Using an alpha magnet to compress the electron bunches from a photocathode RF gun

Abstract

We report here the design, simulation, and characterization of a compact electron injector for the formation of high-current, femtosecond electron bunches from a photocathode RF gun without mandatory use of ultra-short laser pulses and a high power RF supply. The proposed injector consists of a 1.6-cell S-band photocathode RF gun to produce the electron beam and a small bunch compressor to increase the peak current. The RF gun is designed to operate at a 65 MV/m accelerating field gradient, and the bunch compressor is a small α-magnet with a maximum magnetic field gradient of 340 G/cm. The output beam from the gun has 100 pC charge per-bunch that is equivalent to a beam current of ∼15 A, and output beam from the injector has an RMS bunch length of ∼ 439 fs, a peak current of 0∼ 12 A and an RMS normalized horizontal emittance of 1.21 mm-mrad.