Impulse responses of visible phototubes used in National Ignition Facility neutron time of flight diagnostics

P S Datte; M Eckart; A S Moore; W Thompson; G Vergel de Dios

doi:10.1063/1.4962039

Impulse responses of visible phototubes used in National Ignition Facility neutron time of flight diagnostics

Rev Sci Instrum. 2016 Nov;87(11):11D837. doi: 10.1063/1.4962039.

Authors

P S Datte¹, M Eckart¹, A S Moore¹, W Thompson¹, G Vergel de Dios¹

Affiliation

¹ Lawrence Livermore National Laboratory, Livermore, California 94550, USA.

PMID: 27910365
DOI: 10.1063/1.4962039

Abstract

Neutron-induced visible scintillation in neutron time of flight (NToF) diagnostics at the National Ignition Facility (NIF) is measured with 40 mm single stage micro-channel plate photomultipliers and a 40 mm vacuum photodiode, outside the neutron line of sight. In NIF experiments with 14 MeV neutron yields above Y > 10 × 10¹⁵ these tubes are configured to deliver of order 1 nC of charge in the nominally 5 ns NToF into a 50 Ω load. We have examined a number of 40 mm tubes manufactured by Photek Ltd. of St. Leonards on Sea, UK, to determine possible changes in the instrument impulse response as a function of signal charge delivered in 1 ns. Precision NToF measurements at approximately 20 m require that we characterize changes in the impulse response moments to <40 ps for the first central moment and ∼2% rms for the square root of the second central moment with ∼500 ps value. Detailed results are presented for three different diode configurations.