Direct observation of individual SPEAR electron bunch orbit oscillations at frequencies above 30 kHz

Abstract

Using a prototype detector being developed for time-resolved X-ray diffraction, we have recently been able to observe oscillations in SPEAR electron bunch orbits at frequencies corresponding to various resonances in the rf power system. In spite of the fact that the SPEAR beam steering feedback systems were turned on and the orbit was nominally stable, we observed intensity fluctuations of ± 10% or more at frequencies corresponding to various synchrotron resonances in SPEAR. These intensity fluctuations arise from vertical fluctuations in either orbit location σ y or trajectory σ′ y . The experimental geometry implies that σ y and σ′ y can easily be as large as 1.3 mm and 67 μrad, respectively. Different oscillation patterns were seen for the different bunches during the same time frame, implying that each bunch is following its own trajectory and interacting differently with the system resonances. Changes in the single bunch patterns were sometimes observed in times less than 50 μs. The existence of these oscillations has important implications both for machine physicists responsible for beam-position control at the new storage rings and for users considering fast, time-resolved experiments.