Enhanced confinement in the MST reversed-field pinch

Conference · Sun Dec 31 04:00:00 EST 1995

OSTI ID:178186

Chapman, B E; Cekic, M; Den Hartog, D J; Holly, D; Prager, S C; Sarff, J S ^[1]

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1. Univ. of Wisconsin, Madison, WI (United States)

The Madison Symmetric Torus (MST) reversed-field pinch is a toroidal, ohmically-heated, magnetic fusion research device. Recent MST discharges have exhibited energy confinement times, {tau}{sub E}, that are 2--3 times greater than normal. An important benchmark of the MST`s performance, {tau}{sub E} {equivalent_to} (total plasma energy)/(input ohmic heating power) and is about 1 ms in normal discharges. {tau}{sub E} is limited by transport of energy and particles out of the plasma core due primarily to fluctuations in the structure and magnitude of the internal magnetic field. The dominant magnetic fluctuations are sawtooth events, so-named for the shape of their waveform in many plasma parameters. Sawteeth arise due to overpeaking of the current-density profile on the magnetic axis. During each sawtooth, the total plasma energy decreases, and the ohmic heating power increases, resulting in a sharp drop in {tau}{sub E}. Recently, discharges with sawtooth-free periods have been achieved, resulting in enhanced confinement. One method of preventing sawteeth is to actively drive current in the edge plasma. This flattens the normally-peaked current-density profile. The best results with this method have been achieved with careful conditioning by solid-target boronization of the plasma-facing inner wall of the vacuum vessel. Boronization has also led to the spontaneous appearance of sawtooth-free periods, without external current drive. Both driven and spontaneous sawtooth-free periods typically result in a {tau}{sub E} that is 2--3 times greater than in normal discharges. Attempts to further enhance {tau}{sub E} are planned for the Spring of 1995. In addition to more sophisticated utilization of solid-target boronization, deuterium and helium will be used to fuel the discharges (hydrogen is the MST`s usual working gas). Use of different gases will allow a test of the idea that magnetic-fluctuation-induced transport of ions decreases with ion mass.

• OSTI ID: 178186
• Report Number(s): CONF-950612--; ISBN 0-7803-2669-5
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
CHARGED-PARTICLE TRANSPORT
CONFINEMENT TIME
ENERGY TRANSFER
MST DEVICE
PLASMA CONFINEMENT
SAWTOOTH OSCILLATIONS
VACUUM SYSTEMS