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A design of a compact free‐electron laser (FEL), generating ultra‐fast, high‐peak flux, XUV pulses is presented. The FEL is driven by a high‐current, 0.5 GeV electron beam from the Lawrence Berkeley National Laboratory (LBNL) laser‐plasma accelerator, whose active acceleration length is only a few centimeters. The proposed ultra‐fast source (∼10 fs) would be intrinsically temporally synchronized to the drive laser pulse, enabling pump‐probe studies in ultra‐fast science. Owing to the high current (≳10 kA) of the laser‐plasma‐accelerated electron beams, saturated output fluxes are potentially greater than 1013 photons/pulse. Devices based both on self‐amplified spontaneous emission and high‐harmonic generated input seeds, to reduce undulator length and fluctuations, are considered.

The LOASIS Laser Wakefield Accelerator (LWFA) has achieved quasi‐mono‐energetic electron beams with energies up to 1 GeV [1]. These beams offer the potential for use with insertion devices such as wigglers and undulators to create tabletop XUV and x‐ray free‐electron laser (FEL) sources. To achieve a high quality light source producing high brightness radiation requires an electron beam with low energy spread and low emittance. Here we discuss the use of an undulator to generate XUV radiation to characterize in a single shot the electron beam energy spread and emittance with high precision.

Recently it has been pointed out that numerical simulation of some systems containing charged particles with highly relativistic directed motion can by speeded up by orders of magnitude by choice of the proper Lorentz boosted frame. A particularly good example is that of short wavelength free-electron lasers (FELs) in which a high energy (E{sub 0}{>=}250 MeV) electron beam interacts with a static magnetic undulator. In the optimal boost frame with Lorentz factor {gamma}F, the red-shifted FEL radiation and blue shifted undulator have identical wavelengths and the number of required time-steps (presuming the Courant condition applies) decreases by a factor of {gamma}{sub F}{sup 2} for fully electromagnetic simulation.We have adapted the WARP code to apply this method to several FEL problems including coherent spontaneous emission (CSE) from pre-bunched e-beams, and strong exponential gain in a single pass amplifier configuration. We discuss our results and compare with those from the 'standard' FEL simulation approach which adopts the eikonal approximation for propagation of the radiation field.

We summarize the presentations and conclusions of the Working Group on FEL Physics and Numerical Modeling.

The characteristics of a beam propagating in a channel of large aperture quadrupole magnets, and an anisotropy driven instability which transfers thermal energy from the transverse to longitudinal directions, are presented as two examples of phenomena requiring fine numerical resolution to be adequately described. In the first case, adequate resolution of the thin beam‐edge sheath is found necessary to accurately simulate the particles whose orbits are driven unstable by the focusing nonlinearity. In the latter case, the tendency of the unstable mode to occur at longitudinal wavelengths comparable to beam diameter, requires adequate longitudinal resolution for the instability to be observed.