Neutron incident angle and energy distribution at vacuum vessel for beam-injected deuterium plasmas in the Large Helical Device

Assuming a deuterium-beam-injected deuterium plasma confined in the Large Helical Device (LHD), the incident angle distribution and energy spectra of neutrons at various wall positions are evaluated by considering the complex shape of the vacuum vessel and the deuteron velocity distribution function. The effect of anisotropy of this function on the incident flux, the energy spectra, and the incident angle distribution of the neutrons to the vacuum vessel, are examined. In this paper, the neutron spectra are shown to depend on the wall position and the incident direction because of the formation of anisotropic high-energy tail in the deuteron velocity distribution function and the characteristic shape of the vacuum vessel of the LHD.