Cumulative Proton Right-handed Instabilities in the Young Solar Wind Observed by PSP

Abstract We present a detailed linear analysis of right-handed (RH) proton instabilities in beaming bi-Maxwellian/bi-Kappa plasma representative of young solar wind conditions currently explored by the Parker Solar Probe. At lower heliocentric distances, ion (proton) beams are more dense, and the associated wave fluctuations are predominantly RH polarized, strongly suggesting the presence of proton-beam plasma instabilities to explain not only the enhanced fluctuations but also the subsequent particle diffusion in energy and pitch angle. The study systematically investigates the cumulative effects of beam drift velocity and temperature anisotropies on the ion–ion resonant and proton firehose instabilities. By examining the variations in maximum growth rates, resonant factors, and instability thresholds across a broad range of plasma parameters, including beam and core anisotropies, density ratios, plasma beta, and suprathermal populations, this work identifies the key regimes where instabilities are enhanced or suppressed. The influence of suprathermal ions and electrons, modeled using Kappa distributions, is shown to significantly extend the unstable parameter space. Electron temperature anisotropy is also found to strongly modify the growth rates of these instabilities by changing their resonance conditions with beaming particles. This parametric study provides comprehensive guidance for future quasilinear or simulation studies by identifying the most physically relevant and numerically effective regimes for these instabilities in the solar wind and space plasmas.