Abstracts Brochure - CERN

WEPLS — Poster Session 28-Jun-06 16:00 - 18:00
scheme, the energy of an appropriately phased trailing bunch could be multiplied by a large factor, of the order of the
number of drive bunches. Experimental results including plasma density diagnostic using Stark broadening, beam
bunching using CTR and energy gain and loss measurements will be presented.
*V. Yakimenko et al., Phys. Rev. Lett. 91, 014802 (2003).
Longitudinal Phase Space Measurements and Application to Beam-plasma Physics
To be contributed
C.D. Barnes (SLAC)
Studies into Mono-Energetic Electrons Produced by Laser Wakefield Acceleration
Monoenergetic electron beams are of great
interest, particularly as a source of high frequency
coherent light. Recent work has
shown that such beams can be produced in
a shorter distance than conventional acceler-
C.D. Murphy, P.A. Norreys (CCLRC/RAL) K. Kamperidis, K.M.
Krushelnick, S. P. D. Mangles, Z. Najmudin, A. G. R. Thomas (Imperial
College of Science and Technology, Department of Physics)
ators using laser driven plasma waves*. Here we present a detailed study of how, in this scheme, electron bunch
characteristics change as plasma and laser parameters are varied. The experiment used up to 600mJ of laser light in
40fs (15TW) which was focused using two different geometries. This allowed the focal spot size and hence the laser
intensity within the focus to be varied in the range 10 17 – 10 19 W/cm 2 . By controlling the backing pressure of the
gas jet a range of plasma densities were achievable. It was found that within a small density range it was possible to
produce a monoenergetic energy spectrum. Shot to shot variation limited the usefulness of the beam; some recent
results suggest how this can be improved. Simulations of experimental conditions show the how optimization of
laser and plasma parameters can help stabilize the output from a laser plasma accelerator.
*S.P.D. Mangles et al., Nature 431, 535-538, (2004).
Improvement of Electron Generation from a Laser Plasma Cathode through Modified Preplasma
Conditions Using an Artificial Prepulse
We have been studying the effects of laser
prepulses, plasma cavity formation, wave
breaking processes in the laser plasma acceleration.
It is important to control the preplasma
conditions, so as to stabilize the laser
K. Kinoshita, T. Hosokai, K. Kobayashi, A. Maekawa, T. Ohkubo,
T. Tsujii, M. Uesaka (UTNL) A. Yamazaki (KURRI) A.G. Zhidkov
(NIRS)
plasma acceleration. The modification of the conditions of the laser plasma interaction through an artificial prepulse,
magnetic fields, and/or gas density modulation will affect on the characteristics of accelerated electron beams. As the
first step, we carry out experiments with an artificial prepulse. If a shockwave driven by the artificial prepulse matches
the main pulse foccal position, localized wave breaking may occur effectively, and consequent electron generation will
be enhanced. We use a pulse with 10% energy of the main pulse and 300 ps duration to be focused on the interaction
point of the gas jet, to change the plasma distribution there. Using the single-shot diagnosis, we investigate the
mechanism and technique to improve the properties of electron beams. We observed a strong correlation between
the generation of monoenergetic electrons and optical guiding of the main pulse, during the interaction of 11 TW 37
fs laser pulse and He gas jet.
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