Abstract
Compact DC high-voltage photo-electron guns are able to meet the sophisticated demands of high-current applications such as energy recovery linacs. A main design parameter for such sources is the electric field strength, which depends on the electrode geometry and is limited by the field emission threshold of the electrode material. In order to minimize the maximum field strength for optimal gun operation, isogeometric analysis (IGA) can be used to exploit the axisymmetric geometry and describe its cross section by non-uniform rational B-splines, the control points of which are the parameters to be optimized. This computationally efficient method is capable of describing CAD-generated geometries using open source software (GeoPDEs, NLopt, Octave) and it can simplify the step from design to simulation. We will present the mathematical formulation, the software workflow, and the results of an IGA-based shape optimization for a planned high-voltage upgrade of the DC photogun teststand Photo-CATCH at TU Darmstadt. The software builds on a general framework for isogeometric analysis and allows for easy adaptations to other geometries or quantities of interest. Simulations assuming a bias voltage of -300 kV yielded maximum field gradients of 9.06 MV/m on the surface of an inverted insulator electrode and below 3 MV/m on the surface of the photocathode.
Highlights
Advanced applications of electron accelerators such as energy recovery linacs (ERLs) [1,2] require beams with high current and small emittance, placing sophisticated demands on electron sources
In order to minimize the maximum field strength for optimal gun operation, isogeometric analysis (IGA) can be used to exploit the axisymmetric geometry and describe its cross section by nonuniform rational B-splines, the control points of which are the parameters to be optimized. This computationally efficient method is capable of describing computer aided design (CAD)-generated geometries using open source software (GEOPDES, NLOPT, OCTAVE) and it can simplify the step from design to simulation
This paper is dedicated to optimizing the freeform shape of the electrode in terms of CAD basis functions to minimize the electric field strength, which has a crucial impact on field emission and still represents a major design problem depending on the specific geometry of the setup
Summary
Advanced applications of electron accelerators such as energy recovery linacs (ERLs) [1,2] require beams with high current and small emittance, placing sophisticated demands on electron sources. This paper is dedicated to optimizing the freeform shape of the electrode in terms of CAD basis functions to minimize the electric field strength, which has a crucial impact on field emission and still represents a major design problem depending on the specific geometry of the setup. A key limitation of the design optimization process is the manual input and adaption of shapes based on simulations that must be repeated An automation of these steps is desired in order to accelerate and simplify the design process. This is cumbersome for particle tracking and either needs smoothing or dedicated (symmetry preserving, mixed element) meshing To avoid these problems, this paper proposes a spline-based shape optimization workflow using isogeometric analysis (IGA) [35], which integrates finite element analysis into the conventional NURBS-based CAD design workflow and allows for integrated particle tracking.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
