The new superconducting RF system consisting of four single-cell cavity modules is an important part of the CESR Luminosity Upgrade.We describe the commissioning of the first three accelerating modules. This includes in situ testing and conditioning, pulsed power and beam processing of RF windows, commissioning of various cryogenic feedback loops, measuring cavity spacing and phasing with beam, and high-current operation.

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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