Electrostatic Modes of Dusty Plasmas in a Uniform Magnetic Field

Electrostatic dusty plasma waves in a uniform magnetic field are studied.Unless the magnetic field is extremely strong,the dust particles can hardly be magnetized,while however,electrons and ions are easily done so.Electrostatic modes in such dusty plasmas can then be investigated by making use of the “Moderately magnetized” assumption of magnetized electrons and ions,and unmagnetized dust particles.In a high frequency range,due to the existence of dust component.both frequencies of Langmuir waves(parallel to the magnetic field)and upper hybrid waves(perpendicular to the field) are reduced.In the frequency range of ion waves,besides the effect on dust-ion-acoustic waves propagating parallel to the magnetic field.the frequency of ion cyclotron waves perpendicular to the magnetic field is also enhanced.In a very low dust frequency range,we find an “ion-cyclotron-dust-acoustic” mode propagating across the field line with a frequency even slower than dust acoustic waves.     

Characteristics of dust acoustic waves in dissipative dusty plasma in the presence of trapped electrons

The formation and propagation of nonlinear dust acoustic waves(DAWs) as solitary and solitary/shock waves in an unmagnetized, homogeneous, dissipative and collisionless dusty plasma comprising negatively charged micron sized dust grains in the presence of free and trapped electrons with singly charged non-thermal positive ions is discussed in detail. The evolution characteristics of the solitary and shock waves are studied by deriving a modified Korteweg–de Vries–Burgers(mKdV–Burgers) equation using the reductive perturbation method. The mKdV–Burgers equation is solved considering the presence(absence) of dissipation. In the absence of dissipation the system admits a solitary wave solution, whereas in the presence of dissipation the system admits shock waves(both monotonic and oscillatory) as well as a combination of solitary and shock wave solutions. Standard methods of solving the evolution equation of shock(solitary) waves are used. The results are discussed numerically using standard values of plasma parameters. The findings may be useful for better understanding of formation and propagation of waves in astrophysical plasma.     

Three dimensional nonlinear shock waves in inhomogeneous plasmas with different size dust grains and external magnetized field

The evolution of three dimensional nonlinear shock waves is investigated in a dusty plasma with inhomogeneous particles’density,nonadiabatic dust charge variation,external magnetized field and power law dust size distribution.For this purpose,a modified nonlinear Korteweg-de Vries Burgers equation containing variable coefficients is obtained by reductive perturbation method.The effects of inhomogeneity,dust size distribution,external magnetized field,dust charge variation and obliqueness parameter on shock structures are numerically examined in great detail.Furthermore,research results show that oscillatory shock waves and monotone shock waves exist and transform each other in this system.     

Dust Acoustic Shock Waves with Non-Thermal and Vortex-Like Ions in Dusty Plasma

A rigorous investigation is presented on the propagation characteristics of non-linear dust acoustic(DA)waves in an unmagnetized dusty plasma system containing non-thermal and vortex-like ions and Maxwellian electrons under the effect of a fluctuating charged dust fluid.The three-dimensional(3D)Burgers'equation and a new form of a lower degree modified 3D Burgers'equation with their analytical solutions are derived to study the features of shock waves in such plasmas.The effect of the population of non-thermal ions,the vortex-like ion parameter as well as the temperature ratios of ions and electrons on the evolution of shock waves in the presence of dust charge fluctuation is presented.This theoretical investigation might be effectively utilized to unveil the nature of many astrophysical plasma environments(Saturn's spokes etc.)where such plasmas are reported to have existed.     

Influence of dust particles on spatial distributions of particles and fluxes in positive column of glow discharge

The research herein examined the results of numerical simulations of the positive column of a glow discharge in argon dusty plasma using COMSOL Multiphysics software under conditions similar to the project known as PK-4. Various scenarios dealing with formations of spatial distributions of densities and fluxes for charged particles were studied, and evaluations of the influence of dust particles on the discharge were obtained in a wide range of dust densities. Two extreme cases were distinguished: weak dust influence when the densities, fluxes and electric field profiles are not perturbed, and strong dust influence when all three density profiles(electrons, ions and charged dust) in the dust cloud are similar(parallel) to each other, resulting in all created charges in the dust cloud being lost inside the cloud. In such a case, the ambipolar field and the transport of charged particles are decreased in the dust cloud, and any ambipolar flux is almost absent within the cloud.     

Suppression of a spontaneous dust density wave by modulation of ion streaming

Synchronization of a self-excited dust density wave has been experimentally investigated in a strongly coupled dusty plasma. A dust density wave of frequency ~78 Hz is spontaneously generated from the dust void boundary due to the ion streaming instability. The electric field in the dust void region is measured, and the electric field force and ion drag force on the dust particles at the void boundary are estimated to explain the mechanism of spontaneous dust density wave excitation. Synchronization occurring through the suppression mechanism is observed by modulating the ion streaming by applying an external sinusoidal signal to the dust void. At sufficiently high modulation amplitude, the onset of period-doubling bifurcation is observed. Fast Fourier transform spectral analysis is done using time-series data obtained from high-speed video imaging. The van der Pol equation with a force term is used to correlate the observed suppression phenomena.     

Investigation into wideband electromagnetic stealth device based on plasma array and radar-absorbing materials

Manipulation of electromagnetic waves is essential to various microwave applications, and absorbing devices composed of low-pressure gas discharge tubes and radar-absorbing materials (RAM) can bring new solutions to broadband electromagnetic stealth. The microwave transmission method is used to measure the physical parameters of the plasma unit. The designed structure exhibits superior absorption performance and radar cross-section (RCS) reduction capability in the 2–18 GHz band, with unique absorption advantage in the S and C frequency bands. It is found that the combination of the plasma and the RAM can significantly broaden the absorption frequency band and improve the absorption performance with excellent synergistic stealth capability. Experimental and simulation results present that broadband, wide-angle, tunable electromagnetic wave absorption and RCS reduction can be achieved by adjusting the spatial layout of the combined plasma layer and the type of RAMs, which creates opportunities for microwave transmission and selective stealth of equipment. Therefore, the wave manipulation by combined plasma array and RAM provides a valuable reference for developing numerous applications, including radar antenna stealth, spatial filter, and high power microwave shielding.     

Calculation of Electrical Potential and Dust Particle Charge in a Double Dusty Plasma Device

Dusty plasma consists of macroscopic particles of nanometer to micrometer size immersed in a gaseous plasma environment. It can be observed by introducing a flow of molecular impurity in a double plasma device. The impurity particles will be charged quickly, while keeping relatively in low temperature. The particles typically attain several hundred or thousand elementary charges due to the inflow of plasma electron and ions. The dust particles potential and electrical charge in plasma with two ions at different temperatures is calculated. Electrical charge of dust particles is self consistently determined by local plasma electron and ion currents. It is found out that the dust particle potential is strongly affected by the mass and temperature difference of plasma ions.     

Relativistic effect on synergy of electron cyclotron and lower hybrid waves on EAST

In recent experiments on EAST,the electron temperature at the center can be raised to 9.7 keV by injecting electron cyclotron(EC)and lower hybrid(LH)waves simultaneously.With such strong core electron heating,the relativistic effect could play an important role in the interactions between the plasma and waves.In order to explore the relativistic effect on synergy between the EC and LH waves on EAST,ray-tracing/Fokker-Planck simulations are conducted to investigate electron heating for a typical discharge with a center electron temperature of 9.7 keV.It is found that the relativistic effect can cause the EC wave to deposit its power deeper in the plasma core,where the synergy between the EC and LH waves occurs and enhances the absorption of the LH waves.As a result,a high center electron temperature can be achieved.     

Numerical Research of Mode Conversion in an Inhomogeneous Plasma

The linear mode conversion of electromagnetic waves in the hot, unmagnetized inhomogeneous plasma is studied numerically for different density profiles, and the dependence of the absorption coefficient on the incident angles and the wave frequencies are obtained for different electrons＇ temperature. The results show that the shapes of the density profiles and the electron＇s temperature create a certain effect on the coefficients of absorption, which reaches its peak value （about 50%） for appropriate parameters. Effective absorption occurs in a limited range of parameter q.     

Characterization of dust collected in EAST after 2019 campaign

Dust presented in experimental advanced superconducting tokamak(EAST) with mixed plasmafacing materials has been collected and characterized for the first time. Dust at different positions in the vessel was collected by vacuum cleaner after the first experimental campaign in 2019. The shape, composition, and size of dust particles have been analyzed using different methods. About80% of the total number of dust particles have size between 20 and 80 μm, and most of dust particles are spherical, while schistose shape, columnar and irregular shape were also found.With the help of energy-dispersive x-ray spectroscopy different elements of dust have been identified, which is generally consistent with the different plasma-facing components in EAST.Both x-ray fluorescence and inductively coupled plasma emission spectrometer are complementary methods for measuring the dust composition quantitatively. It was found that the major components of dust were lithium dust in the form of lithium carbonate and lithium hydroxide, which is due to the routine lithium wall conditioning during EAST operation.     

Observation of coherent mode induced by a molybdenum dust on EAST

The influence of a molybdenum dust buildup on plasma edge turbulence has been studied in the EAST tokamak.The motion of the dust from the upper divertor region is detected by a fast visible CCD camera,the XUV spectrometer arrays,and the EUV spectrometer.The MoXV emission intensity sharply increases compared with the spectral lines of various ionization states of other elements,which implies that the dust particles are the molybdenum impurities.The radial distribution of Mo14+ion simulated by a simplified 1D transport model indicates that the molybdenum dust mainly deposits in the pedestal bottom region.Moreover,it is observed that the coherent mode(CM)appears at ρ=0.94 after the molybdenum impurities enter the main plasma region.The influx of molybdenum impurities results in increasing pedestal electron density and decreasing pedestal electron temperature in contrast to that before the event of impurities dropping.It is also found that the electron density gradient in the pedestal increases when the ablation of the molybdenum impurities is observed in the pedestal region.The qualitative experimental results indicate that the onset of CM is likely related to the increase of the density gradient and edge collisionality in the pedestal.In comparison to the density gradient,the enhancement of CM amplitude largely depends on the increase of the edge collisionality.     

Experimental Study on the Interaction of Electromagnetic Waves and Glow Plasma

An experimental system was established in order to study the interaction between electromagnetic waves, with a frequency of 300 kHz to 3 GHz, and DC glow discharge plasma. The results show that the DC glow discharge plasma affects the transmission properties of electromagnetic waves, while the waves can change both temperature and density of electrons.     

Preliminary assessment for dust contamination of ITER In-Vessel Transporter

After plasma operations of ITER, radioactive dust will have accumulated in the vacuum vessel (VV). The In-Vessel Transporter (IVT) will be introduced into the VV to remove the shield blanket modules for maintenance or replacement and later reinstall them. The IVT itself also needs to undergo regular maintenance in the Hot Cell Facility (HCF). It is assumed that maintenance workers will be exposed to radioactive dust that has adhered to the surfaces of the IVT. In this study, the areas of the IVT that may be contaminated by dust are evaluated to assess the level of exposure to workers during maintenance work in the HCF. Decontamination processes for the IVT, such as a combination of vacuuming and brushing, were investigated and the dose rate after these processes was evaluated. Even though dust was removed from surfaces where decontamination was possible, the dose rate was very high at some assessment points. To decrease the dose rate in accordance with ALARA policy, a decontamination plan and a maintenance plan, which includes the removal of dust, a radiation shield system, and a reduction in working time are proposed.     

Nonplanar dust acoustic solitary and rogue waves in an ion beam plasma with superthermal electrons and ions

The propagation characteristics of dust acoustic solitary and rogue waves are investigated in an unmagnetized ion beam plasma with electrons and ions following kappa-type distribution in nonplanar geometry. The reductive perturbation method(RPM) is employed to derive the cylindrical/spherical Korteweg–de Vries(KdV) equation, which is further transformed into standard KdV equation by neglecting the geometrical effects. Using new stretching coordinates,nonlinear Schr?dinger equation(NLSE) has been derived from the standard KdV equation to study the different order rational solutions of dust acoustic rogue waves(DARWs). The impact of various physical parameters on the characteristics of dust acoustic solitary waves(DASWs) is elaborated specifically in nonplanar geometry. Further, the effects of ion beam and superthermality of electrons/ions on the characteristics of DARWs are studied. The results obtained in the present investigation may be useful in comprehending a variety of phenomena in Earth's magnetosphere polar cap region where the presence of positive ion beam has been detected and also in other regions of space/astrophysical environments where dust along with superthermal electrons and ions exists.     

Propagation properties of broadband terahertz pulses through a bounded magnetized thermal plasma

An analysis of THz waves propagation in dense, collisional, thermal, magnetized and bounded plasma is presented. By introducing the dielectric constant of a warm magnetoplasma and using the method of impedance transformation with multiple dielectrics, the coefficients of power reflection (R) and absorption (A) are derived for a bounded plasma model by a lossless plate and a conductor plate. The effects of electron temperature, collision frequency, external magnetic field, electron density and thickness of the plasma slab on the absorption coefficient are analyzed numerically. It is found that these plasma parameters can cause significant change in the value of A. Some phenomena, for example negative power absorption, upper-hybrid resonance absorption and geometric resonances absorption, are observed and the behavior of the THz wave propagation inside the plasma model is explained numerically and physically.     

The instability of terahertz plasma waves in cylindrical FET

In this paper, the Dyakonov–Shur instability of terahertz (THz) plasma waves has been analyzed in gated cylindrical field effect transistor (FET). In the cylindrical FET, the hydrodynamic equations in cylindrical coordinates are used to describe the THz plasma wave in two- dimensional electronic gas. The research results show that the oscillation frequency of the THz plasma wave is increased by increasing the component of wave in the circumferential direction, but instability increment of the THz plasma wave are increased by increasing the radius of channel.     

Stationary Potential Formation and Oscillations in Plasma with Immovable Dust Particles

Stationary electrostatic-potential formation in plasma with immovable dust particles was investigated by using one-dimensional kinetic analysis. It is clarified that the density of negatively charged dust particles below the threshold value makes the potential decrease monotonically. When the dust densities are above the threshold, there appears the stationary oscillation in an electrostatic potential due to the streaming plasma. It is found that the wavelength of this mode is of the order of Debye length. These phenomena are different from those of the conventional dust ion-acoustic waves in plasma, where the effect of dust-charging is not taken into account.     

Slowing Down of Neutrons to Very Low Temperature by Cold Solid Hydrogenous Moderators

The slowing down of neutrons to very low energy has been examined with particular reference to cold neutron production. The neutron spectrum formed in very cold light water ice has been measured with time-of-flight technique. It is observed that at extremely low temperature the neutron temperature is much higher than the moderator temperature, whereas in the intermediate range of temperature the neutron temperature does not differ much from the moderator temperature.

It is suggested that there is a limiting neutron temperature below which it does not fall, even when the moderator temperature drops further. This observation can lead to information on the nature of the mechanism for removing small amounts of energy from slow neutrons in cold solid hydrogenous moderators. By using a simplified model for the cold solid hydrogenous moderators, it is shown that low frequency lattice vibrations play an important role in producing cold neutrons. Also, quantitative analysis indicates that while the cold neutron temperature depends only slightly on the neutron absorption, the gain in cold neutron flux is strongly affected by the neutron absorption.     

Dust Acoustic Compressive Waves in a Warm Dusty Plasma Having Non-Thermal Ions and Non-Isothermal Electrons

In this article an investigation is presented on the properties of dust acoustic(DA)compressive solitary wave propagation in an adiabatic dusty plasma,including the effect of nonthermal positive and negative ions and non-isothermal electrons.The reductive perturbation method has been employed to derive the lower degree modified Kadomtsev-Petviashivili(mK-P),3D Schamel-Korteweg-de-Vries equation or modified Kadomtsev-Petviashivili(mK-P) equations for dust acoustic solitary waves in a homogeneous,unmagnetized and collisionless plasma whose constituents are non-isothermal electrons,singly charged positive and negative non-thermal ions and massive charged dust particles.The stationary analytical solutions of the lower degree mK-P and mK-P equations are numerically analyzed,where the effect of various dusty plasma constituents on DA solitary wave propagation is taken into account.It is observed that both the ions in dusty plasma play a key role in the formation of DA compressive solitary waves,and also the ion concentration and non-isothermal electrons control the transformation of the compressive potentials of the waves.