The development of a flexible large area neutron spectrometer for ultra-intense laser-plasma interaction experiments

A flexible multi-channel neutron spectrometer has been constructed to measure both the ion temperature and acceleration mechanisms in ultra-intense laser-plasma interactions. Angularly resolved neutron spectra are required to deduce the momentum distribution of ions accelerated by the intense electric field. The first neutron spectra have been obtained using this instrument in a 100-TW class laser interaction with deuterated plastic targets. These show a slight Doppler shift to lower energy side of the center of mass energy of d(d,n)3He reactions at 2.45 MeV. A three-dimensional Monte-Carlo calculation of the neutron generation confirms the fast ion acceleration from the rear side of a solid target which has a Maxwellian momentum distribution.