The Science and Fundamental Understanding of the Radio Frequency Surface Resistance of Nitrogen Doped SRF cavities

Northwestern University, Evanston IL

Investigators

Abstract

The research enabled by this award will improve the understanding of one of the physical processes that determine, and may ultimately limit, the performance of future particle accelerators. Particle accelerators have a wide variety of uses, from basic research machines for fundamental studies of elementary particle physics to tools and instruments ranging from industrial welding to medical diagnostics and treatment. One of the key limiting factors for particle accelerators can be the performance of superconducting, radio-frequency cavities that are used to accelerate the electrically charged particles. By discovering the mechanisms presently contributing to energy dissipation within such cavities, we can push the technology to theoretical limits for the next generation of superconducting particle accelerators. This research project involves the training of graduate students as the next generation of research leaders with expertise in accelerator science and technology, as well as the physics of superconducting materials for particle accelerators and related technologies. This award supports research and graduate education in the field of superconducting, radio-frequency (RF) accelerator science. The research supported by this award is directed towards a fundamental understanding of the physical processes governing the region of field penetration into Nitrogen-doped Niobium superconductors used in state-of-the-art RF cavities for particle accelerators. The research involves physical and chemical characterization, on the sub-nanometer scale, of the sub-micron deep surface layer near the vacuum-superconducting interface where the RF screening currents flow. Surface profile characterization, from sub-nano-meter to micron length scales, will be carried out, and combined with local electronic and magnetic properties obtained from atom-probe reconstruction, nuclear magnetic resonance spectroscopy, and transport measurements in the normal metallic phase of Niobium. The detailed atomic-scale structure of the surface and screening region will be combined with state-of-the-art theoretical modeling and computational theory for the RF currents under high-field conditions. The overarching goal is to push performance of next-generation superconducting RF cavities to theoretical limits.