Numerical simulation of the activation process of supersonic gas flows by a microwave discharge.

Abstract

Supersonic gas flows activated by microwave discharge are commonly used to obtain thrust for spacecraft. When using a mixture of hydrocarbons and hydrogen as a working gas, the proposed method generates high-speed plasma streams with a high concentration of radicals, allowing it to be used for efficient deposition of diamond films . To optimize diamond synthesis processes, it is necessary to study the effect of various system parameters (geometrical dimensions, radiation power, pressure and others). This abstract presents a numerical simulation of the formation of high-speed gas flow activated by a microwave discharge. The conjugate problem of hydrodynamics and plasma dynamics was solved in the continuum approximation, taking into account impact ionization and thermal dissociation, due to microwave heating of the gas. The simulations were carried out in an axisymmetric formulation. The region of plasma flow formation was a cylindrical chamber (radius 5 cm, height 7 cm). At this stage, hydrogen was chosen as the working gas. The flow outlet is a hole at the center of the lower boundary with fixed pressure of 2 torr. The gas entered the domain at a constant flow rate of 20 l/min through the openings in side wall along its normal. Such flow rate sustained the mean pressure in the chamber at the level 200 torr. Microwave radiation was injected by a coaxial port located above the plasma chamber. The geometrical dimensions of the resonant chamber were selected in order to form the maximum of the electric field intensity over the gas outflow region (total deposited power 1000W). The distributions of velocity, temperature, and concentrations of all components of the hydrogen plasma were estimated. Optimal characteristics of the system were found to reach a high mole fraction of atomic hydrogen, necessary diamond deposition.

Effect of methane flow rate on gas-jet MPCVD diamond synthesis

“…The decomposition of hydrogen in the discharge chamber under the considered conditions of gas jet deposition (pressure, temperature and power of the magnetron) occurs mainly due to thermal dissociation [4,5,21,26,27]. Therefore, information on the temperature of the plasma is necessary for the analysis and search for optimal deposition conditions of diamond structures.…”

“…In [15,20,21], the features of microwave plasma formation in our configuration were studied by numerical methods. In [22,23], a numerical analysis of the flow of gas mixtures from the nozzle in the deposition chamber and their interaction with the substrate was performed.…”