There are two configurations for the chamber assembly, with the only difference being the plugs. The uninstrumented configuration has a top plug which is used for installation of the samples and to support the inert gas lines and maintain a leak tight environment while under water. The instrumented configuration has a chamber extension above the chamber and an "umbilical" to permit inert gas lines, electrical cables and instrumentation cables for an instrumented experiment to connect with heater controls and instrumentation testing equipment in the experiment room.