Dielectric-Lined High-Gradient Accelerator Structure

A future multi-TeV collider requires the development of new technology to achieve its high acceleration gradient. An accelerator structure that embodies a dielectric-lined waveguide, which offers the promise of sustaining a high acceleration gradient, is currently under development. However, the all-metal structures used to achieve the high acceleration gradient have encountered limits from microwave breakdown. Recent evidence has suggested that selected dielectrics, such as diamond, have higher breakdown thresholds than metals. Therefore, this project will design and test dielectric-lined structures and determine their breakdown thresholds under conditions similar to those in an accelerator. In Phase I, both theoretical and computational design studies were carried out for dielectric-lined rectangular waveguides that could be suitable for a future high-gradient linear accelerator. A test cell was designed to determine breakdown thresholds for hydrogenated and dehydrogenated artificial diamond coatings (produced by chemical vapor deposition (CVD)) at 34 GHz, using about 10 MW of available magnicon power. Cold tests, using a mock-up of the high-power test cell, were carried out to confirm the design criteria. In Phase II, engineering designs for the high-power high-gradient test cell will be completed, and the cell will be fabricated and tested using a 34-GHz magnicon test facility. Tests will be conducted on diamond samples that are hydrogenated (as is usual) as well as dehydrogenated, the latter so as to greatly reduce the secondary electron emission coefficient and to raise the breakdown threshold. The results of these tests will be used to extend our understanding of microwave breakdown, thereby enabling the design of high-gradient accelerators for a future multi-TeV collider. Commercial Applications and other Benefits as described by the awardee: High-gradient structures for a future multi-TeV collider, based on use of dielectric-lined waveguides, could create demand for thousands of accelerator structures, as well as for the artificial CVD diamond liners. This is a potential market of hundreds of millions of dollars