Penn, G.
(Gregory Penn)

MOPOS57 Analytic Model of Harmonic Generation in the Low-Gain FEL Regime
Gregory Penn (LBNL/CBP, Berkeley, California), Matthias Reinsch (LBNL, Berkeley, California), Jonathan Wurtele (LBNL, Berkeley, California; UC Berkeley, Berkeley)

Harmonic generation using free electron lasers (FELs) requires two undulators: the first generates energy modulation through the inverse FEL effect; the second undulator uses the subsequently bunched beam to radiate at a higher harmonic. These processes are currently evaluated using extensive calculations or simulation codes which can be slow to evaluate and difficult to set up. We describe a simple algorithm to predict the output of a harmonic generation beamline in the low-gain FEL regime based on trial functions for the output radiation. Full three-dimensional effects are included. This method has been implemented as a Mathematica script which runs rapidly and can be generalized to include effects such as asymmetric beams and misalignments. This method is compared with simulation results using the FEL code GENESIS, both for single stages of harmonic generation and to model the design of LUX, a proposed facility for ultra-short X-ray pulses, where multiple stages upshift the input laser frequency by factors of up to 200.

THPOS51 Harmonic Cascade FEL Designs for LUX, a Facilty for Ultrafast X-ray Science
Corlett John, William M. Fawley, Gregory Penn, Alexander A Zholents (LBNL/CBP, Berkeley, California), Weishi Wan (LBNL/ALS, Berkeley, California), Matthias Reinsch, Jonathan Wurtele (UC Berkeley, Berkeley)

LUX is a proposed facility for ultrafast X-ray science, based on an electron beam accelerated to ~3-GeV energy in a superconducting, recirculating linac.Included in the design are multiple FEL beamlines which use the harmonic cascade approach to produce coherent XUV & soft X-ray emission beginning with a strong input external laser seed at ~200 nm wavelength. Each cascade module generally operates in the low-gain regime and is composed of a radiator together with a modulator section, separated by a magnetic chicane. The chicane temporally delays the electron beam pulse in order that a "virgin" pulse region (with undegraded energy spread) be brought into synchronism with the radiation pulse. For each cascade, the output photon energy can be selected over a wide range by varying the seed laser wavelength and the field strength in the undulators. We present numerical simulation results, as well as those from analytical models, to examine predicted FEL performance. We also discuss lattice considerations pertinent to harmonic cascade FELs, as well as sensitivity studies and requirements on the electron beam.