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Title: Oscillating-Field Current-Drive Experiments in a Reversed Field Pinch

Abstract

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.

Authors:
; ; ;  [1]
  1. University of Wisconsin, Madison, Wisconsin 53706 (United States)
Publication Date:
OSTI Identifier:
20776988
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 96; Journal Issue: 3; Other Information: DOI: 10.1103/PhysRevLett.96.035003; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CURRENTS; ELECTRIC POTENTIAL; HELICITY; INDUCTION; PLASMA; REVERSE-FIELD PINCH; REVERSED-FIELD PINCH DEVICES; STEADY-STATE CONDITIONS

Citation Formats

McCollam, K.J., Blair, A.P., Prager, S.C., and Sarff, J.S. Oscillating-Field Current-Drive Experiments in a Reversed Field Pinch. United States: N. p., 2006. Web. doi:10.1103/PhysRevLett.96.035003.
McCollam, K.J., Blair, A.P., Prager, S.C., & Sarff, J.S. Oscillating-Field Current-Drive Experiments in a Reversed Field Pinch. United States. doi:10.1103/PhysRevLett.96.035003.
McCollam, K.J., Blair, A.P., Prager, S.C., and Sarff, J.S. Fri . "Oscillating-Field Current-Drive Experiments in a Reversed Field Pinch". United States. doi:10.1103/PhysRevLett.96.035003.
@article{osti_20776988,
title = {Oscillating-Field Current-Drive Experiments in a Reversed Field Pinch},
author = {McCollam, K.J. and Blair, A.P. and Prager, S.C. and Sarff, J.S.},
abstractNote = {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.},
doi = {10.1103/PhysRevLett.96.035003},
journal = {Physical Review Letters},
number = 3,
volume = 96,
place = {United States},
year = {Fri Jan 27 00:00:00 EST 2006},
month = {Fri Jan 27 00:00:00 EST 2006}
}
  • Steady-state current sustainment by oscillating field current drive (OFCD) utilizes a technique in which the toroidal and poloidal magnetic fields at the plasma surface are modulated at audio frequencies in quadrature. Experiments on the ZT-40M reversed field pinch (Fusion Technol. 8, 1571 (1985)) have examined OFCD over a range of modulation amplitude, frequency, and phase. For all cases examined, the magnitude of the plasma current is dependent on the phase of the modulations as predicted by theory. However, evidence of current drive has only been observed at relatively low levels of injected power. For larger modulation amplitudes, the data suggestmore » that substantial current drive is offset by increased plasma resistance as a result of modulation enhanced plasma--wall interactions. The initial experimental results and supporting theoretical interpretations of OFCD are discussed.« less
  • Oscillating field current drive (OFCD), also known as F-THETA pumping, is a steady-state current drive technique proposed for the reversed field pinch (RFP). Unlike other current drive techniques, which employ high technology, invasive, and power intensive schemes using radio frequency or neutral particle injection, F-THETA pumping entails driving the toroidal and poloidal magnetic field circuits with low-frequency (audio) oscillating voltage sources. Current drive by this technique is a consequence of the strong nonlinear plasma coupling in the RFP. Because of its low frequency and efficient plasma coupling, F-THETA pumping shows excellent promise as a reactor relevant current drive technique. Amore » conceptual and computational study of this concept, including its experimental and reactor relevance, is explored in this paper.« less
  • Oscillating field current drive on the reversed-field pinch is simulated by using a three-dimensional nonlinear resistive magnetohydrodynamic model in conjunction with a one-dimensional hyper-resistive model. When input from the three-dimensional model is used for fluctuating fields in the hyper-resistive equations, the two models are found to give similar relaxed profiles. Comparisons are made with experiments on the Los Alamos National Laboratory ZT-40M reversed-field pinch device (Nucl. Fusion 25, 1321 (1985)). Simulation results indicate that the oscillation period must be much less than the resistive decay time, but should not be much less than the hyper-resistive relaxation time, in order tomore » maintain reversal without a steady-state driving field.« less
  • 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 thatmore » this could be a very attractive method for high temperature plasmas.« less
  • A model for studying current drive by helicity injection in reversed field pinches (RFP's) is proposed. In this model, the helicity supplied by the external circuits is injected into an exterior vacuum region that models the resistive edge region where skin currents can decay. Full Taylor relaxations allow this injected helicity to penetrate into the bulk of the plasma. Results on Ohmically driven discharges are shown, benchmarking the model with current experiments. Results on oscillating current drive are also presented, including studies of the dependence upon the driving voltages, the edge resistivity, and the number of relaxations per oscillation cycle.