Numerical Tools for Monitoring the ITER-like Antenna at JET
A new Ion Cyclotron Resonance Frequency (ICRF) antenna referred to as the 'ITER-Like Antenna' (ILA) is currently being tested at JET. The ILA has been designed to achieve power densities similar to those required for ITER and to cope with the fast variations in coupling conditions due to ELMs, characteristic for the high confinement regime in which ITER will mainly be operated. The ILA consists of 8 short antenna straps, linked in a T-junction con- figuration to 4 (30W) coaxial transmission lines going to the generator. The plasma in front of the antenna acts as a varying load. In order to minimize the reflected power that comes back along the transmission lines, several elements at different locations on the lines can be adjusted, in particular the values of 8 capacitors situated just behind the straps and of 8 RF mechanical elements (1 stub and 1 phase shifter per resonant double loop or RDL). As the 4 RDLs are coupled, any change on one of the tuning elements affects the required settings of all the other elements. Some adjustments are made in real-time based on reflected and forward voltage measurements but in order to further optimize the different settings and understand the experimental results better, the ILA simulator - a modeling tool based on the theory of Radio-Frequency (RF) wave propagation in a transmission line and on the RF model of the ILA circuit - was developed in order to model the voltage and current at various places in the ILA circuit.