Design Calculation for High-Space-Charge Beam-to-RF Conversion

Upgrades to DOE Nuclear Physics Accelerators, such as the 12 GeV upgrade program at Jefferson Laboratory, require design and computer modeling of continuous wave radio frequency (RF) sources, such as klystrons and inductive output tubes (IOTs), with good efficiency over a range of output powers. Modeling these high-space-charge devices, especially the critical beam-to-RF conversion stage, requires time-domain particle-based electromagnetic solvers. However, existing modeling tools of this nature are plagued by a "stair-step" geometry representation, which introduce 1st-order errors in the critical dimensions affecting frequency and high order modes. Recent advances in new "cut-cell" algorithms now permit very accurate 2nd-order geometry representation in modeling tools, which will significantly reduce design difficulties while simultaneously improving precision. This project will develop and utilize this new capability for the design and modeling of devices that convert bunched-beam kinetic energy to RF energy, with special attention to RF-source-design issues for accelerator upgrade programs. Phase I will evaluate and benchmark the capabilities of the new geometry representation technology as applied to modeling and design of output cavity components of klystron, IOTs, and other beam-to-RF conversion components. Also, the feasibility of applying the modeling capability to other complex-geometry aspects of RF sources, such as the gun and collectors, will be investigated. Commercial Applications And Other Benefits as described by the Applicant: An accurate geometry-modeling technology for RF sources should impact all fields with high-power RF sources, including DOE nuclear physics and fusion research, communications, radar, and other defense applications. The technology also should be of great interest to commercial manufacturers of these RF sources, providing a clear commercial marketplace for products based upon this technology.