Measurement of sputtering yields of CD4, C2D2 and C2D4 at the carbon divertor plate of JT-60U.
T. NAKANO, H. KUBO, S. HIGASHIJIMA, T. SUGIE, N. ASAKURA, K. ITAMI
Japan Atomic Energy Research Institute
Abstract.
Under cold and dense divertor conditions, the chemical erosion process reduces the lifetime of carbon divertor tiles in fusion reactors. It is important to evaluate the chemical sputtering yield at the divertor exposed to the high particle flux in large tokamaks such as JT-60U. Spectral bands of CD and C2 have been measured in order to evaluate the chemical sputtering yields of CD4, C2D2 and C2D4 in L-mode discharges. From the intensities of the spectral bands, the yields of CD4 and C2D2+C2D4 are estimated to be about 1-2% in an ion flux range of 0.2-2 x 1023m-2/s. The yields of CD4 and C2D2+C2D4 in this work are about half compared with laboratory data* in a low ion flux range (~ 2 x 1019m-2/s). However, the ratio of CD4 to C2D2+C2D4 is almost the same in both experiments. The number of carbon atoms originating from C2D2 amd C2D4 is comparable to or larger than that from CD4. Therefore, heavy hydrocarbons as well as CD4 have the contribution to carbon impurity generation in a wide range of the ion flux. This work is the first quantitative estimation of the sputtering yields of C2D2 and C2D4 in tokamaks.
* R.Yamada J.Nucl.Mater. 145-147 (1987) 359.