(Dr. Weston Stacey, advisor)

"Tokamak Density Limits"

Abstract

The measured density limits in the German Tokamak TEXTOR have been analyzed.  For a series of ‘power scan’ shots that ended in multifaceted asymmetric radiation from the edge (MARFE), in which the auxiliary heating power was varied and other operating parameters were held approximately constant, this analysis consisted of: 1) correcting the basic measurements of density and temperature distributions for the background light, Shafranov shift, etc. to obtain ‘measured’ density and temperature profiles for comparison with theory; 2) calculation of neutral atom and impurity ion concentrations in the plasma edge region by attenuating measured gas sources at various plasma-wall interaction locations (limiters) into the plasma with a numerical calculation; 3) identification of uncertainties in the measured and calculated experimental data; 4) evaluation of theoretical prediction of the onset of MARFEs due to thermal instabilities in the plasma edge; and 5) comparison of measured and predicted MARFE onset, taking into account uncertainties.

The parametric dependence of the measured conditions for MARFE onset and for radiative collapse leading to disruption in TEXTOR were compared with the parametric dependence of predictions of MARFE onset and radiative collapse given by thermal instability theory, over a range of values for plasma current, magnetic field and auxiliary heating power and over a range of wall materials and wall conditions.

Based on the agreement between theoretical prediction and experiment found in the TEXTOR analyses, the MARFE and radiative collapse density limits were predicted for the proposed FIRE burning plasma experiment.