  In the ITER equatorial ports containing ICRH antennas, parasitic electrical
resonances can be excited in the nominal 20 mm clearance gap between the port
walls and the plug contained within it. RF calculations have established that
these resonances can be effectively mitigated by a series of suitably located
electrically conducting contacts between the port and plug. These contacts must
allow installation and removal of the antenna but must also make reliable
electrical contact during antenna operation. In addition, the contacts must be
compliant enough to survive deflection of the port during seismic and
disruption events without transmitting large forces to the vacuum vessel. The
distance to be spanned is subject to significant uncertainty, due to the large
manufacturing tolerances of the surrounding components, and this also must be
considered during the design process. This paper outlines progress made in the
design of the grounding system, as well as detailing a number of concepts which
have been investigated and abandoned, leading up to the current reference
design. The current reference design is a simple and robust mechanical solution
consisting of sprung Copper-plated Inconel flaps which use part of the range of
the shimming system included in the antenna design as the actuation mechanism.
This paper also details practical testing of a number of aspects of the design,
including building and testing a prototype to validate mechanical and thermal
analyses.
