A quantitative account of electron energy transport in a National Spherical Tokamak Experiment plasma

Abstract

The first successful quantitative account of the electron thermal conductivity e in a tokamak experiment due to imperfect magnetic surfaces is presented. The unstable spectrum of microtearing instabilities is calculated with the GS2 code for a well-behaved H-mode plasma in the National Spherical Tokamak Experiment [M. Ono, Nucl. Fusion 40, 557 (2000)], with 6 MW deuterium neutral beam heating at Ip =0.75 MA, Bt =0.5 T. The application of existing nonlinear theory shows that the unstable modes can produce overlapping magnetic islands leading to global stochastic magnetic fields. The calculated e based on the present theory is in reasonable agreement with the values from transport analysis of the experimental data over the entire region (0.4