Parker Solar Probe evidence for scattering of electrons in the young solar wind by narrowband whistler-mode waves

Abstract

Observations of plasma waves by the Fields Suite and of electrons by the Solar Wind Electrons Alphas and Protons Investigation (SWEAP) on Parker Solar Probe provide strong evidence for pitch angle scattering of strahl-energy electrons by narrowband whistler-mode waves at radial distances less than ~0.3 AU. We present two example intervals of a few hours that include 8 waveform captures with whistler-mode waves and 26 representative electron distributions that are examined in detail. Two were narrow; 17 were clearly broadened, and 8 were very broad. The two with narrow strahl occurred when there were either no whistlers or very intermittent low amplitude waves. Six of the eight broadest distributions were associated with intense, long duration waves. Approximately half of the observed electron distributions have features consistent with an energy dependent scattering mechanism, as would be expected from interactions with narrowband waves. A comparison of the wave power in the whistler-mode frequency band to pitch angle width and a measure of anisotropy provides additional evidence for the electron scattering by whistler-mode waves. The pitch angle broadening occurs in over an energy range comparable to that obtained for the n=1 (co-streaming) resonance for the observed wave and plasma parameters. The additional observation that the heat flux is lower in the interval with multiple switchbacks may provide clues to the nature of switchbacks. These results provide strong evidence that the heat flux is reduced by narroweband whistler-mode waves scattering of strahl-energy electrons.

19 pages, 4 figures, 1 table

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• Modeling interactions of narrowband large amplitude whistler-mode waves with electrons in the solar wind inside ~.3 AU and at 1 AU using a particle tracing code
• Whistler Wave Observations by \textit{Parker Solar Probe} During Encounter $1$: Counter-Propagating Whistlers Collocated with Magnetic Field Inhomogeneities and their Application to Electric Field Measurement Calibration
• Whistler waves generated inside magnetic dips in the young solar wind: observations of the Search-Coil Magnetometer on board Parker Solar Probe
• Quantifying the diffusion of suprathermal electrons by whistler waves between 0.2 and 1 AU with Solar Orbiter and Parker Solar Probe
• Stochastic diffusion of electrons interacting with whistler-mode waves in the solar wind
• Whistler waves in the young solar wind: statistics of amplitude and propagation direction from Parker Solar Probe Encounters 1-11
• Reconstruction of Polarization Properties of Whistler Waves From Two Magnetic and Two Electric Field Components: Application to Parker Solar Probe Measurements
• Plasma Instabilities Dominate Radioactive Transients Magnetic Fields: The self-confinement of leptons in Type Ia and Core-Collapse Supernovae, and Kilonovae
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