Speaker
Description
The photon energy range of the LCLS-HE upgrade relies heavily on the achievable longitudinal beam brightness. The final peak current and correlated energy spread are both limited by the longitudinal phase space at the exit of the injector, non-linear compression, and collective effects. The initial charge distribution off the cathode effects all of these factors. However, determining an ideal cathode laser temporal profile requires optimization of the entire accelerator configuration. In order to simplify this problem, an idealized longitudinal phase space at the undulator entrance is analytically backtracked to the injector exit. In Astra simulations, the initial charge distribution and injector settings are optimized to match the longitudinal phase space from backtracking while maintaining a small projected emittance. The remainder of the accelerator is simulated in Elegant utilizing the lattice configuration determined by backtracking. The Free Electron Laser performance is simulated in Genesis using the start-to-end beam. Comparing with the nominal Gaussian cathode laser temporal profile, we find significant improvement in both the FEL pulse energy and maximum photon energy.
| Working group | WG5 |
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