Design, tests and results of a second harmonic filter for the ICRH generator of JET

A resistive harmonic filter has been developed to damp the harmonic signals generated by the ICRH power amplifier for the JET ICRH system. This filter has to produce negligible reflection at the fundamental frequency (VSWR<1.1 on a matched load) and has to absorb more than 64% of the second harmonic signal with total reflection at any phase. The filter has been first tested at low power in the full operating frequency range (23–57 MHz) showing that its electrical characteristics correspond to the modelling and fulfil the requested specifications. Tests at high power have already been successfully done on TEXTOR at 2 MW level for pulses exceeding 10 s and will start on JET.