Neutral particle analyzer diagnostics on the TCV tokamak

Experimental apparatus and data analysis techniques used in neutral particle analyzer (NPA) diagnostics on the Tokamak à Configuration Variable (TCV) are described. Two NPAs are used on TCV to measure the energy spectrum of neutral particle fluxes from the plasma. The “five-channel energy analyzer of atomic particles” used in double electrical analysis mode with fast voltage sweeping detect particles without atomic mass discrimination in the energy range of 0.6–8.0keV with a time resolution of 0.5–2.0ms and an energy resolution of 7%–20%. The 28-channel “compact neutral particle analyzer” (CNPA) is an EIIB spectrometer with mass and energy separations designed for medium sized fusion machines featuring a carbon neutral stripping foil, a permanent magnet for dispersion, and channel-electron multiplier detectors. The CNPA simultaneously detects two mass species [hydrogen (H) and deuterium (D) or D and helium (He)] in the 0.5–50keV energy range with a resolution of 60%–10% and a time resolution of 0.5–4.0ms. The CNPA views the plasma across the path of the diagnostic neutral beam and can perform active charge-exchange NPA measurement. Data analysis procedures and numerical algorithms developed for NPA measurement are routinely used on TCV to obtain information on the plasma ion temperature, ion energy distribution function, plasma isotope ratios, and other plasma characteristics.