Critical system size for transition to the asymptotic reconnection-onset regime

Determine the exact flux-tube radius R, normalized by the cold plasma skin depth d_{e0}, at which driven collisionless reconnection in a magnetically dominated electron–positron pair plasma enters the asymptotic onset regime characterized by current-sheet disruption at a thickness a_* much larger than d_{e0}, in the two–force-free–flux-tube configuration studied here.

Background

The paper studies driven collisionless reconnection and plasmoid formation in a magnetically dominated pair plasma using 2D PIC simulations of two force-free flux tubes pushed together. Even for the largest simulated system with R/d_{e0} ≈ 1600, the current sheet at reconnection onset remains at skin-depth scale, a_* ~ d_{e0}.

Based on theoretical expectations, the authors argue that in asymptotically large systems the disruption should occur when a_* ≫ d_{e0}. Their simulations indicate that reaching the asymptotic regime likely requires R ≫ 103 d_{e0}, but they only establish a lower bound. The precise system size at which this transition occurs remains undetermined.

References

Our results thus indicate that the asymptotic regime in a magnetically dominated pair plasma requires $R \gg 103 e0$; the exact size for the presumed transition into the asymptotic regime is presently unknown (i.e., our results only provide a lower bound).

— Onset of Driven Collisionless Reconnection in Strongly Magnetized Pair Plasmas  (2506.06059 - Granier et al., 6 Jun 2025) in Discussion and Conclusion (Section 5)