Nonlinear amplitude osçillations of absolutely unstable electrostatic ion cyclotron waves in an ion beam-plasma system

We have observed experimentally the amplitude oscillations of absolutely unstable electrostatic ion cyclotron waves in an ion beam-plasma system due to nonlinear interaction between the beam ions and electrostatic ion cyclotron waves.     

Ion-beam-excited electrostatic ion cyclotron waves

Self-excited electrostatic ion cyclotron waves were observed in an ion-beam-plasma system produced in a DP-operated Q-machine. The frequency of the waves showed the theoretically predicted variation with the magnetic field.     

Production of nonisothermal electrons and Langmuir waves because of colliding ion holes and trapping of plasmons in an ion hole

We present new simulation studies exhibiting production of nonisothermal electron distributions and Langmuir waves by colliding ion holes and trapping of plasmons in an ion hole. We find that, during head-on ion hole collisions, streams of accelerated electrons are produced by the electrostatic potentials supporting the ion holes. Subsequently, Langmuir waves are excited by a two-stream instability involving energetic electron beams. The resulting Langmuir waves can be trapped in an ion hole. The present ion-hole-Langmuir wave interactions are unique kinetic phenomena which can be dealt with a Vlasov code, which we developed recently. The results can have relevance to the understanding of particle and field data that are forthcoming from different spacecraft missions in Earth's auroral ionosphere and the magnetosphere.     

Absolute and convective instabilities of electrostatic ion cyclotron waves excited in an ion beam-plasma system

Experimental results are presented for the observation of the absolute and convective instabilities of the electrostatic ion cyclotron waves excited in an ion beam-plasma system.     

Laser-generated waves and wakes in rotating ion crystals

Locally excited plasma waves are generated in a Coulomb crystal by "pushing" with radiation pressure on a rotating cloud of laser-cooled 9Be+ ions. The waves form a stationary wake that is directly imaged through the dependence of the ion fluorescence on Doppler shifts, and theoretical calculations in a slab geometry are shown to accurately reproduce these images. The technique demonstrates a new method of exciting and studying waves in cold ion clouds.     

Behaviors of absolute instabilities of electrostatic ion cyclotron waves in an ion beam-plasma system

Experimental results are presented for behaviors of the temporal growth and the threshold beam density of the absolute instability of the electrostatic ion cyclotron waves excited in an ion beam-plasma system, and compared with the linear theory.     

Selective ion heating by energetic ion beam injection into a plasma

High energy neutral beam injected into a plasma has been predicted to be susceptible to microinstabilities. If the growth time of these microinstabilities is shorter than the collisional relaxation time, then the energy transfer from the beam to the plasma may take place, in the initial phase, by collisionless wave-particle interaction. We report here an experiment where this effect has indeed been observed. Here ion Bernstein waves excited by an energetic ion beam lead to selective ion heating of the plasma in a collisionless manner.     

Nonturbulent stabilization of ion fluxes by the fan instability

Resonant interactions between energetic ion fluxes and wave packets they excite through fan instability are studied using self-consistent 3D simulations to explain the nonlinear wave–particle mechanisms at work and to estimate the energy lost by the flux and its sharing between wave emission and particle heating. The saturation of waves and the relaxation of particles are studied over long time periods. The ions are not only diffusing in the waves but are also trapped simultaneously by several potential wells of large amplitude overlapping waves. Estimates of the ion heating energy and rate are given and compared with space observations.     

钠离子和钾离子通道噪声扰动对神经网络 时空模式的影响

研究了钠离子和钾离子通道噪声扰动对Hodgkin-Huxley神经网络放电时空模式的影响. 发现无论钠离子通道噪声还是钾离子通道噪声扰动, 当取定一组温度、噪声强度, 随着耦合强度的增大, 神经网络放电时空斑图总能演化出螺旋波, 而且存在形成螺旋波所需的临界耦合强度. 分析发现钠离子通道噪声有利于神经网络螺旋波的形成, 而钾离子通道噪声不利于螺旋波形成. 结果还表明较低的温度能够使神经网络对噪声更加敏感. 最后, 讨论了特定参数下螺旋波与靶波之间的转化现象.     

Obliquely propagating dust-density plasma waves in the presence of an ion beam

Self-excited dust-density waves are experimentally studied in a dusty plasma under microgravity. Two types of waves are observed: a mode inside the dust volume propagating in the direction of the ion flow and a new mode propagating obliquely at the boundary between the dusty plasma and the space-charge sheath. A model for dust-density waves propagating at an arbitrary angle with respect to the ion-flow direction is presented, which explains the preference for oblique or parallel modes as a function of ion velocity.     

Sounding rocket measurements of suprathermal ion acceleration

Transverse ion acceleration has been observed at rocket altitudes between 500 and 1000 km due to the injection of 100-200-eV argon plasma, auroral electron precipitation, and the injection of electromagnetic waves. Field-aligned currents necessary to neutralize the plasma injection payloads and those naturally occurring in the aurora could be responsible for the ions observed in the first two observations. Associated with the aurora, both bulk heating and tail heating are observed, sometimes simultaneously. In this case, either different masses are accelerated and/or different mechanisms are responsible. The bulk heating is closely correlated with the aurora structure while tail heating is not so well correlated. High-time-resolution rocket ion data have revealed that the transverse acceleration process is of very short duration (~100 ms) and occurs in a very limited volume (a few hundred kilometers along B and on the order of the ion gyrodiameter across B). Such impulse acceleration events are correlated with waves near the lower hybrid resonance. Wave injections of electromagnetic waves near the lower hybrid frequency result in the transverse acceleration of ambient ions     

Stability of electrostatic ion cyclotron waves in a multi-ion plasma

We have studied the stability of the electrostatic ion cyclotron wave in a plasma consisting of isotropic hydrogen ions (H⁺) and temperature-anisotropic positively (O⁺) and negatively (O⁻) charged oxygen ions, with the electrons drifting parallel to the magnetic field. Analytical expressions have been derived for the frequency and growth/damping rate of ion cyclotron waves around the first harmonic of both hydrogen and oxygen ion gyrofrequencies. We find that the frequencies and growth/damping rates are dependent on the densities and temperatures of all species of ions. A detailed numerical study, for parameters relevant to comet Halley, shows that the growth rate is dependent on the magnitude of the frequency. The ion cyclotron waves are driven by the electron drift parallel to the magnetic field; the temperature anisotropy of the oxygen ions only slightly enhance the growth rates for small values of temperature anisotropies. A simple explanation, in terms of wave exponentiation times, is offered for the absence of electrostatic ion cyclotron waves in the multi-ion plasma of comet Halley.     

Radiation of ion acoustic waves in a dispersive positiveion-negative ion plasma

Experimental results that illustrate some properties of the radiation of a longitudinal ion acoustic wave launched from a solid metal disk antenna inserted in a dispersive positive-ion-negative-ion plasma are presented. The negative ions replace the free electrons in the plasma and increase the electron Debye length, hence increasing the dispersion of the plasma. It is observed that the radiation of waves in a dispersive media is significantly more complicated than in a nondispersive media. It is not possible to draw one universal radiation pattern for the radiation of the waves in this case, since so many frequency components are present in the wave and they change as the wave evolves     

Effect of finite ion temperature on modulational instability of ion-acoustic waves

A nonlinear Schrödinger equation for ion-acoustic waves in a collision free plasma, consisting of warm ions and hot isothermal electrons is derived using the KBM method. It is found that for finite ion temperature these waves are modulationally unstable only in a range of wave numbers. As the ratio of ion to electron temperature increases, the range of the unstable region decreases and shifts towards small wave numbers.     

The ion cyclotron resonator in the magnetosphere

Our concern here is to present the idea of the ion cyclotron resonator in the planetary magnetosphere and to discuss briefly the experimental status of the corresponding theory. The resonator confines the ion cyclotron waves to a thin equatorial zone, so that it keeps the wave field from coming into contact with the ionosphere, resulting in a decrease in energy losses. The properties of the resonator are illustrated by adopting a plausible distribution of the magnetic field in the equatorial zone, which yields an expression for the discrete spectrum of the waves just above the gyrofrequency of heavy ions. We show that the resonator is remarkable for many reasons, including the frequency dependence of its size and specific structure of the spectrum.     

二维热离子等离子体中离子声孤波的相互作用

通过使用推广的 Poincar-Lighthill-Kuo 摄动方法,研究了二维热离子等离子体中两个沿不同方向传播的离子声孤波的相互作用,得到了两个分别描述沿ξ和η方向传播的孤波的KdV方程以及两个孤波以任意夹角碰撞后的相移和轨道.同时还研究了离子温度比σ、热容比γ和碰撞夹角α对孤波相移的影响.研究表明,这些参量可以明显地改变孤波的相移,且在该系统中存在压缩型孤波. 关键词： 热离子等离子体 离子声孤波 Poincar-Lighthill-Kuo方法 相移     

Head-on collision of ion acoustic solitary waves in electron-positron-ion plasma with superthermal electrons and positrons

The head-on collision of ion acoustic solitary waves are studied in an electron-positron-ion plasma composed of superthermal electrons, superthermal positrons, and cold ions using the extended Poincaré-Lighthill-Kuo (PLK) method. The effects of the ratio of electron to positron temperature, the spectral index of electron and positron, and the concentration of positron component on the phase shift are studied. It is found that the presence of superthermal electrons and superthermal positrons play a significant role on the collision of ion acoustic solitary waves. It is also been observed that the temperature ratio plays a significant role on the collision of ion acoustic solitary waves.     

Threshold of ion cyclotron parametric instability in a multispecies plasma

Experimental and theoretical studies are presented of ion cyclotron parametric instability into two electrostatic ion cyclotron waves in a multispecies plasma. The instability threshold obtained experimentally is in reasonable agreement with that predicted theoretically.     

On collisionless damping of ion acoustic waves

Exact theoretical treatments show that the damping of ion acoustic waves in collisionless plasmas does not vanish when the derivative of the undisturbed distribution function at the phase velocity equals zero.     

Acceleration of dust grains by means of the high energy ion beam

The acceleration of charged dust grains by a high energy ion beam is investigated by obtaining the dispersion relation. The Cherenkov and cyclotron acceleration mechanisms of dust grains are compared with each other. The role of dusty plasma parameters and the magnetic field strength in the acceleration process are discussed. In addition, the stimulated waves by an ion beam in a fully magnetized dust–ion plasma are studied. It is shown that these waves are unstable at different angles with respect to the external magnetic field. It is also indicated that the growth rates increase by either increasing the ion and dust densities or decreasing the magnetic field strength. Finally, the results of our research show that the high energy ion beam can accelerate charged dust grains.