Vol 45, No 9 (2019)

The influence of electrons trapped between the magnetic mirror and the Debye sheath on the potential profile in the expander of an open trap is considered. A numerical model is developed to calculate the electron distribution function in the self-consistent electrostatic potential. Passing electrons are assumed to be collisionless, while the distribution function of trapped electrons is calculated by solving the bounce-averaged kinetic equation with the Landau collision integral. The self-consistent profile of the potential is obtained. The solution is shown to agree well with Ryutov’s semi-analytical model.

The implosion of combined loads consisting of an outer wire (fiber) array and inner cylindrical target was studied experimentally at the Angara-5-1 facility (3.5 MA, 100 ns) at currents of up to 3.5 MA. The experiments were carried out with 12- and 20-mm-diameter outer arrays made of 15-μm-diameter aluminum wires, composite arrays made of aluminum wires and 25-μm-diameter kapron fibers, and arrays made of kapron fibers with a 1-μm-thick aluminum coating. The number of wires varied from 10 to 40. The targets were made of agar-agar or low-density deuterated polyethylene. The parameters of the Z-pinch plasma were determined using the Angara-5-1 diagnostic complex, which included optical streak cameras, X-ray frame cameras, X-ray detectors, X-ray pinhole cameras, neutron detectors, and a mica-crystal X-ray spectrograph. It is established that the plasma compression dynamics and the formation of local plasma structures generating neutrons depend on the load configuration: the array diameter, the number of wires (fibers), and the diameter and density of the target. The most efficient compression and the highest plasma parameters (the compression ratio and plasma temperature), as well as the highest neutron yield, were achieved in experiments with 12-mm-diameter aluminum wire arrays inside which a 1-mm-diameter deuterated target with a mass density of 0.3 g/cm³ was installed As a result of collision of the bulk of the array mass with the inner target, a compact pinch with a diameter of ≈0.5 mm forms. The pinch formation is accompanied by the generation of a soft X-ray pulse. The development of MHD instabilities in the pinch plasma results in the formation of multiple hot spots (HSs) on the pinch axis with a typical size of 200–300 μm and an electron temperature of 0.4–0.7 keV. The HS formation is accompanied by emission of neutrons with a mean energy of 2.7 ± 0.2 MeV. The maximum neutron yield achieved in these experiments was 2.6 × 10¹⁰ neutrons/shot.

Edge ignition of a cylindrical shell target by a proton beam with a small mass heating depth of about 0.5 g/cm² is analyzed for two values of the initial mass density of the DT fuel, \({{\rho }_{0}} \approx 110\) and 22 g/cm³, and given beam parameters (the intensity \(J \propto {{\rho }_{0}}\) and impact time \(\Delta {{t}_{{{\text{pr}}}}} \propto \rho _{0}^{{ - 1}}\)). By comparing results obtained using different models of heat transfer through the fuel–shell interface, it is shown that application of a strong magnetic field that suppresses heat transfer but does not affect the trajectories of the α-particles produced in the DT reaction reduces the ignition energy by only about 10%. The unsteady detonation wave generated in the course of ignition transforms into a steady-state fast shockless burning wave, in which the cold fuel is heated by α-particles. The wave parameters depend on the deposited energy. As the wave propagates through the fuel, the α-particles escaping from the fuel volume carry away about one-half of their initial power. For one of the simulation versions, the target length H is determined (\({{\rho }_{0}}H \approx 10\) g/cm²) at which the gain reaches a value of \(G = 1250\). An approximate formula is derived that relates the slope of the pressure profile in a steady-state wave to the wave velocity and the heating power per unit mass of the fuel near the wave front. The applicability of the formulas relating the pressure and velocity at the Chapman–Jouguet point to the propagation velocity of a strong detonation wave is demonstrated.

The forces acting on the ensemble of dust grains in a plasma flow are analyzed. It is shown that the nonreciprocal character of the forces results in the appearance of an ion drag force, which depends on the intergrain distance. Results of calculations for two grains and an unbounded hexagonal lattice are presented. Estimates show that the collective ion drag force under typical dusty plasma conditions can be comparable with the weight of an individual grain.

Linear and nonlinear waves in the near-surface plasma at Phobos and Deimos are considered. It is shown that the motion of the solar wind relative to photoelectrons and charged dust grains violates the isotropy of the electron distribution function in the near-surface plasma at the Martian satellites, which leads to the development of instability and excitation of high-frequency waves with frequencies in the range of Langmuir and electromagnetic waves. Moreover, the propagation of dust acoustic waves, which can be excited, e.g., in the terminator regions of the Martian satellites, is possible. Solutions corresponding to the parameters of the plasma–dust systems over the illuminated parts of the Phobos and Deimos surfaces are found in the form of dust acoustic solitons. The ranges of possible Mach numbers and soliton amplitudes are determined.

The spatial structure of giant blue jets in the upper atmospheric layers is considered on the basis of a nonlinear plasma waveguide model of electric gas breakdown. Laser analogues for such waves are proposed, and the azimuthally equidistant conical structure formed by the rays of a giant jet is explained. The field parameters and the electron density required for this process are estimated. Using the model proposed, requirements to the diagnostics of waves in the upper atmosphere are formulated. Similar models for analyzing thunderstorm phenomena in the lower atmosphere are offered.

The interactions between ion acoustic solitary waves (IASWs) are investigated considering completely ionized electron–positron–ion (e–p–i) plasmas consisting of ions with positive and two negative species, nonthermal electrons, and positrons. Two-sided Korteweg–de Vries (KdV) and modified KdV (mKdV) equations are derived using extended Poincaré–Lighthill–Kuo (ePLK) reductive perturbation method. To investigate the production of ion-acoustic rogue waves (IARWs), the rational solution of nonlinear Schrödinger equation (NLSE) is derived from the mKdV equation. Two types of plasmas containing \({\text{A}}{{{\text{r}}}^{ + }}\), \({{{\text{F}}}^{ - }}\), and \({\text{SF}}_{{\text{5}}}^{ - }\) species, as well as \({\text{SF}}_{{\text{5}}}^{ + }\), \({{{\text{F}}}^{ - }}\), and \({\text{SF}}_{{\text{5}}}^{ - }\) species, are taken into account to study their effects on the amplitudes and phase shifts after collision, as well as the production and properties of rogue waves (RWs). It is observed during collision that a high-amplitude wave is produced in the interaction region depending on the type and parameters of plasmas. The nonthermality of electrons and positrons, electron-to-positron temperature ratio, and the density of negative ions modify the phase shift and amplitude of the waves produced during the collision of the two solitons. The amplitude of the RW for the \({\text{A}}{{{\text{r}}}^{ + }}\), \({{{\text{F}}}^{ - }}\), and \({\text{SF}}_{{\text{5}}}^{ - }\) plasmas is found to be larger than that for the \({\text{SF}}_{{\text{5}}}^{ + }\), \({{{\text{F}}}^{ - }}\), and \({\text{SF}}_{{\text{5}}}^{ - }\) plasmas.