Examining energization of kinetic plasmas in phase space is a growing topic of interest, owing to the wealth of data in phase space compared to traditional bulk energization diagnostics. Via the fieldparticle correlation (FPC) technique and using multiple means of numerically integrating the plasma kinetic equation, we have studied the energization of ions in phase space within oblique collisionless shocks. The perspective afforded to us with this analysis in phase space allows us to characterize distinct populations of energized ions. In particular, we focus on ions that reflect multiple times off the shock front through shockdrift acceleration, and how to distinguish these different reflected populations in phase space using the FPC technique. We further extend our analysis to simulations of threedimensional shocks undergoing more complicated dynamics, such as shock ripple, to demonstrate the ability to recover the phasespace signatures of this energization process in a more general system. This work thus extends previous applications of the FPC technique to more realistic collisionless shock environments, providing stronger evidence of the technique’s utility for simulation, laboratory, and spacecraft analysis.
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Abstract 
Magnetic reconnection plays an important role in the release of magnetic energy and consequent energization of particles in collisionless plasmas. Energy transfer in collisionless magnetic reconnection is inherently a twostep process: reversible, collisionless energization of particles by the electric field, followed by collisional thermalization of that energy, leading to irreversible plasma heating. Gyrokinetic numerical simulations are used to explore the first step of electron energization, and we generate the first examples of fieldparticle correlation (FPC) signatures of electron energization in 2D strongguidefield collisionless magnetic reconnection. We determine these velocity space signatures at the xpoint and in the exhaust, the regions of the reconnection geometry in which the electron energization primarily occurs. Modeling of these velocityspace signatures shows that, in the strongguidefield limit, the energization of electrons occurs through bulk acceleration of the outofplane electron flow by parallel electric field that drives the reconnection, a nonresonant mechanism of energization. We explore the variation of these velocityspace signatures over the plasma beta range 0.01 < beta_i < 1. Our analysis goes beyond the fluid picture of the plasma dynamics and exploits the kinetic features of electron energization in the exhaust region to propose a singlepoint diagnostic which can potentially identify a reconnectionmore »

Using the field–particle correlation technique, we examine the particle energization in a threedimensional (one spatial dimension and two velocity dimensions; 1D2V) continuum Vlasov–Maxwell simulation of a perpendicular magnetized collisionless shock. The combination of the field–particle correlation technique with the highfidelity 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 velocityspace signatures of shockdrift 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 selfconsistent 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.