Total stored electron and positron beam currents at the Cornell Electron Storage Ring (CESR) have been limited by the presence of a dipole multibunch longitudinal instability having a threshold at approximately 250mA of total current. A longitudinal feedback system has been under constant development, test, operation and upgrade over the past several years. The result has been an increase in the High Energy Physics (HEP) operating current to over 500mA total. This paper describes the overall design of the present system, using a horizontal stripline kicker to produce combined horizontal and longitudinal bunch by bunch beam stabilization. Some details on specific subsystems, including: receiver design, individual bunch phase DC offset correction, digital signal filtering, and the RF modulator will be given, as well as an outline of plans for further development.

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The operation of CESR as an electron-positron collider using trains of bunches requires the use of beam stabilizing feedback systems at routine operating currents. These systems operate on the longitudinal and both transverse modes of dipole oscillation. The experience in routine operations and feedback system performance will be presented.

Using the silicon strip detector of the CLEO experiment operating at the Cornell Electron-Positron Storage Ring ͑CESR͒, we have observed that the horizontal size of the luminous region decreases in the presence of the beam-beam interaction from what is expected without the beam-beam interaction. The dependence on the bunch current agrees with the prediction of the dynamic beta effect. This is the first direct observation of the effect.

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