Proton-Acoustic Wave Effects on the Relaxation of Proton Transverse Heating in Magnetized Plasmas

arXiv:2509.08106v1 Announce Type: new
Abstract: Transverse electromagnetic and electrostatic plasma wave modes propagating along a background magnetic field $vec{B}_0$ are independent according to linear kinetic theory. However, resonant interactions and energy exchange between waves and particles break this linear decoupling. This work tracks the coupled evolution of Alfv’en-cyclotron (ACWs) and Ion-acoustic waves (IAWs) by solving moment-based quasilinear equations for a collisionless plasma of bi-Maxwellian protons and Maxwellian electrons. Unlike earlier quasilinear studies that adopt the cold-electron limit, our formulation retains the full kinetic response of both species, treating the electrons as a thermal reservoir to isolate proton heating. A parameter survey over $0.01leqbeta_{parallel p}leq10$ and $1le T_e/T_ple10$ shows that an ambient spectrum of ACWs can drive significant perpendicular proton heating and raise the temperature anisotropy from initially isotropic conditions at low $beta_{parallel p}lesssim0.1$, thereby triggering cyclotron instabilities. The quasilinear evolution self-regulates the ACW, driving the system toward a quasi-stationary state with $gamma/Omega_p