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Magnetic reconnection and non-thermal particle distributions associated withcurrent-driven instabilities are investigated by means of resistivemagnetohydrodynamics (MHD) simulations combined with relativistic test particlemethods. We propose a system with two parallel, repelling current channels inan initially force-free equilibrium, as a simplified representation of fluxropes in a stellar magnetosphere. The current channels undergo a rotation andseparation on Alfv\'enic timescales, forming secondary islands and (up totearing unstable) current sheets in which non-thermal energy distributions areexpected to develop. Using the recently developed particle module of ouropen-source grid-adaptive MPI-AMRVAC software, we simulate MHD evolutioncombined with test particle treatments in MHD snapshots. We explore under whichplasma-$\beta$ conditions the fastest reconnection occurs in two-and-a-halfdimensional (2.5D) scenarios and in these settings test particles are evolved.We quantify energy distributions, acceleration mechanisms, relativisticcorrections to the particle equations of motion and effects of resistivity inmagnetically dominated proton-electron plasmas. Due to large resistive electricfields and indefinite acceleration of particles in the infinitely long currentchannels, hard energy spectra are found in 2.5D configurations. Solutions tothese numerical artifacts are proposed for both 2.5D setups and future 3D work.We discuss the magnetohydrodynamics of an additional kink instability in 3Dsetups and the expected effects on energy distributions. The obtained resultshold as a proof-of-principle for test particle approaches in MHD simulations,relevant to explore less idealised scenarios like solar flares and more exoticastrophysical phenomena, like black hole flares, magnetar magnetospheres andpulsar wind nebulae.

Reconnection and particle acceleration in interacting flux ropes I. Magnetohydrodynamics and test particles in 2.5D