Fast neutral particle measurements in LHD and CHS

Abstract

Summary form only. The development of high energy neutral particle measurement system for ion temperature measurements and high energy particle confinement analysis in Large Helical Device (LHD, major radius=3.9 m, average minor radius=0.6 m) is described here. For NBIs, 180 keV hydrogen beams will be used in Phase I of LHD experiment schedule and 360 keV deuterium beams will be used in Phase II. In ICRF heating experiment, the hydrogen and helium-3 will be used as minorities. It is important to observe the pitch angle distribution to investigate the confinement of high energy particles. For this purpose the neutral particle analyzer should have a wide observation energy range above the maximum energy of NBI (or accelerated particle by ICRF heating) and an ability to separate the particle species of hydrogen, deuterium and He-3. The high noise reduction ability for the radiation, especially neutron from DD reaction, is important. We have been improving the time-of-flight (TOF) neutral particle analyzer for LHD which had been developed in ENEA Frascati. The mass rejection factor was improved up to 1/1000 by using a biased diaphragm in front of the stop detector. The fast neutral particle measurement system is constructing now. In Compact Helical System (CHS), the electrostatic neutral particle analyzer (maximum detectable energy of 50 keV hydrogen) is used. We have compared the spectrum obtained from the measurement by a passive method in CHS with that from the calculation by PROCTR code. At the energy range below 1 keV, neutral contribution from the plasma boundary is too large due to the large background neutral density and large charge exchange cross section.