Measurement of radiation asymmetries in MAST Upgrade double null divertor plasmas
A new bolometer camera was installed in the upper divertor chamber of MAST Upgrade between the MU01 and MU02 physics campaigns. Sharing viewing geometry with the existing lower divertor horizontal bolometer camera, this enables direct comparison of the radiated power in the two divertor chambers. We compare the up/down radiation asymmetry in a range of plasmas from the MU02 physics campaign. L mode and H mode plasmas are studied, and the variation in divertor radiation asymmetry with the power crossing the separatrix (Psol) and the vertical position of the magnetic axis (Zref) are shown. The dependence of divertor configuration, comparing conventional and Super-X plasmas, is also presented. Preliminary analysis indicates higher radiation levels in the lower divertor than the upper divertor for nominally connected double null plasmas where the magnetic axis is within a few mm of the midplane. However, this is accompanied by higher core radiation at the top of the confined plasma than at the bottom. This observation is consistent across the different divertor configurations and confinement modes and does not appear to depend strongly on Psol. Where divertor radiation asymmetries are observed, we evaluate the extent to which the radiation is redistributed between the upper outer divertor leg and the inner lower divertor leg. We use the infra-red video bolometer (IRVB) to obtain spatially-resolved radiation profiles at the lower X point and evaluate changes in the radiation levels at the inner divertor.