Improved plasma confinement at high beta

Abstract

A new efficient method of confinement is proposed for use in linear traps. The plasma equilibrium in a linear trap at high β can evolve into a kind of diamagnetic “bubble” with a very small field inside. If the vacuum magnetic field of the trap has a quasi-uniform stretch near its minimum, the roughly cylindrical “bubble” with non-paraxial ends will occupy just this stretch. The “bubble” radius is determined by the balance of particle and energy fluxes, while the force balance corresponds to β ≈ 1 at any radius. The effective mirror ratio of the trap in this diamagnetic regime can become very large, stifling the axial losses, but the cross-field transport inside it increases. The total confinement time can be found from solution of the system of equilibrium and transport equations and is shown to be τE≈τ‖τ⊥. This means that the diamagnetic confinement at high β allows construction of relatively short linear traps as fusion reactors.