High-energy particle measurement using compact neutral using particle energy analyzer in Large Helical Device

In fusion plasma, alpha particle measurement is one of the important issues. Alpha particles emit by the double charge exchange from plasma. However the background neutral from the wall can not reach the plasma center because the plasma size is too large. The pellet charge exchange (PCX) technique which can enhance the charge exchange reaction in plasma center is utilized. Although there is no fusion reaction in the Large Helical Device (LHD), the simulation experiment can be expected by using the ion cyclotron resonance heated (ICH) plasma. The compact neutral- particle analyzer (CNPA) was used. In previous PCX experiment, we have used NDD instead of CNPA. The time resolution was poor when the conventional pulse height analysis (PHA) was used. We have newly installed CNPA (0.8-168 keV, 40 channels) to obtain the high-energy particle spectra in LHD. It has two main tasks: the first one is the passive neutral particle measurement for obtaining the low energy spectra including ion temperature, loss cone behavior and the high energy particle confinement, the second one is to obtain the central particle spectra especially in the ICH plasma combining the diagnostic pellet. In passive measurements (CNPA and TOF-NPA), the plasma parameter dependence of the resonant loss can be obtained. In pellet experiments, the time resolution of 0.1 ms is equal to 5 cm spatial resolution at the pellet speed of 500 m/s. There are two outputs (current/count modes) from preamplifier in order to measure in different modes (with/without pellet). NDD is also installed near the CNPA in order to measure the higher energy particle over 168 keV. Pellet penetration depth determines the possible observable area of the energy spectra. In our experiment, the penetration depth (up to ρ = 0.2) can be obtained at 1 mm diameter pellet. The ablation cloud behavior and the expected particle flux are calculated in typical ICH plasmas using the model. We are comparing the experimental data with the calculation result. (author)