Abstract
Studies of the properties of runaway electron preionized diffuse discharges (REP DDs) and their possible use have been carried out for more than 15 years. Three experimental setups generating a low-temperature atmospheric-pressure plasma and differing in the geometry of a discharge gap were developed. They allow the treatment of surfaces of different materials with an area of several tens of square centimeters. A diffuse discharge plasma was formed in the pulse–periodic mode by applying negative voltage pulses with an amplitude of several tens of kilovolts and a duration of 4 ns to a discharge gap with sharply non-uniform electric field strength distribution. This paper presents experimental results of the study of the surface layer microstructure of copper and steel specimens of different sizes after treatment with the REP DD plasma in nitrogen flow mode and nitrogen circulation mode in the discharge chamber. It was shown that after 105 discharge pulses, the carbon concentration decreases and a disoriented surface layer with a depth of up to 200 nm is formed. Moreover, the results of X-ray phase analysis did not reveal changes in the phase composition of the surface of copper specimens. However, as a result of surface treatment with the REP DD plasma, the copper lattice becomes larger and the microstress increases.
Highlights
IntroductionDiffuse gas discharges initiated by runaway electrons (runaway electron preionized diffuse discharge—runaway electron preionized diffuse discharges (REP DDs)) are intensively investigated [1,2,3,4]
Diffuse gas discharges initiated by runaway electrons are intensively investigated [1,2,3,4]
As it was shown in [5], it is possible to form a diffuse discharge in a gap with an inhomogeneous electric field strength distribution filled with atmospheric-pressure air by applying nanosecond voltage pulses with an amplitude up to several tens of kilovolts to the cathode with a small radius of curvature
Summary
Diffuse gas discharges initiated by runaway electrons (runaway electron preionized diffuse discharge—REP DD) are intensively investigated [1,2,3,4]. As they move towards the anode, runaway electrons produce electrons with lower energy This leads to the development of electron avalanches that overlap and, contribute to the diffuse discharge formation [6]. This type of discharge has a number of unique features: high specific input power (up to 1 GW/cm3 ) [7], generation of X-rays, runaway electron beams with the amplitude of tens of amperes [5,8,9], and a current pulse duration (full-width at half-maximum—FWHM) of ~100 ps [10], as well as powerful UV and VUV radiation [11]. They are a dense plasma, an ultrashort electron beam with a wide energy spectrum, optical radiation, and products of plasma–chemical reactions [12,13]
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