Cleaning and modification of the near-surface layers of metals under the action of runaway electron preionized diffuse discharge

Electric discharges of different types as well as electron beams are now widely used for the modification of near-surface layers of various materials [1]. As is known, a volume discharge can be generated using inhomogeneous electric field in air at atmospheric pressure. For this purpose, high-voltage (~100 kV) pulses of nanosecond duration are applied to a gas filled interelectrode gap. A specific feature of such discharges is the accompanying the formation of the supershort avalanches electron beams (SAEBs) and X-ray emission [2]. A runaway electron preionized diffuse discharge (REP DD) is easily realized in various gases and at different pressures [2, 3]. At the REP DD, the anode is influenced by the dense plasma of a dense nanosecond discharge with the specific input power up to hundreds of megawatt per a cubic centimeter, by the SAEB, shock wave and optical radiation from discharge plasma of various spectral ranges, including UV and VUV. This allows forecasting the REP DD application for modification and cleaning of metal surfaces in different technological processes [3, 4]. We have studied the modification and cleaning of the nearsurface layers of niobium, steel, Al and copper plates and foils under the action of discharge plasma, which was generated in nitrogen, CO2 and air at atmospheric pressure by nanosecond high voltage pulses applied between the plane anode and catho de with a small radius of curvature. It is established that the su rface layer of the discharge treated the steel, AlBe, Al and cop per plates is cleaned from carbon contaminations. The oxygen penetrates up to a depth of about 50 nm was obtained. It has b een found that the treatment of a copper and steel surface by th is type of discharge increases the hardness of the surface layer of copper and steel.