Effect of an angular trajectory kick in a high-gain free-electron laser

Baxevanis, Panagiotis; Huang, Zhirong; Stupakov, Gennady

doi:10.1103/physrevaccelbeams.20.040703

Cited by 6 publications

(9 citation statements)

References 16 publications

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“…7and (8). The result generalizes expressions seen elsewhere [16,17,[24][25][26] to include the effects of quadrupole focusing, emittance, and energy spread for a matched beam,…”

Section: Microbunch Rotation In a Focusing Channelsupporting

confidence: 76%

Microbunch Rotation and Coherent Undulator Radiation from a Kicked Electron Beam

2018

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Coherent emission from a microbunched electron beam is the driving force behind the revolution in light sources, enabling x-ray free-electron lasers (FELs) to emit pulses 9 orders of magnitude brighter than previous sources. Microbunches form perpendicular to the electron travel direction, and the conventional understanding is that they shear rather than rotate in response to a transverse kick, locking FEL facilities into a single-user operating mode. In this paper, we show that microbunches rotate toward the new direction of travel if the electron beam is kicked and defocused. We provide evidence that microbunch rotation explains the unexpectedly large amount of off-axis radiation observed during experiments at the Linac Coherent Light Source. We demonstrate that LCLS can be multiplexed into at least three separate beams using this principle. Finally, we propose using a magnetic triplet to rotate microbunches through significantly larger angles without microbunch degradation. This new understanding of microbunch dynamics can lead to significantly improved multiplexing at FEL facilities, microbunch preservation through a bend, and x-ray pulses with a pulsefront tilt.

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“…7and (8). The result generalizes expressions seen elsewhere [16,17,[24][25][26] to include the effects of quadrupole focusing, emittance, and energy spread for a matched beam,…”

Section: Microbunch Rotation In a Focusing Channelsupporting

confidence: 76%

Microbunch Rotation and Coherent Undulator Radiation from a Kicked Electron Beam

2018

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“…In particular, the contribution to the CSR field from the Coulomb field of the Liénard-Wiechert potential cannot be neglected when calculating entrance transient effects, and in order to correctly model this interaction, these fields must be taken into account. The importance of the transient effects of CSR are significant in terms of minimising the projected emittance growth in bunch compressor systems, and therefore in optimising the accuracy of beam optics matching to the undulator line for high-gain UV and x-ray FELs [41,42]. The observations of this paper are interesting technologically because they suggest that it may be possible to design an optimised magnet (or system of magnets) in which the CSR impact of the magnet itself is partially cancelled by that of the drift directly after it, thereby reducing adverse effects like emittance growth and microbunching gain, particularly in more complex transport systems such as compressive arcs in ERLs.…”

Section: Discussionmentioning

confidence: 99%

Beyond the limits of 1D coherent synchrotron radiation

et al. 2018

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An understanding of collective effects is of fundamental importance for the design and optimisation of the performance of modern accelerators. In particular, the design of an accelerator with strict requirements on the beam quality, such as a free electron laser (FEL), is highly dependent on a correspondence between simulation, theory and experiments in order to correctly account for the effect of coherent synchrotron radiation (CSR), and other collective effects. A traditional approach in accelerator simulation codes is to utilise an analytic one-dimensional approximation to the CSR force. We present an extension of the 1D CSR theory in order to correctly account for the CSR force at the entrance and exit of a bending magnet. A limited range of applicability to this solution-in particular, in bunches with a large transverse spot size or offset from the nominal axis-is recognised. More recently developed codes calculate the CSR effect in dispersive regions directly from the Liénard-Wiechert potentials, albeit with approximations to improve the computational time. A new module of the General Particle Tracer code was developed for simulating the effects of CSR, and benchmarked against other codes. We experimentally demonstrate departure from the commonly used 1D CSR theory for more extreme bunch length compression scenarios at the FERMI FEL facility. Better agreement is found between experimental data and the codes which account for the transverse extent of the bunch, particularly in more extreme compression scenarios.

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“…We will borrow from the fully three-dimensional FEL formalism developed in [7] in order to understand how we may model the FEL as an optical fiber. As such, we consider here a planar undulator without any taper.…”

Section: A Gaussian Beams In Quadratic Optical Fibersmentioning

confidence: 99%

“…Of course, this requires some generalization to the method presented in Section II, in particular to allow for some non-trivial trajectory of the electron beam centroid. We assume that the electron beam centroid is essentially predetermined, primarily by the betatron oscillations associated with the focusing lattice in the FEL, such that we may define the e-beam centroid trajectory x ce (z) with associated angle p x,ce (z) ≡ x ce (z), as was utilized in [7] from which we borrowed the earlier formalism for the FEL equation 6. Since typically there is jitter in both x and y, which may not be equal, we will keep the method as general as possible by allowing some offset in y as well, with similar definitions of the trajectory.…”

Section: Extension To Electron Beam Trajectory Errorsmentioning

confidence: 99%

“…For example, all XFELs are affected by some level of jitter in the trajectory of the driving electron beam, which can lead to degradation of the eventual x-ray pulse energy and pointing jitter of the x-ray beam since most of the final energy in the pulse is developed in the last gain length of the undulator. Some simpler and faster numerical methods have been proposed which can handle these non-ideal effects, however they still implement relatively opaque numerical methods, and interpreting their results correctly demands some nuance which we will discuss here [7].…”

Section: Introductionmentioning

confidence: 99%

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A self-consistent refractive index model for fast simulation of free-electron lasers

Robles¹,

Marcus²,

Huang³

2021

Preprint

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Modern x-ray free-electron lasers (XFELs) produce x-ray pulses of exceptional transverse coherence. This is due largely to the process of optical guiding by which the radiation is both refractively guided by the bunched electron beam and gain guided by the preferential amplification of on-axis radiation. These effects may be summarized by an effective index of refraction, which has been used in the past to study the transverse dynamics of the FEL process with significant simplifications and approximations, but never fully self-consistently. We present here a self-consistent method for studying high gain FELs in the linear regime by approximating the FEL equations to second-order in the lateral displacement from the nominal electron beam axis. This is made possible by casting the FEL equations in the language of optical fibers with an appropriately chosen refractive index. We demonstrate that this approach is both fast and highly accurate, indicating that the most important FEL dynamics are inherently second-order. In its full form our method can capture the effects of transverse offsets in both the x-ray beam and the electron beam, making it a versatile tool for studying non-ideal effects in seeded FELs, regenerative amplifier XFELs, and even self-amplified spontaneous emission (SASE) FELs.

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Effect of an angular trajectory kick in a high-gain free-electron laser

Abstract: Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Cited by 6 publications

References 16 publications

Microbunch Rotation and Coherent Undulator Radiation from a Kicked Electron Beam

Microbunch Rotation and Coherent Undulator Radiation from a Kicked Electron Beam

Beyond the limits of 1D coherent synchrotron radiation

A self-consistent refractive index model for fast simulation of free-electron lasers

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