Performance of a 14-MeV neutron generator as an in situ calibration source for TFTR

TFTR will soon enter its D-T phase with the introduction of tritium. This will result in the production of neutrons having 14 MeV energy which is significantly greater than the 2.5-MeV neutrons encountered during D-D operation. In preparation for the D-T phase, a calibration of the four neutron detection systems was performed using a 14-MeV neutron generator producing 10⁸ n/sec. To account for the spatial extent of the toroidally shaped plasma and for neutrons scattered from surrounding structures, detector responses were determined with the source positioned at many locations inside the vacuum vessel. Before the generator could be used as a calibration source, a characterization of its total yield and angular emission properties was obtained. The total yield was determined by aluminum activation methods to within ±6%, while the angular emission was found to be anisotropic in the forward and reverse cones along the generator axis. After the characterization was performed, the generator was mounted on a moveable track inside the vacuum vessel, where it could be remotely moved across the view of each detector. This paper presents details of the methods and results of the source characterization, together with initial results of the in-vessel D-T neutron calibration