2020 年 15 巻 p. 2405032
In order to understand the decomposition process of hydrocarbons in a hydrogen (H) plasma, a Monte Carlo simulation of collisional transport of a methane (CH4) molecule was developed. The model simulates collision reactions with plasma ions and electrons (including dissociation, excitation, ionization, and charge exchange) and elastic collisions with residual H2 gas. The interaction with a surrounding wall was also considered (reflection from the wall, deposition on the wall, and reemission of carbon (C) and hydrocarbons (CHx) by physical and chemical sputtering). In a low-temperature plasma, because the decomposition process was mainly dominated by charge exchange with plasma ions followed by dissociative recombination with electrons, many neutral C and CHx species were obtained. At high temperature, the ionized Cy+ and CHx+ species were the dominant ones because of the dissociative ionization and excitation by electrons. Comparable to our previous experiment, the calculated decomposition rate of CH4 into neutral and ionized C atoms was ∼50% for a temperature of 15 eV and a density of 3.5 × 1017 m−3. Nevertheless, the calculated distribution of C and CHx deposits on the vessel wall were localized in the upstream of the plasma, which was different from the experimental setup.
