Staged cooling of a fusion-grade plasma in a tokamak thermal quench

In tokamak disruptions where the magnetic connection length becomes comparable to or even shorter than the plasma mean-free-path, parallel transport can dominate the energy loss and the thermal quench of the core plasma goes through four phases (stages) that have distinct temperature ranges and durations. The main temperature drop occurs while the core plasma remains nearly collisionless, with the parallel electron temperature T-e broken vertical bar broken vertical bar dropping in time t as T-e broken vertical bar broken vertical bar proportional to t(-2) and a cooling time that scales with the ion sound wave transit time over the length of the open magnetic field line. These surprising physics scalings are the result of effective suppression of parallel electron thermal conduction in an otherwise bounded, quasineutral, and collisionless plasma, which is different from what are known to date on electron thermal conduction along the magnetic field in a nearly collisionless and quasineural plasma.

Automated summary

In disruptions of tokamak, when the magnetic connection length is comparable to or shorter than the plasma mean-free-path, parallel transport can dominate energy loss. During the thermal quench of the core plasma, there are four distinct phases with different temperature ranges and durations. The main temperature drop occurs in a nearly collisionless state, with the parallel electron temperature decreasing as T-e |∝ t(-2) and a cooling time proportional to the ion sound wave transit time over the length of the open magnetic field line. These unexpected physics scalings result from the effective suppression of parallel electron thermal conduction in a bounded, quasineutral, and collisionless plasma, which is different from what is known about electron thermal conduction in a nearly collisionless and quasineural plasma.