VUV radiation of run-away electron preionized discharge (REP DD) in different gas mixtures is studied. Efficient lasing was achieved on ArF* (193 nm) and F<sub>2</sub>* (157 nm) molecules. Narrowband VUV radiation (near 147 nm), corresponding to the optical transition of a heteronuclear dimer ArXe*, was recorded from the REP DD plasma in (He)-Ar-Xe mixture. Amplifying properties of the discharge plasma related to this radiation were found.
Laser action in run-away electron preionized discharge (REP DD) was studied. Efficient laser emission was obtained in wide spectral range from IR to VUV. It was shown that ultimate efficiency of non-chain chemical lasers on HF (DF) molecules and N<sub>2</sub> laser at 337.1 nm can be achieved in REP DD. New mode of N<sub>2</sub> laser operation with 2 or 3 peaks in successive REP DD current oscillations was found. Efficient lasing on KrF* and XeF* excimer molecules with parameter close to laser parameters of lasers pumped by conventional transverse discharge were demonstrated for the first time. Laser action on F<sub>2</sub>* at 157 nm and rare gas fluorides under REP DD pumping was obtained for the first time, as well. The efficiency and pulse duration of VUV F<sub>2</sub>* laser under REP DD excitation are comparable with those obtained in transverse discharges with preionization. VUV emission of REP DD in binary and ternary Ar-Xe-(He) and Ar-Kr-(He) mixtures at wavelength close to 147 nm was measured. Possibility of VUV lasing in mixtures of rare gases is considered.
Main parameters of plasma formed during the pulse and pulse-periodic runaway electron preionized diffuse discharge (REP DD) in argon, nitrogen and air at high pressure were measured. An electron concentration in the plasma of pulse and pulse-periodic REP DD in the elevated pressure argon was determined. Average for pulse value of electron density in the argon plasma of pulse REP DD was ~ 3·10<sup>15</sup> cm<sup>-3</sup>. Dynamics of electron density in the atmospheric-pressure plasma of the argon during the REP DD was determined. Measured average values of an electron concentration in the plasma of the pulse-periodic REP DD in atmospheric-pressure air and nitrogen were ~ 3·10<sup>14</sup> and ~ 4·10<sup>14</sup> cm<sup>-3</sup>, respectively. In addition, for the plasma formed during the pulse-periodic REP DD in atmospheric-pressure nitrogen and air average values of an electron temperature and reduced electric field, as well their dynamics were determined. Average value of an electron temperature during the pulse duration for nitrogen and air plasmas was ~ 2 eV. Dynamics of an electron temperature and reduced electric field strength was registered. Data on rotational and gas temperatures in the discharge plasma of atmospheric-pressure nitrogen formed in pulse (T<sub>r</sub> ≈ 350 K, T<sub>g</sub> ≈ 380 K) and pulse-periodic (T<sub>r</sub> ≈ 750 K, T<sub>g</sub> ≈ 820 K) modes were obtained. In addition, measured value of vibrational temperature in REP DD’s plasma formed in pulse mode in nitrogen at pressure of 1 bar was T<sub>v</sub> ≈ 3000 K.
Breakdown of the gaps with a non-uniform electric field filled with nitrogen and air as well as with other gases under
high-voltage nanosecond pulses was investigated. It is shown that conditions of obtaining a diffuse discharge without a
source of additional ionization are extended at the voltage pulse duration decreasing. A volume discharge is formed due
to the gap pre-ionization by runaway electrons and X-ray quanta. At a negative polarity of the electrode with a small
radius of curvature, a volume (diffuse) discharge formation is determined by pre-ionization with runaway electrons
which are generated due to the electric field amplification near the cathode and in the gap. At a positive polarity of the
electrode with a small radius of curvature, the X-ray radiation, generated at the runaway electrons braking at the anode
and in the gap, is of great importance in a volume discharge formation. A runaway electrons preionized diffuse discharge
(REP DD) has two characteristic stages. In the first stage, the ionization wave overlaps the gap during a fraction of a
second. The discharge current is determined by the conductivity current in the dense plasma of the ionization wave and
the displacement current in the remaining part of the gap. The second stage of the discharge can be related to the
anomalous glow discharge with a high specific input power. During the second stage, the gap voltage decreases and the
cathode spots formed as a result of explosive electron emission can participate in the electron emission from the cathode.
At the increase of the voltage pulse duration and specific input power, the REP DD transforms into a spark discharge
form. A REP DD is easily realized in various gases and at different pressures; see  and references in . At pressure
decrease was obtained the anode electrons beam current to rise (up to ~2 kA/cm<sup>2</sup> in helium). At the REP DD, the anode
is influenced by the plasma of a dense nanosecond discharge with the specific input power up to hundreds of megawatt
per a cubic centimeter, by the electrons beam, 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 and dielectric surfaces. The REP DD is promising as well for creation of the VUV-range excilamps with a high
radiation power in a pulse. REP DD was use for pumping different gas lasers.