Mechanical design considerations of the centerpost for a spherical torus volumetric neutron source

The mechanical and thermal design issues of the centerpost (CP) for a spherical torus based volumetric neutron source (ST-VNS) is described. It is intended to provide a test bed for developing nuclear technologies as well as for qualifying blanket designs for use in fusion devices. As scoped out, the VNS is capable of staged operation from a neutron wall loading of 0.5-5.0 MW/m² as the physics and engineering design assumptions are raised from modest to aggressive levels. Design margins are ensured since operation will be adequate at a wall loading of 2 MW/m². The device has a major radius of 1.07 m, a minor radius of 0.77 m for an aspect ratio of 1.4, an elongation of 3, triangularity of 0.6 and has a naturally diverted plasma. It can be driven with neutral beams (NB) or ICRF. In the NB driven case, the plasma current is 11.1 MA, and in the ICRF case it is 13.2 MA. The magnetic field at the plasma major radius is 2.13 T and 2.55 T for the NB and the ICRF cases, respectively. This ST-VNS utilizes a single turn unshielded normal conducting CP fabricated from dispersion strengthened Cu, is 15.5 m long, has a diameter of 0.55 m at the midplane, a diameter of 1.2 m at the extremities and, in the ICRF driven case, carries a current of 13.6 MA. For the same case, the ohmic heating at the start of operation is 153 MW, increasing to 178 MW after 3 full power years. Thermal hydraulics, stress analysis and effects of transmutation on the CP have been determined, and a procedure for replacing the CP with minimal down time is described.