Modification of the DD Neutron Emission Spectrum at the 2.4 - 2.5MeV Energy Range in Neutral-Beam-Injection-Heated Plasma and Its Application to Fuel Ion Ratio Diagnostics

In neutral-beam-injection (NBI)-heated plasma, the emission spectra of the neutrons produced by D(d,n)³He and T(d,n)α fusion reactions are known to be distorted from Gaussian distribution functions in both the high and low energy sides along the NBI direction. This study shows that the effect of NBI heating can be applied to the central energy region, i.e., the 2.4 - 2.5MeV range in the D(d,n)³He neutron emission spectrum. Conventionally, the intense spectrum anisotropy appears via the anisotropy in the double-differential D(d,n)³He cross-section. Herein, we have shown the anisotropy in the neutron emission spectrum of the central energy range (2.4 - 2.5 MeV) due to the alteration of the neutron emission spectrum (2.4 - 2.5 MeV). Caused by the modification of the deuteron velocity distribution function is large enough to negate the anisotropy caused by the double-differential D(d,n)³He cross-section. An application of the anisotropy effect to fuel-ion ratio diagnostics is discussed, and the attendant degree of improvement is evaluated.