MOPB059

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URL	https://doi.org/10.18429/JACoW-IPAC2025-MOPB059
Title	Improvements in FLASH operation through the use of the laser heater
Authors	C. Gerth, C. Mohr, C. Mahnke, E. Schneidmiller, I. Hartl, J. Zemella, J. Wood, J. Roensch-Schulenburg, L. Boulton, L. Schaper, M. Tischer, M. Vogt, O. Akcaalan, P. Vagin, S. Wesch, U. Grosse-Wortmann Deutsches Elektronen-Synchrotron DESY P. Amstutz, C. Mai TU Dortmund University
Abstract	FLASH is an XUV and soft X-ray free-electron laser (FEL) facility that comprises a superconducting linear accelerator with a beam energy of up to 1.35 GeV which drives two FEL beamlines in parallel and the plasma wakefield accelerator experiment FLASHForward. Within the upgrade program FLASH2020+, a laser heater was installed upstream of the first bunch compression chicane to mitigate microbunching instability in the linear accelerator by a controlled increase of the uncorrelated energy spread. The effect of the laser heater on microbunching instability and final energy spread has been verified with a transverse deflecting structure. In this paper, we describe the layout of the laser heater and report on improved operational aspects. It has been shown that the laser heater eliminates coherent contributions to visible transition radiation in transverse beam size measurements and, thus, contributes to better electron beam matching. In addition, an increase in the FEL output power is demonstrated, especially for first operation of the 3rd harmonic afterburner with variable polarisation.
Paper	download: MOPB059.pdf
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Conference	16th International Particle Accelerator Conference
Series
Location	Taipei, Taiwan
Date	01-06 Jun 2025
Publisher	JACoW Publishing, Geneva, Switzerland
Editorial Board	* Ming-Chyuan Lin - National Synchrotron Radiation Research Center * Yoichi Sato - KEK * Jui-Che Huang - National Synchrotron Radiation Research Center * David Button - Australian Nuclear Science and Technology Organisation * Ping-Shun Chuang - National Synchrotron Radiation Research Center
Online ISBN	978-3-95450-248-6
Online ISSN	2673-5490
Received	28 May 2025
Revised	03 June 2025
Accepted	03 June 2025
Issued	05 November 2025
DOI	10.18429/JACoW-IPAC2025-MOPB059
Pages	183-186
Copyright	Published by JACoW Publishing under the terms of the Creative Commons Attribution 4.0 license. Any further distribution of this work must maintain attribution to the author(s), the published article's title, publisher, and DOI.