Compact vacuum RF components for front-end mirror plasma cleaning in ITER diagnostics
conference paper
Plasma cleaning of front-end optical mirrors becomes an essential part of ITER optical diagnostics due to the risk of contamination with Be, W and their oxides from reactor sputtering. 10nm of deposits may affect mirror performance. A capacitively-coupled RF gas discharge is considered a candidate technology for optical surface cleaning of the Visual Spectroscopy Reference System (VSRS) diagnostic system. Due to complex design requirements, the RF circuit components, cables and feedthroughs, should be specially developed. Such components must be relatively compact and be capable of delivering necessary power to the front-end optical mirrors. The design foresees 5-15 m long vacuum RF cable feeds, temperatures of vacuum components up to 350 C, total generator power up to 1kW and mirror electrodes connected to the vessel. It is assumed that for the VSRS diagnostic system such electrodes do not need water cooling. The RF vacuum circuitry becomes inaccessible for repair and replacement once the tokamak is assembled. A service time of 10 years is expected. The RF power feeds should be compact to fit in in the duct where other diagnostic hardware and subsystems such as alignment, shutters and calibration are located. In the present report, we analyze a design approach to such RF circuit components for the VSRS system and discuss vacuum mineral-insulated (MI) cables as potential power feeds. The results can be interesting for the design of mirror plasma cleaning systems in other ITER tokamak optical diagnostics as for remote vacuum plasma cleaning applications in semiconductor industry.
TNO Identifier
955562
ISSN
09203796
Publisher
TNO
Source title
31st Symposium on Fusion Technology, SOFT2020, 20-25 September 2020, Dubrovnik, Croatia (virtual)
Collation
1 p.
Place of publication
Delft
Files
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