Spatiotemporal Characteristics of Multiphase AC Arc by High-Speed Visualization*

Fluctuation phenomena of a multiphase AC arc were successfully visualized by the high-speed camera combined with band-pass filters. The multiphase AC arc is one of the most attractive thermal plasma sources because of its unique advantages such as large plasma volume, energy efficiency, and low gas velocity. The multiphase AC arc is expected to be applied to environmental processes, mass production of nanomaterials, and so on. However, fluctuation characteristics of the multi arcs is insufficiently understood whereas those understandings are essential for the application to industrial fields. The purpose of current study is to investigate the spatiotemporal characteristics of the multiphase AC arc based on the high-speed visualization system.

The multiphase AC arc was generated under near atmospheric pressure at 20 kW as a typical condition. The effects of AC driving frequency, plasma gas composition, and ambient pressure on spatiotemporal characteristics of the arcs were systematically investigated. High-speed camera with band-pass filters were mounted on the plasma chamber. Obtained arc images were converted into temperature distributions based on theoretically obtained temperature dependence of emission coefficient ratio at corresponding wavelengths with a consideration of line and continuous spectra under LTE assumption. Arc instability with omega-shaped structure was visualized. Obtained remarks enable us to control the high temperature plasma region appropriately.