Investigation of Ion Drift Waves in the PSI‐2 Using Langmuir‐Probes

The properties of on drift waves observed in the rotating magnetized plasma column of the PSI‐2 are analysed. Their parallel wave numbers are found to be nearly zero, the measured azimuthal dispersion relation is approximately linear, and the azimuthal phase velocity is nearly equal to the azimuthal on drift velocity. Furthermore, the potential fluctuations always lag behind the density fluctuations with a phase shift slightly below π. A simple analytical model, describing the potential‐and density distribution of the ion drift wave, shows the underlying mechanism of the on drift instability. Finally, a classification of the observed on drift instability is given.     

Drift wave turbulence in a dense semi-classical magnetoplasma

A semi-classical nonlinear collisional drift wave model for dense magnetized plasmas is developed and solved numerically. The effects of fluid electron density fluctuations associated with quantum statistical pressure and quantum Bohm force are included, and their influences on the collisional drift wave instability and the resulting fully developed nanoscale drift wave turbulence are discussed. It is found that the quantum effects increase the growth rate of the collisional drift wave instability, and introduce a finite de Broglie length screening on the drift wave turbulent density perturbations. The relevance to nanoscale turbulence in nonuniform dense magnetoplasmas is discussed.     

The application of homodyne spectroscopy to the study of low-frequency microturbulence in the TEXT tokamak

Summary The wave propagation direction of microturbulence in a tokamak plasma has been accurately measured by application of a new homodyne spectroscopy technique. This method has been used in conjunction with a collective far-infrared laser scattering experiment on TEXT. The low-frequency density fluctuations are observed to propagate primarily in the electron diamagnetic drift direction, however, the broadband spectra also possess an appreciable level of fluctuations traveling in the ion drift direction. Application of the homodyne spectroscopy technique represents an inexpensive and easily implemented alternative to the more technically demanding heterodyne schemes available in the far-infrared.     

Collisionless Drift Waves Ranging from Current‐Driven,Shear‐Modified,and Electron‐Temperature‐Gradient Modes

The specific history of collisionless drift waves is marked by focusing upon current‐driven, shear‐modified, and electron‐temperature‐gradient modes. Studies of current‐driven collisionless drift waves started in 1977 using the Innsbruck Q machine and was continued over 30 years until 2009 with topics such as plasma heating by drift waves in fusion‐oriented confinement and space/astrophysical plasmas. Superposition of perpendicular flow velocity shear on parallel shear intensively modifies the drift wave characteristics through the variation of its azimuthal structure, where the parallel‐shear driven instability is suppressed for strong perpendicular shears, while hybrid‐ion velocity shear cause unexpected stabilization of the parallel‐shear‐modified drift wave. An electron temperature gradient can be formed easily by control of thermionic electron superimposed on ECR plasma, and is found to excite low‐frequency fluctuation in the range of drift waves (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

New drift modes in a nonuniform quantum magnetoplasma

We report the existence of two new drift modes in a nonuniform quantum magnetoplasma. By using the electron and ion fluid velocities deduced from the quantum momentum equations, together with the continuity and Poisson equations, we derive the governing equations for the low-frequency drift modes. The equations are then Fourier transformed to obtain linear dispersion relations, which admit new drift modes. The results are relevant for identifying electrostatic fluctuations that can cause cross-field charged particle transport in an inhomogeneous, ultracold magnetized quantum plasma.     

简单磁镜中热电子等离子体的基本特性

本文叙述了简单磁镜中,热电子等离子体的实验结果。微波在基频共振层击穿气体产生等离子体,二次偕振加热产生热电子环。等离子体激发了低频交换模和漂移波,热电子环对等离子体的扰动有稳定作用。     

Suppression of temperature fluctuations and energy barrier generation by velocity shear

First measurements of temperature fluctuations in a region of high velocity shear show that absolute and normalized fluctuation levels are reduced across the shear layer, a result that is consistent with weak parallel electron thermal conduction in the electron temperature dynamics. The concomitant reduction of temperature, density, and electric field fluctuations reduces the anomalous conducted and convected heat fluxes.     

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.     

Ion velocity shear-induced drift wave and momentum transport in non-Maxwellian magnetoplasma flows

We have investigated the diamagnetic flow in a non-uniform partially ionized plasma with non-Maxwellian electron population to explain the dynamics of ion velocity shear-induced low-frequency drift mode and associated instabilities. The dispersion relations are found, and instability threshold conditions are pointed out along with ion-parallel momentum transport due to drift motion with relative phase shift of fluctuating quantities in a non-conservative system. The real frequencies and instability growth rates are studied numerically and illustrated for typical space and laboratory plasmas. This study should be useful in understanding some aspects of low-frequency time-delayed perturbations with sheared flow leading to drift instabilities and cross-field parallel ion momentum transport in nonuniform magnetoplasmas containing a non-Maxwellian electron population.     

Theory of surface polaritons in n-type silicon in the presence of a dc current,including the electron thermal pressure gradient

A theoretical investigation has been made of the effect of a drift current, including the electron thermal pressure gradient, on surface polaritons in n-type Si. The polariton propagation and drift current directions are taken to be either parallel or antiparallel. Retardation is included, but damping is neglected. The specular reflection approach of Kliewer and Fuchs is used to obtain the polariton dispersion relation. The results show that the drift current and surface polaritons interact, leading to evanescent waves for certain frequencies. However, no wave amplification is obtained.     

Angular momentum transport produced by shear flow driven drift waves in a collisional magnetoplasma

A shear flow instability in a nonuniform partially ionized magnetoplasma has been investigated and the angular momentum transport of charged particles caused by drift waves has been estimated. The angular momentum transport of the electrons and ions is not equal because the system is not conservative. The present investigation should help to understand the origin of fluctuations and associated parallel momentum transport of charged particles in nonuniform laboratory and astrophysical plasmas with sheared ion flow.     

Sources of 1/F noise in gallium arsenide IMPATT diodes

The quasistatic approximation is used to analyze 1/F noise in IMPATT diodes in the static and dynamic (self-oscillating) modes. Sources of 1/F noise are defined in accordance with the fluctuator model: allowance is made for fluctuations of the charge of traps and fluctuations of the electron drift velocity caused by their scattering by traps and metastable neutral centers. It is shown that the fluctuations of the voltage across the diode and the fluctuations of the oscillation frequency are mainly determined by the fluctuations of the trap charge, while the fluctuations of the oscillation amplitude are determined by scattering by neutral centers. A method is developed to determine the intensity of noise sources using the results of measurements of the fluctuations in the static and dynamic modes of IMPATT diodes and a method of checking the model as a whole is checked. Experimental results are presented and these show satisfactory agreement with the calculations. Zh. Tekh. Fiz. 67, 65–70 (August 1997)     

Observation of long-distance radial correlation in toroidal plasma turbulence

This Letter presents the discovery of macroscale electron temperature fluctuations with a long radial correlation length comparable to the plasma minor radius in a toroidal plasma. Their spatiotemporal structure is characterized by a low frequency of ～1-3 kHz, ballistic radial propagation, a poloidal or toroidal mode number of m/n=1/1 (or 2/1), and an amplitude of ～2% at maximum. Nonlinear coupling between the long-range fluctuations and the microscopic fluctuations is identified. A change of the amplitude of the long-range fluctuation is transmitted across the plasma radius at the velocity which is of the order of the drift velocity.     

Sheared Flow Driven Drift Instability and Vortices in Dusty Plasmas with Opposite Polarity

Low-frequency electrostatic drift waves are studied in an inhomogeneous dust magnetoplasma containing dust with components of opposite polarity. The drift waves are driven by the magnetic-field-aligned (parallel) sheared flows in the presence of electrons and ions. Due to sheared flow in the linear regime, the electrostatic dust drift waves become unstable. The conditions of mode instability, with the effects of dust streaming and opposite polarity, are studied. These are excited modes which gain large amplitudes and exhibit interactions among themselves. The interaction is governed by the Hasegawa-Mima (HM) nonlinear equation with vector nonlinearity. The stationary solutions of the HM equation in the form of a vortex chain and a dipolar vortex, including effects of dust polarity and electron (ion) temperatures, are studied. The relevance of the present work to space and laboratory four component dusty plasmas is noted.     

Instationary Electric Fields,Ion Transport and Strong Density Fluctuations in Tokamaks with Dominant Anomalous Electron Transport

A common explanation is given for ion transport and strong broadband density fluctuations in tokamaks as a result of large anomalous electron transport near dominant magnetic surfaces (resp. in small magnetic islands). The main mechanism is local density flattening connected with an anomalous electron transport induced instationary radial electric field, which forces the ions via polarization drift to follow the electrons. For the density flattening process an exact solution of the time-dependent diffusion equation for a linear initial profile over the island width is used. From this we also derive an expression for a temporal growing radial electric field. This positive field reaches its maximum at the density plateau. Strong viscous diffusion or instability-induced transport between high and low electric field regions may now reverse the density flattening. Therefore relaxation oscillations result which may also explain the observed strong density and potential fluctuations in tokamaks. Several details of recent measurements of impurity ion behaviour and density fluctuations in tokamaks may be better explained with the theory given here.     

Generation of a sheared plasma rotation by emission, propagation, and absorption of drift wave packets

Collisional electron drift wave turbulence generates drift wave packet structures with density and vorticity fluctuations in the central plasma pressure gradient region of a linear plasma device. Tracking these packets reveals that they follow an outward directed spiral-shaped trajectory in the (r,θ) plane, are azimuthally stretched, and develop anisotropy as they approach an axisymmetric, radially sheared azimuthal flow located at the plasma boundary. Nonlinear energy transfer measurements and time-delay analysis confirm that structure absorption amplifies the sheared flow. Similar mechanisms likely operate at the edge of confined toroidal plasmas and should lead to the amplification of sheared flows at the boundary of these devices as well.     

Interplay of parallel electric field and trapped electrons in kappa-Maxwellian auroral plasma for EMEC instability

In this paper, propagation characteristics of electromagnetic electron cyclotron(EMEC) waves based on kappa-Maxwellian distribution have been investigated to invoke the interplay of the electric field parallel to the Earth's magnetic field and auroral trapped electrons. The dispersion relation for EMEC waves in kappa-Maxwellian distributed plasma has been derived using the contribution of the parallel electric field and trapped electron speed. Numerical results show that the presence of the electric field has a stimulating effect on growth rate, which is more pronounced at low values of wave number. It is also observed that as the threshold value of trapped electron speed is surpassed, it dominates the effect of the parallel electric field and EMEC instability is enhanced significantly. The electric field acts as another source of free energy, and growth can be obtained even in the absence of trapped electron drift speed and for very small values of temperature anisotropy. Thus the present study reveals the interplay of the parallel electric field and trapped electron speed on the excitation of EMEC waves in the auroral region.     

Comment on the growth of electron trapped drift instability with magnetic shear

Finite parallel wavelength is taken into account to discuss the growth rate of electron trapped drift instability with sheared toroidal magnetic system. The growth rate decreases with shear length for the case of long connection length.     

EAST装置上W波段多道极向相关反射仪的研制

在EAST装置上安装了X模极化W波段多道相关反射仪,用于测量等离子体芯部密度涨落。该诊断利用低损耗(<3dB)多工器将4个不同频率(79.2GHz,85.2GHz,91.8GHz和96GHz)的微波耦合在一起,通过同一个天线发射。反射波由两个极向分离(～5cm)的天线接收,通过下变频技术实现外差测量。通过对两个极向天线接收的信号进行相关分析,获得芯部湍流垂直速度。对2018年低约束模式(L模)放电进行分析发现,在电子回旋共振加热(ECRH)等离子体中,芯部湍流垂直速度在电子逆磁漂移方向。而在注入同向中性束(co-NBI)后,芯部湍流垂直速度变为离子逆磁漂移方向。