Scattering of an electromagnetic wave by a radially inhomogenous plasma cylinder with electron density fluctuations

Voronezh Polytechnical Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 33, No. 9, pp. 1055–1059, September, 1990.     

离化靶中多脉冲强流电子束的不稳定性

多脉冲强流电子束轰击轫致辐射靶,在靶面形成等离子体层,将对后续电子束脉冲的稳定性产生影响。从基本等离子理论出发,利用成熟的等离子体粒子模拟程序计算在不同等离子条件下电子束流的稳定性。模拟显示在无外场情况下,当等离子体与电子束的密度比小于1时,能量20 MeV、束流强度2.5 kA、焦斑1.5 mm的电子束出现腊肠不稳定性,但相对靶面焦点区而言,束流稳定;当密度比在1~100时,箍缩不稳定性能够改善电子束的聚焦;当密度比在100~1000时,扭曲不稳定性起主导作用,靶面焦点区电子束流仍然稳定;当密度比大于1000后,成丝不稳定性破坏束流,电子束无法在靶面聚焦。     

离化靶中多脉冲强流电子束的不稳定性

多脉冲强流电子束轰击轫致辐射靶,在靶面形成等离子体层,将对后续电子束脉冲的稳定性产生影响。从基本等离子理论出发,利用成熟的等离子体粒子模拟程序计算在不同等离子条件下电子束流的稳定性。模拟显示在无外场情况下,当等离子体与电子束的密度比小于1时,能量20 MeV、束流强度2.5 kA、焦斑1.5 mm的电子束出现腊肠不稳定性,但相对靶面焦点区而言,束流稳定;当密度比在1~100时,箍缩不稳定性能够改善电子束的聚焦;当密度比在100~1000时,扭曲不稳定性起主导作用,靶面焦点区电子束流仍然稳定;当密度比大于1000后,成丝不稳定性破坏束流,电子束无法在靶面聚焦。     

Charge dependent effects in azimuthal two-particle correlations and cluster production

It is shown that neutral heavy cluster models provide a natural explanation of the recently observed charged dependent effects in azimuthal correlations between produced pions. This may be interpreted as evidence for identical particle effect and π⁺π^? resonance production in clusters.     

The study of turbulence in theta-pinch plasma with azimuthal magnetic field

It has been demonstrated that a small-scale drift instability occurs in a theta-pinch with a superimposed azimuthal magnetic field, subsequently resulting in turbulization of oscillations andheating of the plasma. The data obtained agree well with the available theoretical models.     

Propagation of azimuthal waves in magnetoactive waveguides filled with a current-carrying plasma

It is shown that a cylindrical metallic waveguide fully filled with a magnetoactive plasma can propagate coupled ordinarily polarized bulk and extraordinarily polarized surface waves along its azimuthal direction. Interaction between these waves is studied in the case when an external magnetic field has axial and azimuthal components. For the case of a regular profile, a practically convenient analytical expression for a correction to the eigenfrequency of the waves that is due to the external azimuthal magnetic field is derived.     

Instabilities of electron-hole plasma under impact ionization and microwave emission

The nonlinear stage of the evolution of electron—hole plasma instabilities in semiconductors under impact ionization (static differential conductivity σ_d > 0) is considered for the case of spatially uniform pertubations of density and electric field. If the differential mobility of carriers μ _d > 0, the instability arises only with allowance for the retardation of the process of impact ionization (linear theory of this effect was developed by M. Toda [4]). When μ _d < 0, the instability may appear in the absence of the retardation. Both these instabilities exhibit oscillating form and are due to h.f. negative dynamic differential conductivity. We determine time sweeps of the electric field under condition of fixed current for the case n-InSb at T = 77 K. The amplitude and the frequency (f>10¹⁰Hz) of the oscillations are evaluated and the conditions, when the shape of E(t)-oscillations is essentially non-harmonic, are determined. Microwave emission observed in semiconductors under impact ionization may have resulted from the instabilities at hand.     

Magnetic propulsion of intense lithium streams in a tokamak magnetic field

This paper describes the effect and gives the theory of magnetic propulsion which allows driving free surface plasma facing liquid lithium streams in tokamaks. In the approximation of a thin flowing layer the MHD equations are reduced to one integrodifferential equation which takes into account the propulsion effect, viscosity, and the drag force due to magnetic pumping and other interactions with the magnetic field. A stability criterion is obtained for stabilization of the "sausage" instability of the streams by centrifugal force.     

Analysis of Landau damping in radially inhomogeneous plasma column

The Landau damping behavior in a cylindrical inhomogeneous warm magnetized plasma waveguide has been studied.The radial inhomogeneity for different characteristic lengths(L0) with strong spatial dispersion has been taken into account.The analyses have been considered for two limits ωce ωpe and ωce ωpe. Due to the radial inhomogeneity of the plasma, all essential equations for studying the Landau damping are calculated in the Bessel–Furrier and differential Bessel–Furrier expansions. The dependence of Landau damping on the inhomogeneity, temperature and external magnetic field for electrostatic modes is scrutinized and described in detail through numerical calculations. The associated numerical results are presented and discussed.     

The collisions of two plasma streams

The mutual interaction of two colliding plasma streams is investigated by means of the perturbation method. The disordered random motions of electrons are taken into account. It is shown that electron oscillations occur only when certain conditions as to the density and relative velocity of the colliding streams are fulfilled. The order of magnitude of the thickness of the shock generated by the initial relative motion is estimated on various assumptions.

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Pulse intense metal-ion diode with a vacuum arc plasma anode

An intense pulsed ion beam of metal was extracted from a magnetically insulated ion diode operated in a mode of plasma prefill generated from a vacuum arc discharge, anode plasma source. With this ion diode, an intense metal-ion beam of a high melting-point metal (Ta) was obtained. A variety of operational modes appeared, depending on the amount of plasma in the diode gap at the initiation of the high-voltage pulse. The energy, current, and duration time of the ion beam were 20~100 keV, ~1 kA, and 1 μs, respectively. Measurements of ions were performed with an ion energy analyzer or a biased ion collector located at the end of a long drift tube and a Thomson parabola ion spectrometer. The Ta ions in the first to fifth states of ionization were detected accompanied by C⁺, O⁺, F⁺, and H⁺ . A Ta ion beam current of about half the total ion flux was obtained in this experiment     

Theory of the interaction of intense laser radiation with magnetoactive plasma

Analytical expressions for the density of magnetoactive plasma perturbed by circularly polarized relativistically strong laser radiation are obtained.     

Studies of advanced soft X-ray laser and coherent higher harmonic generation using intense subpicosecond laser produced high density plasma

Current activities on our research of soft X-ray lasers and higher harmonic generations using intense, subpicosecond lasers are reviewed. Especially for soft X-ray lasers we experimentally demonstrate that by longitudinally pumping 2-mm-long molybdenum preformed plasma with high-intensity 475 fs duration laser pulse, a highly directive soft-X-ray laser at 18.9 nm wavelength is generated. The divergence of the beam is evaluated to be of the submilliradian order, and only requires pump laser energy of 150 mJ. Simulations show that the pedestal in the main pump pulse can generate electron density and gain profiles with large spatial gradients, which result in the selective amplification of low-order transverse modes. The present result is the demonstration of an efficient and alternative method of improving the spatial coherence of X-ray lasers with amplified spontaneous emission medium, with possibilities of becoming an excellent tool to explore various application experiments. In higher harmonic generation, topics related to observation of blue shift due to collisionless absorption process is described.     

Instabilities and turbulence in a high pressure plasma carrying transversal current

The excitations of electromagnetic waves in a high pressure plasma, carrying current perpendicular to the applied magnetic field is investigated. We assume that the relative velocity of ions and electrons exceeds the thermal velocity of ions. We have pointed out, that the excitation of kinetic branches of oscillations whith high growth rates referred to the lower hybrid frequency is possible. The paper contains some estimations of the fluctuations level when the saturation occurs and of the limiting values of heated ion temperature.     

Modification of metallic materials by processing with high-temperature pulsed plasma streams

A review is given of investigations of the modification of metallic materials by processing them with high-temperature pulsed plasma streams having incident power densities in the range (3–100)×10⁹ W/m² with pulse durations of between 2–3 and 100 µsec. The main experimental results are presented on changes in the microstructure, the mechanical and tribological characteristics, the corrosion resistance, and the radiation-induced erosion when the modified materials are irradiated with ions. An analysis of these results shows that processing with high-temperature pulsed plasma streams is a comprehensive method for changing in a controlled manner the structural-phase state and various operational properties of materials, the extent of the change being determined by the irradiation conditions (the power density of the incident stream, the type of plasma, etc.), the type of material, and its previous processing.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 109–126, May, 1993.     

Diffraction of electromagnetic waves by a radially inhomogeneous plasma sphere and cylinder

Radiophysics and Quantum Electronics -