Abstract
Laser-plasma accelerators (LPAs) driven by picosecond-scale, kilojoule-class lasers can generate particle beams and x-ray sources that could be utilized in experiments driven by multi-kilojoule, high-energy-density science (HEDS) drivers such as the OMEGA laser at the Laboratory for Laser Energetics (LLE) or the National Ignition Facility at Lawrence Livermore National Laboratory. This paper reports on the development of the first LPA driven by a short-pulse, kilojoule-class laser (OMEGA EP) connected to a multi-kilojoule HEDS driver (OMEGA). In experiments, electron beams were produced with electron energies greater than 200 MeV, divergences as low as 32 mrad, charge greater than 700 nC, and conversion efficiencies from laser energy to electron energy up to 11%. The electron beam charge scales with both the normalized vector potential and plasma density. These electron beams show promise as a method to generate MeV-class radiography sources and improved-flux broadband x-ray sources at HEDS drivers.
Highlights
Laser-plasma accelerators (LPAs) driven by short-pulse, kilojoule-class lasers provide a path to producing compact sources of high-charge, high-energy electron beams for conversion into x-ray and positron sources
The divergence was calculated by fitting the lineout of the transverse profile through the peak of the electron beam with a Lorentzian and taking the full width at half maximum (FWHM)
The total charge in the FWHM was 19 nC. This divergence demonstrates a major step forward in the possible quality of electron beams from self-modulated laser wakefield acceleration (SMLWFA) since it is significantly reduced from the best divergence reported from other SMLWFA experiments (64 × 100 mrad ± 10 mrad6) and is on the order of the divergences (< 10 mrad) of the electron beams produced by laser wakefield accelerator (LWFA) being driven by ultrashort-pulse lasers (τ < λp)
Summary
Laser-plasma accelerators (LPAs) driven by short-pulse, kilojoule (kJ)-class lasers provide a path to producing compact sources of high-charge, high-energy electron beams for conversion into x-ray and positron sources. The laser pulse becomes modulated at the plasma wavelength via the Raman forward scattering[12,13] and/or self-modulation[14,15,16,17] instabilities These modulations lead to a train of laser micropulses coherently driving plasma waves whose longitudinal electric field can trap and accelerate electrons to relativistic energies. The bunch charge is comparable to high-bunch-charge radio-frequency (rf) accelerators (~ 1 μC), but with sub-picosecond durations versus the millisecond durations characteristic of rf sources These electron beams are, to our knowledge, the highest-charge and highest-conversion-efficiency electron beams produced from an LPA
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