Modification of alpha-particle emission spectrum in beam-injected deuterium-tritium plasmas

The alpha (α)-particle and neutron emission spectra in a deuterium-tritium plasma accompanied with neutral-beam-injection (NBI) heating are evaluated in a consistent way by solving the Boltzmann–Fokker–Planck equations for deuteron, triton, and α-particle simultaneously. It is shown that owing to the existence of non-Maxwellian tail component in fuel-ion distribution function due to NBI and/or nuclear elastic scattering, the generation rate of the energetic (≥4 MeV) α-particle increases significantly. When 20 MW intense deuterium beam with 1 MeV beam-injection energy is injected into an 800 m3 plasma (Te=10 keV, ne=6.2×1019 m−3), the enhancement of the fraction of the power carried by α-particles with energy above 4 (3.9) MeV to total α-particle power is almost twice (1.5 times) as much from the value for Gaussian distribution. A verification scenario for the modification of the emission spectrum by using the gamma (γ)-ray-generating B9e(α,nγ)C12 reaction is also presented.