The Structure of the High Frequency Focusing Cells in Linear Ion Accelerators

The versions of the high frequency quadrupole doublets (RFQD) for proton and heavy ion linear accelerators are discussed. Advantages of focusing of this type over magnetic quadrupoles lie in the simplicity of the structure and high efficiency and reliability of focusing. In the multi-gap structures, focusing periods contain a sequence of focusing and accelerating cells. The elaborated technique of the local cell adjustment provides the high acceleration rate. Various RFQD versions for the specific peculiarities of accelerating structures are discussed. Application of the RF-quadrupole doublets in the spoke cavity and CCDTL structures will allow the application of superconductive cavities for proton acceleration in the range of intermediate energies of 5-100 MeV. In the interdigital H-structures, the application of RFQDs will allow to increase the efficiency of ion beam focusing and to expand the energy range of the ions being accelerated over 10 MeV/u.