Long-term performance of neutron detectors during deuterium–tritium operation in the Tokamak Fusion Test Reactor

Abstract

During its tritium campaign the Tokamak Fusion Test Reactor produced more than 750 deuterium–tritium (D–T) shots involving at least one tritium neutral beam, and some 20 000 shots with D beams and no T beams. A calibrated system of four fission chambers and two Si surface barrier threshold detectors (SBDs) monitored the fusion neutron production rate in all these shots, while elemental activation foils measured total yields, Y, on more than 300 D–T shots. The baseline fission-detector current and log-Campbell modes had stable detection efficiencies throughout the D–T campaign, but there were several cross-calibration corrections as large as 10% to the efficiencies of the count-rate and log-Campbell modes of some backup fission chambers and of the collimated SBD detector. For Y>3×1016 neutrons per shot, the ratio of fission-chamber and SBD yields to activation yields varied between 0.88 and 1.1, with an average value of 0.96–0.99 that was fairly constant throughout the D–T period. All detectors and electronics performed reliably in the radiation field except for the uncollimated SBD detector, which had to be replaced periodically because of radiation damage.