This award supports Professor Alan M. Portis of the University of California at Berkeley for collaborative research on high temperature superconductivity with Professor Helmut Piel, Department of Physics, University of Wuppertal. They share an interest in the development of high quality films and coatings of high temperature superconductors for a variety of applications including particle accelerator cavities operating at microwave frequency. The quality of these materials deteriorates at high microwave power levels. Together with Dr. D. W. Cooke of the Los Alamos National Laboratory, they are developing a detailed theoretical model of microwave flux penetration and surface resistance and are also undertaking careful measurements of both phenomena. The development of microwave cavities for particle accelerators has largely been led by Dr. Piel and his students. There is no comparable experience anywhere else. Dr. Portis brings to the collaboration outstanding expertise in the microwave properties of high temperature superconductors. Their goal is to identify the loss processes and to work for their elimination, so as to obtain materials that maintain their quality at high microwave power levels. Verification of a microwave critical state in superconductors would have important scientific and technological benefits. It would indicate that microwave processes in superconductors are much faster than has been thought possible, requiring reexamination of some of our ideas of flux penetration into type II superconductors. It would also improve surface quality at high power by identifying the origin of the observed power dependence in surface resistance in high temperature superconductors. If the loss mechanism does persist into the microwave frequency range, there may well be opportunities for using these materials for high frequency signal- processing. Thus a mechanism that creates a problem for particle accelerators may provide opportunities in an entirely different domain.
