Limits...
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.


Evolution of the electron beam (divergence and normalized transverse emittance) after exit from the plasma.The divergence, calculated from the rate of change of the transverse beam size, increases rapidly over the first few mm and then reaches a limiting value while the emittance monotonically increases. Labels A and B identify locations that correspond to experimental measurements. The beam at location A is probed by the ICS technique, while the measurement at location B relies on the angular size measured on a fluorescent screen (assuming mostly straight electron trajectories). The electron beam is assumed to have an energy of 65 MeV, energy spread of 10%, and charge of 10 pC.
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f4: Evolution of the electron beam (divergence and normalized transverse emittance) after exit from the plasma.The divergence, calculated from the rate of change of the transverse beam size, increases rapidly over the first few mm and then reaches a limiting value while the emittance monotonically increases. Labels A and B identify locations that correspond to experimental measurements. The beam at location A is probed by the ICS technique, while the measurement at location B relies on the angular size measured on a fluorescent screen (assuming mostly straight electron trajectories). The electron beam is assumed to have an energy of 65 MeV, energy spread of 10%, and charge of 10 pC.

Mentions: The evolution of the beam is calculated using a particle-tracking code based on an adaptive mesh and including the effects of space charge35. The measured electron beam parameters (energy, energy spread, spot-size, and divergence) fix the initial emittance of the beam. We assumed the origin to be the point where the plasma effects become negligible. Figure 4 shows the evolution of beam divergence and emittance as a function of propagation distance. The former increases rapidly over the first few mm of propagation and then reaches a limiting value. This arises from the fact that as the transverse spatial extent of the beam increases, the space-charge driven force reduces in magnitude and eventually becomes negligible. The transverse emittance, determined by both the size and angular spread of the beam, increases monotonically, and is more than doubled at 1 m compared to that at the source. In our experiments, we performed measurements of the electron beam parameters at locations A and B, the former by means of ICS, and the latter using a fluorescent screen. It is clear that the divergence growth becomes negligible beyond 3 cm. The expansion rate significantly increases for beams with higher charge or lower energy. We investigated the effects of the pulse duration on the computed results and found them to be not significant within a factor of two change in the assumed temporal duration of the electron pulse (10 fs).


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)

Evolution of the electron beam (divergence and normalized transverse emittance) after exit from the plasma.The divergence, calculated from the rate of change of the transverse beam size, increases rapidly over the first few mm and then reaches a limiting value while the emittance monotonically increases. Labels A and B identify locations that correspond to experimental measurements. The beam at location A is probed by the ICS technique, while the measurement at location B relies on the angular size measured on a fluorescent screen (assuming mostly straight electron trajectories). The electron beam is assumed to have an energy of 65 MeV, energy spread of 10%, and charge of 10 pC.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Evolution of the electron beam (divergence and normalized transverse emittance) after exit from the plasma.The divergence, calculated from the rate of change of the transverse beam size, increases rapidly over the first few mm and then reaches a limiting value while the emittance monotonically increases. Labels A and B identify locations that correspond to experimental measurements. The beam at location A is probed by the ICS technique, while the measurement at location B relies on the angular size measured on a fluorescent screen (assuming mostly straight electron trajectories). The electron beam is assumed to have an energy of 65 MeV, energy spread of 10%, and charge of 10 pC.
Mentions: The evolution of the beam is calculated using a particle-tracking code based on an adaptive mesh and including the effects of space charge35. The measured electron beam parameters (energy, energy spread, spot-size, and divergence) fix the initial emittance of the beam. We assumed the origin to be the point where the plasma effects become negligible. Figure 4 shows the evolution of beam divergence and emittance as a function of propagation distance. The former increases rapidly over the first few mm of propagation and then reaches a limiting value. This arises from the fact that as the transverse spatial extent of the beam increases, the space-charge driven force reduces in magnitude and eventually becomes negligible. The transverse emittance, determined by both the size and angular spread of the beam, increases monotonically, and is more than doubled at 1 m compared to that at the source. In our experiments, we performed measurements of the electron beam parameters at locations A and B, the former by means of ICS, and the latter using a fluorescent screen. It is clear that the divergence growth becomes negligible beyond 3 cm. The expansion rate significantly increases for beams with higher charge or lower energy. We investigated the effects of the pulse duration on the computed results and found them to be not significant within a factor of two change in the assumed temporal duration of the electron pulse (10 fs).

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.