Atmospheric pressure plasma jets in Helium – the electric field and the charge delivered to a dielectric surface

The family of non-thermal atmospheric pressure discharges has been the focus of intense research of a large number of research groups in the last fifteen years, as they are easy and cheap to assemble and run, and exhibit properties that can be used in surface treatment or biological applications. In this discharge family the non-thermal atmospheric pressure plasma jet commands a good deal of attention. The mentioned applications all involve the presence of a surface (target for treatment) in the vicinity of the discharge, and it has been shown that in many cases the presence of the surface alters the properties of the discharge. There are many types of surfaces to consider, from metals, dielectrics, to liquid surfaces, and they all leave a different mark on the discharge properties. Still, most of the research has been done on plasma jets expanding freely into the open air. This paper reports on the electric field and charge measurements delivered to a dielectric surface by an atmospheric-pressure plasma jet working in the bullet mode in helium. Imaging will be presented alongside the measurements of charge, as it will be evident that the charge distribution on the dielectric surface will mirror the observations obtained by imaging. The central results contain the charge packed in one ionization wave leaving the capillary towards the target, around 20 pC. The associated electric fields vary between 3×105 and 6×105 V/m