  Using 3D particle-in-cell simulation, we characterize energy conversion, as a
function of guide magnetic field, in a thin current sheet in semirelativistic
plasma, with relativistic electrons and subrelativistic protons. There,
magnetic reconnection, the drift-kink instability (DKI), and the flux-rope kink
instability all compete and interact in their nonlinear stages to convert
magnetic energy to plasma energy. We compare fully 3D simulations with 2D in
two different planes to isolate reconnection and DKI effects. In zero guide
field, these processes yield distinct energy conversion signatures: ions gain
more energy than electrons in 2Dxy (reconnection), while the opposite is true
in 2Dyz (DKI), and the 3D result falls in between. The flux-rope instability,
which occurs only in 3D, allows more magnetic energy to be released than in 2D,
but the rate of energy conversion in 3D tends to be lower. Increasing the guide
magnetic field strongly suppresses DKI, and in all cases slows and reduces the
overall amount of energy conversion; it also favors electron energization
through a process by which energy is first stored in the motional electric
field of flux ropes before energizing particles. Understanding the evolution of
the energy partition thus provides insight into the role of various plasma
processes, and is important for modeling radiation from astrophysical sources
such as accreting black holes and their jets.
