Third generation synchrotron light sources are characterized by a low emittance and a low emittance coupling. Some light sources are already operating with extremely low coupling close to 0.1%. Measurement of the transverse beam size is generally used to measure the emittance and the coupling. To this end, several systems are currently used and an x-ray pinhole camera is one of them. In this paper we derive the point spread function of the x-ray pinhole camera both analytically and numerically using the Fresnel diffraction integral and taking into account the broadband spectrum of the bending magnet source, and we show that an optimized design allows the measurement of extremely small vertical beam sizes below 5 m. The point spread function of several scintillator screens is also measured, and it shows that the contribution of the diffraction and the screen point spread functions have to be taken into account for an accurate measurement of a low coupling. Finally, we show measurements of the vertical beam sizes as small as 6 m for our nonoptimized setup.
Laser-driven plasma accelerators can generate accelerating gradients three orders of magnitude larger than radio-frequency accelerators and have achieved beam energies above 1 GeV in centimetre long stages. However, the pulse repetition rate and wall-plug efficiency of plasma accelerators is limited by the driving laser to less than approximately 1 Hz and 0.1% respectively. Here we investigate the prospects for exciting the plasma wave with trains of low-energy laser pulses rather than a single high-energy pulse. Resonantly exciting the wakefield in this way would enable the use of different technologies, such as fibre or thin-disc lasers, which are able to operate at multi-kilohertz pulse repetition rates and with wall-plug efficiencies two orders of magnitude higher than current laser systems. We outline the parameters of efficient, GeV-scale, 10-kHz plasma accelerators and show that they could drive compact X-ray sources with average photon fluxes comparable to those of third-generation light source but with significantly improved temporal resolution. Likewise FEL operation could be driven with comparable peak power but with significantly larger repetition rates than extant FELs.
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