Development of a RF plasma torch at atmospheric pressure

Summary form only given, as follows. An RF torch operates by feeding helium or argon gas through two coaxial electrodes that are driven by a 13.56 MHz radio frequency source of power ranging from 40 W to 400 W. In order to prevent an arc discharge, a dielectric material such as quartz is loaded outside of the center electrode which is connected to the RF power source. The inner surface of the outer-grounded electrode is also dielectric loaded. A stable, arc-free discharge was produced at a flow rate of 1.5 l/min of helium gas. Various reactors have been developed which include water grounded electrode. We can observe the bulk plasma generation through water. Therefore, it provides an opportunity to diagnose atmospheric plasma in radial and axial directions. An asymmetric biaxial reactor can ignite plasma at low breakdown voltage which is less than that of symmetric coaxial reactor. However, plasma produced also asymmetrical distribution. The plasma generation in a hot chamber is much more efficient than in a cold chamber. The plasma characteristics are diagnosed, making use of optical emission spectroscopy. The spectral lines are monitored according to various conditions of RF plasma torch. The lines to be analyzed are mostly in the visible and near infrared regions, and are observed through axial direction. We theoretically developed a simple scaling law that would estimate breakdown voltage of atmospheric pressure discharge in a coaxial reactor. Experimental results agree reasonably well with theoretical predictions.