Flying wires at Fermilab

Transverse beam profile measurement systems called flying wires have been installed and made operational in the Fermilab Main Ring and Tevatron accelerators. A flying wire is a device that passes (flies) a 25-μm carbon filament through a particle beam, transversely, at a constant velocity of between 2 and 5 m/s. Collisions between the beam particles and the wire produce secondary particle cascades, which in turn produce photons in a scintillator. A photomultiplier tube and an optical encoder are used to measure the light intensity and the wire position, respectively. A light intensity vs. transverse position plot can then be obtained, from which the beam width is determined. Two wires in the horizontal plane and one wire in the vertical plane, at the appropriate positions in the lattice of a circular accelerator, permit measurements of the beam emittance. These devices are used routinely to measure the emittance of both protons and antiprotons throughout the fill process, and for emittance growth measurements during storage. In the Tevatron, the individual transverse profiles of six proton and six antiproton bunches are obtained simultaneously, with a single pass of the wire through the beam. Essential features of the hardware, software, and system operation are explained