Efficient accelerating structures for low-energy light IONS

The radio-frequency quadrupole (RFQ) accelerator is the best structure immediately after an ion source for accelerating light-ion beams with considerable currents. On the other hand, the higher-energy part of the RFQ is known to be not a very efficient accelerator. We consider alternative room-temperature RF accelerating structures for the beam velocities in the range of a few percent of the speed of light - including H-mode cavities and drift-tube linacs - and compare them with respect to their efficiency, compactness, ease of fabrication, and overall cost. Options for the beam transverse focusing in such structures are discussed. Possible applications include a compact deuteron-beam accelerator up to the energy of a few MeV for homeland defense.