Initial observations in X-point target divertor discharges on MAST-U
The first results of studies of high-power (≥ 3 MW) H-mode discharges in double-null X-point-target (XPT) divertor configuration on MAST-U are presented. By combining the large strike point radius of the Super- X divertor with an additional X-point in the baffled outer divertor chambers, further exhaust benefits in strongly detached conditions are observed over the Super-X configuration. The broader electron density profile near the secondary X-point leads to additional plasma-neutral interactions, evidenced by a broader hydrogenic emission profile, and resulting in larger power and ion sinks. The increase in plasma-neutral interactions also leads to lower target electron temperatures and heat fluxes. These benefits appear to extend to transients, and preliminary evidence of improved ELM buffering in the XPT is presented. These results showcase how multiple alternative divertor configuration strategies can be combined to obtain further exhaust benefits, which may be required for the challenging exhaust conditions of future reactors.