Upgrade to the multichannel neutron collimator

Spatially resolved fluctuation measurements of the 14 MeV neutron emission due to MHD instabilities have recently been obtained during DT operation, using ZnS based NE451 scintillation detectors operated in the current mode on the TFTR multichannel neutron collimator. The observed fluctuations have a frequency range up to 10 kHz. In order to obtain better spatial resolution of the emission, two additional channels viewing the intermediate regions of the plasma core have been added to the collimator array. Initially, these new channels will serve as testing stations to evaluate several prototype scintillator concepts having improved detection efficiency. Both ZnS and plastic based scintillators are presently being studied. The plastic detectors have the advantage of being transparent to scintillation photons and allow an increase in the bulk scintillation material and hence an increase in the number of neutron interactions, while the ZnS based detectors have a greater immunity to gamma-rays. The increased detector efficiency has reduced neutron shot noise and extends the capability of the detector system to higher frequencies. Pulse height distributions and efficiency measurements obtained for each candidate detector using a 14-MeV generator as a neutron source will be presented. Absolute calibration of the new channels using a “jog shot” technique will be discussed