Abstract Details
Abstracts
Author: Yanzeng Zhang
Requested Type: Consider for Invited
Submitted: 2025-02-21 15:52:31
Co-authors:
Contact Info:
Los Alamos National Laboratory
Los Alamos
Los Alamos, 87545
USA
Abstract Text:
Pellet injection is a standard technique for fueling and disruption mitigation in fusion reactors like ITER. They share similar objectives: delivering materials, hydrogen for fueling and high-Z impurities for disruption mitigation, into the fusion core on a very short timescale. The success of the technique hinges on the rapid assimilation of the ablated pellet material along the magnetic field lines, particularly in the context of mitigating thermal quench by replacing plasma power exhaust at the first wall with high-Z impurities line radiation much shorter than 1 ms. One subtlety in this assimilation of ablated materials is the near-collisionless nature of the ambient hot plasma, which is roughly in pressure balance with the cold, dense ablated plasma. Consequently, kinetic effects play a critical role in the process. In this study, we employ kinetic simulations and analytical theory to show the formation of a parallel collisionless shock in such hot-cold ablative mixing plasma that limits both the thermal collapse of the ambient hot plasma and the ablative mixing of cold ions. This shock differs fundamentally from the well-known collisionless shocks that occur when a high-density plasma expands into a rarefied one, but is also ubiquitous in space, astrophysical, and laboratory (including the inertial confinement fusion) plasmas. Its formation has a weak dependence on the plasma pressure but is primarily controlled by the plasma temperatures on both sides. Notably, the speed of the shock front (and hence the mixing of cold ions) is governed by the ablated plasma temperature: the smaller the temperature, the slower the shock speed. Interestingly, although the collisionless electron thermal conduction follows the free-streaming limit itself, its spatial gradient exhibits a convective scaling, ensuring similar characteristic length scales of electron temperature and density evolution.
Characterization: 1.0
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