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>ITFIP>Onde Plasma

Acceleration of electrons to ultra-relativistic energies in a plasma wave created by laser wakefield

(B. Cros, G. Maynard, K. Cassou, F. Wojda, in collaboration with the group of C.G. Wahlström, LLC-Suède, et N. Andreev du IHED Moscou)

  Laser plasma acceleration is an extremely active field of research. The results obtained over the last few years, demonstrating electron acceleration in the range 100 MeV up to 1 GeV, pave the way to a broad range of applications and have attracted the attention of other communities, such as particle and accelerator physicists. This fostered the structuring of the scientific community in Europe around a few ambitious projects. The leader of the ITFIP group (B. Cros) has taken an active role in this coordination:

  • Coordination of the working group on Advanced and Novel Accelerator Development (ANAD) din the European collaborative network ELAN started in 2004 in the frame of the I3 CARE, with the objective to develop exchanges between plasma and accelerator physicists, evaluate the progress of the field, define research strategy, prepare collaborative projects and contribute to the definition of future laser plasma accelerators.
  • Coordination of the European project EuroLEAP, started in September 2006, with the objective to control the properties of the accelerated electron beam up to energies in the GeV range, in terms of spectral quality, emittance, and pulse duration. This project brings together 11 European laboratories with complementary expertise on intense laser, plasmas, accelerators (transport of electron beams) and particle physics (detectors), necessary to the achievement of a laser plasma accelerator.

  On-going experimental and theoretical studies of the ITFIP group on electron beam acceleration are focused on the understanding and control of the structure and stability of the plasma waves able to accelerate electrons with gradients of the order of 10 GeV/m. Simulations have demonstrated that the laser propagates in a capillary tube used as waveguide with a weak attenuation over several centimetres and without phase dispersion. Simulations and analytical calculation have shown that optical diagnostics can be used to characterise the quality of the accelerating electric fields obtained in the linear regime guided over several centimetres. The pump beam creating the plasma wave travels in a plasma which density changes during the pulse duration. This density variation, associated to the creation of the plasma wave, is maximum at the back of the pulse and induces a spectral shift of the pump beam toward the red side of the spectrum, which can be measured after a few centimetres of propagation.

  The plasma wave was measured over lengths of propagation up to 8 cm in an experiment at the Lund Laser Center (Sweden) in January 2008. The success of this experiment is largely due to the improvement of the laser beam quality and stability: a deformable mirror has been implemented, and the main sources of vibration in the laser amplification system have been identified and removed; a device to control actively the pointing stability of the laser in the focal plane is being implemented.


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