Coherent OTR measurements on the LCLS injector[1] drew interest in collective interaction micro-dynamics in e-beams. Studies of micro-bunching, based on 1D analytical model and 3-D simulations, suggested that the e-beam current-noise can be controlled and suppressed by collective interaction in a drift section[2,3]. This is expected to be expressed in the intensity and radiation pattern of measured COTR. We present preliminary results of beam dynamics simulation with GPT code and IMPACT-T code, together with COTR computations corresponding to recent COTR measurements on the LCLS injector. Based on the simulations we compare the OTR radiation pattern in the case of a random distribution beam (shot-noise dominated) to the case of spatially and temporally coherent beam modulation (pre-bunching) and to the case of a partially coherent beam emerging from a collective-interaction section. We discuss the effect of betatron motion on the beam dynamics in these cases.

1. D. Dowell, in Workshop FEL Frontiers, 2007, Elba, Italy, http://www.lnf.infn.it/conference/elba07/

2. A. Gover and E. Dyunin, Phys. Rev. Lett. 102, 154801 (2009).

3. A. Nause, E. Dyunin, A. Gover, Journal of Applied Physics 107, 103101 (2010).