In situ diagnostic for monitoring of deuterium and tritium in re-deposited carbon layers by laser induced desorption

Tritium retention in the plasma facing components and co-deposition in re-deposited layers is a key issue for ITER, since the operation of the machine will be restricted to a maximum inventory of tritium. Development of methods to detect in real time the amount of retained fuel in the in vessel components is urgently required. A promising method for this is the pulsed laser induced desorption, by which the imbedded gas in such layers is released into the plasma where the injected atoms and molecules are excited and ionised and the characteristic line emission is detected spectroscopically. In this paper the release process is investigated in detail for amorphous hydrocarbon layers in a laboratory experiment, as a prerequisite for the later application and determination of conversion factors between line radiation and desorbed flux in TEXTOR plasmas. A Nd:YAG laser has been used with nearly constant output power leading to a smooth controllable increase of layer temperature, resulting in a complete desorption of D2 and CD4 as well as preventing carbon sublimation.