The neutral beam(NB) heating experiments has been studied since 1998 on the Large Helical Device(LHD). The hydrogen neutral beam is tangentially injected at high energy, typically 150-180keV, and the system is based on negative-ion sources[1]. On LHD, the NB port-through power and the shine-though power are directly measured and routinely monitored by using caloriemeter arrays (CMA), which are installed on the counter wall of NB-injector(NBI) ports in the LHD vacuum vessel[2].
In the injection energy range of LHD-NBI, the enhancement of beam stopping cross section was theoretically pointed out by Janev[3] and Boley[4] due to the impact ionization process with impurity ions and the multi-step ionization process. On LHD, discharges with Hydrogen, Helium, Neon or Argon gas-puff are often performed. The experimental evaluation of neutral beam stopping rate due to these ion species will be shown and discussed in the presentation.

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