Abstract
Author(s): Swanson, KK; Tsai, HE; Barber, SK; Lehe, R; Mao, HS; Steinke, S; Van Tilborg, J; Nakamura, K; Geddes, CGR; Schroeder, CB; Esarey, E; Leemans, WP | Abstract: Control of the properties of laser-plasma-accelerated electron beams that were injected along a shock-induced density downramp through precision tailoring of the density profile was demonstrated using a 1.8 J, 45 fs laser interacting with a mm-scale gas jet. The effects on the beam spatial profile, steering, and absolute energy spread of the density region before the shock and tilt of the shock were investigated experimentally and with particle-in-cell simulations. By adjusting these density parameters, the electron beam quality was controlled and improved while the energy (30-180 MeV) and energy spread (2-11 MeV) were independently tuned. Simple models that are in good agreement with the experimental results are proposed to explain these relationships, advancing the understanding of downramp injection. This technique allows for high-quality electron beams with percent-level energy spread to be tailored based on the application.
Highlights
Laser plasma accelerators (LPAs) can produce ultrashort electron bunches at relativistic energies in a short distance [1,2,3,4,5]
Control of the properties of laser-plasma-accelerated electron beams that were injected along a shockinduced density downramp through precision tailoring of the density profile was demonstrated using a 1.8 J, 45 fs laser interacting with a mm-scale gas jet
Simple models that are in good agreement with the experimental results are proposed to explain these relationships, advancing the understanding of downramp injection
Summary
Laser plasma accelerators (LPAs) can produce ultrashort electron bunches at relativistic energies in a short distance [1,2,3,4,5] This compact source can provide electrons for various applications such as the production of x-ray pulses from coherent undulator radiation or Thomson backscattering [6,7,8,9] which can be used for imaging the structural dynamics of chemical and biological systems, highresolution lithography or characterization of nuclear materials [10,11,12]. This injection process is controlled and localized by the downramp, producing small energy spread beams While this scheme has been studied experimentally and quasimonoenergetic beams were produced [21,22,24,25,26], little investigation has been done to tune the electron beam spatial quality and absolute energy spread by tailoring the density profile. By adjusting the density profile and tilt of the shock front, stable beams with tunable energy, improved spatial quality and reduced energy spread were produced, demonstrating that this injection mechanism is reliable and versatile enough to be used for many applications
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