Radio frequency breakdown and electron confinement time in a stellarator

Radio frequency ( f = 350 kHz) inductive breakdown has been studied in a toroidal stellarator. The time delay between the application of the radio frequency pulse and the buildup of detectable plasma density is measured as a function of the discharge parameters. It is shown that the confinement time of energetic electrons (approx.100 eV), produced during the breakdown, may be deduced from the breakdown characteristics. The experimentally determined confinement times are compared with predictions of neoclassical transport theory and are found to have functional dependence on the discharge parameters approximately consistent with plateau scaling, but to be shorter than predicted by the neoclassical diffusion model