Session 6P - TEXT-U, Tore Supra, HBT-EP, and Other Tokamaks.
POSTER session, Wednesday afternoon, November 13
Exhibit Hall - Concourse Level, Adam's Mark
The characteristics of \(\beta\)-limiting and low \itq* disruptions plus the conditions under which they occur have been studied as a function of plasma-wall separation. Coupling between the wall and the plasma is varied by systematically adjusting the radial position, \itb, of a conducting wall section relative to the surface of the plasma of minor radius \ita. MHD instabilities with kink-like helicities, mainly \( m=3, n=1 \), and other long wavelength modes (\ite.g. \( 2/1; 1/1 \)) were observed in conjunction with both classes of disruptions. For low \itq* discharges, the modes developing in the pre-disruption stage were found to change from primarily external to the plasma when \( \langle b\rangle /a = 1.52 \), where \( \langle b\rangle \) is the average radius of the conducting shells, to essentially internal to the plasma when \( b/a \leq 1.2 \). For \(\beta\)-limiting disruptions the pre cursor modes remained predominantly internal even as \( b/a \leq 1.2 \) was changed to \( \langle b\rangle /a = 1.52 \). The conducting wall, placed near the plasma surface, increased discharge lifetime by a factor of 3, enhanced particle heating as measured with soft x-ray diodes by 30% and improved stability for both cases of disruptions.
\smallskip \(^*\)Work supported by US DOE Grant DE--FG02--86ER--53222