29th Symposium on Fusion Technology (SOFT 2016)

P1.082 A DEMO relevant long leg divertor with external poloidal field coils

5 Sep 2016, 14:20

1h 40m

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

Board: 82

Poster E. Magnets and Power Supplies P1 Poster session

Speaker

Simon McIntosh (Culham Centre for Fusion Energy)

Description

It is accepted that plasma exhaust is a major challenge for DEMO and future power plants and the reference approach is to use a design similar to JET and ITER. There is not yet full confidence this will extrapolate successfully and be compatible with a maximum power flux of 5-10 MWm^-2-2 on the Plasma Facing Components. Detachment provides an attractive solution to the power exhaust problem, radiating power across a large area within the divertor and reducing ion energies below the sputtering threshold of the tungsten targets. Extension of the outer target to a large radius reduces power flux flowing along the divertor leg, diluting the detachment threshold to values compatible with the core. The reduction in power flux with increasing radius also provides a stabilising mechanism for the location of the detachment fount. Scaling the long leg concept up to DEMO relevant machines is often considered impractical due to either excessive loading on coil sets external to the TF or due to the requirement for in-vessel coils. Feasibility of a long leg divertor concept is demonstrated here for a 20.3MA DEMO relevant machine using a set of five PF coils placed external to the TF cage. The outer strike point is extended to 1.5 times the X-point radius without significant modification to the shape of the separatrix. Force, current density and placement constraints are respected across a flat top flux swing of 363Vs. The long leg concept requires a TF coil with a circumference 22% greater than the reference configuration. The gain in size of the coils and associated structures will undoubtedly increase their cost. However, foreseen ancillary benefits should likewise be considered. These include a reduction in ripple, perhaps enabling a 16 coil configuration, and a reduction in the complexity of remote maintenance schemes.