A storage ring mode for CEBAF as a commissioning tool

The CEBAF project (under construction in Newport News, Virginia) is a recirculated linear accelerator. Two superconducting accelerating section (240 m each) are connected by semicircular arcs containing beam lines for different energies (4 at one end and 3 at the other). Injected electrons will pass the cavity sections up to 4 times before extraction. The CEBAF accelerator will be equipped with a variety of diagnostic tools. With the aid of computer modeling these diagnostics will help to reach the proposed beam quality: a transverse emittance of 10-9 rad · m and a relative energy spread of 10-4. Nevertheless, some very precise diagnostic tools used in circular accelerators can not be applied at CEBAF. In particular, the measurement of phase advance by resonant excitation of the beam and absolute beam energy measurement using electron spin polarization are not possible in this linear machine. In this paper, the authors propose an extension to the current design that will allow CEBAF to run in a storage ring mode. The optics and configuration of the transport elements required to achieve the new operating mode is presented. Finally, the use of this capability as a commissioning tool is illustrated