Atmospheric-pressure plasma jet

A method of plasma processing of an article, comprising the steps of:

• providing a plasma jet apparatus, comprising:
• a central electrode shaped as a plate having a height extending in a first direction, and a length extending perpendicularly to the height, one or more outer electrodes shaped to extend at both sides of the central electrode and being substantially parallel to the central electrode, each of the outer electrodes having an inner surface facing the central electrode, and an outer surface opposite the inner surface, a dielectric material disposed at the inner surface of one or more outer electrodes and substantially parallel to the central electrode, wherein the dielectric material layer is spaced apart from the central electrode to create a discharge lumen between the dielectric material layer and the central electrode extending in the first direction between a distal end and a proximal end, a supply opening disposed at the distal end of the discharge lumen, for supplying a plasma producing gas to the discharge lumen, the discharge lumen being open to the atmosphere in the first direction at the proximal end, a power source for providing a voltage between the central and the outer electrodes, wherein at the proximal end and at each of both sides of the central electrode the apparatus comprises an extension made of a dielectric material and a return leg made of a dielectric material, wherein the extension is arranged beyond the outer electrode when viewed along the first direction, wherein the extension extends outwardly along a second direction substantially perpendicular to the first direction until the return leg, wherein the return leg extends along the first direction, from the extension towards the distal end and is spaced apart from the outer electrode;
• providing a plasma gas flow through the supply opening;
• providing the article at the proximal end of the discharge lumen so that the outwardly extending part of the insulators faces the article at a distance;
• providing a reactive chemical compound flow through the supply opening and/or through the central electrode introducing the reactive chemical compound in a plasma discharge at the proximal end;
• and
• providing a voltage between 1 and 100 kV between the central electrode and the outer electrode and generating the plasma discharge in the discharge lumen, wherein the plasma discharge jets from the discharge lumen at the proximal end in the first direction toward the article and a plasma afterglow spreads out in the second direction, between the outwardly extending part of the insulators and the article, increasing an activated spot on the article.