CHARACTERIZATION OF HELICON WAVES IN A MAGNETIZED INDUCTIVE DISCHARGE

The propagation of helicon waves and the plasma density has been measu red in a cylindrical, magnetized plasma for a range of magnetic fields and input power levels. A transition in the coupling mechanism from e lectrostatic (E mode) to inductive (H mode) coupling is evidenced by a sharp change in the plasma density coinciding with a change in the wa ve fields from a linearly polarized standing wave, with highest amplit ude close to the antenna to a right-hand elliptically polarized travel ing wave with a phase velocity of about 6 X 10(6) m/s extending into t he downstream region. An explanation of the transition to the H mode i s put forward in terms of the conductivity across the magnetic field a nd an associated skin depth for power deposition. The polarization of the wave fields in the H mode is interpreted in terms of the interfere nce between m = + 1 and - 1 modes (where m is the azimuthal mode numbe r). (C) 1998 American Institute of Physics.