Observations of z-dependent microbunching harmonic intensities using COTR in a SASE FEL

Lumpkin, A.H.; Biedron, Sandra; Dejus, Roger J.; Berg, William J.; Borland, M.; Chae, Y.C.; Erdmann, M.; Huang, Zhirong; Kim, K.-J.; Li, Y.; Lewellen, John W.; Milton, S.V.; Moog, E.R.; Sajaev, V.; Yang, Bingxin

doi:10.1016/b978-0-444-51417-2.50062-6

“…First, there is enough COTR energy to distribute to ⇠ 3⇥ as many filtered cameras as demonstrated here, enabling larger spectral range and density and correspondingly greater resolution. Extensions to shorter λ will be important for diagnosing nano-bunching in LWFA-driven XFELS [43,44] and nano-prebunching schemes [19]. Second, by conveying the e-bunch after the COTR imaging split-off mirror (see Fig.…”

Section: Discussionmentioning

confidence: 99%

3D structure of microbunched plasma-wakefield-accelerated electron beams

Downer,

LaBerge,

Bowers

et al. 2024

Preprint

0

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Plasma wakefield accelerators use tabletop equipment to produce relativistic femtosecond electron bunches. Optical and x-ray diagnostics have established that their charge concentrates within a micrometer-sized volume, but its sub-micrometer internal distribution, which critically influences gain in free-electron lasers or particle yield in colliders, has proven elusive to characterize. Here, by simultaneously imaging different wavelengths of coherent optical transition radiation (COTR) that a laser-wakefield-accelerated e-bunch generated when exiting a metal foil, we elucidated the structure of the coherently-radiating component of bunch charge. Key features of the images correlated uniquely with how plasma electrons injected into the wake: by a plasma-density discontinuity, by ionising high-Z gas-target dopants, or by uncontrolled laser-plasma dynamics. With additional input from electron spectra, spatially-averaged COTR spectra, and particle-in-cell simulations, we reconstructed coherent 3D charge structures. The results demonstrate essential metrology for next-generation X-ray free-electron lasers.

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“…A schematic of the facility is provided elsewhere in these proceedings [10]. These experiments used the photocathode (PC) rf gun, the S-band linac, the chicane bunch compressor [11], and the LEUTL hardware.…”

Section: Experimental Backgroundmentioning

confidence: 99%

Evidence for transverse dependencies in COTR and microbunching in a SASE FEL

Lumpkin¹,

Chae²,

Lewellen³

et al. 2003

Free Electron Lasers 2002

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Using coherent optical transition radiation (COTR) techniques, we have observed transverse dependencies, which in some aspects relate to the electron beam microbunching in a visible wavelength (540 nm) self-amplified spontaneous emission (SASE) free-electron laser (FEL). The experimental COTR observations include the zdependent e-beam sizes, the z-dependent angular distributions, and the z-dependent spectra (which show an x-dependence). A 30-40% narrowing of the observed beam size using COTR is explainable by the mechanism's dependence on the square of the number of microbunched particles. However, additional effects are needed to explain beam size reductions by factors of 2-3 at different z locations. Localized e-beam structure in the gun or induced in the bunch compression process may result in microbunching transverse dependence, and hence the observed COTR effects.

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Evidence for transverse dependencies in COTR and microbunching in a SASE FEL

Lumpkin¹,

Chae²,

Lewellen³

et al. 2003

Nuclear Instruments and Methods in Physics Research Section A:

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Using coherent optical transition radiation (COTR) techniques, we have observed transverse dependencies, which in some aspects relate to the electron beam microbunching in a visible wavelength (540 nm) self-amplified spontaneous emission (SASE) free-electron laser (FEL). The experimental COTR observations include the zdependent e-beam sizes, the z-dependent angular distributions, and the z-dependent spectra (which show an x-dependence). A 30-40% narrowing of the observed beam size using COTR is explainable by the mechanism's dependence on the square of the number of microbunched particles. However, additional effects are needed to explain beam size reductions by factors of 2-3 at different z locations. Localized e-beam structure in the gun or induced in the bunch compression process may result in microbunching transverse dependence, and hence the observed COTR effects.

show abstract

Observations of z-dependent microbunching harmonic intensities using COTR in a SASE FEL

Cited by 3 publications

References 13 publications

3D structure of microbunched plasma-wakefield-accelerated electron beams

3D structure of microbunched plasma-wakefield-accelerated electron beams

Evidence for transverse dependencies in COTR and microbunching in a SASE FEL

Evidence for transverse dependencies in COTR and microbunching in a SASE FEL

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