  We describe use of the Advanced Photon Source (APS) rf thermionic gun, alpha
magnet beamline, and linac to produce a stable high-brightness beam in excess
of 100 amperes peak current with normalized emittance of 10 pi mm-mrad. To
obtain peak currents greater than 100 amperes, the rf gun system must be tuned
to produce a FWHM bunch length on the order of 350 fs. Bunch lengths this short
are measured using coherent transition radiation (CTR) produced when the rf gun
beam, accelerated to 40 MeV, strikes a metal foil. The CTR is detected using a
Golay detector attached to one arm of a Michelson interferometer. The alpha
magnet current and gun rf phase are adjusted so as to maximize the CTR signal
at the Golay detector, which corresponds to the minimum bunch length. The
interferometer is used to measure the autocorrelation of the CTR radiation. The
minimum phase approximation is used to derive the bunch profile from the
autocorrelation. The high-brightness beam is accelerated to 217 MeV and used to
produce SASE in five APS undulators installed in the Low- Energy Undulator Test
Line (LEUTL) experiment hall. Initial optical measurements showed a gain length
of 1.3 m at 530 nm. * Work supported by U. S. Department of Energy, Office of
Basic Energy Sciences, under Contract No. W-31-109-ENG-38.
