Sparc Working Point Optimization for a Bunch with Gaussian Temporal Profile

We present the optimization of the working point with a Gaussian temporal profile for the SPARC photoinjector. Start to end simulations starting from a Gaussian electron beam pulse shape are discussed here, in comparison with the nominal working point performances of a 10ps flat top pulse with rise time of 1ps [1]. Machine parameters have been optimized for the Gaussian pulse shaping both for the standard operating conditions and for the radio-frequency (RF) compressor configuration. In particular, compression factors (C) 2 and 4 have been studied in details. Simulations have been performed using the codes PARMELA [2] and GENESIS [3], for the beam transport along the photoinjector and for the FEL/SASE process respectively. The two pulse shapes we considered, Gaussian and rectangular with rise time of 1 ps, provide the same saturation length and average power of radiation emitted in the undulator, but the higher current in the beam core of the Gaussian pulse gives a higher peak radiation power at the cost of a broader radiation spectrum. These simulations were performed to investigate thoroughly one of the possible operating modes of the SPARC laser system, which naturally produces such Gaussian shaped pulses.