Effect of antenna helicity on discharge characteristics of helicon plasma under divergent magnetic field

The characteristics of blue core phenomenon observed in a divergent magnetic field helicon plasma is investigated by using two different helical antennas, namely, right-handed (RH) and left-handed (LH) helical antennas. The mode transition, discharge image, spatial profiles of plasma density and electron temperature are diagnosed by using a Langmuir probe, a Nikon D90 camera, an intensified charge-coupled device (ICCD) camera, and an optical emission spectrometer (OES), respectively. The results demonstrated that the blue core phenomenon appeared in the upstream region of the discharge tube at a fixed magnetic field under both helical antennas. However, it is more likely to appear in the situation of RH helical antenna, in which the plasma density and ionization rate of helicon plasma are higher. The spatial profiles of the plasma density and the electron temperature are also different both in axial and radial directions for these two kinds of helical antennas. The wavelength calculated based on the dispersion relation of the bounded whistler wave is consistent with the order of magnitude of plasma length. It is proved that the helicon plasma is in the wave mode discharge mechanism.