Does UHV annealing above 1100C as a final surface treatment reduce field emission loading in superconducting cavities

Research on advancing high field capability of Nb microwave cavities for application to future e+e- colliders is being conducted with 1-cell 1500 MHz elliptical cavities, equipped with a high speed temperature mapping diagnostic system. Above 10 MeV/m accelerating field, field emission severely loads cavity Q. One of the most interesting questions addressed regarding field emission (FE) in superconducting cavities is whether heat treatment (HT) reduces emission and permits higher fields, as suggested by dc FE experiments on Nb surfaces, conducted at the U. of Geneva. Comparison between heat treated and chemically treated cavities gives an encouraging picture for the benefits of HT. On the average, 75% higher fields are possible, and the best surface electric and magnetic fields reached were 1260 Oe and 50 MV/m. 8 refs., 5 figs