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arXiv · 1811.05666

On the background-gyroresonant character of the Bell instability

Martin S. Weidl·Dan Winske·Christoph Niemann
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Abstract

We show that the Bell instability, which is widely considered potentially important for cosmic-ray acceleration, is the low-frequency limit of a gyroresonant interaction between the protons of the interstellar medium and shear-Alfvén waves. At large cosmic-ray current densities, its growth rate is therefore limited by the proton gyrofrequency, and two modes emerge from the cold-beam dispersion relation. A third mode driven by electron gyroresonance is only weakly unstable at low current densities. We discuss implications for magnetic-field amplification and its saturation in the vicinity of supernova remnants.

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Martin S. Weidl, Dan Winske, Christoph Niemann. 2018-11-14. On the background-gyroresonant character of the Bell instability. https://doi.org/10.3847/1538-4357%2Faafad0

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