  Compared with conventional accelerators, laser plasma accelerators can
generate high energy ions at a greatly reduced scale, due to their TV/m
acceleration gradient. A compact laser plasma accelerator (CLAPA) has been
built at the Institute of Heavy Ion Physics at Peking University. It will be
used for applied research like biological irradiation, astrophysics
simulations, etc. A beamline system with multiple quadrupoles and an analyzing
magnet for laser-accelerated ions is proposed here. Since laser-accelerated ion
beams have broad energy spectra and large angular divergence, the parameters
(beam waist position in the Y direction, beam line layout, drift distance,
magnet angles etc.) of the beamline system are carefully designed and optimised
to obtain a radially symmetric proton distribution at the irradiation platform.
Requirements of energy selection and differences in focusing or defocusing in
application systems greatly influence the evolution of proton distributions.
With optimal parameters, radially symmetric proton distributions can be
achieved and protons with different energy spread within 5% have similar
transverse areas at the experiment target.
