TFTR natural diamond detectors based D–T neutron spectrometry system

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Abstract
Three natural diamond detectors (NDD) based spectrometry systems have been developed and used on TFTR to perform D–T neutron spectrum and flux measurements. DT neutrons interact with the NDD through the 12C(n, alpha)9Be reaction to produce a narrow peak in the pulse height distribution which has 2%–3% energy resolution and is well isolated from other reactions by ∼2 MeV in energy. The NDD detector is also highly radiation resistant (5×1014 n/cm2) and compact in size (diameter ∼4 mm, thickness ∼0.2 mm). Three detectors have been installed near TFTR. One, installed in a central sight line of the neutron collimator views perpendicularly from below. Two other detectors placed inside radiation shields in the TFTR test cell have tangential and perpendicular cones of view. These three spectrometers provide spectrometry of D–T neutrons escaping the tokamak with angles with respect to plasma current in the ranges close to 90°, 110°–180°, and 60°–120° correspondingly. The fastest standard electronics have been used to reduce the influence of pulse pileup during spectrometry measurements at count rates up to 3×105 counts/s. Results of the first D–T neutron spectra and flux dynamics measurements made with the three NDD based spectrometers during TFTR high power neutral beam injection are presented.

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