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.     

Fast-Wave Resonances near the Ion Cyclotron Frequency

Wave damping has been observed for the fast (compressional) wave at frequencies that are about 10 percent above the second and third harmonics of the ion cyclotron frequency. Preliminary calculations indicate that this shift is the result of collisions. The waves were launched by a 1-turn loop around the cylindrical plasma column and damped in a magnetic beach. The highly ionized hydrogen or deuterium plasma had an average temperature of 2 eV and an average density of about 2.5 × 1020 m-3.     

On the possibility of harmonic operation of cyclotron waveparametric amplifiers

Cyclotron wave amplifiers at the harmonics of the electron cyclotron frequency are investigated. Since the waves on the beam are electrostatic, harmonics are strongly excited in nonrelativistic beams if they are rotating rather than filamentary. These modes at the harmonics can couple to input Cuccia couplers, and pump fields which drive parametric amplification, in very much the same way as they do on filamentary beams at the cyclotron frequency. Harmonic cyclotron wave amplifiers have the possibility of giving rise to a new class of devices at millimeter wave frequencies     

Radiated Electromagnetic Waves in an Inhomogeneous Magnetoplasma near the Upper Hybrid Frequency

Properties of several plasma waves in a wavenumber space are investigated in a hot magnetized plasma. The properties are applied to investigate ray trajectories of radiated electromagnetic waves to an inhomogeneous plasma and mode conversion of the extraordinary mode into electrostatic cyclotron harmonic waves at the upper hybrid frequency layer. The wave fronts of the mode-converted cyclotron harmonie wave from the extraordinary wave are made clear. Furthermore, ray trajectories of radiated cyclotron harmonic waves and the mode-converted extraordinary mode are obtained.     

Cherenkov radiation waves in inhomogeneous dusty plasma

A kinetic theory is employed to study Cherenkov wave in an inhomogeneous dusty plasma. Two different frequency regimes are considered incorporating the plasma species temperatures. The dispersion relation for one-dimensional Cherenkov wave is derived and analyzed. The plasma species temperatures, their cyclotron frequencies, and the plasma density inhomogeneity effect the growth/damping of Cherenkov waves. It is shown that the plasma inhomogeneity contributes to damping of Cherenkov waves.     

Large-signal theory of gyro traveling wave tubes at cyclotronharmonics

A nonlinear theory of gyrotron traveling wave tubes (gyro-TWTs) at cyclotron harmonics has been developed taking into account the electron velocity spread and the possibility of operating with significant Doppler frequency up-shift (CARM operation). It is shown that the orbital efficiency of the relativistic gyro-TWT operating at the second cyclotron harmonic with large frequency up-conversion may exceed 60%. It is also shown that the influence of the axial inhomogeneity of the wave field on the relation between amplitudes of electric and magnetic fields of the wave causes small changes in the efficiency of gyro-TWTs. The results obtained demonstrate the sensitivity of the harmonic gyro-TWT efficiency with respect to electron velocity spread at different axial wave numbers. The expressions for the gain are derived and discussed,     

Landau damping of electrons with bouncing motion in a radio-frequency plasma

One-dimensional particle simulations have been conducted to study the interaction between a radio-frequency electrostatic wave and electrons with bouncing motion. It is shown that bounce resonance heating can occur at the first few harmonics of the bounce frequency (nω_b,n=1,2,3,...). In the parameter regimes in which bounce resonance overlaps with Landau resonance, the higher harmonic bounce resonance may accelerate electrons at the velocity much lower than the wave phase velocity to Landau resonance region, enhancing Landau damping of the wave. Meanwhile, Landau resonance can increase the number of electrons in the lower harmonic bounce resonance region. Thus electrons can be efficiently heated. The result might be applicable for collisionless electron heating in low-temperature plasma discharges.     

Measurements of spatial cyclotron damping in a uniform magnetic field

The dispersion and damping of whistler waves has been measured in an essentially collisionless plasma at frequencies up to 0.92ω_c, the electron cyclotron frequency. The experimental results agree to within ± 10% of the plane wave hot plasma dispersion relation.     

Lower-hybrid absorption at the ion cyclotron harmonics

In the presence of magnetic field gradients, the lower-hybrid wave can be absorbed through linear collisionless damping at the location of cyclotron or cyclotron harmonic resonances acting as singular turning points in the path of the advancing wave-front.     

Generation of cyclotron harmonic waves in the ionosphericmodification experiments

In the present paper, the parametric decay instability of the pump X-mode into electron Bernstein wave (EBW) near second harmonics of electron cyclotron frequency and IBW at different harmonics (ωci; n=2,3,4) is examined. Expressions are derived for homogenous threshold, growth rate and convective threshold for this instability. Applications and relevances of the present investigation to ionospheric modification experiment in the F-layer of the ionosphere as well as during intense electron cyclotron resonance heating in the upcoming MTX tokamak have been given     

Parametric Instability of Surface Waves on the Second Harmonic of Electron Cyclotron Frequency in a Plasma Layer

The parametric instability of surface waves on the second harmonic of electron cyclotron frequency (SWCF) in a plasma filled dielectric wave guide is examined in a kinetic approximation. The studied surface waves are extraordinary polarized modes and propagate across the external steady magnetic field. The amplitude of the electrical pump wave is assumed to be small. Simple expressions for increments of the parametric instability of the SWCF are calculated. The otained results can be used in controlled fusion researches in order to avoid undesirable regimes of plasma periphery heating in that fusion devices which use the resonance electron cyclotron heating method.     

电子迴旋激射不稳定性

本文分析了下述情况下的电子迴旋波的激射不稳定性:当相对性的单能高能电子斜向注入具有背景等离子体的磁场区域内,并且在电子等离子体频率与电子迴旋频率可以比拟时,考虑了背景等离子体密度远大于单能的高能电子的密度,以及与前者相反的两种情况。当单能的高能电子具有弱相对论性效应时,在电子迴旋频率的基频和二次谐波附近,分别有ο模和χ模的不稳定性存在。文中计算了这两种模的增长率,并作了讨论。 关键词：     

Submillimeter wave generation by second harmonic operation of tunable gyrotrons

The gyrotrons developed at the University of Sydney are tunable sources of millimetre and submillimetre radiation. The generation of submillimetre wavelengths requires operation at the second harmonic of the electron cyclotron frequency, or higher. Our latest gyrotron, GYROTRON IVA, has successfully achieved second harmonic operation and obtained frequencies up to 590 GHz (=0.51 mm). The experimental results and conditions for second harmonic operation will be presented. The design of a new gyrotron, GYROTRON V, which is especially optimised for the second harmonic, will also be included.     

Terahertz radiation-induced magnetoresistance oscillations of a high-density and high-mobility two-dimensional electron gas

The terahertz response of a high-density and high-mobility two-dimensional electron gas in 13-nm GaAs quantum wells at frequencies of 0.7 and 1.63 THz has been investigated. Terahertz radiation-induced magnetoresistance oscillations have been discovered. The oscillation maxima coincide with the harmonics of cyclotron resonance. It has been shown that a large number of harmonics (up to the ninth) appear under irradiation at a frequency of 0.7 THz. In this case, the effect is the analogue of microwave-induced oscillations. At a higher frequency, the oscillation amplitude decreases drastically with an increase in the harmonic number. This indicates a transition to the regime of ordinary cyclotron harmonics.     

Electrostatic ion-cyclotron waves in a two-ion component plasma

The excitation of electrostatic ion cyclotron (EIC) waves is studied in a single-ended Q machine in a two-ion component plasma (Ca⁺ and K⁺). Over a large range of relative concentrations of Ca⁺ and K⁺ ions, two modes are excited with frequencies greater than the respective cyclotron frequencies of the ions. The results are discussed in terms of a fluid theory of electrostatic ion cyclotron waves in a two-ion component plasma     

On the low-threshold parametric mechanism of the anomalous power absorption in electron cyclotron resonance heating experiments in toroidal devices

The experimental conditions that facilitate the excitation of parametric decay instabilities upon the electron cyclotron resonance heating of a plasma at the second harmonic extraordinary wave in tokamaks and stellarators and, as a result, make anomalous absorption of microwave power possible have been analyzed. It has been shown that, in the case of a nonmonotonic radial profile of the plasma density, when the beam of electron cyclotron waves passes near the equatorial plane of a toroidal device, the parametric excitation of electron Bernstein waves, as well as the generation of ion Bernstein waves propagating from the parametric decay region to the nearest ion cyclotron harmonic, where they efficiently interact with ions, is possible. The proposed theoretical model can explain the anomalous generation of accelerated ions observed upon electron cyclotron heating in small and moderate toroidal facilities.     

Observation of explosive instability in an electron beam-plasma system

We have observed experimentally the explosive instability of the slow space charge wave of the electron beam and the electrostatic electron cyclotron harmonic wave due to nonlinear wave-particle interaction. These waves interact nonlinearly with the electron beam and grow simultaneously.     

Ion heating with beating electrostatic waves

The nonlinear interaction of a magnetized ion with two beating electrostatic waves (BEW) whose frequencies differ by a cyclotron harmonic can lead, under some conditions [Phys. Rev. E 69, 046402 (2004)], to vigorous acceleration for an ion with arbitrarily low initial velocity. When applied to an ensemble of ions, this mechanism promises enhanced heating over single electrostatic wave (SEW) heating for comparable wave energy densities. The extension of single ion acceleration to heating (SEWH and BEWH) of an ensemble of initially thermalized ions was carried out to compare the processes. Using a numerical solution of the Vlasov equation as a guideline, an analytical expression for the heating level was derived with Lie transforms and was used to show BEWH's superiority over all parameter space.     

Second harmonic generation in scattering of intense beam of radiation by bound electrons near-resonance

Second harmonic generation in near-resonance scattering of intense beams of radiation by bound electrons is investigated by solving the equations of motion exactly to all orders in the intensity of the incident radiation. A two-level model for the atom and a one-mode classical field for the incident radiation is assumed and the rotating wave approximation is taken. It is shown that (i) the second harmonic radiation is an equally spaced triplet, (ii) the middle frequency in these is exactly two times the incident frequency and (iii) the splitting depends on the difference of incident frequency and resonance frequency and on the incident intensity. The counting rates for the three frequencies have been studied in the weak and the high intensity limits.     

Parametrical Instability of Surface Type X-modes Immersed into a Nonmonochromatic Pumping Electric Field

Parametrical excitation of surface type X-modes (STXM) at the second harmonic of electron cyclotron frequency by nonmonochromatic external alternating electric field is under consideration. STXM are the eigenmodes of a planar magnetoactive plasma waveguide structure consisting of a metal wall with dielectric coating and uniform plasma filling. An external steady magnetic field is applied along the plasma interface, so it is perpendicular to the group velocity of the considered extraordinarily polarized waves. Influence of the plasma waveguide parameters on the parametrical instability of the STXM is studied. External alternating electric field is assumed to consist of two fields with different amplitudes and frequencies. A theoretical investigation is carried out using kinetic equation for plasma particles under the conditions of weak plasma spatial dispersion and small amplitudes of external electric fields. The obtained results can be useful for research in branch of edge plasma physics.