Spectrum Of Plasma Oscillations Research Articles

Observation of Parametric Decay of a Pumping Wave in Lower Hybrid Wave Heating and Current Drive Experiments at the FT-2 Tokamak

The systematization of experimental data related to development of the parametric decay instability in tokamak plasma during RF power input within the lower hybrid frequency range was performed, which allows its characteristics to be compared with theoretical representations. The spectra of pumping waves and radiation from the plasma are obtained, which illustrate the appearance of satellites that are shifted from a pump frequency by a value that is a multiple of the ion cyclotron frequencies, toward the “red” and “blue” sides. It is noted that with a rise in density, a considerable broadening of the line of a pumping wave occurs. Values of the RF power and plasma density are observed, which are threshold values for the onset of the development of parametric decay instability. Using the diagnostic complex, the analysis of the low-frequency region of the plasma oscillation spectrum was carried out. The conditions of the development of instability were analyzed within the existing theoretical representations.

Collective oscillations of a two-chain electron system in a conducting channel over liquid helium

The simulation of a low-dimensional electron system over liquid helium was performed. It was shown that inclusion of an additional potential acting in the plane of the charge sheet leads to compression of the system in the direction of the external force. Such a potential arises in experiment when a system of surface electrons is formed over a profiled substrate where the potential is proportional to the holding electric field. It was found that in this case the system passes sequentially through the configurations consisting of several linear chains and undergoes a transition from the state of two-dimensional electron crystal to the zigzag configuration earlier predicted by Chaplik. With further increase in the holding field, the system becomes a single linear chain. The dispersion relations for the collective plasma oscillations of the zigzag configuration of electrons were calculated by the method of the equations of motion. It was found that one of the longitudinal oscillation modes is acoustic, whiles the other is optical. Both transverse oscillation modes were found to be optical. The results were compared with the dispersion relations earlier obtained for a single chain of electrons. It was shown that the dispersion relations of transverse plasma oscillations are more stable than the transverse mode of the oscillations of a single chain. The influence of magnetic field on the spectrum of plasma oscillations of the zigzag configuration of electrons was studied.

Plasma oscillations of massless Dirac electrons in a planar superlattice

The spectrum of plasma oscillations in a lateral superlattice of massless Dirac electrons has been calculated in the weak coupling approximation. The intensity of absorption of electromagnetic waves by plasmons of the superlattice at frequencies near the edges of band gaps has been found.

ECE complex on T-10 tokamak

The structure and main characteristics of ECE complex on T-10 are presented. T-10 ECE system possesses by certain features: measurements are fulfilled simultaneous on 1st and 2nd harmonics; frequency range of every harmonic is widened down; ECE measurements are made in two polarization at the same time; antenna system has narrow angle diagram that permits to discover several dynamic and structure peculiarities of global plasma oscillations in m/n=1/1 mode; ECE equipment is used also for measurement of emission in frequency range of magnetized Langmuir oscillations. Some results of measurements are shown: an unevenness of disturbances motion in space; appearance of rational magnetic surface on half of q=1 surface radius; strong oscillations of longitudinal electron velocity at the central plasma area; stability of distribution function of high energy electrons at plasma edge; spectrum of plasma oscillations in sawtooth regime.

Oscillation spectrum of an electron gas with a small density fraction of ions

The problem is solved of the stability of a nonneutral plasma that completely fills a waveguide and consists of magnetized cold electrons and a small density fraction of ions produced by ionization of the atoms of the background gas. The ions are described by an anisotropic distribution function that takes into account the characteristic features of their production in crossed electric and magnetic fields. By solving a set of Vlasov-Poisson equations analytically, a dispersion equation is obtained that is valid over the entire range of allowable electric and magnetic field strengths. The solutions to the dispersion equation for the m = +1 main azimuthal mode are found numerically. The plasma oscillation spectrum consists of the families of Trivelpiece-Gould modes at frequencies equal to the frequencies of oblique Langmuir oscillations Doppler shifted by the electron rotation and also of the families of “modified” ion cyclotron (MIC) modes at frequencies close to the harmonics of the MIC frequency (the frequencies of radial ion oscillations in crossed fields). It is shown that, over a wide range of electric and magnetic field strengths, Trivelpiece-Gould modes have low frequencies and interact with MIC modes. Trivelpiece-Gould modes at frequencies close to the harmonics of the MIC frequency with nonnegative numbers are unstable. The lowest radial Trivelpiece-Gould mode at a frequency close to the zeroth harmonic of the MIC frequency has the fastest growth rate. MIC modes are unstable over a wide range of electric and magnetic field strengths and grow at far slower rates. For a low ion density, a simplified dispersion equation is derived perturbatively that accounts for the nonlocal ion contribution, but, at the same time, has the form of a local dispersion equation for a plasma with a transverse current and anisotropic ions. The solutions to the simplified dispersion equation are obtained analytically. The growth rates of the Trivelpiece-Gould modes and the behavior of the MIC modes agree with those obtained by numerical simulation.

Room temperature tunable detection of subterahertz radiation by plasma waves in nanometer InGaAs transistors

The authors report on the demonstration of room temperature, tunable terahertz detection obtained by 50nm gate length AlGaAs∕InGaAs high electron mobility transistors (HEMTs). They show that the physical mechanism of the detection is related to the plasma waves excited in the transistor channel and that the increasing of the drain current leads to the transformation of the broadband detection to the resonant and tunable one. They also show that the cap layer regions significantly affect the plasma oscillation spectrum in HEMTs by decreasing the resonant plasma frequencies.

Plasma effects in lateral Schottky junction tunneling transit-time terahertz oscillator

We study the plasma oscillations in a two-dimensional electron channel with a reverse-biased Schottky junction. Using the developed model we show that the negative dynamic conductivity of the Schottky junction associated with the tunneling injection and electrontransit- time effect can result in the self-excitation of plasma oscillations (plasma instability) in the quasineutral portion of the channel serving as a resonant cavity. The spectrum of plasma oscillations and the conditions of their self-excitations are expressed via the structure parameters. The instability can be used in a novel diode device - lateral Schottky junction tunneling transit-time terahertz oscillator.

Plasma oscillations in high-electron-mobility transistors with recessed gate

We calculate the plasma oscillation spectrum in high-electron-mobility transistors (HEMTs) with recessed gate having the highly doped caps adjacent to the source and drain contacts and the windows between the caps and the gate. The resonant plasma frequencies are found as functions of the lengths of the gate, cap, and window regions, the electron concentration in the transistor channel, and the gate voltage. We demonstrate that the effect of cap region can result in a significant reduction of the resonant frequencies in comparison with those calculated for simplified HEMT model. This can provide a plausible explanation of the data obtained in recent experimental studies of the detection of terahertz radiation in and its emission from HEMTs.

Spectrum of Plasma Oscillations in Slot Diode with Two-Dimensional Electron Channel

We strictly calculate the spectrum of plasma oscillations in a slot diode containing a two-dimensional electron channel with strip-like highly conducting contacts. The spectrum of plasma oscillations in a gated two-dimensional electron channel (without contacts) is calculated as well. We use the hydrodynamic electron transport model involving a two-dimensional Poisson equation. It is shown that the features of the structure geometry affect the oscillation spectrum.

New Branch of Intersubband Plasmons in a Nonequilibrium Two-Layer System

The plasma oscillation spectrum for 2D electrons in a double quantum well is calculated. It is shown that an additional branch of intersubband plasmons can exist without experiencing Landau damping in the case of nonequilibrium population of subbands. In an asymmetric structure, this branch is responsible for both the emergence of instabilities and the possibility of amplification of plasma waves.

Plasma oscillations in a slot diode structure with a two-dimensional electron channel

We calculate the spectrum of plasma oscillations in a diode structure with a two-dimensional electron channel in a slot between strip-like short circuited contacts. Hydrodynamic electron transport equations coupled with a two-dimensional Poissons equation for the self-consistent electric potential area used. The obtained results can be useful in designing of devices operating at terahertz frequencies based on two-dimensional electron systems and device optimization.

The plasma oscillations spectrum of a periodically inhomogeneous 2D electron system near the perforation threshold

The transformation of the spectrum of plasma oscillations with the zero reduced wave vector in the spatially modulated two-dimensional electron system moving to the regime of isolated quasi-one-dimensional electron channels is theoretically investigated. The results provide an explanation of the well-known experimental observations of the plasma resonance transformation when a two-dimensional electron system crosses the continuity violation threshold.

Plasma properties of a quasi-one-dimensional ring

The spectrum of plasma oscillations and the frequency of the dielectric relaxation of electrons in a quasi-one-dimensional ring are calculated. The plasmon spectrum is revealed to be equidistant. It is shown that, in contrast to the three-dimensional case, the dielectric relaxation is dispersive and, therefore, the distribution of carriers in quasi-one-dimensional rings can be studied by means of dielectric relaxation spectroscopy.

Effect of an external RF field on the beam-plasma discharge in a magnetic field

The effect of an RF field on a steady-state beam-plasma discharge with a plane electrode placed parallel to a sheetlike electron beam is studied experimentally. The plasma parameters were measured by a single probe, and the electron distribution function was determined with the use of an electrostatic analyzer. The energy and current of the electron beam were EB=2.5 keV and JB=0.05–1.5 A, respectively. The working pressure was p=2×10−5–10−3 torr. The frequency of the external RF field was 13.56 MHz. Both the steady-state regimes in which the RF field had no effect on the plasma parameters and regimes with a pronounced effect of the RF field were observed. The experiments show that the regime of the discharge depends strongly on the plasma density and the magnetic field. The parametric instability is studied theoretically in the weak-turbulence approximation. It is shown that, due to the decay nature of the spectrum of plasma oscillations, the onset of instability is accompanied by the transfer of the energy of fluctuations over the spectrum, from the pump frequency toward its harmonics.

Spectrum of plasma oscillations in structures with a periodically inhomogeneous two-dimensional electron plasma

We develop a rigorous electrodynamic theory of plasma oscillations in a periodically inhomogeneous two-dimensional electron system with a rectangular profile of the spatial modulation of the equilibrium electron concentration. We calculate the frequencies and radiative damping of the main plasma-oscillation types with a zero reduced wave vector. We show that the frequency splitting and the radiative damping of the oscillations are nonmonotonic functions of the modulation percentage and the ratio of the widths of the bands of two-dimensional plasma with low and high electron concentrations. The results of calculations are compared with experimental data and with the results of a perturbation theory developed in earlier work of other researchers. We discuss the physical mechanism for the emergence of radiative damping of plasma oscillations.

Some exact properties of the plasmon spectrum for an inhomogeneous cylindrical interface

It is rigorously shown by means of the conformal transformation that the plasma oscillation spectrum of an arbitrary conducting cylindrical surface consists of only three points, ω→ω p /(1+ϵ 0) 1 2 , ω→0, ω→ω p , as the plasmon wavevector k z along the cylinder axis tends to zero. The frequencies of all types of plasma oscillations are degenerate. The degeneracy is abolished for k z ≠0 and in the multiply-connected geometry of conducting media. A simple exact spectrum is found for a metal cylinder placed above a conducting surface.

On the theory of plasma oscillations in a non-ideal classical plasma

Using the diagram technique, a high-frequency expansion (with respect to powers 1/ omega 2) is obtained for polarization operators defining dielectric function of a plasma at arbitrary strong interaction between particles. On this basis the spectrum of plasma oscillations for non-ideal classical one- and two-component plasmas is studied. There is a good agreement with the data of molecular dynamic calculations without using any adjusting parameters. It is shown that the non-Coulombic nature of interaction between particles has a dramatic influence on the description of the spectrum of plasma oscillations in the classical two-component plasma.

On the possibility of oscillations in the magnetosphere plasma of a pulsar in the region of closed field lines

In this paper, a dispersion relation for the spectrum of plasma oscillations in the region of closed field lines of a pulsar magnetosphere is obtained in a coordinate system rotating uniformly with the netron star. The dispersion relations for oscillations propagating along and at right angles to the closed field lines of the pulsar magnetosphere are analyzed in the cold-plasma approximation. In particular, it is shown that high-frequency cyclotron radio waves can be emitted in the pulsar plasma in the region of closed field lines.

Plasma Oscillations in a Superlattice

AbstractTho spectrum of plasma oscillations, propagating along the superlattice (SL) axis is calculated in the random phase approximation (RPA) taking the umklapp processes into account. In the case of strong screening the plasmon frequency is determined by SL parameters and temperature and found to do not depend on wave number. At weak screening quasineutral electron oscillations occur. In the case of small wave numbers the oscillations follow the acoustic law of dispersion and propagate with a frequency of the same order as the electronic ones along the SL axis. The characteristic feature of plasmons propagating along the SL axis, is the absence of Landau damping since the decay of these plasmons in pairs of quasi‐particles is forbidden by energy‐momentum conservation laws. The existence of plasmons, propagating along the axis, may be an indication of electron tunnelling between layers.

Spectrum of plasma oscillations in atoms

Spectrum of plasma oscillations in atoms