We have developed a new pulsed plasma system of high frequency for chemical conversion. The energy efficiency is improved by increasing the pulse frequency. Methane can be converted to acetylene, hydrogen and amorphous carbon nanoparticles at a commercially feasible rate. Amorphous carbon nanoparticles have a diameter of approximately 50-100 nm. The mechanism of the pulsed plasma is discussed. Some applications are given, such as reduction of particulate matter emission from a diesel engine, production of carbon nanoparticles, coating with a plasma spray and nanoparticles.