The JET wideband matching system

The performance of ICRF systems are often degraded by ELMS. The transient increase in coupling increases VSWR at the generator, which may trip/crowbar the generator. JET plan to insert a tuned length of 105 ohm line into the 30 ohm line between the antenna and the existing stub. At four discrete frequencies, the change in antenna load can then be tracked by the frequency to maintain low VSWR at the generator. The JET system will accept a coupling in the range 2–10 ohms, requiring the electrical length between the antenna and 105 ohm line to be set within a few centimetres, and a frequency scan of 300 kHz with millisecond response time.