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arXiv · 2409.15830

Self-mediation of runaway electrons via self-excited wave-wave and wave-particle interactions

Qile Zhang·Yanzeng Zhang·Qi Tang·Xian-Zhu Tang
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Abstract

Nonlinear dynamics of runaway electron induced wave instabilities can significantly modify the runaway distribution critical to tokamak operations. Here we present the first-ever fully kinetic simulations of runaway-driven instabilities towards nonlinear saturation in a warm plasma where collisional damping is subdominant. It is found that the slow-X modes grow an order of magnitude faster than the whistler modes, and they parametrically decay to produce whistlers much faster than those directly driven by runaways. These parent-daughter waves, as well as secondary and tertiary wave instabilities, initiate a chain of wave-particle resonances that strongly diffuse runaways to the backward direction. This reduces almost half of the current carried by high-energy runaways, over a time scale orders of magnitude faster than experimental shot duration. These results beyond quasilinear analysis may impact anisotropic energetic electrons broadly in laboratory, space and astrophysics.

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Qile Zhang, Yanzeng Zhang, Qi Tang, Xian-Zhu Tang. 2026-03-07. Self-mediation of runaway electrons via self-excited wave-wave and wave-particle interactions. https://arxiv.org/abs/2409.15830

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