Time-resolved imaging for the APS linac beams

The particle-beam imaging diagnostics for the Advanced Photon Source (APS) injector lime have been enhanced by the installation of optical transition radiation (OTR) screens and the use of Ce-doped YAG crystals as beam profile monitors. Both converters have improved spatial resolution and time responses compared to the standard Chromox (Al2O3:Cr) screens used elsewhere in the linac. These enhancements allow us to address the smaller beam sizes (< 100 microm) and the critical micropulse bunch length of higher brightness gun sources For the Linac macropulse of 30-ns duration composed of 86 micropulses at S-band frequency intervals, only the OTR mechanism is prompt enough to separate individual micropulses and to allow streak camera measurements of the micropulse averaged bunch length. Tests have been performed at 400 to 625 MeV using the gated DC thermionic gun source. Beam sizes less than σx = 30 microm have been observed with a micropulse bunch length of σ = 2-3 ps using OTR. First results on the lower-emittance rf thermionic gun are briefly discussed