Rf Focussing - an Instrument for Beam Quality Improvement in Superconducting Rf Guns
نویسنده
چکیده
Rf electron guns require an external magnetic field focussing to produce a low emittance electron beam. A dc magnetic field focuses electrons in the beam already inside the cavity as they leave the photocathode. In superconducting rf guns (srf) the possibility of external magnetic focussing is quite limited. In this paper we investigate an effect of rf focussing in the first half cell of a 3+1/2 cell srf gun cavity without a dc magnetic focussing. The shape of the first half cell is optimized. The calculations were done to fulfil the beam requirements of the injector for the ELBE project [1]. Besides normalized transversal emittances of the order of 1 π mm·mrad for bunch charges up to 1 nC were obtained. In the paper a graphic explanation of the rf focusing effect is represented.
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