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Laser intracavity absorption as a plasma diagnostic aid

Description: Trace levels of lithium are detected on 100 ..mu..sec timescales using an electrooptically tuned cw dye laser, in conjunction with a high resolution 0.03 A spectrometer/optical multichannel analyzer. The spectra of Li/sup 7/ resonance lines at 6708 A are analyzed for their Zeeman splitting patterns, after unfolding the effects of intracavity absorption (ICA) on the lineshape. For these timescales, a sensitivity to approx.1 x 10/sup 7/ lithium atoms/cc at a level of ..delta..I/I approx.10% has been observed, corresponding to enhancement factors over single pass absorption of approx.1000X. Intracavity enhancement of the line structure in the wings of the line, and a weak blue shift asymmetry have also been observed, but always in the presence of a central absorption feature. The 0.1 A instantaneous laser linewidth is usually scanned over a 1 A range, at frequencies up to 30 kHz. Ultimately this detection system will enclose a hot, dense fusion plasma ... intersecting an 80 keV, 10 mA neutral lithium beam to probe the plasma internal magnetic field structure, in a non-intrusive fashion.
Date: January 1, 1985
Creator: Wurden, G.A.
Partner: UNT Libraries Government Documents Department

A rad-hard, steady state, digital imaging bolometer system for ITER

Description: The concept and design of a new type of bolometer system which can function with excellent spatial resolution and good time resolution in the next generation of long-pulse (or steady-state), harsh-neutron environment fusion plasmas, is outlined. It uses a cooled pinhole camera design, employing a robust, passive, segmented radiation absorber, cooled from the back-side. Infrared emission from the absorber`s front surface is relayed by metal mirror optics to a shielded, high-resolution IR video camera with {+-} 0.01 C temperature resolution. It can make thousands of simultaneous ``pixel`` measurements at up to 50--60 Hz, without any signal wires through the vacuum interface.
Date: September 1, 1995
Creator: Wurden, G.A.
Partner: UNT Libraries Government Documents Department

Tokamak physics experiment: Diagnostic windows study

Description: We detail the study of diagnostic windows and window thermal stress remediation in the long-pulse, high-power Tokamak Physics Experiment (TPX) operation. The operating environment of the TPX diagnostic windows is reviewed, thermal loads on the windows estimated, and cooling requirements for the windows considered. Applicable window-cooling technology from other fields is reviewed and its application to the TPX windows considered. Methods for TPX window thermal conditioning are recommended, with some discussion of potential implementation problems provided. Recommendations for further research and development work to ensure performance of windows in the TPX system are presented.
Date: November 1, 1995
Creator: Merrigan, M. & Wurden, G.A.
Partner: UNT Libraries Government Documents Department

Harmonic launching of ion Bernstein waves via mode transformation

Description: Ion Bernstein wave excitation and propagation via finite ion-Larmor-radium mode-transformation are investigated theoretically and experimentally. It is shown that in the ion cyclotron range of frequencies omega less than or equal to 4..cap omega../sub i/, with modest ion temperatures (T/sub i/ less than or equal to 10 eV), the finite-Larmor-radius effect removes the wave singularity at lower-hybrid resonance layer, enabling an externally initiated electron plasma wave to transform continuously into an ion Bernstein wave. In an ACT-1 hydrogen plasma (T/sub e/ approx. = 2.5 eV, T/sub i/ less than or equal to 2.0 eV), externally excited ion Bernstein waves have been observed for omega less than or equal to 2..cap omega../sub i/ as well as for omega less than or equal to 3..cap omega../sub i/. The finite ion-Larmor-radius mode transformation process resulting in strong ion Bernstein wave excitation has been experimentally verified. Detailed measurements of the wave dispersion relation and of the wave-packet trajectory show excellent agreement with theory. The dependence of the excited ion Bernstein wave on the antenna phasing, the plasma density, and on the neutral pressure (T/sub i/) is also investigated.
Date: June 1, 1982
Creator: Ono, M.; Wong, K.L. & Wurden, G.A.
Partner: UNT Libraries Government Documents Department

Ion temperature via laser scattering on ion Bernstein waves

Description: Hydrogen ion temperature has been measured in a warm toroidal plasma with externally launched ion Bernstein waves detected by heterodyne CO/sub 2/ laser scattering. Radial scanning of the laser beam allows precise determination of k/sub perpendicular to/ for the finite ion Larmor radius wave (..omega.. approx. less than or equal to 2..cap omega../sub i/). Knowledge of the magnetic field strength and ion concentration then give a radially resolved ion temperature from the dispersion relation. Probe measurements and Doppler broadening of ArII 4806A give excellent agreement.
Date: October 1, 1981
Creator: Wurden, G.A.; Ono, M. & Wong, K.L.
Partner: UNT Libraries Government Documents Department

Ion Bernstein-wave excitation via finite-Larmor-radius mode-transformation process

Description: It is shown that in the ion cyclotron range of frequency ..omega.. less than or equal to 2 ..cap omega../sub i/, the finite-Larmor-radius effect removes the wave singularity at the lower-hybrid resonance layer, enabling an externally initiated electron plasma wave to propagate freely through the resonance layer, transforming continuously into an ion Bernstein wave. In an ACT-1 hydrogen plasma (T/sub e/ approx. = 2.5 eV, T/sub i/ approx. = 1.5 eV), linear excitation of ion Bernstein waves has been investigated experimentally for ..omega.. approx. = 2..cap omega../sub i/. The mode-transformation process resulting in a strong ..omega.. approx. = 2 ..cap omega../sub i/ ion Berstein wave excitation without observable reflections has been experimentally verified. Detailed measurements of wave dispersion relation and of the wave-packet trajectory show excellent agreement with theory.
Date: July 1, 1981
Creator: Ono, M.; Wong, K.L. & Wurden, G.A.
Partner: UNT Libraries Government Documents Department

Observation of magnetized-ion thermal effects on lower-hybrid waves

Description: Finite ion Larmor radius modification of lower-hybrid waves in the ACT-1 toroidal plasma at frequencies ..omega.. approx. = 4 to 8 ..omega../sub ci/, close to the lower-hybrid resonance layer, is observed experimentally. Probe and CO/sub 2/ laser scans of the wave amplitude show interference patterns at frequencies above each ion cyclotron harmonic. Modeling with a hot-ion, electrostatic ray tracing code and Fourier reconstruction of the waveform suggests that linear mode conversion to hot plasma waves is occurring.
Date: February 1, 1983
Creator: Wurden, G.A.; Wong, K.L.; Skiff, F. & Ono, M.
Partner: UNT Libraries Government Documents Department

Efficient ion heating via finite-Larmor-radius ICRF

Description: Ion heating by externally launched ion Bernstein waves is investigated in the ACT-1 hydrogen plasma. Detailed measurements of wave absorption and of the ion temperature profiles have clearly identified various heating layers near the ion cyclotron harmonics of deuterium-like and tritium-like ions. The observed heating of 10 eV/WATT/10/sup 10/ cm/sup -3/ and the power-balance estimates suggest excellent overall efficiency for FLR-ICRF heating.
Date: March 1, 1983
Creator: Ono, M.; Wurden, G.A. & Wong, K.L.
Partner: UNT Libraries Government Documents Department

Lower hybrid wave resonance cone detection via CO/sub 2/ laser scattering

Description: Lower hybrid waves are studied in the Princeton ACT-I steady-state toroidal plasma device using a radially scanning CO/sub 2/ laser scattering system with both amplitude and phase sensitive detection techniques. Clearly defined resonance cones launched from external electrostatic antennas are seen to disappear as the plasma density is raised. Scaling of LHW laser signal with RF power in the presence of resonance cones shows nonlinearities associated with RF induced changes in the effective laser scattering volume. Absolute fluctuation level estimates suggest this occurs when e PHI/T/sub e/ greater than or equal to 1. Wavefront curvature effects can cause a complete loss of resonance cone laser signals, even though probes indicate that cones are still present. Measurements of the wave k/sub perpendicular/-spectrum in the plasma show direct evidence for electron Landau filtering of the original wave k/sub parallel/-spectrum launched from the antenna at the plasma edge, and strong dependence on antenna phasing. Finally, frequency shifts and loss of the resonance cone signal are associated with high levels of plasma density edge turbulence.
Date: April 1, 1984
Creator: Wurden, G.A.; Wong, K.L. & Ono, M.
Partner: UNT Libraries Government Documents Department

Operational Performance of the Two-Channel 10 Megawatt Feedback Amplifier System for MHD Control on the Columbia University HBT-EP Tokamak

Description: The operational characteristics and performance of the two channel 10 Megawatt MHD feedback control system as installed by Los Alamos National Laboratory on the Columbia University HBT-EP tokamak are described. In the present configuration, driving independent 300 {micro}H saddle coil sets, each channel can deliver 1100 Amperes and 16 kV peak to peak. Full power bandwidth is about 12 kHz, with capabilities at reduced power to 30 kHz. The present system topology is designed to suppress magnetohydrodynamic activity with m=2, n=1 symmetry. Application of either static (single phase) or rotating (twin phased) magnetic perturbations shows the ability to spin up or slow down the plasma, and also prevent (or cause) so-called ''mode-locking''. Open loop and active feedback experiments using a digital signal processor (DSP) have been performed on the HBT-EP tokamak and initial results show the ability to manipulate the plasma MHD mode frequency.
Date: October 6, 1997
Creator: Reass, W.A. & Wurden, G.A.
Partner: UNT Libraries Government Documents Department

Initial Design of the 60 Megawatt Rotating Magnetic Field (RMF) Oscillator System for the University of Washington ''TCS'' Field Reversed Configuration Experiment

Description: This paper presents the initial electrical and mechanical design of two phase-locked 30 Megawatt RMS, 150 kHz oscillator systems used for current drive and plasma sustainment of the ''Translation, Confinement, and Sustainment'' (TCS) field reversed configuration (FRC) plasma. By the application of orthogonally-placed saddle coils on the surface of the glass vacuum vessel, the phase-controlled rotating magnetic field perturbation will induce an electric field in the plasma which should counter the intrinsic ohmic decay of the plasma, and maintain the FRC. Each system utilizes a bank of 6 parallel magnetically beamed ML8618 triodes. These devices are rated at 250 Amperes cathode current and a 45 kV plate voltage. An advantage of the magnetically beamed triode is their extreme efficiency, requiring only 2.5 kW of filament and a few amps and a few kV of grid drive. Each 3.5 uH saddle coil is configured with an adjustable tank circuit (for tuning). Assuming no losses and a nominal 18 kV plate voltage, the tubes can circulate about 30 kV and 9 kA (pk to pk) in the saddle coil antenna, a circulating power of over 33 megawatts RMS. On each cycle the tubes can kick in up to 1500 Amperes, providing a robust phase control. DC high-voltage from the tubes is isolated from the saddle coil antennas and tank circuits by a 1:1 coaxial air-core balun transformer. To control the ML8618's phase and amplitude, fast 150 Ampere ''totem-pole'' grid drivers, an ''on'' hot-deck and an ''off'' hot-deck are utilized. The hot-decks use up to 6 each 3CPX1500A7 slotted radial beam triodes. By adjusting the conduction angle, amplitude may be regulated, with inter-pulse timing, phase angle can be controlled. A central feedback timing chassis monitors each systems' saddle coil antenna and appropriately derives each systems timing signals. Fiber-optic cables are used to isolate ...
Date: October 6, 1997
Creator: Reass, W.A.; Miera, D.A. & Wurden, G.A.
Partner: UNT Libraries Government Documents Department

Experiences with remote collaborations in fusion research

Description: The magnetic fusion research community has considerable experience in placing remote collaboration tools in the hands of real user. The ability to remotely view operations and to control selected instrumentation and analysis tasks has been demonstrated. University of Wisconsin scientists making turbulence measurements on TFTR: (1) were provided with a remote control room from which they could operate their diagnostic, while keeping in close contact with their colleagues in Princeton. LLNL has assembled a remote control room in Livermore in support of a large, long term collaboration on the DIII-D tokamak in San Diego. (2) From the same control room, a joint team of MIT and LLNL scientists has conducted full functional operation of the Alcator C-Mod tokamak located 3,000 miles away in Cambridge Massachusetts. (3) These early efforts have been highly successful, but are only the first steps needed to demonstrate the technical feasibility of a complete facilities on line environment. These efforts have provided a proof of principle for the collaboratory concept and they have also pointed out shortcomings in current generation tools and approaches. Current experiences and future directions will be discussed.
Date: March 1998
Creator: Wurden, G.A.; Davis, S. & Barnes, D.
Partner: UNT Libraries Government Documents Department

Refueling and density control in the ZT-40M reversed field pinch

Description: The effects of pellet injection and gas puff refueling have been studied in the ZT-40M Reversed Field Pinch. Multiple deuterium pellets (less than or equal to 6 x 10/sup 19/D atoms/pellet) with velocities ranging from 300 to 700 m/sec have been injected into plasmas with n-bar/sub e/ approx.1 to 5 X 10/sup 19/m/sup -3/, I/sub phi/ approx.100 to 250 kA, T/sub e/(0) approx.150 to 300 eV and discharge durations of less than or equal to 20 msec. Photographs and an array D/sub ..cap alpha../ detectors show substantial deflection of the pellet trajectory in both the poloidal and toroidal planes, due to asymmetric ablation of the pellet by electrons streaming along field lines. To compensate for the poloidal deflection, the injector was moved up +14 cm off-axis, allowing the pellets to curve down to the midplane. In this fashion, central peaking of the pellet density deposition profile can be obtained. Both electron and ion temperatures fall in response to the density rise, such that ..beta../sub theta/(..beta../sub theta/ identical to n-bar/sub e/(T/sub e/(0) + T/sub i/)/(B/sub theta/(a))/sup 2/) remains roughly constant. Energy confinement is momentarily degraded, and typically a decrease in F (F identical to B/sub phi/(a)/(B/sub phi/)) is seen as magnetic energy is converted to plasma energy when the pellet ablates. As a result of pellet injection at I/sub phi/ = 150 kA we observe T/sub e/(0) ..cap alpha.. n-bar/sub e//sup -.9 +- .1/, while the helicity based resistivity eta/sub k/ transiently varies as n-bar/sub e//sup .7 +- .1/. While the achievement of center-peaked density profiles is possible with pellet injection, gas puffing at rates strong enough to show a 50% increase in n-bar/sub e/ over a period of 10 msec (approx.150 torr-litres/sec) leads to hollow density profiles. The refueling requirements for parameters expected in the next generation RFPs (ZTH, RFX) ...
Date: January 1, 1987
Creator: Wurden, G.A.; Weber, P.G.; Watt, R.G.; Munson, C.P.; Cayton, T.E. & Buechl, K.
Partner: UNT Libraries Government Documents Department

Pellet injection in the RFP (Reversed Field Pinch)

Description: Observation of pellets injected into the ZT-40M Reversed Field Pinch has allowed a new twist on the usual tokamak ablation physics modeling. The RFP provides a strong ohmic heating regime with relatively high electron drift parameter (xi/sub drift/ /approximately/ 0.2), in the presence of a highly sheared magnetic field geometry. In situ photos of the pellet ablation cloud using a grated-intensified CCD camera, as well as two-view integrated photos of the pellet trajectory show substantial modification of the original pellet trajectory, in both direction and speed. Depending on the launch geometry, increases in the initial 500 m/s pellet speed by 50% have been observed, and a ski jump deflector plate in the launch port has been used to counteract strong poloidal curvature. In contrast to the tokamak, the D/sub ..cap alpha../ light signature is strongest near the edge, and weaker in the plasma center. Additional information on ion temperature response to pellet injection with 20 ..mu..sec time resolution has been obtained using a 5-channel neutral particle analyzer (NPA). The energy confinement is transiently degraded while the beta is largely unchanged. This may be indicative of pellet injection into a high-beta plasma operating at fixed beta. 10 refs., 6 figs.
Date: 1988~
Creator: Wurden, G. A.; Weber, P. G.; Munson, C. P.; Cayton, T. E.; Bunting, C. A. & Carolan, P. G.
Partner: UNT Libraries Government Documents Department

Design, construction, and first operational results of a 5 megawatt feedback controlled amplifier system for disruption control on the Columbia University HBT-EP tokamak

Description: This paper presents the electrical design and first operational results of a 5 Megawatt feedback controlled amplifier system designed to drive a 300 uH saddle coil set on the ``HBT-EP`` tokamak. It will be used to develop various plasma feedback techniques to control and inhibit the onset of plasma disruptions that are observed in high ``B`` plasmas. To provide a well characterized system, a high fidelity, high power closed loop amplifier system has been refurbished from the Los Alamos ``ZT-P`` equilibrium feedback system. In it`s configuration developed for the Columbia HBT-EP tokamak, any desired waveform may be generated within a I 100 ampere and 16 kV peak to peak dynamic range. An energy storage capacitor bank presently limits the effective full power pulse width to 10 mS. The full power bandwidth driving the saddle coil set is {approximately}12 kHz, with bandwidth at reduced powers exceeding 30 kHz. The system is designed similar to a grounded cathode, push-pull, transformer coupled, tube type amplifier system. `Me push pull amplifier consists of 6 each Machlett ML8618 magnetically beamed triodes, 3 on each end of the (center tapped) coupling transformer. The transformer has .I volt-seconds of core and a 1:1 turns ratio. The transformer is specially designed for high power, low leakage inductance, and high bandwidth. Each array of ML8618`s is (grid) driven with a fiber optic controlled hotdeck with a 3CXI0,000A7 (triode) output. To linearize the ML8618 grid drive, a minor feedback loop in the hotdeck is utilized. Overall system response is controlled by active feedback of the saddle coil current, derived from a coaxial current viewing resistor. The detailed electrical design of the power amplifier, transformer, and feedback system will be provided in addition to recent HBT-EP operational results.
Date: December 31, 1995
Creator: Reass, W.A.; Alvestad, H.A.; Bartsch, R.R.; Wurden, G.A.; Ivers, T.H. & Nadle, D.L.
Partner: UNT Libraries Government Documents Department

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

Description: 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.
Date: December 1, 2000
Creator: Tobin, S. J.; Reass, W. A.; Schrank, L. S.; Wurden, G. A.; Guo, H. Y.; Hoffman, A. L. et al.
Partner: UNT Libraries Government Documents Department

Atlas chamber, power flow channel, and diagnostic interface design

Description: The Atlas pulsed-power machine, presently being designed at Los Alamos, will deliver a pulse of {approximately} 45 MA, in 4--5 {micro}sec, with energies of up to 6 MJ (from a bank of 36 MJ maximum) to a load assembly, located in vacuum. Design considerations for the vacuum vessel, power flow channel from the vessel inward, are presented. In contrast to Sandia`s PBFA II-Z, where 20 MA currents and 2--2.5 MJ of energy are delivered to ({approximately} 15 mg) loads in {approximately} 100 nsec, the Atlas structures will have to be designed for longer timescales and higher energies to drive heavy lines ({approximately} 70 g). Design issues for the chamber include materials stresses, formation of (and protection from) debris and molten jets, impulse loading, and survivability and ease of replacement of internal structures. For the power flow channel designs, issues are minimizing inductance, preventing movement of conductors during and after firing, damage mitigation, reducing the cost of materials and installation, and electrical insulation. A key issue for damage mitigation is the radius within which total destruction of material objects occurs. Choices of vessel size, insulator materials, cost and ease of manufacturing, and mechanical stability issues are presently in the conceptual design phase. Typical access requirements for diagnostics (including radial and axial X-ray backlighting, flux loops, spectroscopy, interferometry, bolometry, etc.) are provided for in the design.
Date: September 1, 1997
Creator: Wurden, G.A.; Davis, H.A.; Taylor, A.; Bowman, D.; Ballard, E.; Ney, S. et al.
Partner: UNT Libraries Government Documents Department

Triton burnup study in JT-60U

Description: The behavior of 1 MeV tritons produced in the d(d,p)t reaction is important to predict the properties of D-T produced 3.5 MeV alphas because 1 MeV tritons and 3.5 MeV alphas have similar kinematic properties, such as Larmor radius and precession frequency. The confinement and slowing down of the fast tritons were investigated by measuring the 14 MeV and the 2.5 MeV neutron production rates. Here the time resolved triton burnup measurements have been performed using a new type 14 MeV neutron detector based on scintillating fibers, as part of a US-Japan tokamak collaboration. Loss of alpha particles due to toroidal ripple is one of the most important issues to be solved for a fusion reactor such as ITER. The authors investigated the toroidal ripple effect on the fast triton by analyzing the time history of the 14 MeV emission after NB turn-off.
Date: October 1, 1995
Creator: Nishitani, T.; Hoek, M.; Isobe, M.; Tobita, K.; Kusama, Y.; Harano, H. et al.
Partner: UNT Libraries Government Documents Department

Fast electron studies in the ZT-40M edge plasma

Description: Measurements of the edge plasma on the ZT-40M Reversed Field Pinch (RFP) show the presence of a dilute (1 to 10 per cent of the edge density), fast (T{sub H} {approx equal} (2 {minus} 3)T{sub {epsilon}0}) electron tail with a nearly unidirectional flow along B in a toroidal sense that is against the external applied electric field force. These studies have been extended over a wide range of operating conditions including high density and krypton-injected radiation-dominated (P{sub RAD} {approx equal} 0.9 P{sub IN}) discharges. In all cases the current density of the fast electrons is sufficient to account for the current density required to maintain the RFP. For low current 60 kA discharges this result has been confirmed in to a depth 20 mm inside of the reversal surface suggesting that the source of the fast electrons is the core of the discharge. The fast electrons also carry a large power flux parallel to B (several hundreds of MW/m{sup 2}, typically), and radial transport measurements of the fast electrons in the shadow of a movable limiter for 120 kA standard discharges indicate that the fast electrons are the primary electron energy loss channel. The fast electrons are a significant energy loss channel for a broad range of other cases as well. The collisionality of the fast electrons varies widely over the range of cases studied and it is noted that a small backflowing component of fast electrons increases in relative size as the collisionality increases. An estimate of the magnetic field stochastic diffusivity at the edge is made from the fast electron limiter shadow measurements and shows that the stochasticity of the magnetic field is low at the edge relative to the core, in agreement with magnetic fluctuation diffusivity measurements and MHD simulations. 35 refs., 10 figs.
Date: January 1, 1990
Creator: Ingraham, J.C.; Ellis, R.F.; Downing, J.N.; Miller, G.; Munson, C.P.; Pickrell, M.M. et al.
Partner: UNT Libraries Government Documents Department

Recent progress on the National Spherical Torus Experiment (NSTX)

Description: Recent upgrades to the NSTX facility have led to improved plasma performance. Using 5MW of neutral beam injection, plasmas with toroidal {beta}{sub T} (= 2{mu}{sub 0}<p>/B{sub T}{sup 2} where B{sub T} is the vacuum toroidal field at the plasma geometric center) > 30% have been achieved with normalized {beta}{sub N} (={beta}{sub T}aB{sub I}/I{sub p}) {approx} 6% {center_dot} m {center_dot} T/MA. The highest {beta} discharge exceeded the calculated no-wall {beta} limit for several wall times. The stored energy has reached 390kJ at higher toroidal field (0.55T) corresponding to {beta}{sub T} {approx} 20% and {beta}{sub N} = 5.4. Long pulse ({approx}1s) high {beta}{sub p} ({approx}1.5) discharges have also been obtained at higher B{sub {phi}} (0.5T) with up to 6MW NBI power. The highest energy confinement times, up to 120ms, were observed during H-mode operation which is now routine. Confinement times of {approx} 1.5 times ITER98pby2 for several {tau}{sub E} are observed during both H-Mode and non-H-Mode discharges. Calculations indicate that many NSTX discharges have very good ion confinement, approaching neoclassical levels. High Harmonic Fast Wave current drive has been demonstrated by comparing discharges with waves launched parallel and anti-parallel to the plasma current.
Date: January 1, 2002
Creator: Maqueda, R. J. (Ricardo J.); Wurden, G. A. (Glen A.); Gates, D. A.; Bell, M. G.; Bialek, J.; Bigelow, T. et al.
Partner: UNT Libraries Government Documents Department

Active Control of 2/1 Magnetic Islands in the HBT-EP Tokamak

Description: Closed and open loop control techniques were applied to growing m/n=2/1 rotating islands in wall stabilized plasmas in the HBT-EP tokamak. The approach taken by HBT-EP combines an adjustable segmented conducting wall (which slows the growth or stabilizes ideal external kinks) with a number of small (6{degree} wide) saddle coils located between the gaps of the conducting wall. In this paper we report demonstration of 2-phase island rotation control from 5 kHz to 15 kHz and observation of the phase instability which are well modeled by the single-helicity, predictions of nonlinear Rutherford island dynamics for 2/1 tearing modes including important effects of ion inertia and FLR which appears as a damping term in the model equations. The closed loop response of active feedback control of the 2/1 mode at moderate gain was observed to be in good agreement with the theory. We have also demonstrated suppression of the 2/1 island growth using an asynchronous frequency modulation drive which maintains the flow damping of the island by application of rotating control fields with frequencies alternating above and below the natural mode frequency. This frequency modulation control technique was also able to prevent disruptions normally observed to follow giant sawtooth crashes in the plasma core.
Date: November 18, 1997
Creator: Navratil, G.A.; Cates, C.; Mauel, M.E.; Maurer, D.; Nadle, D.; Taylor, E. et al.
Partner: UNT Libraries Government Documents Department