Atmospheric-pressure plasma jet

The invention relates to a plasma jet device for plasma treatment of an object, including: an oblong central electrode (2, 15), an oblong cylindrical outer electrode (1) or two outer electrodes (15, 16) around the central electrode and coaxial thereto, or two electrodes substantially parallel to the central electrode, a electrical insulator (3) or insulators (18, 19) arranged between the outer electrode (s) and the central electrode; there being a delivery flow with a distal end and a proximal end between the central electrode and the electrical insulator (s). Further, there is a supply opening (6) provided at the distal end of the delivery passage for supplying a plasma-forming gas to the delivery passage, and a power source (9) for providing a voltage between the central electrode and the outer electrode. What characterizes the invention is that the electrical insulator has a radial or outward extension (40, 20) at the proximal end, outside the outer surface of the outer electrode (s).