Longitudinal Measurements at the SLAC Gun Test Facility*

The Gun Test Facility (GTF) was built to test high-brightness sources for the proposed Linac Coherent Light Source (LCLS) at SLAC. The longitudinal emittance exiting the gun has been determined by measuring the energy spectrum after the linac as a function of the linac phase. The phase-space parameters defining the beam pulse width, correlated energy spread, and slice energy spread at the linac entrance (~5 MeV beam energy) are fit to the measured energy spectra. A large, linear energy-time correlation is observed for bunch charges from 15 to 300 pC. Possible explanations for this correlated energy spread are discussed. Submitted to 24 International Free Electron Laser Conference, Argonne National Laboratory, Argonne, IL *Work supported by Department of Energy contract DE-AC03-76SF00515 Longitudinal Emittance Measurements at the SLAC Gun Test Facility D.H. Dowell, P.R. Bolton, J.E. Clendenin, S.M. Gierman, C.G. Limborg, B.F. Murphy, J.F. Schmerge, T. Shaftan Stanford Linear Accelerator Center Brookhaven National Laboratory ———————————————————————————————————————————————————————— Abstract The Gun Test Facility (GTF) was built to test high-brightness sources for the proposed Linac Coherent Light Source (LCLS) at SLAC. The longitudinal emittance exiting the gun has been determined by measuring the energy spectrum after the linac as a function of the linac phase. The phase-space parameters defining the beam pulse width, correlated energy spread, and slice energy spread at the linac entrance (~5 MeV beam energy) are fit to the measured energy spectra. A large, linear energy-time correlation is observed for bunch charges from 15 to 300 pC. Preliminary Parmela calculations show this correlation results from the longitudinal space charge forces in this short 2 ps long bunch. PACS codes: 29.25.Bx,29.27.Ac,41.60.Cr,41.85.Ar