Multispecies Ion Acceleration in the Interaction of Multiple Reconnection Current Sheets

Abstract Magnetic reconnection is an important origin of high-energy multispecies ions in the heliosphere, and the interaction of multiple current sheets in reconnection around the kinetic scale is inevitable because of magnetic convection and braiding. Here, we perform hybrid particle-in-cell simulations with kinetic ions and fluid electrons to study the multispecies ion acceleration in this multiple current sheet interaction process. We show that the interaction between multiple current sheets can spontaneously drive turbulence, inducing a power law of −7/3 for the magnetic energy spectrum. We find that both the early reconnection stage and the subsequent turbulence stage can efficiently accelerate ions, with the maximum energy per nucleon species independently increasing as <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ε</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">max</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∝</mml:mo> <mml:msup> <mml:mrow> <mml:mi>t</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>γ</mml:mi> </mml:mrow> </mml:msup> </mml:math> , and we have also reproduced the observed power-law <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ε</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">max</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∝</mml:mo> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mi>Q</mml:mi> <mml:mo>/</mml:mo> <mml:mi>M</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> </mml:msup> </mml:math> , where Q and M are, respectively, the ion charge and mass. Comparing the two stages, we find that the acceleration efficiency in the turbulence stage is higher, with index γ being approximately twice that of the reconnection stage and index α being smaller, indicating that the turbulence can more efficiently accelerate heavier ions with smaller Q / M , and these characteristics are not sensitive to plasma β . We demonstrate that the underlying physics is that the magnetic structure in the turbulence stage has a statistically larger curvature, thereby enhancing the dominant Fermi acceleration. Our results highlight the crucial role of multiple current sheet interactions and the resulting turbulence in multispecies ion acceleration, and will have multiple potential implications on the origin of energetic ions observed in the heliosphere.