Lower hybrid geometrical resonance in linear LISA machine

Plasma heating by radio frequency (r.f.) in the electron cyclotron and lower hybrid frequency ranges has been studied using Langmuir probe, magnetic probe, Faraday cup and optical spectrography in the linear mirror machine LISA. It is found that global modes (ECW) rather than WKB ones, have been excited. The plasma heating was via the electron cyclotron resonance and via a linear mode conversion of the extraordinary mode into an upper-hybrid mode and this mode decays into a Bernstein wave (at r=±3.0 cm). An r.f. source of 2.45 GHz and 1.0 kW was used where r is the plasma inner radius. When an additional r.f. source of 30 MHz and 0.35 kW was introduced it heated the plasma via the lower hybrid resonance at r = 5.0 cm and resulted in a 30%, or more, increase in overall electron temperature and plasma density. (author)