SPEAR3 – a 3 GeV third-generation synchrotron radiation source at Stanford

Stanford Synchrotron Radiation Laboratory (SSRL) was one of the pioneering synchrotron radiation laboratories that started life with the parasitic use of a high-energy accelerator [others from this vintage have been DESY, Frascati and NINA-SRF at Daresbury; see J. Synchrotron Rad. (1997), 4, 315–405 ]. SPEAR has undergone several upgrades but this time a completely new machine has been the goal, with a low emittance of 12–18 nm rad and a design maximum current capability of 500 mA. The machine is capable of incorporating a large number of insertion devices in its straight sections, including narrow-gap undulators.

Eight short months after the last electrons circulated in the original SPEAR storage ring (which began operation in the early 1970s for high-energy physics with parasitic operation for synchrotron radiation), the first electrons circulated in the completely new SPEAR3 ring. Commissioning of the new 3 GeV SPEAR3 light source began on 10 December 2003, with first beam being accumulated five days later. A little over a month later, currents of 70 mA with reasonable lifetimes are already being reached and at-energy injection is very effective. The rapid installation and success of very rapid commissioning is a real testimony to the whole SPEAR3 project staff and collaborators who have built an excellent machine and equipped it with powerful and accessible machine modelling and control programs. The first user run on SPEAR3 is scheduled to begin in March of this year, less than a year after the shutdown to begin the installation of SPEAR3 in April 2003.

The SPEAR3 upgrade at a cost of USD 58 million was made possible by the joint support and funding by the US Department of Energy and the National Institutes of Health. Construction and installation work was performed jointly by contractors and staff from SSRL, along with numerous other divisions at SLAC.

The 3 GeV 500 mA ring boasts a copper vacuum chamber, mode-damped RF cavities and state-of-the-art power supply, and state-of-the-art instrumentation and control systems. The original SSRL beamlines are being upgraded with liquid-nitrogen-cooled monochromators, high-performance mirrors and other optical components in preparation for future 500 mA operation expected to commence towards the end of 2004. While the permanent-magnet insertion devices from SPEAR2 have been retained, two electromagnet wigglers have been replaced with permanent-magnet devices. To take full advantage of the new low-emittance lattice, two new undulator beamlines are already under construction, a soft X-ray undulator serving microscopy and another for materials applications. A hard X-ray in-vacuum undulator for macromolecular crystallography is also being pursued.