The Linac Coherent Light Source (LCLS) is a fourthgeneration light source demonstration project based on the self-amplified spontaneous emission (SASE) free-electron laser (FEL) concept. It will combine a new photoinjector, the Stanford Linear Accelerator Center (SLAC) linac, with two stages of bunch compression and a long undulator to create intense radiation pulses at 1.5 A. Successful operation of the LCLS will require consistent delivery of a highbrightness electron beam to the undulator, in the face of effects such as wakefields and coherent synchrotron radiation (CSR). Because of the sensitivity to beam quality and subtle effects, it is necessary to perform integrated tracking from the cathode through the undulator. We report on the combined use of PARMELA, elegant, and GENESIS to perform these simulations, and in particular the simulation of pulse-to-pulse variation in FEL performance due to rfand laser-related variation in the electron beam.
We investigate ftnite puke effects in self-amplified spontaneous emission (SASE), especially the roIe of coherent spontaneous emission (CSE) in the start and the evolution of the tleeeIectron laser @EL) process. When. the FEL interaction is negligible, we solve the one-dimensional Maxwell equation exactly and clarify the meaning of the slowly varying envelope approximation (SVEA). In the exponential gain regime, we solve the coupled VlasovMaxwell equations and extend the linear theory to a bunched beam with energy spread. A time-dependent nonlinear simulation algorithm is employed to study the CSE effect for a general beam distribution.
INTRODUCTIONCoherent spontaneous emission (CSE) has attracted much attention as the electron bunches become shorter and more intense in current experiments demonstrating the principle of self-ampliiied spontaneous emission (SASE). [4], the evolution of the electric field is studied with the individual particle formulation for a bunched monochromatic beam, and the contribution of the incoherent and the coherent SASE are identified. In this paper, we extend the linear theory to a bunched beam with energy spread and calculate the effect of CSE for the high gain FEL. We also present a time-dependent, nonlhear simulation algorithm that takes CSE into account for an arbitrary beam distribution.
COHERENT SPONTANEOUS EMISSIONThe ID Maxwell equation for the transverse electric field of a plane wave propagating along the undulator axis z is where PO is the permeability of free space, and the charge density term is absent here due LOtransverse uniformity. Writing the transverse current as JA(z, t) = U(Z, t) + c. j=l .where~is the beam cross section, X is the undulator strength parameter for the helical undulator and KIJJl for the planar undulator after averaging over the undulatorpe riod ku. We have also assumed that the jtk electron enters the undulator at t = tj(j = 1,..., N) and z = 0. Thus, the longitudinal position of the electron is Zj(t) = flC(t -tj), where flc is the average Longitudinal velocity. Cl(t) is the step function, i.e., Q(t) = 1 fort> Oaad O otherwise.In the absence of FEL interaction, the electric field in the form fl~= Z??(Z,t) + C.Cis found to be
E=Kl~(e'kf~~Jti)]C(t-tj]
A self-amplified spontaneous emission (SASE) freeelectron laser (FEL) is under construction at the Advanced Photon Source (APS). Five FEL simulation codes were used in the design phase: GENESIS, GINGER, MEDUSA, RON, and TDA3D. Initial comparisons between each of these independent formulations show good agreement for the parameters of the APS SASE FEL.
The nonlinear generation of harmonics in a self-amplified spontaneous emission (SASE) free-electron laser (FEL) continues to be of interest. Complementary to such studies is the search for information on the electron beam microbunching harmonic components, which are revealed by coherent optical transition radiation (COTR) experiments. An initial z-dependent set of data has been obtained with the fundamental at 530 nm and the second harmonic at 265 nm. The latter data were collected after every other undulator in a nine-undulator string. These results are compared to estimates based on GINGER and an analytical model for nonlinear harmonic generation.
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