Abstract
A monoenergetic gamma-ray (MEGa-ray) source based on Compton scattering, targeting nuclear physics applications such as nuclear resonance fluorescence, has been constructed and commissioned at Lawrence Livermore National Laboratory. In this paper, the overall architecture of the system, as well as some of the design decisions (such as laser pulse lengths and interaction geometry) made in the development of the source, are discussed. The performances of the two laser systems (one for electron production, one for scattering), the electron photoinjector, and the linear accelerator are also detailed, and initial $\ensuremath{\gamma}$-ray results are presented.
Highlights
A monoenergetic gamma-ray (MEGa-ray) source based on Compton scattering, targeting nuclear physics applications such as nuclear resonance fluorescence, has been constructed and commissioned at Lawrence Livermore National Laboratory
The Interaction laser system (ILS) subsystem is similar to the Photoinjector drive laser (PDL); it is fed by the same oscillator and uses similar fiber-based amplifiers but operates at 1064 nm, instead of the 1053 nm of the PDL
Assuming a plane wave with wavelength impinging upon an electron traveling with relativistic factor at a 180 interaction angle, performing the Lorentz transformation to the electron rest frame, Compton scattering the laser off the electron, transforming back into the lab frame, yields the scattered photon energy as a function of angle relative to the electron beam direction: E ðÞ
Summary
The T-REX source requires two laser systems that are precisely synchronized: one to generate the electron beam at the photocathode (the ‘‘photoinjector drive laser’’ or PDL), and one to scatter off the focused electron beam at the end of the linac (the ‘‘interaction laser system’’ or ILS). The final fiber amplifier delivers 30 J pulses at 10 kHz. Though the PDL and ILS chirped fiber Bragg gratings both stretch their respective pulses to the few-ns level, the ILS bandwidth is much narrower (0.8 nm vs 8 nm), giving it approximately 10 times the temporal dispersion. Though the PDL and ILS chirped fiber Bragg gratings both stretch their respective pulses to the few-ns level, the ILS bandwidth is much narrower (0.8 nm vs 8 nm), giving it approximately 10 times the temporal dispersion The second measure of the temporal profile came from recording each of the individual pulse energies at the output of the hyper-Michelson stacker, which is done by selectively blocking various delay arms Using this set of energies, coupled with the width measured in the cross correlation, to define Gaussian pulses to sum, the expected pulse shape is shown in the upper plot of Fig. 4 (top-dashed line). Approximately 50% of the 2! energy should be in a 16 ps central peak with the rest of the energy contained in the wide pedestal
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