an rfq resonator for a linear accelerator having a reduced level of interfering modes and producing a quadrupole mode for focusing , bunching and accelerating beams of heavy charged particles , with the construction being characterized by four elongated resonating rods within a cylinder with the rods being alternately shorted and open electrically to the shell at common ends of the rods to provide an lc parallel resonant circuit when activated by a magnetic field transverse to the longitudinal axis .