IMPACT OF MOLYBDENUM AND TUNGSTEN TEST LIMITERS ON ION FLUXES IN THE PLASMA EDGE OF TEXTOR

摘要

Ion fluxes in the scrape-off layer (SOL) of the TEXTOR tokamak were traced by means of the collector probe technique during tests of tungsten and molybdenum limiters. Graphite probes were exposed under different operation conditions: limiter position, plasma density, neon edge cooling and heating mode. Following the exposures, the surfaces were examined with ion beam analysis techniques (RBS, NRA) in order to determine deposition rates of metals, deuterium and other species. Under the same experimental conditions deposition rates of tungsten are found to be 6.5-7.5 times lower than those for molybdenum. The results for both the metals are compared and discussed in terms of processes governing the erosion rate of high-Z metals in tokamaks: physical sputtering and re-deposition of sputtered species. Moreover, the results of the collector probe measurements of fluxes in the SOL are compared with the spectroscopic observations of high-Z impurity atoms in the plasma. (C) 1997 Elsevier Science B.V. [References: 12]