ICRF Heating: The JET Experience and Prospect for ITER

The ITER Ion Cyclotron Resonance Frequency (ICRF) system will comprise two antennas aiming to couple in the long term, 20MW each in ELMy H-mode plasmas with plasma separatrix - antenna distances around 17cm. On JET, the ability to couple ICRF power to H-modes was the main challenge of the past few years. Indeed, the system in place since 1994, could not couple during the fast edge modifications caused by ELMs. The impedance transformers made of mechanical elements and used to match the 30Ohm transmission line to the plasma acting as a load of typically 2-4Ohm, could not react quickly enough during the associated load changes (typically 400% change in 150ms), leading to excessive power reflection, trips of the generator protection and very low averaged coupled power. The system upgrade started by a modification of the transmission line layout of the A2s antenna between 2004 and 2008 that is described in section 2. Secondly, a new ICRF ITER-Like Antenna (ILA), with a closely packed array of short straps, similar to that foreseen for ITER, was installed in 2007. An outlook of the results obtained both L and H-mode is shown in section 3. In order to maximise the achievable ICRF power at large separatrix-antenna distance, the possibility to inject gas to increase the density in front of the ICRF antennas, was investigated and a brief overview of the results is presented in section 4. Finally, the extrapolation of these results for the ITER ICRF systems is reviewed in section 5.
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