SURF III—A new electron storage ring at NIST

Abstract

The National Institute of Standards and Technology (NIST), formerly the National Bureau of Standards (NBS), has operated the Synchrotron Ultraviolet Radiation Facility (SURF), based on an electron accelerator, continuously since the early 1960s. SURF I was established in 1961, utilizing a 180 MeV electron synchrotron at NBS in Washington, D.C. This accelerator was moved to the Gaithersburg, MD site in 1968, specifically for the continuation of SURF I operations. It was converted to an electron storage ring, SURF II, in 1974 under contract with the Physical Sciences Laboratory (PSL) at the University of Wisconsin-Madison (UW), and became a national standard of irradiance in the UV and VUV spectral region. To improve its performance in this application and broaden its spectral range, SURF II has been converted to SURF III, commissioned in December 1998. The design and construction of the new system were overseen by PSL and the Synchrotron Radiation Center at UW. SURF III remains a weak-focusing, single-magnet storage ring with a circular orbit. However the original 140 ton (1.25 MN) laminated iron core magnet has been replaced with one having a 200 ton (1.78 MN) solid iron core of revised geometry, allowing operation over an energy range of 100 MeV–400 MeV. The magnet system design was optimized using both 2-D and 3-D calculations. The predicted circumferential field uniformity of the order of 2 parts in 104, a factor of 40 improvement, was confirmed experimentally over the electron energy range of anticipated radiometric applications. The storage ring vacuum system has been updated, two more radiation ports have been added, and the control system has been modernized. The exceptional magnetic field uniformity in this machine is already giving rise to interesting beam dynamical effects.