ICRF heating for Wendelstein 7-X

The stellarator Wendelstein 7-X is being built in Greifswald, Germany, by the Max-Planck-Institut für Plasmaphysik. Initially, the heating system will consist of 10 MW ECRH and 4 MW ICRF heating (both cw) and 5 MW NBI (for 15 s every 3 min). ECRH is the principal heating method at a magnetic field of B=2.5 T. At other magnetic fields or densities higher than the ECRH cutoff, ICRF heating will sustain the plasmas. The ICRF system is planned to consist of two radially movable antennas powered by two generators with an output power of 2 MW each. The antenna plasma load will be matched in real time to the generator impedance using ferrite loaded transmission line elements. In addition, 3 dB couplers will passively protect the generators from RF power reflections during rapid changes of the antenna plasma load that are too fast for the ferrite matching system.