High Accuracy Momentum Compaction Measurement for the APS Storage Ring with Undulator Radiation

We developed a new technique to measure the electron beam energy centroid and spread. It takes advantage of a sharp feature in the Advanced Photon Source (APS) diagnostic: undulator spectrum, the drop-off in the angle-integrated flux near its fundamental photon energy. The measurement technique has a high resolution and is nearly independent of the storage ring lattice functions. In this work, we present the results of electron beam energy measurements as a function of rf frequency and obtain the momentum compaction factor of the AI% storage ring to be 2.27 * 0.03x104, in good agreement with theoretical value of 2.285x 104. We will also discuss methods to further reduce experimental errors, making the technique potentially the most accurate one for measuring momentum compaction factors of a storage ring.