Affiliation:
1. Theoretical Division, Los Alamos National Laboratory 1 , Los Alamos, New Mexico 87545, USA
2. School of Nuclear Science and Technology, University of Science and Technology of China 2 , Hefei, Anhui 230026, China
Abstract
The thermal collapse of a nearly collisionless plasma interacting with a cooling spot, in which the electron parallel heat flux plays an essential role, is both theoretically and numerically investigated. We show that such thermal collapse, which is known as thermal quench in tokamaks, comes about in the form of propagating fronts, originating from the cooling spot, along magnetic field lines. The slow fronts, propagating with local ion sound speed, limit the aggressive cooling of plasma, which is accompanied by a plasma cooling flow toward the cooling spot. The extraordinary physics underlying such a cooling flow is that the fundamental constraint of ambipolar transport along the field line limits the spatial gradient of electron thermal conduction flux to the much weaker convective scaling, as opposed to the free-streaming scaling, so that a large electron temperature and, hence, pressure gradient can be sustained. The last ion front for a radiative cooling spot is a shock front where cold but flowing ions meet hot ions.
Funder
Advanced Scientific Computing Research
Fusion Energy Sciences
National Energy Research Scientific Computing Center
LANL Institutional computing program