REEMISSION AND THERMAL-DESORPTION OF DEUTERIUM FROM PLASMA-SPRAYED TUNGSTEN COATINGS FOR APPLICATION IN ASDEX-UPGRADE

The trapping and release of deuterium implanted with an energy of 100 eV in wrought and in plasma sprayed tungsten of different manufacture and structure has been investigated by means of re-emission as well as thermal and isothermal desorption spectroscopy. The experimental data for wrought tungsten are compared with model calculations with the PI DAT code in order to estimate the parameters governing diffusion, surf ace recombination and trapping in tungsten. The amount of retained deu terium in tungsten is of the same order of magnitude as in graphite fo r the implantation parameters used in this work. The mobile hydrogen c oncentration in tungsten during the implantation is of the same order of magnitude than the trapped one, being released after the terminatio n of the implantation, The fraction of deuterium trapped to defects in creases strongly with the porosity of the samples. The temperature nee ded for the release of the trapped deuterium (similar to 600 K) are co nsiderably lower than for graphite, due to the smaller trapping energy (less than or equal to 1.5 eV).