The poloidal fuelling location and its effect on the pedestal and H-mode plasma performance in MAST Upgrade

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Abstract
This paper presents the first results exploiting the high-speed video (HSV) diagnostic on MAST Upgrade to infer neutral deuterium quantities from D α emission. We detail the process for absolute calibration of HSV which now produces 2D line-of-sight-integrated brightness (ph sr − 1 m − 2 s − 1 ) of D α emission in the MAST-U main chamber, showing excellent quantitative agreement with other D α and neutral diagnostics. A typical workflow to combine HSV data with a collisional-radiative model, and electron density, n e , and temperature, T e , measurements to produce 1D radial profiles of neutral density, n 0 , and cold deuterium ionisation source rate, S 0 , is documented. The analysis is applied to a series of double null, neutral beam heated H-mode discharges in MAST-U changing the poloidal fuelling location. It is shown how the low-field side (LFS) pedestal electron density is resilient to, and remains largely unaffected by, the choice of poloidal fuelling location, as does n 0 , sep despite differences in neutral pressure measured at the wall. LFS fuelling is seen to increase S 0 , reducing the pedestal electron temperature which decreases edge collisionality, ν ∗ , and allows for core n e to be increased. S 0 is used to constrain inferences of deuterium ion flux, Γ , in a 1D radial transport model. When fuelling from the LFS, Γ becomes increasingly negative at the pedestal top, indicating an inward flux of particles, and is used with the diffusive-convective ansatz showing a negative convective transport coefficient, v , implying an inward particle pinch.
Funding Information
  • Engineering and Physical Sciences Research Council (EP/S022430/1)
  • US DOE (DE-AC05-00OR22725)

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