Vol 44, No 9 (2018)

Geometrical changes in capillary discharges influence the plasma properties and can control exit parameters to certain desired values. For a fixed capillary radius of 2 mm and a 72-μs 43.9-kA peak discharge current, the plasma temperature is about 2.7 eV for different capillary lengths due to the constant input energy, while the number densities tend to saturate for capillary lengths greater than 12 cm. The electrical conductivity reaches 4.02 × 104 Ω⁻¹ m⁻¹ and then tends to saturate for 9-cm capillary length. The maximum bulk velocity at the capillary exit slightly increases with the increase in the capillary length from 6.15 to 6.26 km/s for lengths below 18 cm and decreases to 5.88 km/s for longer capillaries due to the higher amount of ablated mass and increased drag forces. For a 9-cm length with the same 72-μs 43.9-kA peak discharge current, the increase in the capillary radius reduces the energy density, which in turn reduces the total ablate mass, plasma density, electrical conductivity, and exit pressure. It is shown that the plasma temperature decreases from 4.6 to 2.1 eV by increasing the capillary radius and radiant heat flux also drops from 463 to 18.1 GW/m². The exit bulk velocity drops from 8.7 to 5.3 km/s as the radius increases from 0.5 to 3.6 mm, respectively. The design features of a capillary discharge can be adjusted for the radius and length, to produce specific plasma parameters for desired applications. Scaling laws relating exit peak plasma parameters to radius and length are obtained to facilitate quick estimate of plasma parameters. The validation of this model has been confirmed by confronting with experimental measurements.

The properties of oblique propagation of small amplitude ion-acoustic soliton are investigated in a plasma containing weakly relativistic ions and two-temperature electrons (cold and hot electrons). The reductive perturbation method is used to derive the Korteweg−de Vries equation for the present plasma model. It is found that the parameters determining the nature of soliton are different for compressive or rarefactive structures. Moreover, the effects of weakly relativistic ions, the temperature ratio, and the density ratio of hot-to-cold electron species on soliton characters are studied. The theory is applied on the case of relativistic ions observed in the magnetosphere and in the case of nonrelativistic ions observed in tokamaks.

This article is a continuation of the authors’ previous contribution. Plasma-activated water (PAW) prepared by exposure to the point-to-plane dc corona discharge was analyzed, and its biological effect tested on bacteria in planktonic and biofilm forms. Hydrogen peroxide and nitric acid were found as active components of PAW, although the presence of another unknown compound cannot be excluded unambiguously. PAW inhibits rapidly planktonic Gram-positive bacteria, whereas the inhibition of Gram-negative ones is somewhat slower. In biofilm form, this activity was not observed, so that PAW is not able to disinfect bacterial biofilms.

The paper describes the calculation data on the physical parameters of a reactor-stellarator, where the nonuniformities of the helical field are smaller than the toroidal magnetic field nonuniformities: ε_h < ε_t. Unlike the previous studies, where the ion-component transport coefficients had the collision frequency dependence proportional to ν^1/2, this being equivalent to the ε_h > ε_t case, in the present calculations, these coefficients were assumed to be in proportion to the first power of the collision frequency, D_i ∝ ν for ν_eff < 2ω_E, and to D_i ∝ ν⁻¹ for the inverse inequality. Here, ω_E is the rotation frequency of plasma in the radial electric field. As before, the plasma electrons corresponded to the mode of D_e ∝ ν⁻¹. As initial parameters for numerical calculations, a reactor with R = 8 m, r_p = 2 m, and B₀ = 5 Т was taken. A numerical code was used to solve the set of equations that describes the plasma space−time behavior in the reactor-stellarator under the conditions of equal diffusion fluxes. The start of reactor operation in the mode of thermonuclear burning was provided by heating sources with a power of several tens of megawatts. Steady-state operating conditions of a self-sustained thermonuclear reaction were attained by maintaining the plasma density through DT fuel pellet injection into the plasma.

Incoherent scattering of a probing wave by Langmuir fluctuations trapped and enhanced near a local minimum of the electron density (plasma density well) in plasma with a parabolic density profile is considered. Steady-state amplitudes of fluctuations are calculated for arbitrary velocity distribution functions of plasma particles with allowance for electron collisions. It is shown that quasi-periodic oscillations with two characteristic scales can be present in the spectrum of the plasma line. The smaller scale is due to the wellknown effect of discretization of the spectrum of Langmuir fluctuations in a plasma density well. The larger scale is associated with the generation of scattered waves in two spatial regions and subsequent interference of these waves at the exit from the density well. Oscillations with this scale are more stable under unsteady plasma conditions and can be more often observed in experiments. The results of this work can be used to experimentally determine the plasma parameters, such as the electron collision frequency and the size and lifetime of the plasma density well.

Results are presented from experimental studies of a pulsed source of soft X-ray (SXR) emission with photon energies in the range of 0.4–1 keV and an output energy of 2–10 kJ. SXR pulses with a duration of 10–15 μs were generated in collisions of two plasma flows propagating toward one another in a longitudinal magnetic field. The plasma flows with velocities of (2–4) × 10⁷ cm/s and energy contents of 70–100 kJ were produced by two electrodynamic coaxial accelerators with pulsed gas injection. Nitrogen and neon, as well as their mixtures with deuterium, were used as working gases. The diagnostic equipment is described, and the experimental results obtained under different operating conditions are discussed. In particular, X-ray spectroscopy was used to study the high-temperature plasma produced in a collision of two plasma flows. The observed intensities of spectral lines are compared with the results of detailed kinetic calculations performed in a steady-state approximation. The calculations of the nitrogen and neon kinetics have shown that the electron temperature of a nitrogen plasma can be most conveniently determined from the intensity ratio of the resonance lines of He- and H-like nitrogen ions, while that of a neon plasma, from the intensity ratio between the resonance line of He-like Ne IX ions and the 3p−2s line of Li-like Ne VIII ions. In the experiments with plasma flows containing nitrogen ions, the electron temperature was found to be ≈120 eV, whereas in the experiments with plasma flows containing neon ions, it was 160–170 eV.

The problem of collisionless absorption of ultrawideband electromagnetic pulses in the ionosphere is studied analytically. It is shown that absorption has a resonance character if the repetition rate of a train of pulses is equal to the frequency of the excited plasma waves.

An extensive analysis of Ulysses observations of the solar wind speed V from 1990 to 2008 is undertaken. It is shown that the evolution of V with heliocentric distance r depends substantially on both the heliolatitude and the solar activity cycle. Deviations from the predicted Parker’s profile of V(r) are so considerable that cannot be explained by a scarcity of measurements or other technical effects. In particular, the expected smooth growth of the solar wind speed with r is typical only for the solar activity maximum and for low heliolatitudes (lower than ±40°), while at high latitudes, there are two V(r) branches: growing and falling. In the solar activity maximum, V increases toward the solar pole in the North hemisphere only; however, in the South hemisphere, it decreases with heliolatitude. In the minimum of solar activity, the profile of V(r) at low heliolatitudes has a local minimum between 2 and 5 AU. This result is confirmed by the corresponding data from other spacecraft (Voyager 1 and Pioneer 10). Unexpected spatial variations in V at low heliolatitudes can be explained by the impact of coronal hole flows on the V(r) profile since the flows incline to the ecliptic plane. To reproduce the impact of spatial variations of V in the polar corona on the behavior of V at low heliolatitudes, a stationary one-fluid ideal MHD-model is developed with account of recent results on imagery of the solar wind speed in the corona up to 5.5 solar radii obtained on the basis of combined observations from SOHO/UVCS, LASCO, and Mauna Loa.

The measured dependences of the equivalent plasma resistance on the external magnetic field (0–50 G) in a 46-cm-diameter RF inductive plasma source operating at frequencies of 2, 4, and 13.56 MHz and a power of 100–500 W are presented. The experiments were carried out in argon at pressures of 0.1–30 mTorr. The presence of the external magnetic field leads to the appearance of resonance domains of efficient RF power absorption corresponding to the conditions of resonance excitation of helicons coupled with Trivelpiece–Gould modes. It is shown that RF power absorption at frequencies of 2 MHz can be optimized by applying an external magnetic field corresponding to the domains of resonance absorption. The effect is enhanced with increasing operating frequency.

A device is developed to create cold nonequilibrium electron-beam plasma in a supersonic gas flow. The possibility of conversion of natural and associated petroleum gases into products with different chemical compositions by using this plasma is demonstrated. With the use of laboratory equipment, we find various products of oxidative and nonoxidative conversion. The proposed method is promising for industrial application.