Abstract
The scienti c parameters and the technology issues for a modest size spherical torus (ST)
at 10 MA plasma current are discussed. This class of devices includes a DT-capable ST experiment
(DTST, R0 = 1:2 m) for extended plasma performance tests for limited pulse lengths and neutron
uences, and a volume neutron source (VNS, R0 = 1:1 m) for steady state energy technology testing
to high neutron
uences. The scienti c issues of interest for DTST include non-inductive ramp-up of
plasma current on a limited timescale (30 s), the con nement needed for high Q burn, the behaviour
of energetic particles, the physics and techniques to handle intense plasma exhaust, and the possibility
of high performance plasma regimes free of disruptions or large disruption impact. Of further interest
for the VNS would be steady state operation using large external current drive, possibly at a modest
Q (1{2), achieving signi cant neutron wall loading (1 MW/m2 ) and a con guration relatively
amenable to remote maintenance. A much longer timescale would be permitted in a VNS for noninductive
current ramp-up. The centre leg of the toroidal eld coils, possibly multiturn for DTST and
necessarily single turn for a VNS without signi cant nuclear shielding, presents technical and material
issues of unique importance to the ST. Positive ion neutral beam injection and high harmonic fast
wave (80 MHz) heating and current drive systems already available are likely to be adequate for
DTST following pulse length extension to 50 s. Given an adequate physics database, the remaining
enabling technologies needed for the VNS appear largely similar in nature to those of the ITER EDA
