Subpicosecond compression of 0.1-1 nC electron bunches with a magnetic chicane at 8 MeV

After compressing electron bunches with a half-meter long, four-dipole chicane at 8 MeV, we have measured full width at half maximum (FWHM) bunch lengths of less than 1 ps for charges from 0.1 to 1.1 nC. The uncompressed FWHM bunch lengths varied from 10 to 20 ps, and we achieved compression ratios in excess of 40 and peak currents greater than 1 kA. Bunch lengths for low charges were measured using a transversely deflecting rf cavity; bunch lengths for high charges were inferred from the energy spread induced in the beam by its longitudinal space-charge force as it drifted from the end of the compressor to the spectrometer.