ELECTROSTATIC WAVE EXCITATION BY LITHIUM ION BEAM IN UPSTREAM RECION OF AMPTE LITHIUM RELEASES

It is shown that the electron cyclotron harmonic waves and the ion acoustic broad band obsefved in the transition region and the upstream region of the two AMPTE lithium releases can be explained ,by the interaction of the lithium ion beams and the solar wind plasmas.The cycloidal motion of the freshly produced lithium ion in the solaz wind magnetic and electric fields is essential for these wave excitations.Two simplified models in ion velocity distribution are used in the dispersion relation analysis,one is an orientating ion beam, the other is an ion beam ring (the hollow beam).It is shown that the electron cyclotron. harmonics can be effectively excited by both of these beams if they are very cold. Satisfactory consistence of the theory with the observed results is obtained for the harmonic excitations.The strong Iow frequency (much less than the electron cyclotron frequency) noices might be multioriginal.It is also proposed that the interaction of the lithium ion beam and the solar wind protons provides a suitable mechanism for exciting these broad bands.     

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,     

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     

Overlapping of resonances and stochasticity of electron trajectories in cyclotron masers

When an electromagnetic (EM) wave has a large amplitude and electrons have a large energy, the electron cyclotron frequency in the process of interaction with an EM wave can vary significantly. This can lead to overlapping of cyclotron resonances at different harmonics. It is shown that such an overlapping causes the stochasticity of electron orbits. Estimates show that this effect can be present in relativistic gyrodevices currently under development for driving future accelerators.     

Excitation of ion cyclotron waves at the difference frequency of two microwave beams in a semiconductor

This paper presents an investigation of the resonant excitation of the electrostatic ion cyclotron wave at the difference frequency of two microwave beams propagating in a magnetoactive solid state plasma, viz. n InSb. The resonant excitation of the electrostatic ion cyclotron wave occurs when the difference frequency of the two microwave beams and the difference of their propagation vectors satisfy the dispersion relation corresponding to the electrostatic ion cyclotron wave. For typical plasma parameters of n InSb and microwave beams of power densities 1 MW cm^?2, the power density of the excited ion cyclotron wave is 0.40 kW cm^?2 when external magnetic field is $\text{1.46 kG (}\text{Ω}{}_{\mathrm{c}}\text{ω}\text{) = 0.1)}$. The power density of the excited ion cyclotron wave increases with the magnetic field. This study may provide new means for the characterisation and diagnostic of semiconductors.     

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.     

Submillimeter wave induced resistance oscillations in ultra-high mobility two-dimensional electron systems

Submillimeter wave induced resistance oscillations in two ultra-high mobility GaAs/Al_0.24Ga_0.76As quantum well samples have been investigated by means of a backward wave oscillator and far-infrared laser at ³He temperatures. Subnikov–de Haas oscillation, submillimeter wave induced resistance oscillation, and magnetoplasmon resonance occur simultaneously in this frequency regime. The primary radiation induced resistance minimum shifts toward cyclotron resonance with increasing radiation frequency. The positions of these minima agree well with those of the magnetoplasmon resonance. The higher-order harmonics of the resistance oscillation remain around the multiples of the cyclotron resonance frequency. An in situ transmission measurement exhibits an asymmetric broadening of the cyclotron resonance, appearing as a combination of the cyclotron resonance and the magnetoplasmon resonance, but no features directly linked to the microwave induced resistance oscillation can be seen.     

Effective Co-generation of opposite and forward waves in cyclotron-resonance masers

A novel type of the frequency-tunable oscillator based on simultaneous generation of the forward and opposite waves at the same frequency, but at different cyclotron harmonics, is proposed. A spatially periodic helical electron beam allows for strong coupling of the waves. The opposite wave provides the broadband feedback and electron bunching, whereas the forward wave amplifies the arising signal and withdraws the rf power from the interaction region. A 15% efficiency and 5% frequency bandwidth have been achieved in the first experiment.     

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.     

Cooperation of traveling and quasi-cutoff waves in a cyclotron-resonance maser

A new version of a cyclotron-resonance maser is studied theoretically and experimentally. Here, a spatially periodic helical electron beam couples traveling (autoresonance) and quasi-cutoff (gyrotron) waves of the same frequency, interacting with them at different cyclotron harmonics. The theory and early experimental results show that this maser can effectively generate a traveling wave with low quasi-cutoff wave excitation losses using a very simple feedback system.     

Collective and single-electron interactions of electron beams with electromagnetic waves,and free-electron lasers

The field of radiation emission from electron beams is reviewed with special reference to work related to free-electron lasers. Different schemes of interaction in periodic structures, electromagnetic slow-wave structures, and in transverse confining force are distinguished. Various effects and devices such as traveling wave amplifiers, Smith-Purcell radiators, Cerenkov and bremsstrahlung-free electron lasers, cyclotron resonance masers, coherent bremsstrahlung and channeling radiation are discussed and the differences and relations among them are explained. A simple comprehensive model is developed to describe electron-beam interaction with an electromagnetic wave in periodic electromagnetic structures. The model is general enough to describe both collective and single-electron modes of interaction and quantum mechanical, classical and Fermi degenerate regimes. Simplified expressions are developed for the gain by stimulated emission of radiation and for gain conditions of the Smith-Purcell-Cerenkov type free-electron lasers under conditions of very thin electron beams and infinite interaction length. This research is supported by the Air Force Office of Scientific Research under contract AFOSR-76-2933     

Induced radiation of electrons moving in a magnetic field

The problem is considered of the induced radiation of electrons moving in a homogeneous and constant magnetic field under irradiation by an electromagnetic wave of frequency . It is shown that in the case when the electrons have relativistic velocities it is in principle possible to obtain power amplification of the electromagnetic field at the higher harmonics of the cyclotron frequency.     

Forming of Space Charge Wave with Broad Frequency Spectrum in Helical Relativistic Two-Stream Electron Beams

We elaborate a quadratic nonlinear theory of plural interactions of growing space charge wave(SCW) harmonics during the development of the two-stream instability in helical relativistic electron beams. It is found that in helical two-stream electron beams the growth rate of the two-stream instability increases with the beam entrance angle. An SCW with the broad frequency spectrum, in which higher harmonics have higher amplitudes, forms when the frequency of the first SCW harmonic is much less than the critical frequency of the two-stream instability.For helical electron beams the spectrum expands with the increase of the beam entrance angle. Moreover,we obtain that utilizing helical electron beams in multiharmonic two-stream superheterodyne free-electron lasers leads to the improvement of their amplification characteristics, the frequency spectrum broadening in multiharmonic signal generation mode, and the reduction of the overall system dimensions.     

Upconversion of whistler waves by gyrating ion beams in a plasma

A gyrating ion beam, with a ring-shaped distribution in velocity, supports negative energy beam modes near the harmonics of beam gyro-frequency. An investigation of the non-linear interaction of high-frequency whistler waves with the negative energy beam cyclotron mode is made. A non-linear dispersion relation is derived for the coupled modes. It is shown that a gyrating ion-beam frequency upconverts the whistler waves separated by harmonics of beam gyro-frequency. The expression for the growth rate of whistler mode waves has been derived. In Case 1, a high-amplitude whistler wave decays into two lower frequency waves, called a low-frequency mode and a side band of frequency lower than that of pump wave. In Case 2 a high-amplitude whistler wave decays into two lower frequency daughter waves, called the low-frequency mode and whistler waves. Generation mechanism of these waves has application in space and laboratory plasmas.     

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.     

Higher Harmonic Operations of Submillimeter Wave Gyrotrons (Gyrotron FU Series)

Higher harmonic operation of gyrotrons is necessary to obtain high frequencies. Some gyrotrons included in the Gyrotron FU series developed at Fukui University have achieved operation at the third and even fourth harmonics of the electron cyclotron frequency. The output lies in the millimeter to submillimeter wavelength range and the output powers are several watts to several tens of watts. In this paper, the gyrotrons and the conditions under which they operate are described in detail.     

Damped cyclotron harmonic waves at oblique propagation

The dispersion relation of CHW at oblique propagation in a wave magenetoplasma exhibits many damped roots between two successive cyclotron harmonics. The two less damped are those obtained by Tataronis and Crawford.     

Theory of second-order cyclotron resonance as related to the origin of discrete VLF emissions in the magnetosphere

Recent analytical and numerical results concerning the role of the second-order cyclotron resonance effects in formation of discrete emissions in the magnetosphere are reviewed. Peculiarities of whistler cyclotron interactions with energetic particles having sharp (step-like or beam-like) distribution functions evolving in space and time are studied. Formation of such distributions is considered, and an analytical self-consistent theory of the second-order cyclotron resonance effects is developed. In particular, characteristics of electron beams produced by the interaction of a VLF wave packet from a ground-based transmitter are studied. It is shown that spatial and temporal gradients of the parallel velocity of the beams formed can be opposite to the case of a pure adiabatic motion of a single particle. Such a behavior can be significant for the generation of secondary emissions. It is proven that the optimal conditions for the instability occur for a nonstationary quasi-monochromatic wavelets whose frequency changes in time. The theory developed permits one to estimate the wave amplification and spatio-temporal characteristics of these wavelets. Numerical results on beam formation and generation of secondary emissions are presented. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 8, pp. 713–727, August 1999.     

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.