Overview of ITPA R&D Activities in Support of ITER Diagnostics

Full text: The International Tokamak Physics Activity (ITPA) Topical Group (TG) on Diagnostics has been conducting R&D activities to support improved ITER diagnostic performance. In this paper, highlights of the Topical Group activity are overviewed: mitigation of first mirror degradation in optical systems, mirror cleaning techniques have been progressed; in-vessel stray-light has been investigated to reduce its impact on diagnostics; diagnostics of escaping particles, feasibility test of the activation probe technique has progressed under a multimachine joint experiment. Diagnostic systems are essential for machine protection, reliable machine operation and comprehensive understanding of burning plasma behaviour in ITER. In order to achieve the above aims, more than fifty subsystems will be developed for measurement of plasma and plasma facing components in the harsh ITER environment, e.g., higher neutron/γ-ray irradiation and lower accessibility/maintainability compared to that of existing fusion devices. ITPA Diagnostics TG has addressed common physics issues in diagnostics development. The TG activity is mainly directed to high priority research areas (HP); HP-1: Optimization of the life-time of plasma facing mirrors used in optical systems, HP-2: Assessment of impact of in-vessel wall reflections on diagnostic systems, HP-3: Develop methods of measuring the energy and density distribution of escaping 's, HP-4: Plasma control system measurement requirements. HP-5: Develop diagnostic calibration techniques/strategies compatible with the burning plasma environment; and Joint Experiments for Diagnostics (JEX-DIAG) under a framework between ITPA and the Implementing Agreement on Cooperation of Tokamak Programmes of the International Energy Agency (IEA); JEX-DIAG-2: Environmental tests on first mirrors, JEX-DIAG-5: Field test of an activation probe, JEX-DIAG-6: Cross comparisons of charge exchange recombination spectroscopy and X-ray imaging crystal spectroscopy, JEX-DIAG-7: Distributed monitoring of microwave power density, JEX-DIAG-8: Benchmark of wall reflections, JEX-DIAG-9: Spectral MSE (MSE-LS) experiments as design driver for ITER, JEX-DIAG-10: Minimizing microwave absorption in vacuum windows, JEX-DIAG-11: Determination of the runaway electron distribution function by spectral Bremsstrahlung measurements in the -ray energy range. (author)