Based on a 2004 upgrade funded by the Department of Energy and the National Institutes of Health, SPEAR3 is a 3-GeV, high-brightness third generation storage ring typically operating at 500 mA beam current in top-off mode, during which the current is kept constant within 1% by injecting electrons into the ring every five minutes. The X-rays utilized by the different beamlines at SSRL are produced using insertion devices (wigglers and undulators) and bending dipole magnets of its accelerator, SPEAR3.
Beamline 4 uses a 2300mm long, 20 pole (i.e. 230mm period), 2T wiggler insertion device from Danfysik as its X-ray source. The wiggler produces an intense beam of X-rays with a critical energy of 12.26 keV. The radiation fan emitted by the wiggler (with a half width of 8.5 mrad) provides X-rays for the three experimental end stations at beamline 4. The outer portions of the fan is utilized by the spectroscopy side stations BL4-1 and BL4-3, the central 1.25 mrad of the produced X-rays is providing an intense beam of synchrotron radiation for BL4-2.