Ion cyclotron heating and current drive system in ITER

A minimum auxiliary power of 50 MW is required to ignite the ITER plasma under the current global transport scaling laws, impurity scenarios and operating conditions. The ITER auxiliary heating system should also be designed with current drive capabilities, for plasma current profile control, extension of the pulse length and possibly stead state operation. Ion cyclotron radiofrequency (ICRF) heating is at this time regarded as the prime auxiliary heating candidate because it can fulfill ITER requirements with a minimum of technological development. ICRF has in fact a record of well demonstrated capabilities in heating high performance plasmas. Moreover, well developed, efficient and cost effective power sources and transmission equipment are commercially available. The principal approaches to fast wave current drive (FWCD) scenarios are either at a frequency just below ion resonances (∼ 20 MHz), so as to avoid competitive ion damping, or at 6 T/65-70 MHz, where electron damping is also dominant. Although the physics of FWCD is well understood, the experimental database is still sparse. However, despite the low damping per pass prevailing in present day tokamaks, which causes degradation of the antenna directivity by multiple reflections, fast wave current drive has been observed to be consistent with modelling in both Tore Supra and DIII-D. The main challenge for ICRF and ITER is the design of a launching array capable of reliably coupling the RF power in the ITER environment that can withstand the severe thermal and electrodynamic loads arising from the reactor operation and plasma disruptions. In the paper, the features of the ITER ICRF system are outlined and some of the key features of the design are discussed. (author). 6 refs, 3 figs, 1 tab