Initial CTR-based bunch length measurements of linac beams following the APS bunch compressor

The interest in generation and characterization of ultrabright electron beams for experiments at the Advanced Photon Source (APS) resulted in the installation of a four-dipole chicane bunch compressor within the linac. Both RF thermionic guns and an RF photocathode (PC) gun can be used to generate the electron beams with ps-regime bunch lengths. The bunch compressor can then be used to produce subps bunches. In support of this initiative, a coherent transition radiation (CTR) bunch length monitor based on a far-infrared (FIR) Michelson interferometer was also installed at a location just downstream of the compressor. It used a room-temperature Golay cell as the FIR detector. Processing of the autocorrelation data indicated that structures shorter than 500 fs were being generated.