Nonuniform Plasma Research Articles

Research on the propagation properties of THz circularly polarized wave in BGK model inhomogeneous dusty plasma

When a hypersonic vehicle flies near space, a layer of complex dusty plasma will form around the vehicle under the influence of high temperature, which will cause radar signal attenuation (ATT) to different degrees and lead to communication barriers. Therefore, studying the interaction mechanism between electromagnetic waves and dusty plasma is important. In this paper, the Bhatnagar–Gross–Krook collision model of non-uniform dusty plasma is derived on the basis of Boltzmann's approximate equation. In addition, the modified expression of a dielectric coefficient of weakly ionized dusty plasma is obtained under the condition of magnetization. With the Wentzel–Kramers–Brillouin method, the ATT coefficients of terahertz wave with different external magnetic fields and dusty plasma parameters are calculated. Results show that a strong external magnetic field will cause the ATT of the right-hand circular polarized wave to produce a low absorption band, whereas the ATT of the left-hand circular polarized wave will evidently weaken. The electron concentration, dust concentration, dust particle radius, collision frequency, and charging frequency also influence the ATT under the external magnetic field. These studies provide theoretical references for the research on the blackouts of hypersonic vehicles.

Stabilization of energetic-ion driven toroidal Alfvén eigenmode by energetic electrons in tokamak plasmas

Energetic electron effects on an energetic-ion driven toroidal Alfvén eigenmode (TAE) are investigated via hybrid simulations of an MHD fluid interacting with energetic particles. Both energetic electrons and energetic ions described by drift-kinetic equations are included in the present work. It is found that the TAE can be effectively stabilized by off-axis peaked energetic electrons which are located near the mode center, while the centrally peaked energetic electrons fail to stabilize the mode. It is confirmed that the spatially localized pressure profile of energetic electrons causes the stabilization of TAE. The stabilized TAE has a more localized mode structure accompanied by a significant reduction in the energetic ion driving rate. The small change of mode frequency and dissipation rate indicate the stabilization mechanism is different from the so-called pressure gradient stabilization that drives the TAE into continuum. The results suggest that the strong plasma non-uniformity induced by the energetic electron beta profile may be responsible for the change of mode structure. It is also found that this stabilizing effect is more effective for a high-n TAE. Moreover, it is numerically verified that the positive (negative) pressure gradient at the TAE center will increase (decrease) the mode frequency. The wave-particle interactions are also analysed for a case with energetic electrons peaked at the inner side of the TAE center. It is found that the power transfer to a resonant barely trapped energetic electron, which taps energy from the wave, can be comparable to the power transfer from a resonant energetic ion. This suggests that if a sufficient number of resonant barely trapped electrons are present, they might stabilize energetic-ion driven TAE through the wave-particle interaction.

Electrostatic Disturbances of Aerosol Atmospheric Plasma: Beaded Lightning

Numerous sources produce the ionization impact on the planetary atmosphere. The tropospheric cloudiness therewith is originated at such altitudes, which coincide with places of the maximum of the atmospheric ionization that caused by space radiation. Components of cosmic radiation, penetrating down to the stratospheric and tropospheric altitudes, produce in the first place the ionization of aerosols that brings to subsequent amplifying the activity of atmospheric vortices. The ionized aerosol constituent is of primary importance both in the initiation of plasma vortices and in the concentration of energy-mass by air vortices due to the humidity condensation. The ionization process is cascading, that causes the non-linear impact of penetrating rays, which amplifying with growing the air pollution. Various heterogeneities inside plasma subsystems provoke the random intensification of aperiodic electrostatic disturbances, which can exert a significant action on the development of vortices. Sometimes beaded lightning arises during thunderstorm. Using the approach of the Boltzmann kinetic equation, the characteristics of electrostatic oscillations for non-uniform plasma, are analytically derived. The analytical expressions are obtained for non-magnetized plasma. In the limits of the Earth’s atmosphere, these solutions are strictly applicable to the origination of electrostatic modulations along the lines of force of the geomagnetic field and approximately applicable in cases, when the impact of the Earth’s magnetic field is negligible. The explicit expressions are deduced both in the hot plasma approximation and in the cold plasma approximation. It is demonstrated that the formation of chain elements of discharge in hot inhomogeneous plasma is defined by the nonmonotonic distribution of charges and fields. At such conditions, the irregularities breaks up into a cellular structure.

Study on Propagation Characteristics of Obliquely Incident Terahertz Wave in Non-Magnetized Plasma

A transmission model of THz wave in non-uniform and magnetized plasma is established. Based on the analysis of transmission characteristics in Gaussian and uniform plasma environments, theoretical simulations are performed using the continuity conditions of the electric and magnetic fields at the boundary of each layer. The effects of collision frequency, electron density and incident angle on the attenuation of THz wave energy are mainly discussed. The attenuation of the THz wave by the collision frequency does not change monotonously, and the optimal frequency needs to be selected according to the actual situation. THz wave attenuation increases with increase of electron density. And the THz wave attenuation decreases with the increase of the incident angle. Vertical incidence can be used as a means to alleviate the “communication blackout”. The conclusions of this paper provide a good theoretical basis and relevant parameter references for alleviating the “communication blackout” problem.

Laser-induced breakdown self-reversal isotopic spectrometry for isotopic analysis of lithium

Online monitoring or in-situ isotopic analysis techniques in extreme environments are strategic tools in nuclear industry. A new optical method for performing isotopic analysis in solid samples at ambient pressure has been developed: Laser-Induced Breakdown self-Reversal Isotopic Spectrometry (LIBRIS). This method uses self-absorption of atomic or ionic resonance lines that are emitted from a non-uniform laser-induced plasma. It takes advantage of the fact that the spectral width of the absorption dip is much smaller than the spectral width of the emission line profile. Isotopic measurements were carried out on lithium samples by measuring the spectral position of the absorption dip that is shown to have a linear dependence on the 6Li isotopic abundance. Stand-off and real-time analysis can be performed without any sample preparation or pre-treatment. The effect of the laser wavelength, of the ambient gas and of the gate delay is investigated. Optimum conditions lead to a relative uncertainty of about 6% on the isotopic abundance measurement of 6Li. The influence of the spectral shifts due to Stark and Doppler effects on the performance of LIBRIS are discussed.

Enhanced collective stopping and drift of electron beams in fusion plasmas with heavy-ion species

The transport and energy deposition of relativistic electron beams in transversely nonuniform plasmas are investigated with two-dimensional electromagnetic particle-in-cell simulations. For the beam with radius much larger than plasma skin depth, the current filamentation instability excited by the electron beam can be observed, which breaks the beam into filaments and leads to the formation of strong magnetic fields consequently. The effects of plasma ion species are significant and asymmetric transverse magnetic fields are formed in plasmas with heavy-ion species due to the asymmetric neutralization of beam space charge by plasma ions. The asymmetric transverse magnetic fields contribute to the directional drift of beam electrons to lower plasma density regions, which may accelerate the filaments merger process and lead to highly localized beam-energy deposition in plasmas.

Effects of Nonuniform Moving Plasma on the Polarization Properties of Obliquely Incident EM Waves

The effects of nonuniform moving plasma on the polarization properties of electromagnetic (EM) waves were theoretically studied. Taking the ${L}$ -band right-hand circularly polarized (RHCP) wave as an example, based on the nonuniform moving plasma slab moving perpendicularly to the incident wave, the relationship between the polarization properties of the transmitted wave and the normalized velocity of the nonuniform plasma slab was analyzed. The results indicate that the polarization state of the transmitted wave is closely related to the normalized velocity of the nonuniform plasma slab. When the plasma slab approaches to the incident wave, its influence on the polarization properties is greater than that away from the incident wave. In addition, when the change of the polarization state reaches the maximum, the corresponding normalized velocity is mainly determined by the incident angle and the collision frequency. Various interesting features regarding polarization properties were obtained. The results are very important for applications in space exploration.

The study of spatial dispersion effect on electromagnetic waves propagation in the warm non-uniform re-entry plasma sheath

“Communication blackout” is such a consequence that the attenuation of electro-magnetic (EM) waves becomes drastic when the frequency of EM waves is near or below the oscillation frequency of plasmas. Deep comprehension on the propagation characteristics of EM waves in the plasma sheath plays an important role in solving this issue. However, relevant works in the literature are almost based on the cold plasma sheath model, neglecting the temperature of the plasmas as well as the spatial dispersion effect. We apply COMSOL Multiphysics software to simulate and study the spatial dispersion effect in the warm plasma sheath in this paper. The mode conversion between EM waves and Langmuir waves in the warm plasmas is observed. The characteristics of field distributions in the warm plasma sheath are different from the cold plasma sheath distinctly, when the resonance between EM waves and the plasmas happens. The reflection and absorption coefficients are also influenced accordingly. The research in this paper gives an insight into EM waves propagation in the warm re-entry plasma sheath and supplies a better comprehension on the interaction between EM waves and the plasma sheath.

An analysis of the microencapsulation of ceftiofur in chitosan particles using the spray drying technology

Ceftiofur is a third-generation cephalosporin approved to treat numerous infections in production animals. Its commercial formulations are administered daily due to the mean life time, leading to several inconveniences, like operative challenges and non-uniform plasma levels. The objective of this work was to microencapsulate ceftiofur in chitosan particles using spray drying technology to extend the delivery and consequently reduce the dosage frequency. The effect of formulation factors on particle features was studied using a multilevel factorial design. In addition, ceftiofur thermal stability was assayed by differential scanning calorimetry and microbiological assays. Finally, a pharmacokinetic model was developed to predict theoretical plasma concentration in goats. Results showed that ceftiofur thermal stability increased after microencapsulation, indicating a protective effect of chitosan particles. Besides, MIC, IC50 and inhibition halos against E. coli and S. aureus were similar than those of the commercial product. In addition, suitable plasma levels can be theoretically maintained in goats during 48 h with a single injection. These findings suggest that chitosan microparticles could be a good vehicle for ceftiofur administration.

Numerical Simulation of Non-Uniform Magnetic Field Type RF Plasma Thruster Using Fluid Model

Numerical Simulation of Non-Uniform Magnetic Field Type RF Plasma Thruster Using Fluid Model

Drift wave in strong collisional dusty magnetoplasma

The study about the wave mechanism of magnetized dusty plasmas has important value to related experiment, industrial processing and exploring celestial space. The linear and nonlinear fluctuation characteristics of the nonuniform magnetized dust plasma system are researched in this paper. For the homogeneous external magnetic field and the nonuniform environment with density and temperature gradients, a two-dimensional nonlinear dynamic magnetoplasma equation is derived considering the strong impact between dust and neutral particles. The linear dispersion relation is obtained by the linearized method. There are both the damping wave causing by strong collision and the harmonic wave by particle drift. Employing the typical numerical parameters for analysis, the results display that the quantum parameter modifies the system lengths; the real wave frequency is proportion to the drift frequency; the imaginary wave frequency has complex relationship with the collision frequency between dust and neutrals, and the collision of particles causes the dissipation effects to the system. Besides, the analytical solutions of drift shock wave and explosive wave are solved by function change method. The variation about the electrostatic potential with the main physical parameters is discussed in detail. It is shown that the strength of the electrostatic shock wave and the width of the explosive wave increase with increasing the dust density and magnetic field intensity, decrease with increasing the collision frequency, change with the drift velocity. When the space-time phase is small, the electrostatic potential changes quickly; once big enough, the potential tends to be stable value and reaches stable state eventually. Finally, the stability of the system is discussed. It is found that the dusty charge, quantum parameter, drift velocity all appear in the disturbed solution. All these results in the paper show that the strong collision effect, quantum effect, particle drift and magnetic field all play important role to the generation, evolution and stability of drift waves.

Uniformity improvement of fuel target implosion by phase control in heavy ion inertial fusion

A dynamic smoothing method was proposed based on a phase control to stabilize plasma instabilities and smooth plasma non-uniformities. In this paper, the dynamic smoothing method is applied to a spherical fuel target implosion in heavy ion inertial fusion (HIF). We found that the wobbling motion of each heavy ion beam (HIB) axis induces a phase-controlled HIBs energy deposition, and consequently the phase-controlled implosion acceleration is realized, so that the HIBs illumination non-uniformity is successfully smoothed. HIB accelerators provide a well-established capability to oscillate the HIBs axes with a high frequency. In inertial confinement fusion, a fuel implosion uniformity is essentially important to compress the DT fuel and release the fusion energy, and the non-uniformity of the implosion acceleration should be less than a few %. The results in this paper also demonstrate that the wobbling HIBs would provide an improvement in the fusion energy output gain.

Reduced model of high-Z impurity redeposition and erosion in tokamak divertor and its application to DIII-D experiments

A reduced model of high-Z impurities erosion and redeposition is presented to analyze net erosion of tungsten material in divertor attached plasma conditions measured in DIII-D experiments. This reduced model is tailored to quantify the redeposition and the net erosion on high-Z material samples of sufficiently small dimensions to be considered exposed to uniform plasma conditions. For those uniform plasma conditions, the spatial distribution of redeposited high-Z impurities is well approximated by an analytical distribution characterized by a few parameters. The fraction of high-Z impurity eroding and redepositing on a material sample is then obtained by integrating this distribution across the material sample. The ratio of net erosion rates of tungsten measured experimentally from tungsten samples of different sizes exposed to the same attached plasma conditions are well reproduced with this reduced model. It is shown that uncertainties induced by radially non-uniform plasma conditions in experiments can be significantly reduced by exposing samples to high density divertor plasma. Several enhanced experimental setups are proposed to measure and compare net erosion rates from samples of various areas during a single plasma experiment.

Bayesian Spectral Moment Estimation and Uncertainty Quantification

We present a Bayesian spectral fitting method developed for spectroscopic data analysis, particularly (but not solely) in the context of fusion energy research. The presented techniques are particularly valuable to estimating moments and corresponding uncertainties whenever the spectra result from line-integrated measurements in nonuniform plasmas, for which the approximation of atomic line shapes being ideal Gaussians gives poor estimates. We decompose multiple, potentially overlapping spectral lines into a sum of Gauss–Hermite polynomials, whose properties allow efficient truncation and uncertainty quantification, often with only three free parameters per atomic emission line. Tests with both synthetic and experimental data demonstrate the effectiveness and robustness where more standard nonlinear fitting routines may experience difficulties. A parallelized version of our implementation is publicly released under an open source license 1 . 1 https://github.com/Maplenormandy/bsfc

Optimization design of magnetic filter for the prototype RF negative ion source at ASIPP.

For a prestudy of the key science and technology of the RF negative ion source for fusion application, a negative RF ion source test facility was developed at the Institute of Plasma Physics, Chinese Academy of Science (ASIPP). The magnetic filter field in front of the extraction system plays an important role in reducing the loss of negative hydrogen ions and inhibiting coextraction of electrons. The existing filter field of the prototype ion source is generated by permanent magnets arranged on both sides of the expansion chamber; the gradient and the uniformity of the field are poor, resulting in a large plasma distribution unevenness in the experiment. In order to reduce the B→×∇B drift and the beam deflection, the plasma nonuniformity, and the beam alignment, its gradient should be as low as possible, especially near the Plasma Grid (PG), while its strength should be as low as possible inside both the driver and the extraction region. Hence, the magnetic filter field generated by the permanent magnet and the PG current with return wires is proposed. A finite element analysis method is used to calculate the distribution of the magnetic field throughout the ion source, especially the filter profile along the centerline perpendicular to the PG and the section parallel to the PG. Several cases were compared and the final design provides a more uniform magnetic field in the region within 70 mm above the plasma grid, while the field strength is around 5 mT and the integral BdL quantity is greater than 1.2 mTm.

Range Profile Analysis of Hypersonic Vehicles Covered by Inhomogeneous Plasma Sheath Using Physical Optics

Using the parallel physical optics method, the range profile of a hypersonic vehicle with an electrically large size covered by 1-D inhomogeneous plasma sheath was studied. In this article, under the condition of far-field approximation, the improved physical optical method of 1-D nonuniform plasma coating of the conductive target was applied to calculate the scattered electric field of the target at different frequencies; then, 1-D Fourier inversion of the scattered electric field was carried out to obtain the 1-D range profile of the target. Numerical results showed that the temperature and pressure changes inside the plasma will have an impact on the range profile of the aircraft, and the intensity of the range profile of the target is inversely proportional to the temperature and pressure. In addition, the flight Mach parameters of the target aircraft, which affect the 1-D range profile, were also analyzed. The results showed that the larger the flight Mach number, the easier it is to detect the target aircraft. Finally, it was found that the nonuniformity of the plasma significantly influenced the 1-D range profile of the coated target; the intensity value of the range profile of the target aircraft (covered by the plasma sheath) at different flight heights was significantly lower than that of the pure metal target, resulting in the so-called “stealth” effect. This research provides some methods for effectively measuring and controlling hypersonic vehicles in adjacent space and alleviating the interruption of reentry communication.

Shear flow driven counter rotating vortices in non-uniform magnetoplasmas with warm ions and generalized (r, q) distributed electrons

We have analyzed the linear and nonlinear finite amplitude coupled drift ion acoustic waves in a spatially non-uniform plasma consisting of warm ions in the presence of sheared ion flow and electrons whose distribution in high and low phase space density regions is governed by two spectral indices, namely, r and q respectively. It has been found that stationary solution of the nonlinear equations in the form of a counter rotating vortex can be obtained for a particular choice of the equilibrium potential profile. It has been found that the double spectral indices r and q make a very pronounced effect on the formation and size of the counter-rotating vortices in spatially inhomogeneous plasmas and the applicability of the current study in understanding the wave phenomena with reference to space plasmas is also discussed.

Bilinear plasma susceptibility of strongly non-uniform magnetized plasmas

The bilinear plasma susceptibility describing the nonlinear coupling of electromagnetic and two electrostatic waves in strongly non-uniform magnetized plasmas is derived using both the distribution function moments equations and the kinetic approach. The possibility of the drastic enhancement of nonlinear coupling leading to a decrease of the two-plasmon decay instability threshold in strongly inhomogeneous plasmas is demonstrated.

Large-scale azimuthal structures in Hall-type plasma discharges

An explanation of large-scale low-frequency oscillations observed by means of a high-speed camera in different Hall-type plasma devices (magnetrons, Penning discharges, Hall thrusters, etc.) is proposed. They can be interpreted as the beating between high-frequency eigenmodes of gradient drift instability occurring in spatially bounded nonuniform plasmas. The resemblance of the experimental data obtained with the finite exposure time and the calculated characteristics of high-frequency modes beating is highlighted. The main results are obtained analytically in a magnetron-like configuration with the axial magnetic field and the radial electric field.

A simple method for predicting maximum electron density in microwave air breakdown

The electron density in air breakdown reaches the maximum level, when the transmitted electric field decreases to the critical value at which electron ionization balances electron loss. This paper reports a simple method based on the wave equation in nonuniform plasma to fast predict the maximum electron density in air breakdown by plane microwave, when the electron density profile is known. The wave equation is solved numerically by the finite difference method, and the obtained transmitted electric field is consistent with the “exact” solution from the scattered-field finite difference time domain method. When the electron density profile is assumed to be a parabolic distribution in the direction of wave propagation, the effects of air pressure, incident field strength, wave frequency, and plasma thickness on the maximum electron density are investigated. The maximum electron density as a function of air pressure from our simulation shows the same trend as the solutions of Maxwell-plasma equations as well as the experiment.