ATOMIC HYDROGEN-GRAPHITE INTERACTION

The plasma facing materials in future fusion devices are subjected not only to ion bombardment but interact with neutrals (hydrogen atoms and molecules) also. Present work is devoted to investigation of hydrogen desorption kinetics after exposure of graphite samples to the flux of hydrogen atoms. Three types of graphite (pyrolitic (PG), quasimonocristalline (QM) and RG-Ti graphite) were studied. It is shown that sorption of atomic hydrogen occurs in a similar way for all three types of graphite. Two distinct maximums have been observed in thermal desorption spectra obtained during linear heating of the sample after its exposure to hydrogen atoms. While stopping a linear heating at various temperatures some special features of hydrogen desorption kinetics were observed. The rate of desorption decreases at any fixed temperature very fast and its dependence on temperature does not follow neither first nor second order desorption kinetics. Taking into account these peculiarities of desorption process the mathematical model of hydrogen — graphite interaction is proposed. According to this model most of the sorbed hydrogen is situated inside the bulk of the sample and two types of traps with binding energy of 2.4 and 4.1 eV are present there. We believe that both types of traps are due to hydrogen interaction with edge bonds of graphite layers (or edge dislocations). The distinction between trapping energy for these two types of traps results from different sorption places of hydrogen at edge dislocations.