Effects of poloidal magnetic configurations on expansions of electron cyclotron wall conditioning plasma and hydrogen removal in the integrated commissioning phase of JT-60SA

Abstract

Hydrogen ($H_2$) molecules were desorbed from the wall by tokamak discharges with helium (He) working gas. Particle balance analysis revealed that up to the same number of $H_2$ molecules as the injected He atoms were evacuated per He tokamak discharge. Four sequences of Electron Cyclotron Wall Conditioning with He working gas (He-ECWC) performed after the second series of $H_2$ tokamak discharges removed 16% of the $H_2$ molecules that had been retained by the $H_2$ tokamak discharges. The He-ECWC plasma produced by a fundamental ordinary mode (O1-mode) EC wave with a frequency of $f_{\mathrm{EC}}=$ 82 GHz expanded along the poloidal magnetic field line. In the He-ECWC plasma produced by the O1-mode EC wave with $f_{\mathrm{EC}}=$ 82 GHz, the $H_2$ removal ratio relative to the residual $H_2$ molecules was highest with the poloidal magnetic field in a Trapped Particle Configuration (TPC) with an $n$-index of 0.7 at the toroidal magnetic field of $B_T=$ 1.79 and 2.04 T. A comparable $H_2$ removal ratio was observed with the poloidal magnetic field in a horizontal configuration at $B_T=$ 1.79 T. On a second harmonic extraordinary mode (X2-mode) EC wave with $f_{\mathrm{EC}}=$ 110 GHz, the He-ECWC plasma was produced locally. For the He-ECWC with the X2-mode EC wave at $f_{\mathrm{EC}}=$ 110 GHz, the number of removed $H_2$ molecules did not change significantly between the different poloidal magnetic fields in the TPC at $B_T=$ 1.79 and 2.04 T. No He-ECWC plasma was observed with the poloidal magnetic field in the horizontal magnetic configuration at $B_T=$ 1.79 and 2.04 T.