Aspects of target optimization for ADS with light ion beams at energies below 0.5 AGeV

A comparative study about the energy efficiency of proton and light ion beams used for energy production in accelerator driven systems (ADS) is performed. The energy gain G, defined as the ratio of the energy produced to the energy spent to accelerate the beam is used as measure for the energy efficiency. The energy released in the target is obtained through simulation with the code Geant4, and the spent energy is calculated by scaling from the data about the accelerator efficiency for a reference particle. An optimal proton energy of 1.5 GeV is revealed, when the beam is accelerated in a linac. The advantage of light ion beams, especially 7Li at energies below 0.5 AGeV, which allows a reduction of the accelerator length, is substantiated.