LAUSR

The dependence of the sputtering efficiency for a Mo mirror mock-up on the discharge power and the pressure of the working gas (Ar) has been investigated for three options of grounding of the discharge-cell elements in the plasma cleaning system. A gas discharge with a direct current or medium-frequency pulsed current is expected to be used to clean the entrance mirror of CXRS-edge (Active Spectroscopy) diagnostics of ITER. By selecting the electrode-grounding scheme it is possible to obtain different degrees of deceleration of ions that leave the discharge cell and are able to sputter the walls of the diagnostic port. The location of the diagnostic-port walls in close vicinity to the discharge cell and the absence of a working-gas flow through the region of the cleaning discharge are the specific features of the mirror cleaning systems in ITER. These conditions have been simulated by placing a full-scale functional model of the discharge cell into a leaky gas-dynamic fairing, which was made of stainless steel, like the walls of ITER diagnostic port. It is shown that the highest cleaning efficiency is attained when the cathode elements of the discharge cell and the entrance mirror in particular are electrically isolated from the diagnostic-port walls. These results can be used to develop plasma cleaning systems for other optical diagnostics of ITER.