Characterization of helicon waves in a magnetized inductive discharge

The propagation of helicon waves and the plasma density has been measured in a cylindrical, magnetized plasma for a range of magnetic fields and input power levels. A transition in the coupling mechanism from electrostatic (E mode) to inductive (H mode) coupling is evidenced by a sharp change in the plasma density coinciding with a change in the wave fields from a linearly polarized standing wave, with highest amplitude close to the antenna to a right-hand elliptically polarized traveling wave with a phase velocity of about 6×106 m/s extending into the downstream region. An explanation of the transition to the H mode is put forward in terms of the conductivity across the magnetic field and an associated skin depth for power deposition. The polarization of the wave fields in the H mode is interpreted in terms of the interference between m=+1 and −1 modes (where m is the azimuthal mode number).