Thermo-oxidation of DIII-D codeposits on open surfaces and in simulated tile gaps

This work extends previous thermo-oxidation studies [R. Ochoukov, A.A. Haasz, J.W. Davis, Phys. Scr. T124 (2006) 27; A.A. Haasz, C.K. Tsui, J.W. Davis, R. Ochoukov, Phys. Scr. T128 (2007) 55] of DIII-D codeposits to provide reference data prior to performing in situ thermo-oxidation in DIII-D. The present results confirm that codeposit removal by oxidation in dry air or a mixture of O2-He gas is equally effective as in pure O2, given equivalent O2 partial pressures. We have also demonstrated that increasing the oxidation time to 48 h (compared with 2-8 h [R. Ochoukov, A.A. Haasz, J.W. Davis, Phys. Scr. T124 (2006) 27; A.A. Haasz, C.K. Tsui, J.W. Davis, R. Ochoukov, Phys. Scr. T128 (2007) 55]) does not compensate for 'less severe' oxidation conditions of (i) 'low pressure' (0.021 kPa O2 partial pressure) at 'high temperature' (623 K) and (ii) 'low temperature' (523 K) at 'high pressure' (17 kPa O2 partial pressure). The new results also show that thermo-oxidation is equally effective in removing codeposits from open surfaces and from tile gaps accessible by narrow (∼1 mm) passageways, and have extended the range of the linear relationship between D removal rates and inherent D content.