Collisional thermalisation behaviour of highly-charged-ion plasmas in a Penning trap

Abstract We have experimentally investigated the collisional thermalisation of single-component plasmas formed by highly charged ions in a Penning trap by tracking the time evolution of spatial ion distributions in the radial direction. Due to the strong magnetic field of the trap, the axial and radial degrees of freedom behave largely differently. While the previously investigated axial thermalisation is in agreement with measurements and classical theory of plasmas, the presently observed radial thermalisation is faster by several orders of magnitude and needs to be explained by theory that properly describes energy transport perpendicular to the strong magnetic field due to long-range Coulomb collisions in a regime where the Debye length in the plasma is much larger than the ion orbit around the magnetic field. We compare such theory expectations to our measurements and simulations.