Nonself-Sustained Microwave Discharge in a System for Hydrocarbon Decomposition and Generation of Carbon Nanotubes

This paper deals with the investigation of a method for sustainment of high-power microwave discharge in the installation for natural-gas decomposition. The essence of the method is to provide a generation of auxiliary discharge plasma in the area where the main microwave plasma torch burns. The design of the electrode system of auxiliary discharge resembles that for a coaxial plasmatron that consumes an average current of about 0.1 A. Then, the nonself-sustained microwave discharge with a frequency of 2.45 GHz has been obtained at a power level from 1 to 3 kW. Such a discharge has been used in the installation for natural-gas decomposition and generation of the carbon nanotubes. With a typical gas flow of 1 m³/h, the natural-gas conversion achieves 40%-80%. Three types of nanotubes are contained in the final product: multilayer tubes, single-layer tubes, and onion-type tubes.