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The basic problems of the development and construction of charged-particle accelerators using superconducting rf accelerating structures are discussed. The characteristics of the modular systems currently used in high-energy superconducting accelerators and their application to accelerators for tens or hundreds of MeV are examined.A great deal of experience has now been accumulated in the development and operation of accelerators with superconducting accelerating systems [1][2][3][4][5]. More than one kilometer of accelerating superconducting structures has been constructed by 2004 throughout the world. A powerful neutron source based on a 1 GeV high-current superconducting linear proton accelerator is under construction at the Oak Ridge National Laboratory (USA). A design which doubles the energy (up to 12 GeV) of the CEBAF accelerator (USA) has been prepared.It should be noted that modern superconducting accelerating systems have been developed, mainly, for facilities with high-beam energy ranging from hundreds of MeV up to TeV and are constructed according to a modular principle. In the present paper, we present some data on the successful application of superconducting rf accelerating systems for high-energy facilities and accelerators with colliding beams, which could also be helpful for building superconducting systems for small facilities.Complexes Employing RF Superconducting Accelerating Systems. The development, construction, and operation of superconducting accelerating systems of the electron accelerator-recirculator CEBAF, accelerator with colliding beams LEP (CERN), and others of a smaller scale in the USA and Japan are tied to advances in the technology of rf superconductivity which have been made in the last few years. Currently operating superconducting structures give an average rf field intensitỹ 7 MV/m; 25 MV/m has been achieved in serially produced cavities, developed recently, and up to 40 MV/m has been achieved in laboratory samples, which is close to the theoretical limit 50 MV/m for the niobium used in these cavities [2].The LEP superconducting rf accelerating system [6] made it possible to obtain colliding beam energy 209 GeV. It contained 288 cavities with frequency 350 MHz and length 1.7 m. The average accelerating field reached 7.2 MV/m. The total increase in energy with one acceleration was 3600 MeV. The cavities were built using the technology, developed at CERN, for depositing a thin film of niobium on the inner surfaces of copper forms. CEBAF was constructed for obtaining a beam of electrons, accelerated up to 4 GeV, in a CW mode. Subsequently, its parameters were improved and an electron beam with energy 5.8 GeV was obtained. The superconducting accelerating system of CEBAF [7] was made of 338 half-meter assemblies, each with five cavities operating at ~1500 MHz. Initially, the assemblies gave an accelerating field 5 MV/m, which was then increased to 6.9 MV/m. It has now been decided to increase the accelerator energy up to 12 GeV.International activity has already for a long tim...

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