Electron beam quality masurements on the ALPHA-X Laser-plasma wakefield accelerator

Welsh, Gregor H. and Anania, Maria Pia and Aniculaesei, Constantin and Brunetti, Enrico and Burgess, Ronan Timothy Liam and Cipiccia, Silvia and Clark, David and Ersfeld, Bernhard and Islam, Mohammad and Issac, Riju and Manahan, Grace and McCanny, Thomas and Raj, Gaurav and Reitsma, Albert and Shanks, Richard and Vieux, Gregory and Wiggins, Mark and Jaroszynski, Dino and Gillespie, W. A. and MacLeod, A. M. and van der Geer, S.B. and de Loos, M. J.; (2010) Electron beam quality masurements on the ALPHA-X Laser-plasma wakefield accelerator. In: IPAC 2010 contributions to the proceedings. IPAC/ACFA, JPN, pp. 1146-1148. ISBN 9789290833529

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The Advanced Laser-Plasma High-Energy Accelerators towards X-rays (ALPHA-X) programme at the University of Strathclyde is developing laser-plasma wakefield accelerators to produce high energy, ultra-short duration electron bunches as drivers of radiation sources. Coherent emission will be produced in a free-electron laser by focussing the ultra-short electron bunches into an undulator. To achieve net gain, high peak current, low energy spread and low emittance are required. 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 80 - 200 MeV. Beam transport is monitored using a series of Lanex screens positioned along the beam line. 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 r 4 MeV and mean energy spread is 1.1 r 0.4%. We also present pepper-pot measurements of the normalised transverse emittance where mono-energetic electrons are passed through an array of 52ȝm diameter holes in tungsten. The analysis of the pepper-pot results sets an upper limit for the normalised emittance at 5.5 ± 1ʌ mm mrad for an 82 MeV beam. With further acceleration to 1 GeV, the relative energy spread will reduce giving beam parameters that indicate the feasibility of a compact X-ray FEL driven by a plasma-wakefield accelerator.