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Requirements for fast particle measurements on ITER and candidate measurement techniques

Funded under: FP7-EURATOM


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 (He{4},p,D,T,He{3}) 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 delta r = a/10 (a is the minor radius), time resolution is delta tau = 100 ms and accuracy 10-30%. The new proposed measurement requirements for fast particles are spatial resolution ~a/20 (10 cm on ITER), time resolution (minimum) ~100 tau(A) (~100 mu s 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 gamma-ray spectroscopy, fast ion collective Thomson scattering (CTS) and charge exchange recombination spectroscopy (CXRS). gamma-ray spectroscopy detects ions in the energy range 1 < E < 5 MeV 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 such as Krypton are being tested, for the low energy part of spectrum of fast particles. A design study of CTS shows that the requirements are closely 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 frequency below the first ECE harmonic). For CXRS the spatial resolution and accuracy are not achievable for r/a < 0.3 and R&D is needed to assess the minimum figures in terms of accuracy possible for measurements close to the centre.

Additional information

Authors: ORSITTO F P, ENEA-EURATOM Association C R Frascati, Frascati (IT);NOTERDAEME J M, Max-Planck-Institut für Plasmaphysik, Garching (DE);COSTLEY A E, ITER Cadarache Joint Work Site, Cadarache Centre, St Paul-Les-Durance (FR);DONNÉ A J H, FOM-Rijnhuisen, Association EURATOM-FOM, Nieuwegein (NL)
Bibliographic Reference: An article published in: Nuclear Fusion 47 (2007), pp. 1311-1317
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