Gas exhaust cone for an aircraft turbojet, corresponding turbojet and engine plant

A gas ejection cone for an aircraft turbojet, the cone including a hollow main body defining, on the outside, a radially inner skin of an annular primary flow channel, and a device generating turbulence in the primary flow limiting jet noise, mounted so as to move on the main body so as to be able to be displaced from an extracted position in which the device projects toward downstream in relation to a downstream end of the hollow main body, and a retracted position in which the device is retracted into the hollow main body, and vice versa. Further, the device includes a cylindrical support body having an axis parallel to an axis of the ejection cone, and at least one fin supported by the body.