Extending Observations of Phase-Space Holes and Double Layers to Consider Electron Cyclotron Maser Emission

Abstract:

Electron phase-space holes and double layers are ubiquitous in space plasmas. The earliest MMS data is rife with electron phase-space holes, and throughout its mission lifetime, MMS is expected to observe many progenitor double layers in three dimensions. With four-point measurements, the size, speed, and amplitude of nonlinear kinetic structures can be accurately determined for the first time. Although double layers play a strong role in particle acceleration, reconnection, and turbulence, these plasma structures are often neglected by high-energy astrophysical studies. For example, electron cyclotron maser emission, the same mechanism for auroral kilometric radiation at Earth, is now known to be energized by double layers. Double layers are also a primary generation mechanism for electron phase-space holes. These holes mostly serve to re-distribute energy from an initially unstable configuration to a more stable distribution. However, given the correct frame transformation, phase-space holes may contain a positive df/dp_{/perp}, and therefore are susceptible to the electron cyclotron maser instability. Like much of the physics probed by the MMS mission, this process is scalable from our magnetosphere to that of larger planets or even more extreme objects such as neutron stars. Phase-space holes in these environments may be capable of producing observable coherent radiation. As a first step in investigating this hypothesis, we have developed a special relativistic, electrostatic Vlasov simulation that can form phase-space holes and double layers in any frame of motion parallel to the flow. When electron holes are produced in a relativistic, counter streaming plasma, we predict distributions that are unstable to the electron cyclotron maser instability.