Stabilizing effects of chromaticity and synchrotron emission on coupled-bunch transverse dynamics in storage rings

• Main Author: Ryan R. Lindberg
• Format: Article
• Language: English
• Published: American Physical Society 2021-02-01
• Series: Physical Review Accelerators and Beams
• Online Access: http://doi.org/10.1103/PhysRevAccelBeams.24.024402

We present a theory that can compute the transverse coupled-bunch instability growth rates at any chromaticity and for any longitudinal potential provided only that the long-range wakefield varies slowly over the bunch. The theory is expressed in terms of the usual coupled-bunch eigenvalues at zero chromaticity, and when the longitudinal motion is simple harmonic our solution only requires numerical root-finding that is easy to implement and fast to solve; the more general case requires some additional calculations, but is still relatively fast. The theory predicts that the coupled-bunch growth rates can be significantly reduced when the chromatic betatron tune spread is larger than the coupled-bunch growth rate at zero chromaticity. Our theoretical results are compared favorably with tracking simulations for the long-range resistive wall instability, and we also indicate how damping and diffusion from sychrotron emission can further reduce or even stabilize the dynamics.