Review of the JET ILA scattering-matrix arc detection system

Arc detection is an essential protection system for high power RF systems. It is commonly realised by monitoring the Voltage Standing Wave Ratio (VSWR) in the transmission lines. The JET ILA is a load-tolerant ICRF antenna with a low impedance section, for which the standard VSWR protection is ineffective. The Scattering-Matrix Arc Detection (SMAD) was proposed and implemented on JET to protect the low-impedance section around the T-junction against arcing. It is based on a consistency check of the RF signals around this section using a table of coefficients obtained from RF modelling. The paper reviews the SMAD principle, its commissioning on JET and the latest improvements to the system. It shows an example of operation and the time response of the system is analysed. The latest improvements have increased the robustness and reliability of SMAD, making it a choice of arc detection system for critical sections on existing and future RF systems.