Gas breakdown in tokamaks

The initial stage of the charge development in a tokomak is considered theoretically. It is supposed that all electrons produced in neutral gas ionisation process are in the regime of an almost continuous acceleration. The production time of a given electron density is calculated as a function of the neutral gas density and of parameters of the vortex electric field. The mechanism of plasma escape on walls is considered. It is shown that the escaping time is defined by a specific inertial flow of plasma and depends on whether chamber walls are metal or dielectric. The criterion of the gas breakdown in a toroidal system is formulated. The developed theory is shown to explain a strong dependence of the breakdown on the gas initial density