Cooling system for an afterburner nozzle of a turbomachine

The cooling system for a post-combustion pipe having primary gas (2) and secondary air (3) channels has the secondary air channel surrounding the primary gas channel and separated from it by a thermal protection sleeve (4), and flaps (5) surrounding part of the primary gas channel's outlet. The system incorporates a thermal protection jacket (7) inside the secondary air channel at its outlet end, equipped with an annular diaphragm (8) located in front of the flaps and having thrust sectors (11) and inter-sector zones with slits that form gaps between the diaphragm and the thermal protection sleeve.