Ultimate storage ring based on fourth-order geometric achromats

We have designed an ``ultimate'' storage ring for a future light source that would be resided in the positron-electron-project (PEP) tunnel and achieves the diffraction-limited emittances (at 1.5 \AA{}) of 12 pm-rad in both horizontal and vertical planes with a 4.5-GeV electron beam. These emittances include the contribution of intrabeam scattering at a nominal current of 200 mA in 3300 bunches. This quality beam in conjunction with a conventional 4-m undulator in a straight section can generate synchrotron radiation having a spectral brightness above ${10}^{22}\text{ }\text{ }[\mathrm{photons}/\mathrm{s}/{\mathrm{mm}}^{2}/{\mathrm{mrad}}^{2}/0.1%\mathrm{BW}]$ at a 10 keV photon energy. The high coherence at the diffraction limit makes this design competitive with 4th generation light sources based on an energy recovery linac. In addition, the beam lifetime is several hours and the dynamic aperture is large enough to allow off-axis injection. The alignment and stability tolerances, though challenging, are achievable. A ring with all these properties is only possible because of several major advances in mitigating the effects of nonlinear resonances.