Betatron phase and coupling measurements at the Cornell Electron/Positron Storage Ring

Errors in the lattice parameters of a storage ring can come from many sources. For example, the calibration constants used to set quadrupole magnets may be inaccurate, the orbit may pass through the sextupoles off center, or there may be unsuspected quadrupole fields associated with machine elements. To verify that a design lattice has actually been implemented correctly, one or more selected lattice functions must be measured around the ring to be compared with the expected values. At CESR, the Cornell Electron/Positron Storage Ring, exploiting the fact that the quadrupole magnets are individually controlled, one method that has been used is to measure the tune Q as a function of quadrupole strength k. The Twiss parameters bh and by at the quadrupole are then obtained from the standard formula [1]