The goal of this collaborative project is to demonstrate efficient generation of gamma-ray beams and characterize their energy spectra. The emission of MeV photons will be achieved by driving a multi-GigaGauss quasi-static azimuthal magnetic field inside a dense plasma that is rendered transparent by an ultra-high-intensity laser pulse. Plasma electrons serve as a mediator in the conversion of the laser energy into a dense beam of energetic gamma-rays. The confining azimuthal magnetic field facilitates electron energy gain from the laser, while, at the same time, the electron deflections within the magnetic field cause the electrons to emit MeV gamma-rays in the direction of the laser propagation. The extreme magnetic field strength and high electron energy boost the quantum nonlinearity parameter characterizing the photon emission to the level where a single photon can carry an appreciable fraction of the emitting electron’s energy, which ensures high efficiency of gamma-ray emission. The experiments will be performed at the ELI Beamlines laser facility in the Czech Republic using the PW-scale L3 laser and the multi-PW L4 laser that is expected to be available in the last year of the project. The ability of these lasers to reach ultra-high on-target intensity is the key to accessing the desired regime. The experiments will utilize low-mass foam targets to produce a dense plasma whose electron density is well above the classical cutoff density, but below the relativistically adjusted cutoff density for the laser intensities used in the experiments. This choice of target density will enable laser propagation into the plasma.
The project is a collaborative effort that leverages simulation/theory expertise at the University of California – San Diego that is directly relevant to the investigated regime and unique experimental capabilities and experimental expertise at ELI Beamlines. Computational and theoretical research will guide the experiments by identifying ways to increase the magnetic field strength, improve electron acceleration, and control the spectrum of the emitted gamma-rays through laser and target parameters. Directed multi-MeV photon beams containing 10^12 photons that are only a hundred of femtoseconds in duration are an expected outcome of this research project.