Optically controlled laser–plasma electron accelerator for compact gamma-ray sources

Authors

S. Y. Kalmykov, University of Nebraska - LincolnFollow
X. Davoine, CEA, DAM, DIF
I. Ghebregziabher, The Pennsylvania State University
B. A. Shadwick, University of Nebraska - LincolnFollow

ORCID IDs

S Y Kalmykov

Date of this Version

2018

Citation

New J. Phys. 20 (2018) 023047

Comments

© 2018 The Author(s).

Open access

https://doi.org/10.1088/1367-2630/aaad57

Abstract

Generating quasi-monochromatic, femtosecond γ-ray pulses via Thomson scattering (TS) demands exceptional electron beam (e-beam) quality, such as percent-scale energy spread and five-dimensional brightness over 10¹⁶ Am^–2.We show that near-GeV e-beams with these metrics can be accelerated in a cavity of electron density, driven with an incoherent stack of Joule-scale laser pulses through ammsize, dense plasma (n₀ ~ 10¹⁹ cm⁻³). Changing the time delay, frequency difference, and energy ratio of the stack components controls the e-beam phase space on the femtosecond scale, while the modest energy of the optical driver helps afford kHz-scale repetition rate at manageable average power. Blue-shifting one stack component by a considerable fraction of the carrier frequency makes the stack immune to self-compression. This, in turn, minimizes uncontrolled variation in the cavity shape, suppressing continuous injection of ambient plasma electrons, preserving a single, ultra-bright electron bunch. In addition, weak focusing of the trailing component of the stack induces periodic injection, generating, in a single shot, a train of bunches with controllable energy spacing and femtosecond synchronization. These designer e-beams, inaccessible to conventional acceleration methods, generate, via TS, gigawatt γ-ray pulses (or multi-color pulse trains) with the mean energy in the range of interest for nuclear photonics (4–16MeV), containing over 10⁶ photons within a microsteradian-scale observation cone.