Mechanical, thermal and neutronics design aspects of the toroidal field coil centerpost (CP) for a spherical torus based volumetric neutron source (ST-VNS) are presented. It is being investigated with support of a DOE-SBIR under the direction of TSI Research Inc. of Solana Beach, CA. The ST-VNS is to provide a test bed for developing nuclear technologies, as well as qualifying blanket designs for future fusion reactors. The device is scoped to be capable of staged operation with a neutron wall loading range of 0.5–4.0 MW/m2 as the physics and engineering design assumptions are raised from modest to aggressive levels. Margins in the design are ensured, since operation at 2 MW/m2 neutron wall loading will satisfy the mission of the VNS. The device has a naturally diverted plasma with a major radius of 1.1m, a minor radius of 0.78 m for an aspect ratio of 1.4, an elongation of 3, a triangularity of 0.6 and can be driven with neutral beams (NB) or radio frequency (RF). It utilizes a single turn; unshielded normal conducting CP made of dispersion strengthened (DS) Cu that is 15.5 m long and has a diameter of 0.55 m at the midplane. Resistive heating at the start of operation is 153 MW and increases to 178 MW after three full power years. The effect of transmutation in the Cu causes an increase in the resistivity, producing a shift in the CP current towards the center. The results of this shift on power distribution are reported.