Microsecond Microwave Radiation Bursts from a Relativistic Electron Beam Rotating in a Plasma

Coherent curvature radiation from an intense relativistic electron beam rotating in a plasma yielded in the past [1] only very short bursts of microwave radiation. Here we report on extension of the microwave-burst duration to the full width of the beam pulse for two different electron beams: a) 1 MV, 50 kA, 110 ns b) 0.6 MW, 15 kA, 1 , ?s. We show that the short bursts in the past resulted from sudden changes in the plasma density caused by ionization of neutrals, present in the drift tube, by the beam itself. This density change caused a shift away from the resonance condition necessary for coherent radiation. The extension of the pulsewidth was achieved by introducing a plasma gun which did not emit many neutrals. The radiation is mostly in the Ka band (? ? 1 cm) and the power level was ~1 MW.     

Beam Probe Space-Potential Measurement in a Minimum-B Field

A measurement of plasma space potential in a minimum-B magnetic field has been made with a particle beam probe. The diagnostic technique is an extension of conventional heavy ion beam probing in that, among other features, the probing beam is neutral rather than ionized cesium and the parallel-plate electrostatic energy analyzer is fully characterized in a new manner which permits its use in complex magnetic confinement geometries.     

Simulation of laser beam propagation with a paraxial model in a tilted frame

We study the Schrödinger equation which comes from the paraxial approximation of the Helmholtz equation in the case where the direction of propagation is tilted with respect to the boundary of the domain. In a first part, a mathematical analysis is made which leads to an analytical formula of the solution in the simple case where the refraction index and the absorption coefficients are constant. Afterwards, we propose a numerical method for solving the initial problem which uses the previous analytical expression. Numerical results are presented. We also sketch an extension to a time dependent model which is relevant for laser–plasma interaction.     

Initial-value problem for plasma oscillations in a uniform magnetic field

The solution is given of the initial-value problem for the nonrelativistic linearised Vlasov-Maxwell equations describing longitudinal and transverse plasma oscillations in an external uniform magnetic field. The problem is solved for all directions of propagation except normal to the external magnetic field, and the equilibrium distribution is not assumed isotropic. The method of solution is an extension of Van Kampen's eigenfunction expansion technique, already developed considerably by Zelazny and McCure, in which the problem is reduced to the solution of a system of singular integral equations.     

Thermodynamic characteristics of a metastable plasma

The equation of state is obtained for an ion-ion plasma which is stable with respect to recombination processes. The regions of thermodynamic stability of a nonideal plasma and of mixtures of such a plasma with an ideal plasma are determined by considering isotherms. It is shown that such a plasma-gas mixture possesses elastic properties.General Physics Institute, Russian Academy of Sciences, Moscow. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 8–14, January, 1993.     

全相对论性Vlasov－Maxwell方程的解析解

本文给出了全相对论性Ｖｌａｓｏｖ－Ｍａｘｗｅｌｌ方程的解析解。该解是Ｓｗａｄｅｓｈ［１］结果的推广，它既适用于高温聚变等离子体，也适用于有相对论漂移速度的等离子体。     

A simplified model joining the sheath and the plasma in electronegative plasmas

An extension of the previous work which only dealt with the sheath zone is used to analyze the wall-plasma interaction in electronegative plasmas. Ionization is introduced as the presheath mechanism. This extension includes the joining of the sheath and the plasma solutions. For certain plasma parameters a stratified presheath is obtained. In this case, the plasma and the sheath solutions are matched in a very simplified way, by introducing a discontinuity in the electric field. This discontinuity is equivalent to consideration of a negatively charged layer between the presheath and the sheath. The parameter space region in which this matching should be made has been delimited. The model includes the previous one in the limiting case of no ionization.     

Possibility of weakly charged nonlinear solitary dust clouds near the continuum threshold of dust population in a quasi-neutral dusty plasma

Considering the Boltzmann response of the plasma ions and electrons and inertial dynamics of the charged dust grains, the possibility of very weak compressive soliton near the continuum limit of the dust population has been inferred. It is concluded that the behaviour of such coherent structures could be well described by the numerical analysis of the derived nonlinear classical energy integral equation for bounded solutions. These seem to be higher order dispersive structures within acoustic limit of the nonlinear turbulence. It is observed that the dust density enhancement beyond the continuum threshold causes regular increment in width and amplitude of the soliton structures. It is found that the soliton amplitude sensitively depends on the massive impurity’s population. These coherent structures could be visualized as weakly charged solitary dust clouds of finite extension (∼ plasma Debye length) within Boltzmann environment of plasma particles in their local surroundings. The seeding mechanism of such clouds may be attributed to some plasma instabilities driven by either internal or external free energy sources. Numerical analysis of the problem concludes that the experimental observations of such clouds could be possible in low density plasma regime. It is deduced that for plasma density ∼ 10⁶ cm^-3 at temperatures of a few electron volts and for micron to l0nm sized dust grains, the observation of such structures could be possible within wide range variability of the dust population density.     

Multiargument recormalization of a gluon field

An extension of traditional renormalization methods that assigns each element of Feynman diagrams an individual evolution parameter is considered. It is shown that conditions necessary for such an extension to be valid are satisfied in quantum gluodynamics.     

Reversed current structure in a Z-pinch plasma

The current profile of a Z-pinch plasma is investigated using a one-dimensional magnetohydrodynamic code. Simulation results reveal the formation of a reversed current profile, its propagation, and an ejection of plasma at boundary region, which have been observed in previous experiments. A new physical mechanism is proposed to account for such phenomena. The physical mechanism involves the propagation of a shock wave. It is found that a reversed current profile appears when a shock wave reflected at axis expands in a compressing plasma column.     

Self-sustained oscillations in a plasma-wall system with strongly inhomogeneous diffusion of charged particles

A simple system with a hydrogen plasma confined by a magnetic field parallel to the bounding material wall is considered. The charged particles diffuse out of the plasma, recombine on the wall and return into the plasma volume as neutrals, which are ionized by electrons. It is demonstrated that macroscopic self-sustained oscillations are an intrinsic feature of such a system if the diffusion coefficient of charged particles is strongly inhomogeneous in the plasma.     

Internal dynamics of a plasma propelled across a magnetic field

When a plasma is pushed across a magnetic field by some nonelectromagnetic force, ions and electrons get turned in opposite directions by the magnetic field. This creates an internal current as well as sheaths at the plasma surfaces and results in an electric field which allows the plasma to maintain some, or even most of its initial momentum in the form of E&oarr;×B&oarr; drift. An exact analysis of that process is presented for the internal region of the plasma. The energy provided by the initial push is used, in part, to create some gyrations inside the plasma. When the rest energy density of the plasma exceeds twice the magnetic energy density (or when the Alfven speed is less than c), there will be enough energy to spare for the plasma to continue across the magnetic field at half its initial momentum. Two cases are considered: an impulsive start and a gentle push such as provided by gravity. The amplitude of the resulting internal gyrations becomes small in the second case. The frequencies of the gyrations are those of extraordinary modes of very long spatial wavelength     

Mechano-chemical oscillations of a gel bead

We present a formalism which describes the spatio-temporal evolution of a gel submitted to an autocatalytic chemical reaction to which it is responsive. This theory is based on an extension of a hydrodynamical multi-diffusional approach of the gel dynamics, which is plunged into a chemically active mixture. Emergent and autonomous volume self-oscillation dynamics of the gel are obtained from the nonlinear coupling of the elastic deformation, the chemical kinetics and the transport phenomena, that take place in the system. We apply this formalism to a spherical bead of gel plunged in a Belouzov-Zhabotinsky oscillatory chemical reaction, for which Yoshida et al. have obtained numerous experimental results. The case of a gel immersed in an autocatalytic bistable chemical reaction is also considered. We show that such formalism describes the autonomous volume self-oscillation dynamics of the gel beads.     

Méthode d’épuration des gaz rares au moyen de décharges électriques de haute fréquence

Raw krypton and xenon gases obtained from the distillation of air contain impurities such as CF₄ and CH₄, which preclude their use in many applications. These impurities can be abated by having the gas circulating through a microwave-sustained electric discharge. The use of this technique for production proves to be beneficiai in terms of energy consumption, reduction of gas losses, easiness and safety of operation. Plasma purification is therefore an useful extension of the range of available technologies for the design of high performance pure krypton/xenon production plants. It further demonstrates the feasibility and interest of achieving selective chemistry in a plasma that is not in thermodynamic equilibrium.     

Influence of ion species ratio on grid-enhanced plasma source ion implantation

Grid-enhanced plasma source ion implantation (GEPSII) is a newly proposed technique to modify the inner-surface properties of a cylindrical bore. In this paper, a two-ion fluid model describing nitrogen molecular ions N_2^+ and atomic ions N^+ is used to investigate the ion sheath dynamics between the grid electrode and the inner surface of a cylindrical bore during the GEPSII process, which is an extension of our previous calculations in which only N_2^+ was considered. Calculations are concentrated on the results of ion dose and impact energy on the target for different ion species ratios in the core plasma. The calculated results show that more atomic ions N^+ in the core plasma can raise the ion impact energy and reduce the ion dose on the target.     

Characterization of the thermal front inside a 2ω laser produced plasma by its emission in the XUV radiation range

We present for the first time an XUV imaging of a laser produced plasma in the range of 150 Å wavelength. For the moderate Z material used (Al), the more intense observed emissions come from the lithium-like ionized species. The imaging of the spatial emission of these species gives the signature of the thermal front location inside the plasma. The position and the extension of this emission characterize the location and the sharpness of the temperature gradient plasma.     

High-order harmonic generation from ions in a capillary discharge

We demonstrate a significant extension of the high-order harmonic cutoff by using a fully-ionized capillary discharge plasma as the generation medium. The preionized plasma dramatically reduces ionization-induced defocusing and energy loss of the driving laser due to ionization. This allows for significantly higher photon energies, up to 150 eV, to be generated from xenon ions, compared with the 70 eV observed previously. We also demonstrate enhancement of the harmonic flux of nearly 2 orders of magnitude at photon energies around 90 eV when the capillary discharge is used to ionize xenon, compared with harmonic generation in a hollow waveguide. The use of a plasma as a medium for high-order harmonic generation shows great promise for extending efficient harmonic generation to much shorter wavelengths using ions.     

Cyclotron resonance maser as a solar flare trigger

We propose a new mechanism of solar flaring, which is based on explosive phenomena in magnetic traps in the presence of a two-component plasma composed of fast electrons with anisotropic velocity distribution and a dense cold background plasma with high ionization. It is assumed that such a plasma is generated in a coronal magnetic trap in a preflare stage. This system, which is essentially a cyclotron resonance maser, becomes unstable under certain conditions and gives rise to an explosive cyclotron instability, which develops at first in a very small local area and is accompanied by intense heating of the background plasma and release of fast electrons at the trap ends. The energy of fast particles is collected from the entire volume of the magnetic trap and is localized in the form of heat in the explosion area from which thermal and shock waves are propagated. The model makes it possible to explain the main solar flare effects.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 6, pp. 699–712, June, 1996.     

Study of the effects of the prefilled-plasma parameters on theoperation of a short-conduction plasma opening switch

Spectroscopic methods are used to determine the density, the temperature, the composition, the injection velocity, and the azimuthal uniformity of the flashboard-produced prefilled plasma in an 85-ns, 200-kA plasma opening switch (POS). The electron density is found to be an order of magnitude higher than that obtained by charge collectors, which are commonly used to determine the density in such POSs, suggesting that the density in short conduction POS's is significantly higher than is usually assumed. We also find that the plasma is mainly composed of protons. The spectroscopically measured plasma parameters are used here to calculate the conduction currents at the time of the opening predicted by various theoretical models for the POS operation. Comparison of these calculated currents to the measured currents indicates that the plasma behavior during conduction is governed either by plasma pushing or by magnetic-field penetration and less by sheath widening near the cathode, as described by existing models. Also, the conduction current mainly depends an the prefilled electron density and less on the plasma flux, which is inconsistent with the predictions of the erosion (four-phase) model for the switch operation. Another finding is that a better azimuthal uniformity of the prefilled plasma density shortens the load-current rise time