Radial bunch compression: Path-length compensation in an rf photoinjector with a curved cathode

de Loos, M.J. and van der Geer, S.B. and Saveliev, Y.M. and Pavlov, V.M. and Reitsma, A.J.W. and Wiggins, S.M. and Rodier, J. and Garvey, T. and Jaroszynski, D.A. (2006) Radial bunch compression: Path-length compensation in an rf photoinjector with a curved cathode. Physical Review Special Topics: Accelerators and Beams, 9 (8). 084201-1-084201-7. ISSN 1098-4402

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Abstract

Electron bunch lengthening due to space-charge forces in state-of-the-art rf photoinjectors limits the minimum bunch length attainable to several hundreds of femtoseconds. Although this can be alleviated by increasing the transverse dimension of the electron bunch, a larger initial radius causes path-length differences in both the rf cavity and in downstream focusing elements. In this paper we show that a curved cathode virtually eliminates these undesired effects. Detailed numerical simulations confirm that significantly shorter bunches are produced by an rf photogun with a curved cathode compared to a flat cathode device. The proposed novel method will be used to provide 100 fs duration electron bunches for injection into a laser-driven plasma wakefield accelerator.