Correction of nonlinear distortion in high-transverse-emittance ratio-beam production with linear accelerator

Derbenev proposed producing a high quality flat beam of high-transverse-emittance ratio (HTER) with a linear accelerator. Kim also discussed the round-to-flat transformation of angular-momentum-dominated beam. Fermilab/NICADD Photoinjector Laboratory has performed many experiments on HTER beam production. Experiments and simulations, collectively, showed an S-shaped transverse distribution in the flat beam. In this paper, the source of this emittance deterioration in the transformation is identified as the nonlinear rf cavity focusing force; and a solution is proposed