Dynamics of a nonquasineutral plasma in a strong magnetic field

The motion of a nonquasineutral plasma in a strong magnetic field such that is analyzed. It is shown in simple examples that, when the plasma pressure and dissipation are neglected, the only dynamic process in a magnetized plasma is the evolution of the charge-separation electric field and the related magnetic field flux. The equations derived to describe this evolution are essentially the wave Grad-Shafranov equations. The solution to these equations implies that, in a turbulent Z-pinch, a steady state can exist in which the current at a supercritical level is concentrated near the pinch axis.     

Raising the efficiency of a plasma opening switch by applying an external magnetic field

The influence of an external magnetic field on the performance of a high-impedance plasma opening switch is studied experimentally. A 1.5-fold increase in the output voltage of a plasma opening switch operating in the erosion mode is achieved by applying an external magnetic field. The magnetic field strength and the parameters of the plasma opening switch at which the maximum output voltage is attained are determined. It is shown experimentally that the predicted dependence of the maximum output voltage on the Marx generator voltage, U _POS [MV]=3.6 (U _MG [MV])^4/7, is confirmed experimentally.     

Dynamics of a magnetic field in dusty plasma

The problem of the expansion of a magnetic field in a complex (e.g., dusty) plasma is considered, with a focus on the effects produced by the independent transport of charged components that does not break plasma quasineutrality. Solutions to a set of nonlinear equations are obtained for different initial and boundary conditions. In particular, it is shown that the field rapidly penetrates into the plasma when the dust is charged negatively and does not penetrate at all when the dust charge is positive.     

Steady-state vortex structure in a plasma with a strong magnetic field

A study is made of nonquasineutral vortex structures in a plasma with a magnetic field B _z in which the charges separate on a spatial scale equal to the magnetic Debye radius r _B=B _z/4πen _e. The electric field arising due to charge separation leads to radial expansion of the ions, thereby destroying the initial electron vortex. It is shown that the ion pressure gradient stops ion expansion in a nonquasineutral electron vortex and gives rise to a steady structure with a characteristic scale on the order of r _B. With the electron inertia taken into account in the hydrodynamic approximation, the magnetic vortex structure in a hot plas mamanifests itself in the appearance of a “hole” in the plasma density.     

Matching of a multimodule plasma opening switch to a liner load

One of the key problems of the Baikal project, intended to create a superpower pulsed generator for ICF experiments, is that of matching a multimodule plasma opening switch (POS) to a liner load. An intermediate inductance or a separating discharger is proposed to be used as a matching element between the POS and the load. An analysis is made of the effect of both versions of the matching system on the synchronization of the POS modules and the energy transfer from the inductive storage to the load. Methods for optimizing the matching element are examined. It is shown that the POS modules can be synchronized and the inductive storage energy can be efficiently transferred to a low-impedance load. A multigap vacuum discharger with a point anode and plane cathode is to be used as a separating discharger. Such an electrode system make it possible to concentrate the electric field at the point anode and to substantially enhance the electric strength of the inter-electrode gap. Results are presented from experimental studies of vacuum breakdown in such an electrode system with a gap length of about 1 mm.     

Periodic emission bursts accompanying the interaction of plasma flows propagating across a magnetic field

It is found experimentally that the interaction of plasma flows propagating in opposite directions across a magnetic field is accompanied by periodic local bursts of intense optical and soft X-ray emission. It is shown that periodic variations in the emission intensity from the interaction region are related to the excitation of steady-state self-oscillations in the plasma. By varying the frequency and amplitude of these oscillations, it is possible to satisfy the resonance conditions at certain characteristic plasma frequencies.     

Study of the glow dynamics in a laser-produced plasma jet expanding across the magnetic field

Results are presented from experimental studies of the glow dynamics of a plasma jet generated during the irradiation of a plane aluminum target by an iodine laser pulse with the wavelength 1.315 μm. The laser pulse energy was 330–480 J, the pulse duration was 0.5 ns, and the focal spot diameter was 3 mm, the laser intensity on the target surface being ∼10¹³ W/cm². The jet expanded across an external magnetic field with the strength ∼1 kOe. The residual air pressure in the vacuum chamber was ∼10⁻⁵ Torr. The spatiotemporal behavior of the jet glow was investigated using a nine-frame camera in two mutually perpendicular directions (along and across the magnetic field). The results of measurements indicate azimuthal asymmetry of the jet expansion.     

Properties and parameters of the electron beam injected into the mirror magnetic trap of a plasma accelerator

The parameters of the injector of an axial plasma beam injected into a plasma accelerator operating on the basis of gyroresonance acceleration of electrons in the reverse magnetic field are determined. The trapping of the beam electrons into the regime of gyroresonance acceleration is numerically simulated by the particle- in-cell method. The optimal time of axial injection of the beam into a magnetic mirror trap is determined. The beam parameters satisfying the condition of efficient particle trapping into the gyromagnetic autoresonance regime are found.     

Dynamics of rotating flows in plasma accelerator channels with a longitudinal magnetic field

Results are presented from numerical simulations of axisymmetric plasma flows that occur in a coaxial accelerator with a longitudinal magnetic field. The simulations were carried out based on a two-dimensional MHD plasma dynamic model for the general case of a three-component magnetic field. The steady plasma flows are calculated in solving the time-dependent MHD problem by the relaxation method. The results of simulations of steady transonic flows are compared with the solutions that were obtained in the smooth accelerator channel approximation. The main regular features of plasmodynamic processes are revealed. It is found that current sheets arise in the plasma flow in a comparatively strong longitudinal magnetic field.     

Hydrodynamic model of the penetration of a magnetic field into a plasma with two ion species

Hydrodynamic equations are presented that describe the dynamics of a plasma with two ion species in a magnetic field such that . It is shown that there exists a range of values of the ratio of the plasma density to the magnetic field, ν_ii/ω_Bi<(Z ² M/m)^1/4, within which the frictional force caused by ion-ion collisions dominates over that caused by electron-ion collisions. In this range, the effective conductivity, which governs the magnetic field diffusion, is lower than the conventional electron-ion conductivity by a factor of $\sqrt {M/m}$ and can be as low as σ ? enc/B. The equations derived for this three-component plasma make it possible to self-consistently incorporate local changes in the partial mass and partial charge of each of the ion species in relative motion. The characteristic features of the equations obtained are analyzed by applying them to describe the propagation of a current sheath in a transmission line filled with a multispecies plasma. An analogy is drawn between magnetic phenomena in a plasma with two ion species and in a so-called dusty plasma.     

Three-body collisions in a plasma in a strong laser field

Electron-ion collisions in a high-density plasma in strong electromagnetic fields are considered. The applicability condition for the approximate model of pair collisions in strong fields are determined. It is shown that this condition is identical to the condition for the plasma to be transparent. Investigations were carried out by the test particle method generalized to the case of several scattering centers. An accurate calculation of short-range collisions is provided by a “jump” method that is based on the exact solution to the problem of the motion of a particle in a Coulomb potential. This method can also be applied in other approaches to simulating a collisional plasma (such as particle-in-cell and molecular dynamics methods).     

Helicon plasma in a nonuniform magnetic field

The distributions of the electron density in a plasma produced by helicon waves and the correspond-ing wave amplitudes and phases are studied experimentally. The measurements were carried out in an argon plasma at a pressure of 3 mtorr and at an input RF power of up to 600 W. The magnetic field was caried in the range from 0 to 200 G. The efficiency of plasma production in both uniform and nonuniform fields is investigated. It is shown that, in a nonuniform magnetic field, the electron density can be substantially increased (up to 5×10¹² cm^?3) by placing an antenna in the region in which the magnetic field is weaker than in the main plasma.     

Dynamics of magnetotactic bacteria in a rotating magnetic field

The dynamics of the motile magnetotactic bacterium Magnetospirillum gryphiswaldense in a rotating magnetic field is investigated experimentally and analyzed by a theoretical model. These elongated bacteria are propelled by single flagella at each bacterial end and contain a magnetic filament formed by a linear assembly of approximately 40 ferromagnetic nanoparticles. The movements of the bacteria in suspension are analyzed by consideration of the orientation of their magnetic dipoles in the field, the hydrodynamic resistance of the bacteria, and the propulsive force of the flagella. Several novel features found in experiments include a velocity reversal during motion in the rotating field and an interesting diffusive wandering of the trajectory curvature centers. A new method to measure the magnetic moment of an individual bacterium is proposed based on the theory developed.     

Experimental verification of the technique for calculating a plasma opening switch and its matching to the load

A technique for calculating a plasma opening switch in an external magnetic field and its matching to a load the impedance of which increases with time was verified experimentally. The experiments were performed in the RS-20 facility both in the absence of a load and with various inductive loads. The amplitude of the voltage pulse at the input of the plasma opening switch was 0.36–0.84 MV, the current amplitude was 280–320 kA, and the pulse duration was ～2 μs, whereas the corresponding parameters of the output pulse were 0.8–3.2 MV, 0–240 kA, and ～100 ns.     

Study of mechanisms for magnetic field diffusion into an expanding laser plasma

The interaction of plasma clouds generated during laser irradiation of a spherical target in a background gas with a magnetic field was studied on the MKV-4 test bench of the Iskra-5 facility. The dynamics of the plasma cloud expansion in a 300- to 500-Oe magnetic field was investigated using magnetic and probe diagnostics. The results obtained are compared with calculations by different models of laser plasma diffusion in a magnetic field.     

Caenorhabditis elegans transfers across a gap under an electric field as dispersal behavior

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Dynamics of a simple regulatory switch

We consider the dynamics of a model toggle switch abstracted from the genetic interactions operative in a fungal stress response circuit. The switch transduces an external signal and propagates it forward by mediating the transport between compartments of two interacting gene products. The transport between compartments is assumed to be related to the degree of association between the interacting proteins, a fact for which there exists a wealth of biological evidence. The ubiquity and modularity of this cellular control mechanism warrants a detailed study of the dynamics entailed by various modelling assumptions. Specifically, we consider a general gate model in which both of the associating proteins are freely transportable between compartments. A more restrictive, but biologically supported model, is considered in which only one of the two proteins undergoes transport. Under the strong assumption that the disassociation of the interacting proteins is unidirectional we show that the qualitative dynamics of the two models are similar; that is they both converge to unique periodic orbits. From a biophysical perspective the assumption of unidirectional dissociation is unrealistic. We show that the same result holds for the more restrictive model when one weakens the assumption of unidirectional binding or disassociation. We speculate that this is not true for the more general model. This difference in dynamics may have important biological implications and certainly points to promising avenues of research.     

Effect of viscosity on the plasma decay in a magnetic field

The effect of viscosity on the evolution of an axisymmetric plasma column in a longitudinal magnetic field is considered. It is found that, under the action of viscosity, the plasma density profile tends to become Gaussian.     

Osmolality dependence of erythrocyte sedimentation and aggregation in a strong magnetic field

In order to specify the major determinant of the magnetic enhancement of erythrocyte sedimentation observed previously, the dependence of erythrocyte sedimentation rate (ESR) on osmolality was measured under a strong magnetic field. Even at hypotonic osmolality, an increase in ESR due to aggregation was observed in plasma solution as compared with that without aggregation in saline solution. However, the magnetic field did not enhance ESR at hypotonic osmolality, when the cell shape was an isotropic sphere (spherocyte). Thus, we narrowed our search to a mechanism that would explain the enhanced ESR found specifically in anisotropic erythrocytes. It was concluded that the major determinant can only work for anisotropic erythrocytes and is a magnetic field-induced increase in an intermembrane adhesive area due to magnetic orientation of anisotropic erythrocytes.