Coherent x-ray and VUV radiation from storage ring undulators and FELs

Abstract

Undulators operating in a modern electron storage ring can generate tens of milliwatts of broadly tunable coherent power in the spectral region extending from several eV to several keV. The required beam characteristics (energy of ~1-2 GeV, emittance <10−8 m-rad, and several hundred milliamperes of average current) can be achieved in a carefully designed storage ring. Many period (N ≥ 100) and short period length (~3 cm) undulator magnets necessary for this purpose can be designed using permanent magnets. The radiation is transversely fully coherent and has narrow spectral content (λ/Δλ = 100). In addition, full polarization control is possible by using a crossed undulator system. Free electron lasers (FELs) and transverse optical klystrons (TOKs) utilize the density modulation of the electron beam induced by strong beam radiation coupling. In TOKs, coherent radiation is generated at harmonics of an input laser frequency. FELs, either through the use of the feedback mirrors of a high-gain single-pass device, would generate intense, tunable radiation with extremely narrow bandwidths (λ/Δλ ~10−6). A high-gain FEL in an optimized storage ring can potentially deliver tens of megawatts of coherent power at wavelengths shorter than 1000 Å with a 10-Hz repetition rate.