  Proposed fourth generation light sources using SASE FELs to generate short
pulse, coherent, X-rays require demonstration of high brightness electron
sources. The Gun Test Facility (GTF) at SLAC was built to test high brightness
sources for the proposed Linac Coherent Light Source at SLAC. The transverse
emittance measurements are made at nearly 30 MeV by measuring the spot size on
a YAG screen using the quadrupole scan technique. The emittance was measured to
vary from 1 to 3.5 mm-mrad as the charge is increased from 50 to 350 pC using a
laser pulse width of 2 ps FWHM. The measurements are in good agreement with
simulation results using the LANL version of PARMELA.
