Development of the large neutron imaging system for inertial confinement fusion experiments

Abstract

Inertial confinement fusion (ICF) requires a high resolution (~10 μm) neutron imaging system to observe deuterium and tritium (DT) core implosion asymmetries. A new large (150 mm entrance diameter: scaled for Laser MégaJoule [P. A. Holstein, F. Chaland, C. Charpin, J. M. Dufour, H. Dumont, J. Giorla, L. Hallo, S. Laffite, G. Malinie, Y. Saillard, G. Schurtz, M. Vandenboomgaerde, and F. Wagon, Laser and Particle Beams 17, 403 (1999)]) neutron imaging detector has been developed for such ICF experiments. The detector has been fully characterized using a linear accelerator and a (60)Co γ-ray source. A penumbral aperture was used to observe DT-gas-filled target implosions performed on the OMEGA laser facility. [T. R. Boehly, D. L. Brown, R. S. Craxton, R. L. Keck, J. P. Knauer, J. H. Kelly, T. J. Kessler, S. A. Kumpan, S. J. Loucks, S. A. Letzring, F. J. Marshall, R. L. McCrory, S. F. B. Morse, W. Seka, J. M. Soures, and C. P. Verdon, Opt. Commun. 133, 495 (1997)] Neutron core images of 14 MeV with a resolution of 15 μm were obtained and are compared to x-ray images of comparable resolution.

A new compact, high sensitivity neutron imaging system

“…Light is guided along the glass capillaries by the step index between the glass and scintillator. The sensitivity improvement relative to previous designs 5, 6 is due primarily to the elimination of a fiber optic taper reducer between capillaries and light amplifier that was used in the earlier arrays (see Figure 1). The diameter of the capillary array is thus limited to the 40 mm MCP amplifier diameter and coupled to a straight fiber plate that seals the other end of the scintillator vessel.…”

“…Several neutron imaging systems have been developed based on coded aperture imaging techniques, high-spatial resolution detector technology, and precision alignment techniques. [2][3][4][5][6][7] The OMEGA facility is a unique platform for studying ICF physics parameters such as fuel compression, hydrodynamic instabilities, and laser-plasma instabilities with direct-drive implosions. 8 For indirect drive ICF experiments, hohlraum energetic studies were keys to demonstrating multi-cone symmetry tuning.…”

Diagnostics of laser-produced plasmas

“…To complete the panorama, one should cite all diagnostics that are typical for laser-driven inertial fusion experiments: neutron measurements [22], neutron spectroscopy [23], and neutron imaging [24].…”

Using LiF crystals for high-performance neutron imaging with micron-scale resolution

“…Recently, dynamic neutron images have been recorded with a neutron color image intensifier, enabling real-time observation of dynamic phenomena with 30 frames/s video pictures, at a thermal neutron flux of 1.5 × 10 8 n/(cm 2 s) [14] . Recently, great progress in the development of large neutron imaging systems for ICF has allowed 15 µm spatial resolution to be reached in a wide field of view [8] . In such a case neutrons transmitted by the aperture are converted to visible light in a scintillator array that is subsequently recorded by a CCD camera.…”

“…Regardless of the scientific or industrial application, there is a requirement to develop neutron detectors with a spatial resolution improvement of up to 5-10 µm and with a high sensitivity (few percent) to variation in material thickness and structure. For example, in the development of new electrical devices [2][3][4][5] and for neutron source reconstruction from pinhole imaging developed for inertial confined fusion (ICF) experiments using laser irradiation [6][7][8][9] , a spatial resolution on the scale of a few microns is needed.…”