Longitudinal
electron bunch compression schemes using plasma wakefields have been
proposed so far by Andreev et al. [1] and Ferrario et al. [2]. In these
schemes the bunch experiences a compression force due to a gradient
of the longitudinal electric field of the wakefield excited by an ultrashort
and ultraintense laser pulse. In order for these schemes to be effective
some relationships between the bunch injection energy and length and
the wakefield wavelength and amplitude must be satisfied.
A limit of the schemes cited above is the fact that the initial bunch
length must be much smaller than the wavelength, which is linked to
the wakefield phase velocity. Such a phase velocity should be linked
to the initial bunch speed and the wake electric field, in order for
the electrons to remain in the focusing and compressing region of the
wake.
In this talk a novel compression scheme is presented, supported by 1D
simulations. By noting that the phase velocity of the wakefield in a
plasma of nonuniform background density does vary in space, it is possible
to relax the relation linking the wakefield wavelength to the phase
velocity, thus enabling to excite long wavelength but slowly running
wakefields thus improving the compressing performances of the plasma
wakefield.
A multi-dimensional fluid simulation code including beam-charge as well
as density inhomogeneity effects is under development.
[1] N.E. Andreev, S.V. Kuznetsov and I.V. Pogorelsy, ?Monoenergetic
laser wakefield acceleration?, PRST-AB 3, 021301 (2000)
[2] M. Ferrario, T.C. Katsouleas, L. Serafini and I. Ben Zvi, ?Adiabatic
plasma buncher?, IEEE Transactions on Plasma Science, V. 28, N. 4 ,
August 2000.