Measurement of the chemical sputtering yields of CH<iopmath latex="$_4/{\rm CD}_4$"><SUB>4</SUB>/CD<SUB>4</SUB></iopmath> and C<iopmath latex="$_2{\rm H}_{x}/{\rm C}_2{\rm D}_{x}$"><SUB>2</SUB>H<SUB>x</SUB>/C<SUB>2</SUB>D<SUB>x</SUB></iopmath> at the carbon divertor plates of JT-60U

The chemical sputtering yields of CH<iopmath latex="$_4/{\rm CD}_4$">₄/CD₄</iopmath> and C<iopmath latex="$_2{\rm H}_x/{\rm C}_2{\rm D}_x$">₂H_x/C₂D_x</iopmath> have been measured at the divertor plates of JT-60U. Spectroscopic measurements for CH/CD and C₂ spectral bands are applied to estimate the CH<iopmath latex="$_4/{\rm CD}_4$">₄/CD₄</iopmath> and the C<iopmath latex="$_2{\rm H}_x/{\rm C}_2{\rm D}_x$">₂H_x/C₂D_x</iopmath> flux. At the surface temperatures of 380, 440 and 560 K, the CH₄ yield is, respectively, <iopmath latex="$\sim$">~</iopmath>0.8%, 1-2% and 2-3%, the C<iopmath latex="$_2{\rm H}_x$">₂H_x</iopmath> yield 1-2%, 3-4% and 4-5%, and the total sputtering yield by hydrogen ions 3-4%, <iopmath latex="$\sim$">~</iopmath>8% and <iopmath latex="$\sim$">~</iopmath>10%. With increasing ion flux to the divertor plates (<iopmath latex="$\Gamma_{\rm ion}$">Γ_ion</iopmath>), the sputtering yields (Y) decrease, i.e. <iopmath latex="$Y \propto\Gamma_{\rm ion}^{(-0.05 ~ {\rm to}~ -0.40)}$">Y&propto;Γ_ion^{(-0.05 to -0.40)}</iopmath>. With increasing electron temperature (<iopmath latex="$T_{\rme}$">T_e</iopmath>), the sputtering yields increase, i.e. <iopmath latex="$Y \propto T_{\rme}^{ 0.5}$">Y&propto;T_e^0.5</iopmath>. It is concluded from the result of regression analysis of <iopmath latex="$Y \propto T_{\rme}^{ 0.5}$">Y&propto;T_e^0.5</iopmath> that the negative dependence of the yields on the ion flux is attributed to the incident ion energies to the carbon plates. The ratio of the sputtering yields by deuterium ions and hydrogen ions is estimated to be <iopmath latex="$\ge$">&geq;</iopmath>1.5 based on the ion flux measurement by H<iopmath latex="$_\alpha/{\rm D}_\alpha$">_α/D_α</iopmath> intensity. The C<iopmath latex="$_2{\rm H}_x/{\rm C}_2{\rm D}_x$">₂H_x/C₂D_x</iopmath> sputtering yield accounts for <iopmath latex="$\sim$">~</iopmath>80% of the total number of sputtered carbon atoms.