287 ISSN 0020-4412, Instruments and Experimental Techniques, 2017, Vol. 60, No. 2, pp. 287–289. © Pleiades Publishing, Ltd., 2017. Original Russian Text © M.V. Erofeev, V.S. Ripenko, M.A. Shulepov, V.F. Tarasenko, 2017, published in Pribory i Tekhnika Eksperimenta, 2017, No. 2, pp. 140–143. Generators of Diffuse Plasma at Atmospheric Pressure M. V. Erofeev*, V. S. Ripenko, M. A. Shulepov, and V. F. Tarasenko Institute of High Current Electronics, Siberian Branch, Russian Academy of Sciences, Tomsk, 634055 Russia *e-mail: mve@loi.hcei.tsc.ru Received March 31, 2016 Abstract—Devices that form low-temperature diffuse nanosecond-discharge plasma in a flow of various gases at the atmospheric pressure are described. To form diffuse plasma, negative voltage pulses with an amplitude of several tens of kilovolts and a duration of 5 ns were fed to a point–plane gap in the pulse–periodic mode. By varying the geometry of the discharge gap, the shape of the cathode, and the composition of the working gas, it is possible to obtain plasma with a wide range of parameters and modify the surfaces of various mate- rials with areas of up to several tens of square centimeters. DOI: 10.1134/S0020441217020038 Low-temperature nonequilibrium plasma is widely used in modern micro- and nanoelectronics, medi- cine, and biomedical technologies. Diffuse discharges that are initiated (preionized) by runaway electrons (REPDDs) in various atmospheric-pressure gases are the most promising sources of low-temperature plasma among the available ones. This allows the technological process of modifying the surface properties of various materials to be substantially simplified. The generation of a discharge of this type usually occurs in a highly inhomogeneous electric field, which is formed by electrodes with a small radius of curva- ture, when voltage pulses with an amplitude of more than 100 kV, a duration of units–tens of nanoseconds, and a subnanosecond front duration are fed to the electrodes [1]. Electrodes with a small radius of curva- ture provide the electric-field enhancement, as a result of which the generation of runaway electrons and X-ray radiation is observed, thus leading to the discharge- gap preionization and ensures a diffuse character of discharges in gases at elevated pressures. Such sources make it possible to produce dense nanosecond-discharge plasma with a specific power of the energy deposition of several hundred megawatts per cubic centimeter at low pulse-repetition frequen- cies (<10 Hz) [2]. The electron concentration and tem- perature in REPDD plasma depend on the amplitude of the voltage pulse and its time characteristics, as well as on the geometry of the discharge gap. At the atmo- spheric pressure of helium and nitrogen, the average electron temperature in REPDD plasma that is formed by a RADAN-220 generator is several electronvolts [3], while the electron concentration is ~10 15 cm –3 [3] and ~10 14 cm –3 [4], respectively. Inert gases [5], air, SF 6 gas [6], and methane [7] can also be used as the work- ing gases. The possibility of using the REPDD mode for cre- ating diffuse-plasma sources that operate at a pulse repetition frequency of up to 2 kHz was shown in [8]. The maximum electron concentration in volume-dis- charge plasma at the atmospheric pressure is reached at the center of the interelectrode gap. Its values are ~2 × 10 16 cm –3 in argon, ~4 × 10 14 cm –3 in nitrogen, and ~3 × 10 14 cm –3 in air. The maximum electron tem- peratures are 3.5 eV in nitrogen and 3 eV in air. More- over, diffuse discharges may generate plasma chan- nels, which overlap in the gas-discharge gap, without the formation of sparks, thus providing satisfactory uniformity of the effect on the treated surface at the atmospheric pressure. Hence, sources that are able to generate low-tem- perature plasma on the basis of REPDDs in various atmospheric-pressure gases are characterized by highly active plasmochemical processes and allow the possibility of varying the electron density, tempera- ture, and degree of ionization, thus allowing these processes to be used for modifying the surfaces of var- ious materials, including thermosensitive substances. The objective of this study was to develop facilities for processing surfaces of various metals and dielec- trics by dense plasma at the atmospheric pressure of air and other gases. One of the designs of a diffuse-plasma generator, which allows modification of the surfaces of flat circu- lar samples with diameters of up to 10 mm, is shown in Fig. 1. LABORATORY TECHNIQUES