Latest Experience on Insertion Devices at The National Synchrotron Light Source-II

概要

National Synchrotron Light Source-II (NSLS-II) is the latest storage ring of 3 GeV energy at the Brookhaven National Laboratory (BNL) in the U.S.A.
The horizontal emittance of the electron beam with six 3.4m long damping wigglers (DWs) is 0.9 nm.rad, which could be further reduced with more insertion devices (IDs).
Eight in-vacuum undulators (IVUs) with unique side window feature have been installed.
Other in-air devices utilize vacuum chambers coated with Non-Evaporable Getter (NEG).
A three Pole Wiggler (3PW) will be used as an alternative radiation source for conventional bending magnet (BM) users.
Damping wigglers with 100mm period in three symmetric positions are utilized for both beam emittance reduction and high energy photon sources.
2.0m long Apple-II type [1] EPUs are installed for coherent soft-X-ray beam line. Four different types of IVUs are employed at the NSLS-II as of now.
Two 3.0m long U20s (the number indicates the period length in mm), Three 1.5m long U21s for low beta straights and a 3.0m long U22 and two 2.8m long U23 are for high beta straights.
All devices have a side window derived from the experience from the Chess facility at Cornel University
Commissioning devices went very smoothly.
However, we observed a slight misalignment of an IVU could cause significant decrease in injection efficiency at closed gap or create a "hot spot" in downstream chamber.
We have tried to make estimates of the 1st integral contribution from each undulator by measuring the closed orbit distortion (COD) without any feedback when the undulator's gap is closed.
The beam-based integral estimates were obtained from the virtual kicks at the upstream and downstream of the undulator that best fit the measured orbit distortion in a model lattice with Tracy[2].
In some cases, there are fairly large discrepancies between magnetic measurement data and observed integrals by the beam.
The latest experiences on IDs and other accelerator components at the NSLS-II are discussed.

1) S. Sasaki, et al., "A new undulator generating variably polarized radiation," Jpn. J. Appl. Phys. 31 (1992) L1794.
2) J. Bengtsson, E. Forest and H. Nishimura, 'Tracy User Manual"