ITER diagnostic shutters

Numerous plasma-near mirrors of optical diagnostics in ITER require protection from erosion and deposition caused by impinging particles. This is achieved by 63 Diagnostic Shutters, which shall operate in vacuum under high thermal and neutron fluxes over 20 years without maintenance, ruling out standard engineering solutions. In fact, these conditions are unprecedented even on fusion devices. Hence, qualification R&D efforts are extensive, because if a shutter fails, so does the respective diagnostic. Shutter design tasks are widespread among Domestic Agencies and their suppliers, because every shutter is part of the diagnostic it shall protect when not in use. However, as these highly resembling systems have obvious synergy potential, a coordination strategy for all ITER shutters was implemented at IO. An extensive shutter experience collection including failure reports from 14 fusion devices was performed. These are summarized in the present work. For the first time, the state-of-the-art of shutters is thereby defined and assessed as to its applicability to ITER. Furthermore, design-driving environmental effects due to the specific operating conditions are recalled and evaluated. The findings of both assessments are put into context with the current designs of all ITER shutters. In a next step, these are reviewed with emphasis on synergies between different shutter systems. Finally, recommendations on necessary prototyping and generic components are given.