• A. Fukasawa, J.B. Rosenzweig, D. Schiller
  UCLA, Los Angeles, California
• D. Alesini, L. Ficcadenti, B. Spataro
  INFN/LNF, Frascati (Roma)
• L. Faillace, L. Palumbo
  Rome University La Sapienza, Roma

A unique SW/TW hybrid photoinjector are being developed under the collaboration of UCLA, LNF/INFN, and University of Rome. It can produce 240-fs (rms) bunch with 500 pC at 21 MeV. The bunch distribution has a strong spike (54 fs FWHM) and the peak current is over 2kA. As the bunch form factor at 1 THz is 0.43, it can produce coherent radiation at 1 THz. We are considering three types of way to generate it; coherent Cherenkov radiation (CCR), superradiant FEL, and coherent transition/edge radiation (CTR/CER). CCR used hollow dielectric with the outer surface metallic-coated. OOPIC simulation showed 21 MW of the peak power (5 mJ) at 1 THz. For FEL and CTR/CER simulation, QUINDI, which was written at UCLA to solve the Lienard-Wiechert potential, was used to calculate the radiation properties. In the contrast to CCR, their spectra were broad and their pulse lengths were short. They will be useful for fast pumping.

• L. Faillace, L. Palumbo
  Rome University La Sapienza, Roma
• P. Frigola
  RadiaBeam, Marina del Rey
• A. Fukasawa, B.D. O'Shea, J.B. Rosenzweig
  UCLA, Los Angeles, California
• B. Spataro
  INFN/LNF, Frascati (Roma)

The quest for high brightness beams is a crucial key for the SPARX-FEL Project. In this paper, we present the design (including RF modeling, cooling, thermal and stress analyses as well as frequency detuning) of a single feed S-Band RF Gun capable of running near 500 Hz. An alternative design with dual feed has already been designed. Also, experimental results from the RF characterization of the prototype, including field measurements, are presented. The RF design follows the guidelines of the LCLS Gun, but the approach diverges significantly as far as the management of the cooling and mechanical stress is concerned. Finally, we examine the new proprietary approach of RadiaBeam Technologies for fabricating copper structures with intricate internal cooling geometries that may enable very high repetition rate.

* C.Limborg et al., "RF Design of the LCLS Gun".
** P. Frigola et al., "Development of solid freeform fabrication (SFF) for the production of RF Photoinjectors".

• J.B. Rosenzweig, G. Andonian, A. Fukasawa, E. Hemsing, G. Marcus, A. Marinelli, P. Musumeci, B.D. O'Shea, F.H. O'Shea, C. Pellegrini, D. Schiller, G. Travish
  UCLA, Los Angeles, California
• P.H. Bucksbaum, M.J. Hogan, P. Krejcik
  SLAC, Menlo Park, California
• M. Ferrario
  INFN/LNF, Frascati (Roma)
• S.J. Full
  Penn State University, University Park, Pennsylvania
• P. Muggli
  USC, Los Angeles, California

Recent initiatives at UCLA concerning ultra-short, GeV electron beam generation have been aimed at achieving sub-fs pulses capable of driving X-ray free-electron lasers (FELs) in single-spike mode. This uses of very low charge beams, which may allow existing FEL injectors to produce few-100 attosecond pulses, with very high brightness. Towards this end, recent experiments at the Stanford X-ray FEL (LCLS, first of its kind, built with essential UCLA leadership) have produced ~2 fs, 20 pC electron pulses. We discuss here extensions of this work, in which we seek to exploit the beam brightness in FELs, in tandem with new developments at UCLA in cryogenic undulator technology, to create compact accelerator/undulator systems that can lase below 0.15 Angstroms, or be used to permit 1.5 Angstrom operation at 4.5 GeV. In addition, we are now developing experiments which use the present LCLS fs pulses to excite plasma wakefields exceeding 1 TV/m, permitting a table-top TeV accelerator for frontier high energy physics applications.