First measurements of the high-density plasma on the high-field side of the divertor with Thomson scattering on ASDEX Upgrade

After first measurements with the new Thomson scattering diagnostics in the divertor (Divertor-TS), the spectral channels for the analysis of the photon spectra and the laser beam guidance in the vacuum vessel of ASDEX Upgrade were optimized.

The diagnostics went back into operation at the end of January 2021 and now provide reliable data for studying the dynamics of the divertor plasma.

The diagnostics provide density and temperature measurements simultaneously on the low and high field sides (LFS and HFS) and near the X-point (X). For example, in discharge #38585, plasma densities between 5 and 10×1020 m-3 and electron temperatures around 1 ­­­­­­­­– 2 eV were directly measured when varying the heating power.

This is the first time that direct measurements are available in the high density region of the scrape-off layer on the high field side. In contrast, the plasma in the outer divertor shows electron temperatures up to 100 eV.

This confirms the asymmetry between inner and outer divertor.

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