Abstract: Fixtures and methods for clamping workpieces in a workplace to enable the optimized exposure thereof to a stream or flow of a supercritical fluid. Provided is a rotatably indexable chuck or locator mounting the workpiece and enabling orientating the latter in specific static pitch position within a high pressure vessel in order to subject the workpiece to a full frontal exposure to the supercritical fluid stream within the vessel. This mounting arrangement facilitates an optimum positioning of the workpiece being processed in the flow path of the supercritical fluid stream while oriented in selectively indexed rotational positions.