Discharge modes and wave structures using loop antennae in a helicon plasma source

Discharge modes separated by density jumps in a helicon plasma source were controlled successfully by changing the antenna wavenumber spectrum with a two-loop antenna, in addition to varying the filling pressure P and the magnetic field B. For the case of wave excitation with the anti-parallel antenna current direction, the threshold power P-th for a density jump, regardless of B and P, was larger than in the case of a parallel direction, and P-th became larger with the increase in B in both cases. From the excited wave structures, it was found that the helicon wave plasma was observed after the jump with the high field, while with the low field regardless of the density region or with the high held before the jump, an inductively coupled plasma was found. No indication of a major role of the lower hybrid wave and Trivelpiece-Gould wave on the plasma production was observed.