Longitudinal compression and transverse matching of electron bunch for external injection LPWA at ESCULAP

Abstract We present theoretical and numerical studies of longitudinal compression and transverse matching of electron bunch before injecting into the Laser–plasma Wake Field Accelerator (LWFA) foreseen at the ESCULAP project in ORSAY. Longitudinal compression is performed with a dogleg chicane, the chicane is designed based on theory of beam optics, beam dynamics in dogleg is studied with ImpactT (Martin Dohlus and Torsten Limberg, 2004) and cross checked with CSRtrack (Qiang and Steve Lidia, 2006), both 3D space charge (SC) and coherent synchrotron radiation (CSR) effects are included. Simulation results show that the energy chirp at the dogleg entrance should be smaller than the nominal optic design value, in order to compensate the negative energy chirp increase caused by longitudinal SC, while CSR can be ignored in our case. With an optimized configuration, the electron bunch ( ∼ 10 MeV, 10 pC) is compressed from 0.9 ps RMS to 70 fs RMS (53 fs FWHM), with a peak current of 152 A. Transverse matching is realized with a doublet and a triplet, they are matched with Madx and the electron bunch is tracked with ImpactT, simulation results show little difference with the nominal design values, that is due to the SC effect. Finally, by simply adjusting the quadrupole strength, a preliminary optimized configuration has been achieved, that matches the Courant–Snyder (C–S) parameters to α x = 0 . 01 , α y = − 0 . 02 , β x = 0 . 014 m , β y = 0 . 012 m at the plasma entrance.