The stability of Laser Plasma Wakefield Accelerated (LWFA) electron beams and the efficiency of betatron X-ray sources can be controlled using staged gas targets. Implementation of ionization-assisted  and density down-ramp  electron injection allows to change the energy and charge of accelerated electron beams. The double-jet betatron source with a low-density LWFA region and a high-density plasma radiator region produces photons of higher energy and has better efficiency relative to a single-jet gas target source .
In this report, we present the results of LWFA and X-ray generation using monolithic gas jet microarrays at the 40 TW 30 fs at the Lund Laser Centre. The density profiles of gas jets, ejected by micronozzles, were simulated using OpenFOAM compressible steady-flow solver . The propagation of the laser beam and the acceleration of electrons were modelled using spectral FBPIC (Fourier–Bessel Particle-In-Cell) algorithm . The results of the distribution of electron velocities were post-processed to estimate the photon energy of betatron radiation. Low-density gas targets of cylindrical de Laval and slit-shaped nozzles with the dimensions of 0.5 – 2.25 mm were used for electron acceleration. Single and an array of four cylindrical nozzles with the diameter of 200 - 800 µm, producing high-density gas regions at the output, were implemented for the density triggered injection and X-ray plasma radiator. The micronozzles were manufactured from fused silica using hybrid nanosecond laser rear-side processing and femtosecond laser-assisted selective etching technique . The acceleration of electron beams of the energy of 30 -180 MeV and charge of 20 – 600 pC with different energy distribution and formation of double and triple electron beams using the gas jet arrays of pure helium and mixture of 1% nitrogen and helium were demonstrated. The energy of betatron X-ray radiation was 1.5 – 4.5 keV with 2·107 - 1·108 photons per shot. The implementation of the four-jet gas array of 200 µm diameter as the second gas target region resulted in the increase of betatron photon energy by a factor of 1.5 -2. The generated X-ray radiation was used for the transmission imaging of small-scale biological objects and polymer foils with micrometric resolution.
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|Working group||Secondary radiation generation & applications|