RF structures for linear acceleration of radioactive beams

The production and acceleration of secondary, radioactive ion beams differ quite substantially from the case of stable ion beams. The individual production and separation of the specific ion species, low beam currents or short lifetime of the ions as well as the needed energy variability, typically ranging from 1 to 8 MeV/u, have consequences on the layout of the accelerator. Long living isotopes can be bred to higher charge state, like it is done at the REX/ISOLDE project at CERN, and accelerated very efficiently with an accelerator similar to the CERN Lead Linac or the GSI High Charge State Injector. In case of short isotope lifetimes below a few milliseconds charge breeding is not feasible. Therefore, the ions produced in a low charge state have to be accepted by the accelerator. A linac designed for high mass to charge ratio, like the TRIUMF ISAC or the GSI High Current Injector with A/q < 65, which started routine operation in 1999, could serve this task. Due to the low intensities of some of the ion species a high duty cycle is required. Additionally, coincidence experiments profit a lot from a cw ion beam. This contribution will review the basic needs for radioactive beam acceleration and the possible solutions. It covers linacs based on RFQs, quarter wave resonators and H-mode cavities. Room temperature as well as superconducting solutions are discussed. The state of the art and future perspectives will be described