Wave-particle energy exchange directly observed in a kinetic Alfv\xe9n-branch wave

D J Gershman ,Adolfo F-Viñas,Paul M Bellan,Steven J Schwartz,Y Saito ,V N Coffey ,W R Paterson ,R J Strangeway ,M O Chandler ,S A Boardsen ,S A Fuselier ,J Dorelli ,C J Pollock ,B L Giles ,L A Avanov ,R B Torbert ,B Lavraud ,C T Russell ,R E Ergun ,J L Burch

doi:10.1038/ncomms14719

Abstract

Alfvén waves are fundamental plasma wave modes that permeate the universe. At small kinetic scales, they provide a critical mechanism for the transfer of energy between electromagnetic fields and charged particles. These waves are important not only in planetary magnetospheres, heliospheres and astrophysical systems but also in laboratory plasma experiments and fusion reactors. Through measurement of charged particles and electromagnetic fields with NASA’s Magnetospheric Multiscale (MMS) mission, we utilize Earth’s magnetosphere as a plasma physics laboratory. Here we confirm the conservative energy exchange between the electromagnetic field fluctuations and the charged particles that comprise an undamped kinetic Alfvén wave. Electrons confined between adjacent wave peaks may have contributed to saturation of damping effects via nonlinear particle trapping. The investigation of these detailed wave dynamics has been unexplored territory in experimental plasma physics and is only recently enabled by high-resolution MMS observations.

Highlights

Alfven waves are fundamental plasma wave modes that permeate the universe
NASA’s recently launched Magnetospheric Multiscale (MMS) mission[18] consists of four identical observatories deployed in a tetrahedron configuration that measure charged particle and electromagnetic fields orders of magnitude more quickly than previous space missions. This increased temporal sampling combined with a small MMS inter-spacecraft separation enables plasma parameters and their spatial gradients to be determined at kinetic scales
kineticscale Alfven wave (KAW) in turbulent space plasmas are thought to account for heating of plasmas at kinetic scales[5,6,7]

Summary

Introduction

Alfven waves are fundamental plasma wave modes that permeate the universe. At small kinetic scales, they provide a critical mechanism for the transfer of energy between electromagnetic fields and charged particles. For kinetic-scale Alfven waves, non-zero DEp|| fluctuations enable the Landau resonance, where particles with V||Bo/k|| can gain or lose energy through interaction with the wave field These interactions, combined with an imbalance in the number of particles that are moving faster than or slower than the wave, result in net plasma heating or cooling[4]. NASA’s recently launched Magnetospheric Multiscale (MMS) mission[18] consists of four identical observatories deployed in a tetrahedron configuration that measure charged particle and electromagnetic fields orders of magnitude more quickly than previous space missions This increased temporal sampling combined with a small MMS inter-spacecraft separation enables plasma parameters and their spatial gradients to be determined at kinetic scales

Methods

Results

Conclusion