing the final set of questions, participants were administered a Lifeloc FC20 breath alcohol test (±.005 g/dL). Each of the sobriety tests performed better than chance at predicting participant intoxication, but the performance feedback did not enhance awareness of one's risk to drive at a given BAC. Actually, after the sobriety tests, Greek-life females perceived themselves to be less at-risk to drive. PMID:27309028

  16. Electric field induced spin-polarized current

    DOEpatents

    Murakami, Shuichi; Nagaosa, Naoto; Zhang, Shoucheng

    2006-05-02

    A device and a method for generating an electric-field-induced spin current are disclosed. A highly spin-polarized electric current is generated using a semiconductor structure and an applied electric field across the semiconductor structure. The semiconductor structure can be a hole-doped semiconductor having finite or zero bandgap or an undoped semiconductor of zero bandgap. In one embodiment, a device for injecting spin-polarized current into a current output terminal includes a semiconductor structure including first and second electrodes, along a first axis, receiving an applied electric field and a third electrode, along a direction perpendicular to the first axis, providing the spin-polarized current. The semiconductor structure includes a semiconductor material whose spin orbit coupling energy is greater than room temperature (300 Kelvin) times the Boltzmann constant. In one embodiment, the semiconductor structure is a hole-doped semiconductor structure, such as a p-type GaAs semiconductor layer.

  17. Noninductive current drive experiments on DIII-D, and future plans

    SciTech Connect

    Prater, R.; Austin, M.E.; Baity, F.W.

    1994-02-01

    Experiments on DIII-D (and other tokamaks) have shown that improved performance can follow from optimization of the current density profile. Increased confinement of energy and a higher limit on beta have both been found in discharges in which the current density profile is modified through transient means, such as ramping of current or elongation. Peaking of the current distribution to obtain discharges with high internal inductance {ell}{sub i} has been found to be beneficial. Alternatively, discharges with broader profiles, as in the VH-mode or with high beta poloidal, have shown improved performance. Noninductive current drive is a means to access these modes of improved confinement on a steady state basis. Accordingly, experiments on noninductive current drive are underway on the DIII-D tokamak using fast waves, electron cyclotron waves. Recent experiments on fast wave current drive have demonstrated the ability to drive up to 180 kA of noninductive current using 1.5 MW of power at 60 MHz, including the contribution from 1 MW of ECCD and the bootstrap current. Higher power rf current drive systems are needed to strongly affect the current profile on DIII-D. An upgrade to the FWCD system is underway to increase the total power to 6 MW, using two additional antennas and two new 30 to 120 MHz transmitters. Additionally, a 1 MW prototype ECH system at 110 GHz is being developed (with eventual upgrade to 10 MW). With these systems, noninductive current drive at the 1 MA level will be available for experiments on profile control in DIII-D.

  18. Dayside Pi 2 Pulsations Associated with Ionospheric Currents Produced By Oscillating Nightside Field-Aligned Currents

    NASA Astrophysics Data System (ADS)

    Imajo, S.; Yoshikawa, A.; Uozumi, T.; Ohtani, S.; Nakamizo, A.; Yumoto, K.

    2014-12-01

    Pi 2 pulsations are defined as transient dumping oscillations of geomagnetic fields with period between 40 and 150 sec. The source (or energy source) of Pi 2s is believed to be located in the magnetotail because they mainly occur accompanied with onset of nightside auroral intensifications. Pi 2 pulsations are even observed on the day side ground, which means they can propagate to the dayside region from the nightside region. The latitudinal profiles of amplitude and phase difference of dayside H-component Pi 2s supported that electric fields from high-latitude region penetrate equatorward, and then drives the zonal ionospheric current enhanced at the dayside equator due to the Cowling effect. However, it is unclear how the dayside zonal ionospheric current are connected with the source electric field to ensure current continuity. In this study, we investigated the distribution of equivalent ionospheric currents associated with Pi 2 fluctuations on the day side using magnetic data from globally distributed ground-based stations. The equivalent current vectors were determined by rotating the filtered horizontal magnetic field vector by an angle of 90 degrees clockwise. Oscillating equivalent currents flowed equatorward (poleward) in the prenoon sector and poleward (equatorward) in the postnoon sector. Around the noon, the equivalent current flows in the zonal direction. The meridional component of equivalent currents in the prenoon sector is larger than in the postnoon sector and configuration of currents appears to be asymmetric. We also numerically estimated the distribution of ionospheric currents produced by the SCW-like pair of FACs around the midnight. The distribution of the simulated ionospheric current is consistent with that of equivalent currents derived from observed magnetic fields. We conclude that the oscillating ionospheric current system driven by nightside FAC oscillations is the dominant source of dayside Pi 2 pulsations.

  19. NIMROD Simulation of multipulsed edge-current drive in SSPX

    NASA Astrophysics Data System (ADS)

    Lodestro, L. L.; Cohen, B. I.; Hooper, E. B.; McLean, H. S.; Wood, R. D.

    2009-11-01

    Flux amplification (A)---the ratio of poloidal magnetic flux enclosed by a spheromak's toroidal core to an applied edge flux---is a critical parameter for an economic spheromak-based fusion reactor. In [1], measurements of A in SSPX and NIMROD simulations [2] were found to be in good agreement over a range of discharge parameters while A<3. Experiments to study A performed subsequently with the modular capacitor bank gave some indication that |dIgun/dt| played a role and that increasing it might build magnetic field more efficiently, but were limited by gun discharge circuit inductance. In [3], multipulsed gun injection was investigated numerically and the results compared to SSPX. Here we report the continuation of those simulations to longer times. We find trends on timescales much longer than could be studied in SSPX, negligible effect on A of multipulsed injection at frequencies smaller than the fundamental SSPX reconnection frequency, and small increases in A for large frequencies.[4pt] [1] B. Hudson et al., Phys. Plasmas 15, 056112 (2008).[0pt] [2] E.B. Hooper et al., Nucl. Fusion 47, 1064 (2007).[0pt] [3] L.L. LoDestro et al., 50^th DPP, TP6-93 (2008).

  20. Progress on the heating and current drive systems for ITER

    SciTech Connect

    Jacquinot, J.; Beaumont, Bertrand; Bora, D.; Campbell, D.; Darbos, Caroline; Decamps, H.; Graceffa, J.; Gassmann, T.; Hemsworth, R.; Henderson, Mark; Kobayashi, N.; Lamalle, Philippe; Schunke, B.; Tanaka, M.; Tanga, A.; Albajar, F.; Bonicelli, T.; Saibene, G.; Sartori, R.; Becoulet, A.; Hoang, G. T.; Inoue, T.; Sakamoto, K.; Takahashi, K.; Watanabe, K.; Goulding, Richard Howell; Rasmussen, David A; Swain, David W; Chakraborty, A.; Mukherjee, A.; Rao, S. L.; Denisov, G.; Nightingale, M.

    2009-06-01

    The electron cyclotron (EC), ion cyclotron (IC), heating-neutral beam (H-NB) and, although not in the day 1 baseline, lower hybrid (LH) systems intended for ITER have been reviewed in 2007/2008 in light of progress of physics and technology in the field. Although the overall specifications are unchanged, notable changes have been approved. Firstly, it has been emphasized that the H&CD systems are vital for the ITER programme. Consequently, the full 73 MW should be commissioned and available on a routine basis before the D/T phase. Secondly, significant changes have been approved at system level, most notably: the possibility to operate the heating beams at full power during the hydrogen phase requiring new shine through protection; the possibility to operate IC with 2 antennas with increased robustness (no moving parts); the possible increase to 2 MW of key components of the EC transmission systems in order to provide an easier upgrading of the EC power as may be required by the project; the addition of a building dedicated to the RF power sources and to a testing facility for acceptance of diagnostics and heating port plugs. Thirdly, the need of a plan for developing, in time for the active phase, a CD system such as LH suitable for very long pulse operation of ITER was recognised. The review describes these changes and their rationale.

  1. Laboratory simulation of field-aligned currents

    NASA Technical Reports Server (NTRS)

    Wessel, Frank J.; Rostoker, Norman

    1993-01-01

    A summary of progress during the period Apr. 1992 to Mar. 1993 is provided. Objectives of the research are (1) to simulate, via laboratory experiments, the three terms of the field-aligned current equation; (2) to simulate auroral-arc formation processes by configuring the boundary conditions of the experimental chamber and plasma parameters to produce highly localized return currents at the end of a field-aligned current system; and (3) to extrapolate these results, using theoretical and computational techniques, to the problem of magnetospheric-ionospheric coupling and to compare them with published literature signatures of auroral-arc phenomena.

  2. A DEMO relevant fast wave current drive high harmonic antenna exploiting the high impedance technique

    NASA Astrophysics Data System (ADS)

    Milanesio, D.; Maggiora, R.

    2015-12-01

    Ion Cyclotron (IC) antennas are routinely adopted in most of the existing nuclear fusion experiments, even though their main goal, i.e. to couple high power to the plasma (MW), is often limited by rather severe drawbacks due to high fields on the antenna itself and on the unmatched part of the feeding lines. In addition to the well exploited auxiliary ion heating during the start-up phase, some non-ohmic current drive (CD) at the IC range of frequencies may be explored in view of the DEMO reactor. In this work, we suggest and describe a compact high frequency DEMO relevant antenna, based on the high impedance surfaces concept. High-impedance surfaces are periodic metallic structures (patches) usually displaced on top of a dielectric substrate and grounded by means of vertical posts embedded inside the dielectric, in a mushroom-like shape. These structures present a high impedance, within a given frequency band, such that the image currents are in-phase with the currents of the antenna itself, thus determining a significant efficiency increase. After a general introduction on the properties of high impedance surfaces, we analyze, by means of numerical codes, a dielectric based and a full metal solution optimized to be tested and benchmarked on the FTU experiment fed with generators at 433MHz.

  3. A DEMO relevant fast wave current drive high harmonic antenna exploiting the high impedance technique

    SciTech Connect

    Milanesio, D. Maggiora, R.

    2015-12-10

    Ion Cyclotron (IC) antennas are routinely adopted in most of the existing nuclear fusion experiments, even though their main goal, i.e. to couple high power to the plasma (MW), is often limited by rather severe drawbacks due to high fields on the antenna itself and on the unmatched part of the feeding lines. In addition to the well exploited auxiliary ion heating during the start-up phase, some non-ohmic current drive (CD) at the IC range of frequencies may be explored in view of the DEMO reactor. In this work, we suggest and describe a compact high frequency DEMO relevant antenna, based on the high impedance surfaces concept. High-impedance surfaces are periodic metallic structures (patches) usually displaced on top of a dielectric substrate and grounded by means of vertical posts embedded inside the dielectric, in a mushroom-like shape. These structures present a high impedance, within a given frequency band, such that the image currents are in-phase with the currents of the antenna itself, thus determining a significant efficiency increase. After a general introduction on the properties of high impedance surfaces, we analyze, by means of numerical codes, a dielectric based and a full metal solution optimized to be tested and benchmarked on the FTU experiment fed with generators at 433MHz.

  4. Field-aligned currents and ionospheric electric fields

    NASA Technical Reports Server (NTRS)

    Yasuhara, F.; Akasofu, S.-I.

    1977-01-01

    It is shown that the observed distribution of the ionospheric electric field can be deduced from an equation combining Ohm's law with the current continuity equation by using the 'observed' distribution of field-aligned currents as the boundary condition for two models of the ionosphere. The first model has one conductive annular ring representing the quiet-time auroral precipitation belt; the second has two conductive annular rings that simulate the discrete and diffuse auroral regions. An analysis is performed to determine how well the electric-field distribution can be reproduced. The results indicate that the first model reproduces the Sq(p)-type distribution, the second model reproduces reasonably well a substorm-type potential and ionospheric current patterns together with the Harang discontinuity, and that the distribution of field-aligned currents is the same for both models.

  5. Non-Inductive Current Drive Modeling Extending Advanced Tokamak Operation to Steady State

    SciTech Connect

    Casper, T.A.; Lodestro, L.L.; Pearlstein, L.D.; Porter, G.D.; Murakami, M.; Lao, L.L.; Lin-Lui, Y.R.; St. John, H.E.

    2000-06-06

    A critical issue for sustaining high performance, negative central shear (NCS) discharges is the ability to maintain current distributions that are maximum off axis. Sustaining such hollow current profiles in steady state requires the use of non-inductively driven current sources. On the DIII-D experiment, a combination of neutral beam current drive (NBCD) and bootstrap current have been used to create transient NCS discharges. The electron cyclotron heating (ECH) and current drive (ECCD) system is currently being upgraded from three gyrotrons to six to provide more than 3MW of absorbed power in long-pulse operation to help sustain the required off-axis current drive. This upgrade SuPporrs the long range goal of DIII-D to sustain high performance discharges with high values of normalized {beta}, {beta}{sub n} = {beta}/(I{sub p}/aB{sub T}), confinement enhancement factor, H, and neutron production rates while utilizing bootstrap current fraction, f{sub bs}, in excess of 50%. At these high performance levels, the likelihood of onset of MHD modes that spoil confinement indicates the need to control plasma profiles if we are to extend this operation to long pulse or steady state. To investigate the effectiveness of the EC system and to explore operating scenarios to sustain these discharges, we use time-dependent simulations of the equilibrium, transport and stability. We explore methods to directly alter the safety factor profile, q, through direct current drive or by localized electron heating to modify the bootstrap current profile. Time dependent simulations using both experimentally determined [1] and theory-based [2] energy transport models have been done. Here, we report on simulations exploring parametric dependencies of the heating, current drive, and profiles that affect our ability to sustain stable discharges.

  6. Study of lower hybrid current drive towards long-pulse operation with high performance in EAST

    NASA Astrophysics Data System (ADS)

    Ding, B. J.; Li, M. H.; Li, Y. C.; Wang, M.; Shan, J. F.; Liu, F. K.; Wang, S. L.; Wei, W.; Xu, H. D.; Zhao, L. M.; Hu, H. C.; Jia, H.; Cheng, M.; Yang, Y.; Liu, L.; Xu, G. S.; Zang, Q.; Zhao, H. L.; Peysson, Y.; Decker, J.; Goniche, M.; Cesario, R.; Amicucci, L.; Tuccillo, A. A.; Baek, G. S.; Parker, R.; Bonoli, P. T.; Yang, C.; Zhao, Y. P.; Qian, J. P.; Gong, X. Z.; Hu, L. Q.; Li, J. G.; Wan, B. N.

    2015-12-01

    High density experiments with 2.45 GHz lower hybrid current drive (LHCD) in EAST are analyzed by means of simulation and modeling, showing that parametric instabilities (PI), collisional absorption and density fluctuations in the edge region could be responsible for the low CD efficiency at high density. In addition, recent LHCD results with 4.6 GHz are presented, showing that lower hybrid wave can be coupled to plasma with low reflection coefficient, drive plasma current and modify the current profile, and heat plasma effectively. The related results between two systems (2.45 GHz and 4.6 GHz) are also compared, including CD efficiency and PI behavior.

  7. The Argonne Wakefield Accelerator high current photocathode, gun and drive linac

    SciTech Connect

    Schoessow, P.; Chojnacki, E.; Cox, G.

    1995-06-01

    The Argonne Wakefield Accelerator (AWA) is a new facility for advanced accelerator research. A major component of the AWA is its drive linac, consisting of a unique high current short pulse L-Band photocathode based gun and special standing wave preaccelerator designed to produce 100 nC, 30 ps electron bunches at 20 MeV. Commissioning on the drive linac is now underway. We report on our initial operating experience with this novel machine, including bunch length and emittance measurements.

  8. Modeling of the electron distribution based on bremsstrahlung emission during lower hybrid current drive on PLT

    SciTech Connect

    Stevens, J.E.; von Goeler, S.; Bernabei, S.; Bitter, M.; Chu, T.K.; Efthimion, P.; Fisch, N.; Hooke, W.; Hosea, J.; Jobes, F.

    1985-03-01

    Lower hybrid current drive requires the generation of a high energy electron tail anisotropic in velocity. Measurements of bremsstrahlung emission produced by this tail are compared with the calculated emission from reasonable model distributions. The physical basis and the sensitivity of this modeling process are described and the plasma properties of current driven discharges which can be derived from the model are discussed.

  9. On the second harmonic electron cyclotron resonance heating and current drive experiments on T-10 and DIII-D

    SciTech Connect

    Lohr, J.; Forest, C.B.; Lin-Liu, Y.R.; Luce, T.C.; Harvey, R.W. ); Downs, E.A. Cornell Univ., Ithaca, NY ); James, R.A. Lawrence Livermore National Lab., CA ); Bagdasarov, A.A.; Borshegovskii, A.A.; Chistyakov, V.V.; Dremin, M.M.; Gors

    1993-02-01

    Studies of electron cyclotron current drive at the second harmonic resonance have been performed both on the DIII-D and T-10 tokamaks at injected power levels of approximately 0.5 MW. The DIII-D experiment used high held launch of the extraordinary mode at an angle of 15[degree] to the radial. In this experiment, with pulse lengths [approx equal] 500 msec, a loop voltage difference, compared to the value expected from the measured profiles, of [approx equal] 50 mV was ascribed to approximately 50 kA of rf-driven current. When dc electric field and trapped particle effects were considered, this was consistent with theoretical predictions. T-10 experiments planned for the fall of 1992 will use low field launch of the extraordinary mode and an injection angle of 21[degree] off-radial. In preliminary experiments with relatively poor machine conditions and pulse lengths [approx equal] 400 msec, rf current drive was not observed despite the fact that driven currents as low as 10 kA, corresponding to a loop voltage difference for co- versus counter-injection of 20 mV, could have been detected. In this paper we examine the T-10 experiments using ray tracing and transport calculations in an attempt to understand the results. The dependence of the current drive efficiency on discharge parameters, flux penetration, and non-linear effects will be discussed. The results show that the launching geometry can have a significant effect on the observation of electron cyclotron current drive using the loop voltage as a diagnostic. In addition, predictions for the next series of experiments on T-10, for which greater than 2 MW of high frequency power should be available, will be presented.

  10. On the second harmonic electron cyclotron resonance heating and current drive experiments on T-10 and DIII-D

    SciTech Connect

    Lohr, J.; Forest, C.B.; Lin-Liu, Y.R.; Luce, T.C.; Harvey, R.W.; Downs, E.A. |; James, R.A. |; Bagdasarov, A.A.; Borshegovskii, A.A.; Chistyakov, V.V.; Dremin, M.M.; Gorshkov, A.V.; Gorelov, Y.A.; Esipchuk, Y.V.; Ivanov, N.V.; Kislov, A.Y.; Kislov, D.A.; Lysenko, S.E.; Medvedev, A.A.; Mirenskii, V.Y.; Notkin, G.E.; Parail, V.V.; Pavlov, Y.D.; Razumova, K.A.; Roi, I.N.; Savrukhin, P.V.; Sannikov, V.V.; Sushkov, A.V.; Trukhin, V.M.; Vasin, N.L.; Volkov, V.V.; Denisov, G.G.; Petelin, M.I.; Flyagin, V.A.

    1993-02-01

    Studies of electron cyclotron current drive at the second harmonic resonance have been performed both on the DIII-D and T-10 tokamaks at injected power levels of approximately 0.5 MW. The DIII-D experiment used high held launch of the extraordinary mode at an angle of 15{degree} to the radial. In this experiment, with pulse lengths {approx_equal} 500 msec, a loop voltage difference, compared to the value expected from the measured profiles, of {approx_equal} 50 mV was ascribed to approximately 50 kA of rf-driven current. When dc electric field and trapped particle effects were considered, this was consistent with theoretical predictions. T-10 experiments planned for the fall of 1992 will use low field launch of the extraordinary mode and an injection angle of 21{degree} off-radial. In preliminary experiments with relatively poor machine conditions and pulse lengths {approx_equal} 400 msec, rf current drive was not observed despite the fact that driven currents as low as 10 kA, corresponding to a loop voltage difference for co- versus counter-injection of 20 mV, could have been detected. In this paper we examine the T-10 experiments using ray tracing and transport calculations in an attempt to understand the results. The dependence of the current drive efficiency on discharge parameters, flux penetration, and non-linear effects will be discussed. The results show that the launching geometry can have a significant effect on the observation of electron cyclotron current drive using the loop voltage as a diagnostic. In addition, predictions for the next series of experiments on T-10, for which greater than 2 MW of high frequency power should be available, will be presented.

  11. The Effect of Solar Wind Dynamic Pressure on the Physical Processes that Drive the Storm-time Ring Current Development

    NASA Astrophysics Data System (ADS)

    Lemon, C.; Chen, M. W.; Guild, T. B.

    2011-12-01

    Statistical studies suggest that the solar wind dynamic pressure influences the development of the storm-time ring current, with increased dynamic pressure leading to increased ring current energy. But physical understanding of that relationship is lacking. While magnetospheric compressions drive adiabatic energization of plasma and thereby directly increase the ring current energy, this effect should be reversible, and dynamic pressure can vary rapidly in either direction during magnetic storms. Rather, the process of plasma transport from the plasma sheet to the ring current is affected by magnetopause currents that perturb the background field in the magnetosphere. This perturbation will affect both convective transport and gradient/curvature drift of plasma, which will subsequently further perturb the magnetic and electric fields. Using the Rice Convection Model with a force-equilibrated magnetic field (the RCM-E), we are able to simulate the ring current development in response to varying upstream conditions. This study contrasts the development of the ring current in response to different solar wind dynamic pressure inputs: sustained low dynamic pressure, sustained high dynamic pressure, and low dynamic pressure with a superposed pressure pulse. We quantitatively account for the processes that lead to variations in ring current development during these different upstream driving scenarios. These processes include the effect of the magnetopause currents (and ring and tail currents) on plasma drift paths, modifications of the convection electric field due to adiabatic energization of plasma (electric shielding), and the induction electric fields caused by changes in the magnetopause, ring, and tail currents. Our simulations separately investigate the extent to which ring current enhancements are driven by 1) the impact of the magnetopause currents on the magnetic and (indirectly) electric fields of the inner magnetosphere, 2) the coupling of the plasma sheet to

  12. Direct electron heating and current drive with fast waves in DIII-D

    SciTech Connect

    Pinsker, R.I.; Petty, C.C.; Callis, R.W.; Cary, W.P.; Chiu, S.C.; Freeman, R.L.; deGrassie, J.S.; Harvey, R.W.; Luce, T.C.; Mayberry, M.J.; Prater, R.; Porkolab, M.; Bonoli, P.T.; Baity, F.W.; Goulding, R.H.; Hoffmann, D.J.; James, R.A.; Kawashima, H.

    1992-09-01

    Experiments on the DIII-D tokamak have been performed to evaluate noninductive current drive with direct electron absorption of the fast Alfven wave (FW) in the ion cyclotron range of frequencies. These experiments have employed a 2 MW 60 NM transmitter connected to a four-element toroidally phased array of loop antennas located at the outside midplane of the DIII-D vacuum vessel. Efficient direct electron heating was obtained with (0, {pi}, 0, {pi}) antenna phasing; H-mode confinement was obtained with direct electron absorption of the fast wave as the sole source of auxiliary heating. Current drive experiments were performed with (0,{pi}/2,{pi},3{pi}/2) antenna phasing at fast wave power levels up to 1.2 MW. Preheating with 60 GHz ECH was used to increase the single-pass absorption of the fast wave with a directive spectrum. When the fast wave is lunched in the direction that aids the inductively driven current (co-current drive), up to 40% of the 0.4 MA plasma current is sustained noninductively. Counter-current drive strongly affects the sawtoothing behavior, and results in highly peaked electron temperature profiles (T{sub e}(0) {approx_lt} 6 keV) but much smaller driven currents.

  13. Direct electron heating and current drive with fast waves in DIII-D

    SciTech Connect

    Pinsker, R.I.; Petty, C.C.; Callis, R.W.; Cary, W.P.; Chiu, S.C.; Freeman, R.L.; deGrassie, J.S.; Harvey, R.W.; Luce, T.C.; Mayberry, M.J.; Prater, R. ); Porkolab, M.; Bonoli, P.T. ); Baity, F.W.; Goulding, R.H.; Hoffmann, D.J. ); James, R.A. (Lawrence Livermor

    1992-09-01

    Experiments on the DIII-D tokamak have been performed to evaluate noninductive current drive with direct electron absorption of the fast Alfven wave (FW) in the ion cyclotron range of frequencies. These experiments have employed a 2 MW 60 NM transmitter connected to a four-element toroidally phased array of loop antennas located at the outside midplane of the DIII-D vacuum vessel. Efficient direct electron heating was obtained with (0, [pi], 0, [pi]) antenna phasing; H-mode confinement was obtained with direct electron absorption of the fast wave as the sole source of auxiliary heating. Current drive experiments were performed with (0,[pi]/2,[pi],3[pi]/2) antenna phasing at fast wave power levels up to 1.2 MW. Preheating with 60 GHz ECH was used to increase the single-pass absorption of the fast wave with a directive spectrum. When the fast wave is lunched in the direction that aids the inductively driven current (co-current drive), up to 40% of the 0.4 MA plasma current is sustained noninductively. Counter-current drive strongly affects the sawtoothing behavior, and results in highly peaked electron temperature profiles (T[sub e](0) [approx lt] 6 keV) but much smaller driven currents.

  14. A Novel Current Angle Control Scheme in a Current Source Inverter Fed Permanent Magnet Synchronous Motor Drive for Automotive Applications

    SciTech Connect

    Tang, Lixin; Su, Gui-Jia

    2011-01-01

    This paper describes a novel speed control scheme to operate a current source inverter (CSI) driven surface-mounted permanent magnet synchronous machine (SPMSM) for hybrid electric vehicles (HEVs) applications. The idea is to use the angle of the current vector to regulate the rotor speed while keeping the two dc-dc converter power switches on all the time to boost system efficiency. The effectiveness of the proposed scheme was verified with a 3 kW CSI-SPMSM drive prototype.

  15. Field Stability of Piezoelectric Shear Properties in PIN-PMN-PT Crystals Under Large Drive Field

    PubMed Central

    Zhang, Shujun; Li, Fei; Luo, Jun; Xia, Ru; Hackenberger, Wesley; Shrout, Thomas R.

    2013-01-01

    The coercive fields (EC) of Pb(In0.5Nb0.5)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) ternary single crystals were found to be 5 kV/cm, double the value of binary Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMNT) crystals, further increased to 6 to 9 kV/cm using Mn modifications. In addition to an increased EC, the acceptor modification resulted in the developed internal bias (Eint), on the order of ~1 kV/cm. The piezoelectric shear properties of unmodified and Mn-modified PIN-PMN-PT crystals with various domain configurations were investigated. The shear piezoelectric coefficients and electromechanical coupling factors for different domain configurations were found to be >2000 pC/N and >0.85, respectively, with slightly reduced properties observed in Mn-modified tetragonal crystals. Fatigue/cycling tests performed on shear-mode samples as a function of ac drive field level demonstrated that the allowable ac field levels (the maximum applied ac field before the occurrence of depolarization) were only ~2 kV/cm for unmodified crystals, less than half of their coercive field. Allowable ac drive levels were on the order of 4 to 6 kV/cm for Mn-modified crystals with rhombohedral/orthorhombic phase, further increased to 5 to 8 kV/cm in tetragonal crystals, because of their higher coercive fields. It is of particular interest that the allowable ac drive field level for Mn-modified crystals was found to be ≥60% of their coercive fields, because of the developed Eint, induced by the acceptor-oxygen vacancy defect dipoles. PMID:21342812

  16. Spontaneous emission with a cascaded driving field in the same transition channel

    NASA Astrophysics Data System (ADS)

    Liu, Ronggang; Liu, Tong

    2015-11-01

    We study the spontaneous emission spectrum of a driven four-level atom in both Markovian reservoir and non-Markovian reservoir, in which the two driving fields are applied to the same transition channel. It is very interesting that the increase of the Rabi frequency of the first driving field leads to the emission spectrum enhancement in Markovian reservoir, but the increase of the second one can suppress the emission spectrum significantly. The phenomenon originates from the dressed states variation induced by the first driving field. For non-Markovian reservoir case, the rich spectrum behavior is due to a strong coupling between driving fields and modified reservoir.

  17. Electron Energy Confinement For HHFW Heating and Current Drive Phasing on NSTX

    SciTech Connect

    Hosea, J.C.; Bernabei, S.; Biewer, T.; LeBlanc, B.; Phillips, C.K.; Wilson, J.R.; Stutman, D.; Ryan, P.; Swain, D.W.

    2005-09-26

    Thomson scattering laser pulses are synchronized relative to modulated HHFW power to permit evaluation of the electron energy confinement time during and following HHFW pulses for both heating and current drive antenna phasing. Profile changes resulting from instabilities require that the total electron stored energy, evaluated by integrating the midplane electron pressure Pe(R) over the magnetic surfaces prescribed by EFIT analysis, be used to derive the electron energy confinement time. Core confinement is reduced during a sawtooth instability but, although the electron energy is distributed outward by the sawtooth, the bulk electron energy confinement time is essentially unaffected. The radial deposition of energy into the electrons is noticeably more peaked for current drive phasing (longer wavelength excitation) relative to that for heating phasing (shorter wavelength excitation) as is expected theoretically. However, the power delivered to the core plasma is reduced considerably for the current drive phasing, indicating that surface/peripheral damping processes play a more important role for this case.

  18. Lower hybrid current drive at plasma densities required for thermonuclear reactors

    SciTech Connect

    Cesario, R.; Cardinali, A.; Castaldo, C.; Tuccillo, A. A.; Amicucci, L.

    2011-12-23

    Driving current in high-density plasmas is essential for the progress of thermonuclear fusion energy research based on the tokamak concept. The lower hybrid current drive (LHCD) effect, is potentially the most suitable tool for driving current at large plasma radii, consistent with the needs of ITER steady state scenario. Unfortunately, experiments at reactor grade high plasma densities with kinetic profiles approaching those required for ITER, have shown problems in penetration of the LH power into the core plasma. These plasmas represent a basic reference for designing possible methods useful for assessing the LHCD concept in ITER. On the basis of the phenomenology observed during LHCD experiments carried out in different machines, and model of the spectral broadening effect due to parametric instability, an interpretation and possible solution of the related important problem is presented.

  19. Modeling Results for 28 GHz Heating and Current Drive in the National Spherical Torus Experiment Upgrade (NSTX-U)

    NASA Astrophysics Data System (ADS)

    Taylor, G.; Bertelli, N.; Ellis, R. A.; Gerhardt, S. P.; Harvey, R. W.; Hosea, J. C.; Poli, F.; Raman, R.; Smirnov, A. P.

    2013-10-01

    A megawatt-level, 28 GHz electron heating system is being planned to heat non-inductive (NI) start-up plasmas and to provide radially localized electron heating and current drive during H-mode discharges in NSTX-U. NSTX-U will operate at axial toroidal fields of up to 1 T and plasma currents, Ip, up to 2 MA. Development of fully NI plasmas is a critical long-term NSTX-U research goal that supports the design of a Fusion Nuclear Science Facility. 0.6 MW of 28 GHz electron cyclotron (EC) heating is predicted to increase the central electron temperature (Te(0)) of low density NI plasmas generated by Coaxial Helicity Injection (CHI) in NSTX-U from 10 eV to 400 eV in about 20 ms. The increased Te(0) will significantly reduce the plasma current decay rate of CHI plasmas, allowing the coupling of fast wave heating and neutral beam injection. Eventually 28 GHz electron Bernstein wave (EBW) heating and current drive will be used during the Ip flat top in NSTX-U H-mode discharges when the plasma is overdense. This paper will present numerical RF simulation results for 28 GHz EC and EBW heating and current drive for NSTX-U discharges and a conceptual design for the 28 GHz heating system. Work supported by USDOE Contract No. DE-AC02-09CH11466.

  20. Comparison between the electron cyclotron current drive experiments on DIII-D and predictions for T-10

    SciTech Connect

    Lohr, J.; Harvey, R.W.; Luce, T.C.; Matsuda, Kyoko; Moeller, C.P.; Petty, C.C.; Prater, R. ); James, R.A. ); Giruzzi, G. ); Gorelov, Y. ); DeHaas, J. (Joint European Torus Un

    1990-11-01

    Electron cyclotron current drive has been demonstrated on the DIII-D tokamak in an experiment in which {approximately}1 MW of microwave power generated {approximately}50 kA of non-inductive current. The rf-generated portion was about 15% of the total current. On the T-10 tokamak, more than 3 MW of microwave power will be available for current generation, providing the possibility that all the plasma current could be maintained by this method. Fokker-Planck calculations using the code CQL3D and ray tracing calculations using TORAY have been performed to model both experiments. For DIII-D the agreement between the calculations and measurements is good, producing confidence in the validity of the computational models. The same calculations using the T-10 geometry predict that for n{sub e}(0) {approximately} 1.8 {times} 10{sup 13} cm{sup {minus}3}, and T{sub e}(0) {approximately} 7 keV, 1.2 MW, that is, the power available from only three gyrotrons, could generate as much as 150 kA of non-inductive current. Parameter space scans in which temperature, density and resonance location were varied have been performed to indicate the current drive expected under different experimental conditions. The residual dc electric field was considered in the DIII-D analysis because of its nonlinear effect on the electron distribution, which complicates the interpretation of the results. A 110 GHz ECH system is being installed on DIII-D. Initial operations, planned for late 1991, will use four gyrotrons with 500 kW each and 10 second output pulses. Injection will be from the low field side from launchers which can be steered to heat at the desired location. These launchers, two of which are presently installed, are set at 20 degrees to the radial and rf current drive studies are planned for the initial operation. 8 refs., 10 figs.

  1. Interhemispheric Field-Aligned Currents: Simulation Results

    NASA Astrophysics Data System (ADS)

    Lyatsky, Sonya

    2016-04-01

    We present simulation results of the 3-D magnetosphere-ionosphere current system including the Region 1, Region 2, and interhemispheric (IHC) field-aligned currents flowing between the Northern and Southern conjugate ionospheres in the case of asymmetry in ionospheric conductivities in two hemispheres (observed, for instance, during the summer-winter seasons). We also computed the maps of ionospheric and equivalent ionospheric currents in two hemispheres. The IHCs are an important part of the global 3-D current system in high-latitude ionospheres. These currents are especially significant during summer and winter months. In the winter ionosphere, they may be comparable and even exceed both Region 1 and Region 2 field-aligned currents. An important feature of these interhemispheric currents is that they link together processes in two hemispheres, so that the currents observed in one hemisphere can provide us with information about the currents in the opposite hemisphere. Despite the significant role of these IHCs in the global 3-D current system, they have not been sufficiently studied yet. The main results of our research may be summarized as follows: 1) In winter hemisphere, the IHCs may significantly exceed and be a substitute for the local Region 1 and Region 2 currents; 2) The IHCs may strongly affect the magnitude, location, and direction of the ionospheric and equivalent ionospheric currents (especially in the nightside winter auroral ionosphere). 3) The IHCs in winter hemisphere may be, in fact, an important (and sometimes even major) source of the Westward Auroral Electrojet, observed in both hemispheres during substorm activity. The study of the contribution from the IHCs into the total global 3-D current system allows us to improve the understanding and forecasting of geomagnetic, auroral, and ionospheric disturbances in two hemispheres. The results of our studies of the Interhemispheric currents are presented in papers: (note: for publications my last

  2. Status of KSTAR 170 GHz, 1 MW Electron Cyclotron Heating and Current Drive System

    SciTech Connect

    Joung, M.; Bae, Y. S.; Jeong, J. H.; Park, S.; Kim, H. J.; Yang, H. L.; Park, H.; Cho, M. H.; Namkung, W.; Hosea, J.; Ellis, R.; Sakamoto, K.; Kajiwara, K.; Doane, J.

    2011-12-23

    A 170 GHz Electron Cyclotron Heating and Current Drive (ECH/CD) system on KSTAR is designed to launch total 2.4 MW of power for up to 300 sec into the plasma. At present the first 1 MW ECH/CD system is under installation and commissioning for 2011 KSTAR campaign. The 170 GHz, 1 MW, 300 sec gyrotron and the matching optics unit (MOU) will be provided from JAEA under collaboration between NFRI and JAEA. The transmission line consists of MOU and 70 m long 63.5 mm ID corrugated waveguides with the eight miter bends. The 1 MW, 10 sec launcher is developed based on the existing two-mirror front-end launcher in collaboration with Princeton Plasma Physics Laboratory and Pohang University of Science and Technology, and is installed on the low field side in the KSTAR equatorial plane. The mirror pivot is located at 30 cm below from the equatorial plane. 3.6 MVA power supply system is manufactured and now is under commissioning to meet the triode gun operation of JAEA gyrotron. The power supply consists of 66 kV/55 A cathode power supply, mode-anode system, and 50 kV/160 mA body power supply. In this paper, the current status of KSTAR 170 GHz, 1 MW ECH/CD system will be presented as well as the experimental plan utilizing 170 GHz new ECH/CD system.

  3. Status of KSTAR 170 GHz, 1 MW Electron Cyclotron Heating and Current Drive System

    NASA Astrophysics Data System (ADS)

    Joung, M.; Bae, Y. S.; Jeong, J. H.; Park, S.; Kim, H. J.; Yang, H. L.; Park, H.; Cho, M. H.; Namkung, W.; Hosea, J.; Ellis, R.; Sakamoto, K.; Kajiwara, K.; Doane, J.

    2011-12-01

    A 170 GHz Electron Cyclotron Heating and Current Drive (ECH/CD) system on KSTAR is designed to launch total 2.4 MW of power for up to 300 sec into the plasma. At present the first 1 MW ECH/CD system is under installation and commissioning for 2011 KSTAR campaign. The 170 GHz, 1 MW, 300 sec gyrotron and the matching optics unit (MOU) will be provided from JAEA under collaboration between NFRI and JAEA. The transmission line consists of MOU and 70 m long 63.5 mm ID corrugated waveguides with the eight miter bends. The 1 MW, 10 sec launcher is developed based on the existing two-mirror front-end launcher in collaboration with Princeton Plasma Physics Laboratory and Pohang University of Science and Technology, and is installed on the low field side in the KSTAR equatorial plane. The mirror pivot is located at 30 cm below from the equatorial plane. 3.6 MVA power supply system is manufactured and now is under commissioning to meet the triode gun operation of JAEA gyrotron. The power supply consists of 66 kV/55 A cathode power supply, mode-anode system, and 50 kV/160 mA body power supply. In this paper, the current status of KSTAR 170 GHz, 1 MW ECH/CD system will be presented as well as the experimental plan utilizing 170 GHz new ECH/CD system.

  4. Remote Field Eddy Current Transition Zone

    NASA Astrophysics Data System (ADS)

    Dubois, Joseph Maurice Stephane

    1992-01-01

    The Remote Field Eddy Current (RFEC) technique is a non-destructive inspection technique used for anomaly detection in tubulars. The RFEC technique uses exciter and detector coils, both located inside the pipe, to detect interior and exterior corrosion with approximately equal sensitivity. The presence of both direct and indirect electromagnetic coupling paths distinguishes the RFEC technique from conventional reflected impedance eddy current techniques. The RFEC pipe inspection technique normally operates with the detector coil in the remote field region at distances of two or more pipe diameters from the internal exciter coil. At this spacing, the direct coupled field, dominant near the exciter (less than 1 pipe ID), is strongly attenuated and is overshadowed by the indirect field generated by an indirect energy transmission path which diffuses outwardly at the exciter coil location and tends to be guided by the pipe wall. In the remote field region, the field energy is greater outside than inside the pipe and some of the energy diffuses back inside the pipe. In the intermediate region (from 1 to 2 pipe diameters), called the transition zone, direct and indirect fields interact. The transition zone interaction produces a resultant field which is very sensitive to variations in pipe properties or wall thickness. The effect is maximal at the point where the indirect and direct fields have equal magnitudes and opposite phases. Small variations in the indirect field at this crossover point produce large changes in the resultant field. Experimental examples of the resultant axial magnetic field are presented to demonstrate the transition zone characteristics. An improved understanding of the effects of localized inner and outer wall defects and of pipe wall thinning on the direct and indirect field components in the transition zone is needed to better exploit the RFEC technique. Operating the RFEC probe in the transition zone with carefully selected frequency and

  5. Fast wave current drive experiment on the DIII-D tokamak

    SciTech Connect

    Petty, C.C.; Pinsker, R.I.; Chiu, S.C.; deGrassie, J.S.; Harvey, R.W.; Lohr, J.; Luce, T.C.; Mayberry, M.J.; Prater, R. ); Porkolab, M. ); Baity, F.W.; Goulding, R.H.; Hoffman, J.D. ); James, R.A. ); Kawash

    1992-06-01

    One method of radio-frequency heating which shows theoretical promise for both heating and current drive in tokamak plasmas is the direct absorption by electrons of the fast Alfven wave (FW). Electrons can directly absorb fast waves via electron Landau damping and transit-time magnetic pumping when the resonance condition {omega} {minus} {kappa}{sub {parallel}e}{upsilon}{sup {parallel}e} = O is satisfied. Since the FW accelerates electrons traveling the same toroidal direction as the wave, plasma current can be generated non-inductively by launching FW which propagate in one toroidal direction. Fast wave current drive (FWCD) is considered an attractive means of sustaining the plasma current in reactor-grade tokamaks due to teh potentially high current drive efficiency achievable and excellent penetration of the wave power to the high temperature plasma core. Ongoing experiments on the DIII-D tokamak are aimed at a demonstration of FWCD in the ion cyclotron range of frequencies (ICRF). Using frequencies in the ICRF avoids the possibility of mode conversion between the fast and slow wave branches which characterized early tokamak FWCD experiments in the lower hybrid range of frequencies. Previously on DIII-D, efficient direct electron heating by FW was found using symmetric (non-current drive) antenna phasing. However, high FWCD efficiencies are not expected due to the relatively low electron temperatures (compared to a reactor) in DIII-D.

  6. Effects of magnetic shear on toroidal rotation in tokamak plasmas with lower hybrid current drive.

    PubMed

    Rice, J E; Podpaly, Y A; Reinke, M L; Mumgaard, R; Scott, S D; Shiraiwa, S; Wallace, G M; Chouli, B; Fenzi-Bonizec, C; Nave, M F F; Diamond, P H; Gao, C; Granetz, R S; Hughes, J W; Parker, R R; Bonoli, P T; Delgado-Aparicio, L; Eriksson, L-G; Giroud, C; Greenwald, M J; Hubbard, A E; Hutchinson, I H; Irby, J H; Kirov, K; Mailloux, J; Marmar, E S; Wolfe, S M

    2013-09-20

    Application of lower hybrid (LH) current drive in tokamak plasmas can induce both co- and countercurrent directed changes in toroidal rotation, depending on the core q profile. For discharges with q(0) <1, rotation increments in the countercurrent direction are observed. If the LH-driven current is sufficient to suppress sawteeth and increase q(0) above unity, the core toroidal rotation change is in the cocurrent direction. This change in sign of the rotation increment is consistent with a change in sign of the residual stress (the divergence of which constitutes an intrinsic torque that drives the flow) through its dependence on magnetic shear. PMID:24093268

  7. Particle simulation of intense electron cyclotron heating and beat-wave current drive

    SciTech Connect

    Cohen, B.I.

    1987-10-12

    High-power free-electron lasers make new methods possible for heating plasmas and driving current in toroidal plasmas with electromagnetic waves. We have undertaken particle simulation studies with one and two dimensional, relativistic particle simulation codes of intense pulsed electron cyclotron heating and beat-wave current drive. The particle simulation methods here are conventional: the algorithms are time-centered, second-order-accurate, explicit, leap-frog difference schemes. The use of conventional methods restricts the range of space and time scales to be relatively compact in the problems addressed. Nevertheless, experimentally relevant simulations have been performed. 10 refs., 2 figs.

  8. Modeling of electron cyclotron current drive experiments on DIII-D

    SciTech Connect

    Lin-Liu, Y.R.; Chan, V.S.; Luce, T.C.; Prater, R.; Sauter, O.; Harvey, R.W.

    1999-05-01

    Electron Cyclotron Current Drive (ECCD) is considered a leading candidate for current profile control in Advanced Tokamak (AT) operation. Localized ECCD has been clearly demonstrated in recent proof-of-principle experiments on DIII-D. The measured ECCD efficiency near the magnetic axis agrees well with standard theoretical predictions. However, for off-axis current drive the normalized experimental efficiency does not decrease with minor radius as expected from the standard theory; the observed reduction of ECCD efficiency due to trapped electron effects in the off-axis cases is smaller than theoretical predictions. The standard approach of modeling ECCD in tokamaks has been based on the bounce-average calculations, which assume the bounce frequency is much larger than the effective collision frequency for trapped electrons at all energies. The assumption is clearly invalid at low energies. Finite collisionality will effectively reduce the trapped electron fraction, hence, increase current drive efficiency. Here, a velocity-space connection formula is proposed to estimate the collisionality effect on electron cyclotron current drive efficiency. The collisionality correction gives modest improvement in agreement between theoretical and recent DIII-D experimental results.

  9. Lower Hybrid Heating and Current Drive on the Alcator C-Mod Tokamak

    SciTech Connect

    R. Wilson, R. Parker, M. Bitter, P.T. Bonoli, C. Fiore, R.W. Harvey, K. Hill, A.E. Hubbard, J.W. Hughes, A. Ince-Cushman, C. Kessel, J.S. Ko, O. Meneghini, C.K. Phillips, M. Porkolab, J. Rice, A.E. Schmidt, S. Scott,S. Shiraiwa, E. Valeo, G.Wallace, J.C. Wright and the Alcator C-Mod Team

    2009-11-20

    On the Alcator C-Mod tokamak, lower hybrid current drive (LHCD) is being used to modify the current profile with the aim of obtaining advanced tokamak (AT) performance in plasmas with parameters similar to those that would be required on ITER. To date, power levels in excess of 1 MW at a frequency of 4.6 GHz have been coupled into a variety of plasmas. Experiments have established that LHCD on C-Mod behaves globally as predicted by theory. Bulk current drive efficiencies, n20IlhR/Plh ~ 0.25, inferred from magnetics and MSE are in line with theory. Quantitative comparisons between local measurements, MSE, ECE and hard x-ray bremsstrahlung, and theory/simulation using the GENRAY, TORIC-LH CQL3D and TSC-LSC codes have been performed. These comparisons have demonstrated the off-axis localization of the current drive, its magnitude and location dependence on the launched n|| spectrum, and the use of LHCD during the current ramp to save volt-seconds and delay the peaking of the current profile. Broadening of the x-ray emission profile during ICRF heating indicates that the current drive location can be controlled by the electron temperature, as expected. In addition, an alteration in the plasma toroidal rotation profile during LHCD has been observed with a significant rotation in the counter current direction. Notably, the rotation is accompanied by peaking of the density and temperature profiles on a current diffusion time scale inside of the half radius where the LH absorption is taking place.

  10. Stabilization of Neoclassical Tearing Modes in Tokamaks by Radio Frequency Current Drive

    SciTech Connect

    La Haye, R. J.

    2007-09-28

    Resistive neoclassical tearing modes (NTMs) will be the principal limit on stability and performance in the ITER standard scenario as the resulting islands break up the magnetic surfaces that confine the plasma. Drag from rotating island-induced eddy current in the resistive wall can also slow the plasma rotation, produce locking to the wall, and cause loss of high confinement H-mode and disruption. The NTMs are maintained by helical perturbations to the pressure-gradient driven 'bootstrap' current. Thus, this is a high beta instability even at the modest beta for ITER. A major line of research on NTM stabilization is the use of radio frequency (rf) current drive at the island rational surface. While large, broad current drive from lower hybrid waves has been shown to be stabilizing (COMPASS-D), most research is directed to small, narrow current drive from electron cyclotron waves (ECCD); ECCD stabilization and/or preemptive prevention is successful in ASDEX Upgrade, DIII-D and JT-60U, for example, with as little as a few percent of the total plasma current if the ECCD is kept sufficiently narrow so that the peak off-axis ECCD is comparable to the local bootstrap current.

  11. Modeling of electron cyclotron current drive experiments on DIII-D

    SciTech Connect

    Lin-Liu, Y. R.; Chan, V. S.; Luce, T. C.; Prater, R.; Sauter, O.; Harvey, R. W.

    1999-09-20

    A velocity-space connection formula is proposed to estimate the collisionality effect on electron cyclotron current drive efficiency. The collisionality correction gives modest improvement in agreement between theoretical and recent DIII-D experimental results (c) 1999 American Institute of Physics.

  12. 60 MHz fast wave current drive experiment for DIII-D

    SciTech Connect

    Mayberry, M.J.; Chiu, S.C.; Porkolab, M.; Chan, V.; Freeman, R.; Harvey, R.; Pinsker, R. )

    1989-07-01

    The DIII-D facility provides an opportunity to test fast wave current drive appoach. Efficient FWCD is achieved by direct electron absorption due to Landa damping and transit time magnetic pumping. To avoid competing damping mechamisms we seek to maximize the single-pass asorption of the fast waves by electrons. (AIP)

  13. Modeling of the influences of electron cyclotron current drive on neoclassical tearing modes

    SciTech Connect

    Chen, Long; Liu, Jinyuan; Sun, Jizhong; Sun, Guanglan; Duan, Ping

    2015-05-15

    Influences of external current drive on neoclassical tearing modes are studied numerically with a set of compressible magnetohydrodynamics equations. By considering the effects of driven current parameters and its deposition timing, and by examining the relationship between driven current and the missing bootstrap current, the basic requirements of deposition width and external current density for effectively suppressing neoclassical tearing modes are investigated. When the driven current density is able to compensate the missing bootstrap current and the deposition region is comparable with the saturated island, the suppression results are notable. Meanwhile, the pre-emptive strategy of current deposition reported experimentally is also evaluated, and the results agree with the experimental ones that early current deposition can enhance suppression effectiveness greatly. In addition, the deficiencies of continuous driven current are discussed when the plasma rotation has been taken into account, and the application of modulated current drive, which is synchronized in phase with the rotating island, can restore the stabilizing role under some conditions. The favorable parameters of modulation such as duty cycle are also addressed.

  14. Numerical study on the stabilization of neoclassical tearing modes by electron cyclotron current drive

    SciTech Connect

    Wang, Xiaoguang; Zhang, Xiaodong; Wu, Bin; Zhu, Sizheng; Hu, Yemin

    2015-02-15

    It is well known that electron cyclotron current drive (ECCD) around the o-point of magnetic island along the plasma current direction can stabilize neoclassical tearing modes (NTMs) in tokamak devices. The effects of the radial misalignment between the island and the driven current, the phase misalignment, and the on-duty ratio for modulated current drive on NTM stabilization are studied numerically in this paper. A small radial misalignment is found to significantly decrease the stabilizing effect. When a sufficiently large phase misalignment occurs for the modulated ECCD, the stabilization effect is also reduced a lot. The optimal on-duty ratio of modulated ECCD to stabilize NTMs is found to be in the range of 60%–70%. A larger on-duty ratio than 50% could also mitigate the effect of phase misalignment if it is not too large. There is no benefit from modulation if the phase misalignment is larger than a threshold.

  15. Numerical study on the stabilization of neoclassical tearing modes by electron cyclotron current drive

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoguang; Zhang, Xiaodong; Wu, Bin; Zhu, Sizheng; Hu, Yemin

    2015-02-01

    It is well known that electron cyclotron current drive (ECCD) around the o-point of magnetic island along the plasma current direction can stabilize neoclassical tearing modes (NTMs) in tokamak devices. The effects of the radial misalignment between the island and the driven current, the phase misalignment, and the on-duty ratio for modulated current drive on NTM stabilization are studied numerically in this paper. A small radial misalignment is found to significantly decrease the stabilizing effect. When a sufficiently large phase misalignment occurs for the modulated ECCD, the stabilization effect is also reduced a lot. The optimal on-duty ratio of modulated ECCD to stabilize NTMs is found to be in the range of 60%-70%. A larger on-duty ratio than 50% could also mitigate the effect of phase misalignment if it is not too large. There is no benefit from modulation if the phase misalignment is larger than a threshold.

  16. Multiscale field-aligned current analyzer

    NASA Astrophysics Data System (ADS)

    Bunescu, C.; Marghitu, O.; Constantinescu, D.; Narita, Y.; Vogt, J.; Blǎgǎu, A.

    2015-11-01

    The magnetosphere-ionosphere coupling is achieved, essentially, by a superposition of quasi-stationary and time-dependent field-aligned currents (FACs), over a broad range of spatial and temporal scales. The planarity of the FAC structures observed by satellite data and the orientation of the planar FAC sheets can be investigated by the well-established minimum variance analysis (MVA) of the magnetic perturbation. However, such investigations are often constrained to a predefined time window, i.e., to a specific scale of the FAC. The multiscale field-aligned current analyzer, introduced here, relies on performing MVA continuously and over a range of scales by varying the width of the analyzing window, appropriate for the complexity of the magnetic field signatures above the auroral oval. The proposed technique provides multiscale information on the planarity and orientation of the observed FACs. A new approach, based on the derivative of the largest eigenvalue of the magnetic variance matrix with respect to the length of the analysis window, makes possible the inference of the current structures' location (center) and scale (thickness). The capabilities of the FAC analyzer are explored analytically for the magnetic field profile of the Harris sheet and tested on synthetic FAC structures with uniform current density and infinite or finite geometry in the cross-section plane of the FAC. The method is illustrated with data observed by the Cluster spacecraft on crossing the nightside auroral region, and the results are cross checked with the optical observations from the Time History of Events and Macroscale Interactions during Substorms ground network.

  17. Remote-field eddy current signal representation

    SciTech Connect

    Atherton, D.L.; Mackintosh, D.D.; Sullivan, S.P.; Dubois, J.M.S.; Schmidt, T.R. . Dept. of Physics.)

    1993-07-01

    While conventional reflected impedance eddy current testing (ET) techniques are limited by skin depth considerations to near surface defects, the RFEC (remote field eddy current) technique exploits skin effects. The RFEC method is a through-wall inspection technique. Only the field which has made a double transit of the pipe wall is detected. The skin depth equation can be used to predict the approximate effect of metal loss on the RFEC signal. Metal loss effectively reduces the shielding so that the attenuation and phase lag of the field is less. A method of analyzing RFEC defect signals is therefore to compare the signals with the phase and amplitude in uncorroded pipe. RFEC probes are used for inspecting ferromagnetic and nonferromagnetic tubulars for corrosion and, since eddy current detectors are generally well suited to crack detection, there is considerable interest in their potential to detect stress corrosion cracking in pipelines. Here the authors first of all summarize the impedance plane representation and scope monitor displays customarily used for conventional exploring coil ET probes in tubes. They then present the normalized voltage plane and monitor displays that are most appropriate for RFEC probes. They discuss the similarities and differences between the preferred monitor displays.

  18. RF Heating and Current Drive in Magnetically Confined Plasma: a Historical Perspective

    SciTech Connect

    Porkolab, Miklos

    2007-09-28

    The history of high power RF waves injected into magnetically confined plasma for the purposes of heating to fusion relevant temperatures spans nearly five decades. The road to success demanded the development of the theory of wave propagation in high temperature plasma in complex magnetic field geometries, development of antenna structures and transmission lines capable of handling high RF powers, and the development of high power RF (microwave) sources. In the early days, progress was hindered by the lack of good confinement of energetic particles formed by high power RF wave-plasma interactions. For example, in the ion cyclotron resonance frequency regime (ICRF) ions with energies in the multi-100keV, or even MeV range may be formed due to the presence of efficient 'minority species' absorption. Electrons with similar energies can be formed upon the injection of RF waves in the electron cyclotron resonance (ECRH) or lower hybrid range of frequencies (LHRF) because of quasi-linear Landau (cyclotron) interactions between waves and particles. In this paper a summary of four decades of historical evolution of wave heating and current drive results will be given.

  19. Investigations of LHW-plasma coupling and current drive at high density related to H-mode experiments in EAST

    NASA Astrophysics Data System (ADS)

    Ding, B. J.; Li, Y. C.; Zhang, L.; Li, M. H.; Wei, W.; Kong, E. H.; Wang, M.; Xu, H. D.; Wang, S. L.; Xu, G. S.; Zhao, L. M.; Hu, H. C.; Jia, H.; Cheng, M.; Yang, Y.; Liu, L.; Zhao, H. L.; Peysson, Y.; Decker, J.; Goniche, M.; Amicucci, L.; Cesario, R.; Tuccillo, A. A.; Baek, S. G.; Parker, R.; Bonoli, P. T.; Paoletti, F.; Yang, C.; Shan, J. F.; Liu, F. K.; Zhao, Y. P.; Gong, X. Z.; Hu, L. Q.; Gao, X.; Wan, B. N.; Li, J. G.; the EAST Team

    2015-09-01

    Two important issues in achieving lower hybrid current drive (LHCD) high confinement plasma in EAST are to improve lower hybrid wave (LHW)-plasma coupling and to drive the plasma current at a high density. Studies in different configurations with different directions of toroidal magnetic field (Bt) show that the density near the antenna is affected by both the radial electric field induced by plasma without a LHW (Er_plasma) in the scrape off layer (SOL), and the radial electric field induced by LHW power (Er_LH) near the grill. Investigations indicate that Er  ×  Bt in the SOL leads to a different effect of configuration on the LHW-plasma coupling and Er_LH  ×  Bt accounts for the asymmetric density behaviour in the SOL observed in the experiments, where Er is the total radial electric field in the SOL. Modelling of parametric instability (PI), collisional absorption (CA) and scattering from density fluctuations (SDF) in the edge region, performed considering the parameters of high density LHCD experiments in EAST, has shown that these mechanisms could be responsible for the low current drive (CD) efficiency at high density. Radiofrequency probe spectra, useful for documenting PI occurrence, show sidebands whose amplitude in the case of the lithiated vacuum chamber is smaller than in the case of poor lithiation, consistently with growth rates from PI modeling of the respective reference discharges. Since strong lithiation is also expected to diminish the parasitic effect on the LHCD of the remaining possible mechanisms, this appears to be a useful method for improving LHCD efficiency at a high density.

  20. Fast wave heating and current drive in tokamak plasmas with negative central shear

    SciTech Connect

    Forest, C.B.; Petty, C.C.; Baity, F.W.

    1996-07-01

    Fast waves provide an excellent tool for heating electrons and driving current in the central region of tokamak plasmas. In this paper, we report the use of centrally peaked electron heating and current drive to study transport in plasmas with negative central shear (NCS). Tokamak plasmas with NCS offer the potential of reduced energy transport and improved MHD stability properties, but will require non-inductive current drive to maintain the required current profiles. Fast waves, combined with neutral beam injection, provide the capability to change the central current density evolution and independently vary {ital T{sub e}}, and {ital T{sub i}} for transport studies in these plasmas. Electron heating also reduces the collisional heat exchange between electrons and ions and reduces the power deposition from neutral beams into electrons, thus improving the certainty in the estimate of the electron heating. The first part of this paper analyzes electron and ion heat transport in the L-mode phase of NCS plasmas as the current profile resistively evolves. The second part of the paper discusses the changes that occur in electron as well as ion energy transport in this phase of improved core confinement associated with NCS.

  1. Modeling of Optimization and Control of EBW Heating and Current Drive

    NASA Astrophysics Data System (ADS)

    Urban, Jakub; Decker, Joan; Peysson, Yves; Preinhaelter, Josef; Taylor, Gary; Vahala, Linda; Vahala, George

    2009-11-01

    We present a modeling of Electron Bernstein waves (EBWs) by recently coupled AMR (Antenna---Mode-conversion---Ray-tracing) and LUKE (3D Fokker-Planck) codes. The electrostatic EBW is a promising candidate for localized heating and current drive in high-β plasmas, where the standard electron cyclotron O- and X-waves are cutoff. EBW heating and current drive is simulated here in spherical tokamak conditions, particularly in typical NSTX and MAST equilibria and also in equilibria predicted by transport modeling. The EBW injection parameters are varied in order to find optimized scenarios and a possible way to control the deposition location and the driven current. This task is rather challenging because EBW ray trajectories and N spectra are strongly dependent on the plasma parameters.

  2. Electric Circuit Model Suitable for Common Mode Current Paths Distributing in the Motor Drive System

    NASA Astrophysics Data System (ADS)

    Mutoh, Nobuyoshi; Ogata, Mitsukatsu; Harashima, Fumio

    Experimental date are used to analyze conducted EMI noises which are produced in a motor drive system with power converters comprised of a converter and an inverter. The processes are investigated in which common mode noises (voltages and currents) are strongly influenced by voltage fluctuations occurring due to switching operations. It is found that the common mode currents are resonance currents which appear in series resonance circuits distributed in the motor drive system. The circuits have various kinds of resonance frequencies related to voltage fluctuations produced by switching operations and micro-surge voltages generated at the terminal of machines such as an ac rector or a motor. Thus, parameters of the distributed series resonance circuits are estimated using the transient waveforms obtained by separating the common mode current into waves analyzed by the FFT method. It is proved through simulations and experiments that the proposed circuit models closely represent actual electric circuits for common mode current paths distributed in the motor drive system.

  3. Self field triggered superconducting fault current limiter

    DOEpatents

    Tekletsadik, Kasegn D.

    2008-02-19

    A superconducting fault current limiter array with a plurality of superconductor elements arranged in a meanding array having an even number of supconductors parallel to each other and arranged in a plane that is parallel to an odd number of the plurality of superconductors, where the odd number of supconductors are parallel to each other and arranged in a plane that is parallel to the even number of the plurality of superconductors, when viewed from a top view. The even number of superconductors are coupled at the upper end to the upper end of the odd number of superconductors. A plurality of lower shunt coils each coupled to the lower end of each of the even number of superconductors and a plurality of upper shunt coils each coupled to the upper end of each of the odd number of superconductors so as to generate a generally orthoganal uniform magnetic field during quenching using only the magenetic field generated by the superconductors.

  4. Radial transport and electron-cyclotron-current drive in the TCV and DIII-D tokamaks.

    PubMed

    Harvey, R W; Sauter, O; Prater, R; Nikkola, P

    2002-05-20

    Calculation of electron-cyclotron-current drive (ECCD) with the comprehensive CQL3D Fokker-Planck code for a TCV tokamak shot gives 550 kA of driven toroidal current, in marked disagreement with the 100-kA experimental value. Published ECCD efficiencies calculated with CQL3D in the much larger, higher-confinement DIII-D tokamak are in excellent agreement with experiment. The disagreement is resolved by including in the calculations electrostatic-type radial transport at levels given by global energy confinement in tokamaks. The radial transport of energy and toroidal current are in agreement. PMID:12005571

  5. Closure of the single fluid magnetohydrodynamic equations in presence of electron cyclotron current drive

    NASA Astrophysics Data System (ADS)

    Westerhof, E.; Pratt, J.; Ayten, B.

    2015-03-01

    In the presence of electron cyclotron current drive (ECCD), the Ohm's law of single fluid magnetohydrodynamics (MHD) is modified as E + v × B = η(J - JECCD). This paper presents a new closure relation for the EC driven current density appearing in this modified Ohm's law. The new relation faithfully represents the nonlocal character of the EC driven current and its main origin in the Fisch-Boozer effect. The closure relation is validated on both an analytical solution of an approximated Fokker-Planck equation as well as on full bounce-averaged, quasi-linear Fokker-Planck code simulations of ECCD inside rotating magnetic islands.

  6. Numerical study on the influence of electron cyclotron current drive on tearing mode

    SciTech Connect

    Chen, Long; Liu, Jinyuan; Mao, Aohua; Sun, Jizhong; Duan, Ping

    2014-10-15

    Controlling tearing modes by localized current drive is explored by using numerical simulation with a set of compressible magnetohydrodynamics equations. By examining the effects of different characteristics of driven current, such as density distribution, duration time, and deposition location, it is found that a driven current with larger magnitude and more focused deposition region shows a better suppression effect on the tearing modes. Meanwhile destabilizing effects are also observed when a driven current over a certain magnitude is applied continuously. In comparison with those on the X-point of the magnetic island, the results are better when the current deposition is targeted on the O-point. In addition, the timing control of the current deposition will be also addressed.

  7. Compact antenna for two-dimensional beam scan in the JT-60U electron cyclotron heating/current drive system

    SciTech Connect

    Moriyama, S.; Kajiwara, K.; Takahashi, K.; Kasugai, A.; Seki, M.; Ikeda, Y.; Fujii, T.

    2005-11-15

    A compact antenna system was designed and fabricated to enable millimeter-wave beam scanning in the toroidal and poloidal directions of the JT-60U tokamak for electron cyclotron heating (ECH) and electron cyclotron current drive (ECCD) experiments. The antenna consists of a fast movable flat mirror mounted on the tokamak vacuum vessel and a rotary focusing mirror attached at the end of the waveguide that is supported from outside the vacuum vessel. This separate support concept enables a compact structure inside a shallow port (0.68x0.54x0.2 m) that is shared with a subport for an independent diagnostic system. During a plasma shot, the flat mirror is driven by a servomotor with a 3-m-long drive shaft to reduce the influence of the high magnetic field on the motor. The focusing mirror is rotated by a simple mechanism utilizing a push rod and an air cylinder. The antenna has been operated reliably for 3 years after a small improvement to the rotary drive mechanism. It has made significant contributions to ECH and ECCD experiments, especially the current profile control in JT-60U.

  8. Calculations of Alfvén wave driving forces, plasma flow, and current drive in the Tokamak Chauffage Alfvén wave experiment in Brazil (TCABR)

    NASA Astrophysics Data System (ADS)

    Amarante-Segundo, G.; Elfimov, A. G.; Galvão, R. M. O.; Ross, D. W.; Nascimento, I. C.

    2001-01-01

    The current and plasma flows driven by ponderomotive forces are calculated for tokamak plasmas, using a kinetic code in the Alfvén range of frequencies. The rf (radio frequency) ponderomotive force is expressed as a sum of a gradient part and of a wave momentum transfer force, which is proportional to wave dissipation (electron Landau damping and transit time magnetic pumping). Finally, the rf force is balanced by the viscous force in the fluid momentum response to the rf fields in the plasma. The relative magnitudes of the different forces for kinetic and global Alfvén waves with low phase velocities are explicitly calculated. It is shown that, dissipating in electrons, Alfvén waves can drive ion flow via the gradient force, which is dominated in m=0-sideband harmonic resonance induced by toroidal mode coupling. Estimates of power requirements to drive substantial poloidal flow in the Tokamak Chauffage Alfvén wave heating experiment in Brazil (TCABR) [L. Ruchko, M. C. Andrade, R. M. O. Galvão, Nucl. Fusion 30, 503 (1996)] are made.

  9. A current-source inverter fed induction motor drive system with reduced losses

    SciTech Connect

    Espinoza, J.R.; Joos, G.

    1995-12-31

    Standard low and medium induction power motor drives are based on the PWM voltage source inverter (VSI) fed from a diode rectifier. The dual topology, based on the current source inverter/rectifier structure is used in medium and high power applications. This paper addresses some of the drawbacks of this approach compared to the voltage source approach. The proposed drive features: (a) an on-line operated PWM inverter, using instantaneous output capacitor voltage control based on space vector modulation; (b) a line-synchronized PWM rectifier, with dc bus current control; (c) an additional inverter modulation index control loop, ensuring a constant inverter modulation index. The resulting advantages include: (a) ruggedness and inherent continuous regeneration capability; (b) near unity global input power factor; (c) reduced motor voltage distortion; (d) reduced dc bus inductor and switch conduction losses; (e) fast motor dynamic response; (f) elimination of motor circuit resonances. Simulated and experimental results based on a DSP implementation are given.

  10. A Lower Hybrid Current Drive System for Alcator C-Mod

    SciTech Connect

    S. Bernabei; J.C. Hosea; D. Loesser; J. Rushinski; J.R. Wilson; P. Bonoli; M. Grimes; R. Parker; M. Porkolab; D. Terry; P. Woskov

    2001-05-04

    A Lower Hybrid Current Drive system is being constructed jointly by Plasma Science and Fusion Center (PSFC) and Princeton Plasma Physics Laboratory (PPPL) for installation on the Alcator C-Mod tokamak, with the primary goal of driving plasma current in the outer region of the plasma. The Lower Hybrid (LH) system consists of 3 MW power at 4.6 GHz with a maximum pulse length of 5 seconds. Twelve klystrons will feed an array of 4-vertical and 24-horizontal waveguides mounted in one equatorial port. The coupler will incorporate some compact characteristics of the multijunction power splitting while retaining full control of the toroidal phase. In addition a dynamic phase control system will allow feedback stabilization of MHD modes. The desire to avoid possible waveguide breakdown and the need for compactness have resulted in some innovative technical solution which will be presented.

  11. FED-A, an advanced performance FED based on low safety factor and current drive

    SciTech Connect

    Peng, Y.K.M.; Rutherford, P.H.

    1983-08-01

    The FED-A study aims to quantify the potential improvement in cost-effectiveness of the Fusion Engineering Device (FED) by assuming low safety factor q (less than 2 as opposed to about 3) at the plasma edge and noninductive current drive (as opposed to only inductive current drive). The FED-A performance objectives are set to be : (1) ignition assuming International Tokamak Reactor (INTOR) plamsa confinement scaling, but still achieving a fusion power amplification Q greater than or equal to 5 when the confinement is degraded by a factor of 2; (2) neutron wall loading of about 1 MW/m/sup 2/, with 0.5 MW/m/sup 2/ as a conservative lower bound; and (3) more clearly power-reactor-like operations, such as steady state.

  12. X-ray analysis of nonMaxwellian distributions (current drive)

    SciTech Connect

    von Goeler, S.; Stevens, J.; Stodiek, W.

    1983-06-01

    The plasma bremsstrahlung emission is utilized to determine the shape of the electron velocity distribution in situations where it deviates strongly from a Maxwellian distribution. The instrumentation used to measure the hard x-ray emission is briefly discussed. Model calculations show that polarization measurements give best results for unrelativistic tails with tail temperatures T/sub b/ < 50 keV, whereas measurements of the angular distribution of the x-ray emission based on the forward scattering of bremsstrahlung for relativistic electrons yields the best information for T/sub b/ > 50 keV. The techniques were originally developed in order to analyze runaway discharges. Recently, they found new interest because of the formation of energetic electron tails during current drive. The first x-ray results from the current drive during LH heating on PLT are discussed.

  13. Ray-tracing code TRAVIS for ECR heating, EC current drive and ECE diagnostic

    NASA Astrophysics Data System (ADS)

    Marushchenko, N. B.; Turkin, Y.; Maassberg, H.

    2014-01-01

    A description of the recently developed ray-tracing code TRAVIS is given together with the theoretical background, results of benchmarking and examples of application. The code is written for electron cyclotron studies with emphasis on heating, current drive and ECE diagnostic. The code works with an arbitrary 3D magnetic equilibrium being applicable for both stellarators and tokamaks. The equations for ray tracing are taken in the weakly relativistic approach, i.e. with thermal effects taken into account, while the absorption, current drive and emissivity are calculated in the fully relativistic approach. For the calculation of ECCD, an adjoint technique with parallel momentum conservation is applied. The code is controlled through a specially designed graphical user interface, which allows the preparation of the input parameters and viewing the results in convenient (2D and 3D) form.

  14. Redundant drive current imbalance problem of the Automatic Radiator Inspection Device (ARID)

    NASA Technical Reports Server (NTRS)

    Latino, Carl D.

    1992-01-01

    The Automatic Radiator Inspection Device (ARID) is a 4 Degree of Freedom (DOF) robot with redundant drive motors at each joint. The device is intended to automate the labor intensive task of space shuttle radiator inspection. For safety and redundancy, each joint is driven by two independent motor systems. Motors driving the same joint, however, draw vastly different currents. The concern was that the robot joints could be subjected to undue stress. It was the objective of this summer's project to determine the cause of this current imbalance. In addition it was to determine, in a quantitative manner, what was the cause, how serious the problem was in terms of damage or undue wear to the robot and find solutions if possible. It was concluded that most problems could be resolved with a better motor control design. This document discusses problems encountered and possible solutions.

  15. Electron Energy Confinement for HHFW Heating and Current Drive Phasing on NSTX

    SciTech Connect

    J.C. Hosea; S. Bernabei; T. Biewer; B. LeBlanc; C.K. Phillips; J.R. Wilson; D. Stutman; P. Ryan; D.W. Swain

    2005-05-03

    Thomson scattering laser pulses are synchronized relative to modulated HHFW power to permit evaluation of the electron energy confinement time during and following HHFW pulses for both heating and current drive antenna phasing. Profile changes resulting from instabilities require that the total electron stored energy, evaluated by integrating the midplane electron pressure P(sub)e(R) over the magnetic surfaces prescribed by EFIT analysis, be used to derive the electron energy confinement time. Core confinement is reduced during a sawtooth instability but, although the electron energy is distributed outward by the sawtooth, the bulk electron energy confinement time is essentially unaffected. The radial deposition of energy into the electrons is noticeably more peaked for current drive phasing (longer wavelength excitation) relative to that for heating phasing (shorter wavelength excitation) as is expected theoretically. However, the power delivered to the core plasma is reduced consider ably for the current drive phasing, indicating that surface/peripheral damping processes play a more important role for this case.

  16. Recent progress on lower hybrid current drive and implications for ITER

    NASA Astrophysics Data System (ADS)

    Hillairet, J.; Ekedahl, A.; Goniche, M.; Bae, Y. S.; Achard, J.; Armitano, A.; Beckett, B.; Belo, J.; Berger-By, G.; Bernard, J. M.; Corbel, E.; Delpech, L.; Decker, J.; Dumont, R.; Guilhem, D.; Hoang, G. T.; Kazarian, F.; Kim, H. J.; Litaudon, X.; Magne, R.; Marfisi, L.; Mollard, P.; Namkung, W.; Nilsson, E.; Park, S.; Peysson, Y.; Preynas, M.; Sharma, P. K.; Prou, M.; the Tore Supra Team

    2013-07-01

    The sustainment of steady-state plasmas in tokamaks requires efficient current drive systems. Lower hybrid current drive is currently the most efficient method to generate a continuous additional off-axis toroidal plasma current and to reduce the poloidal flux consumption during the plasma current ramp-up phase. The operation of the Tore Supra ITER-like lower hybrid (LH) launcher has demonstrated the capability to couple LH power at ITER-like power densities with very low reflected power during long pulses. In addition, the installation of eight 700 kW/CW klystrons at the LH transmitter has allowed increasing the total LH power in long-pulse scenarios. However, in order to achieve pure stationary LH-sustained plasmas, some R&D is needed to increase the reliability of all the systems and codes, from radio-frequency (RF) sources to plasma scenario prediction. The CEA/IRFM is addressing some of these issues by leading a R&D programme towards an ITER LH system and by the validation of an integrated LH modelling suite of codes. In 2011, the RF design of a mode converter was validated at a low power. A 500 kW/5 s RF window is currently under manufacture and will be tested at a high power in 2012 in collaboration with the National Fusion Research Institute. All of this work aims to reduce the operational risks associated with the ITER steady-state operations.

  17. First principles fluid modelling of magnetic island stabilization by electron cyclotron current drive (ECCD)

    NASA Astrophysics Data System (ADS)

    Février, O.; Maget, P.; Lütjens, H.; Luciani, J. F.; Decker, J.; Giruzzi, G.; Reich, M.; Beyer, P.; Lazzaro, E.; Nowak, S.; the ASDEX Upgrade Team

    2016-04-01

    Tearing modes are MagnetoHydroDynamics (MHD) instabilities that reduce the performance of fusion devices. They can however be controlled and suppressed using electron cyclotron current drive (ECCD) as demonstrated in various tokamaks. In this work, simulations of island stabilization by ECCD-driven current have been carried out using the toroidal nonlinear 3D full MHD code xtor-2f, in which a current source term modeling the ECCD has been implemented. The efficiency parameter, {η\\text{RF}} , has been computed and its variations with respect to source width and location were also computed. The influence of parameters such as current intensity, source width and position with respect to the island was evaluated and compared to the modified Rutherford equation. We retrieved a good agreement between the simulations and the analytical predictions concerning the variations of control efficiency with source width and position. We also show that the 3D nature of the current source term can lead to the onset of an island if the source term is precisely applied on a rational surface. We report the observation of a flip phenomenon in which the O- and X-points of the island rapidly switch their position in order for the island to take advantage of the current drive to grow.

  18. Heating and current drive requirements towards steady state operation in ITER

    SciTech Connect

    Poli, F. M.; Kessel, C. E.; Gorelenkova, M.; Bonoli, P. T.; Batchelor, D. B.; Harvey, B.; Petrov, Y.

    2014-02-12

    Steady state scenarios envisaged for ITER aim at optimizing the bootstrap current, while maintaining sufficient confinement and stability to provide the necessary fusion yield. Non-inductive scenarios will need to operate with Internal Transport Barriers (ITBs) in order to reach adequate fusion gain at typical currents of 9 MA. However, the large pressure gradients associated with ITBs in regions of weak or negative magnetic shear can be conducive to ideal MHD instabilities, reducing the no-wall limit. The E × B flow shear from toroidal plasma rotation is expected to be low in ITER, with a major role in the ITB dynamics being played by magnetic geometry. Combinations of H/CD sources that maintain weakly reversed magnetic shear profiles throughout the discharge are the focus of this work. Time-dependent transport simulations indicate that, with a trade-off of the EC equatorial and upper launcher, the formation and sustainment of quasi-steady state ITBs could be demonstrated in ITER with the baseline heating configuration. However, with proper constraints from peeling-ballooning theory on the pedestal width and height, the fusion gain and the maximum non-inductive current are below the ITER target. Upgrades of the heating and current drive system in ITER, like the use of Lower Hybrid current drive, could overcome these limitations, sustaining higher non-inductive current and confinement, more expanded ITBs which are ideal MHD stable.

  19. Leakage current and commutation losses reduction in electric drives for Hybrid Electric Vehicle

    NASA Astrophysics Data System (ADS)

    Miliani, El Hadj

    2014-06-01

    Nowadays, leakage current and inverter losses, produced by adjustable-speed AC drive systems become one of the main interested subject for researchers on Electric Vehicle (EV) and Hybrid Electric Vehicle (HEV) technology. The continuous advancements in solid state device engineering have considerably minimized the switching transients for power switches but the high dv/dt and high switching frequency have caused many adverse effects such as shaft voltage, bearing current, leakage current and electromagnetic interference (EMI). The major objective of this paper is to investigate and suppress of the adverse effects of a PWM inverter feeding AC motor in EV and HEV. A technique to simultaneously reduce the leakage current and the switching losses is presented in this paper. Based on a discontinuous space vector pulse width modulation (DSVPWM) and a modular switches gate resistance, inverter losses and leakage current are reduced. Algorithms are presented and implemented on a DSP controller and experimental results are presented.

  20. Trace Distance and Level Crossing in Spin-Bosen Model with Added Classical Driving Fields

    NASA Astrophysics Data System (ADS)

    He, Qi-Liang; Xiao, Yong-Jun; Zhou, Rui-Xue; Zhang, Ye-Qi

    2016-07-01

    By making use of the trace distance as a measure we investigate the influence of classical driving fields on a open quantum system when the system and its environment are initially in a correlated state. It is shown that the amount of trace distance is sensitive to the classical driving fields which implies that the information flowing between open system and its environment can be controlled by the classical driving fields. Furthermore, we also explore the dependence of the trace distance on the initial parameters when the total system is considered in the thermal equilibrium state. We find that the trace distance on the coupling strength can be used to demonstrate the level crossing of the ground state of the system. In particular, the classical driving fields have significant effect on the level crossing of the ground state.

  1. Radiation Effects on Current Field Programmable Technologies

    NASA Technical Reports Server (NTRS)

    Katz, R.; LaBel, K.; Wang, J. J.; Cronquist, B.; Koga, R.; Penzin, S.; Swift, G.

    1997-01-01

    Manufacturers of field programmable gate arrays (FPGAS) take different technological and architectural approaches that directly affect radiation performance. Similar y technological and architectural features are used in related technologies such as programmable substrates and quick-turn application specific integrated circuits (ASICs). After analyzing current technologies and architectures and their radiation-effects implications, this paper includes extensive test data quantifying various devices total dose and single event susceptibilities, including performance degradation effects and temporary or permanent re-configuration faults. Test results will concentrate on recent technologies being used in space flight electronic systems and those being developed for use in the near term. This paper will provide the first extensive study of various configuration memories used in programmable devices. Radiation performance limits and their impacts will be discussed for each design. In addition, the interplay between device scaling, process, bias voltage, design, and architecture will be explored. Lastly, areas of ongoing research will be discussed.

  2. Investigation of lower hybrid wave coupling and current drive experiments at different configurations in experimental advanced superconducting tokamak

    SciTech Connect

    Ding, B. J.; Qin, Y. L.; Li, W. K.; Li, M. H.; Kong, E. H.; Zhang, L.; Wang, M.; Xu, H. D.; Hu, H. C.; Xu, G. S.; Shan, J. F.; Liu, F. K.; Zhao, Y. P.; Wan, B. N.; Li, J. G.; Group, EAST; Ekedahl, A.; Peysson, Y.; Decker, J.

    2011-08-15

    Using a 2 MW 2.45 GHz lower hybrid wave (LHW) system installed in experimental advanced superconducting tokamak, we have systematically carried out LHW-plasma coupling and lower hybrid current drive experiments in both divertor (double null and lower single null) and limiter plasma configuration with plasma current (I{sub p}) {approx} 250 kA and central line averaged density (n{sub e}) {approx} 1.0-1.3 x 10{sup 19} m{sup -3} recently. Results show that the reflection coefficient (RC) first is flat up to some distance between plasma and LHW grill, and then increases with the distance. Studies indicate that with the same plasma parameters, the best coupling is obtained in the limiter case (with plasma leaning on the inner wall), followed by the lower single null, and the one with the worst coupling is the double null configuration, explained by different magnetic connection length. The RCs in the different poloidal rows show that they have different coupling characteristics, possibly due to local magnetic connection length. Current drive efficiency has been investigated by a least squares fit with N{sub //}{sup peak}=2.1, where N{sub //}{sup peak} is the peak value of parallel refractive index of the launched wave. Results show that there is no obvious difference in the current drive efficiency between double null and lower single null cases, whereas the efficiency is somewhat small in the limiter configuration. This is in agreement with the ray tracing/Fokker-Planck code simulation by LUKE/C3PO and can be interpreted by the power spectrum up-shift factor in different plasma configurations. A transformer recharge is realized with {approx}0.8 MW LHW power and the energy conversion efficiency from LHW to poloidal field energy is about 2%.

  3. Investigation of lower hybrid wave coupling and current drive experiments at different configurations in experimental advanced superconducting tokamak

    NASA Astrophysics Data System (ADS)

    Ding, B. J.; Qin, Y. L.; Li, W. K.; Li, M. H.; Kong, E. H.; Zhang, L.; Ekedahl, A.; Peysson, Y.; Decker, J.; Wang, M.; Xu, H. D.; Hu, H. C.; Xu, G. S.; Shan, J. F.; Liu, F. K.; Zhao, Y. P.; Wan, B. N.; Li, J. G.; Group, EAST

    2011-08-01

    Using a 2 MW 2.45 GHz lower hybrid wave (LHW) system installed in experimental advanced superconducting tokamak, we have systematically carried out LHW-plasma coupling and lower hybrid current drive experiments in both divertor (double null and lower single null) and limiter plasma configuration with plasma current (Ip) ˜ 250 kA and central line averaged density (ne) ˜ 1.0-1.3 × 1019 m-3 recently. Results show that the reflection coefficient (RC) first is flat up to some distance between plasma and LHW grill, and then increases with the distance. Studies indicate that with the same plasma parameters, the best coupling is obtained in the limiter case (with plasma leaning on the inner wall), followed by the lower single null, and the one with the worst coupling is the double null configuration, explained by different magnetic connection length. The RCs in the different poloidal rows show that they have different coupling characteristics, possibly due to local magnetic connection length. Current drive efficiency has been investigated by a least squares fit with N//peak=2.1, where N//peak is the peak value of parallel refractive index of the launched wave. Results show that there is no obvious difference in the current drive efficiency between double null and lower single null cases, whereas the efficiency is somewhat small in the limiter configuration. This is in agreement with the ray tracing/Fokker-Planck code simulation by LUKE/C3PO and can be interpreted by the power spectrum up-shift factor in different plasma configurations. A transformer recharge is realized with ˜0.8 MW LHW power and the energy conversion efficiency from LHW to poloidal field energy is about 2%.

  4. REMOTE FIELD EDDY CURRENT INSPECTION OF UNPIGGABLE PIPELINES

    SciTech Connect

    Albert Teitsma

    2004-03-01

    The Remote Field Eddy Current (RFEC) technique is ideal for inspecting unpiggable pipelines because all its components can be made much smaller than the diameter of the pipe to be inspected. We reviewed the technique, and used demonstrations from prior work by others in presentations on the technique and how we plan to develop it. Coils were wound; a jig for pulling the coils through the pipe was manufactured; defects were machined in one six-inch diameter, ten-foot long pipe; and the equipment was assembled. After completing first crude pullout test to show that RFEC inspection would work, we repeated the experiment with a proper jig and got excellent results. The test showed the expected behavior, with the direct field dominating the signal to about two pipe diameters from the drive coil, and the remote field dominating for greater separations between the drive coil and the sensing coils. Response of RFEC to a typical defect was measured, as was the sensitivity to defect size. Before manufacturing defects in the pipe, we measured the effect of defect separation and concluded that defects separated by 18 inches or 1/3rd of the pipe diameter did not interfere with each other. We manufactured a set of 13 defects, and measured the RFEC signals. We found a background variation that was eventually attributed to permeability variations in the seamless pipe. We scanned all thirteen defects and got satisfactory results. The two smallest defects did not show a signal, but these were much too small to be reported in a pipeline inspection. We acquired a ten-foot seam welded pipe that has much less background variation. We are measuring the sensitivity of RFEC signals to mechanical variations between the exciter and sensing coils.

  5. Electron Cyclotron / Bernstein Wave Heating and Current Drive Experiments using Phased-array Antenna in QUEST

    SciTech Connect

    Idei, H.; Zushi, H.; Hanada, K.; Nakamura, K.; Fujisawa, A.; Hasegawa, M.; Yoshida, N.; Watanebe, H.; Tokunaga, K.; Nagashima, Y.; Kawasaki, S.; Nakashima, H.; Higashijima, A.; Sakamoto, M.; Ejiri, A.; Takase, Y.; Sakaguchi, M.; Kalinnikova, E.; Ishiguro, M.; Tashima, S.

    2011-12-23

    The phased-array antenna system for Electron Cyclotron/Bernstein Wave Heating and Current Drive experiments has been developed in the QUEST. The antenna was designed to excite a pure O-mode wave in the oblique injection for the O-X-B mode conversion experiments, and its good performances were confirmed at a low power level. The plasma current (<{approx}15 kA) with an aspect ratio of 1.5 was started up and sustained by only RF injection in the low-density operations. The long pulse discharge of 10 kA was also attained for 37 s. The new density window to sustain the plasma current was observed in the high-density plasmas. The single-null divertor configuration with the high plasma current (<{approx}25 kA) was attained in the 17 s plasma sustainment.

  6. Stabilization of tearing modes in DIII-D by localized electron cyclotron current drive

    NASA Astrophysics Data System (ADS)

    Luce, T. C.; La Haye, R. J.; Humphreys, D. A.; Petty, C. C.; Prater, R.

    2001-10-01

    Tearing modes have been shown to limit β and confinement in conventional ELMing H-mode tokamak regimes. The tearing modes grow from a "seed" island due to the destabilizing effect of pressure flattening in the island leading to a reduction in the local bootstrap current. Recent experiments on the DIII-D tokamak have demonstrated stabilization of m=3/n=2 tearing modes in the presence of sawteeth through localized electron cyclotron current drive (ECCD). Variation of the deposition location indicates the ECCD remains localized despite the beam traversing an ELMing edge. The effect of the ECCD on the mode is consistent with predictions that the ECCD must be within the island for stabilization. The calculated EC current density (JEC) is greater than the calculated local bootstrap current density (JBS) also in accord with predictions. A closed-loop feedback scheme has been successfully operated for the first time using position control and magnetic signals as the actuator and sensor, respectively.

  7. Investigation of the second harmonic electron cyclotron current drive efficiency on the T-10 tokamak

    SciTech Connect

    Razumova, K.A.; Alikaev, V.V.; Dremin, M.M.; Esipchuk, Y.V.; Kislov, A.Y.; Notkin, G.E.; Pavlov, Y.D. ); Forest, C.B.; Lohr, J.; Luce, T.C.; Harvey, R.W. )

    1994-05-01

    Experiments on second harmonic electron cyclotron current drive were done on the T-10 tokamak using four gyrotrons. Total powers up to 1.2 MW at a frequency of 140 GHz were injected. Current generation by electron cyclotron (EC) waves was demonstrated in the experiments. The efficiency [eta] of current generation and its dependence on plasma parameters were measured and it was shown that the efficiency is a nonlinear function of input power, more closely predicted by Fokker--Planck calculations than by linear theory. The interaction of EC waves with the tail of the electron distribution was shown to be important. It was also found that current density profile redistribution played an important role in the plasma behavior.

  8. COMPLETE SUPPRESSION OF THE M=2/N-1 NEOCLASSICAL TEARING MODE USING ELECTRON CYCLOTRON CURRENT DRIVE ON DIII-D

    SciTech Connect

    PETTY,CC; LAHAYE,LA; LUCE,TC; HUMPHREYS,DA; HYATT,AW; PRATER,R; STRAIT,EJ; WADE,MR

    2003-03-01

    A271 COMPLETE SUPPRESSION OF THE M=2/N-1 NEOCLASSICAL TEARING MODE USING ELECTRON CYCLOTRON CURRENT DRIVE ON DIII-D. The first suppression of the important and deleterious m=2/n=1 neoclassical tearing mode (NTM) is reported using electron cyclotron current drive (ECCD) to replace the ''missing'' bootstrap current in the island O-point. Experiments on the DIII-D tokamak verify the maximum shrinkage of the m=2/n=1 island occurs when the ECCD location coincides with the q = 2 surface. The DIII-D plasma control system is put into search and suppress mode to make small changes in the toroidal field to find and lock onto the optimum position, based on real time measurements of dB{sub {theta}}/dt, for complete m=2/n=1 NTM suppression by ECCD. The requirements on the ECCD for complete island suppression are well modeled by the modified Rutherford equation for the DIII-D plasma conditions.

  9. Method for producing silicon thin-film transistors with enhanced forward current drive

    DOEpatents

    Weiner, K.H.

    1998-06-30

    A method is disclosed for fabricating amorphous silicon thin film transistors (TFTs) with a polycrystalline silicon surface channel region for enhanced forward current drive. The method is particularly adapted for producing top-gate silicon TFTs which have the advantages of both amorphous and polycrystalline silicon TFTs, but without problem of leakage current of polycrystalline silicon TFTs. This is accomplished by selectively crystallizing a selected region of the amorphous silicon, using a pulsed excimer laser, to create a thin polycrystalline silicon layer at the silicon/gate-insulator surface. The thus created polysilicon layer has an increased mobility compared to the amorphous silicon during forward device operation so that increased drive currents are achieved. In reverse operation the polysilicon layer is relatively thin compared to the amorphous silicon, so that the transistor exhibits the low leakage currents inherent to amorphous silicon. A device made by this method can be used, for example, as a pixel switch in an active-matrix liquid crystal display to improve display refresh rates. 1 fig.

  10. Initial fast wave heating and current drive experiments on the DIII-D tokamak

    SciTech Connect

    Prater, R.; Mayberry, M.J.; Petty, C.C.; Pinsker, R.I.; Chiu, S.C.; Harvey, R.W.; Luce, T.C.; Porkolab, M.; Bonoli, P.; James, R.A.; Kawashima, H.; Baity, F.W.; Goulding, R.H.; Hoffman, D.J.; Becoulet, A.; Moreau, D.; Trukhin, V.

    1991-12-01

    Heating and current drive experiments have been performed on the DIII-D tokamak using a 4-strap fast wave antenna at power up to 1.7 MW at 30--60 MHz. Minority heating experiments using D(H) showed effective wave absorption, confirming that the antenna was launching the fast wave. Experiments on the direct absorption of fast waves by electrons through Landau damping and transit-time magnetic pumping were performed at 60 MHz. These experiments showed effective heating of electrons, with a global heating efficiency comparable to that of neutral injection, even when the calculated single-pass dumping was as small as 5%. It is believed that effective multiple-pass damping is taking place. Fast wave current drive experiments were performed with a toroidally directional spectrum obtained by {pi}/2-phasing of the antenna straps. Although non-inductive currents of up to 160 kA were found, the magnitude of the non-inductive current did not decrease when the wave spectrum was reversed. These results are presently under investigation.

  11. Method for producing silicon thin-film transistors with enhanced forward current drive

    DOEpatents

    Weiner, Kurt H.

    1998-01-01

    A method for fabricating amorphous silicon thin film transistors (TFTs) with a polycrystalline silicon surface channel region for enhanced forward current drive. The method is particularly adapted for producing top-gate silicon TFTs which have the advantages of both amorphous and polycrystalline silicon TFTs, but without problem of leakage current of polycrystalline silicon TFTs. This is accomplished by selectively crystallizing a selected region of the amorphous silicon, using a pulsed excimer laser, to create a thin polycrystalline silicon layer at the silicon/gate-insulator surface. The thus created polysilicon layer has an increased mobility compared to the amorphous silicon during forward device operation so that increased drive currents are achieved. In reverse operation the polysilicon layer is relatively thin compared to the amorphous silicon, so that the transistor exhibits the low leakage currents inherent to amorphous silicon. A device made by this method can be used, for example, as a pixel switch in an active-matrix liquid crystal display to improve display refresh rates.

  12. Numerical studies of electron cyclotron wave current drive on HL-2A tokamak

    SciTech Connect

    Li, J. C.; Gong, X. Y.; Dong, J. Q.; Song, S. D.; Gao, Q. D.; Zheng, P. W.; Du, D.

    2015-06-15

    The electron cyclotron wave (ECW) current drive (CD) for the HL-2A tokamak is investigated numerically with a new ray-tracing and Fokker-Planck code. The code is benchmarked with other well-tested linear and quasilinear codes and is then used to study the electron cyclotron current drive on the HL-2A tokamak. The wave propagation, power deposition, and driven-current profiles are presented. The effect of electron trapping is also assessed. It is found that quasilinear effects are negligible at the present ECW power levels and that when both waves are injected at an angle of 20° on the plasma equatorial plane, the CD efficiency for the HL-2A saturates at ∼0.029 × 10{sup 20 }A/W/m{sup 2} and ∼0.020 × 10{sup 20 }A/W/m{sup 2} for the 0.5 MW/68 GHz first harmonic ordinary (O1) and 1 MW/140 GHz second harmonic extraordinary (X2) modes, respectively. The effects of the plasma density, temperature, and wave-launching position on the driven current are also investigated analytically and numerically.

  13. Driving toroidally asymmetric current through the tokamak scrape-off layer, Part I: Potential for ELM suppression

    SciTech Connect

    Joseph, I; Cohen, R H; Ryutov, D D

    2009-03-31

    A potential technique for suppressing edge localized magnetohydrodynamic instabilities (ELMs) is theoretically analyzed. Recent experiments have shown that externally generated resonant magnetic perturbations (RMPs) can stabilize ELMs by modifying the density profile [T. E. Evans, et al., Nature Phys. 2, 419 (2006); Y. Liang, et al., Phys. Rev. Lett. 98, 265004 (2007)]. Driving toroidally asymmetric current internally, through the scrape-off layer (SOL) plasma itself, can also generate RMPs that are close to the required threshold for ELM control. The limiting ion saturation current densities can be achieved by producing potential differences on the order of the electron temperature. Although the threshold is uncertain in future devices, if driven coherently though the SOL, the upper limit for the resulting field would exceed the present experimental threshold. This analysis provides the tools required for estimating the magnitude of the coherent SOL current and RMP generated via toroidally asymmetric biasing of the target. Flux expansion increases the RMP near the X-point, while phase interference due to the shearing of field lines near the X-point reduces the amplitude of the effective SOL perturbation and makes the result sensitive to both toroidal mode number n and the radial coherence width of the biasing region. If the limiting current density decays rapidly enough radially, both the width and the amplitude of the current density drawn from the target will be reduced. The RMP can still exceed the present threshold at low n if the radial location and width of the biasing region are optimally chosen.

  14. Closure of the single fluid magnetohydrodynamic equations in presence of electron cyclotron current drive

    SciTech Connect

    Westerhof, E. Pratt, J.

    2014-10-15

    In the presence of electron cyclotron current drive (ECCD), the Ohm's law of single fluid magnetohydrodynamics is modified as E + v × B = η(J – J{sub EC}). This paper presents a new closure relation for the EC driven current density appearing in this modified Ohm's law. The new relation faithfully represents the nonlocal character of the EC driven current and its main origin in the Fisch-Boozer effect. The closure relation is validated on both an analytical solution of an approximated Fokker-Planck equation as well as on full bounce-averaged, quasi-linear Fokker-Planck code simulations of ECCD inside rotating magnetic islands. The new model contains the model put forward by Giruzzi et al. [Nucl. Fusion 39, 107 (1999)] in one of its limits.

  15. Thyristor-based current-fed drive with direct power control for permanent magnet-assisted synchronous reluctance generator

    NASA Astrophysics Data System (ADS)

    Baek, J.; Kwak, S.-S.; Toliyat, H. A.

    2015-03-01

    This paper proposes a robust and simple direct power control (DPC) of a thyristor-based current-fed drive for generator applications. A current-fed drive and permanent magnet-assisted synchronous reluctance generator (PMa-SynRG) are investigated to deliver 3 kW power using a combustion engine. The current-fed drive utilises a thyristor-based three-phase rectifier to convert generator power to DC-link power and a single-phase current-fed inverter to supply a single-phase inductive load. In addition, a new control algorithm is developed based on DPC for the current-fed drive. The DC-link voltage-based DPC is proposed in order to directly control the output power. The goal of the DPC is to maintain the DC-link voltage at the required output power operating point. The DPC has advantages such as a simple algorithm for constant speed operation. Another feature of the developed current-fed drive is its inherent capability to provide generating action by making the PMa-SynRG operates as a generator, rectifying the phase voltages by means of the three-phase rectifier and feeding the power into the load. These features make the current-fed drive a good candidate for driving any type of synchronous generators including the proposed PMa-SynRG.

  16. Comparative modelling of lower hybrid current drive with two launcher designs in the Tore Supra tokamak

    NASA Astrophysics Data System (ADS)

    Nilsson, E.; Decker, J.; Peysson, Y.; Artaud, J.-F.; Ekedahl, A.; Hillairet, J.; Aniel, T.; Basiuk, V.; Goniche, M.; Imbeaux, F.; Mazon, D.; Sharma, P.

    2013-08-01

    Fully non-inductive operation with lower hybrid current drive (LHCD) in the Tore Supra tokamak is achieved using either a fully active multijunction (FAM) launcher or a more recent ITER-relevant passive active multijunction (PAM) launcher, or both launchers simultaneously. While both antennas show comparable experimental efficiencies, the analysis of stability properties in long discharges suggest different current profiles. We present comparative modelling of LHCD with the two different launchers to characterize the effect of the respective antenna spectra on the driven current profile. The interpretative modelling of LHCD is carried out using a chain of codes calculating, respectively, the global discharge evolution (tokamak simulator METIS), the spectrum at the antenna mouth (LH coupling code ALOHA), the LH wave propagation (ray-tracing code C3PO), and the distribution function (3D Fokker-Planck code LUKE). Essential aspects of the fast electron dynamics in time, space and energy are obtained from hard x-ray measurements of fast electron bremsstrahlung emission using a dedicated tomographic system. LHCD simulations are validated by systematic comparisons between these experimental measurements and the reconstructed signal calculated by the code R5X2 from the LUKE electron distribution. An excellent agreement is obtained in the presence of strong Landau damping (found under low density and high-power conditions in Tore Supra) for which the ray-tracing model is valid for modelling the LH wave propagation. Two aspects of the antenna spectra are found to have a significant effect on LHCD. First, the driven current is found to be proportional to the directivity, which depends upon the respective weight of the main positive and main negative lobes and is particularly sensitive to the density in front of the antenna. Second, the position of the main negative lobe in the spectrum is different for the two launchers. As this lobe drives a counter-current, the resulting

  17. High efficiency off-axis current drive by high frequency fast waves

    SciTech Connect

    Prater, R.; Pinsker, R. I.; Moeller, C. P.; Porkolab, M.; Vdovin, V.

    2014-02-12

    Modeling work shows that current drive can be done off-axis with high efficiency, as required for FNSF and DEMO, by using very high harmonic fast waves (“helicons” or “whistlers”). The modeling indicates that plasmas with high electron beta are needed in order for the current drive to take place off-axis, making DIII-D a highly suitable test vehicle for this process. The calculations show that the driven current is not very sensitive to the launched value of n{sub ∥}, a result that can be understood from examination of the evolution of n{sub ∥} as the waves propagate in the plasma. Because of this insensitivity, relatively large values (∼3) of n{sub ∥} can be launched, thereby avoiding some of the problems with mode conversion in the boundary found in some previous experiments. Use of a traveling wave antenna provides a very narrow n{sub ∥} spectrum, which also helps avoid mode conversion.

  18. The targeted heating and current drive applications for the ITER electron cyclotron system

    SciTech Connect

    Henderson, M.; Darbos, C.; Gandini, F.; Gassmann, T.; Loarte, A.; Omori, T.; Purohit, D.; Saibene, G.; Gagliardi, M.; Farina, D.; Figini, L.; Hanson, G.; Poli, E.; Takahashi, K.

    2015-02-15

    A 24 MW Electron Cyclotron (EC) system operating at 170 GHz and 3600 s pulse length is to be installed on ITER. The EC plant shall deliver 20 MW of this power to the plasma for Heating and Current Drive (H and CD) applications. The EC system is designed for plasma initiation, central heating, current drive, current profile tailoring, and Magneto-hydrodynamic control (in particular, sawteeth and Neo-classical Tearing Mode) in the flat-top phase of the plasma. A preliminary design review was performed in 2012, which identified a need for extended application of the EC system to the plasma ramp-up, flattop, and ramp down phases of ITER plasma pulse. The various functionalities are prioritized based on those applications, which can be uniquely addressed with the EC system in contrast to other H and CD systems. An initial attempt has been developed at prioritizing the allocated H and CD applications for the three scenarios envisioned: ELMy H-mode (15 MA), Hybrid (∼12 MA), and Advanced (∼9 MA) scenarios. This leads to the finalization of the design requirements for the EC sub-systems.

  19. The targeted heating and current drive applications for the ITER electron cyclotron system

    NASA Astrophysics Data System (ADS)

    Henderson, M.; Saibene, G.; Darbos, C.; Farina, D.; Figini, L.; Gagliardi, M.; Gandini, F.; Gassmann, T.; Hanson, G.; Loarte, A.; Omori, T.; Poli, E.; Purohit, D.; Takahashi, K.

    2015-02-01

    A 24 MW Electron Cyclotron (EC) system operating at 170 GHz and 3600 s pulse length is to be installed on ITER. The EC plant shall deliver 20 MW of this power to the plasma for Heating and Current Drive (H&CD) applications. The EC system is designed for plasma initiation, central heating, current drive, current profile tailoring, and Magneto-hydrodynamic control (in particular, sawteeth and Neo-classical Tearing Mode) in the flat-top phase of the plasma. A preliminary design review was performed in 2012, which identified a need for extended application of the EC system to the plasma ramp-up, flattop, and ramp down phases of ITER plasma pulse. The various functionalities are prioritized based on those applications, which can be uniquely addressed with the EC system in contrast to other H&CD systems. An initial attempt has been developed at prioritizing the allocated H&CD applications for the three scenarios envisioned: ELMy H-mode (15 MA), Hybrid (˜12 MA), and Advanced (˜9 MA) scenarios. This leads to the finalization of the design requirements for the EC sub-systems.

  20. On variational formulation of current drive problem in uniformly magnetized relativistic plasma

    NASA Astrophysics Data System (ADS)

    Hu, Y. M.; Hu, Y. J.

    2016-01-01

    A fully relativistic extension of the variational principle with the modified test function for the Spitzer function with momentum conservation in the electron-electron collision is investigated in uniformly magnetized plasma. The term of the momentum conserving constraint in Hirshman’s variational calculation is studied. The model developed is extended for arbitrary temperatures and covers exactly the asymptotic for u\\gg 1 when {{Z}\\text{eff}}\\gg 1 , and the results obtained are suited to facilitate the development of a rigorous variational formulation of current drive efficiency in tokamak plasma.

  1. Development of a prototype T-shaped fast switching device for electron cyclotron current drive systems

    NASA Astrophysics Data System (ADS)

    Sekiguchi, Kenji; Nagashima, Koji; Honzu, Toshihiko; Saigusa, Mikio; Oda, Yasuhisa; Takahashi, Koji; Sakamoto, Keishi

    2016-09-01

    A T-shaped high-power switching device composed of circular corrugated waveguides with three ports and double dielectric disks made of sapphire was proposed as a fast switching device based on a new principle in electron cyclotron current drive systems. This switching device has the advantages of operating at a fixed frequency and being compact. The design of the prototype switch was obtained by numerical simulations using a finite-difference time-domain (FDTD) method. The size of these components was optimized for the frequency band of 170 GHz. Low-power tests were carried out in a cross-shaped model.

  2. Demonstration of Effective Control of Fast-Ion-Stabilized Sawteeth by Electron-Cyclotron Current Drive

    NASA Astrophysics Data System (ADS)

    Lennholm, M.; Eriksson, L.-G.; Turco, F.; Bouquey, F.; Darbos, C.; Dumont, R.; Giruzzi, G.; Jung, M.; Lambert, R.; Magne, R.; Molina, D.; Moreau, P.; Rimini, F.; Segui, J.-L.; Song, S.; Traisnel, E.

    2009-03-01

    In a tokamak plasma, sawtooth oscillations in the central temperature, caused by a magnetohydrodynamic instability, can be partially stabilized by fast ions. The resulting less frequent sawtooth crashes can trigger unwanted magnetohydrodynamic activity. This Letter reports on experiments showing that modest electron-cyclotron current drive power, with the deposition positioned by feedback control of the injection angle, can reliably shorten the sawtooth period in the presence of ions with energies ≥0.5MeV. Certain surprising elements of the results are evaluated qualitatively in terms of existing theory.

  3. Effects of electron cyclotron current drive on the evolution of double tearing mode

    SciTech Connect

    Sun, Guanglan Dong, Chunying; Duan, Longfang

    2015-09-15

    The effects of electron cyclotron current drive (ECCD) on the double tearing mode (DTM) in slab geometry are investigated by using two-dimensional compressible magnetohydrodynamics equations. It is found that, mainly, the double tearing mode is suppressed by the emergence of the secondary island, due to the deposition of driven current on the X-point of magnetic island at one rational surface, which forms a new non-complete symmetric magnetic topology structure (defined as a non-complete symmetric structure, NSS). The effects of driven current with different parameters (magnitude, initial time of deposition, duration time, and location of deposition) on the evolution of DTM are analyzed elaborately. The optimal magnitude or optimal deposition duration of driven current is the one which makes the duration of NSS the longest, which depends on the mutual effect between ECCD and the background plasma. Moreover, driven current introduced at the early Sweet-Parker phase has the best suppression effect; and the optimal moment also exists, depending on the duration of the NSS. Finally, the effects varied by the driven current disposition location are studied. It is verified that the favorable location of driven current is the X-point which is completely different from the result of single tearing mode.

  4. Non-linear effects in electron cyclotron current drive applied for the stabilization of neoclassical tearing modes

    NASA Astrophysics Data System (ADS)

    Ayten, B.; Westerhof, E.; the ASDEX Upgrade Team

    2014-07-01

    Due to the smallness of the volumes associated with the flux surfaces around the O-point of a magnetic island, the electron cyclotron power density applied inside the island for the stabilization of neoclassical tearing modes (NTMs) can exceed the threshold for non-linear effects as derived previously by Harvey et al (1989 Phys. Rev. Lett. 62 426). We study the non-linear electron cyclotron current drive (ECCD) efficiency through bounce-averaged, quasi-linear Fokker-Planck calculations in the magnetic geometry as created by the islands. The calculations are performed for the parameters of a typical NTM stabilization experiment on ASDEX Upgrade. A particular feature of these experiments is that the rays of the EC wave beam propagate tangential to the flux surfaces in the power deposition region. The calculations show significant non-linear effects on the ECCD efficiency, when the ECCD power is increased from its experimental value of 1 MW to a larger value of 4 MW. The nonlinear effects are largest in the case of locked islands or when the magnetic island rotation period is longer than the collisional time scale. The non-linear effects result in an overall reduction of the current drive efficiency for this case with absorption of the EC power on the low-field side of the electron cyclotron resonance layer. As a consequence of the non-linear effects, also the stabilizing effect of the ECCD on the island is reduced from linear expectations.

  5. Comparison of the theory and the practice of rf current drive

    SciTech Connect

    Karney, C.F.F.; Fisch, N.J.; Jobes, F.C.

    1984-10-01

    The theory of rf-driven plasma currents is applied to the lower-hybrid experiments on the PLT tokamak. Particular emphasis is placed on those experiments in which the plasma current was varying. The comparison between theory and experiment is made with respect to the efficiency with which rf energy was converted to poloidal magnetic field energy. Good agreement is found irrespective of whether the current was increasing, constant, or decreasing.

  6. 4 MW upgrade to the DIII-D fast wave current drive system

    SciTech Connect

    deGrassie, J.S.; Pinsker, R.I.; Cary, W.P.

    1993-10-01

    The DIII-D fast wave current drive (FWCD) system is being upgraded by an additional 4 MW in the 30 to 120 MHz frequency range. This capability adds to the existing 2 MW 30 to 60 MHz system. Two new ABB transmitters of the type that are in use on the ASDEX-Upgrade tokamak in Garching will be used to drive two new water-cooled four-strap antennas to be installed in DIII-D in early 1994. The transmission and tuning system for each antenna will be similar to that now in use for the first 2 MW system on DIII-D, but with some significant improvements. One improvement consists of adding a decoupler element to counter the mutual coupling between the antenna straps which results in large imbalances in the power to a strap for the usual current drive intrastrap phasing of 90{degrees}. Another improvement is to utilize pressurized, ceramic-insulated transmission lines. The intrastrap phasing will again be controlled in pairs, with a pair of straps coupled in a resonant loop configuration, locking their phase difference at either 0 or 180{degrees}, depending upon the length of line installed. These resonant loops will incorporate a phase shifter so that they will be able to be tuned to resonance at several frequencies in the operating band of the transmitter. With the frequency change capability of the ABB generators, the FWCD frequency will thus be selectable on a shot-to-shot basis, from this preselected set of frequencies. The schedule is for experiments to begin with this added 4 MW capability in mid-1994. The details of the system are described.

  7. 3-D Magnetic Field Analysis of Permanent Magnet Motor Considering Magnetizing, Demagnetizing and Eddy Current Loss

    NASA Astrophysics Data System (ADS)

    Miyata, Koji; Aoyama, Yasuaki; Yokoyama, Tomonori; Ohashi, Ken; Kondo, Minoru; Matsuoka, Koichi

    Rare-earth magnets, which have high energy product, have been widely used in several industrial applications such as voice coil motors for hard disk drives, MRI for medical devices and motors for electric vehicle. In order to realize a small and high performance device, the magnetic field analysis techniques are required. In this paper, we applied the magnetic field analysis to design the permanent magnet synchronous motors into the rail traction system. In the inverter fed motor drive, the eddy current loss in the permanent magnet increased. We simulated the effect that eddy current was decreased by using a divided permanent magnet. Furthermore, the permanent magnet tends to be demagnetized due to the effect of a demagnetizing field formed at high temperatures. However, according to our analysis, demagnetization does not occur within the range of our design specifications. Also, we performed magnetic field analysis assuming a pulse-type magnetization process and designed an optimal magnetizing coil.

  8. Review of tokamak experiments on direct electron heating and current drive with fast waves

    SciTech Connect

    Pinsker, R.I.

    1993-12-01

    Results from tokamak experiments on direct electron interaction with the compressional Alfven wave ({open_quote}fast wave{close_quote}) are reviewed. Experiments aimed at electron heating as well as those in which fast wave electron current drive was investigated are discussed. A distinction is drawn between experiments employing the lower hybrid range of frequencies, where both the lower hybrid wave ({open_quote}slow wave{close_quote}) and the fast wave can propagate in much of the plasma, and those experiments using the fast wave in the range of moderate to high ion cyclotron harmonics, where only the fast wave can penetrate to the plasma core. Most of the early tokamak experiments were in the lower hybrid frequency regime, and the observed electron interaction appeared to be very similar to that obtained with the slow wave at the same frequency. In particular, electron interaction with the fast wave was observed only below a density limit nearly the same as the well known slow wave density limit. In the more recent lower frequency fast wave experiments, electron interaction (heating and current drive) is observed at the center of the discharge, where slow waves are not present.

  9. First results on lower hybrid current drive at 2. 45 GHz in ASDEX

    SciTech Connect

    Leuterer, F.; Soldner, F.X.; Buechse, R.; Carlson, A.; Eberhagen, A.; Fahrbach, H.; Gehre, O.; Hassenpflug, F.; Herrmann, W.; Janeschitz, G.; Kornherr, M.; Luce, T.; McKormick, K.; Monaco, F.; Muenich, M.; Murmann, H.; Pelicano, M.; Steuer, K.; Zouhar, M. ); Bartiromo, R.; DeAngelis, R.; Pericoli, V.; Santini, F.; Tuccillo, A. ); Bernabei, S.; Forrest, C. ); ASDEX-team

    1989-07-01

    A new lower hybrid system with 2.45 GHz/3 MW/1 sec has started operation on ASDEX. Current drive effects have been identified up to a density of {bar n}{sub e}=4.7 {center dot} 10{sup 13} cm{sup {minus}3}. Full current drive at I{sub p}=420 kV was achieved up to a density of {bar n}{sub e}=2.1 {center dot} 10{sup 13} cm{sup {minus}3}. The effeciency was maximum at {bar n}{sub e}=1.35 {center dot} 10{sup 13} cm{sup {minus}3} and reached {eta}=1.46 (10{sup 13} cm{sup {minus}3} {center dot} A {center dot} m/W). The electron temperature is peaking and reached peak values up to 6 keV, while the electron density profile flattens. Sawteeth have been stabilized up to a density of {bar n}{sub e}=3.4 {center dot} 10{sup 13} cm{sup {minus}3}. The global confinement times decreases with increasing rf-power. The scaling can be described by an offset linear relation. At low density global confinement is better during the LH-phase than in the OH-phase at the same total power input.

  10. Experimental and modeling uncertainties in the validation of lower hybrid current drive

    NASA Astrophysics Data System (ADS)

    Poli, F. M.; Bonoli, P. T.; Chilenski, M.; Mumgaard, R.; Shiraiwa, S.; Wallace, G. M.; Andre, R.; Delgado-Aparicio, L.; Scott, S.; Wilson, J. R.; Harvey, R. W.; Petrov, Yu V.; Reinke, M.; Faust, I.; Granetz, R.; Hughes, J.; Rice, J.

    2016-09-01

    This work discusses sources of uncertainty in the validation of lower hybrid wave current drive simulations against experiments, by evolving self-consistently the magnetic equilibrium and the heating and current drive profiles, calculated with a combined toroidal ray tracing code and 3D Fokker–Planck solver. The simulations indicate a complex interplay of elements, where uncertainties in the input plasma parameters, in the models and in the transport solver combine and—in some cases—compensate each other. It is concluded that ray-tracing calculations should include a realistic representation of the density and temperature in the region between the confined plasma and the wall, which is especially important in regimes where the LH waves are weakly damped and undergo multiple reflections from the plasma boundary. Uncertainties introduced in the processing of diagnostic data as well as uncertainties introduced by model approximations are assessed. It is shown that, by comparing the evolution of the plasma parameters in self-consistent simulations with available data, inconsistencies can be identified and limitations in the models or in the experimental data assessed.

  11. Simulation study of proposed off-midplane lower hybrid current drive in KSTAR

    NASA Astrophysics Data System (ADS)

    Bae, Young-soon; Shiraiwa, S.; Bonoli, P.; Wallace, G.; Wright, J. C.; Parker, R.; Kim, J. H.; Namkung, W.; Cho, M. H.; Park, B. H.; Yoon, S. W.; Oh, Y. K.; Park, H.

    2016-07-01

    A new proposal of lower hybrid (LH) wave launching is studied for efficient current drive aiming for high performance H-mode operation in Korea Superconducting Tokamak Advanced Research (KSTAR). This new concept is the off-midplane launch which results in a rapid up-shift of the parallel component of refractive index and hence simultaneously maintains good wave accessibility and efficient single pass absorption via Landau damping. In order to locate an optimal position of the launcher in the poloidal direction, the ray-tracing and Fokker–Planck codes were used. Based on a survey of the LH wave launch parameters and operation conditions including the compatibility issues with the existing in-vessel components, the LH wave launch from the top position near the upper X-point of the plasma separatrix provides the possibility to eliminate the accessibility problem and reduce parasitic edge loss for the KSTAR high performance H-mode operation scenario using 5 GHz lower hybrid current drive.

  12. Boost of plasma current with active magnetic field shaping coils in rotamak discharges

    SciTech Connect

    Yang Xiaokang; Goss, Jermain; Kalaria, Dhara; Huang, Tian Sen

    2011-08-15

    A set of magnetic shaping coils is installed on the Prairie View (PV) rotamak for the study of active plasma shape control in the regimes with and without toroidal field (TF). In the spherical tokamak regime (with TF), plasma current I{sub p} can be boosted by 200% when all five shaping coils (connected in series) are energized. The enhancement of current drive efficiency is mainly attributed to the radial compression and the substantially axial extension of the plasma column; this in turn improves the impedance matching and thus increases antenna input power. In the field-reversed configuration (without TF), plasma current can be boosted by 100% when one middle coil is used; the appearance of radial shift mode limits the achievable value of I{sub p}. The experiments clearly demonstrate that the plasma shape control plays a role in effectively driving plasma current in rotamaks.

  13. Modeling of fast wave current drive experiments on DIII-D

    SciTech Connect

    Luce, T.C.; Chiu, S.C.; Harvey, R.W.; Mayberry, M.J.; Petty, C.C.; Pinsker, R.I.; Prater, R.; Tsunoda, S.I.

    1991-09-01

    Modeling of fast wave current drive experiments for D3-D has been improved to include calculation of target temperature profiles consistent with the D3-D database and more accurate modeling of the launched spectrum. The calculations indicate that a measurable current will be driven by fast wave in the near-term (30--200 kA). Modeling of the long-range goal of 2 MA non-inductive at high {beta} indicates the proposed 18 MW of rf power will be adequate. The optimum frequency for the intermediate scenario is 120 MHz; this frequency selection is also adequate for the long-term goals. 8 refs., 2 figs., 2 tabs.

  14. Ion cyclotron and lower hybrid arrays applicable to current drive in fusion reactors

    NASA Astrophysics Data System (ADS)

    Bosia, G.; Helou, W.; Goniche, M.; Hillaret, J.; Ragona, R.

    2014-02-01

    This paper presents concepts for Ion Cyclotron and Lower Hybrid Current Drive arrays applicable to fusion reactors and based on periodically loaded line power division. It is shown that, in large arrays, such as the ones proposed for fusion reactor applications, these schemes can offer, in principle, a number of practical advantages, compared with currently adopted ones, such as in-blanket operation at significantly reduced power density, lay out suitable for water cooling, single ended or balanced power feed, simple and load independent impedance matching In addition, a remote and accurate real time measurement of the complex impedance of all array elements as well as detection, location, and measurement of the complex admittance of a single arc occurring anywhere in the structure is possible.

  15. Field aligned current observations in the polar cusp ionosphere

    NASA Technical Reports Server (NTRS)

    Ledley, B. G.; Farthing, W. H.

    1973-01-01

    Vector magnetic field measurements made during a sounding rocket flight in the polar cusp ionosphere show field fluctuations in the lower F-region which are interpreted as being caused by the payload's passage through a structured field aligned current system. The field aligned currents have a characteristic horizontal scale size of one kilometer. Analysis of one large field fluctuation gives a current density of 0.0001 amp/m sq.

  16. Lower Hybrid Current Drive and ion Bernstein wave heating experiments on PBX-M

    SciTech Connect

    Bernabei, S.

    1994-02-01

    This paper presents an overview of the experiments conducted on PBX-M to control on evaluate the feasibility and effect of current profile and pressure profile control on the plasma stability. Utilizing the inaccessibility of the Lower Hybrid waves, it has been possible to obtain a certain degree of power deposition localization and off-axis current drive. The effect of fast electron diffusion has been studied and found not to be a limiting factor; consequently, the current profile has been modified in a non-transient manner. More serious is the destabilization of global MHD modes, due to the change of the current profile, which can lead to disruption or to a rapid radial redistribution of the fast electron population. Experiments with Ion Bernstein wave heating have shown that power can be deposited off-aids and that the ion temperature can be modified locally. Application of IBW into a strongly Neutral Beam (NBI) heated H-mode plasma causes a substantial increase of thermal and particle confinement in the core of the plasma: this produces a localized bootstrap current sufficient to significantly raise the value of q(O). We propose to refer to this condition as the CH-mode.

  17. The future of biology in driving the field of hyperthermia.

    PubMed

    Dewhirst, Mark W; Lee, Chen-Ting; Ashcraft, Kathleen A

    2016-01-01

    In 2011 Hanahan and Weinberg updated their well-established paper 'The hallmarks of cancer'. The rationale for that review and its predecessor was to produce a conceptual framework for future research in cancer. The original Hallmarks included: cell signalling to enhance tumour cell proliferation, acquisition of ability to evade growth suppressors, developing mechanisms to resist cell death, enabling replicative immortality, initiating angiogenesis and activating processes to enable invasion and metastasis. In the more recent paper, Hanahan and Weinberg added important new features to this composite paradigm. The new features were: (1) altered metabolism, (2) evasion of immune destruction, (3) tumour promoting inflammation, and (4) the cellular microenvironment. These four new features are the main focus of this review. Hanahan and Weinberg did not specifically include the physiological microenvironment which is dominated by hypoxia and acidosis. In this review we will consider these features in addition to the cellular and metabolic components of the microenvironment. The purpose of this review is to present a vision of emerging fields of study in hyperthermia biology over the next decade and beyond. As such, we are focusing our attention on pre-clinical studies, primarily using mice. The application of hyperthermia in human patients has been thoroughly reviewed elsewhere. PMID:26850697

  18. Rotating field eddy current probe for characterization of cracking in non-magnetic tubing

    SciTech Connect

    Capobianco, T.E.

    1998-07-01

    A rotating field eddy current probe was built and tested for use in small diameter, non-magnetic tubing. The rotating field probe is a driver/pickup style with two orthogonally wound drive coils and a pancake pickup coil. The driver coils are excited by two sine waves 90{degree} out of phase with each other. The physical arrangement of the drive coils and the 90{degree} phase shift of the excitation waveforms creates a field which rotates in the test piece under the drive coils. Preliminary tests on electrical discharge machined (EDM) notches show that phased based estimates of notch depth are possible. Probes currently used for detection of cracks in tubing produce responses that have proven unreliable for estimating defect depths. This recently developed version of the rotating field eddy current probe produces a bipolar response in the presence of a crack or a notch. Typically, the phase angle of a bipolar eddy current response is easily identified and measured and is used extensively for estimating depths of volumetric defects. Data are shown relating the phase angle of the rotating field probe`s bipolar response to the depth of circumferential EDM notches.

  19. Variational full wave calculation of fast wave current drive in DIII-D using the ALCYON code

    SciTech Connect

    Becoulet, A.; Moreau, D.

    1992-04-01

    Initial fast wave current drive simulations performed with the ALCYON code for the 60 MHz DIII-D experiment are presented. Two typical shots of the 1991 summer campaign were selected with magnetic field intensities of 1 and 2 teslas respectively. The results for the wave electromagnetic field in the plasma chamber are displayed. They exhibit a strong enrichment of the poloidal mode number m-spectrum which leads to the upshift of the parallel wavenumber, {kappa}{perpendicular}, and to the wave absorption. The m-spectrum is bounded when the local poloidal wavenumber reaches the Alfven wavenumber and the {kappa}{perpendicular} upshifts do not destroy the wave directionality. Linear estimations of the driven current are made. The current density profiles are found to be peaked and we find that about 88 kA can be driven in the 1 tesla/1.7 keV phase with 1.7 MW coupled to the electrons. In the 2 tesla/3.4 keV case, 47 kA are driven with a total power of 1.5 MW, 44% of which are absorbed on the hydrogen minority, through the second harmonic ion cyclotron resonance. The global efficiency is then 0.18 {times} 10{sup 19} A m{sup {minus}2}W{sup {minus}1} if one considers only the effective power going to the electrons.

  20. Controlling Collapse and Revival of Multipartite Entanglement Under Decoherence via Classical Driving Fields

    NASA Astrophysics Data System (ADS)

    Zhang, Jian-Song; Liu, Fen; Chen, Ai-Xi

    2016-09-01

    We investigate the effects of classical driving fields on the dynamics of purity, spin squeezing, and genuine multipartite entanglement (based on the Peres-Horodecki criterion ) of three two-level atoms within three separated cavities prepared in coherent states in the presence of decoherence. The three qubits are initially entangled and driven by classical fields. We obtain an analytical solution of the present system using the superoperator method. We find that the genuine multipartite entanglement measured by an entanglement monotone based on the Peres-Horodecki criterion can stay zero for a finite time and revive partially later. This phenomenon is similar to the sudden death of entanglement of two qubits and can be controlled efficiently by the classical driving fields. The amount of purity, spin squeezing, and genuine multipartite entanglement decrease with the increase of mean photon number of cavity fields. Particularly, the purity and genuine multipartite entanglement could be simultaneously improved by the classical driving fields. In addition, there is steady state genuine multipartite entanglement which can also be adjusted by the classical driving fields.

  1. Requirements on localized current drive for the suppression of neoclassical tearing modes

    NASA Astrophysics Data System (ADS)

    Bertelli, N.; De Lazzari, D.; Westerhof, E.

    2011-10-01

    A heuristic criterion for the full suppression of an NTM was formulated as ηNTM ≡ jCD,max/jBS >= 1.2 (Zohm et al 2005 J. Phys. Conf. Ser. 25 234), where jCD,max is the maximum in the driven current density profile applied to stabilize the mode and jBS is the local bootstrap current density. In this work we subject this criterion to a systematic theoretical analysis on the basis of the generalized Rutherford equation. Taking into account only the effect of jCD inside the island, a new criterion for full suppression by a minimum applied total current is obtained in the form of a maximum allowed value for the width of the driven current, wdep, combined with a required minimum for the total driven current in the form of wdepηNTM, where both limits depend on the marginal and saturated island sizes. These requirements can be relaxed when additional effects are taken into account, such as a change in the stability parameter Δ' from the current driven outside the island, power modulation, the accompanying heating inside the island or when the current drive is applied preemptively. When applied to ITER scenario 2, the requirement for full suppression of either the 3/2 or 2/1 NTM becomes wdep <~ 5 cm and wdepηNTM >~ 5 cm in agreement with (Sauter et al 2010 Plasma Phys. Control. Fusion 52 025002). Optimization of the ITER ECRH Upper Port Launcher design towards minimum required power for full NTM suppression requires an increase in the toroidal injection angle of the lower steering mirror of several degrees compared with its present design value, while for the upper steering mirror the present design value is close to the optimum.

  2. A quasi-optical ray tracing code for EC absorption and current drive

    NASA Astrophysics Data System (ADS)

    Farina, Daniela

    2005-10-01

    A new code GRAY has been developed for the quasi-optical (QO) propagation of a Gaussian beam of EC waves and the relevant absorbed power and driven current in a generic tokamak equilibrium [D. Farina, IFP-CNR Int. Rep. 2005, FP 05/1]. In the framework of the complex eikonal approach [E. Mazzucato, Phys. Fluids, 1, 1855 (1989)], the beam propagation is described by a set of mutually interacting rays. Several theoretical and numerical issues have been addressed and solved, mainly concerning the accurate solution of the complex dispersion relation. A fast numerical algorithm for the solution of the imaginary part of the QO dispersion relation has been implemented. Along each ray, EC wave absorption is computed solving either the weakly or the fully relativistic dispersion relation for EC waves (up to any order in Larmor radius expansion), and EC current drive by means of a neoclassical response function for the current [D. Farina, IFP-CNR Int. Rep. 2003, FP 03/5]. The code has been benchmarked against other existing codes, and used for calculations of EC driven current in ITER plasma.

  3. Recent Results using a 28 GHz EBW Heating and Current Drive System on MAST

    NASA Astrophysics Data System (ADS)

    Bigelow, Tim; Caughman, John; Peng, Martin; Diem, Stephanie; Hawes, Julian; Gurl, Chris; Griffiths, Jonathan; Shevchenko, Vladimir; Finburg, Paul; Mailloux, Joelle; Taylor, Gary

    2013-10-01

    Improvements to a high power 28 GHz gyrotron system have been made to the MAST Electron Bernstein Wave (EBW) heating, start up, and current drive system in the past few years as collaborative research between ORNL and CCFE. Recent EBW heating and CD experiments on MAST have improved upon previous RF generated plasma current levels. The goals of the research were to extend the initial EBW CD study by increasing substantially the power level and pulse length of the gyrotron hardware and improve transmission line efficiency used in initial experiments. A dummy-load power level of up to 200 kW and a pulse length approaching 0.5 s has been achieved. Arcing, localized to the launcher box, has been observed to limit the launched power level to ~80 kW for up to 450 ms. Several days of high power plasma operation have been recently completed with good progress in increasing the previously attainable solenoid-free plasma current levels. Up to 75 kA of plasma current was achieved at this injected power level. This manuscript has been authored by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy.

  4. Dynamics of Dirac strings and monopolelike excitations in chiral magnets under a current drive

    DOE PAGESBeta

    Lin, Shi -Zeng; Saxena, Avadh

    2016-02-10

    Skyrmion lines in metallic chiral magnets carry an emergent magnetic field experienced by the conduction electrons. The inflow and outflow of this field across a closed surface is not necessarily equal, thus it allows for the existence of emergent monopoles. One example is a segment of skyrmion line inside a crystal, where a monopole and antimonopole pair is connected by the emergent magnetic flux line. This is a realization of Dirac stringlike excitations. Here we study the dynamics of monopoles in chiral magnets under an electric current. We show that in the process of creation of skyrmion lines, skyrmion linemore » segments are first created via the proliferation of monopoles and antimonopoles. Then these line segments join and span the whole system through the annihilation of monopoles. The skyrmion lines are destroyed via the proliferation of monopoles and antimonopoles at high currents, resulting in a chiral liquid phase. We also propose to create the monopoles in a controlled way by applying an inhomogeneous current to a crystal. Remarkably, an electric field component in the magnetic field direction proportional to the current squared in the low current region is induced by the motion of distorted skyrmion lines, in addition to the Hall and longitudinal voltage. As a result, the existence of monopoles can be inferred from transport or imaging measurements.« less

  5. Dynamics of Dirac strings and monopolelike excitations in chiral magnets under a current drive

    NASA Astrophysics Data System (ADS)

    Lin, Shi-Zeng; Saxena, Avadh

    2016-02-01

    Skyrmion lines in metallic chiral magnets carry an emergent magnetic field experienced by the conduction electrons. The inflow and outflow of this field across a closed surface is not necessarily equal, thus it allows for the existence of emergent monopoles. One example is a segment of skyrmion line inside a crystal, where a monopole and antimonopole pair is connected by the emergent magnetic flux line. This is a realization of Dirac stringlike excitations. Here we study the dynamics of monopoles in chiral magnets under an electric current. We show that in the process of creation of skyrmion lines, skyrmion line segments are first created via the proliferation of monopoles and antimonopoles. Then these line segments join and span the whole system through the annihilation of monopoles. The skyrmion lines are destroyed via the proliferation of monopoles and antimonopoles at high currents, resulting in a chiral liquid phase. We also propose to create the monopoles in a controlled way by applying an inhomogeneous current to a crystal. Remarkably, an electric field component in the magnetic field direction proportional to the current squared in the low current region is induced by the motion of distorted skyrmion lines, in addition to the Hall and longitudinal voltage. The existence of monopoles can be inferred from transport or imaging measurements.

  6. Physiological responses related to moderate mental load during car driving in field conditions.

    PubMed

    Wiberg, Henrik; Nilsson, Emma; Lindén, Per; Svanberg, Bo; Poom, Leo

    2015-05-01

    We measured physiological variables on nine car drivers to capture moderate magnitudes of mental load (ML) during driving in prolonged and repeated city and highway field conditions. Ecological validity was optimized by avoiding any artificial interference to manipulate drivers ML, drivers were alone in the car, they were free to choose their paths to the target, and the repeated drives familiarized drivers to the procedure. Our aim was to investigate if driver's physiological variables can be reliably measured and used as predictors of moderate individual levels of ML in naturally occurring unpredictably changing field conditions. Variables investigated were: heart-rate, skin conductance level, breath duration, blink frequency, blink duration, and eye fixation related potentials. After the drives, with support from video uptakes, a self-rating and a score made by external raters were used to distinguish moderately high and low ML segments. Variability was high but aggregated data could distinguish city from highway drives. Multivariate models could successfully classify high and low ML within highway and city drives using physiological variables as input. In summary, physiological variables have a potential to be used as indicators of moderate ML in unpredictably changing field conditions and to advance the evaluation and development of new active safety systems. PMID:25857673

  7. Complete stabilization of neoclassical tearing modes with lower hybrid current drive on COMPASS-D. RF teams.

    PubMed

    Warrick, C D; Buttery, R J; Cunningham, G; Fielding, S J; Hender, T C; Lloyd, B; Morris, A W; O'Brien, M R; Pinfold, T; Stammers, K; Valovic, M; Walsh, M; Wilson, H R

    2000-07-17

    Lower hybrid current drive (LHCD) with modest powers ( approximately 10% of the total power input) has been used for the first time to completely stabilize performance limiting neoclassical tearing modes in many COMPASS-D tokamak discharges. The stabilizing effect in these experiments is consistent with a reduction in the free energy available in the current profile to drive tearing modes (i.e., the stability index, delta(')) resulting from favorable current gradients (from the LHCD driven current) around the rational surface. PMID:10991343

  8. ITER ECH launcher options for start-up assist, bulk heating, and EC current drive experiments

    SciTech Connect

    Bigelow, T.S.

    1994-03-01

    Electron Cyclotron Heating (ECH) is proposed for providing plasma start-up, bulk heating, current drive, and other applications on the International Tokamak Experimental Reactor (ITER) project. The requirements for ECH power launching systems for ITER have been investigated, and several possible configurations that have been devised are described in this report. The proposed launcher designs use oversized circular corrugated waveguides that make small penetrations through the blanket modules and radiate into the plasma. The criteria used for the design calls for minimum blanket penetration area, maximum reliability, and optimum launched beam quality. The effects of the harsh plasma edge environment on the launcher are discussed. Power generation systems, windows, and other components of the ECH systems are also investigated. The designs presented are believed to be capable of operating reliably and are relatively easy to maintain remotely.

  9. Electron Cyclotron Current Drive at High Electron Temperature on DIII-D

    SciTech Connect

    Petty, C. C.; Lohr, J.; Luce, T. C.; Prater, R.; Austin, M. E.; Harvey, R. W.; Makowski, M. A.

    2007-09-28

    Experiments on DIII-D have measured the electron cyclotron current drive (ECCD) efficiency for co- and counter-injection in low density plasmas with radiation temperatures from electron cyclotron emission (ECE) above 20 keV. The radiation temperature is generally higher than the Thomson scattering temperature, indicating that there is a significant population of non-thermal electrons. The experimental ECCD profile measured with motional Stark effect (MSE) polarimetry is found to agree with quasi-linear theory except for the highest power density cases (Q{sub EC}/n{sub e}{sup 2}>>1). Radial transport of the energetic electrons with diffusion coefficients of {approx}0.4 m{sup 2}/s is needed to model the broadened ECCD profile at high power density.

  10. Status of the ITER Electron Cyclotron Heating and Current Drive System

    NASA Astrophysics Data System (ADS)

    Darbos, Caroline; Albajar, Ferran; Bonicelli, Tullio; Carannante, Giuseppe; Cavinato, Mario; Cismondi, Fabio; Denisov, Grigory; Farina, Daniela; Gagliardi, Mario; Gandini, Franco; Gassmann, Thibault; Goodman, Timothy; Hanson, Gregory; Henderson, Mark A.; Kajiwara, Ken; McElhaney, Karen; Nousiainen, Risto; Oda, Yasuhisa; Omori, Toshimichi; Oustinov, Alexander; Parmar, Darshankumar; Popov, Vladimir L.; Purohit, Dharmesh; Rao, Shambhu Laxmikanth; Rasmussen, David; Rathod, Vipal; Ronden, Dennis M. S.; Saibene, Gabriella; Sakamoto, Keishi; Sartori, Filippo; Scherer, Theo; Singh, Narinder Pal; Strauß, Dirk; Takahashi, Koji

    2016-01-01

    The electron cyclotron (EC) heating and current drive (H&CD) system developed for the ITER is made of 12 sets of high-voltage power supplies feeding 24 gyrotrons connected through 24 transmission lines (TL), to five launchers, four located in upper ports and one at the equatorial level. Nearly all procurements are in-kind, following general ITER philosophy, and will come from Europe, India, Japan, Russia and the USA. The full system is designed to couple to the plasma 20 MW among the 24 MW generated power, at the frequency of 170 GHz, for various physics applications such as plasma start-up, central H&CD and magnetohydrodynamic (MHD) activity control. The design takes present day technology and extends toward high-power continuous operation, which represents a large step forward as compared to the present state of the art. The ITER EC system will be a stepping stone to future EC systems for DEMO and beyond.

  11. Current Drive and Plasma Heating by Electron Bernstein Waves in MAST

    SciTech Connect

    Shevchenko, V.

    2009-11-26

    Electron Bernstein waves (EBW) have the potential to provide highly localized heating and current drive (CD). EBWs are predominantly electrostatic and they damp on electrons near electron cyclotron harmonics without momentum injection into the plasma. These features represent a powerful tool for understanding transport and stability phenomena by locally perturbing the plasma and providing complementary CD methods in addition to neutral beams. The Mega-Ampere Spherical Tokamak (MAST) has a large cylindrical vacuum vessel and we have taken advantage of this to consider a number of launcher positions for RF power injection. The feasibility of EBW in the extended parameter space of MAST has been explored. Modelling was conducted with the EBW and BANDIT code package using a 'steady state' reference scenario with near zero loop voltage. Clear heating and CD effects have been identified for different launch configurations and frequencies.

  12. HHFW Heating and Current Drive Studies of NSTX H-Mode Plasmas

    SciTech Connect

    Taylor, G.; Hosea, J. C.; LeBlanc, B. P.; Phillips, C. K.; Valeo, E. J.; Wilson, J. R.; Bonoli, P. T.; Wright, J. C.; Green, D. L.; Jaeger, E. F.; Maingi, R.; Ryan, P. M.; Harvey, R. W.

    2011-12-23

    30 MHz high-harmonic fast wave (HHFW) heating and current drive are being developed to assist fully non-inductive plasma current (I{sub p}) ramp-up in NSTX. The initial approach to achieving this goal has been to heat I{sub p} = 300 kA inductive plasmas with current drive antenna phasing in order to generate an HHFW H-mode with significant bootstrap and RF-driven current. Recent experiments, using only 1.4 MW of RF power (P{sub RF}), achieved a non-inductive current fraction, f{sub NI}{approx}0.65. Improved antenna conditioning resulted in the generation of I{sub p} = 650 kA HHFW H-mode plasmas, with f{sub NI}{approx}0.35, when P{sub RF}{>=}2.5 MW. These plasmas have little or no edge localized mode (ELM) activity during HHFW heating, a substantial increase in stored energy and a sustained central electron temperature of 5-6 keV. Another focus of NSTX HHFW research is to heat an H-mode generated by 90 keV neutral beam injection (NBI). Improved HHFW coupling to NBI-generated H-modes has resulted in a broad increase in electron temperature profile when HHFW heating is applied. Analysis of a closely matched pair of NBI and HHFW+NBI H-mode plasmas revealed that about half of the antenna power is deposited inside the last closed flux surface (LCFS). Of the power damped inside the LCFS about two-thirds is absorbed directly by electrons and one-third accelerates fast-ions that are mostly promptly lost from the plasma. At longer toroidal launch wavelengths, HHFW+NBI H-mode plasmas can have an RF power flow to the divertor outside the LCFS that significantly reduces RF power deposition to the core. ELMs can also reduce RF power deposition to the core and increase power deposition to the edge. Recent full wave modeling of NSTX HHFW+NBI H-mode plasmas, with the model extended to the vessel wall, predicts a coaxial standing mode between the LCFS and the wall that can have large amplitudes at longer launch wavelengths. These simulation results qualitatively agree with HHFW

  13. HHFW Heating and Current Drive Studies of NSTX H-Mode Plasmas

    SciTech Connect

    G. Taylor, P.T. Bonoli, D.L. Green, R.W. Harvey, J.C. Hosea, E.F. Jaeger, B.P. LeBlanc, R. Maingi, C.K. Phillips, P.M. Ryan, E.J. Valeo, J.R. Wilson, J.C. Wright, and the NSTX Team

    2011-06-08

    30 MHz high-harmonic fast wave (HHFW) heating and current drive are being developed to assist fully non-inductive plasma current (I{sub p}) ramp-up in NSTX. The initial approach to achieving this goal has been to heat I{sub p} = 300 kA inductive plasmas with current drive antenna phasing in order to generate an HHFW H-mode with significant bootstrap and RF-driven current. Recent experiments, using only 1.4 MW of RF power (P{sub RF}), achieved a noninductive current fraction, f{sub NI} {approx} 0.65. Improved antenna conditioning resulted in the generation of I{sub p} = 650 kA HHFW H-mode plasmas, with f{sub NI} {approx} 0.35, when P{sub RF} {ge} 2.5 MW. These plasmas have little or no edge localized mode (ELM) activity during HHFW heating, a substantial increase in stored energy and a sustained central electron temperature of 5-6 keV. Another focus of NSTX HHFW research is to heat an H-mode generated by 90 keV neutral beam injection (NBI). Improved HHFW coupling to NBI-generated H-modes has resulted in a broad increase in electron temperature profile when HHFW heating is applied. Analysis of a closely matched pair of NBI and HHFW+NBI H-mode plasmas revealed that about half of the antenna power is deposited inside the last closed flux surface (LCFS). Of the power damped inside the LCFS about two-thirds is absorbed directly by electrons and one-third accelerates fast-ions that are mostly promptly lost from the plasma. At longer toroidal launch wavelengths, HHFW+NBI H-mode plasmas can have an RF power flow to the divertor outside the LCFS that significantly reduces RF power deposition to the core. ELMs can also reduce RF power deposition to the core and increase power deposition to the edge. Recent full wave modeling of NSTX HHFW+NBI H-mode plasmas, with the model extended to the vessel wall, predicts a coaxial standing mode between the LCFS and the wall that can have large amplitudes at longer launch wavelengths. These simulation results qualitatively agree with HHFW

  14. Fault diagnosis of motor drives using stator current signal analysis based on dynamic time warping

    NASA Astrophysics Data System (ADS)

    Zhen, D.; Wang, T.; Gu, F.; Ball, A. D.

    2013-01-01

    Electrical motor stator current signals have been widely used to monitor the condition of induction machines and their downstream mechanical equipment. The key technique used for current signal analysis is based on Fourier transform (FT) to extract weak fault sideband components from signals predominated with supply frequency component and its higher order harmonics. However, the FT based method has limitations such as spectral leakage and aliasing, leading to significant errors in estimating the sideband components. Therefore, this paper presents the use of dynamic time warping (DTW) to process the motor current signals for detecting and quantifying common faults in a downstream two-stage reciprocating compressor. DTW is a time domain based method and its algorithm is simple and easy to be embedded into real-time devices. In this study DTW is used to suppress the supply frequency component and highlight the sideband components based on the introduction of a reference signal which has the same frequency component as that of the supply power. Moreover, a sliding window is designed to process the raw signal using DTW frame by frame for effective calculation. Based on the proposed method, the stator current signals measured from the compressor induced with different common faults and under different loads are analysed for fault diagnosis. Results show that DTW based on residual signal analysis through the introduction of a reference signal allows the supply components to be suppressed well so that the fault related sideband components are highlighted for obtaining accurate fault detection and diagnosis results. In particular, the root mean square (RMS) values of the residual signal can indicate the differences between the healthy case and different faults under varying discharge pressures. It provides an effective and easy approach to the analysis of motor current signals for better fault diagnosis of the downstream mechanical equipment of motor drives in the time

  15. High Harmonic Fast Wave Heating Efficiency Enhancemen and Current Drive at Longer Wavelength on the National Spherical Torus Experiment

    SciTech Connect

    J. Hosea, R. E. Bell, B.P. LeBlanc, C.K. Phillips, G. Taylor, E. Valeo, J.R. Wilson, E.F. Jaeger, P.M. Ryan, J. Wilgen, H. Yuh, F. Levinton, S. Sabbagh, K. Tritz, J. Parker, P.T. Bonoli, R. Harvey, and the NSTX Team

    2008-01-14

    High harmonic fast wave heating and current drive (CD) are being developed on the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 41, 1435 (2001)] for supporting startup and sustainment of the ST plasma. Considerable enhancement of the core heating efficiency (η) from 44% to 65% has been obtained for CD phasing of the antenna (strap-to-strap φ = -90o, kφ = -8 m-1) by increasing the magnetic field from 4.5 kG to 5.5 kG. This increase in efficiency is strongly correlated to moving the location of the onset density for perpendicular fast wave propagation (nonset ∝ ΒΦ× k|| 2/w) away from the antenna face and wall, and hence reducing the propagating surface wave fields. RF waves propagating close to the wall at lower BΦ and k|| can enhance power losses from both the parametric decay instability (PDI) and wave dissipation in sheaths and structures around the machine. The improved efficiency found here is attributed to a reduction in the latter, as PDI losses are little changed at the higher magnetic field. Under these conditions of higher coupling efficiency, initial measurements of localized CD effects have been made and compared with advanced RF code simulations

  16. High harmonic fast wave heating efficiency enhancement and current drive at longer wavelength on the National Spherical Torus Experiment

    SciTech Connect

    Hosea, J.; Bell, R. E.; LeBlanc, B. P.; Phillips, C. K.; Taylor, G.; Valeo, E.; Wilson, J. R.; Jaeger, E. F.; Ryan, P. M.; Wilgen, J.; Yuh, H.; Levinton, F.; Sabbagh, S.; Tritz, K.; Parker, J.; Bonoli, P. T.; Harvey, R.

    2008-05-15

    High harmonic fast wave heating and current drive (CD) are being developed on the National Spherical Torus Experiment [M. Ono et al., Nucl. Fusion 41, 1435 (2001)] for supporting startup and sustainment of the spherical torus plasma. Considerable enhancement of the core heating efficiency ({eta}) from 44% to 65% has been obtained for CD phasing of the antenna (strap-to-strap {phi}=-90 deg., k{sub {phi}}=-8 m{sup -1}) by increasing the magnetic field from 4.5 to 5.5 kG. This increase in efficiency is strongly correlated to moving the location of the onset density for perpendicular fast wave propagation (n{sub onset}{proportional_to}Bxk{sub parallel}{sup 2}/{omega}) away from the antenna face and wall, and hence reducing the propagating surface wave fields. Radio frequency (RF) waves propagating close to the wall at lower B and k{sub parallel} can enhance power losses from both the parametric decay instability (PDI) and wave dissipation in sheaths and structures around the machine. The improved efficiency found here is attributed to a reduction in the latter, as PDI losses are little changed at the higher magnetic field. Under these conditions of higher coupling efficiency, initial measurements of localized CD effects have been made and compared with advanced RF code simulations.

  17. High Harmonic Fast Wave Heating Efficiency Enhancement and Current Drive at Longer Wavelength on the National Spherical Torus Experiment

    SciTech Connect

    Hosea, J.; Bell, R. E.; LeBlanc, B; Phillips, Cynthia; Taylor, G.; Valeo, Dr Ernest; Wilson, J. R.; Jaeger, Erwin Frederick; Ryan, Philip Michael; Wilgen, John B; Yuh, H.; Levinton, F.; Sabbagh, S. A.; Tritz, K.; Parker, J.; Bonoli, P.; Harvey, R. W.

    2008-01-01

    High harmonic fast wave heating and current drive CD are being developed on the National Spherical Torus Experiment M. Ono et al., Nucl. Fusion 41, 1435 2001 for supporting startup and sustainment of the spherical torus plasma. Considerable enhancement of the core heating efficiency from 44% to 65% has been obtained for CD phasing of the antenna strap-to-strap = 90 , k= 8 m 1 by increasing the magnetic field from 4.5 to 5.5 kG. This increase in efficiency is strongly correlated to moving the location of the onset density for perpendicular fast wave propagation nonsetBk 2 / away from the antenna face and wall, and hence reducing the propagating surface wave fields. Radio frequency RF waves propagating close to the wall at lower B and k can enhance power losses from both the parametric decay instability PDI and wave dissipation in sheaths and structures around the machine. The improved efficiency found here is attributed to a reduction in the latter, as PDI losses are little changed at the higher magnetic field. Under these conditions of higher coupling efficiency, initial measurements of localized CD effects have been made and compared with advanced RF code simulations.

  18. Field intercomparisons of electromagnetic current meters

    NASA Astrophysics Data System (ADS)

    Guza, R. T.; Clifton, M. C.; Rezvani, F.

    1988-08-01

    In order to assess the performance of current meters within and near the surf zone, data from biaxial electromagnetic current meters with spherical and open frame probe geometries were intercompared. One bottom-mounted flow meter of each type was deployed in a mean depth of 7.0 m for 17 days, and two sensors of each type were deployed in a mean depth of 2.0 m for 5 days. Sensors in the shallow deployment were frequently in the surf zone. Hourly averaged mean flows measured by different sensor types are highly correlated, averaging above 0.98. The largest difference between measured mean flows is a constant bias, typically about 3.0 cm/s, which is roughly equal to the estimated accuracy of the sensor offset calibrations. Root-mean-square deviations from this constant bias are less than 2.0 cm/s, and are contributed to by errors in both gain calibration and sensor orientation. Comparisons of measured (surface gravity wave) oscillatory currents were made both between current meter types and with velocities inferred from the application of linear theory to pressure sensor data. Correlations between time series of UTrms (the rms total oscillatory velocity for a 1-hour record) were all above 0.99 in 7.0-m depth and averaged 0.95 for the shallow deployment. The average UTrms ratio (over all hour-long records) was within 1.0 ±0.07 for all current meter pairs in both deployments, which is consistent with the estimated 5% uncertainties in the flow meter gain calibration. Typical fluctuations of the UTrms ratio of any spherical and open frame sensor pair about its mean ratio, indicative of flow meter gain distortions probably associated with variations in the hydrodynamic environment, were less than 0.04 for any one deployment. Ratios of UTrms from both deployments taken together suggest that the open frame sensor overresponds, relative to the spherical probe, by about 5% at low (about 10.0 cm/s) total (mean + UTrms) speeds, and underresponds by about 5% at higher total

  19. Analysis of field-oriented controlled induction motor drives under sensor faults and an overview of sensorless schemes.

    PubMed

    Arun Dominic, D; Chelliah, Thanga Raj

    2014-09-01

    To obtain high dynamic performance on induction motor drives (IMD), variable voltage and variable frequency operation has to be performed by measuring speed of rotation and stator currents through sensors and fed back them to the controllers. When the sensors are undergone a fault, the stability of control system, may be designed for an industrial process, is disturbed. This paper studies the negative effects on a 12.5 hp induction motor drives when the field oriented control system is subjected to sensor faults. To illustrate the importance of this study mine hoist load diagram is considered as shaft load of the tested machine. The methods to recover the system from sensor faults are discussed. In addition, the various speed sensorless schemes are reviewed comprehensively. PMID:24981890

  20. High Non-inductive Fraction H-mode Discharges Generated by High-harmonic Fast Wave Heating and Current Drive in the National Spherical Torus Experiment

    SciTech Connect

    Taylor, G.; Hosea, J.; Kessel, C. E.; LeBlanc, B; Mueller, D.; Phillips, C. K.; Valeo, E. J.; Wilson, J. R.; Ryan, Philip Michael; Bonoli, P.; Harvey, R. W.

    2012-01-01

    A deuterium H-mode discharge with a plasma current of 300 kA, an axial toroidal magnetic field of 0.55 T, and a calculated non-inductive plasma current fraction of 0.7 1 has been generated in the National Spherical Torus Experiment by 1.4MW of 30MHz high-harmonic fast wave (HHFW) heating and current drive. Seventy-five percent of the non-inductive current was generated inside an internal transport barrier that formed at a normalized minor radius 0.4. Three quarters of the non-inductive current was bootstrap current, and the remaining non-inductive current was generated directly by HHFW power inside a normalized minor radius 0.2. VC 2012 American Institute of Physics.

  1. Nonlinear MHD simulation of current drive by multi-pulsed coaxial helicity injection in spherical torus

    NASA Astrophysics Data System (ADS)

    Kanki, Takashi; Nagata, Masayoshi; Kagei, Yasuhiro

    2011-10-01

    The dynamics of structures of magnetic field, current density, and plasma flow generated during multi-pulsed coaxial helicity injection in spherical torus is investigated by 3-D nonlinear MHD simulations. During the driven phase, the flux and current amplifications occur due to the merging and magnetic reconnection between the preexisting plasma in the confinement region and the ejected plasma from the gun region involving the n = 1 helical kink distortion of the central open flux column (COFC). Interestingly, the diamagnetic poloidal flow which tends toward the gun region is then observed due to the steep pressure gradients of the COFC generated by ohmic heating through an injection current winding around the inboard field lines, resulting in the formation of the strong poloidal flow shear at the interface between the COFC and the core region. This result is consistent with the flow shear observed in the HIST. During the decay phase, the configuration approaches the axisymmetric MHD equilibrium state without flow because of the dissipation of magnetic fluctuation energy to increase the closed flux surfaces, suggesting the generation of ordered magnetic field structure. The parallel current density λ concentrated in the COFC then diffuses to the core region so as to reduce the gradient in λ, relaxing in the direction of the Taylor state.

  2. Magnetic field line reconnection experiments. V - Current disruptions and double layers

    NASA Technical Reports Server (NTRS)

    Stenzel, R. L.; Gekelman, W.; Wild, N.

    1983-01-01

    An investigation is conducted of the stability of a large laboratory plasma current sheet, which has been generated in the process of magnetic field line reconnection, with respect to local current increases. Magnetic flux variations in regions remote from the current sheet generate an inductive voltage in the current loop that drops off inside the plasma in the form of a potential double layer, leading to particle acceleration with velocities much larger than those expected from the steady state electric fields in the plasma. A model for the mechanism of the current disruptions is formulated in which the potential structure leads to ion expulsion, creating a localized density drop. The associated current drop in an inductive circuit drives the potential structure, providing feedback for the disruptive instability. Similarities to, and differences from, magnetospheric substorm phenomena are noted.

  3. Optimization of the ITER electron cyclotron equatorial launcher for improved heating and current drive functional capabilities

    SciTech Connect

    Farina, D.; Figini, L.; Henderson, M.; Saibene, G.

    2014-06-15

    The design of the ITER Electron Cyclotron Heating and Current Drive (EC H and CD) system has evolved in the last years both in goals and functionalities by considering an expanded range of applications. A large effort has been devoted to a better integration of the equatorial and the upper launchers, both from the point of view of the performance and of the design impact on the engineering constraints. However, from the analysis of the ECCD performance in two references H-mode scenarios at burn (the inductive H-mode and the advanced non-inductive scenario), it was clear that the EC power deposition was not optimal for steady-state applications in the plasma region around mid radius. An optimization study of the equatorial launcher is presented here aiming at removing this limitation of the EC system capabilities. Changing the steering of the equatorial launcher from toroidal to poloidal ensures EC power deposition out to the normalized toroidal radius ρ ≈ 0.6, and nearly doubles the EC driven current around mid radius, without significant performance degradation in the core plasma region. In addition to the improved performance, the proposed design change is able to relax some engineering design constraints on both launchers.

  4. Transmission line component testing for the ITER Ion Cyclotron Heating and Current Drive System

    NASA Astrophysics Data System (ADS)

    Goulding, Richard; Bell, G. L.; Deibele, C. E.; McCarthy, M. P.; Rasmussen, D. A.; Swain, D. W.; Barber, G. C.; Barbier, C. N.; Cambell, I. H.; Moon, R. L.; Pesavento, P. V.; Fredd, E.; Greenough, N.; Kung, C.

    2014-10-01

    High power RF testing is underway to evaluate transmission line components for the ITER Ion Cyclotron Heating and Current Drive System. The transmission line has a characteristic impedance Z0 = 50 Ω and a nominal outer diameter of 305 mm. It is specified to carry up to 6 MW at VSWR = 1.5 for 3600 s pulses, with transient voltages up to 40 kV. The transmission line is actively cooled, with turbulent gas flow (N2) used to transfer heat from the inner to outer conductor, which is water cooled. High voltage and high current testing of components has been performed using resonant lines generating steady state voltages of 35 kV and transient voltages up to 60 kV. A resonant ring, which has operated with circulating power of 6 MW for 1 hr pulses, is being used to test high power, low VSWR operation. Components tested to date include gas barriers, straight sections of various lengths, and 90 degree elbows. Designs tested include gas barriers fabricated from quartz and aluminum nitride, and transmission lines with quartz and alumina inner conductor supports. The latest results will be presented. This manuscript has been authored by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy.

  5. Quasi-linear modeling of lower hybrid current drive in ITER and DEMO

    NASA Astrophysics Data System (ADS)

    Cardinali, A.; Cesario, R.; Panaccione, L.; Santini, F.; Amicucci, L.; Castaldo, C.; Ceccuzzi, S.; Mirizzi, F.; Tuccillo, A. A.

    2015-12-01

    First pass absorption of the Lower Hybrid waves in thermonuclear devices like ITER and DEMO is modeled by coupling the ray tracing equations with the quasi-linear evolution of the electron distribution function in 2D velocity space. As usually assumed, the Lower Hybrid Current Drive is not effective in a plasma of a tokamak fusion reactor, owing to the accessibility condition which, depending on the density, restricts the parallel wavenumber to values greater than n∥crit and, at the same time, to the high electron temperature that would enhance the wave absorption and then restricts the RF power deposition to the very periphery of the plasma column (near the separatrix). In this work, by extensively using the "raystar" code, a parametric study of the propagation and absorption of the LH wave as function of the coupled wave spectrum (as its width, and peak value), has been performed very accurately. Such a careful investigation aims at controlling the power deposition layer possibly in the external half radius of the plasma, thus providing a valuable aid to the solution of how to control the plasma current profile in a toroidal magnetic configuration, and how to help the suppression of MHD mode that can develop in the outer part of the plasma. This analysis is useful not only for exploring the possibility of profile control of a pulsed operation reactor as well as the tearing mode stabilization, but also in order to reconsider the feasibility of steady state regime for DEMO.

  6. A survey of electron Bernstein wave heating and current drive potential for spherical tokamaks

    NASA Astrophysics Data System (ADS)

    Urban, Jakub; Decker, Joan; Peysson, Yves; Preinhaelter, Josef; Shevchenko, Vladimir; Taylor, Gary; Vahala, Linda; Vahala, George

    2011-08-01

    The electron Bernstein wave (EBW) is typically the only wave in the electron cyclotron (EC) range that can be applied in spherical tokamaks for heating and current drive (H&CD). Spherical tokamaks (STs) operate generally in high-β regimes, in which the usual EC O- and X-modes are cut off. In this case, EBWs seem to be the only option that can provide features similar to the EC waves—controllable localized H&CD that can be used for core plasma heating as well as for accurate plasma stabilization. The EBW is a quasi-electrostatic wave that can be excited by mode conversion from a suitably launched O- or X-mode; its propagation further inside the plasma is strongly influenced by the plasma parameters. These rather awkward properties make its application somewhat more difficult. In this paper we perform an extensive numerical study of EBW H&CD performance in four typical ST plasmas (NSTX L- and H-mode, MAST Upgrade, NHTX). Coupled ray-tracing (AMR) and Fokker-Planck (LUKE) codes are employed to simulate EBWs of varying frequencies and launch conditions, which are the fundamental EBW parameters that can be chosen and controlled. Our results indicate that an efficient and universal EBW H&CD system is indeed viable. In particular, power can be deposited and current reasonably efficiently driven across the whole plasma radius. Such a system could be controlled by a suitably chosen launching antenna vertical position and would also be sufficiently robust.

  7. High power millimeter wave experiment of ITER relevant electron cyclotron heating and current drive system.

    PubMed

    Takahashi, K; Kajiwara, K; Oda, Y; Kasugai, A; Kobayashi, N; Sakamoto, K; Doane, J; Olstad, R; Henderson, M

    2011-06-01

    High power, long pulse millimeter (mm) wave experiments of the RF test stand (RFTS) of Japan Atomic Energy Agency (JAEA) were performed. The system consists of a 1 MW/170 GHz gyrotron, a long and short distance transmission line (TL), and an equatorial launcher (EL) mock-up. The RFTS has an ITER-relevant configuration, i.e., consisted by a 1 MW-170 GHz gyrotron, a mm wave TL, and an EL mock-up. The TL is composed of a matching optics unit, evacuated circular corrugated waveguides, 6-miter bends, an in-line waveguide switch, and an isolation valve. The EL-mock-up is fabricated according to the current design of the ITER launcher. The Gaussian-like beam radiation with the steering capability of 20°-40° from the EL mock-up was also successfully proved. The high power, long pulse power transmission test was conducted with the metallic load replaced by the EL mock-up, and the transmission of 1 MW/800 s and 0.5 MW/1000 s was successfully demonstrated with no arcing and no damages. The transmission efficiency of the TL was 96%. The results prove the feasibility of the ITER electron cyclotron heating and current drive system. PMID:21721690

  8. High power millimeter wave experiment of ITER relevant electron cyclotron heating and current drive system

    SciTech Connect

    Takahashi, K.; Kajiwara, K.; Oda, Y.; Kasugai, A.; Kobayashi, N.; Sakamoto, K.; Doane, J.; Olstad, R.; Henderson, M.

    2011-06-15

    High power, long pulse millimeter (mm) wave experiments of the RF test stand (RFTS) of Japan Atomic Energy Agency (JAEA) were performed. The system consists of a 1 MW/170 GHz gyrotron, a long and short distance transmission line (TL), and an equatorial launcher (EL) mock-up. The RFTS has an ITER-relevant configuration, i.e., consisted by a 1 MW-170 GHz gyrotron, a mm wave TL, and an EL mock-up. The TL is composed of a matching optics unit, evacuated circular corrugated waveguides, 6-miter bends, an in-line waveguide switch, and an isolation valve. The EL-mock-up is fabricated according to the current design of the ITER launcher. The Gaussian-like beam radiation with the steering capability of 20 deg. - 40 deg. from the EL mock-up was also successfully proved. The high power, long pulse power transmission test was conducted with the metallic load replaced by the EL mock-up, and the transmission of 1 MW/800 s and 0.5 MW/1000 s was successfully demonstrated with no arcing and no damages. The transmission efficiency of the TL was 96%. The results prove the feasibility of the ITER electron cyclotron heating and current drive system.

  9. Calculating electron cyclotron current drive stabilization of resistive tearing modes in a nonlinear magnetohydrodynamic model

    NASA Astrophysics Data System (ADS)

    Jenkins, Thomas G.; Kruger, Scott E.; Hegna, C. C.; Schnack, Dalton D.; Sovinec, Carl R.

    2010-01-01

    A model which incorporates the effects of electron cyclotron current drive (ECCD) into the magnetohydrodynamic equations is implemented in the NIMROD code [C. R. Sovinec et al., J. Comput. Phys. 195, 355 (2004)] and used to investigate the effect of ECCD injection on the stability, growth, and dynamical behavior of magnetic islands associated with resistive tearing modes. In addition to qualitatively and quantitatively agreeing with numerical results obtained from the inclusion of localized ECCD deposition in static equilibrium solvers [A. Pletzer and F. W. Perkins, Phys. Plasmas 6, 1589 (1999)], predictions from the model further elaborate the role which rational surface motion plays in these results. The complete suppression of the (2,1) resistive tearing mode by ECCD is demonstrated and the relevant stabilization mechanism is determined. Consequences of the shifting of the mode rational surface in response to the injected current are explored, and the characteristic short-time responses of resistive tearing modes to spatial ECCD alignments which are stabilizing are also noted. We discuss the relevance of this work to the development of more comprehensive predictive models for ECCD-based mitigation and control of neoclassical tearing modes.

  10. Calculating electron cyclotron current drive stabilization of resistive tearing modes in a nonlinear magnetohydrodynamic model

    SciTech Connect

    Jenkins, Thomas G.; Schnack, Dalton D.; Kruger, Scott E.; Hegna, C. C.; Sovinec, Carl R.

    2010-01-15

    A model which incorporates the effects of electron cyclotron current drive (ECCD) into the magnetohydrodynamic equations is implemented in the NIMROD code [C. R. Sovinec et al., J. Comput. Phys. 195, 355 (2004)] and used to investigate the effect of ECCD injection on the stability, growth, and dynamical behavior of magnetic islands associated with resistive tearing modes. In addition to qualitatively and quantitatively agreeing with numerical results obtained from the inclusion of localized ECCD deposition in static equilibrium solvers [A. Pletzer and F. W. Perkins, Phys. Plasmas 6, 1589 (1999)], predictions from the model further elaborate the role which rational surface motion plays in these results. The complete suppression of the (2,1) resistive tearing mode by ECCD is demonstrated and the relevant stabilization mechanism is determined. Consequences of the shifting of the mode rational surface in response to the injected current are explored, and the characteristic short-time responses of resistive tearing modes to spatial ECCD alignments which are stabilizing are also noted. We discuss the relevance of this work to the development of more comprehensive predictive models for ECCD-based mitigation and control of neoclassical tearing modes.

  11. Temperature compensated current sensor using reference magnetic field

    DOEpatents

    Yakymyshyn, Christopher Paul; Brubaker, Michael Allen; Yakymyshyn, Pamela Jane

    2007-10-09

    A method is described to provide temperature compensation and self-calibration of a current sensor based on a plurality of magnetic field sensors positioned around a current carrying conductor. A reference magnetic field generated within the current sensor housing is detected by a separate but identical magnetic field sensor and is used to correct variations in the output signal due to temperature variations and aging.

  12. Current Status of Protein Force Fields for Molecular Dynamics

    PubMed Central

    Lopes, Pedro E.M.; Guvench, Olgun

    2015-01-01

    Summary The current status of classical force fields for proteins is reviewed. These include additive force fields as well as the latest developments in the Drude and AMOEBA polarizable force fields. Parametrization strategies developed specifically for the Drude force field are described and compared with the additive CHARMM36 force field. Results from molecular simulations of proteins and small peptides are summarized to illustrate the performance of the Drude and AMOEBA force fields. PMID:25330958

  13. Field-Line Resonances in the Current Basis

    NASA Astrophysics Data System (ADS)

    Ostaszewski, Katharina; Glassmeier, Karl-Heinz; Nabert, Christian

    2016-04-01

    The MHD theory of the field-line resonance is of great importance for the understanding of ultra low-frequency waves in the magnetosphere. Most theoretical works concerning field-line resonance use the electric field as the basis set. In an ideal MHD plasma the field-aligned component of the electrical field vanishes because of the frozen-in theorem. However, a field-aligned current flows to maintain quasi-neutrality. This field-aligned current can only be carried by the transverse MHD Alfvèn wave and is therefore a characteristic feature of these types of waves. In this study we investigate the field-line resonance phenomenon using a three dimensional current vector space as the basis set. Using the model of the box magnetosphere of Southwood (1974) we derive an equation for the field-aligned current. This equation provides a simpler and more detailed insight into the coupling process between the fast mode and the Alfvèn mode. Furthermore we investigate the effect of the Hall current on the field-aligned current by including the Hall term in Ohm's law. It is shown that in some situations the Hall current can nullify the filed-aligned current and therefore prevent the resonance.

  14. The evolution of arguments regarding the existence of field-aligned currents

    NASA Technical Reports Server (NTRS)

    Dessler, A. J.

    1984-01-01

    The present understanding of Birkeland (magnetically-field-aligned) currents was not obtained by a direct, logical course. The story is rather more complex. Starting at the end of the 19th century, the Norwegian scientist Kristian Birkeland laid out a compelling case, supported by both theory and experiment, for the existence of field-aligned currents that cause both the aurora and polar geomagnetic disturbances. Sydney Chapman, the British geophysicist, became the acknowledged leader and opinion maker in the field in the decades following Birkeland's death. Chapman proposed, in contradistinction to Birkeland's ideas, equivalent currents that were restricted to flow in the ionosphere with no vertical or field-aligned components. Birkeland's ideas may have faded completely if it had not been for Hannes Alfven, who became involved well after Chapman's ideas gained predominance. Alfven kept insisting that Birkeland's current system made more sense because field-aligned currents were required to drive most of the ionospheric currents. The author became personally involved when Zmuda et al. (1966) submitted to the Journal of Geophysical Research a paper reporting satellite data showing magnetic disturbances above the ionosphere that were consistent with field-aligned Birkeland currents, but which they did not interpret as being due to such currents.

  15. Effect of high-frequency driving current on magnetization reversal in Co-rich amorphous microwires

    SciTech Connect

    Chizhik, A.; Zhukov, A.; Gonzalez, J.; Blanco, J.M.

    2004-09-20

    Influence of high frequency electric current on the magnetization reversal in Co-rich glass covered amorphous microwires has been studied. The strong correlation between the coercivity and the circular magnetization in the outer shell of the wire has been found. The change of the mechanism of magnetization reversal in the presence of high-frequency circular magnetic field, which is related with the impedance properties, is presented.

  16. Method of correcting eddy current magnetic fields in particle accelerator vacuum chambers

    DOEpatents

    Danby, G.T.; Jackson, J.W.

    1990-03-19

    A method for correcting magnetic field aberrations produced by eddy currents induced in a particle accelerator vacuum chamber housing is provided wherein correction windings are attached to selected positions on the housing and the windings are energized by transformer action from secondary coils, which coils are inductively coupled to the poles of electro-magnets that are powered to confine the charged particle beam within a desired orbit as the charged particles are accelerated through the vacuum chamber by a particle-driving rf field. The power inductively coupled to the secondary coils varies as a function of variations in the power supplied by the particle-accelerating rf field to a beam of particles accelerated through the vacuum chamber, so the current in the energized correction coils is effective to cancel eddy current flux fields that would otherwise be induced in the vacuum chamber by power variations (dB/dt) in the particle beam.

  17. Method of correcting eddy current magnetic fields in particle accelerator vacuum chambers

    DOEpatents

    Danby, Gordon T.; Jackson, John W.

    1991-01-01

    A method for correcting magnetic field aberrations produced by eddy currents induced in a particle accelerator vacuum chamber housing is provided wherein correction windings are attached to selected positions on the housing and the windings are energized by transformer action from secondary coils, which coils are inductively coupled to the poles of electro-magnets that are powered to confine the charged particle beam within a desired orbit as the charged particles are accelerated through the vacuum chamber by a particle-driving rf field. The power inductively coupled to the secondary coils varies as a function of variations in the power supplied by the particle-accelerating rf field to a beam of particles accelerated through the vacuum chamber, so the current in the energized correction coils is effective to cancel eddy current flux fields that would otherwise be induced in the vacuum chamber by power variations in the particle beam.

  18. A High-resolution Model of Field-aligned Currents Through Empirical Orthogonal Functions Analysis (MFACE)

    NASA Technical Reports Server (NTRS)

    He, Maosheng; Vogt, Joachim; Luehr, Hermann; Sorbalo, Eugen; Blagau, Adrian; Le, Guan; Lu, Gang

    2012-01-01

    Ten years of CHAMP magnetic field measurements are integrated into MFACE, a model of field-aligned currents (FACs) using empirical orthogonal functions (EOFs). EOF1 gives the basic Region-1/Region-2 pattern varying mainly with the interplanetary magnetic field Bz component. EOF2 captures separately the cusp current signature and By-related variability. Compared to existing models, MFACE yields significantly better spatial resolution, reproduces typically observed FAC thickness and intensity, improves on the magnetic local time (MLT) distribution, and gives the seasonal dependence of FAC latitudes and the NBZ current signature. MFACE further reveals systematic dependences on By, including 1) Region-1/Region-2 topology modifications around noon; 2) imbalance between upward and downward maximum current density; 3) MLT location of the Harang discontinuity. Furthermore, our procedure allows quantifying response times of FACs to solar wind driving at the bow shock nose: we obtain 20 minutes and 35-40 minutes lags for the FAC density and latitude, respectively.

  19. The effect of Birkeland currents on magnetic field topology

    NASA Technical Reports Server (NTRS)

    Peroomian, Vahe; Lyons, Larry R.; Schulz, Michael

    1996-01-01

    A technique was developed for the inclusion of large scale magnetospheric current systems in magnetic field models. The region 1 and 2 Birkeland current systems are included in the source surface model of the terrestrial magnetosphere. The region 1 and 2 Birkeland currents are placed in the model using a series of field aligned, infinitely thin wire segments. The normal component of the magnetic field from these currents is calculated on the surface of the magnetopause and shielded using image current carrying wires placed outside of the magnetosphere. It is found that the inclusion of the Birkeland currents in the model results in a northward magnetic field in the near-midnight tail, leading to the closure of previously open flux in the tail, and a southward magnetic field in the flanks. A sunward shift in the separatrix is observed.

  20. High-Speed Current dq PI Controller for Vector Controlled PMSM Drive

    PubMed Central

    Reaz, Mamun Bin Ibne; Rahman, Labonnah Farzana; Chang, Tae Gyu

    2014-01-01

    High-speed current controller for vector controlled permanent magnet synchronous motor (PMSM) is presented. The controller is developed based on modular design for faster calculation and uses fixed-point proportional-integral (PI) method for improved accuracy. Current dq controller is usually implemented in digital signal processor (DSP) based computer. However, DSP based solutions are reaching their physical limits, which are few microseconds. Besides, digital solutions suffer from high implementation cost. In this research, the overall controller is realizing in field programmable gate array (FPGA). FPGA implementation of the overall controlling algorithm will certainly trim down the execution time significantly to guarantee the steadiness of the motor. Agilent 16821A Logic Analyzer is employed to validate the result of the implemented design in FPGA. Experimental results indicate that the proposed current dq PI controller needs only 50 ns of execution time in 40 MHz clock, which is the lowest computational cycle for the era. PMID:24574913

  1. A New Technique for the Photospheric Driving of Non-potential Solar Coronal Magnetic Field Simulations

    NASA Astrophysics Data System (ADS)

    Weinzierl, Marion; Yeates, Anthony R.; Mackay, Duncan H.; Henney, Carl J.; Arge, C. Nick

    2016-05-01

    In this paper, we develop a new technique for driving global non-potential simulations of the Sun’s coronal magnetic field solely from sequences of radial magnetic maps of the solar photosphere. A primary challenge to driving such global simulations is that the required horizontal electric field cannot be uniquely determined from such maps. We show that an “inductive” electric field solution similar to that used by previous authors successfully reproduces specific features of the coronal field evolution in both single and multiple bipole simulations. For these cases, the true solution is known because the electric field was generated from a surface flux-transport model. The match for these cases is further improved by including the non-inductive electric field contribution from surface differential rotation. Then, using this reconstruction method for the electric field, we show that a coronal non-potential simulation can be successfully driven from a sequence of ADAPT maps of the photospheric radial field, without including additional physical observations which are not routinely available.

  2. Dynamics of Electric Fields Driving the Laser Acceleration of Multi-MeV Protons

    SciTech Connect

    Romagnani, L.; Borghesi, M.; Kar, S.; Fuchs, J.; Antici, P.; Audebert, P.; Ceccherini, F.; Macchi, A.; Cowan, T.; Grismayer, T.; Mora, P.; Pretzler, G.; Toncian, T.; Willi, O.; Schiavi, A.

    2005-11-04

    The acceleration of multi-MeV protons from the rear surface of thin solid foils irradiated by an intense ({approx}10{sup 18} W/cm{sup 2}) and short ({approx}1.5 ps) laser pulse has been investigated using transverse proton probing. The structure of the electric field driving the expansion of the proton beam has been resolved with high spatial and temporal resolution. The main features of the experimental observations, namely, an initial intense sheath field and a late time field peaking at the beam front, are consistent with the results from particle-in-cell and fluid simulations of thin plasma expansion into a vacuum.

  3. Experimental Study on Current Decay Characteristics of Persistent Current HTS Magnet by Alternating Magnetic Field

    NASA Astrophysics Data System (ADS)

    Park, Young Gun; Lee, Chang Young; Hwang, Young Jin; Lee, Woo Seung; Lee, Jiho; Jo, Hyun Chul; Chung, Yoon Do; Ko, Tae Kuk

    This paper deals with a current decay characteristics of a high temperature superconducting (HTS) magnet operated in persistent current mode (PCM). In superconducting synchronous machine applications such as linear synchronous motor (LSM), the superconducting coil is designed to operate in the PCM to obtain steady magnetic field with DC transport current. This superconducting magnet operates on a direct current, but it can be exposed to alternating magnetic field due to the armature winding. When the magnet is subjected to an external time-varying magnetic field, it is possible to result in a decay of the current in PCM system due to AC loss. In this research, a PCM system with armature coil which generates time-varying magnetic field was fabricated to verify current decay characteristics by external alternating magnetic field. The current decay rate was measured by using a hall sensor as functions of amplitude and frequency of armature coil.

  4. Electric Dipole Moment Experiment Systematic from Electric Field Discharge Current

    NASA Astrophysics Data System (ADS)

    Feinberg, B.; Gould, Harvey

    2014-09-01

    A magnetic field, in the direction of the electric field and synchronous with the electric field reversal, will mimic an EDM signal. One might expect a discharge across the electric field plates to produce magnetic fields with only small or vanishing components parallel to the electric field, minimizing its systematic effect. Our experimental model, using simulated discharge currents, found otherwise: the discharge current may be at an angle to the normal, and thus generate a normal magnetic field. Comparison of data from the experimental model with the results from calculations will be presented, along with estimates of the time-averaged normal magnetic field seen by atoms in an electron EDM experiment using a fountain of laser-cooled francium, as a function of discharge current.

  5. Status of the ITER ion cyclotron heating and current drive system

    NASA Astrophysics Data System (ADS)

    Lamalle, P.; Beaumont, B.; Kazarian, F.; Gassmann, T.; Agarici, G.; Montemayor, T. Alonzo; Bamber, R.; Bernard, J.-M.; Boilson, D.; Cadinot, A.; Calarco, F.; Colas, L.; Courtois, X.; Deibele, C.; Durodié, F.; Fano, J.; Fredd, E.; Goulding, R.; Greenough, N.; Hillairet, J.; Jacquinot, J.; Kaye, A. S.; Kočan, M.; Labidi, H.; Leichtle, D.; Loarte, A.; McCarthy, M.; Messiaen, A.; Meunier, L.; Mukherjee, A.; Oberlin-Harris, C.; Patel, A. M.; Peters, B.; Rajnish, K.; Rasmussen, D.; Sanabria, R.; Sartori, R.; Singh, R.; Swain, D.; Trivedi, R. G.; Turner, A.

    2015-12-01

    The paper reports on latest developments for the ITER Ion Cyclotron Heating and Current Drive system: imminent acceptance tests of a prototype power supply at full power; successful factory acceptance of candidate RF amplifier tubes which will be tested on dedicated facilities; further design integration and experimental validation of transmission line components under 6MW hour-long pulses. The antenna Faraday shield thermal design has been validated above requirements by cyclic high heat flux tests. R&D on ceramic brazing is under way for the RF vacuum windows. The antenna port plug RF design is stable but major evolution of the mechanical design is in preparation to achieve compliance with the load specification, warrant manufacturability and incorporate late interface change requests. The antenna power coupling capability predictions have been strengthened by showing that, if the plasma scrape-off layer turns out to be steep and the edge density low, the reference burning plasma can realistically be displaced to improve the coupling.

  6. RF current drive antenna. Final report, August 15, 1993--August 14, 1995

    SciTech Connect

    Probert, P.H.

    1995-09-01

    This work represents an attempt to solve a fundamental problem with all coupling devices in tokamaks intended to launch waves in the ion cyclotron range of frequencies (ICRF), that of excessive voltage levels on the launcher and its feed lines. These voltages can lead to impurity problems in the plasma, and they determine the maximum power that can be coupled to the plasma, since it is when arcs caused by this voltage frequently occur that the power must be reduced. The approach taken is to consider an antenna which is composed of many smaller units, each operating at much lower voltages, stacked on end to provide the equivalent functionality of a conventional launcher. The work described herein involved designing, building, and operating such a launcher in the Phaedrus-T tokamak. The results showed that the antenna worked as expected, reducing the voltage dramatically, while still functioning property, and producing fewer impurity problems and no arcing. A design extrapolating the principles of this idea to reactor-sized tokamaks such as ITER was developed. In addition, a novel decoupling scheme was developed in order to adapt this antenna idea to low frequency current drive schemes.

  7. Enhancement of Localized ICRF Heating and Current Drive in TFTR D-T Plasmas

    SciTech Connect

    = G Schilling, First Author

    1997-04-15

    Theoretical advantages have led to an increased importance of the modification and sustainment of pressure and magnetic shear profiles in plasmas. We have demonstrated electron heating and current drive in TFTR (Tokamak Fusion Test Reactor) plasmas with the existing 43/63.6 MHz ICRF (ion cyclotron range of frequencies) system, both via the fast wave and via mode conversion of the fast wave to an ion-Bernstein wave. In order to achieve both on- and off-axis mode conversion in a pure D-T (deuterium-tritium) plasma, we have changed the operating frequency of two of our transmitters and antennas to 30 MHz and improved the launched directional wave spectrum. As a second step, two new four-strap fast-wave antennas have been installed, and a new four-strap direct-launch IBW antenna has been added as well. This reconfiguration and the resulting operating characteristics of the TFTR ICRF system in a variety of discharges will be presented.

  8. RF Sources for the ITER Ion Cyclotron Heating and Current Drive System

    SciTech Connect

    Hosea, J.; Brunkhorst, C.; Fredd, E.; Goulding, R. H.; Goulding, R. H.; Greenough, N.; Kung, C.; Rasmussen, D. A.; Swain, D. W.; Wilson, J. R.

    2005-10-04

    The RF source requirements for the ITER ion cyclotron (IC) heating and current drive system are very challenging ? 20 MW CW power into an antenna load with a VSWR of up to 2 over the frequency range of 35-65 MHz. For the two present antenna designs under consideration, 8 sources providing 2.5 MW each are to be employed. For these sources, the outputs of two final power amplifiers (FPAs), using the high power CPI 4CM2500KG tube, are combined with a 180? hybrid combiner to easily meet the ITER IC source requirements ? 2.5 MW is supplied at a VSWR of 2 at ? 70% of the maximum tube power available in class B operation. The cylindrical cavity configuration for the FPAs is quite compact so that the 8 combined sources fit into the space allocated at the ITER site with room to spare. The source configuration is described in detail and its projected operating power curves are presented. Although the CPI tube has been shown to be stable under high power operating conditions on many facilities, a test of the combined FPA source arrangement is in preparation using existing high power 30 MHz amplifiers to assure that this configuration can be made robustly stable for all phases at a VSWR up to 2. The possibility of using 12 sources to feed a suitably modified antenna design is also discussed in the context of providing flexibility for specifying the final IC antenna design.

  9. Design of Electron Cyclotron Heating and Current Drive System of ITER

    SciTech Connect

    Kobayashi, N.; Bigelow, T.; Rasmussen, D.; Bonicelli, T.; Ramponi, G.; Saibene, G.; Cirant, S.; Denisov, G.; Heidinger, R.; Piosczyk, B.; Henderson, M.; Hogge, J.-P.; Thumm, M.; Tran, M. Q.; Rao, S. L.; Sakamoto, K.; Takahashi, K.; Temkin, R. J.; Verhoeven, A. G. A.; Zohm, H.

    2007-09-28

    Since the end of EDA, the design of the Electron Cyclotron Heating and Current Drive (ECH and CD) system has been modified to respond to progress in physics understanding and change of interface conditions. Nominal RF power of 20 MW is shared by four upper launchers or one equatorial launcher RF beams are steered by front steering mirrors providing wide sweeping angle for the RF beam. DC high voltage power supply may be composed of IGBT pulse step modulators because of high frequency modulation and design flexibility to three different types of 170 GHz gyrotrons provided by three parties. The RF power from the 170 GHz gyrotron is transmitted to the launcher by 63.5 mm{phi} corrugated waveguide line and remotely switched by a waveguide switch between the upper launcher and the equatorial launcher. The ECH and CD system has also a start-up sub-system for assist of initial discharge composed of three 127.5 GHz gyrotrons and a dedicated DC high voltage power supply. Three of transmission lines are shared between 170 GHz gyrotron and 127.5 GHz gyrotron so as to inject RF beam for the start-up through the equatorial launcher. R and Ds of components for high power long pulse and mirror steering mechanism have been on-going in the parties to establish a reliable ITER ECH and CD system.

  10. Detection and sizing of defects in control rod drive mechanism penetrations using eddy current and ultrasonics

    SciTech Connect

    Light, G.M.; Fisher, J.L.; Tennis, R.F.; Stolte, J.S.; Hendrix, G.J.

    1996-08-01

    Over the last two years, concern has been generated about the capabilities of performing nondestructive evaluation (NDE) of the closure-head penetrations in nuclear-reactor pressure vessels. These penetrations are primarily for instrumentation and control rod drive mechanisms (CRDMs) and are usually thick-walled Inconel tubes, which are shrink-fitted into the steel closure head. The penetrations are then welded between the outside surface of the penetration and the inside surface of the closure head. Stress corrosion cracks initiating at the inner surface of the penetration have been reported at several plants. Through-wall cracks in the CRDM penetration or CRDM weld could lead to loss of coolant in the reactor vessel. The CRDM penetration presents a complex inspection geometry for conventional NDE techniques. A thermal sleeve, through which pass the mechanical linkages for operating the control rods, is inserted into the penetration in such a way that only a small annulus (nominally 3 mm) exists between the thermal sleeve and inside surface of the penetration. Ultrasonic (UT) and eddy current testing (ET) techniques that could be used to provide defect detection and sizing capability were investigated. This paper describes the ET and UT techniques, the probes developed, and the results obtained using these probes and techniques on CRDM penetration mock-ups.

  11. FED-A, an advanced performance FED based on low safety factor and current drive

    SciTech Connect

    Peng, Yueng Kay Martin; Rutherford, P. H.; Hogan, J.T.; Attenberger, S. E.; Holmes, J.A.; Borowski, S. K.; Brown, T. G.; Carreras, B. A.; Ehst, D. A.; Haines, J.R.; Hively, L. M.; Houlberg, Wayne A; Iida, H.; Lee, V. D.; Lynch, S.J.; Reid, R. L.; Rothe, K. E.; Strickler, Dennis J; Stewart, L. D.

    1983-08-01

    This document is one of four describing studies performed in FY 1982 within the context of the Fusion Engineering Device (FED) Program for the Office of Fusion Energy, U.S. Department of Energy. The documents are: 1. FED Baseline Engineering Studies (ORNL/FEDC-82/2), 2. FED-A, An Advanced Performance FED Based on Low Safety Factor and Current Drive (this document), 3. FED-R, A Fusion Device Utilizing Resistive Magnets (ORNL/FEDC-82/1), and 4. Technology Demonstration Facility TDF. These studies extend the FED Baseline concept of FY 1981 and develop innovative and alternative concepts for the FED. The FED-A study project was carried out as part of the Innovative and Alternative Tokamak FED studies, under the direction of P. H. Rutherford, which were part of the national FED program during FY 1982. The studies were performed jointly by senior scientists in the magnetic fusion community and the staff of the Fusion Engineering Design Center (FEDC). Y-K. M. Peng of the FEDC, on assignment from Oak Ridge National Laboratory, served as the design manager.

  12. Standard series of direct-current motors for regulated electric drives

    NASA Astrophysics Data System (ADS)

    Cholewicki, I.; Lubina, M.; Kozhevnikov, V. A.; Kochnev, A. V.; Skoda, K.; Voleskiy, E.

    1984-11-01

    A standard series of d.c. motors for electric drives with speed and torque regulation has been developed. Thyristor-type converters for machine tools with digital program control are also being developed. Meeting future goals requires modification of the motor frame from the conventional round to a nearly square one, a larger ratio of armature stack length to diameter, better cooling, and insulation of a higher temperature class. In addition, it is necessary to laminate the housing partially or completely and to include a compensating winding. The basic motor configuration is 1 M 1001, according to Council of Mutual Economic Assistance (CEMA) Standard 246-78, with at least IP 23S protection and 1C 06 or 1C 05 cooling (shaft height from 112 mm up) and 1C 01 cooling (Shaft height or up to 250 mm). The series will be designed for a reference speed of 1500 rpm with not more than 15% armature current fluctuation, with speeds of 300-3000 rpm depending on voltage and motor size and torque regulation 1:200 (externally cooled motors) or 1;5, 1:10, 1:30 (self-cooled motors). Prototype motors with 132 mm and 355 mm shaft heights have already passed all tests.

  13. Ion cyclotron range of frequencies heating and current drive in deuterium-tritium plasmas

    NASA Astrophysics Data System (ADS)

    Phillips, C. K.; Bell, M. G.; Bell, R.; Bretz, N.; Budny, R. V.; Darrow, D. S.; Grek, B.; Hammett, G.; Hosea, J. C.; Hsuan, H.; Ignat, D.; Majeski, R.; Mazzucato, E.; Nazikian, R.; Park, H.; Rogers, J. H.; Schilling, G.; Stevens, J. E.; Synakowski, E.; Taylor, G.; Wilson, J. R.; Zarnstorff, M. C.; Zweben, S. J.; Bush, C. E.; Goldfinger, R.; Jaeger, E. F.; Murakami, M.; Rasmussen, D.; Bettenhausen, M.; Lam, N. T.; Scharer, J.; Sund, R.; Sauter, O.

    1995-06-01

    The first experiments utilizing high-power radio waves in the ion cyclotron range of frequencies to heat deuterium-tritium (D-T) plasmas have been completed on the Tokamak Fusion Test Reactor [Fusion Technol. 21, 13 (1992)]. Results from the initial series of experiments have demonstrated efficient core second harmonic tritium (2ΩT) heating in parameter regimes approaching those anticipated for the International Thermonuclear Experimental Reactor [D. E. Post, Plasma Physics and Controlled Nuclear Fusion Research, Proceedings of the 13th International Conference, Washington, DC, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 239]. Observations are consistent with modeling predictions for these plasmas. Efficient electron heating via mode conversion of fast waves to ion Bernstein waves has been observed in D-T, deuterium-deuterium (D-D), and deuterium-helium-4 (D-4He) plasmas with high concentrations of minority helium-3 (3He) (n3He/ne≳10%). Mode conversion current drive in D-T plasmas was simulated with experiments conducted in D-3He-4He plasmas. Results show a directed propagation of the mode converted ion Bernstein waves, in correlation with the antenna phasing.

  14. A camera for imaging hard x-rays from suprathermal electrons during lower hybrid current drive on PBX-M

    SciTech Connect

    von Goeler, S.; Kaita, R.; Bernabei, S.; Davis, W.; Fishman, H.; Gettelfinger, G.; Ignat, D.; Roney, P.; Stevens, J.; Stodiek, W.; Jones, S.; Paoletti, F.; Petravich, G.; Rimini, F.

    1993-05-01

    During lower hybrid current drive (LHCD), suprathermal electrons are generated that emit hard X-ray bremsstrahlung. A pinhole camera has been installed on the PBX-M tokamak that records 128 {times} 128 pixel images of the bremsstrahlung with a 3 ms time resolution. This camera has identified hollow radiation profiles on PBX-M, indicating off-axis current drive. The detector is a 9in. dia. intensifier. A detailed account of the construction of the Hard X-ray Camera, its operation, and its performance is given.

  15. A camera for imaging hard x-rays from suprathermal electrons during lower hybrid current drive on PBX-M

    SciTech Connect

    von Goeler, S.; Kaita, R.; Bernabei, S.; Davis, W.; Fishman, H.; Gettelfinger, G.; Ignat, D.; Roney, P.; Stevens, J.; Stodiek, W. . Plasma Physics Lab.); Jones, S.; Paoletti, F. . Plasma Fusion Center); Petravich, G. . Central Research Inst. for Physics); Rimini,

    1993-05-01

    During lower hybrid current drive (LHCD), suprathermal electrons are generated that emit hard X-ray bremsstrahlung. A pinhole camera has been installed on the PBX-M tokamak that records 128 [times] 128 pixel images of the bremsstrahlung with a 3 ms time resolution. This camera has identified hollow radiation profiles on PBX-M, indicating off-axis current drive. The detector is a 9in. dia. intensifier. A detailed account of the construction of the Hard X-ray Camera, its operation, and its performance is given.

  16. Bogi and Capiron fields, Oriente Basin, Ecuador: Similar reservoirs but contrasting drive mechanisms and recoveries

    SciTech Connect

    Sanchez, H.; Morales, M.; Young, R.; Zambrano, H.

    1996-08-01

    Bogi and Capiron fields are being developed under a unit agreement with Petroecuador. These adjoining fields straddle Block 16 in the Oriente Basin and probably share a common oil water contact. Both fields are simple four-way-dip closures which produce heavy oil from Campanian sandstones of similar quality. However, the two fields are remarkably different in terms of oil production and projected recovery as a result of differing structural closures, reservoir distributions and, hence, differing drive mechanisms. The main reservoir at Bogi field is an amalgamation of two fluvial sheet sandstones thought to be low-stand deposits associated with two falls in relative sea level. The reservoir is thick (56-78 ft) and, with an observed oil column of only 38 feet, a bottom-water drive mechanism is ubiquitous. The oil is heavy (18 API) and mobility ratios unfavorable; water production is high and oil recovery from conventional drilling is expected to be 3-5%. In contrast, only the upper fluvial sheet sandstone is present in Capiron field and a reservoir thickness of 32-48 ft combined with an oil column of 99 ft ensures an edge-water drive mechanism over most of the field with concomitant initial low water production and oil recoveries of approximately 30%. The contrast between Bogi and Capiron fields highlights the problems and challenges in the Block 16 area. Small structural closures filled with heavy oil are abundant and an accurate seismic depth map coupled with an understanding of reservoir distribution are vital to economic success.

  17. Instrumentation used to measure residential magnetic fields and currents.

    PubMed

    Lahijanian, H; Yatapanage, K; Rosen, R; Cross, J

    2003-10-01

    The equipment used to measure magnetic fields and electric currents in residences is described. The instrumentation consisted of current transformers, magnetic field probes and locally designed and built signal conditioning modules. The data acquisition system was capable of unattended recording for extended time periods. The complete system was calibrated to verify its response to known physical inputs. PMID:14582878

  18. Quasi-linear modeling of lower hybrid current drive in ITER and DEMO

    SciTech Connect

    Cardinali, A. Cesario, R.; Panaccione, L.; Santini, F.; Amicucci, L.; Castaldo, C.; Ceccuzzi, S.; Mirizzi, F.; Tuccillo, A. A.

    2015-12-10

    First pass absorption of the Lower Hybrid waves in thermonuclear devices like ITER and DEMO is modeled by coupling the ray tracing equations with the quasi-linear evolution of the electron distribution function in 2D velocity space. As usually assumed, the Lower Hybrid Current Drive is not effective in a plasma of a tokamak fusion reactor, owing to the accessibility condition which, depending on the density, restricts the parallel wavenumber to values greater than n{sub ∥crit} and, at the same time, to the high electron temperature that would enhance the wave absorption and then restricts the RF power deposition to the very periphery of the plasma column (near the separatrix). In this work, by extensively using the “ray{sup star}” code, a parametric study of the propagation and absorption of the LH wave as function of the coupled wave spectrum (as its width, and peak value), has been performed very accurately. Such a careful investigation aims at controlling the power deposition layer possibly in the external half radius of the plasma, thus providing a valuable aid to the solution of how to control the plasma current profile in a toroidal magnetic configuration, and how to help the suppression of MHD mode that can develop in the outer part of the plasma. This analysis is useful not only for exploring the possibility of profile control of a pulsed operation reactor as well as the tearing mode stabilization, but also in order to reconsider the feasibility of steady state regime for DEMO.

  19. Self-generated magnetic fields in direct-drive implosion experiments

    NASA Astrophysics Data System (ADS)

    Igumenshchev, I. V.; Zylstra, A. B.; Li, C. K.; Nilson, P. M.; Goncharov, V. N.; Petrasso, R. D.

    2014-06-01

    Electric and self-generated magnetic fields in direct-drive implosion experiments on the OMEGA Laser Facility were investigated employing radiography with ˜10- to 60-MeV protons. The experiment used plastic-shell targets with imposed surface defects (glue spots, wires, and mount stalks), which enhance self-generated fields. The fields were measured during the 1-ns laser drive with an on-target intensity ˜1015 W/cm2. Proton radiographs show multiple ring-like structures produced by electric fields ˜107 V/cm and fine structures from surface defects, indicating self-generated fields up to ˜3 MG. These electric and magnetic fields show good agreement with two-dimensional magnetohydrodynamic simulations when the latter include the ∇Te × ∇ne source, Nernst convection, and anisotropic resistivity. The simulations predict that self-generated fields affect heat fluxes in the conduction zone and, through this, affect the growth of local perturbations.

  20. Self-generated magnetic fields in direct-drive implosion experiments

    SciTech Connect

    Igumenshchev, I. V.; Nilson, P. M.; Goncharov, V. N.; Zylstra, A. B.; Li, C. K.; Petrasso, R. D.

    2014-06-15

    Electric and self-generated magnetic fields in direct-drive implosion experiments on the OMEGA Laser Facility were investigated employing radiography with ∼10- to 60-MeV protons. The experiment used plastic-shell targets with imposed surface defects (glue spots, wires, and mount stalks), which enhance self-generated fields. The fields were measured during the 1-ns laser drive with an on-target intensity ∼10{sup 15} W/cm{sup 2}. Proton radiographs show multiple ring-like structures produced by electric fields ∼10{sup 7} V/cm and fine structures from surface defects, indicating self-generated fields up to ∼3 MG. These electric and magnetic fields show good agreement with two-dimensional magnetohydrodynamic simulations when the latter include the ∇T{sub e} × ∇n{sub e} source, Nernst convection, and anisotropic resistivity. The simulations predict that self-generated fields affect heat fluxes in the conduction zone and, through this, affect the growth of local perturbations.

  1. Self-generated magnetic fields in direct-drive implosion experiments

    SciTech Connect

    Igumenshchev, I. V.; Zylstra, A. B.; Li, C. K.; Nilson, P. M.; Goncharov, V. N.; Petrasso, R. D.

    2014-06-13

    Electric and self-generated magnetic fields in direct-drive implosion experiments on the OMEGA Laser Facility were investigated employing radiography with ~10- to 60-MeV protons. The experiment used plastic-shell targets with imposed surface defects (glue spots, wires, and mount stalks), which enhance self-generated fields. The fields were measured during the 1-ns laser drive with an on-target intensity ~1015 W/cm2. Proton radiographs show multiple ring-like structures produced by electric fields ~107 V/cm and fine structures from surface defects, indicating self-generated fields up to ~3 MG. These electric and magnetic fields show good agreement with two-dimensional magnetohydrodynamic simulations when the latter include the ∇Te × ∇ne source, Nernst convection, and anisotropic resistivity. The simulations predict that self-generated fields affect heat fluxes in the conduction zone and, through this, affect the growth of local perturbations.

  2. Field-aligned particle currents near an auroral arc.

    NASA Technical Reports Server (NTRS)

    Choy, L. W.; Arnoldy, R. L.; Potter, W.; Kintner, P.; Cahill, L. J., Jr.

    1971-01-01

    A Nike-Tomahawk rocket equipped to measure electric and magnetic fields and charged particles from a few eV to several hundred keV energy was flown into an auroral band on April 11, 1970. The purpose of this flight was to obtain evidence of the low-energy electrons and protons that constitute a field-aligned sheet current, and also to obtain the magnetic signature of such a current and the electric field in and near the auroral-arc electric current system. Particular attention was given to a sudden increase in the field-aligned current associated with a prior sudden increase in the electric field and a sudden change in the magnetic field, all occurring near the edge of a visual auroral arc. Data obtained are discussed and analyzed; they present an important contribution to the problem of mapping of atmospheric auroral phenomena to the magnetospheric equatorial plane.

  3. Relationship between Birkeland current regions, particle precipitation, and electric fields

    NASA Technical Reports Server (NTRS)

    De La Beaujardiere, O.; Watermann, J.; Newell, P.; Rich, F.

    1993-01-01

    The relationship of the large-scale dayside Birkeland currents to large-scale particle precipitation patterns, currents, and convection is examined using DMSP and Sondrestrom radar observations. It is found that the local time of the mantle currents is not limited to the longitude of the cusp proper, but covers a larger local time extent. The mantle currents flow entirely on open field lines. About half of region 1 currents flow on open field lines, consistent with the assumption that the region 1 currents are generated by the solar wind dynamo and flow within the surface that separates open and closed field lines. More than 80 percent of the Birkeland current boundaries do not correspond to particle precipitation boundaries. Region 2 currents extend beyond the plasma sheet poleward boundary; region 1 currents flow in part on open field lines; mantle currents and mantle particles are not coincident. On most passes when a triple current sheet is observed, the convection reversal is located on closed field lines.

  4. Controllable optical output fields from an optomechanical system with mechanical driving

    NASA Astrophysics Data System (ADS)

    Xu, Xun-Wei; Li, Yong

    2015-08-01

    We investigate the properties of the optical output fields from a cavity optomechanical system, where the cavity is optically driven by a strong coupling field and a weak probe field and the mechanical resonator is driven by a coherent mechanical pump. When the frequency of the mechanical pump matches the frequency difference between the coupling and probe optical fields, due to the interference between the different optical components at the same frequency, we demonstrate that the large positive or negative group delay of the output field at the frequency of probe field can be achieved and tuned by adjusting the phase and amplitude of the mechanical driving field. Moreover, the strength of the output field at the frequency of an optical four-wave-mixing (FWM) field also can be controlled (enhanced and suppressed) by tuning the phase and amplitude of the mechanical pump. We show that the power of the output field at the frequency of the optical FWM field can be suppressed to zero or enhanced so much that it can be comparable with and even larger than the power of the input probe optical field.

  5. Depolarization of subalfvenic plasma jet generating field-aligned currents

    NASA Astrophysics Data System (ADS)

    Sobyanin, D. B.; Gavrilov, B. G.; Podgorny, I. M.

    2004-01-01

    The subalfvenic magnetized plasma jet propagating across the geomagnetic field generates the field-aligned currents in ionospheric plasma. The transverse polarization electric field Ep = - V × B in the jet is reduced due to a leakage of polarization charges through the field-aligned currents (plasma jet depolarization). These phenomena are investigated in the laboratory experiment. It was revealed that the depolarization is accompanied by appearing of the electric field Ea along the plasma velocity vector and creation of an additional pair of the field-aligned currents being generated at the leading and trailing edge of the moving plasma. The value of Ea is comparable with the transverse electric field Ep. The depolarization results in the plasma jet deflection. The possibility of a manifestation of these effects in the NORTH STAR Russian-American active rocket experiment is discussed.

  6. Field-aligned Currents in Io's Plasma Wake

    NASA Astrophysics Data System (ADS)

    Chen, Chuxin

    2008-09-01

    Since the discovery of Io-controlled decametric radio emissions, the interaction between Io and Jovian magnetosphere has been studied intensively. Two types of interaction have been proposed so far. One is electric circuit model, in which the induced currents flow between Io and the Jovian ionosphere along the magnetic flux tube threading Io. The other is Alfvén wing model. A wing forms in the perturbed magnetic field lines behind Io, the Alfvénic currents develop in the wing rather than along the magnetic flux tubes. More recently, auroral emission associated with Io's footprint and its trailing emission were observed. Such auroral arc may extend longitudinally westward for more than 100 degrees. This trail of aurora is brightest near Io and dims with increasing downstream distance. There is no clear theoretical understanding of the physics that generates this downstream aurora. However it is generally believed that Io's plasma wake is associated with this phenomenon and field-aligned currents lead to downstream emissions. Along with the above two types of the interaction between Io and its surrounding medium, there are also two theoretical frameworks in which these downstream emissions can be interpreted. The first one is corotational lag. When an Io-perturbed (mass loading and/or Io's conductivity) magnetic flux tube moves slowly relative to Jovian magnetosphere, an electric field would be induced at the equatorial plane of the flux tube, which in turn causes a current perpendicular to the field lines that is connected by field-aligned currents. The Lorentz force due to the perpendicular current would play the role of bring the lagged plasma up to corotation. The second is Alfvén wave, in which the Io-perturbed Alfvén wave is reflected between the Jovian ionosphere and the torus edge, driving particles into loss cone. Our present study attempts to use a MHD method to solve the above problem. MHD simulations of Io-Jupiter interaction has been carried out by

  7. Current profile redistribution driven by neutral beam injection in a reversed-field pinch

    NASA Astrophysics Data System (ADS)

    Parke, E.; Anderson, J. K.; Brower, D. L.; Den Hartog, D. J.; Ding, W. X.; Johnson, C. A.; Lin, L.

    2016-05-01

    Neutral beam injection in reversed-field pinch (RFP) plasmas on the Madison Symmetric Torus [Dexter et al., Fusion Sci. Technol. 19, 131 (1991)] drives current redistribution with increased on-axis current density but negligible net current drive. Internal fluctuations correlated with tearing modes are observed on multiple diagnostics; the behavior of tearing mode correlated structures is consistent with flattening of the safety factor profile. The first application of a parametrized model for island flattening to temperature fluctuations in an RFP allows inferrence of rational surface locations for multiple tearing modes. The m = 1, n = 6 mode is observed to shift inward by 1.1 ± 0.6 cm with neutral beam injection. Tearing mode rational surface measurements provide a strong constraint for equilibrium reconstruction, with an estimated reduction of q0 by 5% and an increase in on-axis current density of 8% ± 5%. The inferred on-axis current drive is consistent with estimates of fast ion density using TRANSP [Goldston et al., J. Comput. Phys. 43, 61 (1981)].

  8. On ray stochasticity during lower-hybrid current drive in tokamaks

    SciTech Connect

    Bizarro, J.P.; Moreau, D. )

    1993-04-01

    Using a combined ray-tracing and Fokker--Planck code, a comprehensive and detailed analysis is presented on the importance of toroidally induced ray stochasticity for the modeling of lower-hybrid (LH) current drive in tokamaks and for the dynamics of the launched power spectrum. The injected LH power distribution in poloidal angle and in parallel wave index is accurately represented by taking into account the poloidal extent of the antenna and by efficiently covering the full range of its radiated spectrum. The influence of the balance between the wave damping and the exponential divergence of nearby ray trajectories in determining the shape and robustness of the predicted LH power deposition profiles is emphasized. When stochastic effects are important, code predictions are shown to be stable with respect to small changes in plasma parameters and initial conditions, and to be consistent with experimental data, provided a sufficiently large number of rays is used. Sensitivity studies indicate that the component of the launched power spectrum that is not affected by stochastic effects is well described by a grid in parallel wave index whose spacing may be as large as 10[sup [minus]1], whereas the component that is affected by such effects suffers strong randomization and needs a grid whose spacing must not exceed 10[sup [minus]3]. Ray stochasticity tends to broaden the launched power spectrum, to increase the LH power deposition in the inner half of the plasma, and to favor power deposition profiles that are spread over most of the plasma cross section and whose dependence on the injected LH power distribution in poloidal angle and in parallel wave index is weak. It is found that stochastic effects may be effectively reduced by using bottom launch schemes.

  9. Ultralow-current-density and bias-field-free spin-transfer nano-oscillator

    PubMed Central

    Zeng, Zhongming; Finocchio, Giovanni; Zhang, Baoshun; Amiri, Pedram Khalili; Katine, Jordan A.; Krivorotov, Ilya N.; Huai, Yiming; Langer, Juergen; Azzerboni, Bruno; Wang, Kang L.; Jiang, Hongwen

    2013-01-01

    The spin-transfer nano-oscillator (STNO) offers the possibility of using the transfer of spin angular momentum via spin-polarized currents to generate microwave signals. However, at present STNO microwave emission mainly relies on both large drive currents and external magnetic fields. These issues hinder the implementation of STNOs for practical applications in terms of power dissipation and size. Here, we report microwave measurements on STNOs built with MgO-based magnetic tunnel junctions having a planar polarizer and a perpendicular free layer, where microwave emission with large output power, excited at ultralow current densities, and in the absence of any bias magnetic fields is observed. The measured critical current density is over one order of magnitude smaller than previously reported. These results suggest the possibility of improved integration of STNOs with complementary metal-oxide-semiconductor technology, and could represent a new route for the development of the next-generation of on-chip oscillators. PMID:23478390

  10. Modification of the current profile in high-performance plasmas using off-axis electron-cyclotron-current drive in DIII-D.

    PubMed

    Murakami, M; Wade, M R; Greenfield, C M; Luce, T C; Makowski, M A; Petty, C C; DeBoo, J C; Ferron, J R; Jayakumar, R J; Lao, L L; Lohr, J; Politzer, P A; Prater, R; St John, H E

    2003-06-27

    Recent DIII-D experiments using off-axis electron cyclotron current drive (ECCD) have demonstrated the ability to modify the current profile in a plasma with toroidal beta near 3%. The resulting plasma simultaneously sustains the key elements required for Advanced Tokamak operation: high bootstrap current fraction, high beta, and good confinement. More than 85% of the plasma current is driven by noninductive means. ECCD is observed to produce strong negative central magnetic shear, which in turn acts to trigger confinement improvements in all transport channels in the plasma core. PMID:12857139

  11. Anode current density distribution in a cusped field thruster

    SciTech Connect

    Wu, Huan Liu, Hui Meng, Yingchao; Zhang, Junyou; Yang, Siyu; Hu, Peng; Chen, Pengbo; Yu, Daren

    2015-12-15

    The cusped field thruster is a new electric propulsion device that is expected to have a non-uniform radial current density at the anode. To further study the anode current density distribution, a multi-annulus anode is designed to directly measure the anode current density for the first time. The anode current density decreases sharply at larger radii; the magnitude of collected current density at the center is far higher compared with the outer annuli. The anode current density non-uniformity does not demonstrate a significant change with varying working conditions.

  12. Anode current density distribution in a cusped field thruster

    NASA Astrophysics Data System (ADS)

    Wu, Huan; Liu, Hui; Meng, Yingchao; Zhang, Junyou; Yang, Siyu; Hu, Peng; Chen, Pengbo; Yu, Daren

    2015-12-01

    The cusped field thruster is a new electric propulsion device that is expected to have a non-uniform radial current density at the anode. To further study the anode current density distribution, a multi-annulus anode is designed to directly measure the anode current density for the first time. The anode current density decreases sharply at larger radii; the magnitude of collected current density at the center is far higher compared with the outer annuli. The anode current density non-uniformity does not demonstrate a significant change with varying working conditions.

  13. Simulation of injector dynamics during steady inductive helicity injection current drive in the HIT-SI experiment

    SciTech Connect

    Hansen, C.; Marklin, G.; Victor, B.; Akcay, C.; Jarboe, T.

    2015-04-15

    We present simulations of inductive helicity injection in the Helicity Injected Torus with Steady Inductive helicity injection (HIT-SI) device that treats the entire plasma volume in a single dynamic MHD model. A new fully 3D numerical tool, the PSI-center TETrahedral mesh code, was developed that provides the geometric flexibility required for this investigation. Implementation of a zero-β Hall MHD model using PSI-TET will be presented including formulation of a new self-consistent magnetic boundary condition for the wall of the HIT-SI device. Results from simulations of HIT-SI are presented focusing on injector dynamics that are investigated numerically for the first time. Asymmetries in the plasma loading between the two helicity injectors and progression of field reversal in each injector are observed. Analysis indicates cross-coupling between injectors through confinement volume structures. Injector impedance is found to scale with toroidal current at fixed density, consistent with experimental observation. Comparison to experimental data with an injector drive frequency of 14.5 kHz shows good agreement with magnetic diagnostics. Global mode structures from Bi-Orthogonal decomposition agree well with experimental data for the first four modes.

  14. Finite geometry effects of field-aligned currents

    NASA Technical Reports Server (NTRS)

    Fung, Shing F.; Hoffman, R. A.

    1992-01-01

    Results are presented of model calculations of the magnetic field produced by finite current regions that would be measured by a spaceborne magnetometer. Conditions were examined under which the infinite current sheet approximation can be applied to the calculation of the field-aligned current (FAC) density, using satellite magnetometer data. The accuracy of the three methods used for calculating the current sheet normal direction with respect to the spacecraft trajectory was assessed. It is shown that the model can be used to obtain the position and the orientation of the spacecraft trajectory through the FAC region.

  15. Relationship of the interplanetary electric field to the high-latitude ionospheric electric field and currents Observations and model simulation

    NASA Technical Reports Server (NTRS)

    Clauer, C. R.; Banks, P. M.

    1986-01-01

    The electrical coupling between the solar wind, magnetosphere, and ionosphere is studied. The coupling is analyzed using observations of high-latitude ion convection measured by the Sondre Stromfjord radar in Greenland and a computer simulation. The computer simulation calculates the ionospheric electric potential distribution for a given configuration of field-aligned currents and conductivity distribution. The technique for measuring F-region in velocities at high time resolution over a large range of latitudes is described. Variations in the currents on ionospheric plasma convection are examined using a model of field-aligned currents linking the solar wind with the dayside, high-latitude ionosphere. The data reveal that high-latitude ionospheric convection patterns, electric fields, and field-aligned currents are dependent on IMF orientation; it is observed that the electric field, which drives the F-region plasma curve, responds within about 14 minutes to IMF variations in the magnetopause. Comparisons of the simulated plasma convection with the ion velocity measurements reveal good correlation between the data.

  16. Fourier analysis of polar cap electric field and current distributions

    NASA Technical Reports Server (NTRS)

    Barbosa, D. D.

    1984-01-01

    A theoretical study of high-latitude electric fields and currents, using analytic Fourier analysis methods, is conducted. A two-dimensional planar model of the ionosphere with an enhanced conductivity auroral belt and field-aligned currents at the edges is employed. Two separate topics are treated. A field-aligned current element near the cusp region of the polar cap is included to investigate the modifications to the convection pattern by the east-west component of the interplanetary magnetic field. It is shown that a sizable one-cell structure is induced near the cusp which diverts equipotential contours to the dawnside or duskside, depending on the sign of the cusp current. This produces characteristic dawn-dusk asymmetries to the electric field that have been previously observed over the polar cap. The second topic is concerned with the electric field configuration obtained in the limit of perfect shielding, where the field is totally excluded equatorward of the auroral oval. When realistic field-aligned current distributions are used, the result is to produce severely distorted, crescent-shaped equipotential contours over the cap. Exact, analytic formulae applicable to this case are also provided.

  17. Net field-aligned currents observed by Triad

    NASA Technical Reports Server (NTRS)

    Sugiura, M.; Potemra, T. A.

    1975-01-01

    From the Triad magnetometer observation of a step-like level shift in the east-west component of the magnetic field at 800 km altitude, the existence of a net current flowing into or away from the ionosphere in a current layer was inferred. The current direction is toward the ionosphere on the morning side and away from it on the afternoon side. The field aligned currents observed by Triad are considered as being an important element in the electro-dynamical coupling between the distant magnetosphere and the ionosphere. The current density integrated over the thickness of the layer increases with increasing magnetic activity, but the relation between the current density and Kp in individual cases is not a simple linear relation. An extrapolation of the statistical relation to Kp = 0 indicates existence of a sheet current of order 0.1 amp/m even at extremely quiet times. During periods of higher magnetic activity an integrated current of approximately 1 amp/m and average current density of order 0.000001 amp/sq m are observed. The location and the latitudinal width of the field aligned current layer carrying the net current very roughly agree with those of the region of high electron intensities in the trapping boundary.

  18. Study of lower hybrid current drive efficiency and its correlation with photon temperatures in the HT-7 tokamak

    NASA Astrophysics Data System (ADS)

    Younis, J.; Wan, B. N.; Lin, S. Y.; Shi, Y. J.; Ding, B. J.; Gong, X.; HT-7 Team

    2009-07-01

    Lower hybrid current drive (LHCD) efficiency is a very important parameter. The experimental current drive efficiency is defined as η = IrfneR/PLH, where Irf is the current driven by the lower hybrid waves (LHWs), ne is the central line-average density, R is the major radius of the plasma and PLH is the injected LH wave power absorbed by the plasma through Landau damping. A study of current drive efficiency of LHWs in the HT-7 tokamak has been carried out in the parameter ranges: ne = (1.2-2.5) × 1019 m-3, Ip = (80-200) kA, Bt = 1.8 T, PLH = (188-532) kW in the limiter configuration. Current drive efficiency is investigated through a simple correlation with photon temperature and normalized intensity of fast electron bremstrahlung emission, which is, in the first approximation, proportional to the averaged velocity and population of the fast electrons. The plasma current scanning experiment shows that CD efficiency increase is due to the increase in both the photon temperature and the population of the fast electrons generated by LHWs. The density scanning experiment shows that as the plasma density is increased, an increment in CD efficiency along with the increase in the population of fast electrons is observed. The slowing down through the collisions with bulk electrons is mainly responsible for the decreased photon temperature during the plasma density scan. These experiments strongly suggest the dominant role of the population of fast electrons generated by LHCD and the generation of the current carried by fast electrons.

  19. Electric currents and voltage drops along auroral field lines

    NASA Technical Reports Server (NTRS)

    Stern, D. P.

    1983-01-01

    An assessment is presented of the current state of knowledge concerning Birkeland currents and the parallel electric field, with discussions focusing on the Birkeland primary region 1 sheets, the region 2 sheets which parallel them and appear to close in the partial ring current, the cusp currents (which may be correlated with the interplanetary B(y) component), and the Harang filament. The energy required by the parallel electric field and the associated particle acceleration processes appears to be derived from the Birkeland currents, for which evidence is adduced from particles, inverted V spectra, rising ion beams and expanded loss cones. Conics may on the other hand signify acceleration by electrostatic ion cyclotron waves associated with beams accelerated by the parallel electric field.

  20. The cometary magnetic field and its associated electric currents

    NASA Technical Reports Server (NTRS)

    Ip, W.-H.; Mendis, D. A.

    1975-01-01

    Two different observations of Comet Kohoutek (1973f) seem to suggest the existence of substantial magnetic fields (not less than 100 gammas) in its coma and tail. The effects of the currents and hydromagnetic waves associated with these magnetic fields are considered. It is shown that while the currents closing through the inner coma may represent an important source of ionization in that region, the dissipation of hydromagnetic waves may also be a significant, if not dominant, source of heating there.

  1. Effect of Interhemispheric Field-Aligned Currents on Region-1 Currents

    NASA Technical Reports Server (NTRS)

    Lyatsky, Sonya; Lyatsky, Wladislaw; Khazanov, George V.

    2015-01-01

    An asymmetry in ionospheric conductivity between two hemispheres results in the formation of additional, interhemispheric field-aligned currents flowing between conjugate ionospheres within two auroral zones. These interhemispheric currents are especially significant during summer-winter conditions when there is a significant asymmetry in ionospheric conductivity in two hemispheres. In such conditions, these currents may be comparable in magnitude with the Region 1 field-aligned currents. In this case, the R1 current is the sum of two FACs: one is going from to the solar wind, and another is flowing between conjugate ionospheres. These interhemispheric currents can also cause the formation of auroras extended along the nightside polar cap boundary, which may be related to the so-called double auroral oval. In this study, we present the results of analytical and numerical solutions for the interhemispheric currents and their effect on the Region 1 currents.

  2. Remote field eddy current technique - Phantom exciter model calculations

    NASA Astrophysics Data System (ADS)

    Atherton, D. L.; Czura, W.

    1993-03-01

    High resolution results of finite element calculations for remote field eddy current 'phantom exciter' simulations of slit defect interactions using single through wall transit are presented. These show that fine circumferential slits cause almost no field perturbations in the case of nonferromagnetic tubes but big perturbations in ferromagnetic tubes where high magnetic H fields occur in the slits. Defect-induced magnetic field perturbations must therefore be considered in addition to eddy current perturbations when ferromagnetic materials are inspected, particularly in the case of fine slits orthogonal to the magnetic field direction. Additional details seen are the funnelling of energy into slits in ferromagnetic pipes and precursor disturbances of fields approaching defects. It is suggested that these are due to the reflection of the electromagnetic waves dictated by boundary conditions at the near-side defect boundary.

  3. Remote field eddy current inspection of support plate fretting wear

    SciTech Connect

    Shatat, A.; Atherton, D.L.

    1997-03-01

    This article demonstrates how the remote field eddy current technique might be extended to measure support plate fretting wear in heat exchanger tubes. A finite element analysis was used to examine the plate`s effect on the eddy current signal. Experimental data lend support to a suggested multifrequency method for sizing fretting grooves.

  4. Effective variable switching point predictive current control for ac low-voltage drives

    NASA Astrophysics Data System (ADS)

    Stolze, Peter; Karamanakos, Petros; Kennel, Ralph; Manias, Stefanos; Endisch, Christian

    2015-07-01

    This paper presents an effective model predictive current control scheme for induction machines driven by a three-level neutral point clamped inverter, called variable switching point predictive current control. Despite the fact that direct, enumeration-based model predictive control (MPC) strategies are very popular in the field of power electronics due to their numerous advantages such as design simplicity and straightforward implementation procedure, they carry two major drawbacks. These are the increased computational effort and the high ripples on the controlled variables, resulting in a limited applicability of such methods. The high ripples occur because in direct MPC algorithms the actuating variable can only be changed at the beginning of a sampling interval. A possible remedy for this would be to change the applied control input within the sampling interval, and thus to apply it for a shorter time than one sample. However, since such a solution would lead to an additional overhead which is crucial especially for multilevel inverters, a heuristic preselection of the optimal control action is adopted to keep the computational complexity at bay. Experimental results are provided to verify the potential advantages of the proposed strategy.

  5. Relations between transverse electric fields and field-aligned currents. [in magnetosphere and ionosphere

    NASA Technical Reports Server (NTRS)

    Mallinckrodt, A. J.; Carlson, C. W.

    1978-01-01

    A model for the field-aligned propagation of transverse electric fields and associated field-aligned sheet currents is presented which takes into account the wave nature of the process. The model is applied to the separate cases of ionospheric and magnetospheric sources, and the resulting ionospheric electric field to field-aligned sheet current ratios are determined for comparison with experimental observations. It is found that the magnetospheric wave 'conductivity' for shear mode Alfven waves is small with respect to typical values of the height-integrated ionospheric Pedersen conductivity. For plasma convecting across a stationary disturbance a dynamic equilibrium is achieved in which field-aligned currents flow continuously away from the source on convecting field lines. Consistency with typical ionospheric electric fields requires that the field-aligned sheet currents are limited to around 0.1 A/m for ionospheric polarization sources, while magnetospheric sources are easily capable of 1 A/m or more.

  6. Comparison of Iridium Determined Field-Aligned Current Patterns with MHD Simulations

    NASA Astrophysics Data System (ADS)

    Korth, H.; Anderson, B. J.; Goodrich, C. C.; Waters, C. L.; Merkine, V. G.

    2002-05-01

    The engineering magnetometers aboard the 70+ Iridium satellites arranged in six equally spaced polar orbital planes provide a unique database for determination of global field-aligned currents [Waters et al., 2001]. In this study we compare these field-aligned currents with MHD simulation results to quantitatively evaluate the MHD results in a global way. We report analysis for three events of steady interplanetary magnetic field (IMF) orientation, stable to within 25o of the average direction. The start times of these intervals are August~11, 1999 (22:36), November~23, 1999 (07:15), and August~10, 2000 (22:11), and the events extend between eight and ten hours in duration. The IMF clock angles for the events are -124o, 125o, and 160o, respectively, and the IMF cone angles for all three intervals are within 25o of 90o. The solar wind flow speeds for the events averages 430, 453, and 386~km/s, and the mean solar wind densities are 3.7, 3.6, and 12.0 {cm}-3, respectively. The field aligned current densities in the MHD simulations are evaluated at the inner simulation boundary (2~Re) and mapped on dipole field lines to ionospheric altitudes. Preliminary results show a reasonably good agreement in the morphology of the Region-1 currents, although the field-aligned currents of the MHD simulations are displaced somewhat poleward with respect to the Iridium patterns. DMSP particle source identifications are used to compare source regions of Region 1 in the observed FAC maps with those in the MHD simulations. The Region-2 currents show expectedly larger differences since ring current drift physics necessary to drive these currents in the magnetosphere is not implemented in the MHD evaluations. The ratio between Region~1 and Region~2 is used to measure the relative deficit of Region-2 currents in the MHD simulation results.

  7. Limiting current mechanisms of Bi2223 wires in magnetic fields

    NASA Astrophysics Data System (ADS)

    Kobayashi, S.; Yamade, S.; Kikuchi, M.; Yamazaki, K.; Fujikami, J.; Ayai, N.; Hayashi, K.; Sato, K.; Hata, R.; Kitaguti, H.

    2008-05-01

    Controlled overpressure (CT-OP) processing eliminates pores and heals cracks, which densifies the Bi2223 filaments and increases the critical current of Ag-sheathed Bi2223 wire. High current capacity wires with critical current values around 210 A at 77 K and self-field have been achieved. The enhancement of the current capacity seems to be due to reducing the weak links between Bi2223 grains and improving the flux pinning. In order to understand the mechanisms for transport critical current in Bi2223 wires, the dependence of the critical current on magnetic field and temperature has been investigated. The critical current is measured as a function of the perpendicular and parallel magnetic fields, up to 12 T, at temperatures ranging from 4.2 to 90 K. These results indicate that higher critical current is associated with highly textured and well connected Bi2223 grains. To further improve a critical current of Bi2223 wires, it is necessary to decrease the misalignment angle and reduce the fraction of Bi2212 and secondary phases.

  8. Method and apparatus for improved efficiency in a pulse-width-modulated alternating current motor drive

    DOEpatents

    Konrad, C.E.; Boothe, R.W.

    1996-01-23

    A scheme for optimizing the efficiency of an AC motor drive operated in a pulse-width-modulated mode provides that the modulation frequency of the power furnished to the motor is a function of commanded motor torque and is higher at lower torque requirements than at higher torque requirements. 6 figs.

  9. Method and apparatus for improved efficiency in a pulse-width-modulated alternating current motor drive

    DOEpatents

    Konrad, Charles E.; Boothe, Richard W.

    1994-01-01

    A scheme for optimizing the efficiency of an AC motor drive operated in a pulse-width-modulated mode provides that the modulation frequency of the power furnished to the motor is a function of commanded motor torque and is higher at lower torque requirements than at higher torque requirements.

  10. Method and apparatus for improved efficiency in a pulse-width-modulated alternating current motor drive

    DOEpatents

    Konrad, Charles E.; Boothe, Richard W.

    1996-01-01

    A scheme for optimizing the efficiency of an AC motor drive operated in a pulse-width-modulated mode provides that the modulation frequency of the power furnished to the motor is a function of commanded motor torque and is higher at lower torque requirements than at higher torque requirements.

  11. Are Teens Driving Safer? Cross Currents Issue 4, October 2005. Publication # 2005-16

    ERIC Educational Resources Information Center

    Marin, Pilar S.; Brown, Brett V.

    2005-01-01

    For many teens, learning to drive and obtaining a driver's license are exciting achievements,often allowing them more freedom to socialize, work at a job, or participate in other activities without being totally reliant on a parent or others for transportation. This brief provides an overview of relevant data including teen crash rates and trends,…

  12. Method and apparatus for improved efficiency in a pulse-width-modulated alternating current motor drive

    DOEpatents

    Konrad, C.E.; Boothe, R.W.

    1994-02-15

    A scheme for optimizing the efficiency of an AC motor drive operated in a pulse-width-modulated mode provides that the modulation frequency of the power furnished to the motor is a function of commanded motor torque and is higher at lower torque requirements than at higher torque requirements. 6 figures.

  13. Generation of field-aligned current in the auroral zone

    NASA Technical Reports Server (NTRS)

    Okuda, Hideo

    1991-01-01

    Generation of a magnetic field-aligned current in the auroral zone connecting the magnetospheric and ionospheric plasmas has been studied by means of a three dimensional particle simulation model. The model is of a magnetostatic variety appropriate for a low beta plasma in which the high frequency transverse displacement current has been eliminated. The simulation model is highly elongated along the magnetic field lines in order to model a highly elongated flux tube in the auroral zone. An enhanced field-aligned current was generated by injection of a magnetospheric plasma across the auroral zone magnetic field at the center of the model. Such a plasma injection may correspond to a plasmoid injection at the geomagnetic tail associated with magnetic reconnection during a substorm or a transverse plasma flow along the low latitude magnetopause boundary layer. The results of the simulations show that the field-aligned current can be enhanced over the thermal current by a factor of 5 - 10 via such injection. Associated with the enhanced current are the electrostatic ion cyclotron waves and shear Alfven waves excited in the auroral zone.

  14. Field-aligned currents and the auroral electrojet

    NASA Technical Reports Server (NTRS)

    Cahill, L. J.; Potter, W. E.; Kintner, P. M.; Arnoldy, R. L.; Choy, L. W.

    1974-01-01

    A Nike Tomahawk with fields and particles payload was launched on Nov. 18, 1970, over a strong westward electrojet current and auroral forms moving rapidly to the east. Electron fluxes moving up and down the magnetic field lines were measured. Upward-moving electrons below 1-keV energy were dominant and were equivalent to a net downward electric current that fluctuated between .2 and .6 microamp/sq m during the flight above 130 km. As the rocket traversed this broad region of downward electric current over and to the north of the auroral forms, the horizontal electric field slowly rotated from east to west. The magnetic measurements indicate that the westward electrojet was a horizontal sheet of current several hundred kilometers in north-south extent.

  15. 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

  16. How key periodic orbits drive recollisions in a circularly polarized laser field.

    PubMed

    Kamor, A; Mauger, F; Chandre, C; Uzer, T

    2013-06-21

    We show that a family of key periodic orbits drives the recollision process in a strong circularly polarized laser field. These orbits, coined recolliding periodic orbits, exist for a wide range of parameters, and their relative influence changes as the laser and atomic parameters are varied. We find the necessary conditions for recollision-driven nonsequential double ionization to occur. The outlined mechanism is universal in that it applies equally well beyond atoms: The internal structure of the target species plays a minor role in the recollision process. PMID:23829734

  17. Generating vorticity and magnetic fields in plasmas in general relativity: Spacetime curvature drive

    SciTech Connect

    Asenjo, Felipe A.; Mahajan, Swadesh M.; Qadir, Asghar

    2013-02-15

    Using the generally covariant magnetofluid formalism for a hot plasma, a spacetime curvature driven mechanism for generating seed vorticity/magnetic field is presented. The 'battery' owes its origin to the interaction between the gravity modified Lorentz factor of the fluid element and the inhomogeneous plasma thermodynamics. The general relativistic drive is evaluated for two simple cases: seed formation in a simplified model of a hot plasma accreting in stable orbits around a Schwarzschild black hole and for particles in free fall near the horizon. Some astrophysical applications are suggested.

  18. Current Sheets Formation in Tangled Coronal Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Rappazzo, A. F.; Parker, E. N.

    2013-08-01

    We investigate the dynamical evolution of magnetic fields in closed regions of solar and stellar coronae. To understand under which conditions current sheets form, we examine dissipative and ideal reduced magnetohydrodynamic models in Cartesian geometry, where two magnetic field components are present: the strong guide field B 0, extended along the axial direction, and the dynamical orthogonal field b. Magnetic field lines thread the system along the axial direction that spans the length L and are line-tied at the top and bottom plates. The magnetic field b initially has only large scales, with its gradient (current) length scale of the order of l b . We identify the magnetic intensity threshold b/B 0 ~ l b /L. For values of b below this threshold, field-line tension inhibits the formation of current sheets, while above the threshold they form quickly on fast ideal timescales. In the ideal case, above the magnetic threshold, we show that current sheets thickness decreases in time until it becomes smaller than the grid resolution, with the analyticity strip width δ decreasing at least exponentially, after which the simulations become underresolved.

  19. CURRENT SHEETS FORMATION IN TANGLED CORONAL MAGNETIC FIELDS

    SciTech Connect

    Rappazzo, A. F.; Parker, E. N. E-mail: parker@oddjob.uchicago.edu

    2013-08-10

    We investigate the dynamical evolution of magnetic fields in closed regions of solar and stellar coronae. To understand under which conditions current sheets form, we examine dissipative and ideal reduced magnetohydrodynamic models in Cartesian geometry, where two magnetic field components are present: the strong guide field B{sub 0}, extended along the axial direction, and the dynamical orthogonal field b. Magnetic field lines thread the system along the axial direction that spans the length L and are line-tied at the top and bottom plates. The magnetic field b initially has only large scales, with its gradient (current) length scale of the order of l{sub b}. We identify the magnetic intensity threshold b/B{sub 0} {approx} l{sub b}/L. For values of b below this threshold, field-line tension inhibits the formation of current sheets, while above the threshold they form quickly on fast ideal timescales. In the ideal case, above the magnetic threshold, we show that current sheets thickness decreases in time until it becomes smaller than the grid resolution, with the analyticity strip width {delta} decreasing at least exponentially, after which the simulations become underresolved.

  20. Remote field eddy current-crack and defect detection

    SciTech Connect

    Lord, W.

    1989-03-16

    No single nondestructive evaluation (NDE) technique is currently capable of detecting and characterizing all the defect types that can occur in gas pipeline. Conventional in-line inspection tools for example, have not shown significant sensitivity to intergranular stress corrosion cracking. For this reason considerable research and development work is still needed in order to provide the in-line inspection tools whose results are essential for structural integrity evaluations. The remote field eddy current method shows more promise than conventional eddy current methods, in gas pipeline inspection, due to the increased sensitivity to inner and outer pipe wall inhomogeneities. Even though the fundamental physical principles governing the conventional eddy current method and the remote field eddy current method is one and the same (that of electromagnetic induction), the differences in operating frequencies in the two methods result in field patterns that have different characteristic properties, such as extremely small skin depths associated with conventional eddy currents testing and the phenomena of potential valley'' and phase knot'' associated with remote field eddy current technique. 20 refs., 26 figs.

  1. Critical current density and current distribution in field cooled superconducting disks

    NASA Astrophysics Data System (ADS)

    Bernstein, Pierre; Noudem, Jacques; Dupont, Louis

    2016-07-01

    Applications of bulk superconductors concern superconducting motors and generators, the levitation of vehicles, the generation of high magnetic fields with small size cryo-magnets, the shielding of magnetic fields and other applications. For all of them, it is essential to determine the critical current density, and to understand the effect of the shape and size of the bulks on the properties of interest. In this contribution, we show how the combination of levitation force and trapped field measurements allow one to determine the characteristics and the potential performances of superconducting disks using analytical modeling. As examples of applications we detail the effects of the magnetizing field and of the bulk sheet critical current density on the levitation force. An important result of the reported measurements is that in field-cooled samples, the shielding currents possibly do not flow along the whole thickness of the disks.

  2. Lower hybrid current drive in experiments for transport barriers at high {beta}{sub N} of JET (Joint European Torus)

    SciTech Connect

    Cesario, R. C.; Castaldo, C.; De Angelis, R.; Smeulders, P.; Calabro, G.; Pericoli, V.; Ravera, G.

    2007-09-28

    LHCD has been used in JET experiments aimed at producing internal transport barriers (ITBs) in highly triangular plasmas ({delta}{approx_equal}0.4) at high {beta}{sub N} (up to 3) for steady-state application. The LHCD is a potentially valuable tool for (i) modifying the target q-profile, which can help avoid deleterious MHD modes and favour the formation of ITBs, and (ii) contributing to the non-inductive current drive required to prolong such plasma regimes. The q-profile evolution has been simulated during the current ramp-up phase for such a discharge (B{sub 0} = 2.3 T, I{sub P} = 1.5 MA) where 2 MW of LHCD has been coupled. The JETTO code was used taking measured plasma profiles, and the LHCD profile modeled by the LHstar code. The results are in agreement with MSE measurements and indicate the importance of the elevated electron temperature due to LHCD, as well as the driven current. During main heating with 18 MW of NBI and 3 MW of ICRH the bootstrap current density at the edge also becomes large, consistently with the observed reduction of the local turbulence and of the MHD activity. JETTO modelling suggests that the bootstrap current can reduce the magnetic shear (sh) at large radius, potentially affecting the MHD stability and turbulence behaviour in this region. Keywords: lower hybrid current drive (LHCD), bootstrap current, q (safety factor) and shear (sh) profile evolutions.

  3. Magnetic field and electric current structure in the chromosphere

    NASA Technical Reports Server (NTRS)

    Dravins, D.

    1974-01-01

    The three-dimensional vector magnetic field structure in the chromosphere above an active region is deduced by using high-resolution H-alpha filtergrams together with a simultaneous digital magnetogram. An analog model of the field is made with 400 metal wires representing field lines that outline the H-alpha structure. The height extent of the field is determined from vertical field-gradient observations around sunspots, from observed fibril heights, and from an assumption that the sources of the field are largely local. The computed electric currents (typically 10 mA/sq m) are found to flow in patterns not similar to observed features and not parallel to magnetic fields. Force structures correspond to observed solar features; the dynamics to be expected include: downward motion in bipolar areas in the lower chromosphere, an outflow of the outer chromosphere into the corona with radially outward flow above bipolar plage regions, and motion of arch filament systems.

  4. Optimization of Drive-Bunch Current Profile for Enhanced Transformer Ratio in Beam-Driven Acceleration Techniques

    SciTech Connect

    Lemery, F.; Mihalcea, D.; Prokop, C.R.; Piot, P.; /Northern Illinois U. /Fermilab

    2012-07-08

    In recent years, wakefield acceleration has gained attention due to its high acceleration gradients and cost effectiveness. In beam-driven wakefield acceleration, a critical parameter to optimize is the transformer ratio. It has been shown that current shaping of electron beams allows for enhanced (> 2) transformer ratios. In this paper we present the optimization of the pulse shape of the drive bunch for dielectric-wakefield acceleration.

  5. Pulsed currents carried by whistlers. III. Magnetic fields and currents excited by an electrode

    SciTech Connect

    Urrutia, J.M.; Stenzel, R.L.; Rousculp, C.L.

    1995-04-01

    Detailed measurements and analysis of electromagnetic fields asociated with pulsed plasma currents are reported. The objective is to demonstrate the properties of plasma currents in the electron magnetohydrodynamic regime and their relation to low frequency whistler waves. Short current pulses ({ital f}{sub {ital ce}}{sup {minus}1}{much_lt}{Delta}{ital t}{much_lt}{ital f}{sub {ital ci}}{sup {minus}1}) are injected from an electrode into a large, uniform magnetoplasma. The dynamic fields, B(r,{ital t}), are measured with probes in three-dimensional space and time, and are observed to propagate as wave packets predominantly along the guide magnetic field, B{sub 0}. Four-dimensional fast Fourier transformation of B(r,{ital t}) to B(k,{omega}) verifies that the wave fields fall on the dispersion surface of low-frequency oblique whistlers. The magnetic field topology of the packets consists of linked toroidal and solenoidal contributions in force-free configurations. The wave magnetic helicity is obtained quantitatively. Similarly, the topology of the current density field, J@={bold mc}{times}B/{mu}{sub 0}, is explained by its components, characteristic field lines, and helicity, {integral}J{center_dot}B{ital dV}. It is shown, both theoretically and experimentally, that A, B, and J are nearly parallel to one another. Field energy and helicity decay at the same rate without change in topology. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  6. Quasistationary distributions of dissipative nonlinear quantum oscillators in strong periodic driving fields

    PubMed

    Breuer; Huber; Petruccione

    2000-05-01

    The dynamics of periodically driven quantum systems coupled to a thermal environment is investigated. The interaction of the system with the external coherent driving field is taken into account exactly by making use of the Floquet picture. Treating the coupling to the environment within the Born-Markov approximation one finds a Pauli-type master equation for the diagonal elements of the reduced density matrix in the Floquet representation. The stationary solution of the latter yields a quasistationary, time-periodic density matrix which describes the long-time behavior of the system. Taking the example of a periodically driven particle in a box, the stationary solution is determined numerically for a wide range of driving amplitudes and temperatures. It is found that the quasistationary distribution differs substantially from a Boltzmann-type distribution at the temperature of the environment. For large driving fields it exhibits a plateau region describing a nearly constant population of a certain number of Floquet states. This number of Floquet states turns out to be nearly independent of the temperature. The plateau region is sharply separated from an exponential tail of the stationary distribution which expresses a canonical Boltzmann-type distribution over the mean energies of the Floquet states. These results are explained in terms of the structure of the matrix of transition rates for the dissipative quantum system. Investigating the corresponding classical, nonlinear Hamiltonian system, one finds that in the semiclassical range essential features of the quasistationary distribution can be understood from the structure of the underlying classical phase space. PMID:11031530

  7. Development of long pulse RF heating and current drive for H-mode scenarios with metallic walls in WEST

    SciTech Connect

    Ekedahl, Annika Bourdelle, Clarisse; Artaud, Jean-François; Bernard, Jean-Michel; Bufferand, Hugo; Colas, Laurent; Decker, Joan; Delpech, Léna; Dumont, Rémi; Goniche, Marc; Helou, Walid; Hillairet, Julien; Lombard, Gilles; Magne, Roland; Mollard, Patrick; Nardon, Eric; Peysson, Yves; Tsitrone, Emmanuelle

    2015-12-10

    The longstanding expertise of the Tore Supra team in long pulse heating and current drive with radiofrequency (RF) systems will now be exploited in the WEST device (tungsten-W Environment in Steady-state Tokamak) [1]. WEST will allow an integrated long pulse tokamak programme for testing W-divertor components at ITER-relevant heat flux (10-20 MW/m{sup 2}), while treating crucial aspects for ITER-operation, such as avoidance of W-accumulation in long discharges, monitoring and control of heat fluxes on the metallic plasma facing components (PFCs) and coupling of RF waves in H-mode plasmas. Scenario modelling using the METIS-code shows that ITER-relevant heat fluxes are compatible with the sustainment of long pulse H-mode discharges, at high power (up to 15 MW / 30 s at I{sub P} = 0.8 MA) or high fluence (up to 10 MW / 1000 s at I{sub P} = 0.6 MA) [2], all based on RF heating and current drive using Ion Cyclotron Resonance Heating (ICRH) and Lower Hybrid Current Drive (LHCD). This paper gives a description of the ICRH and LHCD systems in WEST, together with the modelling of the power deposition of the RF waves in the WEST-scenarios.

  8. Development of long pulse RF heating and current drive for H-mode scenarios with metallic walls in WEST

    NASA Astrophysics Data System (ADS)

    Ekedahl, Annika; Bourdelle, Clarisse; Artaud, Jean-François; Bernard, Jean-Michel; Bufferand, Hugo; Colas, Laurent; Decker, Joan; Delpech, Léna; Dumont, Rémi; Goniche, Marc; Helou, Walid; Hillairet, Julien; Lombard, Gilles; Magne, Roland; Mollard, Patrick; Nardon, Eric; Peysson, Yves; Tsitrone, Emmanuelle

    2015-12-01

    The longstanding expertise of the Tore Supra team in long pulse heating and current drive with radiofrequency (RF) systems will now be exploited in the WEST device (tungsten-W Environment in Steady-state Tokamak) [1]. WEST will allow an integrated long pulse tokamak programme for testing W-divertor components at ITER-relevant heat flux (10-20 MW/m2), while treating crucial aspects for ITER-operation, such as avoidance of W-accumulation in long discharges, monitoring and control of heat fluxes on the metallic plasma facing components (PFCs) and coupling of RF waves in H-mode plasmas. Scenario modelling using the METIS-code shows that ITER-relevant heat fluxes are compatible with the sustainment of long pulse H-mode discharges, at high power (up to 15 MW / 30 s at IP = 0.8 MA) or high fluence (up to 10 MW / 1000 s at IP = 0.6 MA) [2], all based on RF heating and current drive using Ion Cyclotron Resonance Heating (ICRH) and Lower Hybrid Current Drive (LHCD). This paper gives a description of the ICRH and LHCD systems in WEST, together with the modelling of the power deposition of the RF waves in the WEST-scenarios.

  9. The interplanetary electric field, cleft currents and plasma convection in the polar caps

    NASA Technical Reports Server (NTRS)

    Banks, P. M.; Clauer, C. R.; Araki, T.; St. Maurice, J. P.; Foster, J. C.

    1984-01-01

    The relationship between the pattern of plasma convection in the polar cleft and the dynamics of the interplanetary electric field (IEF) is examined theoretically. It is shown that owing to the geometrical properties of the magnetosphere, the East-West component of the IEF will drive field-aligned currents which connect to the ionosphere at points lying on either side of noon, while currents associated with the North-South component of the IEF will connect the two polar caps as sheet currents, also centered at 12 MLT. In order to describe the consequences of the Interplanetary Magnetic Field (IMF) effects upon high-latitude electric fields and convection patterns, a series of numerical simulations was carried out. The simulations were based on a solution to the steady-state equation of current continuity in a height-integrated ionospheric current. The simulations demonstrate that a simple hydrodynamical model can account for the narrow 'throats' of strong dayside antisunward convection observed during periods of southward interplanetary IMF drift, as well as the sunward convection observed during periods of strongly northward IMF drift.

  10. Quantum mechanical probability current as electromagnetic 4-current from topological EM fields

    NASA Astrophysics Data System (ADS)

    van der Mark, Martin B.

    2015-09-01

    Starting from a complex 4-potential A = αdβ we show that the 4-current density in electromagnetism and the probability current density in relativistic quantum mechanics are of identical form. With the Dirac-Clifford algebra Cl1,3 as mathematical basis, the given 4-potential allows topological solutions of the fields, quite similar to Bateman's construction, but with a double field solution that was overlooked previously. A more general nullvector condition is found and wave-functions of charged and neutral particles appear as topological configurations of the electromagnetic fields.

  11. Ring Current Modeling in a Realistic Magnetic Field Configuration

    NASA Technical Reports Server (NTRS)

    Fok, M.-C.; Moore, T. E.

    1997-01-01

    A 3-dimensional kinetic model has been developed to study the dynamics of the storm time ring current in a dipole magnetic field. In this paper, the ring current model is extended to include a realistic, time-varying magnetic field model. The magnetic field is expressed as the cross product of the gradients of two Euler potentials and the bounce-averaged particle drifts are calculated in the Euler potential coordinates. A dipolarization event is modeled by collapsing a tail-like magnetosphere to a dipole-like configuration. Our model is able to simulate the sudden enhancements in the ring current ion fluxes and the corresponding ionospheric precipitation during the substorm expansion.

  12. On spontaneous formation of current sheets: Untwisted magnetic fields

    SciTech Connect

    Bhattacharyya, R.; Low, B. C.; Smolarkiewicz, P. K.

    2010-11-15

    This is a study of the spontaneous formation of electric current sheets in an incompressible viscous fluid with perfect electrical conductivity, governed by the magnetohydrodynamic Navier-Stokes equations. Numerical solutions to two initial value problems are presented for a three-dimensional, periodic, untwisted magnetic field evolving, with no change in magnetic topology under the frozen-in condition and at characteristic fluid Reynolds numbers of the order of 500, from a nonequilibrium initial state with the fluid at rest. The evolution converts magnetic free energy into kinetic energy to be all dissipated away by viscosity so that the field settles into a minimum-energy, static equilibrium. The solutions demonstrate that, as a consequence of the frozen-in condition, current sheets must form during the evolution despite the geometric simplicity of the prescribed initial fields. In addition to the current sheets associated with magnetic neutral points and field reversal layers, other sheets not associated with such magnetic features are also in evidence. These current sheets form on magnetic flux surfaces. This property is used to achieve a high degree of the frozen-in condition in the simulations, by describing the magnetic field entirely in terms of the advection of its flux surfaces and integrating the resulting governing equations with a customized version of a general-purpose high-resolution (viz., nonoscillatory) hydrodynamical simulation code EULAG [J. M. Prusa et al., Comput. Fluids 37, 1193 (2008)]. Incompressibility imposes the additional global constraint that the flux surfaces must evolve with no change in the spatial volumes they enclose. In this approach, current sheet formation is demonstrated graphically by the progressive pressing together of suitably selected flux surfaces until their separation has diminished below the minimal resolved distance on a fixed grid. The frozen-in condition then fails in the simulation as the field reconnects through

  13. Rapid current transition in a crossed-field diode

    SciTech Connect

    Verboncoeur, J.P.; Birdsall, C.K.

    1996-03-01

    The transmitted current in a crossed-field gap has been characterized analytically by a number of authors. Using a one dimensional PIC simulation, we explore the behavior of the crossed-field diode at {ital B}={ital B}{sub {ital Hull}}. For mono-energetic (cold) emission, a rapid reduction of transmitted current is observed when the injected current exceeds the critical current by just 1{percent}. The addition of a small electron temperature normal to the cathode eliminates the transition, even for {ital kT}/{ital V}{approximately}10{sup {minus}5} ({ital V}=10 kV, gap = 1 cm, {ital B}=337 G, {ital J}=1.69 A/cm{sup 2}), while an isotropic velocity distribution accelerates the transition. {copyright} {ital 1996 American Institute of Physics.}

  14. Electric fields and current densities under small Florida thunderstorms

    NASA Technical Reports Server (NTRS)

    Deaver, Lance E.; Krider, E. P.

    1991-01-01

    Results are presented of measurements of the electric field E and Maxwell current density that were performed simultaneously under and near small Florida thunderstorms. It is shown that the amplitude of JM is of the order of 1 nA/sq cm or less in the absence of precipitation and that there are regular time variations in JM during the intervals between lightning discharges that tend to have the same shapes after different discharges in different storms. It is argued that the major causes of time variations in JM between lightning discharges are currents that flow in the finitely conducting atmosphere in response to the field changes rather than rapid time variations in the strength of cloud current sources. The displacement current densities that are computed from the E records dominate JM except when there is precipitation, when E is large and steady, or when E is unusually noisy.

  15. POLOIDAL MAGNETIC FIELD TOPOLOGY FOR TOKAMAKS WITH CURRENT HOLES

    SciTech Connect

    Puerta, Julio; Martin, Pablo; Castro, Enrique

    2009-07-26

    The appearance of hole currents in tokamaks seems to be very important in plasma confinement and on-set of instabilities, and this paper is devoted to study the topology changes of poloidal magnetic fields in tokamaks. In order to determine these fields different models for current profiles can be considered. It seems to us, that one of the best analytic descriptions is given by V. Yavorskij et al., which has been chosen for the calculations here performed. Suitable analytic equations for the family of magnetic field surfaces with triangularity and Shafranov shift are written down here. The topology of the magnetic field determines the amount of trapped particles in the generalized mirror type magnetic field configurations. Here it is found that the number of maximums and minimums of Bp depends mainly on triangularity, but the pattern is also depending of the existence or not of hole currents. Our calculations allow comparing the topology of configurations of similar parameters, but with and without whole currents. These differences are study for configurations with equal ellipticity but changing the triangularity parameters. Positive and negative triangularities are considered and compared between them.

  16. Reconfiguring photonic metamaterials with currents and magnetic fields

    SciTech Connect

    Valente, João Ou, Jun-Yu; Plum, Eric; Youngs, Ian J.; Zheludev, Nikolay I.

    2015-03-16

    We demonstrate that spatial arrangement and optical properties of metamaterial nanostructures can be controlled dynamically using currents and magnetic fields. Mechanical deformation of metamaterial arrays is driven by both resistive heating of bimorph nanostructures and the Lorentz force that acts on charges moving in a magnetic field. With electrically controlled transmission changes of up to 50% at sub-mW power levels, our approaches offer high contrast solutions for dynamic control of metamaterial functionalities in optoelectronic devices.

  17. Electric fields and current sheet structure in magnetospheric plasmas

    NASA Astrophysics Data System (ADS)

    Cully, C. M.

    The electric currents of the central plasma sheet play a pivotal role in the dynamics of the Earth's magnetosphere. I describe new instrumentation developed for measuring its properties, and analyze data from existing instruments. The analysis shows the structure and physical current-carrying mechanisms of the quiescent central plasma sheet in new detail. Electric field observations are critical for this work. I discuss two aspects of space-based double-probe electric field experiments: the probe design and the signal processing. I develop a numerical model that self-consistently solves for the interaction between the probes and the nearby plasma environment, including the effects of the spacecraft and its attendant photoelectrons. I also describe the signal processing hardware developed for the 5-satellite THEMIS mission, known as the Digital Fields Boards (DFB). THEMIS was launched in February 2007, and all 5 DFBs are working as intended. Since THEMIS is only recently launched, I analyze data from the 4-satellite Cluster mission, which has similar instrumentation. With Cluster data, the position of the current sheet relative to the satellite can be determined, allowing direct comparisons between observations and models. To encompass the wide variety of possible current-carrying mechanisms, I develop a kinetic model based on the quasi-isotropic formalism of Schindler and Birn [2002]. The model fits many of the observed sheets well. The observations reveal a wide variety of current-carrying mechanisms. Some of the thinnest currents consist entirely of a pair of electron Hall currents which together form a bifurcated current sheet driven by strong inward-pointing electric fields.

  18. Current-drive on the Versator-2 tokamak with a slotted-waveguide fast-wave coupler

    NASA Astrophysics Data System (ADS)

    Colborn, J. A.

    1987-11-01

    A slotted-waveguide fast-wave coupler has been constructed, without dielectric, and used to drive current on the Versator-2 tokamak. Up to 35 kW of net microwave power at 2.45 GHz has been radiated into plasmas with 2 x 10 to the 12th/cu cm less than or equal to mean of n(sub e) less than or equal to 1.2 x 10 to the 13th/cu cm and B(sub tor) approx. = 1.0 T. The launched spectrum had a peak near N(sub parallel) = -2.0 and a larger peak near N(sub parallel) = 0.7. Radiating efficiency of the antenna was roughly independent of antenna position except when the antenna was at least 0.2 cm outside the limiter, in which case the radiating efficiency slightly improved as the antenna was moved farther outside. When the coupler was inside the limiter, radiating efficiency improved moderately with increased mean of n(sub e). Current-drive efficiency was comparable to that of the slow wave and was not affected when the antenna spectrum was reversed; however, no current was driven for mean of n(sub e) less than or equal to 2 x 10 to the 12th/cu cm. These results indicate the fast wave was launched, but a substantial part of the power may have been mode-converted to the slow wave, possible via a downshift in N(sub parallel), and these slow waves may have been responsible for most of the driven current. Relevant theory for waves in plasma, current-drive efficiency, and coupling of the slotted-waveguide is discussed, the antenna design method is explained, and future work, including the construction of a much-improved probe-fed antenna, is described.

  19. Formation of current filaments and magnetic field generation in a quantum current-carrying plasma

    SciTech Connect

    Niknam, A. R.; Taghadosi, M. R.; Majedi, S.; Khorashadizadeh, S. M.

    2013-09-15

    The nonlinear dynamics of filamentation instability and magnetic field in a current-carrying plasma is investigated in the presence of quantum effects using the quantum hydrodynamic model. A new nonlinear partial differential equation is obtained for the spatiotemporal evolution of the magnetic field in the diffusion regime. This equation is solved by applying the Adomian decomposition method, and then the profiles of magnetic field and electron density are plotted. It is shown that the saturation time of filamentation instability increases and, consequently, the instability growth rate and the magnetic field amplitude decrease in the presence of quantum effects.

  20. Space Technology 5 Observations of Auroral Field-Aligned Currents

    NASA Technical Reports Server (NTRS)

    Slavin, James

    2008-01-01

    During its three month long technology validation mission, Space Technology 5 (ST-5) returned high quality multi-point measurements of the near-Earth magnetic field. Its three micro-satellites were launched into a 300 x 4500 km, dawn - dusk, sun synchronous orbit (inclination = 105.60) orbit with a period of 138 min by a Pegasus launch vehicle on March 22, 2006. The spacecraft were maintained in a "pearls on a sting" constellation with controlled spacings ranging from just over 5000 km down to under 50 km. The individual micro-satellites were 48 cm tall octagons with diameters of 50 cm. They were spin-stabilized at approximately 20 rpm at deployment and slowly spun-down to about 15 rpm by the end of the mission. Each spacecraft carried a miniature tri-axial fluxgate magnetometer (MAG) provided by the University of California at Los Angeles mounted at the end of a ultra-low mass 72 cm boom. These data allow, for the first time, the separation of temporal and spatial variations in field-aligned current (FAC) perturbations measured in low-Earth orbit on time scales of 10 sec to 10 min. The constellation measurements are used to directly determine field-aligned current sheet motion, thickness. and current density. Two multi-point methods for the inference of FAC current density that have not previously been possible in low-Earth orbit are demonstrated: 1) the -standard method." based upon s/c velocity, but corrected for FAC current sheet motion. and 2) the "gradiometer method" which uses simultaneous magnetic field measurements at two points with known separation. Future studies will apply these methods to the entire ST-5 data sct and expand to include horizontal ionospheric currents. ULF waves and geomagnetic field gradient analyses.

  1. Space Technology 5 observations of auroral field-aligned currents

    NASA Astrophysics Data System (ADS)

    Slavin, James

    During its three month long technology validation mission, Space Technology 5 (ST-5) returned high quality multi-point measurements of the near-Earth magnetic field. Its three micro-satellites were launched into a 300 x 4500 km, dawn - dusk, sun synchronous orbit (inclination = 105.6o) orbit with a period of 138 min by a Pegasus launch vehicle on March 22, 2006. The spacecraft were maintained in a "pearls on a sting" constellation with controlled spacings ranging from just over 5000 km down to under 50 km. The individual micro-satellites were 48 cm tall octagons with diameters of 50 cm. They were spin-stabilized at approximately 20 rpm at deployment and slowly spun-down to about 15 rpm by the end of the mission. Each spacecraft carried a miniature tri-axial fluxgate magnetometer (MAG) provided by the University of California at Los Angeles mounted at the end of a ultra-low mass 72 cm boom. These data allow, for the first time, the separation of temporal and spatial variations in field-aligned current (FAC) perturbations measured in low-Earth orbit on time scales of 10 sec to 10 min. The constellation measurements are used to directly determine field-aligned current sheet motion, thickness, and current density. Two multi-point methods for the inference of FAC current density that have not previously been possible in low-Earth orbit are demonstrated: 1) the "standard method," based upon s/c velocity, but corrected for FAC current sheet motion, and 2) the "gradiometer method" which uses simultaneous magnetic field measurements at two points with known separation. Future studies will apply these methods to the entire ST-5 data set and expand to include horizontal ionospheric currents, ULF waves and geomagnetic field gradient analyses.

  2. Quasistatic electric field structures and field-aligned currents in the polar cusp region

    NASA Astrophysics Data System (ADS)

    Jacobsen, K. S.; Moen, J. I.; Pedersen, A.

    2010-10-01

    Cluster data have been examined for quasi-stationary electric field structures and field-aligned currents (FACs) in the vicinity of the dayside cusp region. We have related the measurements to the Region 1/Region 2 (R1/R2) current system and the cusp current system. It has been theoretically proposed that the dayside R1 current may be located on open field lines, and experimental evidence has been shown for R1 currents partially on open field lines. We document that R1 currents may flow entirely on open field lines. The electric field structures are found to occur at plasma density gradients in the cusp. They are associated with strong FACs with current directions that are consistent with the cusp currents. This indicates that the electric field structures are closely coupled to the cusp current system. The electric equipotential structures linking the perpendicular electric fields seen at Cluster altitudes to field-aligned electric fields at lower altitudes fall into one of two categories: S shape or U shape. Both types are found at both the equatorward edge of the cusp ion dispersion and at the equatorward edge of injection events within the cusp. Previous studies in the nightside auroral region attributed the S-shaped potential structures to the boundary transition between the low-density polar cap and the high-density plasma sheet, concluding that the shape of the electric potential structure depends on whether the plasma populations on each side of the structure can support intense currents. This explanation is not applicable for the S-shaped structures observed in the dayside cusp region.

  3. Vertical coupling between troposphere and lower ionosphere by electric currents and fields at equatorial latitudes

    NASA Astrophysics Data System (ADS)

    Tonev, P. T.; Velinov, P. I. Y.

    2016-04-01

    Thunderstorms play significant role in the upward electrical coupling between the troposphere and lower ionosphere by quasi-static (QS) electric fields generated by quiet conditions (by slow variations of electric charges), as well as during lightning discharges when they can be strong enough to produce in the nighttime lower ionosphere sprites. Changes are caused in lower ionosphere by the QS electric fields before a sprite-producing lightning discharge which can play role in formation of the stronger sprite-driving transient QS electric fields due to lightning. These changes include electron heating, modifications of conductivity and electron density, etc. We demonstrate that such changes depend on the geomagnetic latitude determining the magnetic field lines inclination, and thus, the anisotropic conductivity. Our previous results show that the QS electric fields in the lower ionosphere above equatorial thunderstorms are much bigger and have larger horizontal extension than those generated at high and middle altitudes by otherwise same conditions. Now we estimate by modeling the electric currents and fields generated in lower ionosphere above equatorial thunderstorms of different horizontal dimensions during quiet periods and of their self-consistent effects to conductivity whose modifications can play role in formation of post-lightning sprite-producing electric fields. Specific electric currents configurations and distributions of related electric fields are estimated first by ambient conductivity. Then, these are evaluated self-consistently with conductivity modification. The electric currents are re-oriented above ~85 km and flow in a narrow horizontal layer where they dense. Respectively, the electric fields and their effect on conductivity have much larger horizontal scale than at middle latitudes (few hundred of kilometers). Horizontally large sources, such as mesoscale convective structures, cause enhancements of electric fields and their effects. These

  4. Ring Current and Field Aligned Currents from Cluster-Swarm Observations

    NASA Astrophysics Data System (ADS)

    Yang, J.; Dunlop, M. W.; Yang, Y.; Xiong, C.; Shen, C.; Luhr, H.; Bogdanova, Y.; Olsen, N.; Zhang, Q. H.; Cao, J.; Ritter, P.; Masson, A.; Carr, C.; Haagmans, R.

    2015-12-01

    We explore the capability of Swarm-Cluster coordination for probing the behavior of the field aligned currents (FAC) adjacent to the ring current (RC) at medium and low orbits and show statistical analysis of the local time variation of R1/R2 FACs. The RC and connecting R2 FACs influence the geomagnetic field at low Earth orbit (LEO) and are sampled in situ by the four Cluster spacecraft. Coordination of the configuration of three Swarm spacecraft configurations with the constellation of the four Cluster spacecraft is possible; providing a set of distributed, multi-point measurements covering this region. Particular events showing close coordination of all spacecraft are considered during the start of the Swarm operations. We report here preliminary results of joint signatures of R1 and R2 FACs and demonstrate the use and application of new analysis techniques derived from the calculation of curl B and magnetic gradients to compare estimates of the current distributions. Multi-spacecraft analysis can access perpendicular currents associated with the FAC signatures at the Swam locations. We also show preliminary statistical results of FAC correlations between Swarm spacecraft to reveal local time behaviour. For context, we identify the associated auroral boundaries determine from FAC intensity gradients in order to help interpret and resolve the R1 and R2 FACs. We also show preliminary results of an extended survey of the ring current crossings for different years, using estimates of the local current density, field curvature and total current.

  5. Ring Current and Field Aligned Currents from Cluster-Swarm Observations

    NASA Astrophysics Data System (ADS)

    Dunlop, Malcolm; Yang, Junying; Yang, Yanyan; Xiong, Chao; Lühr, Hermann; Finlay, Christopher C.; Olsen, Nils; Shen, Chao; Bogdanova, Yulia. V.; Zhang, Qinghe; Cao, Jinbin; Ritter, Patricia; Masson, Arnaud; Carr, Chris; Haagmans, Roger

    2016-04-01

    We explore the capability of Swarm-Cluster coordination for probing the behavior of the field aligned currents (FAC) adjacent to the ring current (RC) at medium and low orbits and show statistical analysis of the local time variation of R1/R2 FACs. The RC and connecting R2 FACs influence the geomagnetic field at low Earth orbit (LEO) and are sampled in situ by the four Cluster spacecraft. Coordination of the configuration of three Swarm spacecraft configurations with the constellation of the four Cluster spacecraft is possible; providing a set of distributed, multi-point measurements covering this region. Particular events showing close coordination of all spacecraft are considered during the start of the Swarm operations. We report here preliminary results of joint signatures of R1 and R2 FACs and demonstrate the use and application of new analysis techniques derived from the calculation of curl B and magnetic gradients to compare estimates of the current distributions. Multi-spacecraft analysis can access perpendicular currents associated with the FAC signatures at the Swam locations. For context, we identify the associated auroral boundaries determine from FAC intensity gradients in order to help interpret and resolve the R1 and R2 FACs. We also show preliminary results of an extended survey of the ring current crossings for different years, using estimates of the local current density, field curvature and total current.

  6. Charges and Fields in a Current-Carrying Wire

    ERIC Educational Resources Information Center

    Redzic, Dragan V.

    2012-01-01

    Charges and fields in a straight, infinite, cylindrical wire carrying a steady current are determined in the rest frames of ions and electrons, starting from the standard assumption that the net charge per unit length is zero in the lattice frame and taking into account a self-induced pinch effect. The analysis presented illustrates the mutual…

  7. Teaching Direct Current Theory Using a Field Model

    ERIC Educational Resources Information Center

    Stocklmayer, Susan

    2010-01-01

    Principles of direct current have long been recognised in the literature as presenting difficulties for learners. Most of these difficulties have been reported in the context of the traditional electron flow model. In this paper, an alternative approach for high school students using a field model is explored. Findings from a range of short pilot…

  8. Effect of the carrier-envelope phase of the driving laser field on the high-order harmonic attosecond pulse

    SciTech Connect

    Zeng Zhinan; Li Ruxin; Yu Wei; Xu Zhizhan

    2003-01-01

    The effect of the carrier-envelope phase of a few-cycle driving laser field on the generation and measurement of high-order harmonic attosecond pulses is investigated theoretically. We find that the position of the generated attosecond soft-x-ray pulse in the cutoff region is locked to the oscillation of the driving laser field, but not to the envelope of the laser pulse. This property ensures the success of the width measurement of an attosecond soft-x-ray pulse based on the cross correlation between the attosecond pulse and its driving laser pulse [M. Hentschel et al., Nature (London) 414, 509 (2001)]. However, there still exists a timing jitter of the order of tens of attoseconds between the attosecond pulse and its driving laser field. We also propose a method to detect the carrier-envelope phase of the driving laser field by measuring the spatial distribution of the photoelectrons induced by the attosecond soft-x-ray pulse and its driving laser pulse.

  9. Large Scale High-Latitude Ionospheric Electrodynamic Fields and Currents

    NASA Astrophysics Data System (ADS)

    Lu, Gang

    2016-07-01

    This paper provides an overview as well as the application of the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure. AMIE synthesizes observations from various ground-based and space-born instruments to derive global patterns of ionospheric conductance, electric fields, ionospheric equivalent current, horizontal currents, field-aligned currents, and other related electrodynamic fields simultaneously. Examples are presented to illustrate the effects of the different data inputs on the AMIE outputs. The AMIE patterns derived from ground magnetometer data are generally similar to those derived from satellite magnetometer data. But ground magnetometer data yield a cross-polar potential drop that is about 15-45 % smaller than that derived from satellite magnetometer data. Ground magnetometers also grossly underestimate the magnetic perturbations in space when compared with the in situ satellite magnetometer data. However, when satellite magnetometer data are employed, AMIE is able to replicate the observed magnetic perturbations along the satellite tracks with a mean root-mean-square (RMS) error of 17-21 %. In addition to derive snapshots of ionospheric electrodynamic fields, the utility of AMIE can be easily expanded to obtain the average distributions of these fields along with their associated variability. Such information should be valuable to the analysis and interpretation of the Swarm observations.

  10. Unconventional pilot steam drive, tar V sand, Long Beach unit, Wilmington Field, CA

    SciTech Connect

    Jung, K.D.

    1984-04-01

    This paper reviews the design, implementation and history of the unconventional pilot steam drive (greater than 2,500 ft measured depth) that has been underway since December 24, 1980 in the Tar reservoir in the Long Beach Unit, Wilmington Field, Los Angeles County, California. This paper describes the project through November 30, 1983. The Tar V reservoir is a series of interbedded sands, siltstones and shales in the Middle Repetto formation of lower Pliocene age. The Tar V reservoir in the Long Beach Unit is approximately 200 acres in areal extent, has a vertical gross thickness of 185 ft and a maximum vertical net oil sand thickness of 90 ft comprised of 8 to 10 separate sand units. Oil in place is estimated at 27 MMbbl of stock tank oil. The study area is 9.2 acres in areal extent with an average net oil sand thickness of 81.7 ft. The pilot steam drive was originally installed as an isolated 5.6 acre inverted 5-spot pattern.

  11. Equilibrium drives of the low and high field side n = 2 plasma response and impact on global confinement

    DOE PAGESBeta

    Paz-Soldan, C.; Logan, N. C.; Haskey, S. R.; Nazikian, R.; Strait, E. J.; Chen, X.; Ferraro, N. M.; King, J. D.; Lyons, B. C.; Park, J. -K.

    2016-03-31

    The nature of the multi-modal n=2 plasma response and its impact on global confinement is studied as a function of the axisymmetric equilibrium pressure, edge safety factor, collisionality, and L-versus H-mode conditions. Varying the relative phase (ΔΦUL) between upper and lower in-vessel coils demonstrates that different n=2 poloidal spectra preferentially excite different plasma responses. These different plasma response modes are preferentially detected on the tokamak high-field side (HFS) or low-field side (LFS) midplanes, have different radial extents, couple differently to the resonant surfaces, and have variable impacts on edge stability and global confinement. In all equilibrium conditions studied, the observedmore » confinement degradation shares the same ΔΦUL dependence as the coupling to the resonant surfaces given by both ideal (IPEC) and resistive (MARS-F) MHD computation. Varying the edge safety factor shifts the equilibrium field-line pitch and thus the ΔΦUL dependence of both the global confinement and the n=2 magnetic response. As edge safety factor is varied, modeling finds that the HFS response (but not the LFS response), the resonant surface coupling, and the edge displacements near the X-point all share the same ΔΦUL dependence. The LFS response magnitude is strongly sensitive to the core pressure and is insensitive to the collisionality and edge safety factor. This indicates that the LFS measurements are primarily sensitive to a pressure-driven kink-ballooning mode that couples to the core plasma. MHD modeling accurately reproduces these (and indeed all) LFS experimental trends and supports this interpretation. In contrast to the LFS, the HFS magnetic response and correlated global confinement impact is unchanged with plasma pressure, but is strongly reduced in high collisionality conditions in both H- and L-mode. This experimentally suggests the bootstrap current drives the HFS response through the kink-peeling mode drive, though

  12. Improved critical current in confined superconductors in parallel field configuration

    NASA Astrophysics Data System (ADS)

    Glatz, Andreas; Aronson, Igor; Wang, Yonglei; Xiao, Zhili

    2015-03-01

    We present results on the re-entrance of the superconducting state in systems placed into a magnetic field parallel to the applied current. In experiments it was observed that the magneto-resistance first increases with magnetic field, but at higher field drops again such that superconductivity is recovered. This effect is strongly temperature dependent and can lead to a suppression of resistance below the measurable threshold over a range of a few kG. We study the vortex dynamics and magneto-resistance in this situation in the framework of a large-scale time-dependent Ginzburg Landau simulation. A small external current as well as the magnetic field are applied in the x-direction, the latter is then ramped up. Our simulations reproduce this effect and reveal the mechanism for the observed behavior: the intermediate resistive state is due to a vortex instability leading to an unwinding of twisted vortex configurations. This leads to a periodic dynamic resistive state. When the field increases these instabilities get stabilized due to a higher vortex density and the resistance drops upon increasing the magnetic field. Work was supported by the Scientific Discovery through Advanced Computing (SciDAC) program funded by U.S. Department of Energy, Office of Science, Advanced Scientific Computing Research and Basic Energy Sciences, and by the Office of Science, Materials Sc.

  13. Electric Field Influence on Driving the Storm-Time Inner Magnetosphere

    NASA Astrophysics Data System (ADS)

    Zaharia, S. G.; Jordanova, V. K.; MacDonald, E.; Reeves, G. D.

    2013-05-01

    We present initial numerical simulation results of the storm-time near-Earth magnetosphere obtained with our newly improved self-consistent model, RAM-SCB. The model represents a 2-way coupling of the kinetic ring current-atmosphere interactions model (RAM) with an Euler potential-based 3D plasma equilibrium code. In our approach, the magnetic field is computed in force balance with the anisotropic pressures in RAM (anisotropy being critically important for wave excitation), and then returned to RAM to guide the particle dynamics. RAM-SCB thus properly treats both the kinetic drift physics crucial in the inner magnetosphere (where gradient/curvature drifts are important) and the self-consistent interaction between plasma and magnetic field (required due to the strong depressions in the field during storms that affect the plasma evolution). Recent improvements in RAM-SCB are the expansion of the boundary from geosynchronous location to 9 RE from Earth and the first-time inclusion of a self-consistent electric field, obtained by closing the field-aligned currents in the ionosphere. This extension makes RAM-SCB the most physically complete inner magnetosphere model in the community, with fully self-consistent 3D magnetic and electric fields. The presentation will analyze, using storm-time simulations of the near-Earth magnetosphere with the improved model, the effect of the self-consistent electric field on ring current dynamics, in comparison with empirical electric field models such as Weimer 01 and Volland/Stern models. We will also compare model results with observations (including global indices such as Dst, but also plasma and field data from available spacecraft, such as Polar, Cluster, GOES and the recently launched Van Allen Probes).

  14. Writing and erasing of temporal cavity solitons by direct phase modulation of the cavity driving field.

    PubMed

    Jang, Jae K; Erkintalo, Miro; Murdoch, Stuart G; Coen, Stéphane

    2015-10-15

    Temporal cavity solitons (CSs) are persisting pulses of light that can manifest themselves in continuously driven passive resonators, such as macroscopic fiber ring cavities and monolithic microresonators. Experiments so far have demonstrated two techniques for their excitation, yet both possess drawbacks in the form of system complexity or lack of control over soliton positioning. Here we experimentally demonstrate a new CS writing scheme that alleviates these deficiencies. Specifically, we show that temporal CSs can be excited at arbitrary positions through direct phase modulation of the cavity driving field, and that this technique also allows existing CSs to be selectively erased. Our results constitute the first experimental demonstration of temporal CS excitation via direct phase modulation, as well as their selective erasure (by any means). These advances reduce the complexity of CS excitation and could lead to controlled pulse generation in monolithic microresonators. PMID:26469612

  15. INCREASED STABLE BETA IN DIII-D BY SUPPRESSION OF A NEOCLASSICAL TEARING MODE USING ELECTRON CYCLOTRON CURRENT DRIVE AND ACTIVE FEEDBACK

    SciTech Connect

    LAHAYE,RJ; HUMPHREYS,DA; LOHR,J; LUCE,TC; PERKINS,FW; PETTY,CC; PRATER,R; STRAIT,EJ

    2002-09-01

    OAK A271 INCREASED STABLE BETA IN DIII-D BY SUPPRESSION OF A NEOCLASSICAL TEARING MODE USING ELECTRON CYCLOTRON CURRENT DRIVE AND ACTIVE FEEDBACK. In DIII-D, the first real-time active control of the electron cyclotron current drive stabilization of a neoclassical tearing mode (here m/n=3/2) is demonstrated. The plasma control system is put into a search and suppress mode to align the ECCD with the island by making either small rigid radial position shifts (of order 1 cm) of the entire plasma (and thus the island) or small changes in toroidal field (of order 0.5%) which radially moves the second harmonic resonance location (and thus the rf current drive). The optimum position minimizes the real-time mode amplitude signal and stabilization occurs despite changes in island location from discharge-to-discharge or from time-to-time. When the neutral beam heating power is programmed to rise after mode suppression by the ECCD, the plasma pressure increases above the peak at the onset of the neoclassical tearing mode until the magnetic island reappears due to the ECCD no longer being on the optimal position. Real-time tracking of the change in location of q=3/2 due to the Shafranov shift with increasing beta is necessary to position the ECCD in the absence of a mode so that higher stable beta can be sustained. The control techniques developed for the m/n=3/2 NTM are also being applied to the more deleterious m/n-2/1 NTM. For the first time in any tokamak, an m/n=2/1 mode has been completely suppressed using radially localized off-axis ECCD.

  16. Quasistatic electric field structures and field-aligned currents in the polar cusp region

    NASA Astrophysics Data System (ADS)

    Jacobsen, Knut; Moen, Joran; Pedersen, Arne

    2010-05-01

    Quasistatic electric field structures in the vicinity of the cusp have been studied using Cluster data. There are two categories of electric potential structures, S-shaped and U-shaped. In previous studies in the nightside auroral region, the S-shaped potential was uniquely related to the boundary transition between low density and high density plasma regimes, leading to the conclusion that the electric field profile depends on whether the plasma populations on each side of the boundary can support intense field-aligned and Pedersen currents. In this study in the dayside cusp this is not the case, and a different explanation has to be sought. Most electric field structures are associated with the start of the cusp ion dispersion or with injection signatures within the cusp, and the field-aligned currents associated with these structures are found to be consistent with the cusp currents expected for the IMF By polarity at the time. This indicates that the electric field structures are generated by the cusp current system, or modified by the cusp current system to be consistent with the required currents. Furthermore, we provide firm evidence for the dayside Region 1 current to be located on open field lines, which have been postulated but to our knowledge heretofore not experimentally verified.

  17. Determinants of the electric field during transcranial direct current stimulation.

    PubMed

    Opitz, Alexander; Paulus, Walter; Will, Susanne; Antunes, Andre; Thielscher, Axel

    2015-04-01

    Transcranial direct current stimulation (tDCS) causes a complex spatial distribution of the electric current flow in the head which hampers the accurate localization of the stimulated brain areas. In this study we show how various anatomical features systematically shape the electric field distribution in the brain during tDCS. We constructed anatomically realistic finite element (FEM) models of two individual heads including conductivity anisotropy and different skull layers. We simulated a widely employed electrode montage to induce motor cortex plasticity and moved the stimulating electrode over the motor cortex in small steps to examine the resulting changes of the electric field distribution in the underlying cortex. We examined the effect of skull thickness and composition on the passing currents showing that thinner skull regions lead to higher electric field strengths. This effect is counteracted by a larger proportion of higher conducting spongy bone in thicker regions leading to a more homogenous current over the skull. Using a multiple regression model we could identify key factors that determine the field distribution to a significant extent, namely the thicknesses of the cerebrospinal fluid and the skull, the gyral depth and the distance to the anode and cathode. These factors account for up to 50% of the spatial variation of the electric field strength. Further, we demonstrate that individual anatomical factors can lead to stimulation "hotspots" which are partly resistant to electrode positioning. Our results give valuable novel insights in the biophysical foundation of tDCS and highlight the importance to account for individual anatomical factors when choosing an electrode montage. PMID:25613437

  18. Current Filament Merging Driven by Cross-Field Plasma Flows

    NASA Astrophysics Data System (ADS)

    Vincena, S.; Gekelman, W.; Collette, A.; Cooper, C.

    2007-05-01

    The study of the penetration and mixing of plasmas with differing density, temperature, and species composition has wide-ranging applicability to space plasma systems such as coronal mass ejections, magnetic clouds, galactic jets, and super novae. In these laboratory experiments, two high-beta plasmas are created using a pair of 1.5J, 8ns lasers which strike facing solid carbon targets at right angles to the background magnetic field. The targets are immersed within a low-beta, helium plasma and the lasers are aimed to produce head-on, or glancing collisions. The cylindrical background plasma is 17 m long (10 parallel Alfven wavelengths) by 60 cm wide (300 ρi or 175 c/ωpe). The laser-produced plasmas (LPPs) expand as diamagnetic cavities, become polarized, and then E× B drift at speeds of Mach 10 (v/cs) across the field. As they do so, the ambient plasma facilitates charge separation between energetic LPP electrons and relatively unmagnetized 1keV LPP ions. One of the many resulting dynamic features is the release of a continuous stream of electrons from each LPP. Downstream from the LPP merging, the fast electron current filaments come together with reconnection-like X-line field patterns and eventually merge with a broadband spectrum of electromagnetic (whistler wave) fluctuations. Near-miss LPP collisions result in elongated current sheet formations and the shedding of magnetic field eddies. Current sheet thicknesses are a few electron inertial lengths and the width is approximately one ion inertial length. These results will be presented along with 3D measurements of the magnetic fields and the underlying current systems. These experiments are conducted at the Basic Plasma Science Facility, in the upgraded Large Plasma Device (LAPD) located at the University of California, Los Angeles, USA. This work is funded by the United States Department of Energy and the National Science Foundation.

  19. High-latitude field-aligned current sources and induced electric fields

    NASA Technical Reports Server (NTRS)

    Barbosa, D. D.

    1979-01-01

    Using a simple, planar model of the high latitude ionosphere with an enhanced conductivity auroral ring, the electric potential is computed for a pair of field-aligned current sheets inferred from observations. The relationship of various characteristics of the electric potential pattern to features of the field-aligned current distribution are elucidated in the context of a generalized field-aligned current Fourier analysis. On the basis of the analysis and observations to date, it is concluded that boundary layer dynamo action is the prevalent mechanism in the solar wind/magnetosphere/ionosphere interaction.

  20. Gandhi and the Environmental Consequences of the Current Drive to Industrialization and Modernization.

    ERIC Educational Resources Information Center

    Sinha, Rajiv K.

    1993-01-01

    Discusses Gandhi's developmental philosophy that small is beautiful in relation to current issues in ecological conservation. Issues include environmental education, economic development, rural development, natural farming, and Gandhi's philosophy among Western nations. (MDH)

  1. Neoclassical tearing modes in DIII-D and calculations of the stabilizing effects of localized electron cyclotron current drive

    SciTech Connect

    Prater, R.; Bernabei, S.; Harvey, R. W.; La Haye, R. J.; Lin-Liu, Y. R.; Lohr, J.; Perkins, F. W.; Wong, K.-L.

    1999-09-20

    Neoclassical tearing modes are found to limit the achievable beta in many high performance discharges in DIII-D. Electron cyclotron current drive within the magnetic islands formed as the tearing mode grows has been proposed as a means of stabilizing these modes or reducing their amplitude, thereby increasing the beta limit by a factor around 1.5. Some experimental success has been obtained previously on Asdex-U. Here we examine the parameter range in DIII-D in which this effect can best be studied. (c) 1999 American Institute of Physics.

  2. Neoclassical tearing modes in DIII-D and calculations of the stabilizing effects of localized electron cyclotron current drive

    SciTech Connect

    Prater, R.; La Haye, R.J.; Lin-Liu, Y.R.; Lohr, J.; Bernabei, S.; Perkins, F.W.; Wong, K.L.; Harvey, R.W.

    1999-05-01

    Neoclassical tearing modes are found to limit the achievable beta in many high performance discharges in DIII-D. Electron cyclotron current drive within the magnetic islands formed as the tearing mode grows has been proposed as a means of stabilizing these modes or reducing their amplitude, thereby increasing the beta limit by a factor around 1.5. Some experimental success has been obtained previously on Asdex-U. Here the authors examine the parameter range in DIII-C in which this effect can best be studied.

  3. Field evaluation of an electromagnetic current meter based vertical profiler

    NASA Astrophysics Data System (ADS)

    Hamblin, P. F.; Marmoush, Y. M. R.; Boyce, F. M.; Smith, A. A.

    1987-10-01

    A current profiler consisting of a vertical array of three electromagnetic current meters has been evaluated through an intercomparison of the three sensors, with reference to nearby current and wave data and by comparison to recent laboratory performance tests (Aubrey and Trowbridge, 1985). Mean flow estimates are too uncertain and variable to allow bottom boundary layer shear stress to be estimated by the conventional logarithmic law method. As well as unexplained sudden shifts in the mean speed response, the comparison with vector-averaged current meter data indicates possible long-term reduction in response due to fouling of the sensors by biological growth. The directional response was less sensitive to fouling effects. The oscillatory response on one occasion after field deployment for 17 days indicates a reduction in response from 41 to 45% at a period of oscillation of 3 s in a combined steady and oscillatory flow field. This study demonstrates that despite careful laboratory calibration, electromagnetic current meters are not at present suitable for quantitative study of dynamics of sediment resuspension in near-bottom shallow-water environments.

  4. Superconducting toroidal field coil current densities for the TFCX

    SciTech Connect

    Kalsi, S.S.; Hooper, R.J.

    1985-04-01

    A major goal of the Tokamak Fusion Core Experiment (TFCX) study was to minimize the size of the device and achieve lowest cost. Two key factors influencing the size of the device employing superconducting magnets are toroidal field (TF) winding current density and its nuclear heat load withstand capability. Lower winding current density requires larger radial build of the winding pack. Likewise, lower allowable nuclear heating in the winding requires larger shield thickness between the plasma and coil. In order to achieve a low-cost device, it is essential to maximize the winding's current density and nuclear heating withhstand capability. To meet the above objective, the TFCX design specification adopted as goals a nominal winding current density of 3500 A/cm/sup 2/ with 10-T peak field at the winding and peak nuclear heat load limits of 1 MW/cm/sup 3/ for the nominal design and 50 MW/cm/sup 3/ for an advanced design. This study developed justification for these current density and nuclear heat load limits.

  5. Driving with Central Visual Field Loss II: How Scotomas above or below the Preferred Retinal Locus (PRL) Affect Hazard Detection in a Driving Simulator

    PubMed Central

    Bowers, Alex R.; Goldstein, Robert; Peli, Eli

    2015-01-01

    We determined whether binocular central scotomas above or below the preferred retinal locus affect detection of hazards (pedestrians) approaching from the side. Seven participants with central field loss (CFL), and seven age-and sex-matched controls with normal vision (NV), each completed two sessions of 5 test drives (each approximately 10 minutes long) in a driving simulator. Participants pressed the horn when detecting pedestrians that appeared at one of four eccentricities (-14°, -4°, left, 4°, or 14°, right, relative to car heading). Pedestrians walked or ran towards the travel lane on a collision course with the participant’s vehicle, thus remaining in the same area of the visual field, assuming participant's steady forward gaze down the travel lane. Detection rates were nearly 100% for all participants. CFL participant reaction times were longer (median 2.27s, 95% CI 2.13 to 2.47) than NVs (median 1.17s, 95%CI 1.10 to 2.13; difference p<0.01), and CFL participants would have been unable to stop for 21% of pedestrians, compared with 3% for NV, p<0.001. Although the scotomas were not expected to obscure pedestrian hazards, gaze tracking revealed that scotomas did sometimes interfere with detection; late reactions usually occurred when pedestrians were entirely or partially obscured by the scotoma (time obscured correlated with reaction times, r = 0.57, p<0.001). We previously showed that scotomas lateral to the preferred retinal locus delay reaction times to a greater extent; however, taken together, the results of our studies suggest that any binocular CFL might negatively impact timely hazard detection while driving and should be a consideration when evaluating vision for driving. PMID:26332315

  6. Nuclear axial currents in chiral effective field theory

    DOE PAGESBeta

    Baroni, Alessandro; Girlanda, Luca; Pastore, Saori; Schiavilla, Rocco; Viviani, Michele

    2016-01-11

    Two-nucleon axial charge and current operators are derived in chiral effective field theory up to one loop. The derivation is based on time-ordered perturbation theory and accounts for cancellations between the contributions of irreducible diagrams and the contributions owing to nonstatic corrections from energy denominators of reducible diagrams. Ultraviolet divergencies associated with the loop corrections are isolated in dimensional regularization. The resulting axial current is finite and conserved in the chiral limit, while the axial charge requires renormalization. As a result, a complete set of contact terms for the axial charge up to the relevant order in the power countingmore » is constructed.« less

  7. Micro-gravity: current distributions creating a uniform force field

    NASA Astrophysics Data System (ADS)

    Vincent-Viry, O.; Mailfert, A.; Colteu, A.; Dael, A.; Gourdin, C.; Quettier, L.

    2001-02-01

    This paper presents two structures of superconducting coils able to give satisfactory solutions to the problem of generation of uniform field of high magnetic forces. The first structure is modeled by the use of purely surface current densities, whereas the second one can be described with volume current densities. Both of these structures proceed from the study of a particular expression of the complex magnetic potential introduced for structures with two-dimensional geometry. This work is carried out in a research collaboration between the GREEN and the DSM-DAPNIA department of the CEA Saclay.

  8. New developments in the collection of stray current field data

    SciTech Connect

    Szeliga, M.J.; Silhan, J.

    1994-12-31

    The collection of accurate stray current field data on existing utility piping has been a serious concern especially in areas of new transit systems. Extensive testing was performed on existing water piping in conjunction with the construction and operation of the new Baltimore Light Rail Transit System. Testing was performed with instruments connected both to piping appurtenances such as hydrants and valves as well as to specially installed test facilities. The test results that were obtained during these stray current investigations revealed critical information. This information included requirements for future testing as well as important information about utility systems in the vicinity of transit systems.

  9. Lightning Return-Stroke Current Waveforms Aloft, From Measured Field Change, Current, and Channel Geometry

    NASA Technical Reports Server (NTRS)

    Willett, J. C.; LeVine, D. M.

    2002-01-01

    Direct current measurements are available near the attachment point from both natural cloud-to-ground lightning and rocket-triggered lightning, but little is known about the rise time and peak amplitude of return-stroke currents aloft. We present, as functions of height, current amplitudes, rise times, and effective propagation velocities that have been estimated with a novel remote-sensing technique from data on 24 subsequent return strokes in six different lightning flashes that were triggering at the NASA Kennedy Space Center, FL, during 1987. The unique feature of this data set is the stereo pairs of still photographs, from which three-dimensional channel geometries were determined previously. This has permitted us to calculate the fine structure of the electric-field-change (E) waveforms produced by these strokes, using the current waveforms measured at the channel base together with physically reasonable assumptions about the current distributions aloft. The computed waveforms have been compared with observed E waveforms from the same strokes, and our assumptions have been adjusted to maximize agreement. In spite of the non-uniqueness of solutions derived by this technique, several conclusions seem inescapable: 1) The effective propagation speed of the current up the channel is usually significantly (but not unreasonably) faster than the two-dimensional velocity measured by a streak camera for 14 of these strokes. 2) Given the deduced propagation speed, the peak amplitude of the current waveform often must decrease dramatically with height to prevent the electric field from being over-predicted. 3) The rise time of the current wave front must always increase rapidly with height in order to keep the fine structure of the calculated field consistent with the observations.

  10. Cathode fall model and current-voltage characteristics of field emission driven direct current microplasmas

    SciTech Connect

    Venkattraman, Ayyaswamy

    2013-11-15

    The post-breakdown characteristics of field emission driven microplasma are studied theoretically and numerically. A cathode fall model assuming a linearly varying electric field is used to obtain equations governing the operation of steady state field emission driven microplasmas. The results obtained from the model by solving these equations are compared with particle-in-cell with Monte Carlo collisions simulation results for parameters including the plasma potential, cathode fall thickness, ion number density in the cathode fall, and current density vs voltage curves. The model shows good overall agreement with the simulations but results in slightly overpredicted values for the plasma potential and the cathode fall thickness attributed to the assumed electric field profile. The current density vs voltage curves obtained show an arc region characterized by negative slope as well as an abnormal glow discharge characterized by a positive slope in gaps as small as 10 μm operating at atmospheric pressure. The model also retrieves the traditional macroscale current vs voltage theory in the absence of field emission.

  11. Optimal control of electric drive with simultaneous control inputs for motor current and flux

    NASA Astrophysics Data System (ADS)

    Pansyuk, V. I.

    1984-08-01

    A detailed mathematical analysis of the optimal control of a dc electric drive with a variable magnetic flux is presented. Expressions are found for the optimal controller. When this controller uses real time microprocessors control hardware, formulas are also derived for the various portions of the optimal process as well as the logic expressions for the switching of these parts of the process. The resulting optimal process differs from previous determinations in that the braking portion, when a resistance moment is present, contains a free run-down (passive braking) region, before and after which there can be regions of active braking, when the motor produces an electromagnetic moment. In one numerical example of step dc motor control, which is used to compare the optimal process found here with one developed earlier, power losses are found to be reduced by 5.44% with the new process. The entire solution of the problem using the procedure presented here reduces to finding the conditional extremum of some function of several variables whose number is no greater than the dimensionality of the system and does not lead to a boundary value problem.

  12. Idealized model of polar cap currents, fields, and auroras

    NASA Technical Reports Server (NTRS)

    Cornwall, J. M.

    1985-01-01

    During periods of northward Bz, the electric field applied to the magnetosphere is generally opposite to that occurring during southward Bz and complicated patterns of convection result, showing some features reversed in comparison with the southward Bz case. A study is conducted of a simple generalization of early work on idealized convection models, which allows for coexistence of sunward convection over the central polar cap and antisunward convection elsewhere in the cap. The present model, valid for By approximately 0, has a four-cell convection pattern and is based on the combination of ionospheric current conservation with a relation between parallel auroral currents and parallel potential drops. Global magnetospheric issues involving, e.g., reconnection are not considered. The central result of this paper is an expression giving the parallel potential drop for polar cap auroras (with By approximately 0) in terms of the polar cap convection field profile.

  13. Synthesis models of dayside field-aligned currents for strong interplanetary magnetic field By

    NASA Astrophysics Data System (ADS)

    Watanabe, Masakazu; Iijima, Takesi; Rich, Frederick J.

    1996-06-01

    Using particle and magnetic field data acquired with DMSP-F6 and DMSP-F7 satellites, we have investigated interplanetary magnetic field (IMF) By dependence of the global pattern of plasma regime and field-aligned currents (FACs) on dayside high latitudes during strong IMF By (averaged |By|>3.7 nT) and geomagnetically disturbed (mainly IMF Bz<0) periods. From particle data we have identified five plasma regimes: inner plasma sheet, outer plasma sheet, cleft, cusp, and mantle. All the plasma domains except the inner plasma sheet show By dependence in spatial distribution. Region 1 and ``traditional cusp'' currents appear in cusp/mantle domains, which we call midday region 1 and region 0 currents, respectively, in this paper. These currents perfectly reverse their flow directions depending on IMF By polarity. Traditional region 1 currents occurring in cleft and outer plasma sheet almost always flow into the ionosphere in the prenoon sector and flow away from the ionosphere in the postnoon sector regardless of By polarity. Thus the midday region 1 and region 0 current system that appears at local noon is not a simple continuation of flankside region 1/region 2 current system. Midday region 1 and region 0 currents are not necessarily balanced in intensity; region 0 current intensity occasionally exceeds midday region 1 current intensity. Furthermore, intensity imbalance also appears in cleft-associated region 1 currents; that is, region 1 current in the farside cleft from the reconnection site (``downstreamside'' cleft) is larger than region 1 current in the nearside cleft (``upstreamside'' cleft). On the basis of these observational facts we discuss the source mechanisms of the dayside FAC system: (1) directly coupled generation of region 0 and midday region 1 current in the cusp/mantle domains around noon and (2) generation of extra region 0 current in the tail magnetopause which is connected to the extra downstreamside cleft-associated region 1 current.

  14. Rotary motion driven by a direct current electric field

    NASA Astrophysics Data System (ADS)

    Takinoue, Masahiro; Atsumi, Yu; Yoshikawa, Kenichi

    2010-03-01

    We report the rotary motion of an aqueous microdroplet in an oil phase under a stationary direct current electric field. A droplet exhibits rotary motion under a suitable geometrical arrangement of positive and negative electrodes. Rotary motion appears above a certain critical electric potential and its frequency increases with an increase in the potential. A simple theoretical model is proposed to describe the occurrence of this rotary motion, together with an argument for the future expansion of this micro rotary motor system.

  15. Suppression of sawtooth oscillations by lower-hybrid current drive in the ASDEX tokamak

    NASA Astrophysics Data System (ADS)

    Söldner, F. X.; McCormick, K.; Eckhartt, D.; Kornherr, M.; Leuterer, F.; Bartiromo, R.; Becker, G.; Bosch, H. S.; Brocken, H.; Derfler, H.; Eberhagen, A.; Fussmann, G.; Gehre, O.; Gernhardt, J.; Gierke, G. V.; Giuliana, A.; Glock, E.; Gruber, O.; Haas, G.; Hesse, M.; Hofmann, J.; Izvozchikov, A.; Janeschitz, G.; Karger, F.; Keilhacker, M.; Klüber, O.; Lackner, K.; Lenoci, M.; Lisitano, G.; Mast, F.; Mayer, H. M.; Meisel, D.; Mertens, V.; Müller, E. R.; Münich, M.; Murmann, H.; Niedermeyer, H.; Pietrzyk, A.; Poschenrieder, W.; Rapp, H.; Riedler, H.; Röhr, H.; Ryter, F.; Schmitter, K. H.; Schneider, F.; Setzensack, C.; Siller, G.; Smeulders, P.; Speth, E.; Steuer, K.-H.; Vien, T.; Vollmer, O.; Wagner, F.; Woyna, F. V.; Zasche, D.

    1986-09-01

    The sawtooth oscillations in tokamak discharges with Ohmic and neutral-beam heating could be suppressed when a large part of the plasma current was driven by lower-hybrid waves (IHF/Ip~=0.5). The stabilization is due to a flattening of the current profile j(r) and an increase of q(0) above 1. Higher central electron temperatures are obtained with neutral-beam heating if the sawteeth are stabilized. The increase in total energy content in this case was 30% higher than in the presence of sawteeth.

  16. Research on Field Emission and Dark Current in ILC Cavities

    SciTech Connect

    Liu, Kexin; Li, Yongming; Palczewski, Ari; Geng, Rongli

    2013-09-01

    Field emission and dark current are issues of concern for SRF cavity performance and SRF linac operation. Complete understanding and reliable control of the issue are still needed, especially in full-scale multi-cell cavities. Our work aims at developing a generic procedure for finding an active field emitter in a multi-cell cavity and benchmarking the procedure through cavity vertical test. Our ultimate goal is to provide feedback to cavity preparation and cavity string assembly in order to reduce or eliminate filed emission in SRF cavities. Systematic analysis of behaviors of field emitted electrons is obtained by ACE3P developed by SLAC. Experimental benchmark of the procedure was carried out in a 9-cell cavity vertical test at JLab. The energy spectrum of Bremsstrahlung X-rays is measured using a NaI(Tl) detector. The end-point energy in the X-ray energy spectrum is taken as the highest kinetic electron energy to predict longitudinal position of the active field emitter. Angular location of the field emitter is determined by an array of silicon diodes around irises of the cavity. High-resolution optical inspection was conducted at the predicted field emitter location.

  17. Polarization induced Z2 and Chern topological phases in a periodically driving field

    PubMed Central

    Pi, Shu-Ting; Savrasov, Sergey

    2016-01-01

    Z2 and Chern topological phases such as newly discovered quantum spin Hall and original quantum Hall states hardly both co–exist in a single material due to their contradictory requirement on the time–reversal symmetry (TRS). We show that although the TRS is broken in systems with a periodically driving field, an effective TRS can still be defined provided the ac–field is linearly polarized or certain other conditions are satisfied. The controllable TRS provides us a route to manipulate contradictory phases by tuning the polarization. To demonstrate the idea, we consider a tight-binding model that is relevant to several monolayered materials as a benchmark system. Our calculation shows not only topological Z2 to Chern phase transition occurs but rich Chern phases are also observed. In addition, we also discussed the realization of our proposal in real materials, such as spin-orbit coupled graphene and crystal Bismuth. This opens the possibility of manipulating various topological phases in a single material and can be a promising approach to engineer new electronic states of matter. PMID:26965181

  18. Polarization induced Z2 and Chern topological phases in a periodically driving field.

    PubMed

    Pi, Shu-Ting; Savrasov, Sergey

    2016-01-01

    Z2 and Chern topological phases such as newly discovered quantum spin Hall and original quantum Hall states hardly both co-exist in a single material due to their contradictory requirement on the time-reversal symmetry (TRS). We show that although the TRS is broken in systems with a periodically driving field, an effective TRS can still be defined provided the ac-field is linearly polarized or certain other conditions are satisfied. The controllable TRS provides us a route to manipulate contradictory phases by tuning the polarization. To demonstrate the idea, we consider a tight-binding model that is relevant to several monolayered materials as a benchmark system. Our calculation shows not only topological Z2 to Chern phase transition occurs but rich Chern phases are also observed. In addition, we also discussed the realization of our proposal in real materials, such as spin-orbit coupled graphene and crystal Bismuth. This opens the possibility of manipulating various topological phases in a single material and can be a promising approach to engineer new electronic states of matter. PMID:26965181

  19. Polarization induced Z2 and Chern topological phases in a periodically driving field

    NASA Astrophysics Data System (ADS)

    Pi, Shu-Ting; Savrasov, Sergey

    2016-03-01

    Z2 and Chern topological phases such as newly discovered quantum spin Hall and original quantum Hall states hardly both co–exist in a single material due to their contradictory requirement on the time–reversal symmetry (TRS). We show that although the TRS is broken in systems with a periodically driving field, an effective TRS can still be defined provided the ac–field is linearly polarized or certain other conditions are satisfied. The controllable TRS provides us a route to manipulate contradictory phases by tuning the polarization. To demonstrate the idea, we consider a tight-binding model that is relevant to several monolayered materials as a benchmark system. Our calculation shows not only topological Z2 to Chern phase transition occurs but rich Chern phases are also observed. In addition, we also discussed the realization of our proposal in real materials, such as spin-orbit coupled graphene and crystal Bismuth. This opens the possibility of manipulating various topological phases in a single material and can be a promising approach to engineer new electronic states of matter.

  20. Axial current generation from electric field: chiral electric separation effect.

    PubMed

    Huang, Xu-Guang; Liao, Jinfeng

    2013-06-01

    We study a relativistic plasma containing charged chiral fermions in an external electric field. We show that with the presence of both vector and axial charge densities, the electric field can induce an axial current along its direction and thus cause chirality separation. We call it the chiral electric separation effect (CESE). On a very general basis, we argue that the strength of CESE is proportional to μ(V)μ(A) with μ(V) and μ(A) the chemical potentials for vector charge and axial charge. We then explicitly calculate this CESE conductivity coefficient in thermal QED at leading-log order. The CESE can manifest a new gapless wave mode propagating along the electric field. Potential observable effects of CESE in heavy-ion collisions are also discussed. PMID:25167486

  1. Magnetic field dependence of critical currents in superconducting polycrystals

    SciTech Connect

    Kugel, K.I.; Lisovskaya, T.Y. ); Mints, R.G. )

    1992-02-10

    The authors study the dependence of critical current j{sub c} on magnetic field H in superconducting polycrystals which are considered as system of superconducting crystallites (isotropic or anisotropic) with Josephson contacts between them. Isotropy or anisotropy of contacts depends on the orientation of their crystallographic axes relatively to edges of contact planes. In this paper it is shown that for a system of randomly oriented isotropic contacts, the dependence j{sub c}(H) in a relatively wide field range has the asymptotic form j{sub c} {approximately} (InH)/H{sup 2}. This differs drastically from j{sub c}(H) for single contacts. Anisotropy effects due to large differences in London penetration depth {lambda} values corresponding to external magnetic field directed along different axes are analyzed in detail. It is shown that for uniaxal crystals with {lambda}{sub 1} = {lambda}{sub 2} {lt} {lambda}{sub 3}, this anisotropy leads to the relation j{sub c} {approximately} {radical}{lambda}{sub 3}/{lambda}{sub 1} for chaotic orientation of crystallites. The form of j{sub c}(H) curves for two different orientations of the magnetic field relatively to the transport current through the sample is found.

  2. Low-latitude field-aligned currents deduced by Swarm

    NASA Astrophysics Data System (ADS)

    Lühr, Hermann; Kervalishvili, Guram; Rauberg, Jan

    2015-04-01

    ESA's constellation mission Swarm was successfully launched on 22 November 2013. The three satellites are orbiting the Earth at 470 km and 520 km altitude. The lower pair Swarm-A and C is flying side-by-side separated by only 1.4° in latitude. Magnetic field readings of this pair are used to determine for the first time field-aligned currents (FAC) uniquely in the ionosphere. Of particular interest for this presentation are FACs at low and equatorial latitudes. Indications for several of such current systems have been deduced from CHAMP observations. Examples to be studied are meridional and vertical currents driven by the F-region dynamo. They are expected to show opposite polarities between noon and sunset. Likewise there are FACs expected to balance the electric potential differences between the foci of the Sq current vortices in the two hemispheres, which should be most prominent during solstice seasons. Another example is the FAC associated with equatorial plasma bubbles. They are expected to flow along the walls of the electron density depleted volume. Due to the limited amount of suitable Swarm data we will focus on June solstice and September equinox 2014 for this presentation.

  3. Remote field eddy current detection of stress-corrosion cracks

    SciTech Connect

    Nestleroth, J.B.

    1990-02-01

    The feasibility of detecting stress-corrosion cracks (SSC) using the Remote Field Eddy Current (RFEC) technique was demonstrated. The RFEC technique interrogates the entire thickness of the pipe and is applicable for in-line inspection. If it can be shown that the RFEC technique is effective in detecting SSC, then the technique is an ideal method for detecting the defects of interest. A defect detection model is proposed for explaining the mechanism for crack detection. For axially oriented, closed cracks, such as SCC, the conventional defect detection model proved to be too simplistic and not applicable. Therefore, a new detection mode that examines the flow of circumferential eddy currents was developed based on experimental results. This model, though not rigorous, provides a general understanding of the applicability of the RFEC technique for finding SSC. The data from the cracks and various artificial defects is presented in three formats: isometric projections, pseudocolor images and line-of-sight data. Though only two cracks were found, the experimental results correlate well with the circumferential eddy current theory. A theoretical analysis of the effects of motion on the output signal of the receiver is presented. This analysis indicates that inspection speed of simple implementations may be limited to a few miles per hour. Remote field eddy current inspection has excellent potential for inspection of gas transmission lines for detecting stress corrosion cracks that should be further developed.

  4. Remote field eddy current defect interactions: Effects on the external field

    SciTech Connect

    Atherton, D.L.; Czura, W.M.; Mackintosh, D.D. . Dept. of Physics)

    1994-11-01

    Finite element calculations for the remote field eddy current (RFEC) through-wall inspection technique show that metal loss on either the inside or the outside affect the exterior field as well as the interior transmitted remote field. In ferromagnetic tubes, wall thinning decreases attenuation and phase lag, as found experimentally. In the nonferromagnetic pipe modeled, attenuation decreased but wall thinning increase the phase lag. The exterior field changes are attributed to inner surface reflections of the field diffusing from the exterior to the interior of the pipe.

  5. Polarization electric field in subalfvenic plasma jet under condition of field- aligned currents generation

    NASA Astrophysics Data System (ADS)

    Sobyanin, D.; Gavrilov, B.; Podgorny, I.

    The subalfvenic magnetized plasma jet propagating across the geomagnetic field generates field-aligned currents in the ionospheric plasma. As a result the transverse polarization electric field Ep =-VxB/c in the jet should be reduced (plasma jet depolarization). These phenomena are investigated in the laboratory experiment. It was revealed that the depolarization is accompanied by the appearing of the electric field E along the plasma velocity vector. The value of E is comparable with theaa transverse electric field. It results in the plasma jet deflection. The possibility of manifestation of these effects in the NORTH STAR Russian-American active rocket experiment is discussed.

  6. The simulation of hard x-ray images obtained during lower hybrid current drive on PBX-M

    SciTech Connect

    Goeler, S. von; Fishman, H.; Ignat, D.

    1994-10-01

    During lower hybrid current drive on PBX-M suprathermal electrons in the 30 to 150 keV range are generated. These electrons emit hard X-ray bremsstrahlung in collisions with plasma ions; the radiation creates images in a hard X-ray pinhole camera. In order to interpret the hard X-ray images, a computer simulation code has been written, the PBXRAY code. It represents an extension of the STEVENS code that calculates the free-free and free-bound radiation for non-Maxwellian relativistic electron tail distributions. The PBXRAY code provides the chord integration in the bean-shaped plasma geometry on PBX-M and integrates over photon energy. The simulations show that the location of the suprathermal electrons can be determined with an accuracy of approximately two centimeters in the plasma. In particular, the authors analyzed discharges whose characteristic ``hollow`` images indicate off-axis LH current drive. A comparison of images taken with different absorber foils reveals that the suprathermal electrons have less than 150 keV parallel energy for the hollow discharges.

  7. Experiments on Helicon Excitation and Off-Axis Current Drive on DIII-D: Status and Plans

    NASA Astrophysics Data System (ADS)

    Pinsker, R. I.; Prater, R.; Moeller, C. P.; Degrassie, J. S.; Tooker, J. F.; Anderson, J. P.; Torreblanca, H.; Hansink, M.; Nagy, A.; Porkolab, M.

    2015-11-01

    Fast waves in the LHRF, also called ``whistlers'' or ``helicons,'' will be studied in experiments on the DIII-D tokamak beginning in autumn 2015. In the first stage, a 12-element traveling wave antenna (``comb-line'') is installed in the DIII-D vessel for operation at very low power (~ 0.1 kW) at 476 MHz, with a well-defined launched n| | spectrum peaked at 3.0. The goals of the low-power experiment include: (1) determining the efficiency with which the desired fast waves can be excited under a variety of plasma conditions in discharges relevant to the subsequent high-power current drive experiments and (2) proving that the radial and poloidal location at which the antenna will be mounted does not cause deleterious effects in the DIII-D discharges with high neutral beam power, and that the antenna is not damaged by fast ion losses, etc. Plans for 1 MW-level experiments with a single klystron beginning in FY17 are discussed. In addition to demonstrating off-axis current drive at an efficiency of ~ 60 kA/MW in high-performance plasmas, these experiments will explore non-linear aspects of wave excitation, propagation and absorption such as ponderomotive effects and parametric decay instabilities. Supported by US DOE DE-FC02-04ER54698, DE-AC02-09CH11466 and DE-FG02-94ER54084.

  8. Status of Advanced Tokamak Scenario Modeling with Off-Axis Electron Cyclotron Current Drive in DIII-D

    SciTech Connect

    M. Murakami; H.E. St.John; T.A. Casper; M.S. Chu; J.C. DeBoo; C.M. Greenfield; J.E. Kinsey; L.L. Lao; R.J. La Haye; Y.R. Lin-Liu; T.C. Luce; P.A. Politzer; B.W. Rice; G.M. Staebler; T.S. Taylor; M.R. Wade

    1999-12-01

    The status of modeling work focused on developing the advanced tokamak scenarios in DIII-D is discussed. The objectives of the work are two-fold: (1) to develop AT scenarios with ECCD using time-dependent transport simulations, coupled with heating and current drive models, consistent with MHD equilibrium and stability; and (2) to use time-dependent simulations to help plan experiments and to understand the key physics involved. Time-dependent simulations based on transport coefficients derived from experimentally achieved target discharges are used to perform AT scenario modeling. The modeling indicates off-axis ECCD with approximately 3 MW absorbed power can maintain high-performance discharges with q{sub min} > 1 for 5 to 10 s. The resultant equilibria are calculated to be stable to n = 1 pressure driven modes. The plasma is well into the second stability regime for high-n ballooning modes over a large part of the plasma volume. The role of continuous localized ECCD is studied for stabilizing m/n = 2/1 tearing modes. The progress towards validating current drive and transport models, consistent with experimental results, and developing self-consistent, integrated high performance AT scenarios is discussed.

  9. Non-Linear Effects on the LH Wave Coupling in Tore Supra and Impact on the LH Current Drive Efficiency

    SciTech Connect

    Ekedahl, A.; Frincu, B.; Goniche, M.; Hillairet, J.; Petrzilka, V.

    2009-11-26

    A strong, non-linear degradation of the Lower Hybrid (LH) wave coupling in Tore Supra can be observed when the LH launcher is screened on both sides by additional side limiters, such as side protections of adjacent Ion Cyclotron (IC) antennas. The power reflection coefficient (RC) at the LH grill mouth is estimated to increase from {approx}20% at low power density (<1 MW/m{sup 2}) up to >40% at high power density (>10 MW/m{sup 2}). Such large RC (>40%) is unacceptably high, in particular for long durations. The screening by the additional side limiters reduces the connection length in front of the LH grill, which results in lower {lambda}{sub n}, {lambda}{sub T}, n{sub e} and T{sub e} at the grill. However, the reduction in ne alone is not enough to explain the non-linear behaviour. Modelling with a code that takes into account a ponderomotive force potential [1], depleting the electron density in front of the grill, shows consistent results. In full non-inductive current drive scenarios, the observed degradation in LH coupling is measurable on the LH current drive efficiency, through the increase in coupled LH power required to maintain V{sub Loop} = 0. These results demonstrate thus the importance of being able to control the LH coupling conditions, in order to optimize the efficiency and power handling of LH systems.

  10. Particle Dynamics Discrimination Between Current Sheet Magnetic Field Reversal and Magnetic Neutral Line Fields

    NASA Astrophysics Data System (ADS)

    Martin, R. F., Jr.; Holland, D. L.; Svetich, J.

    2014-12-01

    We consider dynamical signatures of ion motion that discriminate between a current sheet magnetic field reversal and a magnetic neutral line field. These two related dynamical systems have been studied previously as chaotic scattering systems with application to the Earth's magnetotail. Both systems exhibit chaotic scattering over a wide range of parameter values. The structure and properties of their respective phase spaces have been used to elucidate potential dynamical signatures that affect spacecraft measured ion distributions. In this work we consider the problem of discrimination between these two magnetic structures using charged particle dynamics. For example we show that signatures based on the well known energy resonance in the current sheet field provide good discrimination since the resonance is not present in the neutral line case. While both fields can lead to fractal exit region structuring, their characteristics are different and also may provide some field discrimination. Application to magnetotail field and particle parameters will be presented

  11. A new latch-free LIGBT on SOI with very high current density and low drive voltage

    NASA Astrophysics Data System (ADS)

    Olsson, J.; Vestling, L.; Eklund, K.-H.

    2016-01-01

    A new latch-free LIGBT on SOI is presented. The new device combines advantages from both LDMOS as well as LIGBT technologies; high breakdown voltage, high drive current density, low control voltages, at the same time eliminating latch-up problems. The new LIGBT has the unique property of independent scaling of the input control device, i.e. LDMOS, and the output part of the device, i.e. the p-n-p part. This allows for additional freedom in designing and optimizing the device properties. Breakdown voltage of over 200 V, on-state current density over 3 A/mm, specific on-resistance below 190 mΩ mm2, and latch-free operation is demonstrated.

  12. Predictors of driving exposure and avoidance in a field study of older drivers from the state of Maryland.

    PubMed

    Vance, David E; Roenker, Daniel L; Cissell, Gayla M; Edwards, Jerri D; Wadley, Virginia G; Ball, Karlene K

    2006-07-01

    Using structural equation modeling techniques, this study examines causal models of driving avoidance and exposure among older adults. Prior studies have revealed that past incidence of falls, Useful Field of View (UFOV) test performance, and Trails Making test performance are predictive of subsequent motor vehicle crash involvement [Owsley, C., Ball, K., McGwin Jr., G., Sloane, M.E., Roenker, D.L., White, M.F., Overley, E.T., 1998. Visual processing impairment and risk of motor vehicle crash among older adults. J. Am. Med. Assoc. 279 (14), 1083-1088; Sims, R.V., McGwin, G., Pulley, L., Roseman, J.M., 2001. Mobility impairments in crash-involved older drivers. J. Aging Health 13 (3), 430-438; Stutts, J.C., 1998. Do older drivers with visual nd cognitive impairments drive less? J. Am. Geriatr. Soc. 46, 854-861]. Data analyses used these indices, along with age, health, measures of physical functioning, and additional measures of cognitive functioning, to examine driving exposure and avoidance behaviors. A field sample of 4,234 drivers, 55 years of age and older, were recruited from the Maryland Motor Vehicles Administration after renewing their driver's licenses. A performance-based assessment, which included the Gross Impairment Screening battery and task 2 of the UFOV test, was completed by participants. A sub-sample of participants (n=815) were interviewed by telephone about their health and mobility 3-6 months following the initial assessment at a renewal center. In addition to age and gender, latent variables for health status, physical functioning, cognitive functioning, driving exposure, and driving avoidance were created. Direct and indirect causal paths were specified. Age, gender, health status, and cognitive functioning had direct effects on both driving exposure and driving avoidance; physical functioning did not have a direct effect on driving exposure or avoidance. The implications of these findings are discussed as they relate to designing

  13. Driving with central visual field loss I: Impact of central scotoma on response to hazards

    PubMed Central

    Bronstad, P. Matthew; Bowers, Alex R.; Albu, Amanda; Goldstein, Robert; Peli, Eli

    2012-01-01

    Objective To determine how central field loss (CFL) affects reaction time to pedestrians and test the hypothesis that scotomas lateral to the preferred retinal locus will delay detection of hazards approaching from that side. Methods Eleven participants with binocular CFL (scotoma diameter 7°-25°; VA 0.3-1.0 logMAR) using lateral preferred retinal fixation loci and eleven matched controls with normal vision drove in a simulator for about an hour and a half per session, for two sessions a week apart. Participants responded to frequent virtual pedestrians that appeared on either the left or right sides, and approached the participants’ lane on a collision trajectory that, therefore, caused them to remain in approximately the same area of the visual field. Results CFL participants reacted more slowly to pedestrians that appeared in the area of visual field loss than in non-scotomatous areas (4.3 vs. 2.4 seconds, p<0.001), and had more late and missed responses than controls (29% vs. 3%, p< 0.001). Scotoma size and contrast sensitivity predicted outcomes in blind and seeing areas, respectively. Visual acuity was not correlated with response measures. Conclusions In addition to causing visual acuity and contrast sensitivity loss, the central scotoma per se delayed hazard detection even though small eye movements could potentially compensate for the loss. Responses in non-scotomatous areas were also delayed, though to a lesser extent, possibly due to the eccentricity of fixation. Our findings will help practitioners in advising patients with CFL about specific difficulties they may face when driving. PMID:23329309

  14. Measurement of tidal current fields with SRTM along track interferometry

    NASA Astrophysics Data System (ADS)

    Runge, H.; Breit, H.; Eineder, M.; Flament, P.; Romeiser, R.

    2003-04-01

    Although the Shuttle Radar Topography Mission (SRTM, http://www.dfd.dlr.de/srtm/) SAR interferometer was designed to deliver Digital Elevation Models from across track interferometry it turned out that it contained also an Along Track Interferometer (ATI). The paper describes how the ATI can be used to determine the velocity of moving ground objects. These may be cars, trains and ships but the focus of the paper is on the measurement of fast tidal ocean surface currents. The big advantage of the SAR-ATI method over buoys is that the measurement covers a large area and "images" of surface currents can be obtained.The advatage over the well established altimeter measurements is the much higher geometrical resolution and that it works close to coasts and in river outflows. Finally, the advantages over coastal radars is that a spaceborne system can deliver data from round the world. In the paper the results from two test sites, near Brest in France and in the Dutch Waddenzee, will be presented. Comparisons of the SRTM current fields with available current models of these areas show both a very good agreement. The ATI-method will be used in future SAR missions like TerraSAR-X to provide high resolution current maps from many interesting parts of the world.

  15. A fresh look at electron cyclotron current drive power requirements for stabilization of tearing modes in ITER

    SciTech Connect

    La Haye, R. J.

    2015-12-10

    ITER is an international project to design and build an experimental fusion reactor based on the “tokamak” concept. ITER relies upon localized electron cyclotron current drive (ECCD) at the rational safety factor q=2 to suppress or stabilize the expected poloidal mode m=2, toroidal mode n=1 neoclassical tearing mode (NTM) islands. Such islands if unmitigated degrade energy confinement, lock to the resistive wall (stop rotating), cause loss of “H-mode” and induce disruption. The International Tokamak Physics Activity (ITPA) on MHD, Disruptions and Magnetic Control joint experiment group MDC-8 on Current Drive Prevention/Stabilization of Neoclassical Tearing Modes started in 2005, after which assessments were made for the requirements for ECCD needed in ITER, particularly that of rf power and alignment on q=2 [1]. Narrow well-aligned rf current parallel to and of order of one percent of the total plasma current is needed to replace the “missing” current in the island O-points and heal or preempt (avoid destabilization by applying ECCD on q=2 in absence of the mode) the island [2-4]. This paper updates the advances in ECCD stabilization on NTMs learned in DIII-D experiments and modeling during the last 5 to 10 years as applies to stabilization by localized ECCD of tearing modes in ITER. This includes the ECCD (inside the q=1 radius) stabilization of the NTM “seeding” instability known as sawteeth (m/n=1/1) [5]. Recent measurements in DIII-D show that the ITER-similar current profile is classically unstable, curvature stabilization must not be neglected, and the small island width stabilization effect from helical ion polarization currents is stronger than was previously thought [6]. The consequences of updated assumptions in ITER modeling of the minimum well-aligned ECCD power needed are all-in-all favorable (and well-within the ITER 24 gyrotron capability) when all effects are included. However, a “wild card” may be broadening of the localized

  16. A fresh look at electron cyclotron current drive power requirements for stabilization of tearing modes in ITER

    NASA Astrophysics Data System (ADS)

    La Haye, R. J.

    2015-12-01

    ITER is an international project to design and build an experimental fusion reactor based on the "tokamak" concept. ITER relies upon localized electron cyclotron current drive (ECCD) at the rational safety factor q=2 to suppress or stabilize the expected poloidal mode m=2, toroidal mode n=1 neoclassical tearing mode (NTM) islands. Such islands if unmitigated degrade energy confinement, lock to the resistive wall (stop rotating), cause loss of "H-mode" and induce disruption. The International Tokamak Physics Activity (ITPA) on MHD, Disruptions and Magnetic Control joint experiment group MDC-8 on Current Drive Prevention/Stabilization of Neoclassical Tearing Modes started in 2005, after which assessments were made for the requirements for ECCD needed in ITER, particularly that of rf power and alignment on q=2 [1]. Narrow well-aligned rf current parallel to and of order of one percent of the total plasma current is needed to replace the "missing" current in the island O-points and heal or preempt (avoid destabilization by applying ECCD on q=2 in absence of the mode) the island [2-4]. This paper updates the advances in ECCD stabilization on NTMs learned in DIII-D experiments and modeling during the last 5 to 10 years as applies to stabilization by localized ECCD of tearing modes in ITER. This includes the ECCD (inside the q=1 radius) stabilization of the NTM "seeding" instability known as sawteeth (m/n=1/1) [5]. Recent measurements in DIII-D show that the ITER-similar current profile is classically unstable, curvature stabilization must not be neglected, and the small island width stabilization effect from helical ion polarization currents is stronger than was previously thought [6]. The consequences of updated assumptions in ITER modeling of the minimum well-aligned ECCD power needed are all-in-all favorable (and well-within the ITER 24 gyrotron capability) when all effects are included. However, a "wild card" may be broadening of the localized ECCD by the presence of

  17. Heating and current drive requirements for ideal MHD stability and ITB sustainment in ITER steady state scenarios

    NASA Astrophysics Data System (ADS)

    Poli, Francesca

    2012-10-01

    Steady state scenarios envisaged for ITER aim at optimizing the bootstrap current, while maintaining sufficient confinement and stability to provide the necessary fusion yield. Non-inductive scenarios will need to operate with Internal Transport Barriers (ITBs) in order to reach adequate fusion gain at typical currents of 9 MA. However, the large pressure gradients associated with ITBs in regions of weak or negative magnetic shear can be conducive to ideal MHD instabilities in a wide range of βN, reducing the no-wall limit. Scenarios are established as relaxed flattop states with time-dependent transport simulations with TSC [1]. Fully non-inductive configurations with current in the range of 7-10 MA and various heating mixes (NB, EC, IC and LH) have been studied against variations of the pressure profile peaking and of the Greenwald fraction. It is found that stable equilibria have qmin> 2 and moderate ITBs at 2/3 of the minor radius [2]. The ExB flow shear from toroidal plasma rotation is expected to be low in ITER, with a major role in the ITB dynamics being played by magnetic geometry. Combinations of H&CD sources that maintain reverse or weak magnetic shear profiles throughout the discharge and ρ(qmin)>=0.5 are the focus of this work. The ITER EC upper launcher, designed for NTM control, can provide enough current drive off-axis to sustain moderate ITBs at mid-radius and maintain a non-inductive current of 8-9MA and H98>=1.5 with the day one heating mix. LH heating and current drive is effective in modifying the current profile off-axis, facilitating the formation of stronger ITBs in the rampup phase, their sustainment at larger radii and larger bootstrap fraction. The implications for steady state operation and fusion performance are discussed.[4pt] [1] Jardin S.C. et al, J. Comput. Phys. 66 (1986) 481[0pt] [2] Poli F.M. et al, Nucl. Fusion 52 (2012) 063027.

  18. CO2 Laser Beat-Wave Current Drive in an Unmagnetized Plasma

    NASA Astrophysics Data System (ADS)

    Liu, Fei; Hwang, David; Horton, Robert; Evans, Russell; Huang, Zhuo Fan; Hong, Sean

    2011-10-01

    The ability to remotely generate plasma current in dense plasmas is a basic yet important investigation in experimental plasma physics. Plasma current can be generated through nonlinear beat-wave mixing process by launching two intense electromagnetic waves into an unmagnetized plasma. The beat wave formation process is efficient if the difference frequency of the two pump waves corresponds to the local plasma frequency. Beat wave can accelerate plasma electrons via quasi-linear Landau process, which has been demonstrated in low-density plasma using micro-waves. The high tunability of the CO2 lasers provides many options for the wave-particle interaction experiment at a variety of CTIX plasma densities. Two sections of Lumonics TEA CO2 lasers have been modified at power over 100MW. The development of the tunable CO2 lasers and diagnostics system will be described. A high-density plasma test source and density diagnostics system will also be presented. This line of research will impact experiment such as the PLX facility under initial operation at Los Alamos National Lab. Supported by U.S. DOE Grant DE-FG02-10ER55083.

  19. Interplanetary Electric Field Control of Field-Aligned Currents: Polar Magnetometer Observations

    NASA Astrophysics Data System (ADS)

    Fleishman, M.; Russell, C. T.

    2001-05-01

    ACE and Wind measurements of the solar wind velocity and interplanetary magnetic field have been used to calculate the interplanetary electric field during passages of the Polar spacecraft above the southern auroral oval. Periods of the quasi-steady interplanetary electric field have been identified when the Polar spacecraft was transiting the auroral and polar regions both just in front of the terminator above the lit ionosphere and just behind the terminator above the dark ionosphere. The east-west magnetic perturbation observed was then used as a measure of the local field-aligned current density and extrapolated to a common altitude. Independent of whether the interplanetary electric field (IEF) is from dawn to dusk or dusk to dawn a significant field-aligned current always exists. The magnitude of its perturbation field for dusk to dawn IEF is about 180 nT. For dawn to dusk IEF the magnetic perturbation is roughly proportional to the dawn-dusk component of the IEF. The strength of the field-aligned current does not depend on whether the ionosphere under the spacecraft is in sunlight or in darkness.

  20. Lightning Return-Stroke Current Waveforms Aloft, from Measured Field Change, Current, and Channel Geometry

    NASA Technical Reports Server (NTRS)

    Willett, J. C.; LeVine, D. M.; Idone, V. P.

    2006-01-01

    Three-dimensional reconstructions of six rocket-triggered lightning channels are derived from stereo photographs. These reconstructed channels are used to infer the behavior of the current in return strokes above the ground from current waveforms measured at the channel base and electric-field-change waveforms measured at a range of 5.2 kilometers for 24 return strokes in these channels. Streak photographs of 14 of the same strokes are analyzed to determine the rise times, propagation speeds, and amplitudes of relative light intensity for comparison with the electrical inferences. Results include the following: 1) The fine structure of the field-change waveforms that were radiated by these subsequent return strokes can be explained, in large part, by channel geometry. 2) The average 10 - 90% rise time of the stroke current increased by about a factor of seven in our sample, from an observed 0.31 plus or minus 0.17 microseconds at the surface to an inferred 2.2 plus or minus 0.5 microcseconds at 1 kilometer path length above the surface. 3) The three-dimensional propagation speed of the current front averaged 1.80 plus or minus 0.24 X 10(exp 8) meters per second over channel lengths typically greater than 1 kilometer. 4) Assuming that the measured current was entirely due to the return stroke forced an unreasonably large and abrupt reduction in inferred current amplitude over the first few tens of meters above the surface, especially in cases when the leader was bright relative to its stroke. Therefore, a significant fraction of the current at the surface was probably due to the leader, at least in such cases. 5) Peak return-stroke currents decreased by approximately 37 plus or minus 12% from 100 meters to 1 kilometer of path length above the surface. Because of uncertainty about how to partition the measured current between leader and return stroke, we are unable to infer the variation of current amplitude near the ground.

  1. Vortex Properties of Nanosized Superconducting Strips with One Central Weak Link Under an Applied Current Drive

    NASA Astrophysics Data System (ADS)

    Peng, Lin; Cai, Chuanbing

    2016-06-01

    The static and dynamic properties of vortices in a nanosized superconducting strip with one central weak link (weakly superconducting region or normal metal) are investigated in the presence of external magnetic and electric fields. The time-dependent Ginzburg-Landau equations are used to describe the electronic transport and have been solved numerically by a finite element analysis. Anisotropy is included through the spatially dependent anisotropy coefficient ζ in different layers of the sample. Our results show that the energy barrier for vortices to enter a weak link is smaller than that for vortices to enter the superconducting layers. The magnetization shows periodic oscillations. With the introduction of the weak link, the period of oscillations decreases.

  2. Magnetic ripple and the modeling of lower-hybrid current drive in tokamaks

    SciTech Connect

    Peysson, Y.; Arslanbekov, R.; Basiuk, V.; Carrasco, J.; Litaudon, X.; Moreau, D.; Bizarro, J.P.

    1996-10-01

    Using ray tracing, a detailed investigation of the lower-hybrid (LH) wave propagation in presence of toroidal magnetic field ripple is presented. The local ray behavior is first depicted for a cylindrical equilibrium periodically modulated along the axial direction. Variations along ray trajectories in the component of the wave vector parallel to the equilibrium magnetic field are observed, with a maximum relative amplitude that is locally of the order of the ripple level. For the full rippled toroidal equilibrium, a similar local behavior is found when the ray trajectory crosses a high ripple region. Despite the modest amplitude of the local ray perturbation, its global influence on ray trajectories may be strong, as a consequence of the combined effects of toroidal and poloidal inhomogeneities. By coupling ray tracing with a one-dimensional relativistic Fokker-Planck code, simulations of LH experiments have been performed for the TORE SUPRA tokamak [Equipe TORE SUPRA, in {ital Proceedings of the 15{sup th} Conference on Plasma Physics and Controlled Nuclear Fusion Research}, Seville (International Atomic Energy Agency, Vienna, 1995), Vol. 1, p. 105, Paper IAEA-CN-60/A1-5]. It is shown that magnetic ripple may induce significant modifications in the LH power deposition profiles, mainly in the {open_quote}{open_quote}few passes{close_quote}{close_quote} regime when the wave makes some, but not many, passes inside the plasma before being absorbed. The effect of magnetic ripple leads then to a broadening of the power deposition profile and a shift towards the center of the plasma, and a better coupling with high energy electrons. This behavior may be explained by an increase in the overall ray stochasticity. Taking into account magnetic ripple in LH simulations, a better agreement is found between numerical predictions and experimental observations. {copyright} {ital 1996 American Institute of Physics.}

  3. FPGA-based voltage and current dual drive system for high frame rate electrical impedance tomography.

    PubMed

    Khan, Shadab; Manwaring, Preston; Borsic, Andrea; Halter, Ryan

    2015-04-01

    Electrical impedance tomography (EIT) is used to image the electrical property distribution of a tissue under test. An EIT system comprises complex hardware and software modules, which are typically designed for a specific application. Upgrading these modules is a time-consuming process, and requires rigorous testing to ensure proper functioning of new modules with the existing ones. To this end, we developed a modular and reconfigurable data acquisition (DAQ) system using National Instruments' (NI) hardware and software modules, which offer inherent compatibility over generations of hardware and software revisions. The system can be configured to use up to 32-channels. This EIT system can be used to interchangeably apply current or voltage signal, and measure the tissue response in a semi-parallel fashion. A novel signal averaging algorithm, and 512-point fast Fourier transform (FFT) computation block was implemented on the FPGA. FFT output bins were classified as signal or noise. Signal bins constitute a tissue's response to a pure or mixed tone signal. Signal bins' data can be used for traditional applications, as well as synchronous frequency-difference imaging. Noise bins were used to compute noise power on the FPGA. Noise power represents a metric of signal quality, and can be used to ensure proper tissue-electrode contact. Allocation of these computationally expensive tasks to the FPGA reduced the required bandwidth between PC, and the FPGA for high frame rate EIT. In 16-channel configuration, with a signal-averaging factor of 8, the DAQ frame rate at 100 kHz exceeded 110 frames s (-1), and signal-to-noise ratio exceeded 90 dB across the spectrum. Reciprocity error was found to be for frequencies up to 1 MHz. Static imaging experiments were performed on a high-conductivity inclusion placed in a saline filled tank; the inclusion was clearly localized in the reconstructions obtained for both absolute current and voltage mode data. PMID:25376037

  4. Swarm Observations of Field-Aligned Currents: Case Studies

    NASA Astrophysics Data System (ADS)

    Le, G.; Chi, P. J.; Gjerloev, J. W.; Stolle, C.; Luhr, H.; Park, J.; Rauberg, J.

    2014-12-01

    In this paper, we report the results of a few case studies of multi-point magnetic field measurements of field-aligned currents (FACs) from Swarm constellation mission to understand their temporal and spatial characteristics. During the commissioning phase, the three Swarm spacecraft were in an identical polar orbit with a string-of-pearl configuration with small separations. During the science operational phase (since April, 2014), the three spacecraft were placed in slightly different polar orbits: one spacecraft in a higher altitude orbit (507km x 512km) and two side-by-side in lower altitude orbits (459km x 462km). We analyze a few FAC events in both orbital phases and during periods of active geomagnetic conditions. The multi-point observations enable us to examine the FACs' temporal evolution and separate their temporal and spatial variations.

  5. A cross-field current instability for substorm expansions

    SciTech Connect

    Lui, A.T.Y. ); Chang, C.L.; Mankofsky, A. ); Wong, H.K. ); Winske, D. )

    1991-07-01

    The authors investigate a cross-field current instability (CFCI) as a candidate for current disruption during substorm expansions. The numerical solution of the linear dispersion equation indicates that (1) the proposed instability can occur at the inner edge or the midsection of the neutral sheet just prior to the substorm expansion onset although the former environment is found more favorable at the same drift speed scaled to the ion thermal speed, (2) the computed growth time is comparable to the substorm onset time, and (3) the excited waves have a mixed polarization with frequencies near the ion gyrofrequency at the inner edge and near the lower hybrid frequency in the midtail region. On the basis of this analysis, they propose a substorm development scenario in which plasma sheet thinning during the substorm growth phase leads to an enhancement in the relative drift between ions and electrons. This results in the neutral sheet being susceptible to the CHCI and initiates the diversion of the cross-tail current through the ionosphere. Whether or not a substorm current wedge is ultimately formed is regulated by the ionospheric condition. A large number of substorm features can be readily understood with the proposed scheme. These include (1) precursory activities (pseudobreakups) prior to substorm onset, (2) substorm initiation region to be spatially localized, (3) three different solar wind conditions for substorm occurence, (4) skew towards evening local times for substorm onset locations, (5) different acceleration characteristics between ions and electrons, (6) tailward spreading of current disruption region after substorm onset, and (7) local time expansion of substorm current wedge with possible discrete westward jump for the evening expansion.

  6. A stochastic mean field model for an excitatory and inhibitory synaptic drive cortical neuronal network.

    PubMed

    Hui, Qing; Haddad, Wassim M; Bailey, James M; Hayakawa, Tomohisa

    2014-04-01

    With the advances in biochemistry, molecular biology, and neurochemistry there has been impressive progress in understanding the molecular properties of anesthetic agents. However, there has been little focus on how the molecular properties of anesthetic agents lead to the observed macroscopic property that defines the anesthetic state, that is, lack of responsiveness to noxious stimuli. In this paper, we develop a mean field synaptic drive firing rate cortical neuronal model and demonstrate how the induction of general anesthesia can be explained using multistability; the property whereby the solutions of a dynamical system exhibit multiple attracting equilibria under asymptotically slowly changing inputs or system parameters. In particular, we demonstrate multistability in the mean when the system initial conditions or the system coefficients of the neuronal connectivity matrix are random variables. Uncertainty in the system coefficients is captured by representing system uncertain parameters by a multiplicative white noise model wherein stochastic integration is interpreted in the sense of Itô. Modeling a priori system parameter uncertainty using a multiplicative white noise model is motivated by means of the maximum entropy principle of Jaynes and statistical analysis. PMID:24807952

  7. Surprise signals in the supplementary eye field: rectified prediction errors drive exploration-exploitation transitions.

    PubMed

    Kawaguchi, Norihiko; Sakamoto, Kazuhiro; Saito, Naohiro; Furusawa, Yoshito; Tanji, Jun; Aoki, Masashi; Mushiake, Hajime

    2015-02-01

    Visual search is coordinated adaptively by monitoring and predicting the environment. The supplementary eye field (SEF) plays a role in oculomotor control and outcome evaluation. However, it is not clear whether the SEF is involved in adjusting behavioral modes based on preceding feedback. We hypothesized that the SEF drives exploration-exploitation transitions by generating "surprise signals" or rectified prediction errors, which reflect differences between predicted and actual outcomes. To test this hypothesis, we introduced an oculomotor two-target search task in which monkeys were required to find two valid targets among four identical stimuli. After they detected the valid targets, they exploited their knowledge of target locations to obtain a reward by choosing the two valid targets alternately. Behavioral analysis revealed two distinct types of oculomotor search patterns: exploration and exploitation. We found that two types of SEF neurons represented the surprise signals. The error-surprise neurons showed enhanced activity when the monkey received the first error feedback after the target pair change, and this activity was followed by an exploratory oculomotor search pattern. The correct-surprise neurons showed enhanced activity when the monkey received the first correct feedback after an error trial, and this increased activity was followed by an exploitative, fixed-type search pattern. Our findings suggest that error-surprise neurons are involved in the transition from exploitation to exploration and that correct-surprise neurons are involved in the transition from exploration to exploitation. PMID:25411455

  8. Direct activation of the Mauthner cell by electric field pulses drives ultrarapid escape responses.

    PubMed

    Tabor, Kathryn M; Bergeron, Sadie A; Horstick, Eric J; Jordan, Diana C; Aho, Vilma; Porkka-Heiskanen, Tarja; Haspel, Gal; Burgess, Harold A

    2014-08-15

    Rapid escape swims in fish are initiated by the Mauthner cells, giant reticulospinal neurons with unique specializations for swift responses. The Mauthner cells directly activate motoneurons and facilitate predator detection by integrating acoustic, mechanosensory, and visual stimuli. In addition, larval fish show well-coordinated escape responses when exposed to electric field pulses (EFPs). Sensitization of the Mauthner cell by genetic overexpression of the voltage-gated sodium channel SCN5 increased EFP responsiveness, whereas Mauthner ablation with an engineered variant of nitroreductase with increased activity (epNTR) eliminated the response. The reaction time to EFPs is extremely short, with many responses initiated within 2 ms of the EFP. Large neurons, such as Mauthner cells, show heightened sensitivity to extracellular voltage gradients. We therefore tested whether the rapid response to EFPs was due to direct activation of the Mauthner cells, bypassing delays imposed by stimulus detection and transmission by sensory cells. Consistent with this, calcium imaging indicated that EFPs robustly activated the Mauthner cell but only rarely fired other reticulospinal neurons. Further supporting this idea, pharmacological blockade of synaptic transmission in zebrafish did not affect Mauthner cell activity in response to EFPs. Moreover, Mauthner cells transgenically expressing a tetrodotoxin (TTX)-resistant voltage-gated sodium channel retained responses to EFPs despite TTX suppression of action potentials in the rest of the brain. We propose that EFPs directly activate Mauthner cells because of their large size, thereby driving ultrarapid escape responses in fish. PMID:24848468

  9. Direct activation of the Mauthner cell by electric field pulses drives ultrarapid escape responses

    PubMed Central

    Tabor, Kathryn M.; Bergeron, Sadie A.; Horstick, Eric J.; Jordan, Diana C.; Aho, Vilma; Porkka-Heiskanen, Tarja; Haspel, Gal

    2014-01-01

    Rapid escape swims in fish are initiated by the Mauthner cells, giant reticulospinal neurons with unique specializations for swift responses. The Mauthner cells directly activate motoneurons and facilitate predator detection by integrating acoustic, mechanosensory, and visual stimuli. In addition, larval fish show well-coordinated escape responses when exposed to electric field pulses (EFPs). Sensitization of the Mauthner cell by genetic overexpression of the voltage-gated sodium channel SCN5 increased EFP responsiveness, whereas Mauthner ablation with an engineered variant of nitroreductase with increased activity (epNTR) eliminated the response. The reaction time to EFPs is extremely short, with many responses initiated within 2 ms of the EFP. Large neurons, such as Mauthner cells, show heightened sensitivity to extracellular voltage gradients. We therefore tested whether the rapid response to EFPs was due to direct activation of the Mauthner cells, bypassing delays imposed by stimulus detection and transmission by sensory cells. Consistent with this, calcium imaging indicated that EFPs robustly activated the Mauthner cell but only rarely fired other reticulospinal neurons. Further supporting this idea, pharmacological blockade of synaptic transmission in zebrafish did not affect Mauthner cell activity in response to EFPs. Moreover, Mauthner cells transgenically expressing a tetrodotoxin (TTX)-resistant voltage-gated sodium channel retained responses to EFPs despite TTX suppression of action potentials in the rest of the brain. We propose that EFPs directly activate Mauthner cells because of their large size, thereby driving ultrarapid escape responses in fish. PMID:24848468

  10. Role of energetic electrons during current ramp-up and production of high poloidal beta plasma in non-inductive current drive on QUEST

    NASA Astrophysics Data System (ADS)

    Tashima, Saya; Zushi, H.; Isobe, M.; Hanada, K.; Idei, H.; Nakamura, K.; Fujisawa, A.; Matsuoka, K.; Hasegawa, M.; Nagashima, Y.; Okamura, S.; Banerjee, S.; Kawasaki, S.; Nakashima, H.; Higashijima, A.

    2014-02-01

    A scenario for non-inductive current ramp-up has been demonstrated using electron cyclotron waves in the spherical tokamak QUEST. The configuration was characterized by a high toroidal magnetic mirror ratio of 2 and a steady vertical magnetic field of more than 10% of the toroidal magnetic field. The generation and confinement of energetic electrons having energy greater than 10 keV were studied using hard x-rays. Because of the energetic electron pressure, a natural divertor formed with an inboard poloidal field null at the high poloidal beta (approximately 3-4).

  11. Pile Driving

    NASA Technical Reports Server (NTRS)

    1987-01-01

    Machine-oriented structural engineering firm TERA, Inc. is engaged in a project to evaluate the reliability of offshore pile driving prediction methods to eventually predict the best pile driving technique for each new offshore oil platform. Phase I Pile driving records of 48 offshore platforms including such information as blow counts, soil composition and pertinent construction details were digitized. In Phase II, pile driving records were statistically compared with current methods of prediction. Result was development of modular software, the CRIPS80 Software Design Analyzer System, that companies can use to evaluate other prediction procedures or other data bases.

  12. Eyes wide shut: Transcranial alternating current stimulation drives alpha rhythm in a state dependent manner.

    PubMed

    Ruhnau, Philipp; Neuling, Toralf; Fuscá, Marco; Herrmann, Christoph S; Demarchi, Gianpaolo; Weisz, Nathan

    2016-01-01

    Transcranial alternating current stimulation (tACS) is used to modulate brain oscillations to measure changes in cognitive function. It is only since recently that brain activity in human subjects during tACS can be investigated. The present study aims to investigate the phase relationship between the external tACS signal and concurrent brain activity. Subjects were stimulated with tACS at individual alpha frequency during eyes open and eyes closed resting states. Electrodes were placed at Cz and Oz, which should affect parieto-occipital areas most strongly. Source space magnetoencephalography (MEG) data were used to estimate phase coherence between tACS and brain activity. Phase coherence was significantly increased in areas in the occipital pole in eyes open resting state only. The lag between tACS and brain responses showed considerable inter-individual variability. In conclusion, tACS at individual alpha frequency entrains brain activity in visual cortices. Interestingly, this effect is state dependent and is clearly observed with eyes open but only to a lesser extent with eyes closed. PMID:27252047

  13. Eyes wide shut: Transcranial alternating current stimulation drives alpha rhythm in a state dependent manner

    PubMed Central

    Ruhnau, Philipp; Neuling, Toralf; Fuscá, Marco; Herrmann, Christoph S.; Demarchi, Gianpaolo; Weisz, Nathan

    2016-01-01

    Transcranial alternating current stimulation (tACS) is used to modulate brain oscillations to measure changes in cognitive function. It is only since recently that brain activity in human subjects during tACS can be investigated. The present study aims to investigate the phase relationship between the external tACS signal and concurrent brain activity. Subjects were stimulated with tACS at individual alpha frequency during eyes open and eyes closed resting states. Electrodes were placed at Cz and Oz, which should affect parieto-occipital areas most strongly. Source space magnetoencephalography (MEG) data were used to estimate phase coherence between tACS and brain activity. Phase coherence was significantly increased in areas in the occipital pole in eyes open resting state only. The lag between tACS and brain responses showed considerable inter-individual variability. In conclusion, tACS at individual alpha frequency entrains brain activity in visual cortices. Interestingly, this effect is state dependent and is clearly observed with eyes open but only to a lesser extent with eyes closed. PMID:27252047

  14. Impact of SOL plasma profiles on lower hybrid current drive: Experimental evidence, mitigation and modeling approaches

    NASA Astrophysics Data System (ADS)

    Shiraiwa, S.; Baek, S. G.; Faust, I.; Wallace, G.; Bonoli, P.; Meneghini, O.; Mumgaard, R.; Parker, R.; Scott, S.; Harvey, R. W.; Ding, B. J.; Li, M. H.; Lin, S. Y.; Yang, C.

    2015-12-01

    Recent progress in understanding and mitigating parasitic wave absorption in edge plasmas is presented. Experimental observations collected on Alcator C-Mod suggest multiple physics mechanisms are involved in such losses. Localized measurement of parametric decay instabilities (PDIs) has been performed using RF Langmuir probes. The divertor heat flux due to LH and ionization power loss have been evaluated quantitatively. We observe that the LHCD efficiency can be recovered when the SOL density profile is controlled by operating the tokamak at high current. The experimental progresses motivated a re-examination of the LHCD simulation model based on the ray-tracing/Fokker-Planck code (GENRAY/CQL3D). The effect of introducing a relatively small wave number broadening in the launched power spectrum and using 2D SOL density and temperature profiles was investigated. Comparison with C-Mod experiment indicates that the new model can explain the experimental trend over a wider density range including the density regime where disagreement was seen previously, suggesting that including realistic SOL geometry is a key to improve the simulation accuracy.

  15. 1993 annual report for the Phaedrus-T RF current drive experiments

    SciTech Connect

    Hershkowitz, N.

    1993-10-01

    After a series of antenna modifications and a program of optimizing our Boronization procedures, we have succeeded in coupling 300 kill of rf power to the plasma. Thomson Scattering shows a 20--60% increase in core T{sub e}, and constitutes experimental evidence that the waves are interacting with the electron population. Beam Emission Spectroscopy (BES) data show that the power is deposited in the core and at the edge as predicted by theoretical modeling. Ninety degree phasing of the antenna caused loop voltage drops of 15--25%, which can be interpreted as an increase 5 kA of toroidal plasma current for co-injection phasing versus counter injection phasing. Biased H-modes have been created with a biased electrode. These plasmas have a steeper edge density gradient and reduced edge fluctuations than our normal limiter plasmas and a D{sub alpha} emission drop at the limiter. Radial profiles of soft x-ray line emission have been measured by the Johns Hopkins group and significantly aided in our understanding of impurity generation with rf and in the biased H-mode. Initial reflectometry data shows the presence of rf density fluctuations in the plasma. Different boronization techniques have been tried leading to a higher boron content in the deposited layer and reduced wall recycling. In this report, we outline the series of experiments that we have performed in the last year that led us to our present encouraging results.

  16. Dispersal limitation drives successional pathways in Central Siberian forests under current and intensified fire regimes.

    PubMed

    Tautenhahn, Susanne; Lichstein, Jeremy W; Jung, Martin; Kattge, Jens; Bohlman, Stephanie A; Heilmeier, Hermann; Prokushkin, Anatoly; Kahl, Anja; Wirth, Christian

    2016-06-01

    Fire is a primary driver of boreal forest dynamics. Intensifying fire regimes due to climate change may cause a shift in boreal forest composition toward reduced dominance of conifers and greater abundance of deciduous hardwoods, with potential biogeochemical and biophysical feedbacks to regional and global climate. This shift has already been observed in some North American boreal forests and has been attributed to changes in site conditions. However, it is unknown if the mechanisms controlling fire-induced changes in deciduous hardwood cover are similar among different boreal forests, which differ in the ecological traits of the dominant tree species. To better understand the consequences of intensifying fire regimes in boreal forests, we studied postfire regeneration in five burns in the Central Siberian dark taiga, a vast but poorly studied boreal region. We combined field measurements, dendrochronological analysis, and seed-source maps derived from high-resolution satellite images to quantify the importance of site conditions (e.g., organic layer depth) vs. seed availability in shaping postfire regeneration. We show that dispersal limitation of evergreen conifers was the main factor determining postfire regeneration composition and density. Site conditions had significant but weaker effects. We used information on postfire regeneration to develop a classification scheme for successional pathways, representing the dominance of deciduous hardwoods vs. evergreen conifers at different successional stages. We estimated the spatial distribution of different successional pathways under alternative fire regime scenarios. Under intensified fire regimes, dispersal limitation of evergreen conifers is predicted to become more severe, primarily due to reduced abundance of surviving seed sources within burned areas. Increased dispersal limitation of evergreen conifers, in turn, is predicted to increase the prevalence of successional pathways dominated by deciduous hardwoods

  17. Asymmetric field-aligned currents in the conjugate hemispheres

    NASA Astrophysics Data System (ADS)

    Reistad, J. P.; Ostgaard, N.; Oksavik, K.; Laundal, K. M.

    2012-12-01

    Earlier studies using simultaneous imaging from space of the Aurora Borealis (Northern Hemisphere) and Aurora Australis (Southern Hemisphere) have revealed that the aurora can experience a high degree of asymmetry between the two hemispheres. Using 19 hours of simultaneous global imaging from both hemispheres (IMAGE satellite in north and Polar satellite in south) in conjunction with the entire IMAGE WIC database, we investigate the importance of various mechanisms thought to generate the asymmetries seen in global imaging. In terms of asymmetric or interhemispheric field-aligned currents, three candidate mechanisms have been suggested: 1) Hemispheric differences in solar wind dynamo efficiency mainly controlled by IMF Bx leading to asymmetric region 1 currents; 2) conductivity differences in conjugate areas; and 3) penetration of IMF By into the closed magnetosphere possibly generating a pair of oppositely directed interhemispheric currents. From the 19 hour conjugate dataset we find that the solar wind dynamo is likely to be the most important controlling mechanism for asymmetric bright aurora in the polar part of the nightside oval. Here we present statistical analyses of candidates 1) and 3). Using the entire IMAGE WIC database, a statistical analysis of the auroral brightness distribution along and across the Northern Hemisphere oval is carried out. For each candidate, two extreme cases (+/- IMF Bx for 1) and +/- IMF By for 3)) are compared during times non-favorable for the other two mechanisms. Our results indicate that solar wind dynamo induced currents play an important role for the nightside auroral brightness in an average sense. Also, signatures of interhemispheric currents due to IMF By penetration are seen in our statistics, although this effect is somehow weaker.

  18. The coordinate transformation method for design of polarizers on HL-2A electron cyclotron resonance heating and current drive systems

    SciTech Connect

    Xia, D. H.; Huang, M.; Zhou, J.; Rao, J.; Zhuang, G.

    2013-10-15

    Polarizers are widely used to change the polarization of millimeter waves on the electron cyclotron resonance heating and current drive (ECRH and CD) systems. A new method based on the coordinate transformation and the Fourier expansion (the so-called C-method) has been developed for design of polarizers on the HL-2A ECRH and CD systems. This method transforms the grating problem to an eigenvalue problem, making it easy and clear to understand and solve. The comparison between the C-method, the integral method, and the low power test results is presented. It indicates that the C-method can be considered as a rigorous numerical method for the design of polarizers. Finally, two polarizers were designed based on the C-method which can be used together to achieve almost arbitrary polarization.

  19. Cross-tail current, field-aligned current, and B(y)

    NASA Technical Reports Server (NTRS)

    Kaufmann, Richard L.; Lu, Chen; Larson, Douglas J.

    1994-01-01

    Orbits of individual charged particles were traced in a one-dimensional magnetic field model that included a uniform cross-tail component B(sub yo). The effects of B(sub yo) on the cross-tail current distribution j(sub y)(z), the average cross-tail drift velocity(nu(sub y)z), and the average pitch angle change(delta alpha) experienced during current sheet encounters were calculated. The addition of a B(sub yo) that exceeded several tenths of one nanotesla completely eliminated all resonance effects for odd-N orbits. An odd-N resonance involves ions that enter and exit the current sheet on the same side. Pitch angles of nearly all such ions changed substantially during a typical current sheet interaction, and there was no region of large cross-tail drift velocity in the presence of a modest B(sub yo). the addition of a very large B(sub yo) guide field in the direction that enhances the natural drift produces a large j(y) and small (Delta alpha) for ions with all energies. The addition of a modest B(sub yo) had less effect near even-N resonances. In this case, ions in a small energy range were found to undergo so little change in pitch angle that particles which originated in the ionosphere would pass through the current sheet and return to the conjugate ionosphere. Finally, the cross-tail drift of ions from regions dominated by stochastic orbits to regions dominated by either resonant or guiding center orbits was considered. The ion drift speed changed substantially during such transitions. The accompanying electrons obey the guiding center equations, so electron drift is more uniform. Any difference between gradients in the fluxes associated with electron and ion drifts requires the presence of a Birkeland current in order to maintain charge neutrality. This plasma sheet region therefore serves as a current generator. The analysis predicts that the resulting Birkeland current connects to the lowest altitude equatorial regions in which ions drift to or from a point

  20. Observations of field-aligned currents, waves, and electric fields at substorm onset

    NASA Technical Reports Server (NTRS)

    Smits, D. P.; Hughes, W. J.; Cattell, C. A.; Russell, C. T.

    1986-01-01

    Substorm onsets, identified Pi 2 pulsations observed on the Air Force Geophysics Laboratory Magnetometer Network, are studied using magnetometer and electric field data from ISEE 1 as well as magnetometer data from the geosynchronous satellites GOES 2 and 3. The mid-latitude magnetometer data provides the means of both timing and locating the substorm onset so that the spacecraft locations with respect to the substorm current systems are known. During two intervals, each containing several onsets or intensifications, ISEE 1 observed field-aligned current signatures beginning simultaneously with the mid-latitude Pi 2 pulsation. Close to the earth broadband bursts of wave noise were observed in the electric field data whenever field-aligned currents were detected. One onset occurred when ISEE 1 and GOES 2 were on the same field line but in opposite hemispheres. During this onset ISEE 1 and GOES 2 saw magnetic signatures which appear to be due to conjugate field-aligned currents flowing out of the western end of the westward auroral electrojets. The ISEE 1 signature is of a line current moving westward past the spacecraft. During the other interval, ISEE 1 was in the near-tail region near the midnight meridian. Plasma data confirms that the plasma sheet thinned and subsequently expanded at onset. Electric field data shows that the plasma moved in the opposite direction to the plasma sheet boundary as the boundary expanded which implies that there must have been an abundant source of hot plasma present. The plasma motion was towards the center of the plasma sheet and earthwards and consisted of a series of pulses rather than a steady flow.