Coherent Intermode Energy Transfer and Wave–Particle Energy Partition in Reversed-Shear Alfvén Dynamics

Reversed-shear Alfvén eigenmodes (RSAEs) play an important role in energetic-particle transport and energy redistribution in magnetically confined fusion plasmas. Understanding their nonlinear evolution and potential suppression requires a consistent assessment of mode excitation, intermode energy transfer, wave–particle interactions, and dissipative processes. In this work, we investigate these mechanisms using a combination of global magnetohydrodynamic (MHD) responses and reduced theoretical and numerical models. We first examine phase-dependent energy transfer in a conservative three-wave interaction model, identifying the conditions governing energy exchange between symmetric pump-modes and a resonantly coupled daughter mode. We then investigate the temporal evolution of electromagnetic-field energy and species-resolved free-energy exchange in a local gyroaveraged electron–ion model. The results reveal alternating energy transfer between the thermal species and electromagnetic fields, with electron free-energy release, deuteron ion energy absorption, and polarization and magnetic-field energy storage contributing to the overall balance. An independent electrostatic electron-beam model further illustrates the relationship between electron free-energy release, electric-field growth, and subsequent partial reverse energy transfer. Additional calculations examine resonant particle-orbit interactions, phase-space trapping and distribution rearrangement, as well as the conversion of coherent wave energy into irreversible viscous dissipation. These results identify distinct mechanisms governing intermode energy transfer, particle–field exchange, phase mixing, and dissipative energy conversion. Taken together, the reduced models provide a framework for examining the individual components of RSAE-related energy redistribution and for identifying the quantities required for a self-consistent kinetic description. Establishing their combined influence on RSAE stability and suppression will require coupled simulations that simultaneously resolve wave-field evolution, resonant particle dynamics, species-resolved energy transfer, and radial particle transport. This leads to energy and transport diagnostics may provide useful physical constraints for future physics-informed inverse co-design framework of fusion-plasma operating conditions.