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Narrow spread electron beams from a laser-plasma wakefield accelerator

Wiggins, S. M. and Anania, M. P. and Brunetti, E. and Cipiccia, S. and Ersfeld, B. and Islam, M and Issac, R. C. and Raj, G. and Shanks, Richard and Vieux, G. and Welsh, G. H. and Gillespie, W. A. and MacLeod, A. M. and Jaroszynski, D. A. (2009) Narrow spread electron beams from a laser-plasma wakefield accelerator. In: Proceedings of SPIE 7359. SPIE--The International Society for Optical Engineering., p. 735914. ISBN 9780819476333

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Abstract

The Advanced Laser-Plasma High-Energy Accelerators towards X-rays (ALPHA-X) programme is developing laser-plasma accelerators for the production of ultra-short electron bunches with subsequent generation of incoherent radiation pulses from plasma and coherent short-wavelength radiation pulses from a free-electron laser (FEL). The first quantitative measurements of the electron energy spectra have been made on the University of Strathclyde ALPHA-X wakefield acceleration beam line. A high peak power laser pulse (energy 900 mJ, duration 35 fs) is focused into a gas jet (nozzle length 2 mm) using an F/16 spherical mirror. Electrons from the laser-induced plasma are self-injected into the accelerating potential of the plasma density wake behind the laser pulse. Electron beams emitted from the plasma have been imaged downstream using a series of Lanex screens positioned along the beam line axis and the divergence of the electron beam has been measured to be typically in the range 1-3 mrad. Measurements of the electron energy spectrum, obtained using the ALPHA-X high resolution magnetic dipole spectrometer, are presented. The maximum central energy of the monoenergetic beam is 90 MeV and r.m.s. relative energy spreads as low as 0.8% are measured. The mean central energy is 82 MeV and mean relative energy spread is 1.1 A theoretical analysis of this unexpectedly high electron beam quality is presented and the potential impact on the viability of FELs driven by electron beams from laser wakefield accelerators is examined.