MEASUREMENT OF RETAINED DEUTERIUM BY LASER THERMAL-DESORPTION FOR CARBON EXPOSED TO SUB-EV ATOMIC DEUTERIUM

The retention of hydrogen in first wall structures and associated reactor components (e. g. , wall armor, limiters, etc. ) governs fuel recycle and tritium inventory. Retention levels for sub-ev D**0 atoms in single crystal and pyrolytic graphite were measured using a newly developed Laser Thermal Desorption (LTD) technique. Retention levels for single crystals were approx. 3 multiplied by 10**1**3 D**0/cm**2 for incident fluences of approx. 10**1**9 D**0/cm**2. This is about two orders of magnitude lower than D**0 retention in pyrolytic graphite, and correlates very well with the differences in effective surface areas. The D(**3He, p)**4He Nuclear Reaction Analysis (NRA) was used to confirm retention levels as measured by the LTD technique. A further finding was the influence of a small layer of evaporated tungsten on the sample surface. Such W impurity resulted in an increase of D**0 retention of up to a factor of ten.