Explanation of Ball Lightning by Plasma Oscillations

Ball Lightning (BL) is a “plasma bubble” that has very remarkable properties. Its membrane contains a higher density of charged particles than the ambient medium. They are held together by mutually attracting surface charges, generated by collective oscillations of all unbound electrons inside the membrane. Energy losses by collisions and emission of radiation, as well as losses of charged particles by recombination, are compensated by extracting other ones from atmospheric air. Since that occurs in a special rhythmic way, this leads to “parametric amplification” of the oscillations of all unbound electrons in the plasma membrane. Moreover, BL is attracted by higher concentrations of charged particles in atmospheric air. Too much of them leads to explosion and too few to extinction of visible BL. Since the electric charge of BL is oscillating, it is also attracted by metals, water and glass. It can then heat, melt and vaporize these materials without stored energy. BL is even able to pass through window panes in 3 different ways, but that can also be explained.

On-Line Measurement of Ion Density in Atmospheric Nitrogen Discharge Filaments via Radiation Signals from Plasma Oscillation

Diagnosis of the particle number density of plasma plays an important role in the understanding of plasma sources and processing.Regular radiation signals from plasma oscillation in filaments of atmospheric nitrogen discharge,which were excited by the injection of secondary electron beams during the propagation of the streamer,are employed to determine the ion density of plasma and its evolution in the filaments.Results show that the density of N4＋ in a filament of atmospheric nitrogen discharge is of the order of 1013 cm-3.It is also found that the recombination processes play a dominant role in plasma decay,and that the ion density decreases non-monotonically with time during streamer propagation.

Influence of Superathermal Electrons oll Central Plasma Relaxation Oscillations during Localized Electron Cyclotron Heating on the HL-1M Tokamak

During initial studies of ECRH in the HL-1M tokamak, non-standard central MHD activities,such as saturated sawtooth, partially saturated sawtooth, double sawtooth, and the strong m = 1 bursts have been observed while changing the heating location, the ECRH power, the plasma density. Complete suppression of sawtooth is achieved for the duration of the ECRH, when the heating power is applied on the high-field side of low-density plasma, and exceeds a threshold value of power. The m = 1 bursts riding on the ramp phase of sawtooth can only be excited when the ECRH location is near the q = 1 surface on the high field side. The conditions under which the various relaxation activities are produced or suppressed are described. Experimental results imply that the energetic electrons generated during ECRH are responsible for the modification/or stabilization/or excitation of the instability. Near the q = 1 surface, the passing electrons play the role of reducing the shear and tending to stabilize the sawtooth activity, while the barely-trapped electrons play the role of enhancing or driving an internal kink instability.

Surface plasmon oscillations in a semi-bounded semiconductor plasma

We study the dispersion properties of surface plasmon（SP） oscillations in a semi-bounded semiconductor plasma with the effects of the Coulomb exchange（CE） force associated with the spin polarization of electrons and holes as well as the effects of the Fermi degenerate pressure and the quantum Bohm potential.Starting from a quantum hydrodynamic model coupled to the Poisson equation,we derive the general dispersion relation for surface plasma waves.Previous results in this context are recovered.The dispersion properties of the surface waves are analyzed in some particular cases of interest and the relative influence of the quantum forces on these waves are also studied for a nano-sized Ga As semiconductor plasma.It is found that the CE effects significantly modify the behaviors of the SP waves.The present results are applicable to understand the propagation characteristics of surface waves in solid density plasmas.

Dynamics Behaviors of a Laser Produced Plasma:Theoretical Approach

Assuming that plasma particles are moving on continuous and non-differentiable curves, some dynamic properties in plasma ablation are analyzed via scale-relativity theory: the splitting of plasma plume, multi-peak structures, at various distances from the target surface and plasma oscillations through self-similarity. Our theoretical results are in good agreement with the experimental ones.

Investigation of steady plasma actuation effect on aerodynamic coefficients of oscillating airfoil at low Reynolds number

In this work, numerical study of two dimensional laminar incompressible flow around an oscillating NACA0012 airfoil is proceeded using the open source code Open FOAM. Oscillatory motion types including pitching and flapping are considered. Reynolds number for these motions is assumed to be 12000 and effects of these motions and also different unsteady parameters such as amplitude and reduced frequency on aerodynamic coefficients are studied. For flow control on airfoil, dielectric barrier discharge plasma actuator is used in two different positions on airfoil and its effect is compared for the two types of considered oscillating motions. It is observed that in pitching motion, imposing plasma leads to an improvement in aerodynamic coefficients, but it does not have any positive effect on flapping motion.Also, for the amplitudes and frequencies investigated in this paper, the trailing edge plasma had a more desirable effect than other positions.

Steady and oscillatory plasma properties in the near-field plume of a hollow cathode

Hollow cathodes serve as electron sources in Hall thrusters,ion thrusters and other electric propulsion systems.One of the vital problems in their application is the cathode erosion.However,the basic erosion mechanism and the source of high-energy ions cause of erosion are not fully understood.In this paper,both potential measurements and simulation analyses were performed to explain the formation of high-energy ions.A high-speed camera,a single Langmuir probe and a floating emissive probe were used to determine the steady and oscillatory plasma properties in the near-field plume of a hollow cathode.The temporal structure,electron temperature,electron density,and both static and oscillation of plasma potentials of the plume have been obtained by the diagnostics mentioned above.The experimental results show that there exists a potential hill（about 30 V） and also severe potential oscillations in the near-plume region.Moreover,a simple 2 D particle-in-cell model was used to analyze the energy transition between the potential hill and/or its oscillations and the ions.The simulation results show that the energy of ions gained from the static potential background is about 20 e V,but it could reach to 60 e V when the plasma oscillates.

Simulational Investigation of a High-Efficiency X-Band Magnetically Insulated Line Oscillator

Abstract The magnetically insulated line oscillator （MILO） is a gigawatt-class, coaxial crossed-field microwave tube, which is at present a major hotspot in the field of high-power mi- crowaves （HPM） research. In order to improve the power conversion efficiency and eliminate or at least minimize anode plasma formation in the load region and radio frequency （RF） breakdown in the slow wave structure （SWS） section, an X-band MILO is presented and inyestigated nu- merically with KARAT code. The design idea is briefly presented and the simulation results are given and discussed. In the simulation, HPM is generated with peak power of 3.4 GW, maximum electric field of about 1 MV/cm, and peak power conversion efficiency of 14.0%, when the voltage is 559.1 kV and the current is 43.2 kA. The microwave frequency is pure and falls in the X-band of 9.0 GHz. The theoretical investigation and the simulation results are given to prove that the anode plasma formation and the RF breakdown can be effectively avoided or at least minimized, respectively.

A new approach for modelling the damped Helmholtz oscillator:applications to plasma physics and electronic circuits

In this paper,a new approach is devoted to find novel analytical and approximate solutions to the damped quadratic nonlinear Helmholtz equation(HE)in terms of the Weiersrtrass elliptic function.The exact solution for undamped HE(integrable case)and approximate/semi-analytical solution to the damped HE(non-integrable case)are given for any arbitrary initial conditions.As a special case,the necessary and sufficient condition for the integrability of the damped HE using an elementary approach is reported.In general,a new ansatz is suggested to find a semi-analytical solution to the non-integrable case in the form of Weierstrass elliptic function.In addition,the relation between the Weierstrass and Jacobian elliptic functions solutions to the integrable case will be derived in details.Also,we will make a comparison between the semi-analytical solution and the approximate numerical solutions via using Runge-Kutta fourth-order method,finite difference method,and homotopy perturbation method for the first-two approximations.Furthermore,the maximum distance errors between the approximate/semi-analytical solution and the approximate numerical solutions will be estimated.As real applications,the obtained solutions will be devoted to describe the characteristics behavior of the oscillations in RLC series circuits and in various plasma models such as electronegative complex plasma model.

Studies on the mechanisms of powerful terahertz radiations from laser plasmas

A survey on the mechanisms of powerful terahertz （THz） radiation from laser plasmas is presented.Firstly,an analytical model is described,showing that a transverse net current formed in a plasma can be converted into THz radiations at the plasma oscillation frequency.This theory is applied to explain THz generation in a gas driven by two-color laser pulses.It is also applied to THz generation in a tenuous plasma driven by a chirped laser pulse,a few-cycle laser pulse,a DC/AC bias electric field.These are well verified by particle-in-cell simulations,demonstrating that THz radiations produced in these approaches are nearly single-cycles and linear polarized.In the chirped laser scheme and the few-cycle laser scheme,THz radiations with the peak field strength of tens of MV/cm and the peak power of gigawatt can be achieved with the incident laser intensity less than 10 17 W/cm 2.

Doped ceramics of indium oxides for negative permittivity materials in MHz-kHz frequency regions

Negative permittivity has been widely studied in various metamaterials and percolating composites, of which the anomalous dielectric behavior was attributed to critical structural properties of building blocks.Herein, mono-phase ceramics of indium tin oxides(ITO) were sintered for epsilon-negative materials in MHz-k Hz frequency regions. Electrical conductivity and complex permittivity were analyzed with DrudeLorentz oscillator model. Carriers’ characters were measured based on Hall effect and the magnitude and frequency dispersion of negative permittivity were mainly determined by carrier concentration.Temperature-dependent dielectric properties further proved the epsilon-negative behaviors were closely associated with free carriers’ collective responses. It’s found that negative permittivity of ITO ceramics was mainly caused by plasma oscillations of free carriers, while the dielectric loss was mainly attributed to conduction loss. Negative permittivity realized here was related to materials intrinsic nature and this work preliminarily determined the mechanism of negative permittivity in doped ceramics from the perspective of carriers.

D-shaped fiber optic SPR biosensors based on a metal-graphene structure

We design a D-shaped fiber optic biosensor based on the surface plasmon resonance （SPR） of a metal- graphene layer and simulate this SPR using the finite element method. Using a metal-graphene layer as the sensing material, surface plasma resonance is simulated as the refractive index of the external environment ranges from 1.33 to 1.36. Simulation results show that a metal-graphene layer attached to the D-shaped optical fiber core can couple with light under a specific polarization state and excite strong plasma os- cillations on the layer surface. Calculated transmission coefficients show that the resonance wavelength obviously moves toward longer wavelengths as the refractive index of the test medium increases, and a sen- sitivity of 5400 nm/RIU is obtained. Because of its large surface volume ratio and good biocompatibility, graphene map be utilized in many applications in the field of biosensing.

Research on the detuning system of a cooling electron beam for the dielectronic recombination experiment at CSRm

The storage ring equipped with an electron cooler is an ideal platform for dielectronic recombination （DR） experiments. In order to fulfill the requirement of DR measurements at the main Cooler Storage Ring, a detuning system for the precision control of the relative energy between the ion beam and the electron beam has been installed on the electron cooler device. The test run using 7.0 MeV/u C6＋ beam was performed with recording the Schottky spectra and the ion beam currents. The influence of pulse heights and widths of the detuning voltage on the ion beam was analyzed. For the small pulse height, the experimental results from the Schottky spectra were in good agreement with the theoretical results. The frequency shift in the Schottky spectra was significantly reduced for the short pulse width. For the large pulse height, an oscillation phenomenon was observed and some effective ways to reduce the oscillation were pointed out. The detailed description of the phenomenon and the theoretical model based on the plasma oscillation was discussed in this paper. The overall results show that the new detuning system works properly, and could fulfill the requirements of future DR experiment.

MOF-derived ZrO_(2)/C-polyvinylidene fluoride composite towards negative permittivity regulation mechanism

Composites featuring negative permittivity have garnered significant attention for their potential in novel capacitance designs,coil-less electrical inductors,and electromagnetic shielding applications.In this study,we prepared polyvinylidene fluoride(PVDF)matrix composites filled with ZrO_(2)/C nanoparticles de-rived from metal-organic frameworks(MOFs)via a hot-pressing method.With an increase in the ZrO_(2)/C content to 30 wt.%,electrical percolation was observed,accompanied by a transition mechanism from hopping conduction to metal-like conduction.This enabled the realization of ZrO_(2)/C/PVDF composites with tailorable negative permittivity properties,attributed to the plasmonic oscillation of free electrons in the composites beyond the percolation threshold(30 wt.%).Furthermore,the permittivity transition along to a shift in the electrical behavior of the percolative composites from capacitive to inductive.We explored the regulatory mechanism behind the negative permittivity in this random composite system,and our findings highlight the potential of these tunable negative permittivity media as promising candi-dates for diverse electromagnetic applications.