The H-1 radio frequency system and an initial study of plasma formation

Eight commercial broadcast transmitters rated at 30 kW PEP 4–26 MHz are being commissioned for plasma formation and heating in H-1. These may be either excited separately or combined into two antennas by a set of six power combiners. In this paper we describe the various components of the r.f. power transmission system. We present preliminary results using this system for plasma formation in argon and hydrogen with magnetic fields <2 kG and powers up to 30 kW at 4 and 7 MHz using a single saddle coil loop antenna. We have been able to produce both hollow and centrally peaked plasmas in both gases and have demonstrated that the plasma centre of symmetry shifts with the magnetic field axis as expected. In argon, we have achieved a density in the order of 1018 m−3 peaked on axis.