Implementation of load resilient ion cyclotron resonant frequency (ICRF) systems to couple high levels of ICRF power to ELMy H-mode plasmas in JET

The paper summarizes the continuous developments made to the ion cyclotron resonant frequency (ICRF) system at JET in order to improve the reliability of the power coupled to plasma. It details the changes and improvements made to the system so that more power is coupled during ELMy plasmas as well as increasing the power density to demonstrate reliable operation in the range of the requirements for ITER. Results obtained using the conventional matching (stubs and trombones) system, 3 dB couplers and the conjugate-T scheme with variable matching elements outside the wave launching structure (external conjugate-T) and inside the wave launching structure (ITER-like antenna) are described. The presence of the three different approaches to load resilient ICRF systems at JET creates a unique opportunity to compare these methods under very similar plasma conditions and to assess the results of ICRF power delivery to ELMy plasmas, an important issue for ITER. The impact of the availability of increased levels of reliable ICRF power on plasma physics studies in JET is illustrated.