A modified round to flat beam transformation lattice for angular dispersion induced microbunching technique

Abstract

The angular dispersion induced microbunching (ADM) technique has been proposed to generate high brightness coherent radiation in storage rings by taking advantage of it’s very low vertical emittance. To apply a similar scheme in the linac, it is necessary to reduce the vertical emittance of the electron beam. Generally, angular-momentum-dominated round beams can be generated by immersing the cathode into the axial solenoid magnetic field. The angular momentum can be then removed by skew quadrupoles downstream of the solenoid, resulting in a flat beam with low vertical emittance. In this paper, we propose a possible scheme that holds the possibility to improve the performance of round to flat beam transformation technique by chromatic correction. In this scheme, a chicane is used to introduce the transverse dispersion and sextupoles are employed to correct the chromatic effect. Three-dimensional numerical simulations have been carried out and the results show that a flat beam with transverse emittance ratio of ∼840 can be generated for a bunch charge of 0.5 nC.