Studies on MHD Oscillations on the Text Tokamak
Abstract
Low frequency MHD oscillations in the TEXT tokamak are studied using an array of 40 soft x ray detectors and three arrays of magnetic pickup coils including TEXT standard diagnostics. In the first part of the dissertation, double sawtooth oscillations observed during low q(,lim) discharges are presented. A partial reconnection of magnetic fields under a hollow current profile appears to be responsible for the oscillations. A condition for a partial reconnection in terms of the ratio of the two q = 1 radii is obtained with a simple analytical model based on Kadomtsev's argument, and compared with the experimental results. In the second part of the dissertation, experimental evidence of the correlation between sawtooth period and energy confinement time is presented. Based on Jahns et al.'s heat pulse model, thermal diffusivity constant (chi)(,e) is derived as a function of sawtooth period t(,s) and the q = 1 radius r(,s). The (chi)(,e) estimated using t(,s) and r(,s) is found to give good agreement with the (chi)(,e) estimated from power balance, and it is consistent with Alcator (tau)(,E) scaling the CoppiMazzucato (chi)(,e) scaling. Inconsistency between the scaling of sawtooth period by Jahns et al. and the reconnection time of magnetic field lines due to m = 1 mode by Kadomtsev is discussed. Finally, the third part of this dissertation presents the geometric characteristics of magnetic field fluctuations. Correlation dimensions are estimated for Mirnov oscillations and magnetic turbulence. In a stationary state, the attractor for the Mirnov oscillations is basically circular. This is supported by observations of (1) mode locking with q value using time dependent mode spectrum, and (2) apparent mode coupling using bispectrum estimated in the spatial domain. The magnetic turbulence is essentially stochastic and has no finite correlation dimension.
 Publication:

Ph.D. Thesis
 Pub Date:
 1986
 Bibcode:
 1986PhDT........92K
 Keywords:

 FUSION;
 Physics: Fluid and Plasma