Measuring the betatron x-ray source size from a laser-wakefield accelerator

We have performed experiments using the 200 TW Callisto laser system at LLNL to produce GeV-class electron beams and keV Betatron x-rays. The laser was focused into various gas cells with sizes ranging from 3 to 10 mm that contained a mixture of gases (He, N, Ar). We determined the betatron x-ray source size using a computer model and experimental observations of straight edge Fresnel diffraction. Experimental results are benchmarked against a code that solves the equation of motion of electrons oscillating in the plasma wake and by calculating the corresponding x-ray radiation spectrum and profile.