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Detail of the interface between the thrust chamber and the nozzle extension.

The dirty silver ring is the end of the thrust chamber (the brighter silver ring is the top of the nozzle extension); at the aft end of this ring are vents through which some the turbine exhaust gases flow. The remainder of the gases are routed inside the double-walled nozzle extension, where the gases exit through gaps between the shingles comprising the inner nozzle extension wall.

The turbine exhaust gas is relatively cool (compared to the main combustion gases) and provides film cooling for the interior of the nozzle extension.