RF breakdown by toroidal bounded whistlers

Summary form only given. In a toroidal experimental device bounded whistlers are launched to produce the RF plasma. These waves are toroidal counterparts of helicon waves in thin cylindrical tubes, where poloidal mode coupling plays a significant role. In the steady state average electron density of /spl ap/10/sup 12/ per cc and average electron temperature of /spl ap/20 eV are obtained at 10/sup -3/ mbar of the argon filling pressure and less than 600 G of ambient toroidal magnetic field. In these experiments input power level in the EMHD regime (/spl omega//sub th//spl Lt//spl omega//spl Lt//spl omega//sub cc/) is kept below 1.5 kW. In this paper we shall present their radio frequency breakdown and discharge sustaining capabilities. After breakdown stage, discharge is sustained by toroidal bounded whistlers as confirmed by wave vector measurements. In these pulsed experiments time evolution behaviour of the discharge is studied in four distinct phases of RF breakdown, steady state attainment, decay and afterglow. Experimental results based on toroidal mode structure, background effects, time evolution of distribution function and other plasma parameters of interest will be presented and their implication in understanding the breakdown.