SLAC, Menlo Park, California, USA
FACET-II will be a new test facility, starting construction in 2018 within the main SLAC Linac. Its purpose is to build on the decades-long experience developed conducting accelerator R&D at SLAC in the areas of advanced acceleration and coherent radiation techniques with high-energy electron and positron beams. The positron system design utilizes an existing W-Re target in Linac Sector 19, driven by 4 nC electrons bunches at 10 GeV. We present the design of a 335 MeV, 21.4 m circumference damping ring required to damp emittance from a modified positron return beamline by a factor of 500. The transverse emittance is calculated to be 6 um-rad, fully coupled, with a bunch length of 4 mm and energy spread 0.06 %, at a bunch charge of 1 nC. The arc magnets need to be especially compact due to tight space constraints (installation will be in the existing SLAC Linac tunnel, Sector 10, with 3 m width available) and were a key design challenge. We present a solution with combined function bend/quadrupole/sextupole magnets which have been modelled in 3D using Opera.
