Abstract
The high brightness electron beam required by a short wavelength self-amplified spontaneous emission free-electron laser (FEL) may be reached only with an accurate design of the beam dynamics from the generation in the rf injector up to the undulator. The beam dynamics is affected by strong self-consistent effects at injection, in the compression stage, and during the FEL process. The support of numerical simulations is extensively used in the predictions of the beam behavior in these nonlinear dynamical conditions. I present a review of available simulation techniques, currently exploited in the design of short wavelength free-electron lasers.
Highlights
We usually refer to a high quality e beam as a beam with large brightness Bn ; "nx "ny (1)i.e., high current and small normalized emittances
A proper understanding of the dynamics is essential in the design of short wavelength
spontaneous emission (SASE) freeelectron laser (FEL) projects, low emittance beams are obtained within the present state of the art rf photocathode injectors and the peak current is increased by longitudinal compression
Summary
I.e., high current and small normalized emittances. From a technical point of view, the quality of the electron beam is the main limiting factor in reaching short wavelengths with a self-amplified spontaneous emission (SASE) freeelectron laser (FEL). 1098-4402=03=6(11)=114802(17)$20.00 that of simulating a reduced number of particles, with a scaled charge, each representing a large number of real electrons The introduction of these macroparticles has some unpleasant consequences that need to be properly treated in a correct numerical implementation. The request of minimizing the induced emittance growth is accomplished by tuning the frequency of the first plasma oscillation that the beam executes according to the internal space charge fields and to the focusing due to rf forces and to the solenoid When this frequency is correctly matched, the emittance has a minimum at an energy high enough that the contribution of the betatron motion associated with the thermal emittance overcomes that of the laminar motion. I.e., a beam which is flat transversally and longitudinally, this ‘‘emittance compensation’’ procedure brings the emittance at the end, almost to the same
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