Requirements for fast particle measurements on ITER and candidate measurement techniques

Abstract.Recent JET and JT-60U results, have underlined the need to look into the measurement requirements of fast particles diagnostics in ITER. Not only alpha particles, but all fast ions (He4,p,D,T,He3) present in the plasma should be diagnosed. Furthermore, the electron diagnostics, monitoring the deviations from a Maxwellian distribution function, play a central role in the Electron Cyclotron Heating and Current Drive.In the present ITER measurement requirements only alpha particles and He ions are mentioned: space resolution is δr = a/10 (a is the minor radius), time resolution is δτ = 100 ms, accuracy 10-30%. The new proposed measurement requirements for fast particles are: spatial resolution ~ a/20 (10 cm on ITER); time resolution (minimum) ~ 100 τA ( ~ 100 µs for ITER); density of fast ions: the minority ions could be 4-10% of the plasma density. The candidate diagnostic techniques considered for ITER are amongst others: γ-ray spectroscopy; fast ion Collective Thomson Scattering (CTS); Charge Exchange Recombination Spectroscopy (CXRS). γ-ray spectroscopy detects ions in the energy range 1<E<5MeV, and R&D is needed to demonstrate the feasibility of these measurements in the presence of a neutron background. Techniques using ultraviolet spectroscopy of ions like Krypton are being tested, for the low energy part of spectrum of fast particles. A design study of CTS shows that the requirements are close to be met, the system includes a high power gyrotron operating in a region not yet tested in current applications (i.e. using a gyrotron at a