Types Of Plasma Instabilities Research Articles

Time and space resolved diagnostics for plasma thermal-chemical instability of fuel oxidation in nanosecond plasma discharges

An instability in a nanosecond pulsed dielectric barrier discharge plasma occurring in methane–oxygen–argon mixtures is experimentally observed and measured by 1D time-resolved in situ electric field measurements. This instability, which seems to be created by the positive feedback between plasma kinetics and plasma-assisted low temperature fuel oxidation, is studied using electric field induced second harmonic generation and direct ICCD imaging. The rapid formation of streamers from an originally uniform discharge appears to be caused by the chemical kinetics of plasma-assisted low temperature methane oxidation, which may be resulting in a new type of plasma instability: a thermal-chemical instability. The results also revealed that the occurrence of this possible thermal-chemical instability in a reactive flow drastically changes the plasma properties by forming multiple secondary discharges and possibly leads to micron-sized non-uniform electric distributions. Single shot uncalibrated measurements of the electric field of the micron sized streamers appears to show much greater strengths than the average electric field. Furthermore, one-dimensional data analysis shows the positive feedback loop between the streamers and the low temperature plasma assisted oxidation chemistry in the plasma thermal-chemical instability. The present finding advances the understanding plasma instability growth and provides a new way to control plasma uniformity in plasma-assisted combustion and plasma fuel reforming.

On the dispersion relation of the transit time instability in inverted fireballs

Recently discovered inverted fireballs are non-linear plasma phenomena, which are formed in hollow grid anodes with high transparency in an existing background plasma. If a sufficiently large potential is applied, accelerated electrons from the bulk start to oscillate through the grid. Experimental investigations have shown that they produce different types of plasma instabilities. One of those oscillations is a transit time instability which originates from strong electron beams that travel through the inverted fireball. This type of instability is similar to vircator reflex oscillations and produces radio frequency waves. Hence, it is suitable to convert DC signals into signals oscillating in the MHz range. This paper analyses the dispersion relation of the transit time instability for three different plasma regimes. The regimes can be divided into a collision less regime, a regime with high collisionality and one in between those former two. It is demonstrated that the plasma properties of the surrounding background plasma have a strong influence on the behavior of the instability itself.

Plasma Instability Noise in InP n+nn+Structures: Monte Carlo Simulation

The plasma instabilities (PI) are promising mechanisms for high frequency microwave generation in semiconductor nnn structures. The two types of PI at near collisionless (NCL) and optical phonon emission dominated (OPED) electron transport conditions in the nnn structures are considered by Ryzhij et al. [1]. They found that both types of PI’s can lead to current self-oscillations up to the plasma frequency, which depends on the carrier concentration in the n-region of the nnn structure (see Ref. [1] and references therein). The regularity of selfoscillations is sensitive to the spatial resonance conditions for space charge waves periodically growing and decaying due to the PI, i.e. there exists the optimum length of n-region at the given doping of this region. In real nnn structures the OPED and especially NCL plasma instabilities are suppressed by the lattice (mainly due to accoustic phonons) and impurity scatterings. However, the progress in manufacturing structures with remote doped conducting channels recently gave the second breath to PI investigations. Also the recent achievements in THz frequency noise measurements have opened new directions in PI investigation. It is well known that the noise spectrum contains integrated information about physical processes such as carrier scattering, various instabilities, including PI, etc. Therefore, the identification of noise spectrum pecularities such as the peaks in the noise spectra related to the certain process is important.

Three-dimensional particle simulation of plasma instabilities and collisionless reconnection in a current sheet

Generation of anomalous resistivity and dynamical development of collisionless reconnection in the vicinity of a magnetically neutral sheet are investigated by means of a three-dimensional particle simulation. For no external driving source, two different types of plasma instabilities are excited in the current layer. The lower hybrid drift instability (LHDI) is observed to grow in the periphery of current layer in an early period, while a drift kink instability (DKI) is triggered at the neutral sheet in a late period as a result of the nonlinear deformation of the current sheet by the LHDI. A reconnection electric field grows at the neutral sheet in accordance with the excitation of the DKI. When an external driving field exists, the convective electric field penetrates into the current layer through the particle kinetic effect and collisionless reconnection is triggered by the convective electric field earlier than the DKI is excited. It is also found that the anisotropic ion distribution is formed through the anomalous ion heating by the DKI.

Particle simulation of collisionless reconnection in three dimensions

Generation of anomalous resistivity and dynamical development of collisionless reconnection in the vicinity of a magnetically neutral sheet are investigated by means of a three-dimensional particle simulation. For no external driving source, two different types of plasma instabilities are excited in the current layer in the same way as the two-dimensional case. The lower hybrid drift instability is observed to grow in the periphery of the current layer, but it cannot penetrate into a high-beta region near the neutral sheet. Instead, a low-frequency electromagnetic (EM) instability is excited at the neutral sheet after saturation of the lower hybrid drift wave. Thus, the interaction between this EM wave and charged particles can cause an anomalous resistivity in the neutral sheet. When an external driving flow exists, collisionless reconnection is triggered by the particle kinetic effect and the anisotropic ion distribution is formed through the anomalous ion heating inside the current layer.

Multiple contraction of gas-discharge plasma in crevice channels

The phenomenon of multiple contraction of gas-discharge plasma in helium and its mixtures with other gases at intermediate pressures (1–100 Torr) within crevice channels has been discovered. This type of plasma instability has been treated within the model which considers plasma as the transverse-laminar medium with different values of differential conductivity. The criterion for the development of instability is found and the expression for the wavelength of the periodic structure formed is obtained.

Propagation angle dependence of radar auroral E-region irregularities

The Sweden and Britain Radar aurora Experiment (SABRE) measures the phase velocity and backscatter amplitude of 1 m wavelength irregularities in the auroral zone E-region. These irregularities are produced by two types of plasma instabilities and theory predicts that the variation in backscatter amplitude with the angle between the electron drift velocity V d and the radar vector k, the so called propagation angle, is different for the two cases. An isotropic angular dependence is expected for gradient drift instabilities, but for the alternative two stream instability process a minimum is produced in the backscatter amplitude for directions orthogonal to the flow. The SABRE data have been averaged to remove small scale fluctuations and for drift velocities less than ~200 ms −1 the backscatter dependence on the propagation angle is isotropic, strongly suggesting that gradient drift processes are dominant. At higher drift velocities anisotropies develop in the angular dependence with deep minima at approximately 90° to the flow and a subsidiary minimum at 0° to this direction. Although these characteristics suggest a two stream instability mechanism, there are features in the experimental data that are not predicted by this simple theory. It is suggested that ion drifts may in part be responsible for these additional features.

Attachment instability in an externally ionized discharge

A new type of plasma instability is described in an electron-beam ionized discharge. This instability occurs in the form of current oscillations in gas mixtures in which the dissociative attachment rate increases strongly with electric field. It has been observed experimentally in He : H2O 74 : 2 and in He : CO2 1 : 1 and 9 : 1 mixtures. A theoretical analysis which describes the onset of instability is presented, and a physical explanation is given. The region of instability in parameter space of ionization source function S and electric field E is presented for certain gas mixtures. The transient phenomena in this type of discharge appear to be controlled by electron attachment, and a theoretical explanation of the observed current overshoot has been provided.

An electron attachment plasma instability

A new type of plasma instability is described in an electron-beam ionized discharge. This instability occurs in gas mixtures in which the dissociative attachment rate increases strongly with electric field. It has been observed experimentally in He:H2O 740:20 and in He:CO2 1:1 and 9:1 mixtures. The values of the ionization source function S and of the electric field E at which the wave instability occurs are predicted using a Fourier analysis of the linearized kinetic rate equations. This yields the condition for instability as S < (1/α)[Eδβ/δE) − β]2, where α is the electron-ion recombination coefficient and β is the electron neutral attachment rate.

Some additional features of radar returns from the equatorial electrojet

This paper reports the results of recent VHF experiments designed to investigate the fine structure of the equatorial electrojet. The results of two separate experiments are reported. The first result shows that during the course of the experiments, except for midday periods, the vertical structure of the echoing region as observed by VHF radar techniques exhibits a pronounced bifurcation. The second experiment demonstrates the existence of movements of irregularities embedded in the electrojet region. The velocity of these movements inferred from the data are seen to be substantially below the velocity ascribed to the plane wave irregularities produced by a two-stream plasma instability which account for the major part of the reflected VHF radar signal. The observed motions may be associated with another type of plasma instability or may possibly be horizontal drifts of large irregularities in the region.