• Y. Cai, K.L.F. Bane, K.J. Bertsche, A. Chao, R.O. Hettel, X. Huang, Z. Huang, C.-K. Ng, Y. Nosochkov, A. Novokhatski, T. Rabedeau, J.A. Safranek, G.V. Stupakov, L. Wang, M.-H. Wang, L. Xiao
  SLAC, Menlo Park, California

Over the past year, we have worked out a baseline design for PEP-X, as an ultra-low emittance storage ring that could reside in the existing 2.2-km PEP-II tunnel. The design features a hybrid lattice with double bend achromat cells in two arcs and theoretical minimum emittance cells in the remaining four arcs. Damping wigglers reduce the horizontal emittance to 86 pm-rad at zero current for a 4.5 GeV electron beam. At a design current of 1.5 A, the horizontal emittance increases, due to intra-beam scattering, to 164 pm-rad when the vertical emittance is maintained at a diffraction limited 8 pm-rad. The baseline design will produce photon beams achieving a brightness of 10²² (ph/s/mm²/mrad²/0.1% BW) at 10 keV in a 3.5-m conventional planar undulator. Our study shows that an optimized lattice has adequate dynamic aperture, while accommodating a conventional off-axis injection system. In this paper, we will present the study of the lattice properties, nonlinear dynamics, intra-beam scattering and Touschek lifetime, and collective instabilities. Finally, we discuss the possibility of partial lasing at soft X-ray wavelengths using a long undulator in a straight section.