Laser Neutron Source Simulation Based On Photonuclear Reaction And Convergent Plasma Collision

Neutron has been widely studied in non-destructive testing, activation analysis and other material defects because of its strong penetrating characteristics and electrically neutral, since Chadwich has found it in 1930s. The neutron source has been widely concerned in both basic neutron research and applied neutron research. At present, neutron usually produced by accelerators and nuclear reactors, etc. But those devices are too huge, the pulse width of neutron source is too long and the neutron fluence is not high, they could not meet the FNRR technology needs. In recent years, with the development of laser technology, the use of ultrashort laser-produced high-yield, high-fluence neutron beam research has become widespread concern.Currently, the main method of ultrashort laser producing neutron are nuclear fusion reactions and photonuclear reaction. Generally, the nuclear fusion reaction method is using thin target irradiated with the ultra-intense laser to produce energetic ions, and then bombard these ions into the convert target, after that the "beam-target" approach occurs neutron beam. This method has a high-contrast laser requirements. Spherical target approach is proposed in order to generate the laser neutron source in low-contrast conditions. Simulation study found that the ultrashort intense laser incident into a spherical hohlraum-like deuterium target, the majority energy of the laser is deposited inside the cavity, the deuterium ions forming the spherical shell was accelerated inward the center of cavity under the influence of the sheath field, forming the high temperature and high density regions. For nuclear fusion reactions, enhancing ion density and increase the duration of nuclear reactions would significantly improve the neutron yield, while the cross section of nuclear fusion reactions closely related to the particle temperature. Therefore, the temperature, density and duration of the region are the focus of our attention.In this paper, particle dynamics program is used to simulate the process of laser incident spherical shell targets, and obtain particle density, particle temperature, sheath field distribution, energy conversion efficiency information. The duration of the implosion region and ion density information are analyzed by changing the target density of spherical shell and laser intensity and it is found that at a low laser power density and high-density spherical shell target conditions implosion region can achieve higher density and maintain a longer time for the occurrence of nuclear fusion reactions. Meanwhile, the paper also describes the structure of the electromagnetic field generated in the column cavity targets experiment, femtosecond laser incident in opening column cavity targets. The ions are inwardly accelerated into the shell center and focused at the center of the spherical target, generating an electromagnetic field structure, while using picosecond laser bombardment a copper target to generate proton beam, the protons photograph the structure of electromagnetic fields after traverse a uniform grid, and collected the information by radiochromic film, confirming the central of column cavity forming a strong electromagnetic field structure.On the other hand, for the method of using photonuclear reactions to produce neutron, the paper simulates the generation of photonuclear neutrons in the full-physical process by use of several numerical simulation codes. At first, use ID radiation hydrodynamics code to simulate the process of ultraintense laser prepulse interacting with Cu target, acquiring the preplasma electrons density profile. Then got hot electrons information by 3D PIC code to simulate ultraintense laser main pulse interacting with the preplasma. The last paper acquire the yield, spectrum and angular spectrum of photonuclear neutrons when the hot electrons impinging with Cu target simulated by Monte Carlo code. The simulation results show that the photonuclear neutrons yield up to 1.2×108/J can be obtained when using ultraintense laser with intensity 1022W/cm2 interactions with Cu cylinder target which the thickness and diameter are 4cm. The energy of neutrons up to tens of MeV, but accounted for more than 98%of the number of neutron energy is concentrated below 5MeV. The short pulse feature of neutron beam from photonuclear reaction can effectively enhance the resolution of fast neutron resonance radiography and improve detection accuracy.