Design and analysis of first mirror plasma cleaning electrical circuit for Edge Thomson scattering ITER diagnostics

• Published in: Fusion engineering and design 2022-04, Vol.177, p.113079, Article 113079
• Main Authors: Stephan, Ulf, Steinke, Olaff, Ushakov, Andrey, Verlaan, Ad, Yatsuka, Eiichi, Yokoyama, Masahito, Rijfers, André, Ribeiro, Diogo, Moser, Lucas, Bassan, Michele, Maniscalco, Matthew P., van Beekum, Erik, Hatae, Takaki
• Format: Article
• Language: English
• Subjects: Argon; Circuit design; Circuits; Cleaning; Contaminants; Edge Thomson scattering; Electron energy; First mirror; Helium plasma; Inductance; ITER diagnostics; Liquid cooling; Matching; Notch filter; Notch filters; Plasma cleaning; Plasma control; Radio frequency plasma; Radio-frequency discharges; RF cables; Thomson scattering; Transmission circuits; Vacuum; Water purification
• ISSN: 0920-3796; 1873-7196
• DOI: 10.1016/j.fusengdes.2022.113079

•Modeling includes RF electrical circuit for ETS First Mirror plasma cleaning.•Compact vacuum notch-filter structure is considered for several frequencies.•Matching with a passive vacuum pre-matcher suits low plasma impedances.•Plasma impedance is measured in a representative geometry in helium and argon plasma.•Generator power of 1 kW may be needed to produce sufficient ion flux in cleaning plasma. The ITER Edge Thomson scattering system provides measurements of the electron temperature and density profiles at the periphery plasma of the ITER tokamak for physics studies and advanced plasma control. The front-end of the system contains a relatively large 23 cm × 25.8 cm metal first mirror (FM). Radio-frequency plasma is considered to remove contaminants from the FM. The new design approach for the power transmission circuit for plasma cleaning includes a pre-matching element next to the FM and a notch-filter. The FM is water-cooled and the water cooling pipe length is tuned as a notch filter for the driving frequency. The power dissipation in the circuit elements was analyzed in a series of simulations at frequencies 30, 40 and 50 MHz. New plasma impedance values used for the model were measured in argon and helium plasma at 1–10 Pa in a special mock-up of the front-end optics compartment. The results define inductance, capacitance and geometry of pre-matching elements and help to predict the performance of the plasma cleaning circuit.