Science and technology of the 10 MA spherical tori

The scientific parameters and the technology issues for a modest size spher ical torus (ST) at 10 MA plasma current are discussed. This class of device s includes a DT-capable ST experiment (DTST, R-o = 1.2 m) for extended plas ma performance tests for limited pulse lengths and neutron fluences, and a volume neutron source (VNS, R-o = 1.1 m) for steady state energy technology testing to high neutron fluences. The scientific issues of interest for DT ST include non-inductive ramp-up of plasma current on a limited timescale ( similar to 30 s), the confinement needed for high Q burn, the behaviour of energetic particles, the physics and techniques to handle intense plasma ex haust, and the possibility of high performance plasma regimes free of disru ptions or large disruption impact. Of further interest for the VNS would be steady state operation using large external current drive, possibly at a m odest Q (similar to 1-2), achieving significant neutron wall loading (simil ar to 1 MW/m(2)) and a configuration relatively amenable to remote maintena nce. A much longer timescale would be permitted in a VNS for noninductive c urrent ramp-up. The centre leg of the toroidal field coils, possibly multit urn for DTST and necessarily single turn for a VNS without significant nucl ear shielding, presents technical and material issues of unique importance to the ST. Positive ion neutral beam injection and high harmonic fast wave (similar to 80 MHz) heating and current drive systems already available are likely to be adequate for DTST following pulse length extension to similar to 50 s. Given an adequate physics database, the remaining enabling techno logies needed for the VNS appear largely similar in nature to those of the ITER EDA design.