Conceptual Design, Development and Preliminary Tests of a Compact Neutron Spectrometer for the JET Experiment

Abstract

A Compact Neutron Spectrometer (CNS) has been developed to measure the neutron emission spectra in Joint European Torus (JET) fusion plasma experiments. The spectrometer, based on a liquid scintillation detector (BC501A), is equipped with a Digital Pulse Shape Discrimination (DPSD) acquisition system for neutron (n) and gamma-ray separation. The CNS enables recording the n and pulse height spectra (PHS) up to total count rates of s . Energy resolution, after PHS unfolding, will be % for 14 MeV neutrons and % for 2.5 MeV neutrons. The work done by ENEA-Frascati and Physikalisch-Technische Bundesanstalt (PTB) respectively in the assembly and test of DPSD and scintillation detector, along with the first results obtained by the spectrometer in JET plasma experiments are presented. The experience obtained with CNS in JET will contribute to the development of neutron spectrometers suitable for applications in the International Thermonuclear Experimental Reactor (ITER).Index Terms-Compact neutron spectrometer, digital signal processing, liquid organic scintillator, tokamak diagnostics.

Response function of single crystal synthetic diamond detectors to 1-4 MeV neutrons for spectroscopy of D plasmas

“…The measurements showed a very reproducible narrow shoulder, related to the scattering recoil on 12 C, whose position depends on the neutron energy and does not suffer gain drift due fast count rate changes or temperatures, as it is often the case with liquid scintillators. [27][28][29] Although high resolution neutron spectroscopy at these energies is prevented by the absence of a well separated peak directly associated to the neutron interaction, as occurs in SDs measurement for 14 MeV neutrons in DT plasmas, 9 a moderate resolution spectroscopy can still be achieved. This is of interest, for example, in scenarios aimed at studying the physics of deuterons accelerated to the MeV range by radio frequency heating.…”

Tomographic analysis of neutron and gamma pulse shape distributions from liquid scintillation detectors at Joint European Torus

“…Since the installation of the new digitizers, 8,12 algorithms were developed to process KN3 and KM12 digital data either to remove offsets induced by the noisy measurement environment or to identify pile-ups in the recorded pulse shapes. In case of KM12, data are also corrected for PMT gain variations using LED pulse shapes as a reference.…”

“…7 A new compact spectrometer (KM12) based on BC501A liquid scintillation material was installed at JET in 2010. 3,8 The detector cell is a cylinder of 2.54 cm diameter and 2.54 cm thickness equipped with a LED control and monitoring system. With suitable high voltage settings of the PMT, KM12 allows for measurement of neutron energy in the range 1-20 MeV such that it can be used as a compact broadband neutron spectrometer to measure simultaneously the 2.45 MeV and 14 MeV neutrons from D and DT plasmas.…”

“…KM12 has already demonstrated such capability by measuring 14 MeV neutrons due to triton burn-up fusion reactions in D plasmas during high power shots of JET experimental campaign C27. [8][9][10] Measurements of instrument response function, detector setup, and calibration were performed at the Physikalisch-Technische Bundesanstalt (PTB, Braunschweig, Germany). 11 Both KN3 and KM12 instruments implement the same type of digital data acquisition system based on 200 MSample/s 14-bit digitizers capable of count rate up to 5 × 10 5 Cps designed by ENEA Frascati (Italy).…”

“…11 Both KN3 and KM12 instruments implement the same type of digital data acquisition system based on 200 MSample/s 14-bit digitizers capable of count rate up to 5 × 10 5 Cps designed by ENEA Frascati (Italy). 8,12 …”