PAL, Pohang, Kyungbuk
In 1994, ESRF in Grenoble opened the era of third-generation light sources, and the first batch of third-generation machines immediately followed with ALS, Elettra, TLS, PLS, and Spring-8 in hard and soft X-ray regimes. For high brightness, these machines adopted a low-emittance storage-ring lattice and many straight sections for advanced undulators. With ever-growing user demands from materials science to life science research, many more facilities followed in this decade. The machine operations dramatically improved for more effective user services, along with technological advances in advanced diagnostics and controls, survey and alignments, top-up injections, super-conducting cavities, and in-vacuum undulators. There are now about 70 light sources in the world, and important scientific discoveries are driven from these facilities, including research resulting in a few Nobel Prizes. In this paper, we review the advancement of these third-generation machines.
SLAC, Menlo Park, California
Recently a new concept*, ** for FEL seeding has been proposed that should allow generation of much higher harmonics of the laser modulation than previously envisioned. The Echo-enabled Harmonic Generation (EEHG) FEL uses two modulators in combination with two dispersion sections to generate in the beam a high-harmonic density modulation starting with a relatively small initial energy modulation of the beam. The EEHG seeding technique makes feasible a one stage seeding of soft x-ray FELs. An experimental installation is now being constructed at SLAC to demonstrate the EEHG in the NLCTA facility.
*G. Stupakov, PRL, 102, 074801 (2009).
**D. Xiang and G. Stupakov, PRSTAB, 030702 (2009).