Impact of spurious versus physical plasmoids on measured reconnection rate

Determine whether the distinction between spurious plasmoids produced by under-resolved numerical simulations and physical plasmoids arising from the plasmoid instability significantly affects the magnetic reconnection rate measured in resistive magnetohydrodynamic simulations of forming current sheets (e.g., the Orszag–Tang vortex) within the plasmoid regime; in particular, ascertain whether spurious plasmoids can artificially trigger the fast reconnection regime and thereby bias the inferred reconnection rate across a range of Lundquist numbers.

Background

The paper establishes diagnostic criteria to distinguish physical plasmoids from spurious ones that arise in under-resolved simulations of resistive MHD current sheets, using the Orszag–Tang vortex as a testbed. It shows that well-resolved pseudo-spectral simulations require appropriately timed and sufficiently strong perturbations with suitable spectral content to trigger physical plasmoids, whereas under-resolved runs can exhibit spurious plasmoids seeded by numerical noise.

Given that plasmoids can alter reconnection dynamics and rates, the authors identify a key unresolved issue: whether the presence of spurious (resolution-induced) plasmoids biases measurements of the reconnection rate, potentially by artificially entering a fast reconnection regime. They note that answering this would require a systematic study over a range of Lundquist numbers within the plasmoid regime, which is beyond the scope of the present work.