Rate equations model for multiple magnetic mirrors in various thermodynamic scenarios

Abstract

Axial particle loss is one of the main challenges for fusion aimed, linear magnetic mirror plasma configurations. One way to mitigate this disadvantage and increase the confinement time is to use a multiple mirrors setup. The idea is to reduce the outgoing flux by collisions in the outer magnetic cells. Here, we develop a rate equation model for the ions density dynamics, including scattering within the magnetic cell and the transmission between neighboring cells. The dominant parameter is the ions' mean free path, which depends on the temperature and density in each cell. The steady-state flow is studied, analytically and numerically, for three thermodynamic scenarios: isothermal plasma, adiabatic expansion, and constant diffusion. It is found that the confinement time varies about five-fold over the different scenarios, where the adiabatic cooling is the best confining scenario. However, even in the best performing confinement scenario, the multiple mirror sections would need to be extremely long to approach fusion conditions.