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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.


Related in: MedlinePlus

Layout of the experimental setup and a typical single-shot dataset.(a) Experimental setup. Spectral characteristics of an electron beam are measured using a magnetic spectrometer and a fluorescent LANEX screen. X-ray beam imaging is performed with high (0.4 mrad) angular resolution (as a function of polar angle θ) using the CdTe spectroscopic x-ray imaging detector. See Methods for additional information. (b) The x-ray profile measured with a CsI scintillator coupled to a 14-bit high-gain CCD. When the CdTe detector was operated, the CsI was removed from the path of the x-ray beam. (c) LANEX image of the dispersed electron beam. (d) Reconstructed electron beam spectrum based on the response function of the magnetic spectrometer. The beam has a charge of 2.4 ± 0.4 pC, central energy of 60 ± 1 MeV, and 10 ± 1% energy spread (FWHM). (d) Measured x-ray signal on the CdTe detector with charge sharing correction. Each dot represents a single photon event. (f) X-ray spectrum, measured with the CdTe detector (black, error bars represent standard deviations based on Poisson statistics), central energy is 85 ± 1 keV with 24 ± 2% energy spread (FWHM, averaged over 6-mrad cone) and simulated spectrum based on the electron beam spectrum (red). Figures (c–f) correspond to the same shot.
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f1: Layout of the experimental setup and a typical single-shot dataset.(a) Experimental setup. Spectral characteristics of an electron beam are measured using a magnetic spectrometer and a fluorescent LANEX screen. X-ray beam imaging is performed with high (0.4 mrad) angular resolution (as a function of polar angle θ) using the CdTe spectroscopic x-ray imaging detector. See Methods for additional information. (b) The x-ray profile measured with a CsI scintillator coupled to a 14-bit high-gain CCD. When the CdTe detector was operated, the CsI was removed from the path of the x-ray beam. (c) LANEX image of the dispersed electron beam. (d) Reconstructed electron beam spectrum based on the response function of the magnetic spectrometer. The beam has a charge of 2.4 ± 0.4 pC, central energy of 60 ± 1 MeV, and 10 ± 1% energy spread (FWHM). (d) Measured x-ray signal on the CdTe detector with charge sharing correction. Each dot represents a single photon event. (f) X-ray spectrum, measured with the CdTe detector (black, error bars represent standard deviations based on Poisson statistics), central energy is 85 ± 1 keV with 24 ± 2% energy spread (FWHM, averaged over 6-mrad cone) and simulated spectrum based on the electron beam spectrum (red). Figures (c–f) correspond to the same shot.

Mentions: The experimental setup is shown in Fig. 1(a). A high-energy, ultrashort pulse from a Ti:Sapphire laser system is split in two using a beamsplitter, each part is then independently compressed. The first pulse is used to accelerate electron beams in the double-stage gas target via the process of laser-wakefield acceleration. The second pulse scatters from the electron beam at an angle of 170 deg. and generates x-rays via the process of ICS6,26. A typical x-ray beam profile, obtained from the CsI detector, is shown in Fig. 1(b). A complete set of data from all detectors, obtained in a single shot, is shown in Fig. 1(c–f). The dispersed image of the electron beam on the LANEX screen, shown in Fig. 1(c), is used to obtain the spectrum of the electron beam, shown in Fig. 1(d). The image of the x-ray beam on the CdTe detector (with charge sharing correction) for a single shot is shown in Fig. 1(e). The pulse height information is converted to energy using the measured response function of the detector. The resulting x-ray spectrum is shown in Fig. 1(f) (red curve). The black curve in Fig. 1(f) shows the simulated x-ray spectrum. Spectroscopic imaging allowed us to precisely measure the x-ray energy spread, which was found to be 24 ± 2%. This energy spread is comparable to the x-ray bandwidth from conventional RF-LINAC-based Compton sources34, and, to the best of our knowledge, is the narrowest yet reported from an all-laser ICS x-ray light source. Prior results reported energy spreads of 40%5 and 50%6.


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)

Layout of the experimental setup and a typical single-shot dataset.(a) Experimental setup. Spectral characteristics of an electron beam are measured using a magnetic spectrometer and a fluorescent LANEX screen. X-ray beam imaging is performed with high (0.4 mrad) angular resolution (as a function of polar angle θ) using the CdTe spectroscopic x-ray imaging detector. See Methods for additional information. (b) The x-ray profile measured with a CsI scintillator coupled to a 14-bit high-gain CCD. When the CdTe detector was operated, the CsI was removed from the path of the x-ray beam. (c) LANEX image of the dispersed electron beam. (d) Reconstructed electron beam spectrum based on the response function of the magnetic spectrometer. The beam has a charge of 2.4 ± 0.4 pC, central energy of 60 ± 1 MeV, and 10 ± 1% energy spread (FWHM). (d) Measured x-ray signal on the CdTe detector with charge sharing correction. Each dot represents a single photon event. (f) X-ray spectrum, measured with the CdTe detector (black, error bars represent standard deviations based on Poisson statistics), central energy is 85 ± 1 keV with 24 ± 2% energy spread (FWHM, averaged over 6-mrad cone) and simulated spectrum based on the electron beam spectrum (red). Figures (c–f) correspond to the same shot.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Layout of the experimental setup and a typical single-shot dataset.(a) Experimental setup. Spectral characteristics of an electron beam are measured using a magnetic spectrometer and a fluorescent LANEX screen. X-ray beam imaging is performed with high (0.4 mrad) angular resolution (as a function of polar angle θ) using the CdTe spectroscopic x-ray imaging detector. See Methods for additional information. (b) The x-ray profile measured with a CsI scintillator coupled to a 14-bit high-gain CCD. When the CdTe detector was operated, the CsI was removed from the path of the x-ray beam. (c) LANEX image of the dispersed electron beam. (d) Reconstructed electron beam spectrum based on the response function of the magnetic spectrometer. The beam has a charge of 2.4 ± 0.4 pC, central energy of 60 ± 1 MeV, and 10 ± 1% energy spread (FWHM). (d) Measured x-ray signal on the CdTe detector with charge sharing correction. Each dot represents a single photon event. (f) X-ray spectrum, measured with the CdTe detector (black, error bars represent standard deviations based on Poisson statistics), central energy is 85 ± 1 keV with 24 ± 2% energy spread (FWHM, averaged over 6-mrad cone) and simulated spectrum based on the electron beam spectrum (red). Figures (c–f) correspond to the same shot.
Mentions: The experimental setup is shown in Fig. 1(a). A high-energy, ultrashort pulse from a Ti:Sapphire laser system is split in two using a beamsplitter, each part is then independently compressed. The first pulse is used to accelerate electron beams in the double-stage gas target via the process of laser-wakefield acceleration. The second pulse scatters from the electron beam at an angle of 170 deg. and generates x-rays via the process of ICS6,26. A typical x-ray beam profile, obtained from the CsI detector, is shown in Fig. 1(b). A complete set of data from all detectors, obtained in a single shot, is shown in Fig. 1(c–f). The dispersed image of the electron beam on the LANEX screen, shown in Fig. 1(c), is used to obtain the spectrum of the electron beam, shown in Fig. 1(d). The image of the x-ray beam on the CdTe detector (with charge sharing correction) for a single shot is shown in Fig. 1(e). The pulse height information is converted to energy using the measured response function of the detector. The resulting x-ray spectrum is shown in Fig. 1(f) (red curve). The black curve in Fig. 1(f) shows the simulated x-ray spectrum. Spectroscopic imaging allowed us to precisely measure the x-ray energy spread, which was found to be 24 ± 2%. This energy spread is comparable to the x-ray bandwidth from conventional RF-LINAC-based Compton sources34, and, to the best of our knowledge, is the narrowest yet reported from an all-laser ICS x-ray light source. Prior results reported energy spreads of 40%5 and 50%6.

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