Instability of Electromagnetic Ion Cyclotron Harmonic Waves in Plasmas

The stability of electromagnetic ion cyclotron harmonic waves propagating normal to an external magnetic field is studied for plasmas whose ions possess loss cone type velocity distributions. It is found that, if the ions are stationary, no instability develops except in the extreme case when the ratio of parallel to perpendicular "temperatures" of the ions is of the order mi/me, where mi and me are the ion and electron masses respectively. However, for the case of two counterstreaming ion beams in a neutralizing background of electrons, instability at zero frequency and near the first several ion cyclotron harmonics can occur if the streaming velocity is of the order of the electron thermal speed.     

Parametric Mechanism of Anomalous Microwave Power Absorption in Experiments on Electron Cyclotron Heating in Toroidal Magnetic Traps

The nonlinear stage of the parametric decay instability of an extraordinary wave is analyzed in the presence of a nonmonotonic density profile. The decay excites an electron Bernstein wave, which is localized in the vicinity of a local density maximum, and an ion Bernstein wave, which leaves a nonlinear interaction region and is absorbed by ions in the vicinity of the harmonics of the ion cyclotron frequency. The main mechanism of instability saturation is considered to be a cascade of decays of a primary daughter electron Bernstein wave, which leads to the excitation of localized secondary electron Bernstein waves and ion cyclotron (Bernstein) waves. The localization of electron Bernstein waves causes a significant decrease in the secondary- decay excitation threshold, which is thought to provide saturation of the primary instability at the lowest level. The saturation of the primary parametric decay instability of a pump wave and the anomalous absorption of the pump power are analytically estimated. A numerical simulation is performed using the parameters that are typical of the experiments on the electron cyclotron resonance heating of plasma at the second resonance harmonic in TCV tokamak.     

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.     

Ion cyclotron production by a four-wave interaction with a helicon pump

Ion cyclotron waves at approximately 0.7 the ion gyrofrequency have been observed experimentally in the large volume helicon reactor WOMBAT. These waves are highly localized along the axis of the device where a 8 cm diameter, 2 m long. Ar II plasma column is produced. Spectral measurements reveal a four-wave interaction where energy is down-converted to the ion cyclotron mode from the helicon pump. The experimental results are explained in terms of a filamentation type instability.     

Eigenoscillations of the ion cyclotron beam-whistler turbulence excited in collisionless parallel shock waves

Eigenstructures and growth rates are obtained for the ion cyclotron beam-whistler plasma instability near the leading edge of a shock wave propagating along the magnetic field.     

等离子体高频不稳定性的高阻抗探针测量

采用高阻抗探针，测量了热电子等离子体的高频扰动，扰动频率与外磁场的关系及爆发区域匠实验观察表明，高频扰动为离子漂移回旋不稳定性。     

Stochastic heating of ions in a modulated electron beam-plasma system

A modulation of an electron beam density at frequencies lower than an ion cyclotron frequency enhanced the low frequency instability of broad band and heated plasma ions in a beam-plasma system. The heating of ions is explained by the stochastic process of a weakly turbulent plasma.     

Nonlinear Effects Related to the Simultaneous Excitation of Three Instabiities in Magnetized Plasma

Experimental results are presented on the nonlinear effects related to the simultaneous excitation of three low‐frequency instabilities in the magnetized plasma column of a Q‐machine, namely the potential relaxation instability, the electrostatic ion‐cyclotron instability and the Kelvin‐Helmholtz instability. The influence of electron drift and magnetic field intensity on appearance, dynamics and mutual interaction of these instabilities was investigated (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On a new scenario for the saturation of the low-threshold two-plasmon parametric decay instability of an extraordinary wave in the inhomogeneous plasma of magnetic traps

The most probable scenario for the saturation of the low-threshold two-plasmon parametric decay instability of an electron cyclotron extraordinary wave has been analyzed. Within this scenario two upperhybrid plasmons at frequencies close to half the pump wave frequency radially trapped in the vicinity of the local maximum of the plasma density profile are excited due to the excitation of primary instability. The primary instability saturation results from the decays of the daughter upper-hybrid waves into secondary upperhybrid waves that are also radially trapped in the vicinity of the local maximum of the plasma density profile and ion Bernstein waves.     

A phase-imaging technique for cyclotron-frequency measurements

A novel approach to mass measurements at the 10^?9 level for short-lived nuclides with half-lives well below one second is presented. It is based on the projection of the radial ion motion in a Penning trap onto a position-sensitive detector. Compared with the presently employed time-of-flight ion-cyclotron-resonance technique, the novel approach is 25-times faster and provides a 40-fold gain in resolving power. Moreover, it offers a substantially higher sensitivity since just two ions are sufficient to determine the ion’s cyclotron frequency. Systematic effects specific to the technique that can change the measured cyclotron frequency are considered in detail. It is shown that the main factors that limit the maximal accuracy and resolving power of the technique are collisions of the stored ions with residual gas in the trap, the temporal instability of the trapping voltage, the anharmonicities of the trapping potential and the uncertainty introduced by the conversion of the cyclotron to magnetron motion.     

Current-Driven Kink-Like Instability in Collisional Plasmas

The stability of left-hand circularly polarized waves propagating along an external magnetic field with wavelengths much larger than the ion Larmor radius is studied for fully-ionized collisional plasmas carrying a field-aligned current. It is found that, in the presence of electron-ion collisions, this "kink-like" instability has two branches of unstable wavenumbers: a main branch and a resistive branch. The resistive branch owes its existence to electron-ion collisions, but its growth rate is much smaller than that of the main branch, which is typically some fraction of the ion cyclotron frequency. The effect of collisions on the main branch is to reduce its maximum growth rate while extending the range of unstable wavenumbers to larger values. However, these changes are significant only when the electron-ion collision frequency is comparable to the electron cyclotron frequency. The dispersion relation is solved numerically for plasma and magnetic field parameters appropriate to the UCLA arcjet plasma. The results show that, within the framework of an infinite and homogeneous theory, the kink-like instability should occur in this plasma device.     

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.     

The dispersion relation of the charge and current compensated relativistic electron beam-plasma system

Analysing the general dispersion relation numerically, the unstable regions of the relativistic electron-beam plasma system were determined. The external parameters were varied to ensure more effective instability excitations. The full charge and current compensation presumptions lead to new synchronism predictions. The return current's slow space charge wave and return current's slow cyclotron wave are synchronous with the plasma ion wave.     

On the Resistive Electromagnetic Ion Cyclotron Instability

An investigation is made on the conditions for validity of the analytical results for the resistive electromagnetic ion cyclotron instability discussed in a recent paper by Lee and Luhmann. The regions of validity in wavenumber space are determined numerically for various conbinations of plasma density, magnetic field, and electron drift velocity. It is concluded that the analytical results are good approximations over a large region of wavenumber space.     

离子通道回旋电子注受激辐射非线性理论

文中对散射波自洽增长的时间响应进行了数值模拟计算,研究了离子密度、电子注入射能量对电磁散射波的功率、频率以及工作效率的非线性影响 关键词： 电磁辐射 非线性 高功率毫米波源 等离子体     

Stability of second harmonic minority heating in magnetic mirror systems

A dispersion relation has been derived to study the stability of ion cyclotron (IC) propagation at the second harmonic of the minority component deuterium in a mirror confined plasma that has hydrogen as the majority species. We have worked in the frame of the majority ions; our dispersion relation can thus be used to study IC propagation in a single ion plasma also. Analysis of the dispersion relation yields two modes — one below and the other above the ion gyro-frequency Θ_H of hydrogen. The expression for the growth rate is used to explicitly show that an instability can arise in the plasma when the loss-cone indexj⩾3; this instability being a result of the coalescing of the two modes supported by the plasma. Unfortunately, the minority component deuterium does not decrease this instability and thus the proposed scheme of IC heating at the second harmonic of the minority component seems unsuited to mirror devices.     

托卡马克等离子体逃逸放电中的驰豫振荡与电子回旋激射不稳定性

我们研究了托卡马克等离子体进制电子引起的电子回旋激射不稳定性发生的条件，发现由反常多普勒效应及切伦科夫效应确定的准稳态速度分布又会激发电子回旋激射不稳定性，且其对本底电子回旋辐射的放大频段低于回旋频率，这与ＨＬ－１实验观察一致。     

Electromagnetic Instability in Counterstreaming Collisional Plasmas in a Magnetic Field

The stability of low frequency electromagnetic waves is studied for collisional, counterstreaming plasmas situated in a steady magnetic field. Based on the cold fluid equations, it is found that obliquely propagating waves are unstable when the parallel component of the phase velocity is smaller than the electron streaming velocity. The frequency of the instability is of the order of but always smaller than the ion cyclotron frequency. The growth rate is proportional to the electron-ion collisional frequency.     

束—等离子体放电中低频等离子体波的非稳定性研究

本文采用非中性冷等离子体模型,研究了沿磁场入射的电子束和等离子体相互作用引起的低频等离子体波的非稳定性。计算表明,在束-等离子体放电情况下,振动频率和增长率都随电子束密度增加而增加,当束电流一定时,它们随l增加而略有增加。l=1时其频率数量级与离子迴旋频率相同。l≥3时,振动频率几乎不随k_z变化,其振动频率和增长率数量级与低混杂振荡频率相同,实质是低混杂漂移非稳定性。理论结果与实验一致。     

Low-threshold absolute parametric decay instabilities in experiments on electron cyclotron resonance heating in tokamaks

We have analyzed experimental conditions for the excitation of absolute parametric decay instabilities accompanying the electron cyclotron resonance heating (ECRH) of plasma at the second harmonic of resonance in tokamaks. It has been shown that, in the case of a nonmonotonic radial profile of the plasma density, when a heating beam passes near the equatorial plane of a tokamak, the parametric excitation of resonances of ion Bernstein waves accompanied by the generation of the backscattered microwave radiation can occur. The threshold of absolute instability thus developed is determined by the dissipation of an ion Bernstein wave and can be exceeded in current experiments on the ECRH of a plasma in tokamaks.