Visitors coming to the ITER site will from now on have one more attraction to discover: The mock-up of an ITER absolute valve seal and test rig, used to demonstrate the feasibility of the largest high pressure, all-metal valve, ever to be manufactured.
ITER will rely on two very powerful neutral beam injectors to heat the plasma to fusion temperatures. A third injector will also be installed – the diagnostic neutral beam injector – which is used as a diagnostic for the plasma.
Each injector contains a vacuum vessel which needs to be vented to atmospheric pressure independently from the torus vacuum vessel in case of an incident. An absolute valve has thus been developed by the Swiss company VAT to ‚absolutely’ isolate the vacuum in the torus from the neutral beam vacuum systems.
The valve uses seals made of stainless steel with silver coating to ensure high vacuum tightness up to a pressure differential of 0.1 MPa across the plate while maintaining a leak rate of less than 1·10-8 Pa·m3/s 1, but can withstand up to 0.2 MPa without incurring damage. With a nominal bore dimension of 1600 mm this absolute valve will be the largest ever manufactured, approximately five times bigger than existing products.