Abstract
Microbunching instability (MBI) driven by beam collective effects is known to be detrimental to high-brightness storage rings, linacs, and free-electron lasers (FELs). One known way to suppress this instability is to induce a small amount of energy spread to an electron beam by a laser heater. The distribution of the induced energy spread greatly affects MBI suppression and can be controlled by shaping the transverse profile of the heater laser. Here, we present the first experimental demonstration of effective MBI suppression using a LG_{01} transverse laser mode and compare the improved results with respect to traditional Gaussian transverse laser mode at the Linac Coherent Light Source. The effects on MBI suppression are characterized by multiple downstream measurements, including longitudinal phase space analysis and coherent radiation spectroscopy. We also discuss the role of LG_{01} shaping in soft x-ray self-seeded FEL emission, one of the most advanced operation modes of a FEL for which controlled suppression of MBI is critical.
Highlights
Introduction.—Free-electron lasers (FELs) provide ultrashort, extremely bright coherent radiation at wavelengths down to the angstrom level and have been demonstrated to be powerful experimental tools in condensed matter physics, chemistry, and structural biology [1,2,3,4,5,6]
microbunching instability (MBI) can be suppressed by a laser heater (LH) [8], which was first installed at the Linac Coherent Light Source (LCLS) and has been widely used in other free-electron lasers (FELs) facilities [9,15,20,23]
In this Letter, we investigate the use of a Laguerre-Gaussian 01 (LG01) mode laser at the LCLS and its influence in MBI suppression and FEL performance
Summary
Jingyi Tang ,1,2 Randy Lemons, Wei Liu, Sharon Vetter, Timothy Maxwell, Franz-Josef Decker, Alberto Lutman ,1 Jacek Krzywinski, Gabriel Marcus, Stefan Moeller ,1 Zhirong Huang, Daniel Ratner, and Sergio Carbajo 1,3,*. The electron-beam (e-beam) quality can be degraded due to microbunching instability (MBI) caused by collective effects like longitudinal space charge [8,9] and coherent synchrotron radiation [10,11,12,13,14], which are extensively studied both in theory and in experiment [15,16,17,18,19] This instability amplifies the e-beam energy and density modulation and increases its energy spread up to a level that can be detrimental to the FEL gain process [9,20], and to the beam brightness in storage rings and linacs [21,22]. A transverse Laguerre-Gaussian 01 (LG01) mode provides Gaussian-shaped energy distribution and results in an exponential suppression in microbunching gain [24,25]
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