High resolution electron beam measurements on the ALPHA-X laser–plasma wakefield accelerator

Gregor H. Welsh, Mark Wiggins, Riju Issac, Enrico Brunetti, Grace Manahan, Mohammad Islam, Silvia Cipiccia, Constantin Aniculaesei, Bernhard Ersfeld, Dino Jaroszynski

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)


The Advanced Laser–Plasma High-Energy Accelerators towards X-rays
(ALPHA-X) programme at the University of Strathclyde is developing laser–
plasma accelerators for the production of ultra-short high quality electron bunches. Focussing such LWFA bunches into an undulator, for example, requires particular attention to be paid to the emittance, electron bunch duration and energy spread. On the ALPHA-X wakefield accelerator beam line, a high intensity ultra-short pulse from a 30 TW Ti:Sapphire laser is focussed into a helium gas jet to produce femtosecond duration electron bunches in the range of 90–220 MeV. Measurements of the electron energy spectrum, obtained using a high resolution magnetic dipole spectrometer, show electron bunch r.m.s. energy spreads down to 0.5%. A pepper-pot mask is used to obtain transverse emittance measurements of a 128±3 MeV mono-energetic electron beam. An average normalized emittance of εrms,x,y = 2.2±0.7, 2.3±0.6 π-mm-mrad is measured, which is comparable to that of a conventional radio-frequency accelerator. The best measured emittance of εrms,x, = 1.1±0.1 π-mm-mrad corresponds to the resolution limit of the detection system. 3D particle-in-cell simulations of the ALPHA-X accelerator partially replicate the generation of low emittance, low energy spread bunches with charge less than 4 pC and gas flow simulations indicate both long density ramps and shock formation in the gas jet nozzle.
Original languageEnglish
Pages (from-to)393-399
Number of pages7
JournalJournal of Plasma Physics
Issue numberspecial issue 04
Early online date27 Feb 2012
Publication statusPublished - 2012


  • high resolution
  • electron beam measurements
  • alpha-x
  • laser–plasma wakefield accelerator
  • ultra-short high quality electron bunches


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