An active clearance control for a turbomachine

An apparatus for active gap control (1) for a turbomachine, in particular an aircraft propulsion, which has a rotor and a rotor forming a rotor gap surrounding housing (4), said device (1) comprises arranged on the outer circumference of the rotor housing the cooling duct (3) projecting from a plenum (2) is supplied with cooling air, characterized by the fact that the cross section of the cooling duct (3) from the plenum (2) decreases forth in the circumferential direction. This results in a homogeneous cooling is ensured and reduces the weight of the device.