Abstract Details
Abstracts
Author: Yashika Ghai
Requested Type: Consider for Invited
Submitted: 2025-02-21 23:51:18
Co-authors: D. del-Castillo-Negrete, D. A. Spong, M. T. Beidler
Contact Info:
Oak Ridge National Laboratory
1 Bethel Valley Road
Oak Ridge, 37922
USA
Abstract Text:
Resonant interactions between high-energy runaway electrons (REs) and whistler waves significantly modify RE dynamics by scattering electrons to higher pitch angles and enhancing synchrotron radiation losses. Recent DIII-D experiments have demonstrated that externally launched whistler waves can mitigate RE damage to plasma-facing components [1,2]. Yet, a comprehensive framework for the complex transport processes of REs in whistler fields remains lacking.
To bridge this gap, we coupled two advanced computational models—AORSA, which computes whistler eigenmodes in a given plasma equilibrium, and KORC, a kinetic orbit code tracking RE trajectories in prescribed wave fields. Using the combined AORSA+KORC framework and statistical analysis, our simulations reveal that RE transport in whistler fields is not uniformly diffusive. Instead, it can exhibit super-diffusive, sub-diffusive, or diffusive behavior, depending on the REs’ initial kinetic energy and pitch angle.
Further examination of the statistical moments of instantaneous pitch angle and kinetic energy kicks shows that the pitch angle changes depart from Gaussian statistics, displaying asymmetric distributions with Gaussian-like cores and heavy-tailed, Laplacian characteristics. Similarly, the kinetic energy kick distributions follow power-law behavior, signaling the presence of nontrivial transport regimes. These findings challenge conventional Gaussian-diffusive approximations and offer new insights into the underlying physics of whistler-driven RE transport.
By unveiling the non-Gaussian and non-diffusive nature of RE-whistler interactions, our study enhances the theoretical understanding of RE transport in fusion plasmas and establishes a foundation for refining runaway mitigation strategies in future tokamak experiments.
References:
[1] D. A. Spong et al., Phys. Rev. Lett., 120, 155002 (2018).
[2] W. W. Heidbrink at al., Plasma Phys. Control. Fusion, 61, 14007 (2019).
Characterization: 1.0
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