# Temporal Stability of Modified Surfaces of Insulating HV Devices Using Atmospheric Pressure Plasma
## 1 Introduction to Plasma Generation  
In the technology of production and modification of dielectric surfaces, generated plasma under atmospheric pressure [1] finds new applications in the modification of electrical properties of the upper layers of material surfaces. It is also used for the modification of various parameters in terms of mechanical properties and at the molecular and atomic level [2, 3]. For these purposes and to achieve physical or chemical changes on the surface of the target material, plasma sources [4] are used to achieve repeatable outputs under predefined boundary and initial conditions. The proposed industrial applications for HV technology cannot readily use vacuum plasma-engineered plasma generation (PECVD). Therefore, the use of high-frequency electric discharge sources [3] that produce plasma under atmospheric pressure proves to be a viable route. The methods of generating non-thermal high-frequency plasma discharge are used in various industries [2, 3]. The advantage of atmospheric pressure plasma discharge generation techniques lies in the ability to easily and efficiently modify the surface and create a local structure of the surface through its modification [5, 6]. Another option is surface treatment using the gaseous [7, 8] or the liquid precursors [9]. The electromagnetohydrodynamic properties of the plasma discharges [1] are influenced by the design of both the electrical generator and the design of the chamber used to excite the plasma [10; 11; 12]. For the industrial deployment of plasma discharge material processing technology, the use of a slit chamber [4] in a plasma source system, as opposed to plasma pens for local exposure [11; 12], is very effective. The generator for industrial deployment includes an electrical generator and a high-frequency electrode with a working frequency of \(f=13.56\) MHz, a slit plasma chamber [4], and a detection system for recording plasma discharge parameters [13]. A radio-frequency method for recording frequency spectra [13] has proved to be a suitable detection system, which is typical for the applied discharge setup parameters (gas type, i.e., Ar, N or O, set output power of the RF generator, type of frequency of the basic RF signal, type of precursors, etc.) When the plasma source is in operation, an atmosphere composed of argon, nitrogen and other gases, either alone or also with an admixture of precursor gases or substances, flows through the slotted chamber [14]. The qualitative and quantitative parameters of the electromagnetic discharge depend mainly on y the geometrical arrangement of the chamber, electrodes, the shape of the excitation signal of the RF generator and related parameters [13; 14; 15; 16]. Plasma sources at atmospheric pressure can have different geometries and properties of the generated discharge, and their possible applications depend on this. Corona discharge [17; 18; 19] and dielectric barrier discharge (DBD) [20; 21] are not suitable for surface treatment of complex, often large, 3D products of HV insulators due to their unsuitable geometry. The low-pressure glow discharges are quite efficient in the surface modification of materials [22; 23]. However, using low-pressure plasma techniques in the industrial setting is not quite feasible because the implementation and operation of vacuum systems are too expensive compared with the required costs of HV insulator product applications. However, the situation may be different for plasma jets. In one of our earlier publications [5], we compared four different plasma sources. These plasma sources included the Plasmatreat rotating plasma jet (treated area diameter 33 mm), AFS PlasmaJet(r) (treated area diameter 8 mm), SurfaceTreat gliding arc jet (treated area diameter 27-36 mm), and the low-temperature RF plasma slit jet working in argon with a plasma width of 150 mm (our plasma nozzle described in this work).