Survey techniques developed to align stacked beamlines at CEBAF

The Continuous Electron Beam Accelerator Facility (CEBAF) in Newport News, Virginia is a new accelerator designed to produce 4GeV 200 micro-amp continuous wave beams for nuclear physics research. It consists of two super-conducting linacs each accelerating electrons by 400 MeV and linked by arcs allowing five pass recirculation. These linacs form the straight sections in a racetrack shaped accelerator contained in over 1.3km of tunnel. The beam lines will consist of 42 superconducting accelerating cryomodules (in the linacs only), over 400 dipoles, 650 quadrupoles, and 100 sextupoles, most of the which are concentrated in the two arc sections of the machine. It is here that the single beam line from the linacs is split into five beams of differing energy and transported to the opposite linac where it is recombined into a single beam to again pass through a linac and receive additional acceleration. These recirculation arcs are designed to maintain beam quality through a lattice which is achromatic, isochronous and whose length is equal to a multiple number of RF wavelengths (1). The short term relative alignment tolerances coupled with the beam line design reflect the beam quality issues while absolute positioning determines the range of adjustment needed to match the RF phase in the linac segments. The alignment techniques which use a monumented control network as a reference, are designed to position stacked magnets and their support systems to these tolerances. Specialized procedures were tailored from existing hardware and software systems to address each phase or step of the alignment process. This allowed a relatively rapid expansion of alignment services at a new laboratory where surveying support was not seriously addressed until more then one third of the enclosure had been built.