A phase-space beam position monitor for synchrotron radiation

Abstract

The stability of the photon beam position on synchrotron beamlines is critical for most if not all synchrotron radiation experiments. The position of the beam at the experiment or optical element location is set by the position and angle of the electron beam source as it traverses the magnetic field of the bend-magnet or insertion device. Thus an ideal photon beam monitor would be able to simultaneously measure the photon beam's position and angle, and thus infer the electron beam's position in phase space. X-ray diffraction is commonly used to prepare monochromatic beams on X-ray beamlines usually in the form of a double-crystal monochromator. Diffraction couples the photon wavelength or energy to the incident angle on the lattice planes within the crystal. The beam from such a monochromator will contain a spread of energies due to the vertical divergence of the photon beam from the source. This range of energies can easily cover the absorption edge of a filter element such as iodine at 33.17 keV. A vertical profile measurement of the photon beam footprint with and without the filter can be used to determine the vertical centroid position and angle of the photon beam. In the measurements described here an imaging detector is used to measure these vertical profiles with an iodine filter that horizontally covers part of the monochromatic beam. The goal was to investigate the use of a combined monochromator, filter and detector as a phase-space beam position monitor. The system was tested for sensitivity to position and angle under a number of synchrotron operating conditions, such as normal operations and special operating modes where the photon beam is intentionally altered in position and angle at the source point. The results are comparable with other methods of beam position measurement and indicate that such a system is feasible in situations where part of the synchrotron beam can be used for the phase-space measurement.

Source size measurement options for low-emittance light sources

“…The double-slit interferometry can be used in both x-ray and visible light regimes, but most of the existing systems are using visible light. Recently, a phase-space beam position and size monitor (ps-BPM) system was developed for the full characterization of the electron source position, angle, size, and divergence [12,13]. It was shown to have potential in measuring small source sizes as well [14].…”

Optimization of a phase-space beam position and size monitor for low-emittance light sources

“…The K-edge spectrum depends on the core-level width, which is normally described by a Lorenz function (Babanov et al, 1998). In this work, to be consistent with the experimental results (Samadi et al, 2015), a Gaussian function is used.…”

“…The vertical profiles of the filtered and unfiltered beams contain the information of the electron-source position, angle, size and divergence (Samadi et al, 2015). The position of the K-edge location in the filtered beam, y edge , is a direct measure of the electron-source position, y eSource .…”

“…The vertical phase-space beam position and size monitor (ps-BPM) system (Samadi et al, 2015(Samadi et al, , 2019 developed at the Canadian Light Source (CLS) has demonstrated the ability to measure the source size and divergence, as well as the source position and angle in the vertical plane, at a single location and time. In this article, we will report on the process of optimizing the ps-BPM system for ultra-small electron-source-size measurements and provide an example for the Advanced Photon Source Upgrade (APS-U) project (Borland et al, 2018).…”

A real-time phase-space beam emittance monitoring system

“…The ps-BPM system measures the electron beam position and angle in real time (Samadi et al, 2015). The measurement of the source size and divergence does require longer integration time (a few seconds in the current setup).…”