Secondary Ion Populations as Regulators of Low-Beta Stability from Solar Wind to Laboratory Plasmas

Plasma instability thresholds derived from linear theory effectively constrain the observed parameters of solar wind velocity distributions and define boundaries of "allowed" parameters where the plasma remains stable. These instabilities typically account for a single source of free energy, such as temperature anisotropy or a drifting secondary component, with respect to other parameters, e.g. the ratio of thermal to magnetic pressure (plasma beta). When the plasma evolves beyond these thresholds, the system emits energy, transferring it from particles to waves, resulting in the particles moving towards a more stable configuration. Given the prominent proton and alpha beams seen in the inner heliosphere by Parker Solar Probe and Solar Orbiter, defining the stability conditions in this more complex space is necessary to characterize the role ion-scale waves play in the inner heliosphere. We investigate the interaction between core thermal protons and secondary populations and their effects on the linear stabilization of low-beta plasmas commonly observed in young solar wind. Our analysis conclusively demonstrates the limit for the lowest stable value of plasma beta is determined by the drift of the secondary populations via a resonant drift instability. Finally, we extend our analysis to conditions of strongly drifted beams characteristic for laboratory chambers where the unstable conditions are achieved by excess parallel pressure and regulation of the VDF is governed by firehose instabilities.