Abstract
We report on the characterisation of an x-ray source, generated by a laser-driven plasma wakefield accelerator. The spectrum of the optimised source was consistent with an on-axis synchrotron spectrum with a critical energy of keV and the number of photons per pulse generated above 1 keV was calculated to be . The x-ray beam was used to image a resolution grid placed 37 cm from the source, which gave a measured spatial resolution of 4 µm × 5 µm. The inferred emission region had a radius and length of 0.5 ± 0.2 µm and 3.2 ± 0.9 mm respectively. It was also observed that laser damage to the exit aperture of the gas cell led to a reduction in the accelerated electron beam charge and a corresponding reduction in x-ray flux due to the change in the plasma density profile.
Highlights
Laser-driven plasma wakefield acceleration (LWFA) [1] is an established technique for the acceleration of electrons over very short distances [2,3,4]
The brass exit plate to the gas cell had a conical shape with an aperture at the tip
Throughout the experiment, the exit aperture sustained damage from the laser making it increase in size — from a few hundred μm to around 3 mm
Summary
Laser-driven plasma wakefield acceleration (LWFA) [1] is an established technique for the acceleration of electrons over very short distances [2,3,4]. GeV scale energies in just a few millimeters, while transverse oscillations of the electron beams results in a bright femtosecond pulse of multi-keV x-rays [5]. The accelerating electric field in a laser wakefield accelerator can be estimated using the wave breaking limit for a cold non-relativistic plasma wave, Ewb = cmeωp/e [9] From this it can be calculated that acceleration gradients on the order of 100 GeV m−1 can be generated at a density of ne ∼ 1018 cm−3. For the experimental parameters considered in this paper, the critical energy, Ec = ħωc, is on the order of tens of keV These x-rays can be used for both medical [17, 18] and industrial [19, 20] radiography to image micron-scale features in the internal structure of a material in a single shot of the drive laser. The effects of gradual damage sustained by the plasma source during operation were investigated
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