Wave-particle energy transfer directly observed in an ion cyclotron wave

TL;DR

This study directly observed wave-particle energy transfer in an ion cyclotron wave using Parker Solar Probe data, revealing a 3-6% energy transfer rate consistent with local wave generation in the solar wind.

Contribution

It introduces a novel method combining Flux Angle mode and electric field data to measure wave-particle energy exchange on wave timescales.

Findings

Energy transfer from fields to particles is about 3-6% of electromagnetic flux.

Wave-particle coupling occurs on the timescale of a cyclotron period.

Ion cyclotron wave likely generated locally in the solar wind.

Abstract

Context. The first studies with Parker Solar Probe (PSP) data have made significant progress toward the understanding of the fundamental properties of ion cyclotron waves in the inner heliosphere. The survey mode particle measurements of PSP, however, did not make it possible to measure the coupling between electromagnetic fields and particles on the time scale of the wave periods. Aims. We present a novel approach to study wave-particle energy exchange with PSP. Methods. We use the Flux Angle operation mode of the Solar Probe Cup in conjunction with the electric field measurements and present a case study when the Flux Angle mode measured the direct interaction of the proton velocity distribution with an ion cyclotron wave. Results. Our results suggest that the energy transfer from fields to particles on the timescale of a cyclotron period is equal to approximately 3-6% of the electromagnetic energy flux. This rate is consistent with the hypothesis that the ion cyclotron wave was locally generated in the solar wind.