| Paper | Title | Page |
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| WEB02 | Wire-Scanners with Sub-Micrometer Resolution: Developments and Measurements | 307 |
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Monitors of the beam transverse profile with ever more demanding spatial resolution and minimal invasivity are required by the FEL community. In order to improve the spatial resolution towards the sub-micrometer limit as well as to decrease the impact on the lasing process, nano-fabricated wire-scanners have been manufactured independently at PSI and FERMI by means of a lithographic technique [1,2]. Experimental tests carried out at SwissFEL at a low emittance demonstrated the capability of such innovative wire-scanner solutions to resolve beam transverse profiles with a size of 400-500 nm without being affected by any resolution limit. Status and outlook of nano-fabricated wire-scanners will be presented.
[1] M. Veronese et al., NIM-A, 891, 32-36, (2018). [2] S. Borrelli et al., Comm. Phys.-Nature, 1, 52 (2018). |
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Slides WEB02 [11.196 MB] | |
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEB02 | |
| About • | paper received ※ 24 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019 | |
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THB03 |
Emittance Measurements and Minimization at SwissFEL | |
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| The transverse emittance of the electron beam is a fundamental parameter that determines the performance of free-electron-lasers (FELs). In this contribution, we present emittance measurements carried out at SwissFEL, the X-ray FEL facility that recently started to operate at PSI in Switzerland, including a description of our measurement methods and optimization procedures. We obtained slice emittance values at the undulator entrance down to ~200 nm for an electron beam with a charge of 200 pC and an r.m.s. duration of ~30 fs. Furthermore, we achieved slice emittances as low as ~100 nm for 10 pC beams with few femtosecond duration. | ||
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Slides THB03 [6.285 MB] | |
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| THP061 | Bayesian Optimisation for Fast and Safe Parameter Tuning of SwissFEL | 707 |
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| Parameter tuning is a notoriously time-consuming task in accelerator facilities. As tool for global optimization with noisy evaluations, Bayesian optimization was recently shown to outperform alternative methods. By learning a model of the underlying function using all available data, the next evaluation can be chosen carefully to find the optimum with as few steps as possible and without violating any safety constraints. However, the per-step computation time increases significantly with the number of parameters and the generality of the approach can lead to slow convergence on functions that are easier to optimize. To overcome these limitations, we divide the global problem into sequential subproblems that can be solved efficiently using safe Bayesian optimization. This allows us to trade off local and global convergence and to adapt to additional structure in the objective function. Further, we provide slice-plots of the function as user feedback during the optimization. We showcase how we use our algorithm to tune up the FEL output of SwissFEL with up to 40 parameters simultaneously, and reach convergence within reasonable tuning times in the order of 30 minutes (< 2000 steps). | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP061 | |
| About • | paper received ※ 13 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019 | |
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| THP085 | Status of Athos, the Soft X-Ray FEL Line of SwissFEL | 753 |
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| The Athos line will cover the photon energy range from 250 to 1900 eV and will operate in parallel to the hard X-ray line Aramis of SwissFEL. The paper will describe the current layout of the Athos FEL line starting from the fast kicker magnet followed by the dogleg transfer line, the small linac and the 16 APPLE undulators. From there the photon beam passes through the photonics front end and the beamline optics before reaching the experimental stations AMO and FURKA. The focus of this contribution will be on the two bunch operation commissioning (two bunches in the same RF macropulse), which started in 2018, and the characterization of the major components like the APPLE X undulator UE38, the CHIC chicane and the dechirper. The Athos installation inside the tunnel is alternating with Aramis FEL user operation and the first lasing is planned for winter 2019 / 2020. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP085 | |
| About • | paper received ※ 30 July 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |