Abstract: A hyper-rapid circuit breaker is described which is assisted by a semiconductor control circuit, including a repulsion coil, a repulsion disk (37) associated with a contact bridge (39) carrying the movable contacts (41), the repulsion disk (37) collaborating with the repulsion coil (35), a maintaining spring for retaining the contacts in the closed state acting on a tail piece integrally connected to the repulsion disk (37), and a damping assembly which includes a plunger rod (95) integrally connected to the repulsion disk (37), and a reservoir (99) containing fluid intended to absorb the kinetic energy of the repulsion disk (37)/tail piece (43)/plunger rod (95) assembly upon repulsion by the repulsion coil (35), by adaptation of the shapes of the plunger rod (95) and of the reservoir (99) with respect to each other so as to have available fluid-removal sections which can vary as a function of the travel of the plunger rod (95), the travel taking place in two stages, acceleration with a large passage section