UVSOR transforms into a third-generation UV source

UVSOR, a second-generation synchrotron light source at the Institute for Molecular Science, Okazaki, Japan, has been successfully upgraded to UVSOR-II, providing a smaller emittance and a larger number of straight sections for insertion devices. The reconstruction of the accelerators was completed earlier this year and UVSOR-II has just become operational for users. The original UVSOR (UVSOR-I), a 750 MeV storage ring, had operated for about 20 years as a national VUV light source in Japan. Its circumference was 53 m with a four-fold symmetry and a double-bend achromat magnetic lattice. The beam emittance of UVSOR-I was 160 nm rad. The magnetic lattice of the storage ring has been modified to have a much smaller emittance of 27 nm rad with eight straight sections, six of which are available for insertion devices. The circumference has been kept the same. The quadrupole triplets between the bending magnets have been replaced by two quadrupole doublets and a short straight section of length 1.5 m. To save space, sextupole magnets have been integrated into the quadrupole magnets. The doublets on both sides of the longer straight sections have also been replaced. As a result, the lengths of the straight sections have been increased from 3 m to 4 m.

On 30 July, UVSOR-II succeeded in operating in the low-emittance mode of 27 nm rad. In the first week of September, operation for users was started at UVSOR-II with a filling beam current of 300 mA. An upgrade of the RF cavity is planned for the fiscal year 2004. At present, UVSOR-II has three undulators: a helical undulator and two in-vacuum short-period undulators. The test operations of the in-vacuum undulators have shown that these devices can be operated with narrow pole gaps of 15 mm without reducing the beam lifetime. Spectral flux and brilliance for the UVSOR-II are comparable with some of the most brilliant devices on third-generation storage rings (see Fig. 1).

Figure 1 The photon flux and brilliance of UVSOR-II compared with other third-generation storage rings.