Cooling flow regime of a plasma thermal quench

TL;DR

This paper investigates the cooling flow dynamics in nearly collisionless plasmas during a thermal quench, revealing how electron thermal conduction leads to propagating fronts and shock formation in magnetized environments.

Contribution

It demonstrates that electron thermal conduction in collisionless plasmas follows convective scaling, resulting in propagating fronts and shock-driven thermal collapse.

Findings

Cooling flow aggregates mass toward the cooling spot.

Thermal collapse involves four propagating fronts.

A shock front causes deep cooling.

Abstract

A large class of Laboratory, Space, and Astrophysical plasmas is nearly collisionless. When a localized energy or particle sink, for example, in the form of a radiative cooling spot or a black hole, is introduced into such a plasma, it can trigger a plasma thermal collapse, also known as a thermal quench in tokamak fusion. Here we show that the electron thermal conduction in such a nearly collisionless plasma follows the convective energy transport scaling in itself or in its spatial gradient, due to the constraint of ambipolar transport. As the result, a robust cooling flow aggregates mass toward the cooling spot and the thermal collapse of the surrounding plasma takes the form of four propagating fronts that originate from the radiative cooling spot, along the magnetic field line in a magnetized plasma. The slowest one, which is responsible for deep cooling, is a shock front.