Fusion energy balance in mirror machines

This is the authors' abstract. We don't add key points for this paper.

Motivated by the encouraging outlook for stable confinement of fusion plasmas by `minimum-B' magnetic mirrors, we have recalculated Q, the ratio of total fusion energy released to the injection energy required to replenish mirror losses by collisions. We solve numerically Fokker-Planck equations for ion and electron energy distributions with special attention toward ion cooling by electrons and the effect of the ambipolar potential on the velocity loss cone. We find that both these effects enhance mirror losses much more than was supposed previously. Consequently, for a D-T plasma our Q is a factor 4 or more smaller than previous estimates, and Q is maximum at a higher energy, 200-300 keV. For a mirror ratio R = 3, the maximum is Q = 1.5, and, for larger R, Q scales approximately as log10R. We find a negligible benefit from ion heating by collisions with trapped α-particles from fusion reactions.