In this special issue, the present status and the prospects of the development of laser driven neutron sources are reviewed. Compact neutron sources have been widely interested, explored and developed for accelerator and laser systems. In this chapter, the uniqueness, the merits and the critical issues of laser driven neutron sources are described in comparison with accelerator driven neutron sources. The uniqueness is the small system size and the merits are “small size and short pulse of sources”, which are important for the higher spatial resolution of imaging and high energy resolution in spectroscopy. On the other hand, the critical issue of laser driven neutron sources is the low neutron flux in comparison with the accelerator driven neutron sources. In the following chapters, the above merits, critical issues, and the prospects are described in some details.

抄録全体を表示

An overview of the development of the compact neutron source is briefly described. Recent development of a neutron source as well as measurement technique is opening a new era for a small neutron source as a practical probe for materials science. In order to utilize neutron beam as a research probe, there are several ingredients such as handling technique of the neutron beam, the development of time-of-flight measurement technique, and the development of high efficiency neutron detectors, and none of them can lack for a practical instrument. It is also emphasized that the protection from radiation and costs for construction as well as daily operation are two more indispensable factors to be carefully considered.

抄録全体を表示

Laser-driven neutron sources offer a unique characteristic as a brightness neutron source because they provide a short pulse duration (less than ns) in time and a small spot size (a few mm2) in space at the source point. The peak flux per driver energy reaches 1017 n/cm2/s/J, which is 1,000 times higher than that achieved by an accelerator-driven source. We compared the characteristics of a laser-driven neutron source with those achieved by an accelerator-driven source by focusing on the amount of neutron production numbers on the source as a function of driver energy. We also present the technological status or perspective of laser-driven neutron sources in order to achieve an average production rate 1011 n/sr/sec that obtained by a compact accelerator-driven neutron source.

抄録全体を表示

High-average-power femtosecond lasers with terawatt and petawatt peak powers are essential for the practical achievement of such new technologies as laser-driven accelerators and laser-driven neutron sources. Although the average power of petawatt lasers is currently approaching 100 W, estimates suggest that an average power of the order of 10 kW is required for laser-driven neutron sources. To discuss the feasibility of a petawatt laser with an ultrahigh average power of 10 kW, we present two directions of disk and fiber lasers and propose a conceptual design of a Ti:sapphire chirped-pulseamplification system with an output pulse energy of 100 J and a repetition rate of 100 Hz.

抄録全体を表示

Repetition rate of a petawatt-class laser using Ti:Sapphire and optical parametric amplification is limited by a high energy pump source. Increasing the repetition rate (average power), in addition to efficient heat removal from the laser material of the pump source, thermal distribution is a significant problem, which results in wavefront distortion. Active-mirror is one of the promising amplifiers due to its high heat removal and insensitivity to thermal wavefront distortion. A 10 J, 100 Hz, 1 kW active-mirror laser will be demonstrated in 2018‒2019 as a feasibility study for 100 J.

抄録全体を表示

Recently, increasing interest has been focused on the neutron generation by high intensity laser. Especially in this review, we summarize experimental studies on the neutron generation based on “Pitcher-Cather” method, where ions are accelerated by the laser from a thin foil (Pitcher) up to MeVenergy and bombards some materials (Catcher) that generates neutrons via nuclear reactions. We demonstrate a semi-empirical scaling low found on the neutron generation efficiency as a function of the laser intensity, independently of the parameters of Pitcher and Catcher.

抄録全体を表示

Inertial Electrostatic Confinement (IEC) fusion devices have great advantages for their use as commercially available compact neutron sources. The principle, history, and recent research activities of the IEC fusion devices are briefly introduced. The prospect of the IEC neutron source is also discussed while comparing it with other small neutron sources.

抄録全体を表示

We numerically evaluated the pulse width of a laser-driven neutron source for electron- and protondriven pitcher-catcher schemes with a light water moderator. Particle-in-cell simulations were conducted to simulate laser irradiation on the pitchers that generate energetic charged particles. The simulated results of the charged particle fluxes were passed to Monte Carlo simulations, which calculated the nuclear reactions in the catchers to evaluate the neutron pulse width. The results of our simulations suggest that laser-driven neutron sources have better energy resolution than conventional acceleratordriven neutron sources.

抄録全体を表示

We present results from experimental investigations to generate a high flux source of energetic neutrons using a short pulse high rep rate laser system. Interactions of the laser pulse with a heavy water stream target allowed the generation of ~105 neutrons/second at an energy of ~2.45 MeV. We used liquid scintillators with pulse shape analysis along with bubble detectors to confirm neutron production. Further optimization of the target as well as an increase in the rep rate of such laser systems has the potential to enable the development of a high flux laser driven portable neutron source.

抄録全体を表示

We developed a new laser metal deposition method for cladding functional metals with multiple laser beams and a powder flow. In this method, the temperature of the flying powders in a powder flow was spatially homogeneous at a substrate surface since they were heated with laser beams while flying. When all the powders and the substrate surface were increased to their melting temperatures, a deposition layer was formed on the substrate since a condition of the powders’ welding with the substrate surface was satisfied in the boundary between the powders and the substrate surface. We achieved precise cladding since the size of the dilution layer was minimized in this method. A cobalt base alloy (Stellite 6) film, which was 400 μm thick with a 5 μm dilution zone, was formed on the SUS 304 base plate.

抄録全体を表示