Collisionless conduction in a high-beta plasma: a collision operator for whistler turbulence

Journal Article · 08 January 2025 · Journal of Plasma Physics

DOI: https://doi.org/10.1017/s002237782400151x · OSTI ID:2504545

Yerger, Evan L. ^[1]; Kunz, Matthew W.  ^[2]; Bott, Archie F.A.  ^[3]; Spitkovsky, Anatoly  ^[4]

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1. Princeton Univ., NJ (United States); Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States); Univ. of New Hampshire, Durham, NH (United States)
2. Princeton Univ., NJ (United States); Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
3. Princeton Univ., NJ (United States); Univ. of Oxford (United Kingdom)
4. Princeton Univ., NJ (United States)

The regulation of electron heat transport in high-β, weakly collisional, magnetized plasma is investigated. A temperature gradient oriented along a mean magnetic field can induce a kinetic heat-flux-driven whistler instability (HWI), which back-reacts on the transport by scattering electrons and impeding their flow. Previous analytical and numerical studies have shown that the heat flux for the saturated HWI scales as β$$^{-1}_{e}$$. These numerical studies, however, had limited scale separation and consequently large fluctuation amplitudes, which calls into question their relevance at astrophysical scales. To this end, we perform a series of particle-in-cell simulations of the HWI across a range of β$$_e$$ and temperature-gradient length scales under two different physical set-ups. The saturated heat flux in all of our simulations follows the expected β$$^{-1}_{e}$$ scaling, supporting the robustness of the result. We also use our simulation results to develop and implement several methods to construct an effective collision operator for whistler turbulence. The results point to an issue with the standard quasi-linear explanation of HWI saturation, which is analogous to the well-known 90° scattering problem in the cosmic-ray community. Despite this limitation, the methods developed here can serve as a blueprint for future work seeking to characterize the effective collisionality caused by kinetic instabilities.

• Research Organization: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
• Sponsoring Organization: USDOE; National Aeronautics and Space Administration (NASA); National Science Foundation (NSF); UK Research and Innovation (UKRI)
• Grant/Contract Number: SC0019046; SC0019047; AC02-09CH11466
• OSTI ID: 2504545
• Journal Information: Journal of Plasma Physics, Journal Name: Journal of Plasma Physics Journal Issue: 1 Vol. 91; ISSN 0022-3778
• Publisher: Cambridge University PressCopyright Statement
• Country of Publication: United States
• Language: English