Multi-bunch instabilities and current-dependent phenomena in the Cornell Electron Storage Ring
A current-limiting instability affecting horizontal betatron motion of multiple bunches of positrons in the Cornell Electron Storage Ring (CESR) is diagnosed and shown to be attributable to a damping phenomenon nonlinear in beam current. This damping is characterized as long-range, low-frequency, and broad band. A multi-bunch/multi-turn formalism, combining long-range wake field phenomena with betatron frequency spread effects, is presented. The wake fields and impedances of a layered resistive-dielectric-conductive wall and horizontal electrostatic separator plates are calculated. Landau damping from a fixed frequency spread is analyzed, showing how branch cuts and poles relate to decoherence and exponential solutions, respectively. Quantitative evaluation of bunch centroid response to shock excitation is given for the Lorentzian and rectangular betatron frequency distributions. Analytical results are confirmed by computer simulation. A phenomenological model of transverse beam stability in CESR is constructed to provide a predictive framework for both single-bunch and multi-bunch coherent damping rates.
- Research Organization:
- Cornell Univ., Ithaca, NY (USA)
- OSTI ID:
- 5879675
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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