Abstract
Using the field–particle correlation technique, we examine the particle energization in a three-dimensional (one spatial dimension and two velocity dimensions; 1D-2V) continuum Vlasov–Maxwell simulation of a perpendicular magnetized collisionless shock. The combination of the field–particle correlation technique with the high-fidelity representation of the particle distribution function provided by a direct discretization of the Vlasov equation allows us to ascertain the details of the exchange of energy between the electromagnetic fields and the particles in phase space. We identify the velocity-space signatures of shock-drift acceleration of the ions and adiabatic heating of the electrons arising from the perpendicular collisionless shock by constructing a simplified model with the minimum ingredients necessary to produce the observed energization signatures in the self-consistent Vlasov–Maxwell simulation. We are thus able to completely characterize the energy transfer in the perpendicular collisionless shock considered here and provide predictions for the application of the field–particle correlation technique to spacecraft measurements of collisionless shocks.
Highlights
Shock waves, disturbances propagating faster than the largest local wave speed, are ubiquitous in space and astrophysical plasmas
Diagnosing the velocity-space signatures of particle energization in this perpendicular electromagnetic shock. To obtain these velocity-space signatures, we describe our tool of choice for our analysis of the high-quality distribution function data provided by the continuum kinetic simulation: the field–particle correlation technique
We have examined a self-consistent perpendicular collisionless shock using the continuum Vlasov–Maxwell solver in the Gkeyll simulation framework and our results can be summarized as follows: (i) we have identified the velocity-space signatures of shock-drift acceleration of ions in figure 5(d) and adiabatic heating of electrons in figure 12(a); (ii) using simplified models of single-particle motion through idealized models of the electromagnetic fields through the shock transition, we identified the conditions under which we expect to observe these velocity-space signatures for these energization processes. (a) We determined that the velocity-space signature of shock-drift acceleration can be seen clearly in a reflected ion population and is robust to the presence of the Downloaded from https://www.cambridge.org/core
Summary
Disturbances propagating faster than the largest local wave speed, are ubiquitous in space and astrophysical plasmas. To understand the observed velocity-space signatures and connect the resulting signatures to known mechanisms for plasma energization, we construct simplified analytical models for ions and electrons being energized by similar processes absent of the complications of a fully self-consistent shock, and compute the field–particle correlation on the particle distribution functions predicted by these idealized models. These simplified models allow us to proceed pedagogically and connect the two distinct pictures, the Eulerian point-of-view for identifying where in phase space the particles are being energized and the Lagrangian point-of-view for analysing how individual particles gain and lose energy.
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