Stationary efflux into a vacuum by a dual-temperature fully ionized plasma

It is shown that the macroscopic process of plasma discharge from an expanding nozzle is determined, when the thermal conductivity of electrons and heat transfer between the components are taken into account, by a unique dimensionless parameter: the adiabaticity parameter characterizing the transition from adiabatic flow of a dense plasma to the flow of comparatively rarefied plasma when the free path length of the particles is commensurate with the characteristic dimension of the nozzle. A numerical method is used to find the distribution of gas-dynamic and electrical parameters of the plasma stream, and the relationship between the generalized output parameters. It is shown that the energy associated with the ions at infinity, in the latter case, can be tens of times greater than the energy in adiabatic efflux, because of the high thermal conductivity with respect to electrons, but unrealistically large expansion of the nozzle is needed in order to attain it. Singular flow patterns occurring when stationary discharge of plasma at infinity is calculated are also discussed.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 10–20, November–December, 1971.In conclusion, the author thanks I. K. Fetisov for helpful discussion.     

Surface action of a heat pulse in a tangential flow

The three-dimensional unsteady problem of the action of a localized radiation pulse on an aluminum plate of finite thickness in a tangential airflow is solved on the basis of the Euler equations in the gas phase and the heat conduction equation in the solid. The process is accompanied by the intense evaporation of plate material and the subsequent (after the action of the radiation pulse ceases) intense condensation of aluminum vapor and condensate particles on the surface. The problem is solved on the assumption that the surface is not screened by its disintegration products and the processes associated with the self-radiation of the gas are disregarded. Heat pulses of intensityq=10⁶−10⁷ W/cm² and durationt _i ≈10⁻⁴ sec are investigated. Various regimes are calculated and the effect of the governing parameters on the impulse transmitted to the surface and ablation of the target material is established. A nontraditional approach, based on the idea of statistical modeling of the motion of an inviscid non-heat-conducting gas at the kinetic level, is used for solving the gas dynamic problem. The application of the approach in question to the solution of problems of this class is justified. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.1, pp. 139–146, January–February, 1994.     

Recombination of electrons in a plasma expanding into a vacuum

As noted in a paper by one of the authors [1], when a hot ionized gas expands into a vacuum, at a certain moment ionization equilibrium must necessarily break down. Shortly after this point, which may be found by the method indicated in [1], ionizing events become very rare and only recombination occurs in the gas. In [1] photorecombination and triple collisions with the capture of an electro to the ground level of the atom were considered. Here the recombination did not proceed to the end: on expanding to infinity and cooling to zero the gas remained partially ionized.Papers have recently appeared [2–7] in which the significant role of triple collisions with the capture of electrons to upper atomic levels is noted. The recombination process has a cascade character at low temperatures and densities which are not excessively small. At first, the electron is captured by one of the upper atomic levels in a triple collision with an ion and another electron. Subsequently, as a result of electron collisions of the second kind, and later also as a result of radiative transitions, the bound electron descends through the energy levels to the atomic ground state. The recombination coefficient for such a process depends much more strongly on the electron temperature T than for a triple collision with capture directly by the ground level (as T^–9/2 as opposed to T^–1), and at low temperatures cascade recombination proceeds much more quickly than capture to the ground level. Since this casts doubt upon the conclusions of [1] regarding the residual ionization when a plasma expands into a vacuum, we were led to re-examine the question, which, as will be clear from what follows, is not considerably more complicated.     

Dynamics of a bubble in a liquid under laser pulse action

Simulation was performed of the behavior of a vapor bubble in a liquid under laser irradiation in laboratory experiments. A mathematical model was developed to analyze the effect of heat conduction, diffusion, and mass transfer on the bubble dynamics under compression and expansion. It is found that at the stage of collapse, intense condensation occurs on the bubble wall, which results in a significant (more than 15fold) decrease in bubble mass and an increase in pressure (to 10⁵ atm) and temperature (to 10⁴ K(. Results of numerical calculations of the radius of the first rebound and the amplitude of the divergent shock wave in water are compared with experimental data. It is shown that small (:about 1%) additives of an incondensable gas lead to a considerable decrease in mass transfer on the bubble wall.     

Transient response analysis of a steel beam with vacuum packed particles

In this paper the method of semi-active damping of vibrations is presented. Free vibrations of a cantilever steel beam encapsulated in a sleeve, filled with the granular material are investigated. Various values of the partial vacuum generated in the granular structure allow to control the global dissipative properties of the discussed system. The loose grains encapsulated in the hermetic, polyvinyl chloride (PVC) envelope transform into a rigid, viscoplastic body as the jamming mechanism occurs when the underpressure is generated. Such phenomenon enables original strategies for semi-active damping. A detailed discussion related to the experimental results concerning the amplitude of vibration, damping, stiffness, and frequency of the continuous granular beam system is provided. The simplified Finite Element Model succeeded in describing the dynamic response of the structure.     

Bow shocks formed by plasma collisions in laser irradiated semi-cylindrical cavities

The formation of shocks in plasmas created by short pulse laser irradiation (λ = 800 nm, I ≈ 1 × 10¹² W cm^?2) of semi-cylindrical cavities of different materials was studied combining visible and soft X-ray laser interferometry with simulations. The plasma rapidly converges near the axis to form a dense bright plasma focus. Later in time a long lasting bow shock is observed to develop outside the cavity, that is shown to arise from the collision of plasmas originating from within the cavity and the surrounding flat walls of the target. The shock is sustained for tens of nanoseconds by the continuous arrival of plasma ablated from the target walls. The plasmas created from the heavier target materials evolve more slowly, resulting in increased shock lifetimes.     

Experimental evidence of a phenomenon of fast randomization in a collisionless plasma

Summary This paper describes a phenomenon of fast randomization of a collisionless plasma observed in the so called plasma sac of a constricted discharge. The phenomenon seems to be related to the achievement, in the constriction, of a critical Mach number, close to unity, in the drifting electron gas. A tentative interpretation and the experimental evidence of electro-acoustic waves related to the phenomenon are also presented.This work was supported in part by the U.S.A.E.C. under Contract AT(30-1)3100 and in part by a grant of the Esso Educational Foundation.     

Probe diagnosis of a flow of particles desorbed from the surface of a solid by a low-density plasma jet

Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 5, pp. 144–150, September–October, 1993.     

On the global stability of a nonlinear functional differential equation with pulse action

We give sufficient conditions for the global stability of the zero solution of a functional differential equation with pulse action and with nonlinear function satisfying the conditions of negative feedback and sublinear growth. __________ Translated from Neliniini Kolyvannya, Vol. 10, No. 2, pp. 258–269, April–June, 2007.     

On the expansion into a vacuum of a rarefied plasma with two sorts of ions

The one-dimensional expansion of a plasma with different temperatures and two sorts of ions into a vacuum is examined. When the ion velocity distribution in the plasma is Maxwellian, propagation of a rarefaction wave is observed, the boundary of which is a weak discontinuity moving with the velocity of ionic sound in the plasma. The value of this velocity is found for the plasma in question. Attention is mainly focused on finding the first two moments of the distribution functions, i.e., the mean velocities and the densities of the heavy particles. An approximate asymptotic solution is obtained for the system of transport equations in the case when the two kinds of ions have similar masses, and the system is solved numerically by computer. Some features of the solutions, typifying a plasma in which the different sorts of ions have different masses, are analyzed in detail.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, Vol. 9, No. 1, pp. 32–38, January–February, 1970.In conclusion the author thanks N. T. Pashchenko for suggesting the problem and showing unfailing interest.     

Numerical experiments on the transient motions of a flapping foil

The flow field generated by a foil during transient motions is investigated by means of numerical experiments. The numerical simulations have some advantages with respect to laboratory experiments. Indeed, having access to the velocity and pressure fields both in space and in time, it is possible to 'measure' quantities like vorticity, forces and torques which are quite difficult to obtain in laboratory. Moreover, data can be easily gained for different foil kinematics. The obtained results show that the time history of the propulsive force strongly depends on the details of the kinematics of the foil. Moreover, the numerical simulations have allowed to understand the main mechanisms employed by fish to propel themselves during fast starts and to identify the values of the parameters providing optimal propulsive performances.     

Emission of dimers from the substrate during vacuum deposition of thin films

Emission of dimers from the substrate to the vapor medium during silver vapor deposition onto an ideal substrate is calculated. Dimers are demonstrated to form on the substrate owing to random collisions of atoms during their surface migration, and emission of dimers is caused by thermal fluctuations of the crystal lattice of the substrate. Calculations based on Langmuir’s modified model of sorption show that emission mainly occurs at the stage of filling of the first atomic layer on the substrate and in regimes of “condensation failure” when intense condensation does not occur even at high levels of supersaturation and nucleation frequency because of the low energy of bonding of vapor atoms with the substrate. A relation of emission of dimers to the intensity of condensation and condensate microroughness on the substrate is found.