Thermal desorption of hydrogen isotopes trapped in carbon materials is of interest for fusion applications. There are many publications on TDS after ion implantation, but not much is published about TDS after plasma impact and after saturation from gas. The results published in literature are often contradictive. This work is devoted to comparison of TDS obtained from fine grain graphite MPG-8 after irradiation by deuterium ions, exposure in deuterium gas, and after deuterium plasma impact. It was found that desorption of D2 after ion implantation takes place in the range of 700-1600K in agreement with literature. TDS consist of non-resolved peaks and appear as a broad peak with the maximum at about 1100-1200K. Desorption of D2 after exposure in gas at 800K took place in a wide temperature range from 300 to 1400K with the main quantity released in peaks at 500-600 and 800K. TDS of D2 after plasma impact revealed both low temperature release with maxima at 500 and 800K and high temperature release peaked at 1100K. In fact, the maxima had various features, and it seems they consisted of several peaks with pure resolution. Desorption of HD, CD4, and HDO molecules was also measured. TDS spectra of these molecules were different but the maxima positions were approximately the same as for D2. Spectra of all D-containing molecules were rather similar after plasma impact and after saturation from gas except CD4. After ion implantation, the spectra were different in shape, but positions of maxima were similar to those obtained in experiments with plasma and gas. It was concluded that there is a variety of sites available for D with very different (4 times) binding energies. All these sites participate in trapping during exposure in gas, ion implantation, and plasma impact. The difference in the TDS shapes is connected with difference in accessibility of the sites for D atoms incoming with different energies and ability of production of radiation damage. Water remarkably influences desorption of trapped deuterium.
The work was supported by ISTC Grant 2805.
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