Introduction to the Special Issue on Recent Advances in RF Heating of Plasmas

The international experimental reactor ITER (Nuclear Facility INB-174) near Cadarache in France is currently under construction, a ground-breaking project that will bring the world to the verge of sustainable positive net energy gain from fusion. Such a massive undertaking, which includes contributions from Europe, China, India, Japan, Korea, Russia, and the USA, brings with it massive challenges. To create fusion conditions for its magnetically confined plasma, the ITER tokamak will require heating and current drive (H&CD) systems, a combination of neutral beams (NBs) and radio frequency (RF) H&CD systems operating at the electron cyclotron (EC) and ion cyclotron (IC) resonances. The EC system is designed to couple a sustained 20 MW to the plasma at a frequency of 170 GHz. To achieve this formidable goal, the EC system will have 24 gyrotron oscillators as its driving source, each one capable of generating 1 MW. A series of highly efficient low-loss transmission lines consisting of overmoded corrugated waveguide and steerable launcher reflectors will be used to deliver the gyrotrons’ power to the tokamak. The IC system will provide another 20 MWof power to the plasma at 50 MHz, using large pressurized coaxial lines, each capable of transmitting up to 6 MW. This system will have its own complex matching network to minimize power transfer losses. With such power levels, sustaining stable conditions for plasma heating becomes an interesting engineering endeavor. Heating of RF components leads to thermal expansion, mechanical stresses, and changing material properties, all of which must be mitigated while avoiding electrical breakdown caused by high fields. The annual Workshop on RF Heating Technology of Fusion Plasmas, a joint meeting between experts in the USA, Japan, and Europe, has proven to be an invaluable resource for the ITER tokamak’s designers, engineers, and scientists. The lessons learned from the various J Infrared Milli Terahz Waves (2016) 37:1–3 DOI 10.1007/s10762-015-0222-0