Large Diameter rf Plasma for Pre-Ionization in Confinement Devices

Abstract

A large diameter rf quiescent plasma has been created using a helical ``L'' coil fed radially with 12‐cm wavelength cw microwave power. The radial profiles of electron temperature and ion saturation current show that the plasma is uniform in a 15‐cm‐diam region. The plasma is produced in electron‐cyclotron‐resonance (ECR) conditions, but it can be maintained by increasing the magnetic field up to a value four times larger than the resonant one. The plasma existence regions vs neutral gas pressure and magnetic field are studied. The performances of this plasma seem to be important in facing pre‐ionization problems in confinement devices.