Beam uniformity studies based on neutrons measured with a scintillator array at SPIDER with Cs injection

The full size ITER NBI ion source SPIDER has recently produced the first neutrons generated by Deuterium-Deuterium beam-target fusion reactions (2.45 MeV) with Caesium (Cs) seeding in the ion source. A principle aim of SPIDER regarding the negative ion beam is to achieve better than 90% uniformity at low beam divergence. In Deuterium operation, the neutron diagnostic can provide an additional measurement of the beam uniformity by comparing the neutron flux measured in a spatially resolved manner with a 2D matrix of scintillators. The diagnostic consists of an array of plastic, crystal, and liquid scintillators capable of neutrongamma discrimination and a single NaI crystal gamma-ray spectrometer. Since the previous SPIDER deuterium campaign, performed without Cs, the scintillator setup has been re-arranged and upgraded, with the addition of three more detectors and the installation of an LED control and monitoring system. In this work, the new experimental setup of the neutron diagnostic is presented and the results of the two campaigns (with and without Cs) are compared. Despite some technical limitations, the system has successfully measured the first Cs enhanced D-D neutrons and working challenges of the diagnostics have been identified and targeted for improvement.