In ITER, an ion cyclotron resonance frequency (ICRF) system, having a capability to couple 20 MW of radio frequency power into the plasma, is planned for the initial operating phase. One of the essential elements of such a system is the antenna which is rather like the resonant part in an RLC (Resistor, Inductor and Capacitor) electric circuit, connecting the power source and the plasma. The plasma density in front of the antenna is critical. If it is too low, the RF wave cannot pass. The power is then reflected towards the transmitter instead of being transmitted to the plasma, which could be harmful.

Power coupling in the H-mode scenario (considered as the baseline scenario in ITER) is a crucial issue. Indeed, the plasma environment is characterized by periodical fast pressure relaxations at the edge plasma, due to localized Magneto-hydro-dynamics instabilities (so-called Edge Localized Modes, ELM). Such phenomena generate sudden increases of antenna coupling which, if not compensated by the electrical circuit, creates a mismatch which results in repetitive tripping of the power source.

In the framework of the ICRF heating development at CEA Cadarache, an ITERlike prototype (ILP) antenna based on the load-resilient electrical layout foreseen for ITER has been built. This prototype has been recently validated in Tore Supra where plasma exhibiting fast perturbations forced at the edge plasma were used to mimic the sudden increases of the coupling provoked by ELMs. The antenna and its subsystems (phase/power control, arc detection) have behaved as expected and the robustness of an ITER-like array under degraded and perturbed plasma coupling conditions has been validated. The results obtained with the ILP represent a significant milestone on the way towards future integration of IC launchers on ITER and will continue with the commissioning and operation of the JET ITER-like antenna, now installed on the JET device (see related article).

Provided by K. Vulliez and Tuong Hoang on behalf of the Tore Supra Team, Association Euratom-CEA, CEA/DSM/IRFM CEA Cadarache.