Energy Conversion Pathways Inside Kelvin-Helmholtz Vortices

Energy transfer, cross-scale coupling, and dissipation in astrophysical plasmas remain fundamental unresolved problems. The velocity-shear–driven Kelvin–Helmholtz instability (KHI), ubiquitous in plasmas, is a key multiscale mechanism enabling plasma mixing, particle energization and the solar wind–magnetosphere coupling, making it a critical process for understanding how plasma flow energy is converted from large to kinetic scales. Although in situ observations and simulations have linked KHI to turbulence onset and plasma heating, the precise pathways of energy transfer remain unexplored. By leveraging high-resolution, multi-point Magnetospheric Multiscale (MMS) observations, we quantify, for the first time, KHI energy conversion channels via pressure–strain and (Formula presented.) diagnostics. Inside vortices, thermal-to-flow energy transfer dominates, coinciding with local non-thermal features. Notably, energy pathways seem influenced by vortex evolution: rolled-up vortices tend to convert flow energy into thermal energy, whereas early-stage vortices mostly convert thermal energy back into flow. This study provides the first energy-balance-based description of KHI dynamics and further reveals the complexity of velocity shear energy dissipation into heat.