29th Symposium on Fusion Technology (SOFT 2016)

P2.047 Conceptual study of fast-swept divertor strike points suppressing ELM heat flux

6 Sep 2016, 14:20

1h 40m

Foyer 2A (2nd floor), 3A (3rd floor) (Prague Congress Centre)

Board: 47

Poster C. Plasma Engineering and Control P2 Poster session

Speaker

Jan Horacek (Tokamak)

Description

In order to avoid surface melting of divertor targets of big tokamak fusion reactors by localized ELM heat loads, we study a technique of spreading the flux by harmonic divertor strike point sweeping with a dedicated in-vessel twin-coil. If the sweep frequency gets above 1/t_ELM^decaydecay~300 Hz, local ELM plasma heat flux suppresses significantly (by factor=1+2λsweep/λdivetor) where prediction for λ_divetor^ITERITER=1-2 cm [1] is very thin (assuming midplane/divertor flux expansion of 10). Such a high frequency is the principal difference from the similar concept [2]. We ran dedicated Fiesta simulations for strike point harmonic sweep amplitude λsweep=7 cm, which requires coil current Isweep=55 kA for a device of the size and geometry of DEMO tokamak (Ip=21 MA, B0=6 T, R0=9 m). This could be achieved with 5 cm thick Aluminum coil twin (requiring water cooling of 2 MW ohmic losses), driven by a power source (14 kV, 1 kA) in a resonant circuit of the coil with 2.3 mF capacitor banks. The technique seems orders of magnitude less demanding on the coil current supply than alternative divertor concepts like the Snowflake, or Super-X divertor [3]. This 55 kA sweep coil would yield ELM heat flux suppression by factor~10, which can be further enhanced by additional techniques (e.g. pellet injection, RMP ...). We discuss plans for experimental test on tokamak COMPASS (6 kAturns in 2 mm thick coil, driven by existing 1 kV, 1 kHz switching power supply), should yield factor~4.   [1] T. Eich et al. Phys. Rev. Letters 107, 215001 (2011)   [2] M. Li et al. Fusion Engineering and Design 102 (2016) 50–58   [3] H. Reimerdes et al. 2015 EPS Conference on Plasma Physics, P4.117