放射光第巻第号

()海外情報

SPEAR 3: A High Flux Synchrotron Light Source†
JeŠ Corbett and Tom ElioŠ for the SPEAR 3 Technical StaŠ
Stanford Synchrotron Radiation Laboratory*To better serve the expanding SSRL user community,
SSRL will replace all major technical systems in a SPEAR
upgrade in 2003. The 4-year, 58 M$ SPEAR 3 upgrade
project is funded jointly by the DOE and the NIH. The main
goals of the project are to increase photon ‰ux and provide
stable photon beams to the user community. To achievethese goals, SSRL will replace the entire tunnel ‰oor, support rafts, vacuum chamber, magnet lattice, RF system,
power supplies and cable plant in a 6-month shutdown
period. The existing arrangement of 27 experimental beamlines with wiggler, undulator and bend magnet source points
will remain largely unchanged.
The new SPEAR 3 storage ring will have 18 nm-radianemittance and straight sections available for up to 13 insertion devices. SPEAR 3 will provide stable, 3 GeV beam oper-Figure 1.

ation with currents up to 500 mA and beam lifetimes of À15hours. Much of the storage ring hardware is based on PEP-II
B-Factory technology, including the copper vacuum chamber and mode-damped rf cavities.
The accelerator layout of SPEAR 3 is shown in Fig. 1 withthe standard cell structure and ˆrst article raft assemblyshown in Fig. 2 and 3. All systems are designed for a top
energy of 3.3 GeV (350 mA). At 3.0 GeV, SPEAR 3 will provide 10–100 times higher ‰ux density than SPEAR 2 opening
new research opportunities in the ˆelds of materials technology, high-throughput protein crystallography and environmental science.
Several features of the SPEAR 3 lattice have been optimized to improve photon beam quality. First, the emittanceand betatron functions were reduced to decrease horizontal

SPEAR 3 Light Source.

† Work supported in part by DOE Contract DE–AC03–76SF00515 and O‹ce of Basic Energy Sciences, Division of Chemical Sciences.

* Stanford Synchrotron Radiation Laboratory, P.O. Box 4349, Bin 69 Stanford, California 94309–0210, USA
TEL: ＋16509263645 FAX: ＋16509264100 E-mail: corbett＠slac.stanford.edu――(C) 2001 The Japanese Society for Synchrotron Radiation Research

放射光Table 1.

()

Parameters for SPEAR 2 and SPEAR 3SPEAR 2Energy

Figure 2.

第巻第号

SPEAR 3

3 GeV

3 GeV

CurrentID)
Emittance (w W

100 mA
160 nm-rad

500 mA18 nm-radRF frequency

358.5 MHz476.3 MHzRF gap voltage
Lifetime＠Imax

1.6 MV30 h

3.2 MVÀ18 hCritical energy
Tunes (x, y, s)

4.8 keV
7.18, 5.28, 0.019

7.6 keV
14.19, 5.23, 0.007

e-s (x, y, s)–ID

2.0, 0.05, 23 mm

0.43, 0.03, 4.9 mm

e-s (x, y, s)–dipole
Injection energy

0.79, 0.20, 23 mm
2.3 GeV0.16, 0.05, 4.9 mm
3 GeVStandard cell assembled on three support rafts.

Figure 3.

First Article Raft Assembly.

beam size from 2 mm to 430 micron. In the process, the dipole magnet strength was raised to boost critical energy from
4.8 to 7.6 keV. In the 20 keV range, bend magnet beam lines
will produce photon beam ‰ux densities comparable to themost intense wiggler beam in SPEAR 2 (BL 10–2). To provide for future dipole beam line expansion, 14 of the 18 magnet cells will have dipole-beam exit ports. For comparison,
the main machine and electron beam parameters for SPEAR
2 and SPEAR 3 are shown in Table 1.
In addition, four 2.3 m straight sections in SPEAR 2 wereincreased to 4.8 m. Three of these 4.8 m straights will beavailable for new beamlines. ID sources under consideration
include a 3.8-m elliptically polarized undulator for soft x-ray(250–2600 eV) applications. Finally, the collider physics
straight sections were optimized to provide two 7.6 mstraights. One of these straights will contain four PEP–II RFcavities. The other straight is available for either a long undulator or two 2-m, in-vacuum small-gap undulators forhigh brightness hard x-ray applications (À6 keV).
Along with the SPEAR 3 project comes a parallel beamline upgrade program to utilize the high power radiation
beams. Existing bend magnet and wiggler beam lines will be
optimized for applications exploiting high ‰ux density photon beams with modest beam collimation (macromolecular
crystallography measurements, XAS, etc.). Two 9 period 2.0
T wigglers will replace older 4 period, 1.8 T wigglers to further enhance output.
The current status of the SPEAR 3 project is approximately 70z completion of the overall technical systems designand 40z completion of machine fabrication. The SPEAR 3
magnets are being produced in collaboration with IHEP withover 50z delivered. The production of the copper vacuum
chamber is fully underway utilizing the SLAC e-beam welder. The 1.2 MW klystron for the RF system has been
received, and the RF cavities will be delivered by the end ofthe 2001. Shielding modiˆcations will be 75z complete thisyear.
All technical systems are scheduled to be assembled 3months ahead of the April 2003 shutdown. To minimize interruption to the user program, modiˆcations to buildings
and utilities will be made during maintenance periods before
the 2003 shutdown. The SPEAR 3 accelerator will deliver
beam at the earliest possible date in 2004.

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