A Possible Redesign of the SLAC SLC Damping Rings ’

We describe a possible replacement for the SLC damping rings that would generate beams with normalized horizontal emittances of rcz = 9 x 10B6 m-rad when uncoupled; this is more than three times smaller than that generated by the current rings. The primary difference between the new design and the current ring is the arc cell structure; the insertion regions, the kickers, and the RF are essentially unchanged. The new cell uses a single combined function bending magnet, roughly 70 cm in length, to replace the two bends, defocusing quadrupole, and defocusing sex-tupoles in the current FODO cell; the focusing quadrupole and sextupoles, used in the current cell, are also used in the new structure. The length of the new cell is identical to that of the current cell and thus nine of these new cells would simply replace the nine FODO cells in each arc of the rings. .-_ Introduction In this paper, we will describe a possible replacement for the Stanford Linear Accelerator (SLC) damping rings. The SLC damping rings [l] are very compact storage rings, ope;-aiing-at 1.19 GeV with a circumference of 35.28 meters. They have transverse damping times of 3.5 ms and equilibrium rms emittances of ycz = 3 x 10m5 m-rad. The rings. are composed of 18 FODO bending cells plus two insertion regions for injection/extraction, kickers, and RF. Although the equilibrium emittance of the SLC damp-'ing rings is very small, given the recent performance of the SLC, we can consider the possibility of transporting even smaller emittances to the IP (21. The minimum emittance at the IP is set by the synchrotron radiation emittance growth through the SLC arcs. In normalized units, this is roughly ycr = 1.3 x 10m5 and ycv = 0.1 x 10m5m-rad. These emittances will be added to the emittances at the end of the SLC linac and thus we used these values as a goal for the emittances of a future damping ring; one has diminishing returns when achieving values significantly smaller.-We will first discuss the constraints on the replacement ring and then we will describe the lattice and the bending magnets. Next, we describe the dynamic aperture _ limitations and a possible correction scheme, and finally, we discuss other possible upgrades to the SLC damping rings. Emittance Reduction and Lattice Choice When considering a replacement, one is constrained to the same energy, the same, or faster, damping times, …