• M. Boscolo, M. Ferrario, V. Fusco, B. Spataro, C. Vaccarezza
  INFN/LNF, Frascati (Roma)
• L. Giannessi, M. Quattromini, C. Ronsivalle
  ENEA C.R. Frascati, Frascati (Roma)
• M.  Migliorati, L. Palumbo
  Rome University La Sapienza, Roma
• L. Serafini
  INFN-Milano, Milano

The first phase of the SPARX project is essentially an R&D activity focused on developing techniques and critical components for future X-ray FEL facilities. The SPARXINO test facility will generate ultra-high peak brightness electron beams at 1 GeV, thanks to the upgrade of the existing Frascati 800 MeV linac. This facility will allow driving a single pass FEL experiment in the range of 3-5 nm, both in SASE and SEEDED FEL configurations. A peculiarity of this linac design is the choice of integrating a rectilinear RF compressor in the early stage of the acceleration, producing a 300-500 A beam, with a magnetic chicane afterwards, for a further compression up to 1 kA. In this paper we discuss the dynamics of the beam, which is in the space charge dominated regime throughout almost all the linac. Start to end simulations and preliminary stability studies taking into account some significant parameter fluctuations are also reported.

• G.M. wang, J.-E. Chen, Y.T. Ding, J. Hao, S.L. Huang, L. Lin, X.Y. Lu, S.W. Quan, L.F. Wang, R. Xiang, B.C. Zhang, K. Zhao, F. Jiao, D. Xie, L. Yang, F. Zhu, C. Liu, F. Wang, W. Xu, Z. Liu
  PKU/IHIP, Beijing
• Y.G. Wang
  Peking University, School of Physics, Beijing

Funding: NSFC, MOST of China

Beam loading experiments on DC-SC photoinjector test facility have been finished at 4.4 K. Upon the present experiments, the gradient of 6 MV/m is achieved. The maximum energy gain is 1.1 MeV at 4.4 K. With average beam current of 270 mA, the measured rms emittance is about 5 mm-mrad at the beam energy of 500 keV. Experiments on the test facility has validated that the DC-SC photoinjector is a good choice to provide moderate average current electron beams with low bunch charge and very high repetition rate.

• M. Trovo, M.B. Danailov, G. Penco
  ELETTRA, Basovizza, Trieste
• W. Graves
  MIT, Middleton, Massachusetts
• S.M. Lidia
  LBNL, Berkeley, California

In the framework of the FERMI@ELETTRA project, aimed to build an X-ray FEL source, a crucial role is played by the electron source, which has to produce a very high quality bunch, in terms of low emittance and uncorrelated energy spread. We have investigated the effects of low- (100-300 5m) and high- ( 10^-50 5m) frequency modulation of the beam charge deriving from intensity modulation of the laser pulse incident on the photocathode on the downstream beam distribution. Following other proposals, we have investigated the use of a short laser 'heater' to increase the effective incoherent energy spread and reduce the gain in the longitudinal density modulation instability. We present results from simulation of the beam generation at the photocathode, and transport through the photoinjector, initial acceleration modules and the laser heater.

• G. Penco, M. Trovo
  ELETTRA, Basovizza, Trieste
• S.M. Lidia
  LBNL, Berkeley, California

In the framework of the FERMI@ELETTRA project, aimed to build an x-ray FEL source based on laser-seeded harmonic generation, a crucial role is played by the electron source, which has to produce a very high quality beam, in terms of low emittance and uncorrelated energy spread. A very attractive solution is the SLAC/BNL/UCLA 1.6 cell s-band gun III based upon the demonstrated high performance of this design and its descendants. This paper describes the results of the optimization studies based on the gun III design and carried out with two space charge tracking codes (GPT and ASTRA) for nominal operating parameters. In particular two different bunch charge regimes has been explored: low (few hundreds of pC) and high (~1nC) . In the first case, the limited charge extracted from the photo-cathode allows to propagate a bunch with an initial higher density and to compress it along the linac down to a few hundreds of fs, attaining a high peak current bunch with a very low slice emittance. The second case has been investigated in order to verify the possibility to produce a "1 ps plateau" bunch with acceptable peak current and a slice emittance lower than 2 mm mrad. We present simulation results for both cases.