SURFACE MODIFICATION OF PYROLYTIC-GRAPHITE DUE TO DEUTERIUM AND HELIUM ION BOMBARDMENTS

Pyrolytic graphite is one of the promising materials for the first wall of thermonuclear fusion devices because of its low-Z, refractory nature, and ease in fabrication. To understand mechanisms of the modification of graphite and its effects on the trapping states of hydrogen isotopes, the authors measured the process of graphite modification due to deuterium and helium ion bombardments by means of XPS and Raman spectroscopy. Three types of radiation damage were distinguished. One of them is the electronic defect observed as the damage shift of the C1s peak. The second one is the reduction of crystallite size observed as the decrease in the intensity ratio, R, in Raman spectra. The third one is the bond angle disorder observed as the broad band around 1500 cm** minus **1.