FEL options for the proposed UK fourth generation light source (4GLS)

4GLS is a novel low-energy light source proposed as a complementary facility to the DIAMOND X-ray project for the UK, and could probably replace the present SRS at Daresbury in about 6 years time. This facility will use a combination of three separate FELs, undulators and bending magnets to provide a unique source of high-brightness continuous and pulsed radiation from the IR to XUV <f>(∼100 eV)</f>. Here, we give a brief description of the proposed FELs in the IR and VUV followed by a pre-design parameter study of the more technically challenging XUV high-gain FEL. The electron beam source for this FEL is a <f>600 MeV</f> superconducting energy recovery linac with peak currents of a few kA, normalised rms emittance <f>∼3π mm mrad</f> and rms energy spread <f>∼5×10−4</f>. Computer simulations using the 3-D FEL code GENESIS 1.3 are used to investigate a feasible undulator and beam focussing scheme, allowing estimates for achievable radiation power and saturation length to be made. [Copyright &y& Elsevier]