Demonstration of a Narrow Energy Spread,∼0.5  GeVElectron Beam from a Two-Stage Laser Wakefield Accelerator

Abstract

Laser wakefield acceleration of electrons holds great promise for producing ultracompact stages of GeV scale, high-quality electron beams for applications such as x-ray free electron lasers and high-energy colliders. Ultrahigh intensity laser pulses can be self-guided by relativistic plasma waves (the wake) over tens of vacuum diffraction lengths, to give >1 GeV energy in centimeter-scale low density plasmas using ionization-induced injection to inject charge into the wake even at low densities. By restricting electron injection to a distinct short region, the injector stage, energetic electron beams (of the order of 100 MeV) with a relatively large energy spread are generated. Some of these electrons are then further accelerated by a second, longer accelerator stage, which increases their energy to ∼0.5 GeV while reducing the relative energy spread to <5% FWHM.

Concurrence of monoenergetic electron beams and bright X-rays from an evolving laser-plasma bubble

“…Image plate 2 was pasted on the side of the magnet to measure the electron energy spectrum from 6 to 100 MeV. Image plates 3 and 4 were located at 155 and 205 cm away from the exit of the gas jet, respectively, which provided unambiguous energy spectrum measurement of the high-energy electrons (8,32). A 1.5-mm-thick Be-window was used to seal the vacuum.…”

Energy Spread Reduction of Electron Beams Produced via Laser Wake

“…If electron beams produced from LWFA are ever to be comparable to those produced in conventional RF linear accelerators the energy spread must be reduced to the percent level. The next chapter describes a modification to the gas cell target platform that achieves this goal, generating a 0.46 GeV electron beam with 5% energy spread using the ionization-induced injection mechanism [17].…”

“…This thesis presents an experimental investigation of laser wakefield acceleration in the blowout regime which produced for the first time a narrow energy spread beam of ∼0.5 GeV, ionization-injected electrons from LWFA [17].…”

“…This scheme has successfully allowed electron trapping at densities where self-trapping did not occur, i.e. below 4x10 18 cm −3 [17,13], and will be discussed in greater detail in the experimental results chapters where the technique was employed to increase the electron beam energy and reduce the energy spread.…”

“…Alternative injection schemes relying on ionization of higher-Z gases (ionization-induced injection) [15,16] than the traditional H 2 or He plasmas have been shown to be effective at densities several factors below the self-trapping threshold, but have generally led to large energy spread electron beams reminiscent of SMLWFA [13]. However, by tailoring the longitudinal gas composition of the target to limit the ionization-induced injection region, a 0.46 GeV electron beam with 5% energy spread has successfully been demonstrated [17]. This technique should be directly scalable to multi-GeV electron energies with presently available laser systems, and even higher energies once short-pulse laser systems advance to petawatt power capabilities.…”