| Paper | Title | Page |
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| THPOPT065 | Operation of X-Ray Beam Position Monitors with Zero Bias Voltage at Alba Front Ends | 2747 |
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| Blade-type X-ray Beam Position Monitors (XBPMs) are customarily operated with a negative bias voltage applied to the blades in order to prevent the transference of photoelectrons between the blades, and hence to maximize the signal at each blade and to avoid cross-talk. This was the selected approach at ALBA since the start of its operation for users in 2012. However, over the years the insulation provided by the ceramic pieces separating the blades from the support structure has degraded progressively, giving rise to an ever-increasing leakage current not related with the photon beam to be monitored. On 2020 the level of these leak currents had already become comparable to the photocurrents generated by the photon beam itself, making the readings from many of the XBPMs unreliable. Following the example from other facilities, we decided to remove the bias voltage from the blades and to test the performance of the XBPMs under these conditions, with such good results that we apply this method also for the new, non degraded, XBPMs. In this paper we present the approach used at ALBA to analyse XBPM data, and our experience operating them with zero bias voltage. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT065 | |
| About • | Received ※ 07 June 2022 — Revised ※ 10 June 2022 — Accepted ※ 14 June 2022 — Issue date ※ 29 June 2022 | |
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| THPOPT067 | Propagation of Gaussian Wigner Function Through a Matrix-Aperture Beamline | 2755 |
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Funding: This work is supported by the US Department of Energy, Office of Basic Energy Sciences under Award No. DE-SC0020593. We develop a simplified beam propagation model for x-ray beamlines that includes partial coherence as well as the impact of apertures on the beam. In particular, we consider a general asymmetric Gaussian Schell model, which also corresponds to a Gaussian Wigner function. The radiation is thus represented by a 4x4 symmetric second moment matrix. We approximate rectangular apertures by Gaussian apertures, taking care that the loss in flux is the same for the two models. The beam will thus stay Gaussian through both linear transport and passage through the apertures, allowing a self-consistent picture. We derive expressions for decrease in flux and changes in second moments upon passage through the aperture. We also derive expressions for the coherence lengths and analyze how these propagate through linear transport and Gaussian apertures. We apply our formalism to cases of low emittance light source beamlines and develop a better understanding about trade-offs between coherence length increase and flux reduction while passing through physical apertures. Our formulae are implemented in RadiaSoft’s Sirepo Shadow application allowing easy use for realistic beamline models. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT067 | |
| About • | Received ※ 09 June 2022 — Accepted ※ 11 June 2022 — Issue date ※ 17 June 2022 | |
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| THPOPT068 | Linear Canonical Transform Library for Fast Coherent X-Ray Wavefront Propagation | 2759 |
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Funding: This work is supported by the US Department of Energy, Office of Basic Energy Sciences under Award No. DE-SC0020593. X-ray beamlines are essential components of all synchrotron light sources, transporting radiation from the stored electron beam passing from the source to the sample. The linear optics of the beamline can be captured via an ABCD matrix computed using a ray tracing code. Once the transport matrix is available, one may then include diffraction effects and arbitrary wavefront structure by using that same information in a Linear Canonical Transform (LCT) applied to the initial wavefront. We describe our implementation of a Python-based LCT library for 2D synchrotron radiation wavefronts. We have thus far implemented the separable case and are in the process of implementing algorithms for the non-separable case. Rectangular apertures are also included. We have tested our work against corresponding wavefront computations using The Synchrotron Radiation Workshop (SRW) code. LCT vs. SRW timing and benchmark comparisons are given for undulator and bending magnet beamlines. This algorithm is being included in the Sirepo implementation of the Shadow ray tracing code. Finally, we describe our plans for application to partially coherent radiation. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT068 | |
| About • | Received ※ 15 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 01 July 2022 | |
| Cite • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |