MAST Upgrade centre column design and analysis

The MAST-U (Mega-Amp Spherical Tokamak Upgrade) experiment is now being designed and will involve significant advances over the existing MAST machine, including increasing the toroidal field from 0.52 to 0.78 Tesla, the solenoid flux swing from 0.9 to 1.7 volt-seconds and the pulse length from 0.5 to 5 seconds (at 0.54 Tesla toroidal field). To meet these and other enhancements, the existing MAST centre column sub-assembly will be completely replaced in MAST-U. This sub-assembly comprises (a) the centre rod which forms the inner legs of the TF circuit, (b) the solenoid which fits closely over the centre rod, (c) the “air side” coils which are for plasma shaping – one within the bore of the centre rod (Pc) and one outside the solenoid (Px), (d) the two stainless steel crowns which are keyed and bonded to the ends of the centre rod for torsional support and (e) axial supports for the solenoid and airside coils. This paper describes the detailed design of the centre rod and the solenoid magnets and the means to manage the increased twisting torque on the centre rod (138 kNm in MAST-U compared with 58 kNm on MAST) due to the interaction of these two magnets.