Origin of current instability in GaAs/AlGaAs heterostructures

We propose a mechanism to explain the electric instability often observed in modulation-doped heterostructures GaAs/AlGaAs when current is passed along the heterostructure layers. The instability is caused by hot electron transport in AlGaAs layer that is not only heavily doped, but also strongly compensated due to the presence of DX-centers. This layer contains a large-scale random potential of significant magnitude, which strongly affects electron transport. The heating of electrons in the percolation cluster net and electron transfer from the cluster into the random potential wells result in the appearance of latent negative differential conductivity causing the current instability. When the instability gives rise to the formation of a high electric field domain, one of the domain walls blocks the current flow through the two-dimensional electron gas. Experimental results supporting this mechanism are given.     

Geodesic mode instability driven by the electron current in tokamak plasmas

Effect of the parallel electron current on Geodesic Acoustic Modes (GAM) in a tokamak is analyzed by kinetic theory taking into the account the ion Landau damping and diamagnetic drifts. It is shown that the electron current modeled by shifted Maxwell distribution may overcome the phase velocity threshold and ion Landau damping thus resulting in the GAM instability when the parallel electron current velocity is larger than the effective parallel GAM phase velocity Rqω. The instability occurs due to its cross term of the current with the ion diamagnetic drift. Possible applications to tokamak experiments are discussed.     

Effect of the return plasma current radial profile on the dynamics of resistive hose instability of a relativistic electron beam propagating in a dense gas-plasma medium

The effect of the return plasma current with a characteristic radius differing from the relevant radius of the current density in a relativistic electron beam on the dynamics of the resistive hose instability of the beam is analyzed. The equations are derived for the linear stage of instability evolution. It is shown that when the return plasma current is broader in the radial direction (as compared to the beam), the resistive hose instability becomes noticeably weaker.     

A New Type Of Terahertz Frequency Range Instability of DC Current in “Thick” Ballistic Field-Effect Transistors

A new type of dc current instability in a ballistic field-effect transistor (FET) is proposed, which emerges due to the finite thickness of the 2D current-carrying channel. The physical origin of the instability in thick ballistic FETs is the nonlocality of the relation between the surface electron density and field potential. The instability arises at wavelengths of the order of the characteristic scale length of this nonlocality, which is determined by the FET geometry and vanishes for infinitesimal thickness of the current-carrying channel. The dispersion equation is derived and the domain of parameters under which the system becomes unstable is determined. Estimates show that this new type of instability is promising for driving a high-gain source of THz radiation.     

Return current instability and its effects on beam-plasma system

The return current induced in a plasma by a relativisitc electron beam generates a new electron-ion two-stream instability (return current instability). Although the effect of these currents on the beam-plasma e-e instability is negligible, there exists a range of wave numbers which is unstable only to return current (RC) instability and not to e-e instability. The electromagnetic waves propagating along the direction of the external magnetic field, in which the plasma is immersed, are stabilized by these currents but the e.m. waves with frequencies,ω ²≪Ω _e ² ≪ω _pe ² (Ω _e andω _pe being cyclotron and plasma frequency for the electrons of the plasma respectively) propagating transverse to the magnetic field get destabilized. Heuristic estimates of plasma heating, due to RC instability and due to decay of ion-acoustic turbulence generated by the return current, are made. The fastest time scale on which the return current delivers energy to the plasma due to the scattering of ion-sound waves by the electrons can be ∼ω _pi ⁻¹ (ω _pi being the plasma frequency for the ions).     

Filamentation Instability in a Current‐Carrying Plasma in the Presence of Quantum Effects

The filamentation instability of a current‐carrying plasma under the diffusion condition is investigated taking into account the Bohm potential and the Fermi electron pressure. Using quantum hydrodynamic equations, the dispersion relation and growth rate of the instability is obtained. It is found that the filamentation instability, in the presence of quantum effects, depends on various characteristic parameters such as: electron Fermi velocity, plasma number density, ion thermal velocity and electron drift velocity. Moreover, the wavelength region in which the instability occurs is more restricted and the minimum size of filaments is larger, in comparison with the classical case. It is also found that the growth rate of the instability is smaller in the presence of quantum effects. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Observations of an ion-driven instability in non-neutral plasmas confined on magnetic surfaces

The first detailed experimental study of an instability driven by the presence of a finite ion fraction in an electron-rich non-neutral plasma confined on magnetic surfaces is presented. The instability has a poloidal mode number m=1, implying that the parallel force balance of the electron fluid is broken and that the instability involves rotation of the entire plasma, equivalent to ion-resonant instabilities in Penning traps and toroidal field traps. The mode appears when the ion density exceeds approximately 10% of the electron density. The measured frequency decreases with increasing magnetic field strength, and increases with increasing radial electric field, showing that the instability is linked to the E x B flow of the electron plasma. The frequency does not, however, scale exactly with E/B, and it depends on the ion species that is introduced, implying that the instability consists of interacting perturbations of ions and electrons.     

激光等离子体不稳定性的入射光强度效应

用3维粒子模拟程序研究了相对论强激光和高密度等离子体相互作用引起的电磁不稳定。数值模拟表明,在线偏振强激光作用下,等离子体表面出现了电磁不稳定性。形成的不稳定结构随时间发展和激光功率密度的增加进一步深入到等离子体内部,最终使等离子体表面处激发饱和自生磁场。这种由电子速度各向异性而产生的自生磁场对激光有质动力推开电子时所形成的电子热流产生抑制作用,并将直接影响电子加速效率。     

Electron-beam induced instability during filamentary current transport inn-GaAs

We report experimental investigations on the current transport ofn-GaAs under the conditions of impact ionization avalanche breakdown at low temperatures. The spontaneous formation of a single current filament was observed by means of low-temperature scanning electron microscopy. An electron-beam induced instability occurs at the onset of filamentation. We demonstrate this instability to be due to the local disturbance at the boundaries of the current filament. Our results are compared to the similar behavior ofn-GaAs under IR irradiation (firing wave instability).     

X-ray backlighting of two-wire Z-pinch plasma using X-pinch

Two 50-μm Mo wires in parallel used as a Z-pinch load are electrically exploded with a pulsed current rising to 275 kA in 125 ns and their explosion processes are backlighted using an X-pinch as an x-ray source.The backlighting images show clearly the processes similar to those occurring in the initial stages of a cylindrical wire-array Z-pinch,including the electric explosion of single wires characterised by the dense wire cores surrounded by a low-density coronal plasma,the expansion of the exploding wire,the sausage instability (m=0) in the coronal plasma around each wire,the motion of the coronal plasma as well as the wire core toward the current centroid,the formation of the precursor plasma column with a twist structure something like that of higher mode instability,especially the kink instability (m=1).     

相对论电子束在等离子体中的能量沉积

 用3维粒子模拟程序LARED-P研究了束-等离子体不稳定性, 不稳定性激发的强电磁场使电子束在非常短的距离内沉积能量。对于10 MeV的单能电子束,束电子数目占总电子数目5％的情况下,最终约损失14％的束能量。推导了等离子体的色散关系,得出了增长率。     

电子束在周期场中的稳定性

本文讨论了强流电子束通过周期性静电场和静磁场的稳定性。说明了圆柱形电子束通过简谐电磁场和周期性非简谐场例如锯齿形,矩形,等腰梯形等静电场的稳定和不稳定区域。将各种场的主要不稳定区进行比较,表明锯齿形场的主要不稳定区宽度最小。指出当空间电荷效应不可略去时,电子束在稳定区内并不是无条件稳定而是有条件稳定的。这与空间电荷电流大小以及电子束的振幅有关。     

On the nonlinear theory of current instability of short-wave drift oscillations

The paper deals with the studies of current instability in the inhomogeneous plasma resulting in excitation of short-wave drift oscillations with a frequency near the low-hybrid resonance.It is shown that the saturation of such an instability is associated with the spectral pumping of oscillations into the short-wave region that occurs due to the modulation instability; and maximum amplitudes of the electrical fields of oscillations are determined. The effective frequency of electron collisions due to current instability is calculated. It is indicated that the diffusion model of the Parker-Sweet magnetic field reconnection modified taking into account the anomalous resistance mechanism studied here leads to the estimate of the magnetopause width being in satisfactory agreement with the experiment.     

Effect of the current rise rate in a relativistic electron beam pulse propagating in the ion focusing regime on the dynamics of ion hose instability

The effect of the current rise rate in a relativistic electron beam pulse propagating in the ion focusing regime on the spatial dynamics of the ion hose instability is considered. Numerical analysis of the formulated equations shows that the lower rate of current rise in the beam pulse at the linear stage of evolution of the instability noticeably reduces the amplitude of hose oscillations.     

Electron current driven ion acoustic standing wave instability

By means of a positively biased grid an electron current driven instability is excited in a single ended Q-machine. The instability shows the behaviour of a half standing ion acoustic wave with nodes at the hot plate and the grid. For high grid biases an increased plasma temperature is found.     

Quantum-size effects on the characteristics of single-electron tunneling

Effects of single-electron tunneling charging and Coulomb blockade in a cluster structure (molecular transistor) with regard to the quantization of electron levels in an island electrode are investigated. The spectrum of electrons is calculated for small disk-shaped clusters. Restrictions connected with the Coulomb instability of the cluster and electron relaxation are introduced in the theory. The current gap and its voltage asymmetry are calculated for single-electron transistors based on small gold clusters. The effect of the cluster shape on the current gap is investigated.     

Secondary instabilities and vortex formation in collisionless-fluid magnetic reconnection

It is shown that the pattern of current layers formed within a magnetic island in the nonlinear phase of magnetic field line reconnection in a collisionless two-dimensional fluid plasma is subject to the onset of a secondary instability, the effect of which increases with decreasing electron temperature. In the cold electron limit the saturation of the island growth is accompanied by a turbulent redistribution of the current layers and by the development of long lived fluid vortices while, in the opposite limit, the current layer structure remains regular.     

Explosive instability in a backward wave oscillator

A plasma filled backward wave oscillator supports Trivelpiece-Gould (TG) and TM modes. The former can be driven unstable by a relativistic electron beam via Cerenkov interaction or by the plasma return current as two stream instability. This unstable TG mode can parametrically couple to a TM mode via a negative energy beam mode giving rise to an explosive instability     

空间电荷效应对阴极微凸起热不稳定性的影响

 由于金属微凸起爆炸电子发射的预发射电流密度一般都超过108 A/cm2,因此必须考虑其空间电荷效应的影响。基于金属微凸起爆炸电子发射起始过程模型,通过理论分析和数值模拟,给出了考虑预发射电流空间电荷效应的微凸起爆炸发射延迟时间随二极管平均电场的变化关系。与不考虑预发射电流空间电荷效应的结果进行对比表明,预发射电流的空间电荷效应可以显著增加金属微凸起的爆炸发射延迟时间。     

Resistive Electrostatic Ion Cyclotron Instability in Plasmas

The stability of electrostatic ion cyclotron waves propagating obliquely with respect to the background magnetic field is studied for collisional, fully-ionized plasmas in which there is a relative field-aligned streaming between electrons and ions. It is found that electron-ion collisions, in conjunction with electron streaming, provides a mechanism for instability. The role of electron streaming is to supply a source of free energy and the role of electron-ion collisions is to restrict the field-aligned mobility of the electrons, thus preventing them from establishing a Boltzmann equilibrium. Ion-ion collisions and finite ion Larmor radius are found to exert a stabilizing influence. The instability is analyzed for both current-carrying plasmas and counterstreaming-beam-plasma systems.