Berkeley Lab - Scientific Computing Seminar

Date:

Wednesday, August 27, 2008

Time:

1:00pm-2:00pm

Location:

Building 50F, 1647 Conference Room

Seminar Speaker:

Braxton Osting
Department of Applied Physics & Applied Mathematics
Columbia University

Title:

Particle Accelerator Cavity Design with PDE Constrained Optimization

Abstract:

In the design of particle accelerators, one wishes to find the shape of a cavity that produces the optimal electromagnetic field distribution -- one with maximal quality factor for the accelerating mode and minimal quality factor for higher-order modes. Unfortunately, these are often competing goals and the lengthy procedure of manually attempting to find the optimal shape is undesirable. We formulate the design procedure as a constrained optimization problem for a parameterization of the shape where the constraint is a quadratic eigenvalue problem resulting from the discretization of the time-harmonic Maxwell equations with radiating boundary conditions. The resulting nonlinear optimization problem may be solved using a line-search based reduced-space quasi-Newton method where the shape sensitivities are computed using the adjoint method. Using a simple one-dimensional model arising in the design of the index of refraction for photonic crystals, we demonstrate the effectiveness of this method. We conclude with the results of a massively parallel computation for the optimal shape of a choke cavity.

Sponsor of Seminar:

Esmond G. Ng

Scientific Computing

Contact Esmond G. Ng EGNg@lbl.gov