Neutron sources from laser plasma interactions

This dissertation presents three different approaches to generate neutron sources based on laser plasma interactions. In the first approach, relativistic electron beams driven by laser wakefield accelerations (LWFA) were utilized to produce ultrashort neutron sources. The experiment was carried out on a 10 TW Ti:Sapphire laser with an average peak intensity of ~1.5×10¹⁸W/cm², which interacted with a He-Nitrogen mixed gas target to create a cylindrical plasma channel. Electron beams of ~80 pC with Gaussian distribution centered on ~37 MeV were produced via laser wakefield acceleration (LWFA). Neutron sources with fluences of ~2.4×10⁶ per shot and ~300 ps temporal length were generated through bremsstrahlung and the subsequent photo-neutron reactions in a tungsten neutron converter. Neutron yield was significantly improved compared to the previous experiments (cite previous experiments) using the same strategy. Neutron measurements were verified with Monte-Carlo simulations in GEANT4, showing agreement in neutron fluence, neutron angular distribution and conversion ratio. The second approach involves laser-driven high temperature D-D nuclear fusion reactions in novel solid targets with an unprecedented high peak flux (>10²³ n/cm²/s) and high neutron yield (>10⁸ n/J). The fusion temperature (~200 keV) were found one order of magnitude higher than any previous laser induced D-D fusion neutron sources. The high-temperature plasma is generated from thin (~2 μm) deuterium ice targets, produced by a cryogenic jet, irradiated by a ~130 J petawatt laser with a plasma mirror installed to clean the pre-pulses in order to reach volumetric heating. The heating mechanism involved is distinct from the previously explored coulomb explosion on cluster targets, the shockwave heating in inertial confinement fusion (ICF) study and the conventional laser-plasma interaction. The third approach relies on the output from laser-ion acceleration. Neutrons were created by impinging the ions (protons and deuterons) on a beryllium or copper neutron converter via 9Be(d,n), 9Be(p,n) or deuteron breakup reactions. These experiments were carried out on the 1 PW, ~140 J, Texas Petawatt Laser (TPW) in the US and the medium repetition 4 PW, ~100 J, CoReLS Laser in South Korea, which is also the first neutron experiment performed on this type of laser system. Very thin films (30 nm~2μm) made from plastic (CH₂), deuterated plastic (CD₂), diamond like carbon (DLC) or gold were used as targets. Neutron yield of ~4×10⁸ n/J and ~2×10⁷ n/J were observed on the TPW and CoReLS, respectively. The neutron spectrum in both cases follow an exponential distribution with energy up to ~70 MeV and ~15 MeV, respectively. The neutron outputs in TPW are comparable to the highest yield observed in Trident laser in Los Alamos National Lab (LANL). In the experiment conducted on CoReLS laser, the ion sources were systematically studied in order to understand and control the neutron generation process. The maximum ion energies from both CH₂ and CD₂ targets were found to increase linearly with the laser intensity. The highest attainable energy for a certain ion species scales proportionally to its charge square over mass ratio. This scaling law share similarity with the laser ponderomotive force on ions. The scaling factor also have a positive correlation with the target. The ion results are in good agreement with the measured neutron source properties