The effect of poloidal fuelling location on the neutral density, ionisation source, and performance of MAST Upgrade H-mode plasmas

We observe that the poloidal location of gas fuelling in connected double-null (CDN) H-mode plasmas on MAST Upgrade has no influence on the neutral density [1] at the low-field side (LFS) separatrix, and the LFS electron density at the top of the pedestal. This holds for fuelling from the high-field side, LFS, and divertor regions. LFS fuelling, however, did increase the ionisation source rate [1] by at least a factor of 2 which caused a decrease in electron temperatures in the edge of Te ≈ 200→120eV and in the core of Te ≈ 1000→800eV. This work primarily focuses on neutral information inferred through analysis of the high-speed video diagnostic [2,3] – a high refresh rate (up to 30 kHz) wide-angle view camera with a D-alpha optical filter (wavelength λ = 656.1nm) with ≈ 5mm spatial resolution in the pedestal region. Separatrix neutral densities on the order of 10^15m^-3 were measured, which are compared with analysis from other D-alpha diagnostics (e.g., charge-exchange spectrometer, and linear D-alpha camera), and with neutral pressure estimates from fast ion gauges. These measurements will enable inference of edge radial particle transport, and a comparison of its response to the varied fuelling locations. Work is ongoing to compare our results with outputs from KN1D and edge turbulence diagnostics (e.g., BES and DBS).

[1] A. Rosenthal et al., Nucl. Fusion, 13, 056103 (2023)

[2] T. Farley et al., Rev. Sci. Instrum., 90, 093502 (2019)

[3] D. Odstrˇcil et al., Rev. Sci. Instrum., 87, 123505 (2016)