JLAB, Newport News, Virginia
ATF, Boulder
Mesa+, Enschede
We report on the design, and broadly tunable operation, of a high average power free-electron laser using edge-outcoupling. For this type of outcoupling, the cavity mode has a larger area than the mirror diameter, and the mode ‘spills” around it. While used in positive branch unstable resonators, in this case, the resonator was in a stable configuration. Using an edge-outcoupler composed of an aluminum-coated sapphire substrate, the IR Upgrade FEL at Jefferson Lab achieved a maximum power of 260W at 3.87 microns, with an output power of 20 W or higher from 0.8 to 4.2 microns. Measurements of gain, loss, and output mode are compared with our models.
JLAB, Newport News, Virginia
UW-Madison/SRC, Madison, Wisconsin
We discuss the use of multipass recirculation and energy recovery in CW SRF drivers for short wavelength FELs. Benefits include cost management (reduced system footprint, RF and SRF hardware, and associated infrastructure such as cryogenic systems), ease in radiation control (low exhaust drive beam energy), ability to accelerate and deliver multiple beams of differing energy to multiple FELs, and opportunity for seamless integration of multistage bunch length compression into the longitudinal matching scenario. Issues include those associated with ERLs, compounded by the challenge of generating and preserving the CW electron beam brightness required by short wavelength FELs. We thus consider the impact of space charge, BBU and other environmental wakes and impedances, ISR and CSR, potential for microbunching, intra-beam and beam-residual gas scattering, ion effects, RF transients, and halo, as well as the effect of traditional design, fabrication, installation and operational errors (lattice aberations, alignment, powering, field quality). Context for the discussion is provided by JLAMP, the proposed VUV/X-ray upgrade to the existing Jefferson Lab FEL.