Growth of emittance in laser-plasma electron acceleration in guiding structures

We study angular characteristics, such as emittance and fraction of electrons emitted into a prescribed solid angle, for electron bunches that are accelerated in wake fields generated in various guiding structures – capillary waveguides and plasma channels, in which intense laser pulses propagate. The investigation is performed at various injection energies, which simulate input conditions to different cascades of a multistage electron accelerator. It is shown that, in contrast to the limitations issuing from the requirement of trapping and accelerating a substantial part of bunch electrons, the condition of maintaining the low emittance of the bunch, needed for successful transfer of the accelerated bunch to the entry of the next acceleration cascade or other device, imposes much more strict limitations on the accuracy of focusing of laser radiation to the guiding structure.