Helical orbit studies in the Tevatron

The Tevatron is running very close to the beam-beam limit. Therefore, in order to increase the luminosity, the proton and antiproton beams must be separated to eliminate unwanted beam crossings. To achieve this beam-beam separation, the proton and antiproton beams must travel on separate helical orbits, except at the collision areas. Particles moving on helical orbits in the Tevatron have both their tune and coupling changed with no measurable change in their chromaticity or lifetime. The tune and coupling changes are due to b₂ multipole errors in the main bending magnets. The size of the changes depends on the phase of the helical orbit relative to the distribution of b₂ errors around the ring. For the upgraded Tevatron with separated orbits, the protons and antiprotons live on different helical orbits. Therefore, the antiprotons are tune-shifted relative to the protons by ~0.01 in both the horizontal and vertical planes, and they experience a different skew quadrupole field (Q_s) of ~0.2×10^-2 m^-1