Assessment of Collateral Effects of Thermo-Oxidation on DIII-D In-Vessel Components in Preparation for In Situ Oxidation in DIII-D

Carbon-based codeposits formed in carbon-containing fusion devices have the potential to dominate tritium retention in the torus. One of the tritium removal techniques currently being studied is thermo-oxidation, which is unique in its ability to remove tritium from codeposits without mechanical intervention in the torus and in its ability to remove tritium from codeposits in tile gaps and shaded areas. In preparation for an oxidation experiment planned to be performed in DIII-D, we have investigated the potential collateral effects of thermo-oxidation on DIII-D in-vessel components. Laboratory oxidation experiments were performed at 2 Torr ([approximately]270 Pa) and 15 Torr ([approximately]2 kPa) O₂ pressure and temperatures in the range 100 to 350°C (373 to 623 K) for 2 to 8 h. After oxidation, components were examined for visual or mechanical change, and when appropriate, mass changes were also obtained. In some cases, optical diagnostics were also performed. The specimens were mostly spare/surplus components and spanned a wide variety of materials and functions, e.g., cryopump components; structural, mechanical, and diagnostic components; and fast-wave antennas. The effect of oxidation was found to be negligible for nearly all DIII-D components and materials tested.