An automatic matching system for the ICRF antenna at TOMAS: Development and experimental proof

The TOMAS device is equipped with an Ion Cyclotron Range-of-Frequency (ICRF) system enabling systematic investigations of Ion Cyclotron Wall Conditioning (ICWC) in a toroidal geometry complementing plasma-wall interaction and plasma production research in larger devices.

The ICRF system on the TOMAS device has a varying load as the plasma may change in density, pressure, magnetic field and species (H/D/He/Ar) depending on the required experimental conditions. Therefore, a T-matching capacitor network is installed. To correctly control these variable capacitors in order to achieve efficient power transmission to the plasma, in this paper, multiple algorithms were developed. The first kind of algorithm requires voltage probes along a coaxial line connecting the power source to the antenna, for these kinds algorithms at least 4 inputs are necessary: at least 3 voltage probe measurements along the line and the amplitude of the forward voltage, either measured directly or inferred using the requested power gain. For the second form of algorithm the amplitude of both the forward and reflected wave need to be measured as well as their phase difference. System parameters were investigated over the course of simulations and afterwards tests of one of the algorithms were carried out on the TOMAS machine, confirming its effectiveness.