Collimated ZnS (Ag)-detector array for Tokamak Fusion Test Reactor neutron source strength radial profile measurements

Time-resolved radial profile measurements of neutron source strength and Ti are required to determine ion energy balance especially during sawtooth oscillations and adiabatic compression. We describe the Tokamak Fusion Test Reactor (TFTR) vertical multichannel (10) collimator, two channels of which are now being completed. ZnS detectors will be used (Bicron 720) to reject γ rays and scattered neutrons, and operated in both count rate and current modes. The frequency response is limited by counting statistics and sampling times, but resolves compression times ≂15–30 ms and Ti collapse times during sawtooth ≂2–3 ms. The collimator consists of the 6-ft test cell floor plus ∼2-ft detector shield. Detector cross talk is calculated to be negligible. The dynamic range of the detectors is ≳106, covering the range from ohmically heated deuterium (2.5 MeV neutron emissions of ≳1013 s−1) to deuterium-beam heated tritium plasmas (14 MeV, ≲1019 s−1).