Characteristics of Cleaning and Carbonizing Plasmas in TEXTOR

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Abstract
Plasma parameters for discharge cleaning and carbonization in TEXTOR (Torus Experiment on Technology Oriented Research in the Kernforschungsanlage Julich) have been measured with Langmuir probes. In the rf-assisted glow (RG) discharge of hydrogen, at 1.6×10-1 Pa, the plasma density is n e = 3.0-4.0×108 cm-3, the electron temperature T e = 10-12 eV, and the space potential V s≦265 V. In the electron cyclotron resonance (ECR) discharge, at 1.1 × 10-2 Pa, n e=2.0-2.7×1010 cm-3, T e=3.5-5.2 eV, and V s=20 V in the resonance region. The width of this region is about 20 cm. In the carbonization by the RG discharge with an admixture of methane into deuterium at a volume ratio of 33%, at 1.7×10-1 Pa, n e = 0.9-1.4×109 cm-3, T e = 2.7-3.3 eV and V s≦280 V. The flux of ions and neutral atoms are estimated from measured parameters. In RG(H2), both H+ 2 and H are effective for cleaning. In ECR, an appreciable flux of H is obtained, and the H+ 2 flux, though reduced by the radial magnetic field, has an effect of cleaning. In RG(CH4/D2), the positive ion flux of the order of 6×1013 cm-2s-1 is responsible for the carbonization.