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The new FAIR facility at GSI will include a research program with antiproton beams besides a largely extended activity with heavy ion beams. The requested antiproton production rate of 7•10 10 has to be achieved with a linac-synchrotron SIS12-SIS100 accelerator configuration. Therefore GSI needs now a high intensity, pulsed proton linac as an independent new linac, additionally to the heavy ion linac injector UNILAC. A novel compact p linac for an operating frequency of 352 MHz has been designed. It is based on an RFQ of the 4-rod type or alternatively of the 4window type followed by a CrossBar H-type (CH)-DTL ranging from 3 MeV up to 70 MeV. At an aperture diameter of 20 mm these structures will reach effective shunt impedances between 100 MΩ/m and 40 MΩ/m (high energy end). 11 independently phased cavities with focusing quadrupole triplets in the intertank sections will provide 67 MV effective voltage gain within a total length of 21 m. Beam dynamics studies are promising. Depending on the beam current, the needed transverse emittance is defined by the multiturn injection scheme into the horizontal phase space of SIS12. It is aimed to fill up to 7•10 12 protons into SIS12 within 25µs at linac currents around 70 mA and at a normalized horizontal beam emittance of 3 µm. The energy spread has to be kept within ± 1•10-3. This design was also guided by available 352 MHz klystrons with peak rf power levels slightly above 1 MW.

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The combined zero degree structure (KONUS) is a quasiperiodic structure. It was developed for the low-energy part of multigap drift tube linacs with H-type cavities. Their rf efficiency depends very much on a low electrical capacity of the drift tube structure, while in E-type structures like the Alvarez-DTL this is a minor effect. Therefore, instead of having quadrupole singlets integrated in voluminous drift tubes, KONUS allows one to develop a separated function drift tube linac (DTL) with a large voltage gain between two lenses. Very low beam injection energies can be realized, as the drift tube lengths can range down to around 10 mm. One KONUS period consists of a triplet lens, a rebuncher with a few gaps at a synchronous phase around −35°, and the main multigap acceleration designed for a hypothetical zero degree synchronous particle. The longitudinal beam dynamics along this main acceleration section and the layout of the quadrupole triplet channel are explained in detail. Two examples for pulsed high current proton and heavy ion acceleration are included.

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