Multimode investigations on rf losses and field limitations of single-cell niobium cavities at L- and S-band frequencies

Systematic measurements on single-cell cavities are best suited for a better understanding of anomalous and fundamental rf loss mechanisms of superconductors. In this paper, the authors report on test series for several elliptically shaped accelerator cavities fabricated from high purity Nb. By means of an adjustable input and output coupling system six modes (TM010) and 3.5 GHz including the TE011 mode can be excited properly. For all of these modes rf loss distributions and field limitations have been investigated by temperature mapping and discussed on the basis of URMEL and URMEL T calculations. First measurements have given for the TE011 mode magnetic surface fields up to 100 mT at Q values well 1010