High power coupler for the TESLA superstructure cavities

More and more accelerators are built with superconducting cavities operating at cryogenic temperatures, and the probability of a ceramic window failure presents increasing problems because of the resulting contamination of the cavities' surfaces and the resulting accelerating electric field degradation. Double ceramic window couplers are required to reduce this risk. The TESLA superstructure cavity requires a new coupler for the higher power input and the coupling characteristics. A cost effective design and fabrication method for these couplers has been developed to meet these demands. This new design presents an alternative to the present TESLA cylindrical ceramic windows, uses two planar disc windows separated by a vacuum space, and is optimized for RF input power, vacuum characteristics, and thermal properties. Two couplers with this design have been fabricated and are presently being tested at DESY, Germany on the RF high power testing stand and will also be tested on a test cryomodule. The design will be discussed in this paper.