New accelerator facilities (like the proposed Electron-Ion Collider) require polarized electron beam of unprecedented intensity. The eRHIC project requires average polarized electron currents on the order of 50 mA, whereas existing polarized electron sources typically operate in the 100-200 μA range and have achieved average currents of about 1 mA only with very short lifetimes. MIT-Bates investigates a possibility to build a very high intensity polarized electron gun to investigate techniques for increasing polarized electron intensities for an Electron-Ion Collider.
The gun has “inverse” geometry. The chamber is made from stainless steel, and the cathode block is suspended in the middle of the chamber with ceramic pipes. The gun is equipped with a preparation chamber for cathode activation and a load–lock to load cathodes into the gun without venting the gun and preparation chambers. A magnetic-coupled manipulator is used to transfer the cathodes between load-lock, preparation and gun chambers.
Three main features are implemented to achieve very high intensity. The cathode is actively cooled to avoid its overheating by the intense laser beam. The cathode active area is very large to reduce ion bombardment effects. The ion bombardment mostly affects the central area of the cathode. In order to reduce this effect farther, the laser beam is ring shaped, leaving the most vulnerable central area of the cathode unused.