SPRG Seminars
April 9, 2013:
"Collisionless Shocks at Electron Scales"
David Sundkvist, Space Sciences Laboratory, University of California at Berkeley
Collisionless shocks are nonlinear shock waves that are ubiquitous in our plasma universe and play an important role in redistributing kinetic energy in supersonic flow to heated plasma and energetic particles. In this seminar I will present results for shocks when approaching electron scales, using data from the Cluster and Themis missions. By analyzing shock steepening in two-fluid theory it is found that a shock has dispersive features at electron scales and should radiate energy away from the shock in the form of Poynting flux carried by whistler waves. The steepening of supercritical dispersive shocks could therefore be balanced by both dispersion and nonlinearity. We use Cluster data to measure the Poynting flux of a dispersive shock for the first time. While the ions are well understood and account for most of the dissipation, the shock electron problem is still not fully resolved. We use Themis high-resolution data of electron distribution functions and fields to assess the electron heating, energy partition, adiabaticity, reversible vs irreversible dissipation and the role of high-frequency fluctuations and cross-shock potential for heating and isotropizing electrons through the shock layer.