FWCD technology issues for DEMO Available to Purchase

The technology implications of potential FWCD systems have been assessed at two frequencies of relevance to DEMO as part of a wider study of heating and current drive systems for the EFDA Power Plant Physics and Technology (PPP&T), based upon two reference DEMO designs. Using the results of Van Eester et al [1], systems studies carried out for a 62MHz mid-harmonic system mounted on a 23MA 5.74T 8.5m major radius DEMO suggested that antenna voltages close to 50kV, and the handling of the resultant sheath power loadings, are likely to be required if all of the 12.9MA non-bootstrap current drive is to be provided by FWCD. The "wall plug" electrical efficiency of the midharmonic option of 0.18A/W.m², potentially rising to 0.23A/W.m² with the future development of solid state generators, however, looks very attractive, and the coupling is less sensitive to plasma edge parameters than for existing antennas, due to the low k_// of 2.8m⁻¹. The design could be based upon that presently under consideration for ITER, except for the replacement of insulating vacuum windows located relatively close to the plasma with all-metal designs [2]. A 352MHz high-harmonic option also looks technologically feasible, using a waveguide-based design and a port plug layout has been provided. This option might bring sheath effect and voltage hold-off benefits, but this is far from proven. In this case, systems studies were not feasible due to a lack of firm results from the physics studies. For both options: (a) the RF generators, power supplies and transmission line components required are either already available, or are under development for ITER, and (b) mechanical and material issues associated with the proposed FWCD antenna structures appear challenging, but will need solving on a wider basis across DEMO.