Kavli Affiliate: Tom Abel
| First 5 Authors: Samuel Totorica, Masahiro Hoshino, Tom Abel, Frederico Fiuza,
| Summary:
Magnetic reconnection is a fundamental plasma process that is thought to play
a key role in the production of nonthermal particles associated with explosive
phenomena in space physics and astrophysics. Experiments at high-energy-density
facilities are starting to probe the microphysics of reconnection at high
Lundquist numbers and large system sizes. We have performed particle-in-cell
(PIC) simulations to explore particle acceleration for parameters relevant to
laser-driven reconnection experiments. We study particle acceleration in large
system sizes that may be produced soon with the most energetic laser drivers
available, such as at the National Ignition Facility. In these conditions, we
show the possibility of reaching the multi-plasmoid regime, where plasmoid
acceleration becomes dominant. Our results show the transition from textit{X}
point to plasmoid-dominated acceleration associated with the merging and
contraction of plasmoids that further extend the maximum energy of the
power-law tail of the particle distribution for electrons. We also find for the
first time a system-size-dependent emergence of nonthermal ion acceleration in
driven reconnection, where the magnetization of ions at sufficiently large
sizes allows them to be contained by the magnetic field and energized by direct
textit{X} point acceleration. For feasible experimental conditions, electrons
and ions can attain energies of $epsilon_{max,e} / k_{B} T_{e} > 100$ and
$epsilon_{max,i} / k_{B} T_{i} > 1000$. Using PIC simulations with binary
Monte Carlo Coulomb collisions we study the impact of collisionality on
plasmoid formation and particle acceleration. The implications of these results
for understanding the role reconnection plays in accelerating particles in
space physics and astrophysics are discussed.
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