Plasma Dipole Research Articles

Tunable wideband terahertz absorber based on single-layer patterned graphene

In this study, we propose and validate a broadband terahertz perfect absorber. The absorber has a simple structure, which consists of a gold (Au) substrate, a TOPAS dielectric layer and a patterned graphene layer. By the simulations, a broad absorption band can be obtained with a high absorption above 90% between 3.31 THz and 7.15 THz, and the relative bandwidth reaches 73.4%. Meanwhile, the absorption higher than 99% is between 3.81 THz and 6.6 THz with a relative bandwidth of 53.6%. The mechanism of the surface excited plasma (SPP) and electromagnetic dipole resonance are responsible for its almost perfect broadband absorption. By changing the Fermi energy level of the graphene layer, the flexible broadband absorption spectra can be acquired. By varying the geometrical parameters of the structure, a wider spectral range of absorption wavelengths can be realized. For both TE and TM polarization, the absorption can remain above 90% over a wide range of incidence angles. Due to the independent tunability and high absorption of the proposed device, it has great potential applications in terahertz imaging, smart absorption, detectors and communications.

Intense narrowband terahertz pulses produced by obliquely colliding laser pulses in helium gas

A practical configuration for generating narrowband terahertz (THz) pulses based on plasma dipole oscillations (PDOs) is studied using two-dimensional particle-in-cell simulations. In this scheme, two slightly detuned laser pulses collide obliquely in a helium gas. Plasma strips are generated along the paths of the laser pulses by field ionization. The PDO created in the overlap region of the two laser pulses emits a THz pulse with a peak electric field strength of a few gigavolt per meter. An energy conversion efficiency of 0.542 × 10 − 3 is achieved for laser pulse intensities 4.82 × 10 16 W / c m 2, a spot radii of 5 μ m, and a collision angle of 10.8 °. A force balance model is extended for the obliquely colliding configuration of the pulses. As the complications, such as generating plasmas separately or aligning the beams with preformed plasma, are eliminated from our new configuration, this makes a future experimental study of PDO more straightforward.

Terahertz emission from a plasma dipole oscillation

Terahertz emission from a plasma dipole oscillation

Experimental Characterization of a Plasma Dipole in the UHF Band

The experimental characterization of a plasma dipole in the ultrahigh frequency band is presented. The antenna consists on two customized plasma sources disposed as the arms of a conventional metallic dipole. The commercial electrodes used to produce the plasma act also as signal coupler. First, the plasma parameters have been measured to compute the electric permittivity. Subsequently, the reflection coefficient and the antenna gain have been derived through computer simulations and measurements in a portion of the spectrum centered at 0.435 GHz.

Generation and collective interaction of giant magnetic dipoles in laser cluster plasma

Interaction of circularly polarized laser pulses with spherical nano-droplets generates nanometer-size magnets with lifetime on the order of hundreds of femtoseconds. Such magnetic dipoles are close enough in a cluster target and magnetic interaction takes place. We investigate such system of several magnetic dipoles and describe their rotation in the framework of Lagrangian formalism. The semi-analytical results are compared to particle-in-cell simulations, which confirm the theoretically obtained terrahertz frequency of the dipole oscillation.

Numerical Suite for Gaseous Plasma Antennas Simulation

A gaseous plasma antenna (GPA) is a device in which a plasma medium is used to transmit or receive electromagnetic (EM) waves. This work is devoted to the presentation of a numerical suite for the simulation of a GPA that consists of a plasma module for the estimation of the plasma parameters (e.g., electron density profile) and its electrical response, along with an EM module to compute the antenna properties (e.g., radiation pattern and input impedance). The two problems are handled separately: first, the plasma discharge is solved, and then, the antenna properties are computed. In particular, the plasma module has been implemented on the C++ library OpenFOAM, whereas the EM module relies on the well-established commercial numerical tool CST Microwave Studio. The results of the plasma module have been compared against experimental measurements performed on a discharge driven by a hollow cathode and a cold cathode fluorescence lamp (CCFL). Finally, the numerical suite has been exploited to characterize a realistic plasma dipole: higher values of discharge current (equivalently of plasma density) allow to achieve higher maximum gain and an input impedance closer to the one of a metallic dipole. Moreover, the possibility of electronically shifting the resonance frequency by tens of megahertz has been proved.

Study of the microwave streamer evolution using a new semi-analytical model

A microwave (MW) plasma channel (filament, plasmoid, and plasma dipole) shows promise for its applications for off-body non-electrode modification of a gas flow (plasma aerodynamics) and in the plasma assisted combustion process. A full-scale study of the plasma channel evolution requires a self-consistent solution of Maxwell's equations, plasma chemical kinetics equations, and gasdynamics equations. An attempt is made to develop a simple electrodynamic (based on the solution of Maxwell's equations) “fast” model for studying the evolution of the plasma channel in conjunction with a fairly complete system of plasma chemical reactions. The model is based on a simplifying assumption about the shape of the channel, which converts a 3D problem into a 1D one. The results of numerical calculations in air within the pressure range P = 20–150 Torr are presented. An experimental study of plasmoid development was carried out to verify the predictions of the model. The calculated results agree well with all available experimental data within the pressure range P = 20–150 Torr. The proposed electrodynamic approach made it possible to reveal (i) the mechanism of self-organization during the development of a MW streamer and (ii) the reason for a sharp decrease in the velocity of its elongation, as well as to obtain relations connecting the main characteristics of the streamer (the amplitude of the electric field in the channel and on its heads, the velocity of ionization waves, and the characteristic scale of their fronts). The proposed model will be useful both for estimating the channel parameters and for deciphering the dynamics of radiation scattered by the plasma dipole. The development of such an approach will allow one to study the evolution of multiplasmoid structures of a high-pressure MW discharge.

Reconstruction of plasma density profiles by measuring spectra of radiation emitted from oscillating plasma dipoles

We suggest a new method for characterising non-uniform density distributions of plasma by measuring the spectra of radiation emitted from a localised plasma dipole oscillator excited by colliding electromagnetic pulses. The density distribution can be determined by scanning the collision point in space. Two-dimensional particle-in-cell simulations demonstrate the reconstruction of linear and nonlinear density profiles corresponding to laser-produced plasma. The method can be applied to a wide range of plasma, including fusion and low temperature plasmas. It overcomes many of the disadvantages of existing methods that only yield average densities along the path of probe pulses, such as interferometry and spectroscopy.

Particle balance in a steady state plasma in a dipole magnetic field

Detailed experiments and modeling are performed to investigate spatial (r and θ) dependence of particle production (Z), loss (Lp) and retention (Z − Lp) rates in a steady state plasma in a dipole magnetic field. A mathematical model is developed that solves the particle balance equation, considering generation through ionization, losses through diffusion and recombination, and by taking into account the measured values of plasma parameters and dipole fields in space. Depending upon the pressure p and angle θ, Z is found to peak ∼r = (3 – 6) × 10−2 m from the center of the magnet and decreases downstream, whereas Lp steadily increases toward the chamber wall. Particle balance (Z = Lp) is realized either at a single point in space or over a wider region, and can be tuned by varying p, whereas Z − Lp is found to be a maximum at an optimum pressure (∼1.0 mTorr). Results indicate that while the diffusion is primarily classical (∼1/B2), the recombination coefficient scales as ∼1/B0.5, as a result of its implicit dependence on the magnetic field through the electron temperature. The ionization coefficient is rather high and approximately uniform until ∼0.02 Tesla, and thereafter decreases linearly at lower fields.

Theoretical modeling of resonant wavelength in 3-layered plasma antennas

ABSTRACT In contrast to conventional metallic antennas, the resonant wavelength of a plasma dipole antenna is very much different from the predicted ∼λ/2 rule. In this paper, an implicit relation is derived to calculate the effective wavelength λeff and thus the resonant wavelength of a single element 3-layered plasma dipole antenna made of a glass tube filled with the plasma gas. An explicit relation is then derived in terms of the λ using reasonable assumptions. It is shown that this relation could be modeled by a linear formula λeff = m1 +m2λ in which the coefficients m1 and m2 depend on the geometry and material properties. Comparison of the results from the full-wave electromagnetic simulation, the numerical solution of the surface wave dispersion equations and the derived relations shows a reasonable match, verifying the theoretical approach.

Near-Field of a VLF Electric Dipole in an Anisotropic Plasma

In this paper, we proposed a semianalytical method for evaluating the near-zone field of a very low frequency (VLF) electric dipole in a homogeneous and anisotropic plasma. Due to the different attenuation properties for the ordinary wave (O-wave) and the extraordinary wave (E-wave), the integrals corresponding to their contributions should be truncated at different locations of the real axis and need to be separately treated. By applying the complex function theory and a speed-up convergence algorithm, the original oscillating integral for the near-field is transformed into two fast convergent integrals plus an analytical solution. Computations show that, in the near zone, the O-wave still has comparable amplitudes with the E-wave, and its influence on the total field should not be neglected. It is also observed from the radiation pattern that there exists a pronounced “cohesion effect” for the E-wave along the direction of the geomagnetic field, while the phase mutations of the O-wave exactly coincide with the minima of its field strength. Moreover, it is found that the radiation ability of a VLF electric dipole in an anisotropic plasma will increase with the operating frequency.

A reconfigurable solid-state plasma dipole antenna based on SPiN diodes

This paper proposes an innovative reconfigurable antenna concept based on the dynamic definition of metal-like conductive solid-state plasma in high-resistivity silicon which are activated by the injection of direct current. By investigating of the solid-state plasma characteristics, the metallic properties of solid-state plasma are verified. And a demonstration prototype of plasma dipole reconfigurable antenna, which comprises 36 SPiN diodes, has been designed, fabricated, and tested. The results show that the resonance frequencies at 69 GHz, 64.3 GHz and 60 GHz can be easily achieved when the antenna works in the three different states by turning on or off different sections of the antenna, selectively. In addition, it is confirmed that the proposed reconfigurable antenna has the unique characteristics compared with the conventional one.

High-Energy, Short-Duration Bursts of Coherent Terahertz Radiation from an Embedded Plasma Dipole

Emission of radiation from electrons undergoing plasma oscillations (POs) at the plasma frequency has attracted interest because of the existence of intriguing and non-trivial coupling mechanism between the electrostatic PO and the emitted electromagnetic wave. While broadband emission from plasma waves in inhomogeneous plasma is well known, the underlying physics of narrowband emission at the plasma frequency observed in experiments and in solar radio-bursts is obscure. Here we show that a spatially-localized plasma dipole oscillation (PDO) can be generated when electrons are trapped in a moving train of potential wells produced by the ponderomotive force of two slightly detuned laser pulses that collide in plasma and give rise to a burst of quasi-monochromatic radiation. The energy radiated in the terahertz spectral region can reach an unprecedented several millijoules, which makes it suitable for applications requiring short pulses of high-intensity, narrowband terahertz radiation.

A novel reconfigurable radiating plasma antenna array based on Yagi antenna technology

An electronically controlled plasma reflector antenna array is presented in term of Yagi antenna technology and plasma theory in this paper. The array comprised of a plasma symmetrical dipole in the center and 6 plasma column antennas uniformly around the dipole. When only the active plasma dipole and one of passive columns are energized, they perform like conductive metals capable to radiate radio signal like a two-element plasma Yagi antenna. Pattern reconfigurability of the antenna array can be achieved by sequentially exciting one of 6 plasma columns, and the plasma antenna array also produces better gain through increasing the number of plasma reflectors. Due to the adoption of equal amplitude and phase feeding technology, it greatly reduces the technical difficulty of the implementation of pattern reconfigurability. On the other hand, if all of plasma columns are off, there is only minor reflection from dielectric tubes, and hence, the plasma antenna array has stealth performance.

Analytical and Numerical Study of a Gaseous Plasma Dipole in the UHF Frequency Band

Gaseous plasma antennas are appealing in applications in which reconfigurability is desired, because the radiation properties can be changed by tuning the plasma parameters. In this paper, an analytical and numerical analysis of a gaseous plasma dipole that works in the 0.3–3 GHz frequency range is presented; the plasma dipole is comprised of two discharges that are arranged similar to the arms of a center-fed metallic dipole. The analytical approach can provide the short- and open-circuit resonance frequencies of the plasma dipole, which have been proven reconfigurable by adjusting the discharge length and by adjusting the density of the plasma therein. Thanks to the numerical approach, the role of the type and pressure of the neutral gas species, and the magneto-static field on the reflection coefficient, and the gain function has been investigated. Finally, a feasibility study of an actual plasma dipole is presented; specifically, the choice of coupling the signal to be radiated by means of electrodes immersed in the plasma is a key to achieve radiation efficiency close to 90%.

Internal Charmonium Evolution in the Quark–Gluon Plasma

We employ a time-dependent Schrödinger equation to study the evolution of a cc‾ dipole in a quark-gluon plasma (QGP). Medium effects on the heavy-quark potential in the QGP are found to significantly affect the timescales of the internal evolution of the dipole. Color-screening can enhance the overlap of the expanding wavepackage with excited states at high temperature, while it is reduced at lower temperatures where the dipole favors the formation of the charmonium ground state. We investigate the consequences of this mechanism on the double ratio of charmonium nuclear modification factors, RAAψ(2S)/RAAJ/ψ, in heavy-ion collisions. The impact of the transition mechanisms on this ratio turns out to be rather sensitive to the attractive strength of the potential, and to its temperature dependence.

Investigation of structured microwave discharge based on data from the scattered radiation

The development of a microwave discharge is accompanied by noticeable scattering of the incident electromagnetic field. The scattered radiation includes information about the time evolution of the discharge formation and its integral parameters. In this work a method of diagnostics using scattered radiation to study a single thin plasma channel (plasmoid, plasma dipole) and corresponding experimental results in air within the pressure range P = 70–150 Torr are presented. A simple analytical model for analysis of the experimental results of microwave scattering from a plasmoid is proposed. Information concerning the average elongation velocity of the plasma channel in the direction parallel to the incident electric field and the induced dipole moment of the plasmoid is obtained. Based on information about the dipole moment as well as the form and sizes of the plasma dipole the effective cross section, the total charge, the current averaged over the channel length, the plasma density and conductivity averaged over the channel volume, the electric field amplitude in the central region of the channel and the absorbed power are estimated. The estimated value of the plasma density is shown to agree with experimental results obtained using spectroscopic methods.

Emission spectroscopy of a dipolar plasma source in hydrogen under low pressures

Low-temperature hydrogen plasma has been investigated under the conditions of electron cyclotron resonance by emission spectroscopy. The molecular distribution functions over the low rotational and vibrational levels of the hydrogen molecule in the triplet state have been measured. The translational, rotational, and vibrational temperatures of the ground and excited triplet states of the hydrogen molecule are determined. The obtained translational and vibrational temperatures indicate that low-temperature hydrogen plasma under the conditions of electron cyclotron resonance is a more efficient source of vibrationally excited hydrogen molecules in comparison with the other gas discharges.

Quasistatic dipole in magnetized plasma in resonance frequency band. Response of the receiving antenna, and charge distribution on the antenna wire

The paper discusses issues related to the radiation and reception of quasi-electrostatic waves by short antennas in resonance conditions (in the whistler range) in magnetized plasma. First, the response of the receiving antenna on the incident field of slow quasipotential waves is analyzed. It made it possible to explain in detail the results of the two-point rocket experiment OEDIPUS-C in the Earth’s ionosphere. Second, the problem of the charge distribution along the short transmission (reception) dipole antenna is considered. The corresponding integral equation is obtained and solved analytically. The impedance of the antenna is found. It is shown that in the majority of cases, charge distribution along the dipole length can be considered constant.

A Simple Equivalent Circuit Model for Plasma Dipole Antenna

Plasma antenna is an emerging technology that utilizes ionized gas as a conducting medium instead of metal. It is often convenient to represent the input impedance of the antenna by a lumped-element-equivalent circuit. Input impedance of the plasma dipole antenna is deduced using finite integration technique. A five-lumped-element equivalent circuit for the plasma dipole antenna variation with plasma frequency is investigated and optimized using the genetic algorithm (GA). The effect of plasma frequency and collision frequency of the ionized gas on input impedance variations of the plasma dipole antenna is studied with the help of the equivalent circuit model. Another equivalent circuit is synthesized using a rational function and GA. The Cauer realization method is used to deduce a new lumped-element equivalent circuit.