| Paper | Title | Page |
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| WE6RFP075 | Scaled Simulation Design of High Quality Laser Wakefield Accelerator Stages | 2970 |
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Funding: Funded by the U.S. DOE Office of Science HEP including contract DE-AC02-05CH11231 and SciDAC, and by U.S. DOE NA-22, DARPA, and NSF Collider and light source applications of laser wakefield accelerators will likely require staging of controlled injection with multi-GeV accelerator modules to produce and maintain the required low emittance and energy spread. We present simulations of upcoming 10 GeV-class LWFA stages, towards eventual collider modules for both electrons and positrons*. Laser and structure propagation are controlled through a combination of laser channeling and self guiding. Electron beam evolution is controlled through laser pulse and plasma density shaping, and beam loading. This can result in efficient stages which preserve high quality beams. We also present results on controlled injection of electrons into the structure to produce the required low emittance bunches using plasma density gradient** and colliding laser pulses. Tools for accurately modeling emittance and energy spread will be discussed***. *E. Cormier-Michel et al., Proc. Adv Accel. Workshop 2008. |
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| FR5PFP083 | Accurate and Efficient Study of RF Cavities by Using a Conformal FDTD Method | 4503 |
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Funding: DoD FA9451-07-C-0025 This work introduces a conformal finite difference time domain (CFDTD) method as implemented in VORPAL to accurately and efficiently study RF cavities. For illustration, an A6 magnetron cavity has been employed and the corresponding dispersion relation has been carried out. The accuracy of the CFDTD method is measured by comparing with SUPERFISH calculations. To verify the accuracy of the CFDTD simulations, a geometric model has been constructed in VORPAL and simulated with different mesh numbers as 10,000, 40,000, 90,000, 160,000, and 250,000 for three DMFRAC values equal to 0.75, 0.5 and 0.25, respectively. The results show an accuracy of 99.4% can be achieved by using only 10,000 meshes with Dey-Mittra algorithm. By comparison, a mesh number of 360,000 need be used to preserve an accuracy of 99% in the conventional FDTD method. One should be careful using conventional FDTD to study systems with complicated geometry as the staircased meshes fail to conform the boundary correctly. The simulation time of studying the interaction of particles with fields inside cavities can be dramatically reduced by using CFDTD particle-in-cell simulation without losing accuracy. * C. Nieter, J. R. Cary, J. Comput. Phys. 196, 448-473 (2004). |
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| FR5PFP085 | Benchmarking Multipacting Simulations in VORPAL | 4505 |
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Funding: Department of Energy SBIR grant DE-FG02-05ER84172 We will present the results of benchmarking simulations run to test the ability of VORPAL to model multipacting processes in Superconducting Radio Frequency structures. VORPAL is an electromagnetic (FDTD) particle-in-cell simulation code originally developed for applications in plasma and beam physics. The addition of conformal boundaries and algorithms for secondary electron emission allow VORPAL to be applied to multipacting processes. We start with simulations of multipacting between parallel plates where there are well understood theoretical predictions for the frequency bands where multipacting is expected to occur. We reproduce the predicted multipacting bands and demonstrate departures from the theoretical predictions when a more sophisticated model of secondary emission is used. Simulations of existing cavity structures developed at Jefferson National Laboratories will also be presented where we compare results from VORPAL to experimental data. |