Abstract: A side-coupled standing-wave linear accelerator for accelerating a particle beam, includes a cascade of accelerating resonant cavities linearly located along the axis of the particle beam and coupled in series through drift tubes allowing passage of the particle beam. Each pair of adjacent accelerating resonant cavities is electromagnetically coupled by a side-coupling cavity. At least one side-coupling cavity is a non-resonant type switchable between a first position of electromagnetically coupling a given pair of adjacent accelerating cavities and a second position of electromagnetically decoupling the same given pair of accelerating cavities.