Funneling multiple bunches of high-charge polarized electrons

The future electron ion collider (eRHIC) at Brookhaven National Laboratory requires a polarized electron source with a high average current, short bunch length and small emittance. The state-of-the art single GaAs-based electron source is far from delivering the required 50mA current due to ion back-bombardment and the limit on surface charge. Currently, we are designing and constructing a high-average current, polarized electron-source based on the principle of the Funneling gun. Our funneling gun is designed such that the electron bunches generated from 20 photocathodes in a 220 kV DC gun, funnel to one common beam-axis. This article details our design of a high-average-current polarized electron source, encompassing its mechanical design, the preparation of the cathode, the beam's dynamics and diagnostics, and the laser system. We also discuss our recent progress in building the funneling gun.