Femtosecond Electron Beam Bunch Compression by Using an Alpha Magnet and a Chicane Magnet at the PAL Test Linac

The Pohang Accelerator Laboratory (PAL) Test Linac which consists of a half-cell thermionic RF-gun, an alpha magnet, and two S-band accelerating columns can provide a bunched electron beam with a beam energy of up to 85 MeV, a pulse length of 3 μs, a pulse current of 100 mA, and a repetition rate of 10 Hz. The bunch length measured with a streak camera is 4 ps, which was obtained by optimizing the bunch compression along the alpha magnet. For further bunch compression to a few hundred femtoseconds, another magnetic bunch compression system using a chicane magnet is being prepared. The PARMELA code simulation result shows that the bunch length can be shortened to sub-picoseconds. The mechanism of bunch compression for the alpha magnet and the chicane magnet is described and the simulation result is presented. As applications of a femtosecond electron beam, femtosecond parametric X-ray and far-infrared radiation are reviewed briefly.