Abstract Details
Abstracts
Author: Yanzeng Zhang
Requested Type: Consider for Invited
Submitted: 2026-02-28 23:37:05
Co-authors: Xian-Zhu Tang
Contact Info:
University of Science and Technology of China
Huangshan Rd, No. 443
Hefei, 230027
China
Abstract Text:
Pellet injection is a cornerstone technique for core fueling and disruption mitigation in reactor-scale fusion devices such as ITER. Despite their distinct operational goals, both applications rely on the rapid assimilation of ablated material along magnetic field lines. A key subtlety in this assimilation process arises from the near-collisionless nature of the ambient hot plasma, which remains approximately in pressure balance with the cold, dense ablated cloud. As such, classical fluid transport models become inadequate, and kinetic processes govern the mixing dynamics.
By combining fully kinetic simulations with analytical theory, we demonstrate the formation of a unique parallel collisionless shock at the hot-cold ablative interface. It limits both the thermal collapse of the background plasma and the inward mixing of cold ablated ions, thereby regulating the efficacy of thermal quench mitigation. Remarkably, the shock is driven primarily by the electron temperature gradient and is therefore fundamentally distinct from conventional explosive shocks driven by strong pressure gradients. The propagation speed of the shock front, and hence the rate of cold-ion assimilation, is governed by the ablated plasma temperature, with lower temperatures yielding proportionally slower shock propagation. Notably, although the electron thermal conduction locally approaches the free-streaming limit, its spatial gradient follows a convective scaling in both upstream and downstream regions. This constraint enforces finite characteristic length scales of electron temperature gradients that are essential for shock formation.
These results establish a new kinetic paradigm for pellet assimilation in reactor plasmas, in which ablative mixing is intrinsically shock-regulated rather than conduction-limited. They further highlight the broader universality of temperature-driven collisionless shocks in hot-cold mixing plasmas across laboratory, space, and astrophysical environments.
Characterization: 1.0
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