First observation of simultaneous alpha buckets in a quasi-isochronous storage ring.

We present the first experimental evidence confirming the theoretical predictions of alpha buckets in an electron storage ring. By controlling both the first- and second-order momentum compaction factors, we succeeded in storing electrons simultaneously in a pair of alpha buckets or in either bucket alone. The two electron bunches are separated in energy by slightly less than 1% and the energy is tunable over a narrow range. The energy difference was directly measured using synchrotron light from an undulator. Simultaneous two-color light beams from an undulator were generated. By changing the rf voltage, we were able to vary the normally fixed longitudinal bunch separation.