Energy Balance and Confinement of a Magnetized Plasma

Abstract

Under laboratory conditions particle losses from a magnetized plasma will produce a neutral particle flux reentering from the surrounding vessel walls into the plasma region. Even at very high temperatures, where the plasma is almost fully ionized, this gives rise to interactions between charged and neutral particles which cannot always be neglected. Three types of interactions are discussed: ionization, charge exchange, and elastic collisions with neutrals. The conservation laws of mass, charge, momentum, and energy are reconsidered for a two-fluid system with ionization, charge exchange, and elastic scattering of neutral particles taken into account. It is found not necessary to derive the energy equation in terms of the joint action of electromagnetic and mechanical changes of state. It has earlier been concluded from the motion of a single particle that a very strong confinement can be obtained in a rotating plasma situated in the magnetic field of a current loop (Bonnevier and Lehneat). These results are verified in a macroscopic theory including the energy balance of stationary motion. It is found that the main part of the heating of the plasma and the scattering of ions are not provided by coulomb collisions, but by collisions with reentering neutral particles. Twomore » special cases are treated in detail, one with vanishing heat conductivity and one with infinite heat conductivity in the direction along the magnetic field. For the latter, which is more likely to occur in a high temperature plasma, the energy loss by escaping particles is deduced. The theory predicts that this loss should be several orders of magnitude less in the current loop configuration than in earlier described homopolar machines. Finally, some comments are given on the nonexistence of interchange instabilities in systems with volume currents.« less