Laser-Cluster Fusion and Electron-Positron Pair Production Experiments Using High-Power Lasers

Abstract

In this dissertation, two distinct research topics using high-power lasers at Center for Relativistic Laser Science (CoReLS) are presented: laser-cluster fusion and electron-positron pair production. First, we present a time-resolved analysis of Rayleigh scattering measurements to determine the average size of methane clusters. We measure Rayleigh scattering and obtain the average size of methane clusters with various backing pressure. Our ion time-of-flight measurements indicate that we have produced energetic deuterium ions with kT=52±2 keV from the Coulomb explosion of CD4 clusters. We find that this ion temperature agrees with the predicted temperature from our pre-measured cluster jet. Then, we investigate fusion plasmas from the experiments using deuterium clusters and high-power lasers. We vary the laser spot size, pulse duration, and energy to control the ion temperature from 1 keV to 24 keV. The ion temperature and neutron yield are measured using time-of-flight measurements of microchannel plates and self-made neutron detectors, respectively. In addition, the size and density of deuterium clusters are obtained from Mach-Zehnder interferometry and Rayleigh scattering measurements. Finally, we present a novel approach for generating charge-neutral electron-positron beams with energies in the GeV range, utilizing bremsstrahlung gamma rays. The produced pair beams exhibit neutrality across all converter thicknesses throughout the energy spectrum ranging from 10 MeV to 1.8 GeV. The experimental results are in excellent agreement with our Geant4 Monte Carlo simulations. In conclusion, this dissertation provides valuable insights into laser-cluster fusion and electron-positron pair production, thereby making a meaningful contribution to the field of laser plasma physics.