N. BABOI, M. LIEPE, J. SEKUTOWICZ (DESY), M. FERRARIO, (INFN)
A new cavity-chain layout has been proposed for the main linac of the TESLA linear collider . This superstructure-layout is based upon four 7-cell superconducting standing-wave cavities, coupled by short beam pipes. The main advantages of the superstructure are an increase in the active accelerating length in TESLA and a saving in rf components, especially power couplers, as compared to the present 9-cell cavities. The proposed scheme allows to handle the field-flatness tuning and the HOM damping at sub-unit level, in contrast to standard multi-cell cavities. The superstructure-layout is extensively studied at DESY since 1999. Computations have been performed for the rf properties of the cavity-chain, the bunch-to-bunch energy spread and multibunch dynamics. A copper model of the superstructure has been built in order to compare with the simulations and to test the field-profile tuning and the HOM damping scheme. A 'proof of principle' niobium prototype of the superstructure is now under construction and will be tested with beam at the TESLA Test Facility in 2001. In our paper we present latest results of these investigations.
 J. Sekutowicz, M. Ferrario and Ch. Tang, Phys. Rev. ST Accel. Beams, vol. 2, No. 6 (1999)
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