Measurement and adjustment of the differential positions of colliding bunches at CESR

In CESR, 9 trains of 4 or 5 bunches of electrons and positrons collide at the interaction point, but bypass each other in the arcs of the storage ring using electrostatically separated orbits (pretzels). The parasitic bunch crossings resulting from the use of pretzel separation causes the bunches to have different orbits and, thus, the luminosity to be sensitive to the relative transverse positions of colliding bunches. We measure the bunch-by-bunch position projected to the interaction point from information available from the transverse feedback systems used for beam stabilisation. Some modification of the feedback systems has permitted the application of a bunch-by-bunch deflection designed to adjust the relative positions of colliding bunches. Observation of bunch-by-bunch position during collisions and the effect of relative position adjustments will be presented.