| Paper | Title | Page |
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| TUOAAB01 | Self-Consistent Simulations of Multipacting in Superconducting Radio Frequencies | 769 |
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Multipacting continues to be an important issue in Superconducting Radio Frequency (SRF) cavities, particularly near waveguide couplers. Most modern simulations of multipacting are not self-consistent, using the fields from a purely electromagnetic simulation to drive the motion of multipacting electrons. This approach works well for the onset on multipacting but as the electron density increases in the cavity it can have an effect on the cavity mode. Recently VORPAL* has demonstrated its ability to mode the electrodynamics of SRF cavities using finite difference time domain (FDTD) algorithms coupled with the Dey-Mittra** method for modeling conformal boundaries. The FDTD approach allows us to easily incorporate multipacting electrons as PIC particles in the simulations. To allow multipacting simulations to be done with EM-PIC we have been developing particle boundaries for the cut-cells. Recently we have added particle removal boundaries at the particle sinks which will correct the unphysical build up of image charge at the boundaries. Work has begun on incorporating secondary electron emission into these boundaries so VORPAL can model multipacting trajectories self-consistently.
* C. Nieter, J. R. Cary, J. Comp. Phys. 196 (2004) 448.** S. Dey, R. Mittra, IEEE Microwave and Guided Wave Letters 7 (1997) 273. |
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| TUOAAB02 | Measurement and Simulation of Space-Charge Dependent Tune Separation in FNAL Booster | 772 |
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In recent years, a number of space-charge studies have been performed in the FNAL Booster. The Booster is the first circular accelerator in the Fermilab chain of accelerators, with an injection energy of 400 MeV. The combination of this relatively low injection energy and improving beam intensity for Booster's high intensity applications necessitates a study of space charge dynamics. Measurement and simulation of space charge coupling in the Booster will be presented. The coupling measurement was performed using a standard technique, albeit repeated for different injected beam intensities. The initial transverse tune separation was minimized (Qx=Qy=6.7), followed by a systematic skew quadrupole strength variation. Transverse beam oscillation frequencies were recorded while exciting the beam. These frequencies were recorded for a range of 1.0·1012 to 3.5·1012 particles. A linear increase in the measured tune separation with beam intensity was observed. For comparison, beam coupling was also simulated with the space-charge code Synergia. This code has successfully modeled the space-charge tune shift in the Booster*, and compares favorably to other space charge codes and analytic results.
* Synergia: A 3D Accelerator Modelling Tool with 3D Space Charge. Journal of Computational Physics, Volume 211, Issue 1 , 1 January 2006, Pages 229-248. |
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