Abstract Details
Abstracts
Author: Qile Zhang
Requested Type: Consider for Invited
Submitted: 2025-02-21 21:20:59
Co-authors: Yanzeng Zhang, Qi Tang, Xian-Zhu Tang
Contact Info:
Los Alamos National Laboratory
2290 B 39th street
Los Alamos, NM 87544
United States
Abstract Text:
One of the most efficient ways to generate relativistic electrons in a dilute plasma is runaway acceleration by a strong electric field along the magnetic field, coupled with avalanche growth via knock-on
collisions between runaways and background cold electrons. Plasma wave instabilities excited by these relativistic runaway electrons (RE) and their roles in modifying the RE distribution through
nonlinear wave-particle interaction, have piqued long-standing
interest from both a basic plasma physics perspective and the
practical need of mitigating REs in tokamak plasmas. The latter comes about because the runaways can cause severe damage on the plasma-facing components during both tokamak startup and major disruptions. More broadly, interaction of energetic electrons and their self-induced waves plays critical roles in regulating the transport and heat flux induced by these energetic electrons, for example, in Earth’s magnetosphere, solar flares and astrophysical intracluster medium. To facilitate these and similar applications, we must understand the basic plasma physics of runaway-wave interaction
and its nonlinear saturation.
Here we present the first-ever fully kinetic simulations of runaway-driven instabilities towards nonlinear saturation in a warm plasma as in tokamak start up. 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 much faster than experimental shot duration. These results beyond quasilinear analysis may impact anisotropic energetic electrons broadly in laboratory, space and astrophysics.
Characterization: 1.0
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