Keldysh Research Center

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Keldysh Research Center

Russia
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Shagayda A.A.,Keldysh Research Center
Journal of Propulsion and Power | Year: 2013

The area of application of the Hall effect thrusters is constantly expanding, both in the direction of reduced power and toward an increase of power and specific impulse. The two main problems are studied in this paper. The first is to examine the possibility of providing the similarity of plasma parameters in Hall effect thrusters, and the second is to estimate the best achievable output characteristics when scaling Hall effect thrusters. It is shown that a strict similarity of plasma parameters is possible only for the same type of propellant at the same discharge voltage at invariance of at least two dimensionless scaling parameters. Based on the analysis of the similarity criteria and available experimental data, a speculative assertion is made, that in the optimal mode, all the geometrical dimensions of the Hall thruster should be changed in the same proportion. For this type of scaling, the semi-empirical expression for the mass utilization efficiency is obtained under the invariance of the heat flux on the discharge-channel walls. This expression is used to investigate the regularities of performance changes in the optimal mode by varying the discharge power and discharge voltage, and using different types of propellants. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc.


Polyanskiy M.N.,Keldysh Research Center | Savushkina S.V.,Keldysh Research Center
Journal of Surface Investigation | Year: 2014

Results of experiments on development of the method of the lateral layer-by-layer nanostructuring of coatings prepared by plasma spraying in order to improve their working characteristics under thermal cycling loads are presented. Coating deposition is performed through a mask with holes while maintaining dynamic vacuum in the chamber. Analysis of the morphology of the zirconium-oxide coatings using a scanning electron microscope shows that the structure of the coating obtained in the "shaded" regions almost completely consists of submicron particles and nanoparticles. An estimate explaining the formation of regions in the coating consisting of nanoparticles due to heterogeneous condensation of the vapor phase of the sprayed material in the Prandtl-Meyer expansion formed in the supersonic plasma flow around the barrier is given. © 2014 Pleiades Publishing, Ltd.


Golovin A.I.,Keldysh Research Center
Applied Physics | Year: 2016

Equations were suggested to estimate energetic efficiency of a run-away electron beam generation by stationary open discharge. It was shown that equation for the efficiency differs from that for electron guns with high-voltage glow discharge because of formation of secondary electrons in cathode potential drop area.


Golovin A.I.,Keldysh Research Center
Applied Physics | Year: 2015

Secondary electrons appearing in stationary open discharge are taken into account in the suggested early mathematical model of processes in the discharge. This allowed estimating an energy distribution of the beam of run-away electrons. It was shown that at high voltages the energy of a significant portion of secondary electrons slightly differs from the energy of primary electrons which corresponds to an applied accelerating voltage.


Golovin A.I.,Keldysh Research Center
Applied Physics | Year: 2015

The mathematical model of processes in glow discharge with run-away electrons (an open discharge) suggested before allows to take into account influence of anode position and effective transparency of the anode on the volt-ampere curve. Numerical analyses of dependences of dimensionless parameters had been done, which have shown that in most cases influence of anode characteristics is negligible; the result is in agreement with the known experimental data.


Analytical studies and numerical simulations show that the electron velocity distribution function in a Hall thruster discharge with crossed electric and magnetic fields is not Maxwellian. This is due to the fact that the mean free path between collisions is greater than both the Larmor radius and the characteristic dimensions of the discharge channel. However in numerical models of Hall thrusters, a hydrodynamic approach is often used to describe the electron dynamics, because discharge simulation in a fully kinetic approach requires large computing resources and is time consuming. A more accurate modeling of the electron flow in the hydrodynamic approximation requires taking into account the non-Maxwellian character of the distribution function and finding its moments, an approach that reflects the properties of electrons drifting in crossed electric and magnetic fields better than the commonly used Euler or Navier-Stokes approximations. In the present paper, an expression for the electron velocity distribution function in rarefied spatially homogeneous stationary plasma with crossed electric and magnetic fields and predominance of collisions with heavy particles is derived in the relaxation approximation. The main moments of the distribution function including longitudinal and transversal temperatures, the components of the viscous stress tensor, and of the heat flux vector are calculated. Distinctive features of the hydrodynamic description of electrons with a strongly non-equilibrium distribution function and the prospects for further development of the proposed approach for calculating the distribution function in spatially inhomogeneous plasma are discussed. © 2012 American Institute of Physics.


Shagayda A.A.,Keldysh Research Center
IEEE Transactions on Plasma Science | Year: 2015

The field of application of Hall effect thrusters (HETs) is constantly expanding toward increased power and specific impulse and also toward reduced power. The modern level of plasma simulations does not allow accurate prediction of a thruster performance in advance. Therefore, the methods of scaling play an important role in the creation of new thrusters with desired characteristics. This paper describes a scaling model of HETs based on an analytical assessment of the anode mass utilization efficiency and the available experimental data. Empirical coefficients of the model are found using an extensive database containing published test results of many thrusters. The obtained expressions allow for predicting the performance of HETs for various kinds of propellant when the discharge power and voltage vary over a wide range. © 2014 IEEE.


Tomilin D.,Keldysh Research Center
Physics of Plasmas | Year: 2013

This paper presents a linear analysis of gradient plasma instabilities in Hall thrusters. The study obtains and analyzes the dispersion equation of high-frequency electromagnetic waves based on the two-fluid model of a cold plasma. The regions of parameters corresponding to unstable high frequency modes are determined and the dependence of the increments and intrinsic frequencies on plasma parameters is obtained. The obtained results agree with those of previously published studies. © 2013 American Institute of Physics.


Golovin A.I.,Keldysh Research Center
Technical Physics Letters | Year: 2015

A simple mathematical model developed previously for the description of processes in electron beam generators based on high-voltage glow discharge with runaway electrons (open discharge) has been used to express the dependence of the discharge current on the applied voltage. The influence of the gas type on the character of discharge has been analyzed, and the obtained dependences are compared to experimental data. © 2015, Pleiades Publishing, Ltd.


Cherkasov S.G.,Keldysh Research Center
High Temperature | Year: 2011

Heat conducting radiating ribs are widely used in the thermal control systems of spacecraft, and quantitative characteristics of heat exchange in such ribs have been studied well enough based on the numerical solution of the problem. Some interesting conclusions can be made when analyzing the thermal flux fed to the rib. This heat flux is determined by the temperature profile in the vicinity of the hot rib butt and, since the asymptotic solution for temperature describes well the temperature near this butt, the asymptotic solution for the heat flux gives almost exact values in the case of a rib with a finite length as well. It can be seen that the asymptotic solution in the aggregate makes it possible to calculate the heat flux at any rib length with an error smaller than 13%. The asymptotic solutions describing the temperature distribution along the rib and the thermal flux passing through the rib butt have been obtained for long and short heat conducting radiating ribs.

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