Front-to-end simulations of the design of a laser wakefield accelerator with external injection

The authors report the design of a laser wakefield accelerator (LWA) with external injection by a radiofrequency photogun and acceleration by a linear wakefield in a capillary discharge channel. The design process is complex due to the large no. of intricately coupled free parameters. To alleviate this problem, the authors performed front-to-end simulations of the complete system. The tool the authors used was the general particle-tracking code, extended with a module representing the linear wakefield by a 2-dimensional traveling wave with appropriate wavelength and amplitude. Given the limitations of existing technol. for the longest discharge plasma wavelength (.apprx.50 mm) and shortest electron bunch length (.apprx.100 mm), the authors studied the regime in which the wakefield acts as slicer and buncher, while rejecting a large fraction of the injected bunch. The optimized parameters for the injected bunch are 10 pC, 300 fs at 6.7 MeV, to be injected into a 70 mm long channel at a plasma d. of 7 * 1023 m-3. A linear wakefield is generated by a 2 TW laser focused to 30 mm. The simulations predict an accelerated output of 0.6 pC, 10 fs bunches at 90 MeV, with energy spread