High energy neutral particle analyzer

The paper describes a high energy neutral particle analyzer (HENPA) developed in the Ioffe Institute for the diagnostics of alpha particles in the megaelectronvolt energy range, as well as other charged fusion products and ion cyclotron resonance frequency-driven minority ions in a plasma. Megaelectronvolt ions can be neutralized in the plasma by charge exchange reactions with low energy atoms or impurity ions, and by recombination. The density of target particles for neutralization can be increased in the plasma by neutral beam or pellet injection. The operation of the HENPA is based on stripping megaelectronvolt atoms by means of a carbon foil, and subsequent E | B analysis of secondary ions. Eight (or 2 × 8, depending on the version) detectors that consist of (CsI + TI) scintillators 2–25 μm thick optically coupled to photomultiplier tubes are used to detect secondary ions. The detection efficiency of the detectors for megaelectronvolt ions is close to 100%; it drops to 10−4 − 10−8 for D-T neutrons, and to much lower values for D-D neutrons and gamma quanta in the energy range above 1 MeV. The HENPA is calibrated using megaelectronvolt H0-He0 beams from the cyclotron, starting from 0.4 MeV for He0 and 0.1 MeV for H. The energy ratio of simultaneously detected particles is EmaxEmin ≈ 4. The energy widths of the channels are 6%–15%. The HENPA can operate in a stray magnetic field up to 0.07 T. Some examples of results obtained by the HENPA are presented.