Magnetohydrodynamic Instability with Neutral-Beam Heating in the ISX-BTokamak

Abstract

This paper describes observations of magnetohydrodynamic instability with neutralbeam heating in the ISX-.B tokamak and the theory specifically developed to support these experiments. The observed magnetohydrodynamic activity is explained by the resistive model presented but is not responsible for the observed degradation of confinement. Increasingly important n > 1 pressure-driven modes are predicted by the theory for the higher experimental pp values, but there is no experimental verification of their presence.

Magnetohydrodynamic Activity in High-β, Currentless Plasmas in Heliotron-E

“…Signals from a soft x-ray diode array show sawtooth oscillations accompanied by smaller sinusoidal fluctuations, which are qualitatively similar to the sawtooth oscillations seen in tokamaks. 10 The fall of the sawtooth coincides with spikes in the signals from the uncollimated (total power) bolometer, the hydrogen H^-line monitor, and the edge plasma ion-saturation-current probes and with # bursts in the poloidal magnetic field fluctuations (B 9 ) measured by Mirnov coils at the vacuum chamber wall. During the bursts, the quantity B 0 (wall)IB e (t= 1) reaches -1%; here B 9 {t = 1) = (0.1a/R)B T is the calculated vacuum poloidal field at the t= 1 surface and is used for convenience.…”

“…These findings are unchanged when a pressure profile based on the assumption 7} (7) = T e (T) [rather than the measured 7} (7)] is used in the analysis. At higher /3, our nonlinear resistive MHD simulations 15 show a breakup of magnetic surfaces near t=l, the formation of island structures similar to those seen in tokamaks, 10 and substantial deformations of the pressure profile. Simulations of the soft x-ray wave forms for these stronger instabilities show many of the features observed in higher-/?…”

“…Signals from a soft x-ray diode array show sawtooth oscillations accompanied by smaller sinusoidal fluctuations, which are qualitatively similar to the sawtooth oscillations seen in tokamaks. 10 The fall of the sawtooth coincides with spikes in the signals 2242 …”

Compound sawtooth study in ohmically heated TFTR plasmas

“…This m = odd mode can thus stabilize itself without any rapid relaxation. although a saturated m = 1 mode under particular conditions [18] and an m = 1 successor after an internal disruption [19] have been observed before, the exact mechanism for these phenomena is still under study.…”

High Beta Results in Isx-B With Intense Neutral Beam Injection

“…These modes are experimentally observed. Detailed comparisons between theoretically predicted mode structure and experimental observations have been made, 15 and the agreement is excellent even to the fine grain details of the wave forms, as can be seen in Fig. 12.…”