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

Abstract 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.

[1]  Ferenc Krausz,et al.  Emittance and divergence of laser wakefield accelerated electrons , 2010 .

[2]  D. Habs,et al.  Miniature magnetic devices for laser-based, table-top free-electron lasers , 2007 .

[3]  Ursula van Rienen,et al.  3D Space-charge model for GPT simulations of high-brightness electron bunches , 2003 .

[4]  R. J. Clarke,et al.  Image plate response for conditions relevant to laser–plasma interaction experiments , 2008 .

[5]  P. P. Rajeev,et al.  Gamma-rays from harmonically resonant betatron oscillations in a plasma wake , 2011 .

[6]  Ferenc Krausz,et al.  Laser-driven soft-X-ray undulator source , 2009 .

[7]  K. Nakamura,et al.  GeV electron beams from a centimetre-scale accelerator , 2006 .

[8]  B. Ersfeld,et al.  High resolution, single shot emittance measurement of relativistic electrons from laser-driven accelerator , 2011, Optics + Optoelectronics.

[9]  R Bingham,et al.  Efficiency and energy spread in laser-wakefield acceleration. , 2005, Physical review letters.

[10]  Edward Ott,et al.  Self‐focusing of short intense pulses in plasmas , 1987 .

[11]  Sebastian M. Pfotenhauer,et al.  A compact synchrotron radiation source driven by a laser-plasma wakefield accelerator , 2008 .

[12]  M. R. Islam,et al.  Narrow spread electron beams from a laser-plasma wakefield accelerator , 2009, Optics + Optoelectronics.

[13]  Esarey,et al.  Nonlinear interaction of intense laser pulses in plasmas. , 1989, Physical review. A, Atomic, molecular, and optical physics.

[14]  V Malka,et al.  Emittance measurements of a laser-wakefield-accelerated electron beam. , 2004, Physical review letters.

[15]  Wei Lu,et al.  OSIRIS: A Three-Dimensional, Fully Relativistic Particle in Cell Code for Modeling Plasma Based Accelerators , 2002, International Conference on Computational Science.

[16]  Hitoshi Kobayashi,et al.  High-precision pepper-pot technique for a low-emittance electron beam , 1992 .

[17]  M. Tzoufras,et al.  Generating multi-GeV electron bunches using single stage laser wakefield acceleration in a 3D nonlinear regime , 2007 .

[18]  A. E. Dangor,et al.  Monoenergetic beams of relativistic electrons from intense laser–plasma interactions , 2004, Nature.

[19]  Antoine Rousse,et al.  Production of a keV x-ray beam from synchrotron radiation in relativistic laser-plasma interaction. , 2004, Physical review letters.

[20]  R Issac,et al.  Radiation sources based on laser–plasma interactions , 2006, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[21]  S. M. Wiggins,et al.  Low emittance, high brilliance relativistic electron beams from a laser-plasma accelerator. , 2010, Physical review letters.

[22]  W. A. Gillespie,et al.  High quality electron beams from a laser wakefield accelerator , 2010, CLEO/QELS: 2010 Laser Science to Photonic Applications.

[23]  T. Tajima,et al.  Laser Electron Accelerator , 1979 .

[24]  Z. Najmudin,et al.  Current filamentation instability in laser wakefield accelerators. , 2011, Physical review letters.

[25]  V Malka,et al.  Controlling the phase-space volume of injected electrons in a laser-plasma accelerator. , 2009, Physical review letters.

[26]  Y. Glinec,et al.  Controlled injection and acceleration of electrons in plasma wakefields by colliding laser pulses , 2006, Nature.

[27]  Erik Lefebvre,et al.  Few femtosecond, few kiloampere electron bunch produced by a laser-plasma accelerator , 2011 .

[28]  W. W. Buechner,et al.  Broad‐Range Magnetic Spectrograph , 1956 .

[29]  K. Schmid.  Supersonic Micro-Jets And Their Application to Few-Cycle Laser-Driven Electron Acceleration , 2009 .