SPEAR 3 Design Report
The SPEAR storage ring was originally designed for electron-positron colliding beam experiments spanning an energy range of 1-4 GeV per beam. A racetrack lattice was chosen to create two long straight sections in the East and West ''pits''. A modified FODO lattice was chosen for the arcs, with the FODO cells separated by 3.1 m straight sections. Special matching-cell magnet configurations were required on either side of the East and West pits. Electrons and positrons were injected into the ring from the main SLAC linear accelerator (LINAC) at a maximum energy of 2.4 GeV, a level limited by the ratings of the transport line and SPEAR septum magnet. In 1972, SPEAR 1 was commissioned with an operating energy of 2.4 GeV, a level limited by the RF and magnet power supply systems. In 1974, these systems were upgraded for approximately 4 GeV operation. Soon after the SPEAR 2 upgrade became operational, the charmed {Psi}/J-particle was discovered at an energy of 1.5 GeV (per beam). SPEAR continued to operate at or near that energy for colliding beam experiments until the end of the high-energy physics program in the late 1980's. Two Nobel Prizes were awarded for work done at SPEAR: one for the discovery of the {Psi}/J, and another for discovering the electron-like {tau} particle in 1975. The first synchrotron radiation experiments took place in 1973 as part of the Synchrotron Radiation Pilot Project. The first Stanford Synchrotron Radiation Project (SSRP) beam line was commissioned in 1974, operating parasitically with the high-energy physics program. As more beam lines were added, and the experimental program gathered momentum, SSRP evolved into a full-fledged laboratory. In 1977, under the aegis of NSF funding, SSRP became known as SSRL. Two years later, SPEAR operation was divided between the high-energy physics and the synchrotron radiation physics communities. SSRL operated in the 3-3.5 GeV energy range so as to produce a higher-energy photon spectrum, and at currents up to 100 mA (at 3 GeV), a level limited by photon-absorber power ratings. The straight sections in the modified FODO lattice proved fortuitous for the development of synchrotron radiation technology as the first wiggler and undulator insertion devices used for synchrotron radiation experiments were installed in SPEAR 2. In 1982, SSRL became a DOE-funded laboratory. SPEAR was operated by SLAC until the end of the 1980's, with SSRL officially an experimental user of the facility. At the end of the high-energy physics program, SPEAR became a fully dedicated synchrotron radiation source, SSRL became a department within SLAC, and SSRL took over responsibility for SPEAR operations. By the late 1980's, the availability of the SLAC LINAC for SPEAR injection had become limited by the SLAC Linear Collider (SLC) project, which required full-time LINAC operation. In 1991, the problem was resolved by the completion of a dedicated electron injector composed of a LINAC pre-injector and a synchrotron booster. While the booster was designed for 3 GeV operation, the transport line and SPEAR septum magnet ratings still limit the SPEAR injection energy to a maximum of 2.4 GeV, the routine injection energy is now 2.3 GeV. A new SPEAR lattice configuration, which lowered the emittance from 470 nm-rad to 160 nm-rad by altering ring-magnet strengths, was also implemented in 1991. Two previous attempts to reduce emittance, one in 1976 and one in 1985, were unsuccessful because the lattice configurations were not compatible with the two-kicker injection bump then in use. The problem was resolved during the 1991 lattice re-configuration by adding a third electron injection kicker. In 1994, the magnet strengths were altered again, without changing emittance, to reduce the strength of the strong-focusing quadrupole magnets in the East and West pits. Currently, SPEAR operations benefit from an ongoing accelerator improvement program that has increased accelerator reliability and beam quality. However, certain user experiments could profit from improvements in flux, focused flux density, and brightness. To reach the performance level expected of third-generation synchrotron light sources, SPEAR 3 would need to increase photon brightness by at least an order of magnitude. The SPEAR 3 upgrade project will achieve this increase by replacing (1) the existing magnet lattice, (2) the vacuum chamber and (3) the RF system. The new lattice will reduce beam emittance by an order of magnitude. As beam lines are upgraded, stored beam current will increase--first by a factor of two, and later by as much as fivefold. Although beam lines must be modified to accept higher power densities, the majority of the beam line infrastructure (including insertion devices) will be reused for SPEAR 3 to minimize the total downtime.
- Research Organization:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (US)
- DOE Contract Number:
- AC03-76SF00515
- OSTI ID:
- 808721
- Report Number(s):
- SLAC-R-609; TRN: US0302588
- Resource Relation:
- Other Information: PBD: 2 Dec 2002
- Country of Publication:
- United States
- Language:
- English
Similar Records
The Stanford Synchrotron Radiation Laboratory, 20 years of synchrotron light
1997 Annual Site Environmental Report (ASER)