Application of ECWR for tin removal with prospective use in tokamaks with liquid metal divertor

Abstract One of the problems of the liquid metal tokamak divertor technology is the redeposition of the released metal on the tokamak vessel walls. In this work an investigation of the removal of the redeposited metals from grounded conducting walls of tokamak was done by a low-temperature Ar plasma generated by electron cyclotron waves, radiofrequency electron cyclotron wave resonance (RF-ECWR), at 13.56 MHz in a new/modified system with a tunable plasma potential. The plasma potential was controlled in this system in the range from 0–270 V. The plasma potential control was achieved by adding an additional DC voltage supply on ECWR electrode via a suitable inductor having high impedance at the 13.56 MHz frequency. Metallic Sn thin films were deposited in the first step on the conducting doped Si wafer by means of medium frequency pulsed magnetron sputtering from pure Sn target. In the next step, the Sn films were removed from the Si substrate by ion etching (ion sputtering) by accelerated Ar ion fluxes. The etching efficiency was investigated in dependence on different values of the applied RF power and different values of the adjusted plasma potential. The ion density, electron temperature and the ion flux density impinging on the sample were determined by an RF probe system at different ECWR plasma conditions. The etching efficiency of Sn coatings was evaluated by profilometry measurement, SEM photography and electron microprobe analysis. It was found that this new/modified configuration of the ECWR plasma source can prospectively be used for cleaning of the grounded walls of tokamak from deposited Sn layers.