The magnet lattice of the LBL 1-2 GeV synchrotron radiation source

This paper describes the magnet lattice chosen for the LBL 1-2 GeV Synchrotron Radiation Source. The structure has a circumference of 196.8 m, with 12 dispersion free straight sections that can accommodate insertion devices up to 5 m long. The achromatic arcs that connect these straight sections feature combined function (gradient) bending magnets. Utilization of three such magnets in the so-called three-bend-achromat (TBA) arrangement, has several beneficial effects: (1) it reduces the amplitude of the vertical beta-function in the bending magnets, thereby minimizing the required aperture; (2) it changes the damping partition number in such a way as to reduce the natural emittance; and (3) it produces separation of the beta-functions such that relatively low sextupole strengths are sufficient for chromatic correction. The result is a structure with very low emittance (4 nm-rad at 1.5 GeV) that is correctable with only two families of sextupoles while maintaining excellent chromatic properties and acceptable dynamic aperture