Abstract
This paper explains an analytical formula for longitudinal coherent oscillations in an electron storage ring, including path-length oscillations. A path-length oscillation produced by closed orbit distortion was experimentally identified in the NewSUBARU electron storage ring and found to be harmful to normal operations. Such oscillations are also a potential problem in other advanced light sources especially in a quasi-isochronous operation.
Highlights
There are two possible external sources of longitudinal oscillation in an electron storage ring
Phase oscillation amplitudes were estimated from a fastFourier transform (FFT) power spectrum of the beam signal, which was picked up from a pickup button electrode (PUE) placed in a dispersion-free section
In the normal operations at NewSUBARU, it has become clear that the main source of low-frequency energy fluctuations is the path-length fluctuation and that of the beam phase fluctuation is the rf system
Summary
There are two possible external sources of longitudinal oscillation in an electron storage ring. It has long been known that a COD changes the path length and can excite longitudinal motion [13,14], most published works on synchrotron radiation rings do not consider this effect. Some works using the proton storage ring studied this effect at a frequency close to the synchrotron frequency and paid no attention to a small off-resonant movement. That longitudinal movement can be more serious in the quasiisochronous operation of an electron storage ring. According to some reports of quasi-isochronous storage ring operation, longitudinal coherent fluctuations or oscillations can impose a practical limit on the bunch shortening. The sources of the coherent oscillations observed at NewSUBARU were identified and the path-length fluctuation was found to be a problem, even at off-resonance frequencies. In this article we use the word ‘‘oscillation’’ to express the fluctuations for a convenience of the frequency domain analysis, offresonant movement is not always oscillatory
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