Compression of High-Charge Electron Bunches

The A0 Photoinjector at Fermilab can produce high charge (10-14 nC) electron bunches of low emittance (20 pi mm-mrad for 12 nC). We have undertaken a study of the optimal compression conditions. Off-crest acceleration in the 9-cell capture cavity induces an energy-time correlation, which is rotated by the compressor chicane (4 dipoles). The bunch length is measured using streak camera images of optical transition radiation. We present measurements under various conditions, including the effect of the laser pulse length (2 ps sigma Gaussian vs. 10 ps FWHM flat top). The best compression to date is for a 13.2 nC bunch with sigma = 0.63 mm (1.89 ps), which corresponds to a peak current of 2.8 kA.