Temperature Relaxation Rates for Strongly Magnetized Plasmas in Antimatter Traps

Antimatter appears in nature only in tiny quantities relative to matter for reasons not yet fully understood. To address this open question, a better understanding of the fundamental physics governing antimatter is needed. The ALPHA experiment at CERN is working to improve our understanding of antimatter by trapping and studying antihydrogen. The plasmas used to form the antihydrogen fall into the very strongly magnetized regime, meaning that the gyrofrequency exceeds the plasma frequency and in the moderate Coulomb coupling regime denoting that the potential energy of interaction is on the order of the kinetic energy. These regimes modify the Coulomb collision frequency making traditional theories invalid. Our goal is to develop the theoretical plasma physics models in these regimes to better understand the dynamics of these non-neutral plasmas, which may in turn aid in antihydrogen production.

Using a recently developed generalized Boltzmann kinetic theory for strongly magnetized plasmas, the electron-ion temperature relaxation rates in both parallel and perpendicular directions are calculated. In this regime, the particles will emit radiation in the perpendicular direction producing an anisotropy between the parallel and perpendicular temperatures which is transferred to the other species via Coulomb collisions. These results have relevance in several processes used in the ALPHA experiment, including antiproton cooling via Coulomb collisions with electrons, the thermal equilibration between antiprotons and positrons during recombination, and the sympathetic cooling of positrons on laser-cooled Beryllium. The improved understanding of temperature relaxation presented here will contribute to a more complete fluid model in this novel plasma regime.