Background and radiation resistance tests of neutral particle analyzer detectors for ITER by using a fast neutron beam

A comparative analysis of the sensitivity of CsI (Tl), ZnO(Ga), and YAG(Ce) scintillators to the plasma background radiation under operating conditions of the ITER tokamak reactor

“…Figure 2 shows measurement results of the back ground sensitivity of the detector for crystals of three types. The formation mechanism for similar spectra is considered in [3]. Note that in the low energy region (of about several hundreds of kiloelectronvolts), the spectrum shape is determined by detecting electrons and γ quanta, while, when energy E α ≥ 1 MeV, the detection of protons and α particles resulting from nuclear reactions on fast neutrons gives the main con tribution.…”

“…To ensure the minimum sensitivity to the background radiation, the scintillation crystals should be of a small thickness, which does not exceed the projected range of detected ions (from unities to several tens of microns). In [3], we already presented the measured background characteristics of the scintillation detec tor based on a H8500D HAMAMATSU photomulti plier tube (PMT) and thin CsI(Tl) crystals. The pur pose of this work is to study scintillators of two new types and compare the obtained results and corre sponding data for the CsI(Tl) crystals.…”

“…Therefore, spectrometric scintillation detectors were selected as the NPA detectors. In addi tion, these detectors possess a high radiation resis tance, which is over two orders of magnitude higher than, e.g., that of semiconductors detectors [3]. To ensure the minimum sensitivity to the background radiation, the scintillation crystals should be of a small thickness, which does not exceed the projected range of detected ions (from unities to several tens of microns).…”

Development of the NPA based diagnostic complex in ITER

“…With the collimator and the neutron shield installed, the neutron flux at the location of the HENPA detector system during plasma discharges is estimated as ∼10 7 -10 8 cm −2 s −1 . Because of the above, the NPAs are equipped with a specially designed detector system that is radiation hard and has low sensitivity to the background (10 −6 -10 −7 pulse/neutron) [5,6]. To improve the signal-to-background ratio, the energy of secondary ions entering the LENPA analyzer is increased by 100 keV, which is achieved by installing an electrostatic accelerator in front of the analyzer (see figure 1).…”

“…According to the preliminary assessments, the peak/background ratio will be equal to 1.6 for LaBr 3 (Ce) and 1.1 for HPGe. In measurements of 17 MeV gammas produced in the T(d, γ) 5 He reaction, which is a weak branch of the DT reaction, the counting rate of the LaBr 3 (Ce) at E > 15 MeV, will be 3.8 × 10 5 s −1 . Thus, the system will provide the fusion-born and confined alpha particle diagnostics with temporal resolution of less than 100 ms and measurement accuracy of better than 20%.…”