Method for determining the shape and size of a knock-on tail using the Doppler-broadened γ-ray emission spectrum

Analysis and experimental validation of energetic non-Maxwellian components formed in ion velocity distribution functions enhance our understanding of important physical phenomena in burning plasmas. As one such energetic component, knock-on tails appear due to nuclear elastic scattering (NES). It is important to experimentally validate the NES effects and analysis model of knock-on tails. For this purpose, we propose a method for determining the shape and size of a knock-on tail from the Doppler-broadened γ-ray emission spectrum in a proton-beam-injected deuterium plasma confined in an ITER-like experimental fusion device. In the proposed method, we adopt a two-temperature Maxwellian model and utilize the γ-ray-generating ⁶Li(d,nγ)⁷Be and ⁶Li(d,pγ)⁷Li nuclear reactions. We discuss both the validity of the proposed method and the expected accuracy of the shape and size of the measured knock-on tail.