University of Maryland
Atlantic Building, Room 2400 4:30 PM Monday, September 23, 2019
Coffee, Tea & Snacks 4:15-4:30 PM

Qile Zhang
Department of Physics, University of Maryland

Particle Heating and Turbulence in Low Beta Reconnection with a Guide Field

Kinetic Riemann simulations are used to explore particle heating and turbulence during reconnection with a guide field in the low-beta environment of the inner heliosphere and the solar corona. The reconnection exhaust is bounded by two rotational discontinuities (RDs) with two slow shocks (SSs) that form in the exhaust as in magnetohydrodynamic (MHD) models. At the RDs, ions are accelerated by the magnetic tension to drive the reconnection outflow and flows in the out-of-plane direction. The out-of-plane flows stream toward the midplane and meet to drive the SSs. The turbulence at the SSs is weak so the shocks are laminar and produce little dissipation, which differs greatly from the MHD treatment. Downstream of the SSs the counter-streaming ion beams lead to higher density and therefore to a positive potential that confines the downstream electrons to maintain charge neutrality. The potential accelerates electrons from upstream of the SSs to downstream and traps a small fraction but only produces modest electron heating. In the low-beta limit little energy goes to electrons. We explore the role of turbulence in the dynamics in greater depth. In 2D the exhaust develops large-amplitude striations resulting from electron-beam-driven ion cyclotron waves. However, in 3D the additional dimension results in strong Buneman and electron-electron streaming instabilities at the RDs which suppress electron beam formation and therefore striations. The streaming instabilities at the RD are more unstable with a lower ratio of the electron thermal speed to Alfven Speed. In 3D an ion-ion streaming instability partially thermalizes the counterstreaming ion beams at the SSs. This instability will be stable with a low ratio of the sound speed to Alfven speed. The results suggest that when 1>>beta>m_e/m_i, the kinetic-scale turbulence that develops in the exhaust will be too weak to play a significant role in energy conversion. The results of heating and turbulence can be tested by Parker Solar Probe.