Calibration issues of the Tokamak Fusion Test Reactor multichannel neutron collimator

The calibration procedures for the detectors in the neutron collimator are reviewed. The absolute calibration was performed for the NE451 detectors, in situ, by moving a DT neutron generator in the Tokamak Fusion Test Reactor (TFTR) vacuum vessel across each sight line. This calibration was transferred to other detectors in the same channel. Four new sight lines have been installed at a different toroidal location, which view the plasma through the vacuum vessel port cover rather than through thinned windows. The new detectors are cross calibrated to the NE451 detectors with a "jog shot" procedure, where the plasma is quickly shifted in major radius over a distance of 30 cm. The jog shot procedure shows that scattered neutrons account approximately for 30% of the signal of the new central channels. Corrections for detector nonlinearity are discussed. The neutron source strength from the collimator agrees within 10% with the source strength from global neutron monitors in the TFTR test cell.