A bunch killer for the NSLS X-ray electron storage ring

In the NSLS X-ray electron storage ring, which operates at a harmonic number of 30, the beam may be stored in many different bunch patterns. The minimum spacing between bunches is approximately 19 nsec. While most of the experimenters are primarily interested in photon flux, some experiments are sensitive to bunch spacing. Time resolved nuclear resonance scattering experiments, for example, need pulses of X-rays spaced of the order of 100 nsec apart and a very low noise floor (10^-6) between pulses. Perhaps even more important than the level of the background is that it be reproducible and homogeneous in time. It has been found in practice that a small number of electrons always get trapped in the “empty” rf buckets during injection into the storage ring and remain as low level stray bunches. These extra bunches produce an unacceptable temporally localized, nonreproducible background which is difficult if not impossible to correct for. A “bunch killer” system based on the rf knockout technique has been developed and installed on the ring to remove the unwanted bunches. We describe the operation of this system and present experimental results to illustrate its effectiveness