The wakefields and loss factors in superconducting accelerating cavities for TESLA collider

The first stage of TTF superconducting electron linac is a in its final state of assembling. Many of superconducting accelerating cavities attained already the planned for collider accelerating fields of 25 MV/m. However the problem of cost reduction of TESLA accelerating system is still actual. The propositions concerning modifications in accelerating cavities were signalled at several TESLA Meetings and reported also at the PAC97 Conference. The cavities are the main source of wakefields, leading to beam instabilities in a linear collider. In the framework of international scientific cooperation part of the work concerning wakefield generation in the new structures proposed by DESY was carried done in our Institute. The room temperature copper models of the new type cavities were also produced in Swierk and will undergo the tests at DESY. In this report the calculated longitudinal and transverse loss factors in an enlarged iris cavity proposed previously and in a superstructure composed of four 7-cell cavities are compared with the corresponding values in cavities currently used in TTF.