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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.

No MeSH data available.


The x-ray and electron beams’ source size measurement.(a) Image of the test pattern (taken with an image plate). White box shows the area used for the source size analysis. (b) Intensity profile across the edge of the pattern (black squares) and it fits with Gauss error functions (solid lines). Red curve corresponds to an optimal fit.
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f3: The x-ray and electron beams’ source size measurement.(a) Image of the test pattern (taken with an image plate). White box shows the area used for the source size analysis. (b) Intensity profile across the edge of the pattern (black squares) and it fits with Gauss error functions (solid lines). Red curve corresponds to an optimal fit.

Mentions: Knife-edge measurements were performed to determine the source size of both the x-ray and electron beams (it should be the same for both, since the scattering laser pulse is much larger than the electron beam at the interaction point). A 2-mm thick steel pattern with different slits was placed at a distance of 2 m from the source; its shadows were imaged at a distance of 5.3 m with an image plate (30-um pixel size), yielding a magnification of 2.7. To obtain sufficiently high signal on the image plate, 100 shots were accumulated. An area with an edge shadow on the captured image (shown as a white box on Fig. 3(a)) was chosen, and its profile was plotted (see Fig. 3(b)). Each point on the profile plot shows the median of a row on the image plate picture. The use of the median improves the signal-to-noise ratio of the signal by filtering out outliers. The edge shadow profile is a convolution of the intensity distribution of the x-ray source at its origin and the edge transmission. Assuming a Gaussian intensity distribution of the source and step-transmission function of the edge, one should expect a Gauss error function as a shadow profile, with a width depending on the x-ray’s source size. After pointing fluctuation correction (2 mrad RMS), we obtained σr = 4 ± 1 um (RMS) as a final value for the source size. Such a small source size is ideal for radiography, since it permits resolution of microscopic features15. This also represents an improvement on the best results obtained by means of a different approach: namely, scanning the scattering laser pulse across the electron beam (5 ± 3 um RMS)26. Even though the presented measurement is multiple-shot (and might therefore overestimate source-size), it can be performed in a single shot given a high enough x-ray photon flux.


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)

The x-ray and electron beams’ source size measurement.(a) Image of the test pattern (taken with an image plate). White box shows the area used for the source size analysis. (b) Intensity profile across the edge of the pattern (black squares) and it fits with Gauss error functions (solid lines). Red curve corresponds to an optimal fit.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: The x-ray and electron beams’ source size measurement.(a) Image of the test pattern (taken with an image plate). White box shows the area used for the source size analysis. (b) Intensity profile across the edge of the pattern (black squares) and it fits with Gauss error functions (solid lines). Red curve corresponds to an optimal fit.
Mentions: Knife-edge measurements were performed to determine the source size of both the x-ray and electron beams (it should be the same for both, since the scattering laser pulse is much larger than the electron beam at the interaction point). A 2-mm thick steel pattern with different slits was placed at a distance of 2 m from the source; its shadows were imaged at a distance of 5.3 m with an image plate (30-um pixel size), yielding a magnification of 2.7. To obtain sufficiently high signal on the image plate, 100 shots were accumulated. An area with an edge shadow on the captured image (shown as a white box on Fig. 3(a)) was chosen, and its profile was plotted (see Fig. 3(b)). Each point on the profile plot shows the median of a row on the image plate picture. The use of the median improves the signal-to-noise ratio of the signal by filtering out outliers. The edge shadow profile is a convolution of the intensity distribution of the x-ray source at its origin and the edge transmission. Assuming a Gaussian intensity distribution of the source and step-transmission function of the edge, one should expect a Gauss error function as a shadow profile, with a width depending on the x-ray’s source size. After pointing fluctuation correction (2 mrad RMS), we obtained σr = 4 ± 1 um (RMS) as a final value for the source size. Such a small source size is ideal for radiography, since it permits resolution of microscopic features15. This also represents an improvement on the best results obtained by means of a different approach: namely, scanning the scattering laser pulse across the electron beam (5 ± 3 um RMS)26. Even though the presented measurement is multiple-shot (and might therefore overestimate source-size), it can be performed in a single shot given a high enough x-ray photon flux.

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.