Ion current on the inner surface of a pipe by plasma-based ion implantation and deposition

Four ring-probes were pasted on the inner surface of a pipe via an insulator sheet and the ion current was separately measured at each position by applying a negative pulse voltage in order to obtain the current distribution on the inner wall of the pipe, which was immersed in a cathodic arc plasma with a current of 80 A dc produced in a nitrogen gas at a pressure of 8 Pa. The probe current inside the pipe decreases rapidly, because the ion sheath thickness increases with time to arrive at the center of the pipe, which causes extinction of the plasma during the application of the pulse voltage to the pipe. Not only multiple setting of the arc sources but also the operation of a high frequency with a short pulse duration are necessary to realize a uniform treatment by a cathodic arc plasma-based ion implantation and deposition