Microwave Joining of Ceramic Structures for Advanced High Energy Accelerators Using a Novel Quasi-Optical Elliptical Cavity

79503S Increasing the voltage gradient of radio frequency (RF) linear accelerator structures is an ongoing objective within the High Energy Physics Program of the Department of Energy. Recent advances in the use of dielectric loaded waveguides hold the promise of fulfilling this need. However, the proposed method of configuring the dielectric within the metal waveguide requires precise manufacturing and assembly technologies to negate field enhancement at the joints and assure dielectric constant uniformity along the waveguide structure. This project will develop a joining technology, based on high-frequency high-powered focused-beam microwave heating, for the one-meter long tubes that will be needed for the dielectric loaded waveguide accelerator structures being developed for the Next Linear Collider (NLC). To exploit the beam forming capability of the microwave driven heating system, a novel quasi-optical elliptical microwave cavity will be designed, fabricated and tested. In Phase I, hot-pressed alumina tubes will be joined using a proprietary reactive braze in a microwave beam heating system. These tubes will then be evaluated for microstructural uniformity and crystallinity in the joined area. The tubes will then be assembled into a cold-test facility and tested for impedance matching. Commercial Applications and Other Benefits as described by the awardee: The ability to join advanced ceramics in specific well-defined areas without significant heating of the surrounding material should find widespread use beyond the application for high energy physics. One possible application would be the joining of very high-temperature-capable (> 2500 degC) mixed carbide tubes proposed for the next generation of reactors for space based thermal propulsion.