This structure uses an essentially T.E. field instead of a T.M. one like in an Alvarez linear accelerator. The drift tubes are alternately connected to conducting plates fastened to the waveguide, so that the device operates on a ¿ mode. The shunt impedance is roughly proportional to ß 1/2, so that this structure is convenient for injectors or heavy ions accelerators. This shunt impedance is higher than for an Alvarez structure for energies lower than about 20 MeV/nucleon in the case of a small diameter of drift-tubes (grid focusing), and lower than a few MeV/nucleon in the case of larger diameters (strong focusing). The wavelengths to be used are longer than in an Alvarez, so that the defocusing forces are weaker and focusing is easier. For a given acceleration, such a machine, using a ¿ mode, can be about twice as short as an Alvarez. A model accelerating deutons from 40 keV to 350 keV has been built and operates properly.