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Intrinsic beam emittance of laser-accelerated electrons measured by x-ray spectroscopic imaging.

Golovin G, Banerjee S, Liu C, Chen S, Zhang J, Zhao B, Zhang P, Veale M, Wilson M, Seller P, Umstadter D - Sci Rep (2016)

Bottom Line: Reported here is a novel, non-destructive, single-shot method that overcame this problem.It employed an intense laser probe pulse, and spectroscopic imaging of the inverse-Compton scattered x-rays, allowing measurement of an ultra-low value for the normalized transverse emittance, 0.15 (±0.06) π mm mrad, as well as study of its subsequent growth upon exiting the accelerator.The technique and results are critical for designing multi-stage laser-wakefield accelerators, and generating high-brightness, spatially coherent x-rays.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Astronomy, University of Nebraska, Lincoln NE 68588, USA.

ABSTRACT
The recent combination of ultra-intense lasers and laser-accelerated electron beams is enabling the development of a new generation of compact x-ray light sources, the coherence of which depends directly on electron beam emittance. Although the emittance of accelerated electron beams can be low, it can grow due to the effects of space charge during free-space propagation. Direct experimental measurement of this important property is complicated by micron-scale beam sizes, and the presence of intense fields at the location where space charge acts. Reported here is a novel, non-destructive, single-shot method that overcame this problem. It employed an intense laser probe pulse, and spectroscopic imaging of the inverse-Compton scattered x-rays, allowing measurement of an ultra-low value for the normalized transverse emittance, 0.15 (±0.06) π mm mrad, as well as study of its subsequent growth upon exiting the accelerator. The technique and results are critical for designing multi-stage laser-wakefield accelerators, and generating high-brightness, spatially coherent x-rays.

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Related in: MedlinePlus

Single-shot angular-resolved x-ray spectrum measured using spectroscopic x-ray imaging.(a) X-ray photon spectrum as a function of polar angle. (b) Mean energy of the x-rays as a function of polar angle. (c) Dependence of the spectral width (FWHM) on the polar angle. Electron beam parameters were: central energy −65 ± 1 MeV; energy spread (FWHM) −8.9 ± 0.1 MeV; and divergence (FWHM) −4.1 ± 0.4 mrad (measured on the LANEX screen). Blue curves on (b,c) show simulated dependences based on these electron beam parameters. Red curves on (b,c) show simulated dependences based on electron beam parameters, obtained from angular-resolved x-ray spectrum: central energy −66 ± 1 MeV; energy spread (FWHM) −8.5 ± 3.5 MeV; and divergence (FWHM) −2.1 ± 0.7 mrad. Error bars represent 95% confidence bands, calculated based on least-squares fits of spectral data. Photon flux at the source is 104. See details on this measurement in the supplementary.
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f2: Single-shot angular-resolved x-ray spectrum measured using spectroscopic x-ray imaging.(a) X-ray photon spectrum as a function of polar angle. (b) Mean energy of the x-rays as a function of polar angle. (c) Dependence of the spectral width (FWHM) on the polar angle. Electron beam parameters were: central energy −65 ± 1 MeV; energy spread (FWHM) −8.9 ± 0.1 MeV; and divergence (FWHM) −4.1 ± 0.4 mrad (measured on the LANEX screen). Blue curves on (b,c) show simulated dependences based on these electron beam parameters. Red curves on (b,c) show simulated dependences based on electron beam parameters, obtained from angular-resolved x-ray spectrum: central energy −66 ± 1 MeV; energy spread (FWHM) −8.5 ± 3.5 MeV; and divergence (FWHM) −2.1 ± 0.7 mrad. Error bars represent 95% confidence bands, calculated based on least-squares fits of spectral data. Photon flux at the source is 104. See details on this measurement in the supplementary.

Mentions: The spectroscopic x-ray imaging detector allowed us to measure angular-dependent ICS x-ray spectrum for every shot; the result is shown in Fig. 2(a). We fitted the spectra, corresponding to individual polar angles, with Gaussian functions, and extracted the resulting dependencies of central energy and energy spread on angle. The dependence of central energy of the x-rays on polar angle, shown in Fig. 2(b), arises from the dependence of the resonant scattered frequency on the polar angle (see Methods, eq. 2). The dependence of the spectral width on the polar angle, shown in Fig. 2(c), is more complex and requires accounting for both the spectral and angular characteristics of the electron beam.


Intrinsic beam emittance of laser-accelerated electrons measured by x-ray spectroscopic imaging.

Golovin G, Banerjee S, Liu C, Chen S, Zhang J, Zhao B, Zhang P, Veale M, Wilson M, Seller P, Umstadter D - Sci Rep (2016)

Single-shot angular-resolved x-ray spectrum measured using spectroscopic x-ray imaging.(a) X-ray photon spectrum as a function of polar angle. (b) Mean energy of the x-rays as a function of polar angle. (c) Dependence of the spectral width (FWHM) on the polar angle. Electron beam parameters were: central energy −65 ± 1 MeV; energy spread (FWHM) −8.9 ± 0.1 MeV; and divergence (FWHM) −4.1 ± 0.4 mrad (measured on the LANEX screen). Blue curves on (b,c) show simulated dependences based on these electron beam parameters. Red curves on (b,c) show simulated dependences based on electron beam parameters, obtained from angular-resolved x-ray spectrum: central energy −66 ± 1 MeV; energy spread (FWHM) −8.5 ± 3.5 MeV; and divergence (FWHM) −2.1 ± 0.7 mrad. Error bars represent 95% confidence bands, calculated based on least-squares fits of spectral data. Photon flux at the source is 104. See details on this measurement in the supplementary.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4835856&req=5

f2: Single-shot angular-resolved x-ray spectrum measured using spectroscopic x-ray imaging.(a) X-ray photon spectrum as a function of polar angle. (b) Mean energy of the x-rays as a function of polar angle. (c) Dependence of the spectral width (FWHM) on the polar angle. Electron beam parameters were: central energy −65 ± 1 MeV; energy spread (FWHM) −8.9 ± 0.1 MeV; and divergence (FWHM) −4.1 ± 0.4 mrad (measured on the LANEX screen). Blue curves on (b,c) show simulated dependences based on these electron beam parameters. Red curves on (b,c) show simulated dependences based on electron beam parameters, obtained from angular-resolved x-ray spectrum: central energy −66 ± 1 MeV; energy spread (FWHM) −8.5 ± 3.5 MeV; and divergence (FWHM) −2.1 ± 0.7 mrad. Error bars represent 95% confidence bands, calculated based on least-squares fits of spectral data. Photon flux at the source is 104. See details on this measurement in the supplementary.
Mentions: The spectroscopic x-ray imaging detector allowed us to measure angular-dependent ICS x-ray spectrum for every shot; the result is shown in Fig. 2(a). We fitted the spectra, corresponding to individual polar angles, with Gaussian functions, and extracted the resulting dependencies of central energy and energy spread on angle. The dependence of central energy of the x-rays on polar angle, shown in Fig. 2(b), arises from the dependence of the resonant scattered frequency on the polar angle (see Methods, eq. 2). The dependence of the spectral width on the polar angle, shown in Fig. 2(c), is more complex and requires accounting for both the spectral and angular characteristics of the electron beam.

Bottom Line: Reported here is a novel, non-destructive, single-shot method that overcame this problem.It employed an intense laser probe pulse, and spectroscopic imaging of the inverse-Compton scattered x-rays, allowing measurement of an ultra-low value for the normalized transverse emittance, 0.15 (±0.06) π mm mrad, as well as study of its subsequent growth upon exiting the accelerator.The technique and results are critical for designing multi-stage laser-wakefield accelerators, and generating high-brightness, spatially coherent x-rays.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Astronomy, University of Nebraska, Lincoln NE 68588, USA.

ABSTRACT
The recent combination of ultra-intense lasers and laser-accelerated electron beams is enabling the development of a new generation of compact x-ray light sources, the coherence of which depends directly on electron beam emittance. Although the emittance of accelerated electron beams can be low, it can grow due to the effects of space charge during free-space propagation. Direct experimental measurement of this important property is complicated by micron-scale beam sizes, and the presence of intense fields at the location where space charge acts. Reported here is a novel, non-destructive, single-shot method that overcame this problem. It employed an intense laser probe pulse, and spectroscopic imaging of the inverse-Compton scattered x-rays, allowing measurement of an ultra-low value for the normalized transverse emittance, 0.15 (±0.06) π mm mrad, as well as study of its subsequent growth upon exiting the accelerator. The technique and results are critical for designing multi-stage laser-wakefield accelerators, and generating high-brightness, spatially coherent x-rays.

No MeSH data available.


Related in: MedlinePlus