The new GSI prestripper linac for high current heavy ion beams

The original UNILAC injector uses PENNING type ion sources and charge states up to 10+ for uranium beams. The beam intensities for very heavy ion species out of that injector are too low by almost a factor 300 to fill the Heavy Ion Synchrotron SIS up to its space charge limit. At present only ion sources like CHORDIS (1+ and 2+ charged ions) or MEVVA, which generates charge states up to 4+ above mass 180 can provide the requested beam intensities during a pulse duration of 100 μs. The IH-DTL with its high acceleration efficiency offers the possibility to replace the 34 MV prestripper linac by a new 91 MV linac while keeping the positions of the pre-injectors and of the gas stripper untouched. The actual prestripper frequency of 27 MHz will be replaced by 36 MHz, being one third of the poststripper linac frequency. The beam dynamics of 'Combined Zero Degree Synchronous Particle Sections' is applied on the two IH cavities.They generate averaged effective voltage gains of 4.3 MV/m. The paper describes the new linac, especially focusing on the rf structures and on the beam dynamics along the IH-DTL. (author)