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Sample records for beam current drive

  1. 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)

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. LANSCE beam current limiter

    SciTech Connect

    Gallegos, F.R.

    1996-06-01

    The Radiation Security System (RSS) at the Los Alamos Neutron Science Center (LANSCE) provides personnel protection from prompt radiation due to accelerated beam. Active instrumentation, such as the Beam Current Limiter, is a component of the RSS. The current limiter is designed to limit the average current in a beam line below a specific level, thus minimizing the maximum current available for a beam spill accident. The beam current limiter is a self-contained, electrically isolated toroidal beam transformer which continuously monitors beam current. It is designed as fail-safe instrumentation. The design philosophy, hardware design, operation, and limitations of the device are described.

  10. LANSCE beam current limiter

    SciTech Connect

    Gallegos, F.R.

    1997-01-01

    The Radiation Security System (RSS) at the Los Alamos Neutron Science Center (LANSCE) provides personnel protection from prompt radiation due to accelerated beam. Active instrumentation, such as the beam current limiter, is a component of the RSS. The current limiter is designed to limit the average current in a beamline below a specific level, thus minimizing the maximum current available for a beam spill accident. The beam current limiter is a self-contained, electrically isolated toroidal beam transformer which continuously monitors beam current. It is designed as fail-safe instrumentation. The design philosophy, hardware design, operation, and limitations of the device are described. {copyright} {ital 1997 American Institute of Physics.}

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Beam current sensor

    DOEpatents

    Kuchnir, Moyses; Mills, Frederick E.

    1987-01-01

    A current sensor for measuring the DC component of a beam of charged particles employs a superconducting pick-up loop probe, with twisted superconducting leads in combination with a Superconducting Quantum Interference Device (SQUID) detector. The pick-up probe is in the form of a single-turn loop, or a cylindrical toroid, through which the beam is directed and within which a first magnetic flux is excluded by the Meisner effect. The SQUID detector acts as a flux-to-voltage converter in providing a current to the pick-up loop so as to establish a second magnetic flux within the electrode which nulls out the first magnetic flux. A feedback voltage within the SQUID detector represents the beam current of the particles which transit the pick-up loop. Meisner effect currents prevent changes in the magnetic field within the toroidal pick-up loop and produce a current signal independent of the beam's cross-section and its position within the toroid, while the combination of superconducting elements provides current measurement sensitivites in the nano-ampere range.

  17. Beam current sensor

    DOEpatents

    Kuchnir, M.; Mills, F.E.

    1984-09-28

    A current sensor for measuring the dc component of a beam of charged particles employs a superconducting pick-up loop probe, with twisted superconducting leads in combination with a Superconducting Quantum Interference Device (SQUID) detector. The pick-up probe is in the form of a single-turn loop, or a cylindrical toroid, through which the beam is directed and within which a first magnetic flux is excluded by the Meisner effect. The SQUID detector acts as a flux-to-voltage converter in providing a current to the pick-up loop so as to establish a second magnetic flux within the electrode which nulls out the first magnetic flux. A feedback voltage within the SQUID detector represents the beam current of the particles which transit the pick-up loop. Meisner effect currents prevent changes in the magnetic field within the toroidal pick-up loop and produce a current signal independent of the beam's cross-section and its position within the toroid, while the combination of superconducting elements provides current measurement sensitivities in the nano-ampere range.

  18. 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.

  19. 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}

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. LANSCE Beam Current Limiter (XL)

    SciTech Connect

    Gallegos, F.R.; Hall, M.J.

    1997-01-01

    The Radiation Security System (RSS) at the Los Alamos Neutron Science Center (LANSCE) is an engineered safety system that provides personnel protection from prompt radiation due to accelerated proton beams. The Beam Current Limiter (XL), as an active component of the RSS, limits the maximum average current in a beamline, thus the current available for a beam spill accident. Exceeding the pre-set limit initiates action by the RSS to mitigate the hazard (insertion of beam stoppers in the low energy beam transport). The beam limiter is an electrically isolated, toroidal transformer and associated electronics. The device was designed to continuously monitor beamline currents independent of any external timing. Fail-safe operation was a prime consideration in its development. Fail-safe operation is defined as functioning as intended (due to redundant circuitry), functioning with a more sensitive fault threshold, or generating a fault condition. This report describes the design philosophy, hardware, implementation, operation, and limitations of the device.

  5. 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.

  6. High transformer ratio drive beams for wakefield accelerator studies

    SciTech Connect

    England, R. J.; Ng, C.-K.; Frederico, J.; Hogan, M. J.; Litos, M.; Muggli, P.; Joshi, C.; An, W.; Andonian, G.; Mori, W.; Lu, W.

    2012-12-21

    For wakefield based acceleration schemes, use of an asymmetric (or linearly ramped) drive bunch current profile has been predicted to enhance the transformer ratio and generate large accelerating wakes. We discuss plans and initial results for producing such bunches using the 20 to 23 GeV electron beam at the FACET facility at SLAC National Accelerator Laboratory and sending them through plasmas and dielectric tubes to generate transformer ratios greater than 2 (the limit for symmetric bunches). The scheme proposed utilizes the final FACET chicane compressor and transverse collimation to shape the longitudinal phase space of the beam.

  7. 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.

  8. 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.

  9. LEDA beam diagnostics instrumentation: Beam current measurement

    NASA Astrophysics Data System (ADS)

    Barr, D.; Day, L.; Gilpatrick, J. D.; Kasemir, K.-U.; Martinez, D.; Power, J. F.; Shurter, R.; Stettler, M.

    2000-11-01

    The Low Energy Demonstration Accelerator (LEDA) facility located at Los Alamos National Laboratory (LANL) accelerates protons to an energy of 6.7 MeV and current of 100 mA operating in either a pulsed or cw mode. Two types of current measurements are used. The first is an AC or pulsed-current measurement which uses three LANL built toroids. They are placed in the beamline in such a way as to measure important transmission parameters and act as a differential current-loss machine protection system. The second system is a DC current measurement used to measure cw beam characteristics and uses toroids from Bergoz Inc. There are two of these systems, so they can also be used for transmission measurements. The AC system uses custom processing electronics whereas the DC system uses a modified Bergoz® electronics system. Both systems feature data acquisition via a series of custom TMS320C40 Digital Signal Processing (DSP) boards. Of special interest to this paper is the operation of these systems, the calibration technique, the differential current loss measurements and fast-protection processing, current droop characteristics for the AC system, and existing system noise levels. This paper will also cover the DSP system operations and their interaction with the main accelerator control system.

  10. 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.

  11. Nondestructive synchronous beam current monitor

    SciTech Connect

    Covo, Michel Kireeff

    2014-12-15

    A fast current transformer is mounted after the deflectors of the Berkeley 88-Inch Cyclotron. The measured signal is amplified and connected to the input of a lock-in amplifier. The lock-in amplifier performs a synchronous detection of the signal at the cyclotron second harmonic frequency. The magnitude of the signal detected is calibrated against a Faraday cup and corresponds to the beam intensity. It has exceptional resolution, long term stability, and can measure the beam current leaving the cyclotron as low as 1 nA.

  12. 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.

  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. 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. 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

  16. 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

  17. 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

  18. 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.

  19. High-energy tritium beams as current drivers in tokamak reactors

    SciTech Connect

    Mikkelsen, D.R.; Grisham, L.R.

    1983-04-01

    The effect on neutral-beam design and reactor performance of using high-energy (approx. 3-10 MeV) tritium neutral beams to drive steady-state tokamak reactors is considered. The lower current of such beams leads to several advantages over lower-energy neutral beams. The major disadvantage is the reduction of the reactor output caused by the lower current-drive efficiency of the high-energy beams.

  20. 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.

  1. Fabrication of Beam-rotating Actuator for Multiple-beam Disk Drive

    NASA Astrophysics Data System (ADS)

    Kim, Boung Jun; Kim, Soo Hyun; Kwak, Yoon Keun

    2002-05-01

    Current trends in computer and communication industries are towards increasingly higher resolution images and video processing techniques. However, such sophisticated processing tasks require massive storage systems such as a compact disk read only memory (CD-ROM) and digital versatile disc (DVD). Current demands in the development of such systems are higher data density storage media and an improved data transfer rate. The latter is discussed in this paper. A multiple-beam optical disk drive is presented as a method for improving the effective data transfer rate by increasing the beam spot number formed on an optical disk. The beam-rotating actuator is necessary for positioning the multiple-beam onto more than one track. Ray tracing was also employed for the real system setup. The beam-rotating actuator is made up of piezoelectric material, a high-stiffness wire hinge and a dove prism. The actuator has an approximately 1 kHz resonance frequency and a suitable operational range. The dynamic equation for the actuator is derived for the control of the real system.

  2. 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.

  3. In-line beam current monitor

    NASA Astrophysics Data System (ADS)

    Ekdahl, C. A., Jr.; Frost, C. A.

    1984-11-01

    An intense relativistic electron beam current monitor for a gas neutralized beam transport line includes a first foil for conducting plasma current to the wall where it is measured as it traverses an inductive loop formed by a cavity in the wall. An insulator foil separates the first foil from a second conducting foil which returns the current to the plasma environment.

  4. In-line beam current monitor

    DOEpatents

    Ekdahl, Jr., Carl A.; Frost, Charles A.

    1986-01-01

    An intense relativistic electron beam current monitor for a gas neutralized beam transport line includes a first foil for conducting plasma current to the wall where it is measured as it traverses an inductive loop formed by a cavity in the wall. An insulator foil separates the first foil from a second conducting foil which returns the current to the plasma environment.

  5. In-line beam current monitor

    DOEpatents

    Ekdahl, C.A. Jr.; Frost, C.A.

    1984-11-13

    An intense relativistic electron beam current monitor for a gas neutralized beam transport line includes a first foil for conducting plasma current to the wall where it is measured as it traverses an inductive loop formed by a cavity in the wall. An insulator foil separates the first foil from a second conducting foil which returns the current to the plasma environment.

  6. Precision Absolute Beam Current Measurement of Low Power Electron Beam

    SciTech Connect

    Ali, M. M.; Bevins, M. E.; Degtiarenko, P.; Freyberger, A.; Krafft, G. A.

    2012-11-01

    Precise measurements of low power CW electron beam current for the Jefferson Lab Nuclear Physics program have been performed using a Tungsten calorimeter. This paper describes the rationale for the choice of the calorimeter technique, as well as the design and calibration of the device. The calorimeter is in use presently to provide a 1% absolute current measurement of CW electron beam with 50 to 500 nA of average beam current and 1-3 GeV beam energy. Results from these recent measurements will also be presented.

  7. 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.

  8. High current ion beam transport using solenoids

    SciTech Connect

    Hollinger, R.; Spaedtke, P.

    2008-02-15

    In the framework of the future project FAIR several upgrade programs and construction of new facilities are in progress such as the U{sup 4+} upgrade for the existing high current injector and the new 70 MeV proton injector. For both injectors solenoids in the low energy beam transport section are foreseen to inject the beam into the following rf accelerator. The paper presents beam quality measurements of high current ion beams behind a solenoid using a slit-grid emittance measurement device, viewing targets, and a pepper pot measurement device at the high current test bench at GSI.

  9. JINR test facility for studies FEL bunching technique for CLIC driving beam

    SciTech Connect

    Dolbilov, G.V.; Fateev, A.A.; Ivanov, I.N.

    1995-12-31

    SILUND-21 linear induction accelerator (energy up to 10 MeV, peak current about of 1 kA, pulse duration 50 - 70 ns) is constructed at JINR in the framework of experimental program to study free electron laser physics, a problem of two-beam acceleration and microwave electronics. In this paper we present project of an experiment to adopt the FEL bunching technique for generation of the CLIC driving beam.

  10. 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. )

  11. 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.

  12. Crossed-beam energy transfer in direct-drive implosions

    SciTech Connect

    Seka, W; Edgell, D H; Michel, D T; Froula, D H; Goncharov, V N; Craxton, R S; Divol, L; Epstein, R; Follett, R; Kelly, J H; Kosc, T Z; Maximov, A V; McCrory, R L; Meyerhofer, D D; Michel, P; Myatt, J F; Sangster, T C; Shvydky, A; Skupsky, S; Stoeckl, C

    2012-05-22

    Direct-drive-implosion experiments on the OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] have showed discrepancies between simulations of the scattered (non-absorbed) light levels and measured ones that indicate the presence of a mechanism that reduces laser coupling efficiency by 10%-20%. This appears to be due to crossed-beam energy transfer (CBET) that involves electromagnetic-seeded, low-gain stimulated Brillouin scattering. CBET scatters energy from the central portion of the incoming light beam to outgoing light, reducing the laser absorption and hydrodynamic efficiency of implosions. One-dimensional hydrodynamic simulations including CBET show good agreement with all observables in implosion experiments on OMEGA. Three strategies to mitigate CBET and improve laser coupling are considered: the use of narrow beams, multicolor lasers, and higher-Z ablators. Experiments on OMEGA using narrow beams have demonstrated improvements in implosion performance.

  13. 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).

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. Beam-halo measurements in high-current proton beams

    SciTech Connect

    Allen, C.K.; Chan, K.C.D.; Colestock, P.L.; Crandall, K.R.; Garnett, R.W.; Gilpatrick, J.D.; Lysenko, W.; Qiang, J.; Schneider, J.D.; Schulze, M.E.; Sheffield, R.L.; Smith, H.V.; Wangler, T.P.

    2002-01-11

    We present results from an experimental study of the beam halo in a high-current 6.7-MeV proton beam propagating through a 52-quadrupole periodic-focusing channel. The gradients of the first four quadrupoles were independently adjusted to match or mismatch the injected beam. Emittances and beamwidths were obtained from measured profiles for comparisons with maximum emittance-growth predictions of a free-energy model and maximum halo-amplitude predictions of a particle-core model. The experimental results support both models and the present theoretical picture of halo formation.

  2. Laser-beam zooming to mitigate crossed-beam energy losses in direct-drive implosions.

    PubMed

    Igumenshchev, I V; Froula, D H; Edgell, D H; Goncharov, V N; Kessler, T J; Marshall, F J; McCrory, R L; McKenty, P W; Meyerhofer, D D; Michel, D T; Sangster, T C; Seka, W; Skupsky, S

    2013-04-01

    Spherically symmetric direct-drive-ignition designs driven by laser beams with a focal-spot size nearly equal to the target diameter suffer from energy losses due to crossed-beam energy transfer (CBET). Significant reduction of CBET and improvements in implosion hydrodynamic efficiency can be achieved by reducing the beam diameter. Narrow beams increase low-mode perturbations of the targets because of decreased illumination uniformity that degrades implosion performance. Initiating an implosion with nominal beams (equal in size to the target diameter) and reducing the beam diameter by ∼ 30%-40% after developing a sufficiently thick target corona, which smooths the perturbations, mitigate CBET while maintaining low-mode target uniformity in ignition designs with a fusion gain ≫ 1. PMID:25166997

  3. Polarized electron beams at milliampere average current

    SciTech Connect

    Poelker, Matthew

    2013-11-01

    This contribution describes some of the challenges associated with developing a polarized electron source capable of uninterrupted days-long operation at milliAmpere average beam current with polarization greater than 80%. Challenges will be presented in the context of assessing the required level of extrapolation beyond the performance of today's CEBAF polarized source operating at ~ 200 uA average current. Estimates of performance at higher current will be based on hours-long demonstrations at 1 and 4 mA. Particular attention will be paid to beam-related lifetime-limiting mechanisms, and strategies to construct a photogun that operate reliably at bias voltage > 350kV.

  4. Bi-axial magnetic drive for scanned beam display mirrors

    NASA Astrophysics Data System (ADS)

    Sprague, Randy B.; Montague, Tom; Brown, Dean

    2005-01-01

    A novel MEMS actuation technique has been developed for scanned beam display and imaging applications that allows driving a two-axes scanning mirror to wide angles at high frequency. This actuation technique delivers sufficient torque to allow non-resonant operation as low as DC in the slow-scan axis while at the same time allowing one-atmosphere operation even at fast-scan axis frequencies great enough to support SXGA resolutions. Several display and imaging products have been developed employing this new MEMS actuation technique. Exceptionally good displays can be made by scanning laser beams much the same way a CRT scans electron beams. The display applications can be as diverse as an automotive head up display, where the laser beams are scanned onto the inside of the car"s windshield to be reflected into the driver"s eyes, and a head-worn display where the light beams are scanned directly over the viewer"s vision. For high performance displays the design challenges for a MEMS scanner are great. The scanner represents the system"s limiting aperture so it must be of sufficient size; it must remain flat to fractions of a wavelength so as to not distort the beam"s wave front; it must scan fast enough to handle the many millions of pixels written every second; and it must scan in two axes over significant angles in order to "paint" a wide angle, two-dimensional image. Using the new actuation method described, several MEMS scanner designs have been fabricated which meet the requirements of a variety of display and imaging applications.

  5. 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.

  6. 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.

  7. 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.

  8. Numerical Simulation of Non-Inductive Current Driven Scenario in EAST Using Neutral Beam Injection

    NASA Astrophysics Data System (ADS)

    Li, Hao; Wu, Bin; Wang, Jinfang; Wang, Ji; Hu, Chundong

    2015-01-01

    For achieving the scientific mission of long pulse and high performance operation, experimental advanced superconducting tokamak (EAST) applies fully superconducting magnet technology and is equiped with high power auxiliary heating system. Besides RF (Radio Frequency) wave heating, neutral beam injection (NBI) is an effective heating and current drive method in fusion research. NBCD (Neutral Beam Current Drive) as a viable non-inductive current drive source plays an important role in quasi-steady state operating scenario for tokamak. The non-inductive current driven scenario in EAST only by NBI is predicted using the TSC/NUBEAM code. At the condition of low plasma current and moderate plasma density, neutral beam injection heats the plasma effectively and NBCD plus bootstrap current accounts for a large proportion among the total plasma current for the flattop time.

  9. 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.

  10. Indirectly sensing accelerator beam currents for limiting maximum beam current magnitude

    DOEpatents

    Bogaty, John M.; Clifft, Benny E.; Bollinger, Lowell M.

    1995-01-01

    A beam current limiter for sensing and limiting the beam current in a particle accelerator, such as a cyclotron or linear accelerator, used in scientific research and medical treatment. A pair of independently operable capacitive electrodes sense the passage of charged particle bunches to develop an RF signal indicative of the beam current magnitude produced at the output of a bunched beam accelerator. The RF signal produced by each sensing electrode is converted to a variable DC voltage indicative of the beam current magnitude. The variable DC voltages thus developed are compared to each other to verify proper system function and are further compared to known references to detect beam currents in excess of pre-established limits. In the event of a system malfunction, or if the detected beam current exceeds pre-established limits, the beam current limiter automatically inhibits further accelerator operation. A high Q tank circuit associated with each sensing electrode provides a narrow system bandwidth to reduce noise and enhance dynamic range. System linearity is provided by injecting, into each sensing electrode, an RF signal that is offset from the bunching frequency by a pre-determined beat frequency to ensure that subsequent rectifying diodes operate in a linear response region. The system thus provides a large dynamic range in combination with good linearity.

  11. Indirectly sensing accelerator beam currents for limiting maximum beam current magnitude

    DOEpatents

    Bogaty, J.M.; Clifft, B.E.; Bollinger, L.M.

    1995-08-08

    A beam current limiter is disclosed for sensing and limiting the beam current in a particle accelerator, such as a cyclotron or linear accelerator, used in scientific research and medical treatment. A pair of independently operable capacitive electrodes sense the passage of charged particle bunches to develop an RF signal indicative of the beam current magnitude produced at the output of a bunched beam accelerator. The RF signal produced by each sensing electrode is converted to a variable DC voltage indicative of the beam current magnitude. The variable DC voltages thus developed are compared to each other to verify proper system function and are further compared to known references to detect beam currents in excess of pre-established limits. In the event of a system malfunction, or if the detected beam current exceeds pre-established limits, the beam current limiter automatically inhibits further accelerator operation. A high Q tank circuit associated with each sensing electrode provides a narrow system bandwidth to reduce noise and enhance dynamic range. System linearity is provided by injecting, into each sensing electrode, an RF signal that is offset from the bunching frequency by a pre-determined beat frequency to ensure that subsequent rectifying diodes operate in a linear response region. The system thus provides a large dynamic range in combination with good linearity. 6 figs.

  12. 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.

  13. SPALLATION NEUTRON SOURCE BEAM CURRENT MONITOR ELECTRONICS.

    SciTech Connect

    KESSELMAN,M.; DAWSON,W.C.

    2002-05-06

    This paper will discuss the present electronics design for the beam current monitor system to be used throughout the Spallation Neutron Source (SNS) under construction at Oak Ridge National Laboratory. The beam is composed of a micro-pulse structure due to the 402.5MHz RF, and is chopped into mini-pulses of 645ns duration with a 300ns gap, providing a macro-pulse of 1060 mini-pulses repeating at a 60Hz rate. Ring beam current will vary from about 15ma peak during studies, to about 50Amps peak (design to 100 amps). A digital approach to droop compensation has been implemented and initial test results presented.

  14. Charged particle beam current monitoring tutorial

    SciTech Connect

    Webber, R.C.

    1994-10-01

    A tutorial presentation is made on topics related to the measurement of charged particle beam currents. The fundamental physics of electricity and magnetism pertinent to the problem is reviewed. The physics is presented with a stress on its interpretation from an electrical circuit theory point of view. The operation of devices including video pulse current transformers, direct current transformers, and gigahertz bandwidth wall current style transformers is described. Design examples are given for each of these types of devices. Sensitivity, frequency response, and physical environment are typical parameters which influence the design of these instruments in any particular application. Practical engineering considerations, potential pitfalls, and performance limitations are discussed.

  15. Beam current controller for laser ion source

    SciTech Connect

    Okamura, Masahiro

    2014-10-28

    The present invention relates to the design and use of an ion source with a rapid beam current controller for experimental and medicinal purposes. More particularly, the present invention relates to the design and use of a laser ion source with a magnetic field applied to confine a plasma flux caused by laser ablation.

  16. Upgrade of the Drive LINAC for the AWA Facility Dielectric Two-Beam Accelerator

    SciTech Connect

    Power, John; Conde, Manoel; Gai, Wei; Li, Zenghai; Mihalcea, Daniel; /Northern Illinois U.

    2012-07-02

    We report on the design of a seven-cell, standing-wave, 1.3-GHz rf cavity and the associated beam dynamics studies for the upgrade of the drive beamline LINAC at the Argonne Wakefield Accelerator (AWA) facility. The LINAC design is a compromise between single-bunch operation (100 nC {at} 75 MeV) and minimization of the energy droop along the bunch train during bunch-train operation. The 1.3-GHz drive bunch-train target parameters are 75 MeV, 10-20-ns macropulse duration, and 16 x 60 nC microbunches; this is equivalent to a macropulse current and beam power of 80 A and 6 GW, respectively. Each LINAC structure accelerates approximately 1000 nC in 10 ns by a voltage of 11 MV at an rf power of 10 MW. Due to the short bunch-train duration desired ({approx}10 ns) and the existing frequency (1.3 GHz), compensation of the energy droop along the bunch train is difficult to accomplish by means of the two standard techniques: time-domain or frequency-domain beam loading compensation. Therefore, to minimize the energy droop, our design is based on a large stored energy rf cavity. In this paper, we present our rf cavity optimization method, detailed rf cavity design, and beam dynamics studies of the drive beamline.

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. 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).

  2. 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.

  3. Polarized electron beams at milliampere average current

    SciTech Connect

    Poelker, M.

    2013-11-07

    This contribution describes some of the challenges associated with developing a polarized electron source capable of uninterrupted days-long operation at milliAmpere average beam current with polarization greater than 80%. Challenges will be presented in the context of assessing the required level of extrapolation beyond the performance of today’s CEBAF polarized source operating at ∼ 200 uA average current. Estimates of performance at higher current will be based on hours-long demonstrations at 1 and 4 mA. Particular attention will be paid to beam-related lifetime-limiting mechanisms, and strategies to construct a photogun that operate reliably at bias voltage > 350kV.

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. Note: A real-time beam current density meter

    SciTech Connect

    Liu Junliang; Yu Deyang; Ruan Fangfang; Xue Yingli; Wang Wei

    2013-03-15

    We have developed a real-time beam current density meter for charged particle beams. It measures the mean current density by collimating a uniform and large diameter primary beam. The suppression of the secondary electrons and the deflection of the beam were simulated, and it was tested with a 105 keV Ar{sup 7+} ion beam.

  9. 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.}

  10. 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.

  11. Current Control in ITER Steady State Plasmas With Neutral Beam Steering

    SciTech Connect

    R.V. Budny

    2009-09-10

    Predictions of quasi steady state DT plasmas in ITER are generated using the PTRANSP code. The plasma temperatures, densities, boundary shape, and total current (9 - 10 MA) anticipated for ITER steady state plasmas are specified. Current drive by negative ion neutral beam injection, lower-hybrid, and electron cyclotron resonance are calculated. Four modes of operation with different combinations of current drive are studied. For each mode, scans with the NNBI aimed at differing heights in the plasma are performed to study effects of current control on the q profile. The timeevolution of the currents and q are calculated to evaluate long duration transients. Quasi steady state, strongly reversed q profiles are predicted for some beam injection angles if the current drive and bootstrap currents are sufficiently large.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Neutral beam current driven operation of the DIII-D tokamak

    SciTech Connect

    Simonen, T.C.; Bhadra, D.K.; Burrell, K.H.; Callis, R.W.; Chance, M.S.; Chu, M.S.; Colleraine, A.P.; Greene, J.M.; Groebner, R.J.; Harvey, R.W.; Hill, D.N.; Kim, J.; Lao, L.; Matsuoka, M.; Petersen, P.I.; Porter, G.D.; St. John, H.; Stallard, B.W.; Stambaugh, R.D.; Strait, E.J.; Taylor, T.S.

    1988-03-01

    Neutral beam current drive experiment in the DII-D tokamak with a single null poloidal divertor are described. A plasma current of 0.34 MA has been sustained entirely by neutral beams with H-mode quality energy confinement. Poloidal beta values reach 3.5 without disruption or coherent magnetic activity, suggesting that these plasmas may be entering the second stability regime. 12 refs., 2 figs.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Precision intercomparison of beam current monitors at CEBAF

    SciTech Connect

    Kazimi, R.; Dunham, B.; Krafft, G.A.; Legg, r.; Liang, C.; Sinclair, C.; Mamosser, J.

    1995-12-31

    The CEBAF accelerator delivers a CW electron beam at fundamental 1497 MHz, with average beam current up to 200 {mu}A. Accurate, stable nonintercepting beam current monitors are required for: setup/control, monitoring of beam current and beam losses for machine protection and personnel safety, and providing beam current information to experimental users. Fundamental frequency stainless steel RF cavities have been chosen for these beam current monitors. This paper reports on precision intercomparison between two such RF cavities, an Unser monitor, and two Faraday cups, all located in the injector area. At the low beam energy in the injector, it is straightforward to verify the high efficiency of the Faraday cups, and the Unser monitor included a wire through it to permit an absolute calibration. The cavity intensity monitors have proven capable of stable, high precision monitoring of the beam current.

  3. 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.

  4. 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.

  5. REX, a 5-MV pulsed-power source for driving high-brightness electron beam diodes

    SciTech Connect

    Carlson, R.L.; Kauppila, T.J.; Ridlon, R.N.

    1991-01-01

    The Relativistic Electron-beam Experiment, or REX accelerator, is a pulsed-power source capable of driving a 100-ohm load at 5 MV, 50 kA, 45 ns (FWHM) with less than a 10-ns rise and 15-ns fall time. This paper describes the pulsed-power modifications, modelling, and extensive measurements on REX to allow it to drive high impedance (100s of ohms) diode loads with a shaped voltage pulse. A major component of REX is the 1.83-m-diam {times} 25.4-cm-thick Lucite insulator with embedded grading rings that separates the output oil transmission line from the vacuum vessel that contains the re-entrant anode and cathode assemblies. A radially tailored, liquid-based resistor provides a stiff voltage source that is insensitive to small variations of the diode current and, in addition, optimizes the electric field stress across the vacuum side of the insulator. The high-current operation of REX employs both multichannel peaking and point-plane diverter switches. This mode reduces the prepulse to less than 2 kV and the postpulse to less than 5% of the energy delivered to the load. Pulse shaping for the present diode load is done through two L-C transmission line filters and a tapered, glycol-based line adjacent to the water PFL and output switch. This has allowed REX to drive a diode producing a 4-MV, 4.5-kA, 55-ns flat-top electron beam with a normalized Lapostolle emittance of 0.96 mm-rad corresponding to a beam brightness in excess of 4.4 {times} 10{sup 8} A/m{sup 2} {minus}rad{sup 2}. 6 refs., 13 figs.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Conceptual Design of the Drive Beam for a PWFA-LC

    SciTech Connect

    Pei, S.; Hogan, M.J.; Raubenheimer, T.O.; Seryi, A.; Braun, H.H.; Corsini, R.; Delahaye, J.P.; /DESY

    2009-08-03

    Plasma Wake-Field Acceleration (PWFA) has demonstrated acceleration gradients above 50 GeV/m. Simulations have shown drive/witness bunch configurations that yield small energy spreads in the accelerated witness bunch and high energy transfer efficiency from the drive bunch to the witness bunch, ranging from 30% for a Gaussian drive bunch to 95% for bunch with triangular shaped longitudinal profile. These results open the opportunity for a linear collider that could be compact, efficient and more cost effective than the present microwave technologies. A concept of a PWFA-based Linear Collider (PWFA-LC) has been developed by the PWFA collaboration. Here we will describe the conceptual design and optimization of the drive beam, which includes the drive beam linac and distribution system. We apply experience of the CLIC drive beam design and demonstration in the CLIC Test Facility (CTF3) to this study. We discuss parameter optimization of the drive beam linac structure and evaluate the drive linac efficiency in terms of the drive beam distribution scheme and the klystron/modulator requirements.

  11. 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).

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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)

  18. 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.

  19. 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).

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Direct drive heavy-ion-beam inertial fusion at high coupling efficiency

    SciTech Connect

    Logan, B.G.; Perkins, L.J.; Barnard, J.J.

    2008-05-16

    Issues with coupling efficiency, beam illumination symmetry, and Rayleigh-Taylor instability are discussed for spherical heavy-ion-beam-driven targets with and without hohlraums. Efficient coupling of heavy-ion beams to compress direct-drive inertial fusion targets without hohlraums is found to require ion range increasing several-fold during the drive pulse. One-dimensional implosion calculations using the LASNEX inertial confinement fusion target physics code shows the ion range increasing fourfold during the drive pulse to keep ion energy deposition following closely behind the imploding ablation front, resulting in high coupling efficiencies (shell kinetic energy/incident beam energy of 16% to 18%). Ways to increase beam ion range while mitigating Rayleigh-Taylor instabilities are discussed for future work.

  5. 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).

  6. 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.

  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.

    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.

  8. 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.

  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. )

    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

  10. 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

  11. 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

  12. Transverse distribution of beam current oscillations of a 14 GHz electron cyclotron resonance ion source.

    PubMed

    Tarvainen, O; Toivanen, V; Komppula, J; Kalvas, T; Koivisto, H

    2014-02-01

    The temporal stability of oxygen ion beams has been studied with the 14 GHz A-ECR at JYFL (University of Jyvaskyla, Department of Physics). A sector Faraday cup was employed to measure the distribution of the beam current oscillations across the beam profile. The spatial and temporal characteristics of two different oscillation "modes" often observed with the JYFL 14 GHz ECRIS are discussed. It was observed that the low frequency oscillations below 200 Hz are distributed almost uniformly. In the high frequency oscillation "mode," with frequencies >300 Hz at the core of the beam, carrying most of the current, oscillates with smaller amplitude than the peripheral parts of the beam. The results help to explain differences observed between the two oscillation modes in terms of the transport efficiency through the JYFL K-130 cyclotron. The dependence of the oscillation pattern on ion source parameters is a strong indication that the mechanisms driving the fluctuations are plasma effects. PMID:24593488

  13. Suppression of current fluctuations in an intense electron beam

    SciTech Connect

    Harris, J. R.; Lewellen, J. W.

    2010-10-15

    When an intense beam encounters an aperture, the transmitted current depends on the properties of the beam and the transport channel, as well as those of the aperture itself. In some cases, an increase in the incident beam current will be exactly compensated by an increase in the incident beam area, so that the current density at the aperture remains unchanged. When this occurs, the transmitted beam current becomes independent of changes in the incident beam current, providing a passive means for suppressing current fluctuations in the beam. In this article, a key requirement for the existence of this condition is derived. This requirement is shown to be fulfilled in the case of an idealized uniform focusing channel in the small-signal limit, but to be violated when the current fluctuations are not small. Even in this case, the apertured transport system retains the ability to suppress--but not totally eliminate--fluctuations in the transmitted beam current for a wide range of incident beam currents.

  14. 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.

  15. Online diagnoses of high current-density beams

    SciTech Connect

    Gilpatrick, J.D.

    1994-07-01

    Los Alamos National Laboratory has proposed several CW-proton-beam facilities for production of tritium or transmutation of nuclear waste with beam-current densities greater than 5 mA/mm{sup 2}. The primary beam-diagnostics-instrumentation requirement for these facilities is provision of sufficient beam information to understand and minimize beam-loss. To accomplish this task, the beam-diagnostics instrumentation must measure beam parameters such as the centroids and profiles, total integrated current, and particle loss. Noninterceptive techniques must be used for diagnosis of high-intensity CW beam at low energies due to the large quantity of power deposited in an interceptive diagnostic device by the beam. Transverse and longitudinal centroid measurements have been developed for bunched beams by measuring and processing image currents on the accelerator walls. Transverse beam-profile measurement-techniques have also been developed using the interaction of the particle beam with the background gases near the beam region. This paper will discuss these noninterceptive diagnostic Techniques.

  16. High-current beam dynamics and transport, theory and experiment

    SciTech Connect

    Reiser, M.

    1986-01-01

    Recent progress in the understanding of beam physics and technology factors determining the current and brightness of ion and electron beams in linear accelerators will be reviewed. Topics to be discussed including phase-space density constraints of particle sources, low-energy beam transport include charge neutralization, emittance growth due to mismatch, energy exchange, instabilities, nonlinear effects, and longitudinal bunching.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Laser diagnostic for high current H{sup {minus}} beams

    SciTech Connect

    Shafer, R.E.

    1998-05-05

    In the last 5 years, significant technology advances have been made in the performance, size, and cost of solid-state diode-pumped lasers. These developments enable the use of compact Q-switched Nd:YAG lasers as a beam diagnostic for high current H{sup {minus}} beams. Because the threshold for photodetachment is only 0.75 eV, and the maximum detachment cross section is 4 {times} 10{sup {minus}17} cm{sup 2} at 1.5 eV, a 50 mJ/pulse Q-switched Nd:YAG laser can neutralize a significant fraction of the beam in a single 10-ns wide pulse. The neutral beam maintains nearly identical parameters as the parent H{sup {minus}} beam, including size, divergence, energy, energy spread, and phase spread. A dipole magnet can separate the neutral beam from the H{sup {minus}} beam to allow diagnostics on the neutral beam without intercepting the high-current H{sup {minus}} beam. Such a laser system can also be used to extract a low current proton beam, or to induce fluorescence in partially stripped heavy ion beams. Possible beamline diagnostic systems will be reviewed, and the neutral beam yields will be calculated.

  3. 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

  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. High illumination uniformity scheme with 32 beams configuration for direct-drive inertial confinement fusion

    NASA Astrophysics Data System (ADS)

    Li, Li; Gu, Chun; Xu, Lixin; Zhou, Shenlei

    2016-04-01

    The self-adapting algorithms are improved to optimize a beam configuration in the direct drive laser fusion system with the solid state lasers. A configuration of 32 laser beams is proposed for achieving a high uniformity illumination, with a root-mean-square deviation at 10-4 level. In our optimization, the parameters such as beam number, beam arrangement, and beam intensity profile are taken into account. The illumination uniformity robustness versus the parameters such as intensity profile deviations, power imbalance, intensity profile noise, the pointing error, and the target position error is also discussed. In this study, the model is assumed a solid-sphere illumination, and refraction effects of incident light on the corona are not considered. Our results may have a potential application in the design of the direct-drive laser fusion of the Shen Guang-II Upgrading facility (SG-II-U, China).

  6. High-speed reference-beam-angle control technique for holographic memory drive

    NASA Astrophysics Data System (ADS)

    Yamada, Ken-ichiro; Ogata, Takeshi; Hosaka, Makoto; Fujita, Koji; Okuyama, Atsushi

    2016-09-01

    We developed a holographic memory drive for next-generation optical memory. In this study, we present the key technology for achieving a high-speed transfer rate for reproduction, that is, a high-speed control technique for the reference beam angle. In reproduction in a holographic memory drive, there is the issue that the optimum reference beam angle during reproduction varies owing to distortion of the medium. The distortion is caused by, for example, temperature variation, beam irradiation, and moisture absorption. Therefore, a reference-beam-angle control technique to position the reference beam at the optimum angle is crucial. We developed a new optical system that generates an angle-error-signal to detect the optimum reference beam angle. To achieve the high-speed control technique using the new optical system, we developed a new control technique called adaptive final-state control (AFSC) that adds a second control input to the first one derived from conventional final-state control (FSC) at the time of angle-error-signal detection. We established an actual experimental system employing AFSC to achieve moving control between each page (Page Seek) within 300 µs. In sequential multiple Page Seeks, we were able to realize positioning to the optimum angles of the reference beam that maximize the diffracted beam intensity. We expect that applying the new control technique to the holographic memory drive will enable a giga-bit/s-class transfer rate.

  7. 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

  8. Design study of longitudinal dynamics of the drive beam in 1 TeV relativistic klystron two-beam accelerator

    SciTech Connect

    Li, H.; Yu, S.S.; Sessler, A.M.

    1994-10-01

    In this paper the authors present a design study on the longitudinal dynamics of a relativistic klystron two-beam accelerator (RK-TBA) scheme which has been proposed as a power source candidate for a 1 TeV next linear collider (NLC). They address the issue of maintaining stable power output at desired level for a 300-m long TBA with 150 extraction cavities and present their simulation results to demonstrate that it can be achieved by inductively detuning the extraction cavities to counter the space charge debunching effect on the drive beam. They then carry out simulation study to show that the beam bunches desired by the RK-TBA can be efficiently obtained by first chopping an initially uniform beam of low energy into a train of beam bunches with modest longitudinal dimension and then using the {open_quotes}adiabatic capture{close_quotes} scheme to bunch and accelerate these beam bunches into tight bunches at the operating energy of the drive beam. The authors have also examined the {open_quotes}after burner{close_quotes} scheme which is implemented in their RK-TBA design for efficiency enhancement.

  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. Computation of lower hybrid, neutral beam and bootstrap currents in consistent MHD equilibria

    SciTech Connect

    Devoto, R.S.; Blackfield, D.T.; Fenstermacher, M.E.; Bonoli, P.T.; Porkolab, M.

    1989-02-01

    A possible scenario for steady state current drive in large, high- temperature tokamaks includes current driven by lower hybrid (LH) waves in the outer region with high-energy neutral beams (NB) used for current drive in the core. In addition, provided the poloidal beta is sufficiently high, there can be substantial bootstrap (BS) current, as observed in the TFTR and JET experiments. In work reported previously, a computer code, ACCOME, was written to obtain a solution to the MHD equations which is consistent with current driven by neutral beams, electric fields, and neoclassical (bootstrap) effects. For the computation of the solution to the Grad-Shafranov equation, the SELENE code is used. Iteration is necessary between SELENE and the current-drive computations to obtain a consistent solution. In this paper we describe modifications to ACCOME to enable the computation of LH current in addition to the NB, BS, and OH currents. The next section describes the models used and then the final section presents an application to ITER. 4 refs., 4 figs.

  11. 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}.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  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. 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

  18. Electrical measurement techniques for pulsed high current electron beams

    SciTech Connect

    Struve, K.W.

    1986-04-01

    The advent of high current (1 to 100 kA), moderate energy (>10 MeV), short pulse (1 to 100 ns) electron accelerators used for charged particle beam research has motivated a need to complement standard diagnostics with development of new diagnostic techniques to measure electron beam parameters. A brief survey is given of the diagnostics for measuring beam current, position, size, energy, and emittance. While a broad scope of diagnostics will be discussed, this survey will emphasize diagnostics used on the Experimental Test Accelerator (ETA) and Advanced Test Accelerator (ATA). Focus is placed on diagnostics measuring beam current, position and size. Among the diagnostics discussed are resistive wall current monitors, B/sub theta/ loops, Rogowski coils, Faraday cups, and x-ray wire diagnostics. Operation at higher current levels also increases radiation and electromagnetic pulse interference. These difficulties and methods for circumventing them are also discussed.

  19. Limiting current of intense electron beams in a decelerating gap

    NASA Astrophysics Data System (ADS)

    Nusinovich, G. S.; Beaudoin, B. L.; Thompson, C.; Karakkad, J. A.; Antonsen, T. M.

    2016-02-01

    For numerous applications, it is desirable to develop electron beam driven efficient sources of electromagnetic radiation that are capable of producing the required power at beam voltages as low as possible. This trend is limited by space charge effects that cause the reduction of electron kinetic energy and can lead to electron reflection. So far, this effect was analyzed for intense beams propagating in uniform metallic pipes. In the present study, the limiting currents of intense electron beams are analyzed for the case of beam propagation in the tubes with gaps. A general treatment is illustrated by an example evaluating the limiting current in a high-power, tunable 1-10 MHz inductive output tube (IOT), which is currently under development for ionospheric modification. Results of the analytical theory are compared to results of numerical simulations. The results obtained allow one to estimate the interaction efficiency of IOTs.

  20. Drift distance survey in DPIS for high current beam production

    SciTech Connect

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

    2009-09-20

    In a laser ion source, plasma drift distance is one of the most important design parameters. Ion current density and beam pulse width are defined by plasma drift distance between laser target and beam extraction position. In direct plasma injection scheme (DPIS), which uses a laser ion source and Radio Frequency Quadrupole (RFQ) linac, we can apply relatively higher electric field at the beam extraction due to the unique shape of a positively biased electrode. However, when we aim at very high current acceleration like several tens of mA, we observed mismatched beam extraction conditions. We tested three different ion current at ion extraction region by changing plasma drift distance to study better extraction condition. In this experiment, C{sup 6+} beam was accelerated. We confirmed that the matching condition can be improved by controlling plasma drift distance.

  1. Neutral-beam current-driven high-poloidal-beta operation of the DIII-D tokamak

    SciTech Connect

    Simonen, T.C.; Matsuoka, M.; Bhadra, D.K.; Burrell, K.H.; Callis, R.W.; Chance, M.S.; Chu, M.S.; Greene, J.M.; Groebner, R.J.; Harvey, R.W.; and others

    1988-10-10

    Neutral-beam current-drive experiments in the DIII-D tokamak with a single null poloidal divertor are described. A plasma current of 0.34 MA has been sustained by neutral beams alone, and the energy confinement is of H-mode quality. Poloidal ..beta.. values reach 3.5 without disruption or coherent magnetic activity suggesting that these plasmas may be entering the second stability regime.

  2. Dynamics of a high-current relativistic electron beam

    SciTech Connect

    Strelkov, P. S.; Tarakanov, V. P.; Ivanov, I. E. Shumeiko, D. V.

    2015-06-15

    The dynamics of a high-current relativistic electron beam is studied experimentally and by numerical simulation. The beam is formed in a magnetically insulated diode with a transverse-blade explosive-emission cathode. It is found experimentally that the radius of a 500-keV beam with a current of 2 kA and duration of 500 ns decreases with time during the beam current pulse. The same effect was observed in numerical simulations. This effect is explained by a change in the shape of the cathode plasma during the current pulse, which, according to calculations, leads to a change in the beam parameters, such as the electron pitch angle and the spread over the longitudinal electron momentum. These parameters are hard to measure experimentally; however, the time evolution of the radial profile of the beam current density, which can be measured reliably, coincides with the simulation results. This allows one to expect that the behavior of the other beam parameters also agrees with numerical simulations.

  3. Low Impedance Bellows for High-current Beam Operations

    SciTech Connect

    Wu, G; Nassiri, A; Waldschmidt, G J; Yang, Y; Feingold, J J; Mammosser, J D; Rimmer, R A; Wang, H; Jang, J; Kim, S H

    2012-07-01

    In particle accelerators, bellows are commonly used to connect beamline components. Such bellows are traditionally shielded to lower the beam impedance. Excessive beam impedance can cause overheating in the bellows, especially in high beam current operation. For an SRF-based accelerator, the bellows must also be particulate free. Many designs of shielded bellows incorporate rf slides or fingers that prevent convolutions from being exposed to wakefields. Unfortunately these mechanical structures tend to generate particulates that, if left in the SRF accelerator, can migrate into superconducting cavities, the accelerator's critical components. In this paper, we describe a prototype unshielded bellows that has low beam impedance and no risk of particulate generation.

  4. Method for measuring and controlling beam current in ion beam processing

    DOEpatents

    Kearney, Patrick A.; Burkhart, Scott C.

    2003-04-29

    A method for producing film thickness control of ion beam sputter deposition films. Great improvements in film thickness control is accomplished by keeping the total current supplied to both the beam and suppressor grids of a radio frequency (RF) in beam source constant, rather than just the current supplied to the beam grid. By controlling both currents, using this method, deposition rates are more stable, and this allows the deposition of layers with extremely well controlled thicknesses to about 0.1%. The method is carried out by calculating deposition rates based on the total of the suppressor and beam currents and maintaining the total current constant by adjusting RF power which gives more consistent values.

  5. Effective shielding to measure beam current from an ion source

    SciTech Connect

    Bayle, H.; Delferrière, O.; Gobin, R.; Harrault, F.; Marroncle, J.; Senée, F.; Simon, C.; Tuske, O.

    2014-02-15

    To avoid saturation, beam current transformers must be shielded from solenoid, quad, and RFQ high stray fields. Good understanding of field distribution, shielding materials, and techniques is required. Space availability imposes compact shields along the beam pipe. This paper describes compact effective concatenated magnetic shields for IFMIF-EVEDA LIPAc LEBT and MEBT and for FAIR Proton Linac injector. They protect the ACCT Current Transformers beyond 37 mT radial external fields. Measurements made at Saclay on the SILHI source are presented.

  6. Laser diagnostic for high current H{sup {minus}} beams

    SciTech Connect

    Shafer, R.E.

    1998-01-01

    Laser photodetachment can be used on high current, high energy H{sup {minus}} beams to carry out a wide variety of beam diagnostic measurements parasitically during normal operation, without having to operate the facility at either reduced current or duty cycle. Suitable Q-switched laser systems are small, inexpensive, and can be mounted on or near the beamline. Most of the proposed laser-based diagnostics techniques have already been demonstrated.

  7. A RF--linac, FEL based drive beam injector for CLIC

    SciTech Connect

    Barletta, W.A. Department of Physics, UCLA, 405 Hilgard Avenue, Los Angeles, California ); Bonifacio, R. )

    1992-07-01

    We describe a means of producing at train of 40 kA pulses of 3 ps duration as the drive beam for CLIC using an RF--linac driven free electron laser (FEL) buncher. Potential debunching effecs are discussed. Finally we describe a low energy test experiment.

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

    SciTech Connect

    Murakami, Masanori; Park, Jin Myung

    2011-01-01

    revised for electron cyclotron current drive including parallel momentum conservation effects and for neutral beam current drive with finite orbit and magnetic pitch effects.

  9. 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

  10. 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)].

  11. Cumulative Beam Breakup in Linear Accelerators with Arbitrary Beam Current Profile

    SciTech Connect

    Jean Delayen

    2003-06-01

    An analytical formalism for the solution of cumulative beam breakup in linear accelerators with arbitrary time dependence of beam current is presented, and a closed-form expression for the time and position dependence of the transverse displacement is obtained. It is applied to the behavior of single bunches and to the steady state and transient behavior of dc beams and beams composed of point-like and finite length bunches. This formalism is also applied to the problem of cumulative beam breakup in the presence of random displacement of cavities and focusing elements, and a general solution is presented.

  12. Current Correlations in a Majorana Beam Splitter

    NASA Astrophysics Data System (ADS)

    Haim, Arbel; Berg, Erez; von Oppen, Felix; Oreg, Yuval

    We study current correlations in a T-junction composed of a grounded topological superconductor and of two normal-metal leads which are biased at a voltage V. We show that the existence of an isolated Majorana zero mode in the junction dictates a universal behavior for the cross correlation of the currents through the two normal-metal leads of the junction. The cross correlation is negative and approaches zero at high bias voltages as - 1 / V . This behavior is robust in the presence of disorder and multiple transverse channels, and persists at finite temperatures. In contrast, an accidental low-energy Andreev bound state gives rise to non-universal behavior of the cross correlation. We employ numerical transport simulations to corroborate our conclusions.

  13. Current correlations in a Majorana beam splitter

    NASA Astrophysics Data System (ADS)

    Haim, Arbel; Berg, Erez; von Oppen, Felix; Oreg, Yuval

    2015-12-01

    We study current correlations in a T junction composed of a grounded topological superconductor and of two normal-metal leads which are biased at a voltage V . We show that the existence of an isolated Majorana zero mode in the junction dictates a universal behavior for the cross correlation of the currents through the two normal-metal leads of the junction. The cross correlation is negative and approaches zero at high bias voltages as -1 /V . This behavior is robust in the presence of disorder and multiple transverse channels, and persists at finite temperatures. In contrast, an accidental low-energy Andreev bound state gives rise to nonuniversal behavior of the cross correlation. We employ numerical transport simulations to corroborate our conclusions.

  14. Beam loading compensation of traveling wave linacs through the time dependence of the rf drive

    SciTech Connect

    Towne N.; Rose J.

    2011-09-30

    Beam loading in traveling-wave linear accelerating structures leads to unacceptable spread of particle energies across an extended train of bunched particles due to beam-induced field and dispersion. Methods for modulating the rf power driving linacs are effective at reducing energy spread, but for general linacs do not have a clear analytic foundation. We report here methods for calculating how to modulate the rf drive in arbitrarily nonuniform traveling-wave linacs within the convective-transport (power-diffusion) model that results in no additional energy spread due to beam loading (but not dispersion). Varying group velocity, loss factor, and cell quality factor within a structure, and nonzero particle velocity, are handled.

  15. A determination of the current density in electron beams

    NASA Technical Reports Server (NTRS)

    Beil, R. J.

    1982-01-01

    Current gathering rotating probe techniques were used to examine the envelope shape and power density profile of electron beams used in electron beam welding devices. The electron power density contours which determine the shape of the weld vapor cavity, penetration, and local heat distribution were considered. A mathematical analysis consistent with a rotating probe technique necessary to determine the current density distribution (assumed symmetrically radial) in a cross-section of the beam is provided. An explanation of the experimental technique for obtaining data, a BASIC language computer program to determine the current density from the data, and a study indicating the level of confidence to be associated with results obtained are also provided. An example of the application of the analysis to some experimental electron beam data is included.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Examination of the CLIC drive beam pipe design for thermal distortion caused by distributed beam line

    SciTech Connect

    C. Johnson; K. Kloeppel

    1997-01-01

    Beam transport programs are widely used to estimate the distribution of power deposited in accelerator structures by particle beams, either intentionally as for targets or beam dumps or accidentally owing the beam loss incidents. While this is usually adequate for considerations of radiation safety, it does not reveal the expected temperature rise and its effect on structural integrity. To find this, thermal diffusion must be taken into account, requiring another step in the analysis. The method that has been proposed is to use the output of a transport program, perhaps modified, as input for a finite element analysis program that can solve the thermal diffusion equation. At Cern, the design of the CLIC beam pipe has been treated in this fashion. The power distribution produced in the walls by a distributed beam loss was found according to the widely-used electron shower code EGS4. The distribution of power density was then used to form the input for the finite element analysis pro gram ANSYS, which was able to find the expected temperature rise and the resulting thermal distortion. As a result of these studies, the beam pipe design can be modified to include features that will counteract such distortion.

  3. 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.

  4. Space charge templates for high-current beam modeling

    SciTech Connect

    Vorobiev, Leonid G.; /Fermilab

    2008-07-01

    A computational method to evaluate space charge potential and gradients of charged particle beam in the presence of conducting boundaries, has been introduced. The three-dimensional (3D) field of the beam can be derived as a convolution of macro Green's functions (template fields), satisfying the same boundary conditions, as the original beam. Numerical experiments gave a confidence that space charge effects can be modeled by templates with enough accuracy and generality within dramatically faster computational times than standard combination: a grid density + Poisson solvers, realized in the most of Particle in Cell codes. The achieved rapidity may significantly broaden the high-current beam design space, making the optimization in automatic mode possible, which so far was only feasible for simplest self-field formulations such as rms envelope equations. The template technique may be used as a standalone program, or as an optional field solver in existing beam dynamics codes both in one-passage structures and in rings.

  5. 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.

  6. 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.

  7. 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.

  8. Profile, Current, and Halo Monitors of the PROSCAN Beam Lines

    SciTech Connect

    Doelling, Rudolf

    2004-11-10

    PROSCAN, an extended medical facility using proton beams for the treatment of deep-seated tumors and eye melanoma, is under construction at PSI. Ionization chambers and secondary emission monitors will be used as current monitors and in a multi-strip configuration as profile monitors at the PROSCAN beam lines. A thin and a thick version of these detectors are in preparation as well as a 4-segment ionization chamber to detect the beam halo. Electromagnetic and microphonic noise from the signal and high-voltage cables, saturation due to recombination, and the evaluation of the profiles are discussed, as well as measures to detect failures of the detectors during operation.

  9. 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.

  10. 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

  11. 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.

  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. Current limiting mechanisms in electron and ion beam experiments

    NASA Technical Reports Server (NTRS)

    Olsen, R. C.

    1990-01-01

    The emission and collection of current from satellites or rockets in the ionosphere is a process which, at equilibrium, requires a balance between inward and outward currents. In most active experiments in the ionosphere and magnetosphere, the emitted current exceeds the integrated thermal current by one or more orders of magnitude. The system response is typically for the emitted current to be limited by processes such as differential charging of insulating surfaces, interactions between an emitted beam and the local plasma, and interactions between the beam and local neutral gas. These current limiting mechanisms have been illustrated for 20 years in sounding rocket and satellite experiments, which are reviewed here. Detailed presentations of the Spacecraft Charging at High Altitude (SCATHA) electron and ion gun experiments are used to demonstrate the general range of observed phenomena.

  14. 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.

  15. 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

  16. 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

  17. Focusing of high-current laser-driven ion beams

    NASA Astrophysics Data System (ADS)

    Badziak, J.; Jabłoński, S.

    2007-04-01

    Using a two-dimensional relativistic hydrodynamic code, it is shown that a dense high-current ion beam driven by a short-pulse laser can be effectively focused by curving the target front surface. The focused beam parameters essentially depend on the density gradient scale length of the preplasma Ln and the surface curvature radius RT. When Ln⩽0.5λL (λL is the laser wavelength) and RT is comparable with the laser beam aperture dL, a significant fraction of the accelerated ions is focused on a spot much smaller than dL, which results in a considerable increase in the ion fluence and current density. Using high-contrast multipetawatt picosecond laser pulses of relativistic intensity (˜1020W/cm2), focused ion (proton) current densities approaching those required for fast ignition of DT fuel seem to be feasible.

  18. Plasma charge current for controlling and monitoring electron beam welding with beam oscillation.

    PubMed

    Trushnikov, Dmitriy; Belenkiy, Vladimir; Shchavlev, Valeriy; Piskunov, Anatoliy; Abdullin, Aleksandr; Mladenov, Georgy

    2012-01-01

    Electron beam welding (EBW) shows certain problems with the control of focus regime. The electron beam focus can be controlled in electron-beam welding based on the parameters of a secondary signal. In this case, the parameters like secondary emissions and focus coil current have extreme relationships. There are two values of focus coil current which provide equal value signal parameters. Therefore, adaptive systems of electron beam focus control use low-frequency scanning of focus, which substantially limits the operation speed of these systems and has a negative effect on weld joint quality. The purpose of this study is to develop a method for operational control of the electron beam focus during welding in the deep penetration mode. The method uses the plasma charge current signal as an additional informational parameter. This parameter allows identification of the electron beam focus regime in electron-beam welding without application of additional low-frequency scanning of focus. It can be used for working out operational electron beam control methods focusing exactly on the welding. In addition, use of this parameter allows one to observe the shape of the keyhole during the welding process. PMID:23242276

  19. Plasma Charge Current for Controlling and Monitoring Electron Beam Welding with Beam Oscillation

    PubMed Central

    Trushnikov, Dmitriy; Belenkiy, Vladimir; Shchavlev, Valeriy; Piskunov, Anatoliy; Abdullin, Aleksandr; Mladenov, Georgy

    2012-01-01

    Electron beam welding (EBW) shows certain problems with the control of focus regime. The electron beam focus can be controlled in electron-beam welding based on the parameters of a secondary signal. In this case, the parameters like secondary emissions and focus coil current have extreme relationships. There are two values of focus coil current which provide equal value signal parameters. Therefore, adaptive systems of electron beam focus control use low-frequency scanning of focus, which substantially limits the operation speed of these systems and has a negative effect on weld joint quality. The purpose of this study is to develop a method for operational control of the electron beam focus during welding in the deep penetration mode. The method uses the plasma charge current signal as an additional informational parameter. This parameter allows identification of the electron beam focus regime in electron-beam welding without application of additional low-frequency scanning of focus. It can be used for working out operational electron beam control methods focusing exactly on the welding. In addition, use of this parameter allows one to observe the shape of the keyhole during the welding process. PMID:23242276

  20. Design of an LED-based compound optical system for a driving beam system.

    PubMed

    Ge, Aiming; Wang, Wei; Du, Zhengqing; Qiu, Peng; Wang, Junwei; Cai, Jinlin; Song, Xiaobo

    2013-04-20

    This paper proposes an LED-based compound optical system, which can be involved in the design of the driving beam system in automotive headlamps with high system efficiency and low power consumption. The compound system can meet the requirements announced in the UNECE regulation "Addendum 111: Regulation No. 112 Revision 2." Also, it is composed of a nonspherical reflector, a compound lens, and a two-dimensional diverging lens. Using a single device of high-brightness LED of merely 7.6 W, the specified illumination requirements for the driving beam can be achieved. As we have expected, on the test screen at a distance of 25 m, the simulation results, as well as the testing results for the prototype, can reach the illuminance distribution requirements, including all specified regions and key points. Moreover, this compound system enjoys the features of high compactness, high energy efficiency, and feasibility of manufacturing. PMID:23669678

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. Effective shielding to measure beam current from an ion source.

    PubMed

    Bayle, H; Delferrière, O; Gobin, R; Harrault, F; Marroncle, J; Senée, F; Simon, C; Tuske, O

    2014-02-01

    To avoid saturation, beam current transformers must be shielded from solenoid, quad, and RFQ high stray fields. Good understanding of field distribution, shielding materials, and techniques is required. Space availability imposes compact shields along the beam pipe. This paper describes compact effective concatenated magnetic shields for IFMIF-EVEDA LIPAc LEBT and MEBT and for FAIR Proton Linac injector. They protect the ACCT Current Transformers beyond 37 mT radial external fields. Measurements made at Saclay on the SILHI source are presented. PMID:24593447

  6. DPSS Laser Beam Quality Optimization Through Pump Current Tuning

    SciTech Connect

    Omohundro, Rob; Callen, Alice; Sukuta, Sydney; /San Jose City Coll.

    2012-03-30

    The goal of this study is to demonstrate how a DPSS laser beam's quality parameters can be simultaneously optimized through pump current tuning. Two DPSS lasers of the same make and model were used where the laser diode pump current was first varied to ascertain the lowest RMS noise region. The lowest noise was found to be 0.13% in this region and the best M{sup 2} value of 1.0 and highest laser output power were simultaneously attained at the same current point. The laser manufacturer reported a M{sup 2} value of 1.3 and RMS noise value of .14% for these lasers. This study therefore demonstrates that pump current tuning a DPSS laser can simultaneously optimize RMS Noise, Power and M{sup 2} values. Future studies will strive to broaden the scope of the beam quality parameters impacted by current tuning.

  7. 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

  8. 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.

  9. A neutron diagnostic for high current deuterium beams

    SciTech Connect

    Rebai, M.; Perelli Cippo, E.; Cavenago, M.; Dalla Palma, M.; Pasqualotto, R.; Tollin, M.; Croci, G.; Gervasini, G.; Ghezzi, F.; Grosso, G.; Tardocchi, M.; Murtas, F.; Gorini, G.

    2012-02-15

    A neutron diagnostic for high current deuterium beams is proposed for installation on the spectral shear interferometry for direct electric field reconstruction (SPIDER, Source for Production of Ion of Deuterium Extracted from RF plasma) test beam facility. The proposed detection system is called Close-contact Neutron Emission Surface Mapping (CNESM). The diagnostic aims at providing the map of the neutron emission on the beam dump surface by placing a detector in close contact, right behind the dump. CNESM uses gas electron multiplier detectors equipped with a cathode that also serves as neutron-proton converter foil. The cathode is made of a thin polythene film and an aluminium film; it is designed for detection of neutrons of energy >2.2 MeV with an incidence angle < 45 deg. CNESM was designed on the basis of simulations of the different steps from the deuteron beam interaction with the beam dump to the neutron detection in the nGEM. Neutron scattering was simulated with the MCNPX code. CNESM on SPIDER is a first step towards the application of this diagnostic technique to the MITICA beam test facility, where it will be used to resolve the horizontal profile of the beam intensity.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  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. 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.

  16. Nested folded-beam suspensions with low longitudinal stiffness for comb-drive actuators

    NASA Astrophysics Data System (ADS)

    Hou, Max T.; Huang, Ming-Xian; Chang, Chao-Min

    2014-12-01

    Nested folded-beam suspensions with a low longitudinal spring constant and a high lateral spring constant have been used in comb-drive actuators. In the new design, every two flexible beams and two stiff members form a parallelogram flexure, which is considered as an ‘element’ of the nested folded-beam suspension. A set of these flexures of increasing size were placed one outside another to compose a nested structure. In this way, a serial mechanical connection between adjacent parallelogram flexures was formed; thus, a longer output stroke was obtained by combining the stroke displacements of all flexures in an additive fashion. The designed suspensions were theoretically analyzed and numerically simulated. Furthermore, comb-drive actuators with conventional and new suspensions were fabricated and tested to verify the predicted function. In the testing cases, the longitudinal spring constants of suspensions with two (conventional), three and four parallelogram flexures on each side were measured as 2.77, 1.75 and 1.36 N m-1. The ratio among these three values was approximately 6:4:3, which is consistent with the theoretical predictions and simulation results. Microfabricated folded beams in series were achieved.

  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. Return Current Electron Beams and Their Generation of "Raman" Scattering

    NASA Astrophysics Data System (ADS)

    Simon, A.

    1998-11-01

    For some years, we(A. Simon and R. W. Short, Phys. Rev. Lett. 53), 1912 (1984). have proposed that the only reasonable explanation for many of the observations of "Raman" scattering is the presence of an electron beam in the plasma. (The beam creates a bump-on-tail instability.) Two major objections to this picture have been observation of Raman when no n_c/4 surface was present, with no likely source for the electron beam, and the necessity for the initially outward directed beam to bounce once to create the proper waves. Now new observations on LLE's OMEGA(R. Petrasso et al), this conference. and at LULI(C. Labaune et al)., Phys. Plasma 5, 234 (1998). have suggested a new origin for the electron beam. This new scenario answers the previous objections, maintains electron beams as the explanation of the older experiments, and may clear up puzzling observations that have remained unexplained. The new scenario is based on two assumptions: (1) High positive potentials develop in target plasmas during their creation. (2) A high-intensity laser beam initiates spark discharges from nearby surfaces to the target plasma. The resulting return current of electrons should be much more delta-like, is initially inwardly directed, and no longer requires the continued presence of a n_c/4 surface. Scattering of the interaction beam from the BOT waves yields the observed Raman signal. Experimental observations that support this picture will be cited. ``Pulsation'' of the scattering and broadband ``flashes'' are a natural part of this scenario. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460.

  19. Electron beam current in high power cylindrical diode

    SciTech Connect

    Roy, Amitava; Menon, R.; Mitra, S.; Sharma, Vishnu; Singh, S. K.; Nagesh, K. V.; Chakravarthy, D. P.

    2010-01-15

    Intense electron beam generation studies were carried out in high power cylindrical diode to investigate the effect of the accelerating gap and diode voltage on the electron beam current. The diode voltage has been varied from 130 to 356 kV, whereas the current density has been varied from 87 to 391 A/cm{sup 2} with 100 ns pulse duration. The experimentally obtained electron beam current in the cylindrical diode has been compared with the Langmuir-Blodgett law. It was found that the diode current can be explained by a model of anode and cathode plasma expanding toward each other. However, the diode voltage and current do not follow the bipolar space-charge limited flow model. It was also found that initially only a part of the cathode take part in the emission process. The plasma expands at 4.2 cm/mus for 1.7 cm anode-cathode gap and the plasma velocity decreases for smaller gaps. The electrode plasma expansion velocity of the cylindrical diode is much smaller as compared with the planar diode for the same accelerating gap and diode voltage. Therefore, much higher voltage can be obtained for the cylindrical diodes as compared with the planar diodes for the same accelerating gap.

  20. Beam Dynamics Aspects of High Current Beams in a Superconducting Proton Linac

    NASA Astrophysics Data System (ADS)

    Bellomo, Giovanni; Pagani, Carlo; Pierini, Paolo

    1997-05-01

    High current CW proton linac accelerators have been recently proposed for nuclear waste transmutation and concurrent energy production. In most of the designs the high energy part (100 MeV up to 1-2 GeV) of the linac employs low frequency superconducting structures (352-700 MHz). Here we present beam dynamics issues for the high current (10-50 mA) beams in the superconducting section of such an accelerator, based on 352 MHz β-graded, LEP style cavities, as proposed at Linac 96(C. Pagani, G. Bellomo, P. Pierini, ``A High Current Proton Linac with 352 MHz SC Cavities'', Proceedings of the XVIII Int. Linear Acc. Conf., eds. C. Hill, M. Vretenar, CERN 96-07, 15 November 1996). In particular, smooth beam propagation along the linac has been reached with decreasing phase advances along the linac, and the design has been updated to match the beam dynamics results. Mismatching oscillations are discussed, as they are considered to cause beam halo and, consequently, beam losses.

  1. Innovative real-time and non-destructive method of beam profile measurement under large beam current irradiation for BNCT

    NASA Astrophysics Data System (ADS)

    Takada, M.; Kamada, S.; Suda, M.; Fujii, R.; Nakamura, M.; Hoshi, M.; Sato, H.; Endo, S.; Hamano, T.; Arai, S.; Higashimata, A.

    2012-10-01

    We developed a real-time and non-destructive method of beam profile measurement on a target under large beam current irradiation, and without any complex radiation detectors or electrical circuits. We measured the beam profiles on a target by observing the target temperature using an infrared-radiation thermometer camera. The target temperatures were increased and decreased quickly by starting and stopping the beam irradiation within 1 s in response speed. Our method could trace beam movements rapidly. The beam size and position were calibrated by measuring O-ring heat on the target. Our method has the potential to measure beam profiles at beam current over 1 mA for proton and deuteron with the energy around 3 MeV and allows accelerator operators to adjust the beam location during beam irradiation experiments without decreasing the beam current.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Characterization of beam-driven instabilities and current redistribution in MST plasmas

    NASA Astrophysics Data System (ADS)

    Parke, E.

    2015-11-01

    A unique, high-rep-rate (>10 kHz) Thomson scattering diagnostic and a high-bandwidth FIR interferometer-polarimeter on MST have enabled characterization of beam-driven instabilities and magnetic equilibrium changes observed during high power (1 MW) neutral beam injection (NBI). While NBI leads to negligible net current drive, an increase in on-axis current density observed through Faraday rotation is offset by a reduction in mid-radius current. Identification of the phase flip in temperature fluctuations associated with tearing modes provides a sensitive measure of rational surface locations. This technique strongly constrains the safety factor for equilibrium reconstruction and provides a powerful new tool for measuring the equilibrium magnetic field. For example, the n = 6 temperature structure is observed to shift inward 1.1 +/- 0.6 cm, with an estimated reduction of q0 by 5%. This is consistent with a mid-radius reduction in current, and together the Faraday rotation and Thomson scattering measurements corroborate an inductive redistribution of current that compares well with TRANSP/MSTFit predictions. Interpreting tearing mode temperature structures in the RFP remains challenging; the effects of multiple, closely-spaced tearing modes on the mode phase measurement require further verification. In addition to equilibrium changes, previous work has shown that the large fast ion population drives instabilities at higher frequencies near the Alfvén continuum. Recent observations reveal a new instability at much lower frequency (~7 kHz) with strongly chirping behavior. It participates in extensive avalanches of the higher frequency energetic particle and Alfvénic modes to drive enhanced fast ion transport. Internal structures measured from Te and ne fluctuations, their dependence on the safety factor, as well as frequency scaling motivate speculation about mode identity. Work supported by U.S. DOE.

  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. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. A review of high beam current RFQ accelerators and funnels

    SciTech Connect

    Schneider, J.D.

    1998-12-01

    The authors review the design features of several high-current (> 20-mA) and high-power (> 1-mA average) proton or H{sup {minus}} injectors, RFQs, and funnels. They include a summary of observed performance and will mention a sampling of new designs, including the proposed incorporation of beam choppers. Different programs and organizations have chosen to build the RFQ in diverse configurations. Although the majority of RFQs are either low-current or very low duty-factor, several versions have included high-current and/or high-power designs for either protons or H{sup {minus}} ions. The challenges of cooling, handling high space-charge forces, and coupling with injectors and subsequent accelerators are significant. In all instances, beam tests were a valuable learning experience, because not always did these as-built structures perform exactly as predicted by the earlier design codes. They summarize the key operational parameters, indicate what was achieved, and highlight what was learned in these tests. Based on this generally good performance and high promise, even more challenging designs are being considered for new applications that include even higher powers, beam funnels and choppers.

  15. 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.

  16. 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.

  17. Beam position and total current monitor for heavy ion fusion beams

    SciTech Connect

    Berners, D.; Reginato, L.L.

    1992-10-01

    Heavy Ion Fusion requires moderate currents, 1-10A, for a duration of about 1 {mu}s. For accurate beam transport, the center of charge must be located to within {plus_minus} 100 {mu}m. Beam position and intensity may be excited at frequencies approaching 10 MHz, and the monitoring system must have adequate bandwidth to respond at these frequencies. We have modified the Rogowski technique by using distributed reactance multiturn magnetic loops so that it is suitable for measuring current position as well as amplitude. Four identical stripline coils are wound one per quadrant around a non magnetic core. The sensitivity is similar to that of a lumped coil system, with the added advantage of increased bandwidth. The voltages induced on the four separate coils are compared and suitable signal conditioning is performed to recover beam position and intensity information.

  18. Beam position and total current monitor for heavy ion fusion beams

    SciTech Connect

    Berners, D.; Reginato, L.L.

    1992-10-01

    Heavy Ion Fusion requires moderate currents, 1-10A, for a duration of about 1 [mu]s. For accurate beam transport, the center of charge must be located to within [plus minus] 100 [mu]m. Beam position and intensity may be excited at frequencies approaching 10 MHz, and the monitoring system must have adequate bandwidth to respond at these frequencies. We have modified the Rogowski technique by using distributed reactance multiturn magnetic loops so that it is suitable for measuring current position as well as amplitude. Four identical stripline coils are wound one per quadrant around a non magnetic core. The sensitivity is similar to that of a lumped coil system, with the added advantage of increased bandwidth. The voltages induced on the four separate coils are compared and suitable signal conditioning is performed to recover beam position and intensity information.

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Hybrid monitor for both beam position and tilt of pulsed high-current beams

    SciTech Connect

    Pang, J. He, X.; Ma, C.; Zhao, L.; Li, Q.; Dai, Z.

    2014-09-15

    A Hybrid beam monitor, integrated with both azimuthal and axial B-dot probes, was designed for simultaneous measurement of both beam position and beam angle for pulsed high-current beams at the same location in beam pipe. The output signals of axial B-dot probes were found to be mixed with signals caused by transverse position deviation. In order to eliminate the unwanted signals, an elimination method was developed and its feasibility tested on a 50-Ω coaxial line test stand. By this method, a waveform, shape-like to that of input current and proportional to the tilt angle, was simulated and processed by following integration step to achieve the tilt angle. The tests showed that the measurement error of displacement and tilt angle less than 0.3 mm and 1.5 mrad, respectively. The latter error could be reduced with improved probes by reducing the inductance of the axial B-dot probe, but the improvement reached a limit due to some unknown systemic mechanism.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.