Plasma Bunch Research Articles

CIRCULAR POLARIZATION IN PULSARS DUE TO CURVATURE RADIATION

The beamed radio emission from relativistic plasma (particles or bunches), constrained to move along the curved trajectories, occurs in the direction of velocity. We have generalized the coherent curvature radiation model to include the detailed geometry of the emission region in pulsar magnetosphere and deduced the polarization state in terms of Stokes parameters. By considering both the uniform and modulated emissions, we have simulated a few typical pulse profiles. The antisymmetric type of circular polarization survives only when there is modulation or discrete distribution in the emitting sources. Our model predicts a correlation between the polarization angle swing and sign reversal of circular polarization as a geometric property of the emission process.

Interaction of a plasma plume induced by a pulsed plasma thruster with an incident flow of rarefied magnetized plasma

A three-dimensional computational model and the results of the calculation for the dynamics of a plasma plume induced by a pulsed plasma thruster (PPT) in a magnetized flow of the ambient plasma are presented. A nonstationary expansion process of a PPT-induced plasma plume is studied in the ionospheric plasma over 100 µs after the start of a 6-microsecond plasma pulse. The parameters of the plasma plume in the PPT outlet section simulate the performance characteristics of a pulsed thruster PPT-4 (Pulsed Plasma Thruster 4 [3]) utilizing solid Teflon propellant. The magnetohydrodynamic (MHD) model of the process is based on the approximation of the ideal magnetic gas dynamics and makes it possible to predict the dynamics of a plasma bunch after the pulse termination during its interaction with the ambient medium and the magnetic field as well as the induced electric fields and currents in the vicinity of the expanding plasma

Generation of terahertz radiation by a moving bunch of nonequilibrium electron-hole plasma

We report on properties of coherent radiation from nonequilibrium electron-hole $(e\text{\ensuremath{-}}h)$ plasma bunch excited by an ultrashort laser pulse crossing a semiconducting slab subject to transverse bias voltage. Self-consisted calculations of nonequilibrium Boltzmann and Maxwell equations have established the fundamental role of uniformly moving bunch of $e\text{\ensuremath{-}}h$ plasma in coherent generation of terahertz radiation. We have shown that predicted properties crucially depend on the physics of dissipation mechanisms, current configurations, and relative traveling velocities of $e\text{\ensuremath{-}}h$ plasma bunch and terahertz radiation pulse. It has distinguished two major regimes of terahertz emission, single pulse emission, and firing twinned pulses at the moments of creation and extinction of moving bunch of $e\text{\ensuremath{-}}h$ plasma related to the front and rare boundaries of semiconducting slab, respectively. The results of developed theory are applied to enhance the performance of photoconductive terahertz emitters.

Renormalization-group symmetries for solutions of nonlinear boundary value problems

About 10 years ago, the method of renormalization-group symmetries entered the field of boundary value problems of classical mathematical physics, stemming from the concepts of functional self-similarity and of the Bogoliubov renormalization group treated as a Lie group of continuous transformations. Overwhelmingly dominating practical quantum field theory calculations, the renormalization-group method formed the basis for the discovery of the asymptotic freedom of strong nuclear interactions and underlies the Grand Unification scenario. This paper draws on lectures delivered at the XIII School for Nonlinear Waves, Nizhnii Novgorod, Russia, 1–7 March 2006 [see V F Kovalev, D V Shirkov "Renormalization group symmetry for solutions of boundary value problems" in Nonlinear Waves 2006 (Ed. by A V Gaponov-Grekhov) (N. Novgorod: IAP RAS, 2007) p. 433] to describe the logical framework of a new algorithm based on the modern theory of transformation groups and to present the most interesting results of application of the method to differential and/or integral equation problems and to problems that involve linear functionals of solutions. Examples from nonlinear optics, kinetic theory, and plasma dynamics are given, where new analytic solutions obtained with this algorithm have allowed describing the singularity structure for self-focusing of a laser beam in a nonlinear medium, studying generation of harmonics in weakly inhomogeneous plasma, and investigating the energy spectra of accelerated ions in expanding plasma bunches.

Study of dense plasma-surface interaction by a Filippov type plasma focus device

In this paper we have tried to investigate of dense plasma-material interaction in a Filippov type plasma focus (90KJ, 25KV, 288µf) facility. Dense plasma focus discharges are known as a remarkable source of hot plasma bunches and fast streams, fast neutrons, hard and soft X-rays, and energetic particles such as ions and electrons. The Aluminum made targets with 20cm in diameter and thickness 5mm, were placed at the central part of plasma focus cathode. These targets were exposed to perpendicular dense high temperature plasma stream incidence. The working gases for these experiments were Argon, Deuterium +Krypton, Helium, and pure Deuterium. We took advantage of changeable targets surface and used SEM technique for analyzing irradiated samples by various working gases. As it shown from SEM pictures and surface profiles, melt layer erosion by melt motion, surface smoothing, and bubble formation were some of different effects caused by diverse working conditions.

Experimental study of electron vortex structures in an electrostatic plasma lens

Results are presented from experimental studies of electron vortex bunches in a cold ion-beam plasma consisting of strongly magnetized electrons and a beam of almost free positive ions. The existence of electron vortex bunches was detected from local minima of the electric potential on surfaces perpendicular to the magnetic field lines. It is found that the vortices have the form of magnetic-field-aligned filaments, in which electrons rotate with a velocity significantly exceeding both the velocity of the vortex as a whole and the electron velocity in the ambient plasma. It is shown that, in a sufficiently strong magnetic field, the accumulation of electrons in the vortices terminates when the condition for the longitudinal confinement of electrons by the electric field fails to hold.

Plasma parameters in the upgraded Trimyx-M Galathea

Results are presented from measurements of the plasma parameters in the upgraded Trimyx-M Galathea. After the barrier magnetic field and the energy of the injected hydrogen plasma bunch were increased to B bar ∼ 0.1 T and W 0 ≈ 200 J, respectively, the following plasma parameters were achieved: the density n ∼ 5 × 1013 cm−3, the plasma confinement time τ* = 800–900 μs, the elergy of the confined plasma W 1 ∼ 100 J, the ratio of the plasma pressure to the barrier magnetic pressure β 0 ∼ 0.2, the electron temperature T e ∼ 20 eV, and the ion temperature T i ∼ 2T e . The maximum time during which the plasma density decreased e-fold, τ p , was found to be 300 μs at B bar = 0.1 T, which agrees with the classical transport model.

Coaxial injector of a plasma opening switch operating in the nonsteady arc-discharge mode

Results are presented from interferometric studies of a coaxial injector operating in the nonsteady arc-discharge mode. The discharge was initiated and stabilized by pulsed gas puffing into the interelectrode gap of the injector. The dynamics of the plasma bunch formation and the spatial characteristics of the bunch are investigated, and the density of the generated plasma is determined.

Computer tomography imaging of fast plasmachemical processes

Results are presented from experimental studies of the interaction of a high-enthalpy methane plasma bunch with gaseous methane in a plasmachemical reactor. The interaction of the plasma flow with the rest gas was visualized by using streak imaging and computer tomography. Tomography was applied for the first time to reconstruct the spatial structure and dynamics of the reagent zones in the microsecond range by the maximum entropy method. The reagent zones were identified from the emission of atomic hydrogen (the Hα line) and molecular carbon (the Swan bands). The spatiotemporal behavior of the reagent zones was determined, and their relation to the shock-wave structure of the plasma flow was examined.

Features of coronal mass ejections of minimum size

The coronal mass ejections (CME) with small angular dimensions (d ≤ 10°) have the simplest form, much simpler than large CME. This fact simplifies the problem of analyzing the CME structure and studying their origin. On the basis of the analysis of the LASCO C2 (SOHO) data, we show in this paper that the motion of a CME having small dimensions proceeds within a magnetic tube (a ray with increased brightness) of the streamer belt and leads to an “explosion-like” increase in the angular dimensions (rapid expansion) of the tube. A hypothesis is put forward that a small CME represents a “plasmoid” (a plasma bunch bounded in space, with its own magnetic field) thrown into the base of the magnetic tube and moving along it away from the Sun.

Asymmetry in electron and ion charge collection in a drifting plasma bunch

We report on the different behavior of electron and ion currents recorded by a Faraday cup in a plasma bunch generated via laser ablation. An excimer laser was employed to irradiate a Ge target. The current signals were recorded equipping the Faraday cup collector by a set of diaphragms. We found that the electron time-of-flight spectra were fairly similar to the ion ones, but the collected charge yield for electrons was up to 200 times larger than the corresponding ion yield. We ascribed such a discrepancy to the different cup collection efficiency for ions and electrons forming the plasma which was heavily influenced by the plume geometry, the energy of the particles, as well as the diaphragm size. Our findings would suggest that the overall electron charge “tended” to be collected, unlike the ion charge which scaled upon the collection solid angle.

Dynamics of plasma flow formation in a pulsed accelerator operating at a constant pressure

Features in the dynamics of plasma flow formation at a constant pressure in a pulsed coaxial accelerator have been studied. The temperature and density of electrons in a plasma bunch have been determined using a probe technique.

Effect of magnetic barrier on the plasma parameters in a Trimix-M galatea

The parameters of plasma trapped in a Trimix-M galatea with increased values of the magnetic barrier and the energy of a hydrogen plasma bunch injected in the trap have been determined. For a barrier magnetic field of B b ∼ 0.1 T, the plasma confinement time in the trap is τp ≈ 300 μs (which agrees with estimates obtained using formulas describing the classical transfer), the maximum electron density is n e ∼ 5 × 1013 cm−3, and the electron and ion temperatures are T e ≈ 20 eV and T i ∼ 2T e, respectively. The energy of trapped plasma is ∼110 J, and the ratio of the gaskinetic to magnetic pressure in the plasma is β0 ∼ 0.2.

Research of multipole magnetic trap-galatea “Trimyx”

The experimental unit “Galatea-3” is briefly described. It consists of the coaxial plasma gun, the plasma guide and the trap-galatea “Trimyx” with three myxine. The parameters of plasma bunch in the plasma guide and in the trap are presented. It is shown, that plasma can be efficiently entrapped by the trap and spread out along it.Therewith the cross-section dimensions of the confined plasma configuration are found to go beyond the Ohkawa surfaces. Estimations show that the particles losses from the trap are on the order of the classic ones.

A comparison of ultrarelativistic electron- and positron-bunch propagation in plasmas

Beam-driven acceleration of electrons and positrons by the electric field of the plasma wakefield is considered in detail using a self-consistent relativistic cylindrical particle-in-cell code with implicit electromagnetic solver. The plasma characteristics, such as the particle motion, the density, the temperatures, the wake fields, and the energies and their transfer, are investigated. Strong local energization and heating of the plasma electrons are observed. Small groups of ions in the wake can also attain temperatures higher than the secondary ionization potential of lithium vapor. It is verified that an electron bunch indeed excites a wakefield of higher energy than a positron bunch, which, in fact, behaves like a negative charge plasma bunch because of the suck-in of background plasma electrons.

Expansion of planar and spherical plasma bunches

We discuss the expansion of finite plasma bunches in two different geometries: planar and spherical. We show that, soon after the plasma formation, a steady state configuration between the hot electrons and the cold ions is reached in a few electron plasma times. Such an equilibrium configuration plays a crucial role in the subsequent plasma expansion and ion acceleration. We provide a description of this state and we investigate the ion dynamics by both analytical models and numerical simulations.

Analytical models of laser-trigged ion acceleration

We review the recent advances in constructing analytical solutions of self-consistent Vlasov-Poisson equations in plasma. These solutions describe different physical phenomena, such as the ion acceleration in the adiabatic expansion of a plasma bunch and the Coulomb explosion of cluster plasma. The particle distribution function, mean velocity, and density distribution, as well as the energy spectra for accelerated ions, are discussed.

Plasma trapping and confinement dynamics in a Trimix galatea

The Galatea-3 (MIREA) setup comprising a coaxial plasma gun, a plasma guide, and a Trimix galatea (containing three myxines) is briefly described. The plasma bunch parameters in the plasma guide and trap have been determined. It is demonstrated that plasma can be effectively trapped and spread in the proposed trap system. The confined plasma bunch protrudes out of the Ohkawa contour. Estimates show that the loss of particles from the trap is on a classical diffusion level.

Collisionless expansion of a Gaussian plasma into a vacuum

The collisionless expansion into a vacuum of a one-dimensional Gaussian plasma bunch of size much larger than the Debye length is studied both analytically and with a hybrid Lagrangian code. Both the case of an isothermal plasma fed by an external energy source and the case of an energy-conserving plasma are studied. It is shown that charge-separation effects are responsible for deviations with respect to known self-similar solutions. In particular, wave breaking occurs because the inner parts of the expanding plasma acquire faster velocities than the outer parts. As a result an ion front appears at the edge of the plasma. In the isothermal case the self-similar solution progressively applies to the whole plasma, while the fastest ion’s velocity asymptotically reaches the same values as in the sharp boundary case. In the energy-conserving case the self-similar description only applies to a part of the plasma, which approximately corresponds to the part which was initially quasineutral, and the final velocity of the fastest ions is significantly smaller than in the sharp boundary case.

Direct acceleration of solid-density plasma bunch by ultraintense laser

The interaction of a petawatt laser with a small solid-density plasma bunch is studied by particle-in-cell simulation. It is shown that when irradiated by a laser of intensity >10(21) W/cm2, a dense plasma bunch of micrometer size can be efficiently accelerated. The kinetic energy of the ions in the high-density region of the plasma bunch can exceed ten MeV at a density in the 10(23)-cm(-3) level. Having a flux density orders of magnitude higher than that of the traditional charged-particle pulses, the laser-accelerated plasma bunch can have a wide range of applications. In particular, such a dense energetic plasma bunch impinging on the compressed fuel in inertial fusion can significantly enhance the nuclear-reaction cross section and is thus a promising alternative for fast ignition.