A neutron diagnostic has been designed to achieve high energy neutron spectroscopy in large γ background. The concept of this diagnostic is based on the association of a Micromegas detector with a neutron-to-charged particle converter. 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. We plan to use such spectrometer on future high power laser installation (Laser MegaJoule in France or National Ignition facility in USA).