Experimental investigation of beam-target neutron emission at the ELISE neutral beam test facility

A dedicated experiment on beam-target neutron emission has been performed at the ELISE neutral beam test facility to investigate the accuracy of Local Mixing Model based calculations of neutron emission of relevance for the design of neutron diagnostics at the SPIDER neutral beam prototype. Compared to a previous experiment, we make use of fully developed infra-red and calorimetry diagnostics to include accurate data on beam profile and current in the calculations. Results show that variations of the neutron emission can be predicted with an accuracy better than 10%, which compares to 30% in our previous investigation. At the same time, convincing evidence of diffusion effects beyond the Local Mixing Model is identified in the data. Implications of these findings for neutron emission at SPIDER are discussed.