Further studies on the ITER ICRF antenna grounding

Abstract

The ITER ICRF antenna is a port-plug antenna. There is a clearance gap surrounding the antenna between the antenna plug walls and the vacuum vessel, creating a cavity in which resonant modes can be excited. The frequency response of the antenna array is perturbed by the excitation of a TE0,1 (p=1) mode in the ITER frequency band (around 45MHz) in the clearance gap in absence of any additional grounding. Different grounding options have been proposed and both numerically studied and tested on a scaled low-power mock-up of the ITER antenna. These studies however did not take the Faraday screen into account. In view of the technical difficulties to implement the proposed grounding options the present contribution revisits the need for grounding based on new gap voltage measurements on a reduced-scale mock-up of the ITER ICRH antenna and numerical modeling, including the presence of the Faraday screen.