Abstract
A time domain dynamic modeling and simulation tool for beam-cavity interactions in the Low Energy Ring (LER) and High Energy Ring (HER) at the Positron-Electron Project (PEP-II) is presented. Dynamic simulation results for PEP-II are compared to measurements of the actual machine. The motivation for this tool is to explore the stability margins and performance limits of PEP-II radio-frequency (RF) systems at future higher currents and upgraded RF configurations. It also serves as a test bed for new control algorithms and can define the ultimate limits of the low-level RF (LLRF) architecture. The time domain program captures the dynamic behavior of the beam-cavity-LLRF interaction based on a reduced model. The ring current is represented by macrobunches. Multiple RF stations in the ring are represented via one or two macrocavities. Each macrocavity captures the overall behavior of all the 2 or 4 cavity RF stations. Station models include nonlinear elements in the klystron and signal processing. This enables modeling the principal longitudinal impedance control loops interacting via the longitudinal beam model. The dynamics of the simulation model are validated by comparing the measured growth rates for the LER with simulation results. The simulated behavior of the LER at increased operation currents is presented via low-mode instability growth rates. Different control strategies are compared and the effects of both the imperfections in the LLRF signal processing and the nonlinear drivers and klystrons are explored.
Highlights
High-current accelerators exhibit dynamics between the beam-loaded radio-frequency (RF) systems and the particle beams
To counteract coupled-bunch instabilities due to the RF cavity fundamental impedance, some RF systems employ feedback techniques which act to reduce the impedance interacting with the particle beam and increase the stability of the beam
This paper presents results from a nonlinear simulation study of the RF systems in the Positron-Electron Project (PEP-II) B-Factory collider, and highlights the design and topology of the low-level RF (LLRF) feedback systems
Summary
High-current accelerators exhibit dynamics between the beam-loaded radio-frequency (RF) systems and the particle beams. This paper presents results from a nonlinear simulation study of the RF systems in the Positron-Electron Project (PEP-II) B-Factory collider, and highlights the design and topology of the low-level RF (LLRF) feedback systems. The simulation model is verified against measured accelerator dynamics, and the likely operational limits for the existing LLRF system implementation are predicted. It compares the growth rates of simulation and physical system for the same operating points. X mentions some of the potential projects involving the simulation and future measurements related to this work
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