We present the construction and the test of a generic neutrons detector for fusion experiments : OMEGA and NIF(USA), LMJ and APPOLON (FRANCE). The detector can be also used as a safety device on particle physics accelerator (ESS, Sweeden), Spiral2(France) etc.. .
This detector is based on the technology CEA / IRFU MICROMEGAS 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 during last november (Switzerland), and AMANDE(CEA).
In Inertial Confinement Fusion experiment on facilities such as Laser MegaJoule (LMJ) in France and the National Ignition Facility (NIF) and OMEGA, LLE Rochester, USA 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).
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 technics.
In this Inertial Confinement Fusion experiments, we have to deal with huge flux of neutrons. We present here the fast-front end electronics (rise time<800 ps, gain 40dB, noise<450µVrms) which is able to deals with high flux without saturates, with a good dynamic range (to see neutrons from hundred of KeV to14 MeV and above).
The data acquisition system is a digitization system.
A digitization system offers more flexibility for on-line or off-line treatments than a TOT device (Time Over Threshold) for example.
We present the whole electronic-chain (front-end and digitizers). Cable and connectors are described, as a matter of fact, a special care has been given for EMC effects during the study, in order to be able to deals with the huge electromagnetic pulses caused by the shot.
The design and the construction of the Micromegas detector are presented.