Authors: Alberto Felix (University of Iowa), Gregory Howes (University of Iowa), Collin Brown (Naval Research Laboratory), Colby Haggerty (University of Hawai'i Manoa)

In collisionless supercritical quasiperpendicular shocks there is a splitting of incoming ions
at the shock interface between distinct subpopulations based on whether they transmit
through the shock immediately or are reflected upstream by the cross shock electric field
and magnetic field gradient. Here we examine the formation of these subpopulations, the
energization mechanisms that affect them and the division of energy flux between them in
a suite of shock simulations. These simulations span a range of Alfven Mach numbers MA
and shock-normal angles θBn and are generated through the parallel hybrid code
dHybridR. Through our novel subpopulation analysis method we are able to separate these
subpopulations using volumes in velocity space which trace out the expected trajectories of
these ions. Using a symbolic regression algorithm we are able to determine how the
fraction of energy flux within reflected ions varies with Alfven Mach number and
shock-normal angle. We find that this ratio tends to increase as −1/MA for lower MA ∼ 3
while increasing more linearly at higher MA ∼ 15. We also find that this ratio tends to be
higher for lower shock-normal angles save for θBn = 45◦.