<i>In situ</i>plasma cleaning of ITER diagnostic mirrors in noble-gas RF discharge

Abstract

The development of the first mirror cleaning and recovery system is one of the challenges for all optical diagnostics in ITER. This study is focused on capacitively coupled radio frequency (CCRF) discharge as a promising method for removal of metal deposits. The physical aspects of the RF discharge application are discussed with a focus on implementation under ITER conditions. The effective sputtering rates of Be, W and Mo were calculated as a function of applied frequency and absorbed power for noble gases—He, Ne, Ar, Kr, Xe, taking into account complex shape of the ion energy distribution function in the electrode sheaths. Helium is shown to be a good candidate for cleaning Mo mirrors from Be deposits in the frequency range ∼80–100 MHz and pressure of a few Pa.