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We present the construction and the test of a generic neutrons detector for fusion experiment : OMEGA and NIF(USA) LMJ and APPOLON (France), usable also on particle physics accelerators such as ESS(Sweden), SPIRAL2(France), Berkley (USA) and for magnetic fusion facilities WEST, ITER (France), DIIID(USA).
This detector is based on the MICROMEGAS technology detector. This diagnostic has been designed to achieve neutron spectroscopy in large γ background. Tests have been performed on the 60 beams, 30 kJ OMEGA laser system at the University of Rochester(LLE), and on LINAC4 accelerator at CERN (Switzerland), and AMANDE(CEA).
In Inertial Confinement Fusion experiment on facilities such as Laser MegaJoule (LMJ) in France and the National Ignition Facility (NIF) in the U.S.we plan to achieve the ignition of capsules by compression deuterium-tritium (DT) or a deuteriumdeuterium (DD) filled target, and thus initiate a thermonuclear burn wave. In these experiments <ρ.R> may be measured using neutrons output from the imploded capsule, like secondary and tertiary neutrons produced respectively in DD and DT targets. Measurement of these neutrons remains a challenge as the γ-rays and scattered neutrons induced by primary neutronsinteractions on the experimental hardware can blind detectors.
The concept is based on the association of a Micromegas detector with a neutron-to-charged particle converter associated to a fast low noise electronics (<800ps).
A dedicated study has been performed for the neutron to converter particle (ncp) in order to be efficient of few hundred KeV energy neutrons to 14 MeV neutrons.
Electrons produced by γ-rays go through the Micromegas with a low ionization probability, making the detector γ-rays insensitive. This low γ sensitivity makes this concept appealing for inertial confinement fusion experiments. The good time resolution of the apparatus allows the reconstruction of neutron energy spectra with the time-of-flight
technique.
A time-of-flight spectrometer must satisfy a numberof requirements to perform hr:Ri measurement. Main
characteristics are the time resolution, the detection efficiency, the dynamic range (The dynamic range is an important characteristic sincethe primary neutron yield can vary from several decades (nowadays on OMEGA Facility to future experiments on LMJ andNIF), but also transparency to different types of background.
We present the main characteristics of the detector and the Front-end and Digitizer boards. The data acquisition system is a digitization system. It allows more flexibility foronline or offline treatments and is particularly useful in the
prototyping or early phases of the experiments.
A special attention has been given to electromagnetic compatibility(EMC) during the design to sustend the huge electromagnetic pulse caused by the shot, shieldings and connectors are described.
This diagnostic can also be usefull for particle physics accelerator as safety diagnostic.
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