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Accueil > Séminaires > Séminaires passés > Séminaires de 2008 > Laser Plasma Accelerators : Principle and Applications

Victor Malka

Laser Plasma Accelerators : Principle and Applications

Jeudi 27 novembre 2008, à 16h00

In laser-plasma electron accelerators, a longitudinal accelerating electric field of the order of 300 GV/m is produced by space charge separation driven by the ponderomotive force of an ultra-short and ultra-intense laser. We have shown recently that electrons from the plasma itself can be injected into the wakefield with a sufficient initial energy so that they can be trapped and accelerated. Experimentally, two injection mechanisms have permitted the generation of high quality quasi-monoenergetic electron beams. In the first mechanism, the so-called “bubble regime”, a single laser pulse is used. The second mechanism is based on the use of several laser pulses. The first laser pulse, the “pump” pulse creates a wakefield whereas the second laser, the “injection” pulse will only be used for injecting electrons. Although this scheme is more complicated experimentally, it offers more flexibility : experiments have shown that the e-beam energy can be tuned from 10 to 250 MeV. The e-beam has a quasi-monoenergetic distribution with energy spread in the 1 to 10 % range, charges in the 10-100 pC range and its parameters are stable within 5-10%. This approach is promising for the control of the e-beam parameters, it allows to tune the charge as well as the energy spread.

Electron beams produced with laser plasma accelerators have properties of interest in many fields such as material science, medicine, and chemistry. The shortness of the electron beam is of interest for example for fast chemistry. For material science, the collimation, the charge and the energy of electron beam which, by interacting with a dense target, can produce a sub-millimetric source of energetic photons (-rays) much smaller than those available with conventional accelerators. Such sources of radiation are of interest for a non destructive inspection of dense matter in aircraft or automobile industries. In medicine, several millions of patients with cancer tumours are treated in the world with X rays with energies of a few MeV. This treatment represents the majority of ionising radiations used for cancer radiotherapy. They are used successfully in many hospitals because they are produced using flexible, compact and affordable machines. Higher quality, Very High Energy (VHE) electron beams, such as those produced by laser plasma accelerator, could be used for radiotherapy and provide better clinical results.

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V. Malka et al., Nature Physics 4, (2008)