The conceptional design of the proposed linear electron-positron collider TESLA is based on 9-cell 1.3 GHz superconducting niobium cavities with an accelerating gradient of E acc $ 25 MV͞m at a quality factor Q 0 $ 5 3 10 9 . The design goal for the cavities of the TESLA Test Facility (TTF) linac was set to the more moderate value of E acc $ 15 MV͞m. In a first series of 27 industrially produced TTF cavities the average gradient at Q 0 5 3 10 9 was measured to be 20.1 6 6.2 MV͞m, excluding a few cavities suffering from serious fabrication or material defects. In the second production of 24 TTF cavities, additional quality control measures were introduced, in particular, an eddy-current scan to eliminate niobium sheets with foreign material inclusions and stringent prescriptions for carrying out the electronbeam welds. The average gradient of these cavities at Q 0 5 3 10 9 amounts to 25.0 6 3.2 MV͞m with the exception of one cavity suffering from a weld defect. Hence only a moderate improvement in production and preparation techniques will be needed to meet the ambitious TESLA goal with an adequate safety margin. In this paper we present a detailed description of the design, fabrication, and preparation of the TESLA Test Facility cavities and their associated components and report on cavity performance in test cryostats and with electron beam in the TTF linac. The ongoing research and development towards higher gradients is briefly addressed.

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The beam intensity of the DORIS e+-e storage ring is limited to about 100 mA average circulation current as a result of instabilities driven by higher order rf cavity modes. Thus an investigation has been made of the higher order mode impedances of the DORIS rf accelerator cavities. These cavities are the same as the normally conducting inductively coupled 500 MHz 5-cell structures used in PETRA. The results of the investigation were applied for the construction of in ductive and capacitive attenuation antennae correspon ding to specific mode spectra and mode impedances. The antennae must fit into the existing 35 mm pick up flanges of the cavities and in spite of these size and position limitations they must be efficient in redu cing the shunt impedances of the dangerous modes.

Superconducting 500 MHz cavities have been developed at DESY for the purpose of increasing the e beam energy of the HERA storage ring. A complete prototype model has been built by industry and was tested successfully under laboratory and storage ring conditions. Meanwhile 16 superconducting 4-cell cavities, 8 cryostats and the LHe distribution system are under industrial production and will be installed in the HERA tunnel until summer 1990. We report in detail about RF and cryogenic measurements and discuss recent improvements of individual components.

SummaryA 1 GHz 9-cell superconducting cavity was installed and tested in the PETRA electron-positron storage ring. 2 mA were injected at 7 GeV and stored by a superconducting cavity with a maximum gradient of 2.5 MV/m. With the addition of normal-conducting 500 MHz cavities the superconducting cavity transferred 27.5 kW to a 8 mA beam current. The resonator is kept at LHe temperature since February 1985 to gain long-time experience on superconducting cavities in the storage ring environment. The maximum achievable field and the quality factor have not changed up to now.