Abstract
ECR discharge cleaning (ECR-DC) was carried out in GAMMA 10 tandem-mirror device of University of Tsukuba. By the use of microwave (2.45 GHz, 2 kW), a hydrogen cleaning plasma with the electron density and temperature of 2 ×1016 m-3 and 4.5 eV, respectively, was produced in a hydrogen pressure range of 210 × 10-5 Torr. The cleaning was conducted for 30 hrs. The effectiveness was examined by (1) residual gas analysis, (2) SAGE (surface analysis of adsorbed gas by electron impact outgassing), (3) Outgas measurement by ICRF (Ion Cyclotron Range of Frequency) pulse plasma, (4) electron density measurement, (5) relation between electron line density and diamagnetic signal of ICRF plasma, (6) optical spectroscopy and (7) electron temperature mesurement. The ECR-DC for 30 hrs accelerated the surface conditioning to the same level as that after 10001500-shots-ICRF pulsed discharge cleaning. This indicates that we can save about 23 weeks of wall surface conditioning after venting to air.
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