Transverse profile imager for ultrabright electron beams

Abstract

A transverse profile imager for ultrabright electron beams is presented, which overcomes resolution issues in present designs by observing the Scheimpflug imaging condition as well as the Snell-Descartes law of refraction in the scintillating crystal. Coherent optical transition radiation emitted by highly compressed electron bunches on the surface of the crystal is directed away from the camera, allowing to use the monitor for profile measurements of electron bunches suitable for X-ray free electron lasers. The optical design has been verified by ray tracing simulations, and the angular dependency of the resolution has been verified experimentally. An instrument according to the presented design principles has been used in the SwissFEL Injector Test Facility, and different scintillator materials have been tested. Measurements in conjunction with a transverse deflecting radiofrequency structure and an array of quadrupole magnets demonstrate a normalized slice emittance of 25 nm in the core of a 30 fC electron beam at a pulse length of 10 ps and a particle energy of 230 MeV.

SwissFEL Aramis beamline photon diagnostics

“…The photon profile monitor (PPRM) is a tool that uses a scintillating screen, a mirror, a lens, and a high-speed camera to acquire the photon beam images on a shot-to-shot basis. The PPRM uses a unique design developed at PSI for the transverse measurement of electron beams (Ischebeck et al, 2015), using the same scintillator-and-mirror geometry and tilted camera to compensate for the Scheimpflug effect (Sheimpflug, 1904), as shown in Fig. 8, to always observe the same transverse area in the chamber.…”

Nanofabricated free-standing wire scanners for beam diagnostics with submicrometer resolution

“…Conventional WS solutions -as normally in operation in several free-electron lasers (FELs) -are realized according to the standard technique to fix and stretch a metallic wire (beam-probe) onto a metallic frame (fork). They are able to attain a spatial resolution at the micrometer scale [10] which is at least an order of magnitude higher than the spatial resolution of a typical view-screen operating in a FEL [11,12]. Low charge and low emitance machine operation modes -presently under investigation in several FEL facilities -requires the characterization of ever smaller beam profiles.…”

Demonstration of two-color x-ray free-electron laser pulses with a sextupole magnet

“…Any of the six available sextupoles can impose the beam tilt required for two-pulse generation, as discussed above. Two transverse-deflecting structures (TDS) [35], streaking in the vertical plane, can be used in combination with a profile monitor [36] to measure longitudinal electron properties such as bunch length and current profile, as well as horizontal slice properties such as slice emittance, beam tilt and optics mismatch [37]. The undulator beamline contains 13 planar variable-gap undulator modules with a period of 15 mm.…”