Effect of longitudinal space-charge waves of a helical relativisticelectron beam on the cyclotron maser instability

The influence of the longitudinal space-charge waves of a coherently gyrophased helical relativistic electron beam on the cyclotron maser instability is investigated in a cylindrical waveguide configuration using a three-dimensional kinetic theory. A dispersion relation that includes waveguide effects is derived. The stability properties of the cyclotron maser interaction are examined in detail. It is shown that, in general, the effects of space-charge waves on a coherently gyrophased beam are suppressed in a waveguide geometry, in comparison with an ideal one-dimensional cyclotron maser with similar beam parameters     

The effect of two-magnon scattering on parallel-pump instability threshold

The effect of two-magnon scattering on the threshold field is calculated using the quantum kinetic equations. Such approach makes it possible to improve the existing theory.     

Dissipative instability of a highly relativistic electron beam through the excitation of surface waves on a conducting medium

The possibility of the dissipative instability of a relativistic electron beam streaming near a conducting medium is investigated. The development of this dissipative beam instability through the surface wave excitation slightly disturbs the beam leading to the slightly heating of the conducting medium.     

Dependence of the electron-cloud instability on the beam energy

The electron cloud (EC) can be formed in the beam pipe of a circular accelerator if the secondary emission yield (SEY) of the inner surface is larger than 1, and it can detrimentally affect the circulating beam. Understanding the underlying physics and defining the scaling laws of this effect is indispensable to steer the upgrade plans of the existing machines and the design of new ones. The single bunch EC instability (ECI) is shown to be strongly affected by the transverse beam size. Transversely, smaller beams going through an electron cloud generate higher electron peak densities and lower the intensity threshold to make the beam unstable. In particular, since higher energy beams have smaller transverse sizes (for equal normalized transverse emittances), the scaling of the ECI threshold with the beam energy turns out to be surprisingly unfavorable.     

The character of cyclotron instability of hydromagnetic waves

The method of energy balance is used for calculating the growth rate of hydromagnetic waves ( _H in the regime of a cyclotron resonance. The HM waves are propagated at an angle to the external magnetic field. A tenuous beam of charged particles with a finite Larmor radius penetrating through a cold plasma is assumed to be responsible for the cyclotron instability process.The author is grateful to Assoc. Prof. Dr. A. Hruka CSc. for helpful discussions and remarks concerning the problem. He is also indebted to Mrs. E. Lomecká for the graphical work.     

Effect of a capillary meniscus on the Faraday instability threshold

Threshold for Faraday instability has been experimentally measured for slightly viscous liquids. Changing the size of the container containing the fluid allows us to emphasize the role played by the capillary meniscus on the onset for instability. As the container is getting smaller, an upset of the critical acceleration is observed. Below a given container diameter, eigenmodes are observed along the stability curve. A dissipation term is proposed for considering the viscous dissipation against the walls of the container.     

The dissipative instability of a relativistic electron beam

The theory of the wall instabilities of surface waves excited by an electron beam is developed. Their classification, linear, quasilinear and nonlinear theory is given. It is shown that dissipative instabilities convert practically all the energy lost by the beam into the heating of the lossy walls confining the beam.     

Modulation instability of whistler waves

The Karpman and Krushkal criterion has been applied to nonlinear Schrödinger equation derived for whistler waves propagating through magnetoplasma containing parallel electrostatic field. The role of parallel electrostatic field on the frequency spectrum and growth rate of modulational instability has been discussed.     

Modulational instability of ion-acoustic waves

The modulational instability of ion-acoustic waves in a collisionless plasma is studied taking into account the effect of ion temperature. It is found that the critical wavenumber is strongly dependent upon the ion temperature. In the limiting case of vanishing ion temperature, we recover the result that the modulational instability sets in fork>k _c, where the critical wavenumber isk _c=1.47.     

Nonlinear stabilization of beam instability

If a high-frequency field affects the dielectric properties of the plasma, it can be shown that this results in a dependence of the frequency of natural plasma oscillations on the field amplitude. So, the beam and the excited waves get out of resonance, the instability weakens and sometimes may totally vanish.     

The D'yakov-kontorovich instability of shock waves in real gases

In the 1950s, D'yakov and Kontorovich predicted that under certain conditions perturbed shock waves in nonideal gases can become unstable by emitting undamped sound and entropy-vortex waves. For the last 45 years, though, little progress has been made in the identification and numerical modeling of physical conditions for which this phenomenon might occur. Using a van der Waals equation of state, we present for the first time a dynamical simulation of a D'yakov-Kontorovich instability. The two-dimensional emission pattern of acoustic waves appearing in the simulation agrees with the prediction of a linearized theory.     

The influence of transverse magnetic field on Gunn effect threshold

The effect of magnetic field has been studied on the Gunn effect threshold electric field for short planar Gunn devices. For low magnetic fields, experimental results are in good agreement with the theoretical results but a large increase in threshold electric field has been observed for higher magnetic fields.     

The Rayleigh-Taylor instability and internal waves in quantum plasmas

Influence of quantum effects on the internal waves and the Rayleigh-Taylor instability in plasma is investigated. It is shown that quantum pressure always stabilizes the RT instability. The problem is solved both in the limit of short-wavelength perturbations and exactly for density profiles with layers of exponential stratification. In the case of stable stratification, quantum pressure modifies the dispersion relation of the inertial waves. Because of the quantum effects, the internal waves may propagate in the transverse direction, which was impossible in the classical case. A specific form of pure quantum internal waves is obtained, which do not require any external gravitational field.     

微波谐振腔Q值对磁激子振幅不稳定态阈值的影响

基于Safonov和Yamazaki所发展的激励自旋波非线性辐射衰减的理论［J. MMM. 161 (1996 ) 275］, 考虑磁激子与磁激子以及磁激子与光子的两种非线性相互作用过程，计算了微波谐振腔Q值对磁激子振幅不稳定态阈值的影响，结果与实验数据基本一致. 关键词： 磁激子 谐振器 铁磁体