First snowflake divertor experiments in MAST-U.

First snowflake (SF) divertor experiments demonstrated steady-state snowflake-plus divertor configurations in 400 kA ohmic L-mode plasmas. The experimental equilibria confirmed the expected SF magnetic geometry properties, namely the increased connection lengths and strike point flux expansion due to the second poloidal field (PF) null (cf. the standard divertor with one null). The infra-red video bolometer diagnostic showed the radiated power peaking around the PF nulls. The divertor ion fluxes measured by the target Langmuir probes showed increased ion flux in the secondary SF strike point region, suggesting that some particle and heat redistribution might have taken place in the convective SF zone. Comparisons with previously reported simulation results obtained with the UEDGE multi-fluid transport code will be discussed. A unique aspect of the SF implementation in MAST-U is the up-down divertor symmetry that could potentially lead to sharing heat and particle exhaust among eight divertor strike points.