Laser plasma based accelerators have the potential to reduce dramatically the size and cost of future particle colliders and light sources. Production of high quality beams along with reproducibility, tunability, and efficiency are required for many applications. We present design principles for two-pulse colliding laser pulse injection mechanisms, which can meet these requirements. Simulations are used to determine the best conditions for the production of high quality beams: high charge, low energy spread, and low emittance. Simulations also allow access to the internal dynamics of the interaction, providing insight regarding further improvement of the beam quality. We find that a 20 pC beam can be accelerated to 300 MeV in 4 mm with only a few percent energy spread and transverse normalized emittance close to 1 mm mrad, using a 10 TW laser. We demonstrate that this design scales according to linear theory. Control of the laser pulse mode content and subsequent evolution in the plasma channel are shown to be critical for achieving the highest beam quality.

Compact short pulse positron source in the energy range of a few tens of MeV driven by laser plasma accelerator is a promising tool for many applications, such as materials science and source of colliders. A collection and transmission system based on laser plasma accelerators is proposed to intensify and narrow the beam divergence for positrons generated from converters. The system is composed of a converter, a collimator, a solenoid, quadrupoles, and a slit in the exit. Numerical simulations were performed to demonstrate the feasibility and robustness of the design. The designed system can work in the center energy range from 15 to 40 MeV within ±10% energy spread (FWHM) and greatly improve the quality of collected positron beams with a divergence of around 50 mrad.

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