A scheme for a fully superconducting electron injector

In this paper, the authors report on a scheme of a fully superconducting electron injector, i.e., which does not use a room temperature section (as does CEBAF) and that could be used for a superconducting linac. The authors have supposed the availability of 5-cell 1.5 GHz cavities as described. The difficulty to make such a cavity capture electrons arises from the far extending fringing field due to its large apertures that decelerates the incoming electrons. A possible solution would be to use a very high voltage gun. This has been done at Darmstadt with a 250 kV gun and 3 GHz cavities. With a 1.5 GHz cavity, the theory predicts a still better capture. Simulations show effectively that with a 170kV gun and 7 MV/m accelerating field, one could obtain the required bunches. However, this would result in a more complicated gun system than with a more usual low emittance 100kV gun. The complication is even more important for a possible polarized electron source. The authors propose using a single cell S.C. cavity for preacceleration followed by 2 standard 5-cell cavities for capture and acceleration. The fabrication of a single cell cavity does not require a special study as it is a necessary step in the design of the 5-cell cavities. Only a different cryostat will have to be built