Instability threshold currents vs. energy in CESR

CESR has been observed to have two coupled bunch instabilities, one horizontal and the other longitudinal, which can limit the total beam current when operating with trains of bunches. Feedback has been employed for some time to counter these instabilities. This paper reports on the threshold current for the onset of the longitudinal instability when feedback is turned off vs. beam energy over a range from 1.9 GeV to 5.2 GeV and compares the change in threshold current with that expected from the change in radiation damping. Operating performance with feedback in use will also be reported for both longitudinal and horizontal instabilities.