“…Therefore, advances in energetic particle confinement were expected [38][39][40] through the neutron diagnostics [41][42][43][44][45][46][47][48][49] because neutrons are mainly created by so-called beam-thermal reactions [50]. Energetic particle confinement research, e.g., energetic particle confinement in magnetohydrodynamic quiescent plasmas [51][52][53], visualization of energetic particle transport [54][55][56][57][58][59], and demonstration of MeV ion confinement [60,61], has progressed [62,63]. Recently the beam ion energy spectrum has been studied using D-D neutron energy spectrometers [64][65][66][67][68].…”