Paper  Title  Page 

TUOAAB01  SelfConsistent Simulations of Multipacting in Superconducting Radio Frequencies  769 


Multipacting continues to be an important issue in Superconducting Radio Frequency (SRF) cavities, particularly near waveguide couplers. Most modern simulations of multipacting are not selfconsistent, 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 DeyMittra** 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 EMPIC we have been developing particle boundaries for the cutcells. 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 selfconsistently.
* 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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THPAS015  ThreeDimensional Integrated Green Functions for the Poisson Equation  3546 


Funding: Supported by US DOE Office of Science: Offices of Nuclear Physics, grant DEFG0203ER83796; High Energy Physics; and Advanced Scientific Computing Research, SciDAC Accelerator Science and Technology. The standard implementation of using FFTs to solve the Poisson equation with open boundary conditions on a Cartesian grid loses accuracy when the change in G rho (the product of the Green function and the charge density) over a mesh cell becomes nonlinear; this is commonly encountered in high aspect ratio situations and results in poor efficiency due to the need for a very large number of grid points. A modification which solves this problem, the integrated Green function (IGF), has been implemented in two dimensions using linear basis functions and in three dimensions using constant basis functions. But, until recently, it has proved to be very difficult to implement IGF in three dimensions using linear basis functions. Recently significant progress has been made. We present both the implementation and test results for the threedimensional extension. 

FROBAB01  Simulationdriven Optimization of Heavyion Production in ECR Sources  3786 


Funding: Work supported by the U. S. DOE Office of Science, Office of Nuclear Physics, under grant DEFG0205ER84173. Nextgeneration heavyion beam accelerators require a great variety of high charge state ion beams (from protons to uranium) with up to an order of magnitude higher intensity than demonstrated with conventional Electron Cyclotron Resonance (ECR) ion sources. Optimization of the ion beam production for each element is therefore required. Efficient loading of the material into the ECR plasma is one of the key elements for optimizing the ion beam production. Highfidelity simulations provide a means to understanding where along the interior walls the uncaptured metal atoms are deposited and, hence, how to optimize loading of the metal into the ECR plasma. We are currently extending the plasma simulation framework VORPAL with models to investigate effective loading of heavy metals into ECR ion sources via alternate mechanisms, including vapor loading, ion sputtering and laser ablation. Here we will present the models, simulation results of vapor loading and initial comparisons with experiments at the VENUS source at LBNL. 

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