  Laser wakefield acceleration (LWFA) in a gas cell target separating injection
and acceleration section has been investigated to produce high-quality electron
beams. A detailed study has been performed on controlling the quality of
accelerated electron beams using a combination of truncated ionization and
density downramp injection mechanisms. For this purpose, extensive
two-dimensional Particle-In-Cell (PIC) simulations have been carried out
considering a gas cell target consisting of a hydrogen and nitrogen mixture in
the first part and pure hydrogen in the second part. Such a configuration can
be realized experimentally using a specially designed capillary setup. Using
the parameters already available in the existing experimental setups, we show
the generation of an electron beam with a peak energy of 500-600 MeV, relative
energy spread less than 5%, normalized beam emittance around 1.5 mm-mrad, and
beam charge of 2-5 pC/micrometer. Our study reveals that the quality of the
accelerated electron beam can be independently controlled and manipulated
through the beam loading effect by tuning the parameters, e.g., laser focusing
position, nitrogen concentration, and gas target profile. These simulation
results will be useful for future experimental campaigns on LWFA, particularly
at ELI Beamlines.
