Lattice Design for PEP-X Ultimate Storage Ring Light Source

SLAC expertise in designing and operating high current storage rings and the availability of the 2.2-km PEP-II tunnel present an opportunity for building a next generation light source - PEP-X - that would replace the SPEAR3 storage ring in the future. The PEP-X 'baseline' design, with 164 pm-rad emittance at 4.5 GeV beam energy and a current of 1.5 A, was completed in 2010. As a next step, a so-called 'ultimate' PEP-X lattice, reducing the emittance to 11 pm-rad at zero current, has been designed. This emittance approaches the diffraction limited photon emittance for multi-keV photons, providing near maximum photon brightness and high coherence. It is achieved by using 7-bend achromat cells in the ring arcs and a 90-m damping wiggler in one of the 6 long straight sections. Details of the lattice design, dynamic aperture, and calculations of the intra-beam scattering effect and Touschek lifetime at a nominal 0.2 A current are presented. Accelerator-based light sources are in high demand for many experimental applications. The availability of the 2.2-km PEP-II tunnel at SLAC presents an opportunity for building a next generation light source - PEP-X - that would replace the existing SPEAR3 light source in the future. The PEP-X study started in 2008, and the 'baseline' design, yielding 164 pm-rad emittance at 4.5 GeV beam energy and a current of 1.5 A, was completed in 2010. This relatively conservative design can be built using existing technology. However, for a long term future, it is natural to investigate a more aggressive, so-called 'ultimate' ring design. The goal is to reduce the electron emittance in both x and y planes to near the diffraction limited photon emittance of 8 pm-rad at hard X-ray photon wavelength of 0.1 nm. This would provide a near maximum photon brightness and significant increase in photon coherence. This study was motivated by the advances in low emittance design at MAX-IV. The latter was used as a starting point for the PEP-X arc lattice, however new features were included into the design for better tuning capabilities and compensation of non-linear optics effects. Further emittance reduction is achieved with a 90-m damping wiggler. Finally, intra-beam scattering (IBS) and Touschek lifetime effects were estimated and cross-checked using various codes