Commissioning of the ITER-like ICRF antenna for JET

Abstract

The new JET ion cyclotron resonance frequency (ICRF) ITER-like antenna (ILA), which was assembled during 2006, was commissioned on the JET RF testbed prior to installation on the JET torus. The 4 resonant double loops (RDL) of the ILA were tested at high power at 42 MHz up to 42 kV for 5 s in 10 min intervals. Low power matching studies using a saltwater load placed in front of the ILA have allowed testing and optimizing proposed matching algorithms on single RDLs, paired RDLs and finally on the full array. The upper limit of the frequency range of the ILA appears to be limited to 47–49 MHz due to the effect on the electrical lengths of the connection between the capacitors and the conjugate T point. Capacitor position scans have allowed obtaining the necessary data to confirm the RF model of the RDL which is necessary for the scattering matrix arc detection. The latter is deemed necessary in order to detect arcs at the low impedance conjugate T of the circuit. The antenna was installed onto JET during August 2007 and commissioning on plasma started May 2008. At present the commissioning of the ILA on JET is ongoing in a series of dedicated experimental campaigns.