Multispecies Ion Acceleration in 3D Magnetic Reconnection with Hybrid-Kinetic Simulations

Area of Science:

• Space physics
• Plasma astrophysics
• Particle acceleration

Background:

• Magnetic reconnection is a fundamental process driving particle acceleration throughout space and astrophysical plasmas.
• Understanding the acceleration of multiple ion species, especially heavy ions, is crucial for explaining observed cosmic phenomena.

Purpose of the Study:

• To investigate the acceleration of multispecies ions, including heavy ions, during magnetic reconnection.
• To identify the dominant acceleration mechanism and its dependence on ion properties.

Main Methods:

• Performed the first 3D hybrid simulations (fluid electrons, kinetic ions) with adequate scale separation.
• Focused on the role of fragmented flux ropes in particle acceleration.
• Analyzed the acceleration of ion species up to iron (Fe).

Main Results:

• Demonstrated nonthermal acceleration of all ion species into power-law spectra via Fermi acceleration.
• Identified upstream ion velocity as critical for initial injection and Fermi reflection.
• Observed delayed Fermi acceleration onset for ions with lower charge-mass ratios (Q/M).
• Established a species-dependent maximum energy per nucleon scaling with charge-mass ratio: energy/nucleon ∝(Q/M)^{α}.

Conclusions:

• Fermi acceleration is the dominant mechanism for multispecies ion acceleration in reconnection regions.
• Flux rope dynamics and ion charge-mass ratio significantly influence acceleration efficiency and energy limits.
• Findings align with in situ observations of particle acceleration in space plasmas.