The Moment Code BEDLAM

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Abstract
BEDLAM is a fourth-order moment simulation code. The beam at the input to a linear accelerator is specified as a collection of moments of the phase-space distribution. Then the moment equations, which describe the time evolution of the moments, are numerically integrated. No particles are traced in this approach. The computed distribution, the external forces, and the space-charge forces are computed consistently to a given order of accuracy. Although BEDLAM includes moments to fourth order only, it could be systematically extended to any order. Another feature of this method is that physically interesting and intuitive quantities, such as beam sizes and rms emittances, are computed directly. This paper describes the status of BEDLAM and presents the results of some tests. We simulated a section of radio-frequency quadrupole (RFQ) linac, neglecting space charge, to test the new code. Agreement with a Particle-In-Cell (PIC) simulation was excellent. We also verified that the fourth-order solution is more accurate than the second-order solution, which indicates the convergence of the method. We believe these results justify the continued development of moment simulation codes.

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