Experimental investigation of steady state power balance in double null and single null H mode plasmas in MAST Upgrade

Global power balance calculations in steady state H mode plasmas varying the distance between separatrices ($d{r}_{sep}$) and the divertor configuration have been performed in MAST Upgrade. As $d{r}_{sep}$ becomes more negative, more of the power crossing the separatrix goes to the lower divertor. The inner divertor receives a higher fraction of the power exhaust in a Super-X divertor plasma compared to a conventional divertor plasma at similar negative $d{r}_{sep}$, which is a concern for high power devices employing alternative divertor configurations for power exhaust handling. Global power accounting suggests $>\text{30}\text{\%}$ of the input power is unaccounted for with the power loss channels quantified in this work. Charge exchange and orbit losses from the NBI could account for a large fraction of unaccounted power but it is not possible to precisely determine this without further diagnostic calibration.