Production of high-density hydrogen plasmas by helicon waves in a simple torus

摘要

High-density plasma production by helicon waves in a simple torus has been investigated. The measured plasma density n(p) versus external magnetic field B-0 peaks at a condition close to the lower-hybrid resonance in H-2, D-2, and He. Three density regions are observed in the variation of rf power P-rf. In the low-density region, helicon waves are not excited and plasmas are produced by an antenna induction field. In the medium- and high-density (H) regions, helicon waves with the m=+1 azimuthal mode are excited and plasmas are produced by the waves. In H-2 plasmas, the second-radial mode is dominant over the first-radial mode at P-rf>10 kW in the H region. The measured k(z)-n(p) relation (k(z) is the wave number parallel to B-0) of helicon waves in the H region shows deviation from that of the m=+1 mode derived using the uniform-plasma assumption. The k(z)-n(p) relation is calculated for various radial-n(p) profiles; parabolic, modified-parabolic, and Gaussian profiles. The difference in the k(z)-n(p) relation of the m=+1 mode between the uniform- and nonuniform-plasma models is explained by adding a vacuum region between a uniform plasma and the radial boundary. (C) 2004 American Institute of Physics. [References: 48]