Plasma characteristics of a high power helicon discharge

摘要

A new high power helicon (HPH) plasma system has been designed to provide input powers of several tens of kilowatts to produce a large area (0.5 m(2)) of uniform high-density, of at least 5 x 10(17) m(-3), plasma downstream from the helicon coil. Axial and radial plasma characteristics show that the plasma is to a lesser extent created in and near the helicon coil and then is accelerated into the axial and equatorial regions. The bulk acceleration of the plasma is believed to be due to a coupling of the bulk of the electrons to the helicon field, which in turn transfers energy to the ions via ambipolar diffusion. The plasma beta is near unity a few centimetres away from the HPH system and Bdot measurements show Delta B perturbations in the order of the vacuum magnetic field magnitude. In the equatorial region, a magnetic separatrix is seen to develop roughly at the mid-point between the helicon and chamber wall. The magnetic perturbation develops on the time scale of the plasma flow speed and upon the plasma reaching the chamber wall decays to the vacuum magnetic field configuration within 200 mu s.