XXXV international conference on plasma physics and CF, February 11 – 15, 2008, Zvenigorod.
CONTROLLED ELECTRON INJECTION INTO THE BREAKING WAKE WAVE VIA
PLASMA DENSITY GRADIENT
Brantov A.V., Bychenkov V.Yu, *Bulanov S.V., *Esirkepov T.
P.N. Lebedev Physics Institute of RAS, Moscow, Russia, brantov@sci.lebedev.ru
*
Kansai Photon Science Institute, Japan Atomic Energy Agency, Kyoto, 619-0215 Japan
The laser wakefield accelerator (LWFA) [1] concept is one of the most promising approaches for
compact higher-energy electron sources. In the conventional LWFA scheme the properly injected
electrons are accelerated by strong wake plasma wave excited by a short relativistic laser pulse. A
production of high quality electron beams requires the electron injection into the acceleration phase
of the wake field, which can be achieved ether by standard external electron injection or by selfinjection due to longitudinal or transverse wake wave breaking. To control electron self-injection in
the wake field it was also proposed to use plasma inhomogeneity along propagation direction of the
laser pulse. Substantial contribution to improvement of the LWFA scheme could be made with
controlled electron injection into the breaking wake wave. Here we associate this with electron selfinjection in the wake wave due to the tailored plasma density profile as proposed in Refs. [2,3]. In
this scheme two main mechanisms are responsible for the electron injection. There are wave
breaking due to gradually decreasing of the wake wave phase velocity at the smooth density
gradient [2] and wave breaking due to the phase mixing at the plasma density discontinuity [3]. In
this report on the base of 2D PIC simulation we present trapping condition analysis for electrons
injected due to wake wave breaking at the density inhomogeneity. We show that wave breaking at
the sharp density gradient not necessary results in electron trapping. The optimal conditions for the
acceleration of electrons injected at a descending plasma density region have been found that
demonstrates good quality of the electron beam produced at the optimal density gradient and
accelerated behind it in the homogeneous plasma. Space-temporal, angular and energy
characteristics of the accelerated electron bunch are presented.
This work was partly supported by the Russian Foundation for Basic Research (Grant No 06-0216103).
References
[1]. T. Tajima, J.M. Dawson, Laser Electron Accelerator // Phys. Rev. Lett. 1979 V. 43, P. 267.
[2]. S.V. Bulanov, N. Naumova, F. Pegoraro, J. Sakai, Particle injection into the wave
acceleration phase due to nonlinear wake wave breaking // Phys. Rev. E 1998 V. 58, P.
R5257.
[3]. H. Suk, N. Barov, J.B. Rosenzweig, E. Esarey, Plasma Electron Trapping and Acceleration in
a PlasmaWake Field Using a Density Transition // Phys. Rev. Lett. 2001 V. 86, P. 1011.
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