Single-component relativistic electron flux

Two models of a single-component relativistic electron flux are considered, which can be of interest for practical applications. The models differ with respect to allowance for the self-magnetic field. Since only one situation can be realized (under otherwise identical conditions) in a real experiment, one of the two models can be more or less expedient.     

Recombination instability of a dusty plasma of non-self-sustained discharge

The stability of a dusty plasma of low pressure non-self-sustained discharge is studied. It is shown that aperiodic recombination instability can be developed in plasma in a wide wavenumber range. The physical mechanism of instability is discussed. The dependence of conditions of instability development and its increment on discharge parameters is analyzed.     

Evolution of rf instability in a steady-state plasma accelerator

For the first time experimental data are obtained which indicate a stable relation between the microwave radiation intensity of a steady-state plasma accelerator and the rate of bulk erosion of the accelerating channel walls. The frequency range of the electromagnetic radiation corresponds to the excitation of a specific beam instability of the plasma flux at the edge of the accelerating channel, caused, in the opinion of the authors, by electron emission from the eroded part of the dielectric walls. Pis’ma Zh. Tekh. Fiz. 23, 37–41 (May 26, 1997)     

Microwave instability in electron storage rings

Tracking simulations, with the aim of studying the microwave regime with short and intense bunches, suggest different instability mechanisms, according to the impedance model. In order to get a better insight of the source of the instability, i.e. azimuthal or radial mode coupling, we choose to follow the Sacherer (IEEE Trans. Nucl. Sci. NS-24, 1977 1393) approach to investigate the stability of the stationnary solution. The generalized Sacherer's integral, including mode coupling and potential well distortion, is then solved by using the “step function technique” for the expansion of the radial function, as proposed by Oide and Yokoya (KEK Preprint-90-10, April, 1990). For illustration, the effect of the resonant frequency of a broadband resonator in the SOLEIL storage ring is studied. When the resonator frequency is much higher than the bunch spectrum width, azimuthal mode coupling can occur before radial mode coupling. When the resonator frequency is lower, radial mode coupling comes usually first, but two or more bunchlets are produced at relatively low current. The diffusion process between the bunchlets, which leads to the well-known “saw-tooth” behavior, originates actually from a fast-growing microwave instability. Lastly, the beneficial effect of an harmonic cavity on the microwave instability is estimated and discussed.     

The effect of dissipation on the instability of a superthreshold electron beam

We have studied the effect of dissipation on the development of instability in a superthreshold electron beam. The instability is related to an aperiodic modulation of the beam current density in a medium with negative dielectric permittivity. It is shown that the dissipative instability increment in a superthreshold electron beam depends on the dissipation level stronger than in a subthreshold beam.     

Dynamics of plasma and ion flux in a vacuum neutron tube

Results of the numerical simulation of the formation of the ion beam in the accelerating gap of a vacuum neutron tube are presented. Calculations are performed with the KARAT code in a two-dimensional nonstationary formulation for plasma formed in arc discharge and inflowing into an accelerating gap with the given time dependences of parameters (density, expansion velocity). The small duration of the vacuum arc leads to a considerable change of parameters of inflowing plasma during the accelerating pulse. Two geometries are considered: the conventional and sectioned diode, in which the total voltage is divided between the anode, intermediate electrode, and cathode.     

Investigation of the ionization rate in a low-temperature nonequilibrium plasma flux

Results are presented of a determination of the ionization rate constants of a low-temperature lithium plasma on the basis of measuring the plasma parameters in a longitudinal discharge and of numerical processing of the experimental data.     

Universal plasma electron source

The construction of universal plasma electron sources that allows to generate both focused electron beams and large cross-section beams within stationary and pulse mode of operation is proposed, without any essential change in the construction of the source. The special feature of the source is the stability of electron beam parameters over a wide range of pressure (up to 10⁻² mbar), which makes it possible to use it in difficult vacuum conditions caused by intensive gas emission from the treated surface. High stability of the focused electron beam parameters is achieved due to a special configuration of electric and magnetic fields in the region of electron extraction. Generating large cross-section beams, a weak dependence of beam parameters of gas pressure, is achieved by using the method of double-grid stabilization of the emitting plasma surface. Physical processes causing an increase in parameter stability are discussed.     

Heterogeneous flux formation in plasma pulse deposition

Conclusions Measurements have been made on the trends in the formation of heterogeneous plasma flows in a coaxial plasma accelerator as affected by the design and technological parameters.There are large spreads in the thermokinetic and concentration parameters when the powder is supplied to a cylindrical tube in the accelerator. The optimum heterogeneous-flow organization is obtained in a new plasma accelerator design that provides a uniform particle distribution in velocity and concentration in the cross section of the plasma jet and compression of the plasma cloud along the jet. The powder use factor is increased by a factor 1.3-1.5.An Ar+H₂ mixture as the plasma-forming gas gives high-grade homogeneous coatings with low porosity.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 27, No. 4, pp. 60–66, July–August, 1991.     

Evaluation of electron concentration in plasma of a reflex klystron

Conclusion The basic function of the above method consists in evaluating electron concentration of plasma with a precision adequate for the requirements of plasma diagnostics. This method serves to study internal processes which occur in klystron plasma and to simulate the effect on the klystron output parameters of various electromagnetic factors which deform the flows. This method can also be used in klystron vacuum technology for determining the degree of purity of a vacuum bulb.     

Microgravity investigations of instability and mixing flux in frontal displacement of fluids

The goal of the present study is to investigate analytically, numerically and experimentally the instability of the displacement of viscous fluid by a less viscous one in a two-dimensional channel, and to determine characteristic size of entrapment zones. Experiments on miscible displacement of fluids in Hele-Shaw cells were conducted under microgravity conditions. Extensive direct numerical simulations allowed to investigate the sensitivity of the displacement process to variation of values of the main governing parameters. Validation of the code was performed by comparing the results of model problems simulations with experiments and with the existing solutions published in literature. Taking into account non-linear effects in fluids displacement allowed to explain new experimental results on the pear-shape of fingers and periodical separation of their tip elements from the main body of displacing fluid. Those separated blobs of less viscous fluid move much faster than the mean flow of the displaced viscous fluid. The results of numerical simulations processed based on the dimensions analysis allow to introduce criteria characterizing the quality of displacement. The functional dependence of the dimensionless criteria on the values of governing parameters needs further investigations.     

Large-scale electron vortex structure formation in a plasma lens

The first experimental data on the observation of electron vortices in an electrostatic plasma lens at a considerable radial gradient of electron density are reported. It is established that anharmonic potential waves of large amplitude appear and propagate in the azimuthal direction. The results of measurements of the electric field distribution show that electron bunches formed as a result of instability development contain trapped particles, which rotate at a large velocity around the centers of bunches, thus creating vortices. The main factor leading to limitation of the maximum amplitude of vortices in a strong magnetic field has been experimentally established.     

Instability induced in a relativistic plasma flux by the excitation of surface waves

An analysis is made of the instability of a plasma flux caused by the excitation of a new type of cylindrical surface electromagnetic waves at the interface between the flux and a stationary plasma. It is shown that, unlike the conventional case ε₁>0 and ε₂,<0, at the interface of a relativistic plasma beam there exist growing surface waves at frequencies corresponding to positive values of the permittivities on both sides of the discontinuity. For a given geometry and plasma density the critical parameter for the excitation of these waves is the wave radius of the flux. Pis’ma Zh. Tekh. Fiz. 23, 76–79 (March 12, 1997)     

The trapped ion–electron instability in an electron storage ring with a gap in the bunch train

The trapped ion–electron instability in an electron storage ring is studied for a broad distribution of natural ion oscillation frequencies, termed ion bounce frequencies. A gap in the train of electron bunches may be used to create bands of unstable ion bounce frequencies, so that an ion species is ejected from regions of the ring where its horizontal or vertical bounce frequency is unstable. Expressions are obtained for the reduction in the incoherent tune shifts and trapped ion–electron instability growth rates resulting from the gap.     

Nitriding of stainless steel in plasma of a pulse electron beam

The formation of a hardened layer with low-temperature (400°C)nitriding of grade 12Kh18N10T stainless steel in plasma of a pulse electron beam which is generated under continuous and pulse conditions at equal average current (2.6 A) and electron energy (200 eV) is studied. In spite of intense ion sputtering of the surface during the pulse, both nitriding conditions yielded equal quantities of thickness and hardness of the layer, which indicated that neutral atomic nitrogen plays a main role during nitriding.     

Determining the efficiency of a plasma thruster with closed electron drift

We propose a new method for the analysis of the efficiency of ion generation and acceleration, which can be used to determine the ion current in a plasma accelerator (thruster) with closed electron drift. The method is based on the measurement of the energy and angular distributions of ions in the plasma jet, the discharge power, and the jet thrust. The laws of variation of the plasma thruster efficiency as a function of the discharge voltage in the interval of 300–1000 V have been studied.     

Production of low electron temperature ECR plasma for plasma processing

Low-electron-temperature ECR plasma with high electron density was realized under the mirror magnetic field configuration in the H₂ and the Ar/N₂ plasma. Especially, the electron temperature was observed to be less than 2 eV in the Ar/N₂ plasma. It was found from the calculation of particle and power balance in steady state that the decrease in the electron temperature observed in the Ar/N₂ plasma was due to the effect of the magnetic-mirror confinement of the N₂ plasma. Furthermore, our calculated results suggest that the effect of magnetic-mirror on the decrease in the electron temperature depends on the collisional cross section between electrons and neutral particles.