TFTR MULTICHANNEL NEUTRON COLLIMATOR

The TFTR multichannel neutron collimator provides time-resolved neutron emission profiles from ten vertical chords spaced in major radius across the vacuum vessel. An in situ calibration of the system has been made using a 120 mCi 252Cf source scanned inside the vacuum vessel. A mapping of the effective neutron acceptance aperture was performed and showed reasonable agreement with the optical predictions testifying to the effectiveness of the interstitial shielding material. Crosstalk between channels was evaluated and found to be negligible. Periodic renormalization of the system has shown a standard deviation among the sensitivities of only 2.0% over the first seven months of operation.