共查询到20条相似文献,搜索用时 15 毫秒
1.
I.O. Girka 《等离子体物理论文集》2001,41(1):33-44
Distribution of electromagnetic wave fields within the local Alfven resonance is studied under the resonant condition such that a period of the fundamental harmonic of radio ‐ frequency wave in the axial direction is twice as large as the period of the steady bumpy magnetic field. Account for the ripples of the steady magnetic field is shown to remove infinite discontinuity of the wave fields, that takes place in straight magnetic field. Arising of the gap in the Alfven continua caused by the ripples is discussed. 相似文献
2.
LaRose Alan R. Tang Ting-wei Caron Paul R. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1974,2(4):291-296
An experiment is described in which an electromagnetic wave (extraordinary mode) is propagated across a magnetized plasma and second harmonic generation is detected. The generation of the plasma and the second harmonic wave is associated with resonant conditions of electron cyclotron resonance and upper hybrid resonance. By adjusting the intensity of axial magnetic field, the second harmonic generation can be made solely due to the electron cyclotron resonance, the upper hybrid resonance or both. The experiment is qualitatively in agreement with previous similar experiments and can be explained in terms of the spatial variations of the magnetic field intensity and the electron number density. A technique for diagnosing peak number density is developed from the observed second harmonic power characteristics. 相似文献
3.
Sh. M. Khalil F. Sharaf B. F. Mohamed 《International Journal of Theoretical Physics》1993,32(11):2053-2058
The nonlinear generation of second harmonic electromagnetic waves in a thin inhomogeneous (dense and rarefied) plasma layer (of lengthd) by obliquely and normally incident light waves is analyzed. We consider the effect of an external time-dependent magnetic field on the generation and amplification of waves. Two cases are considered, when the magnetic field oscillates at a frequency (i) equal to and (ii) double that of the incident wave. For normal incidence, waves are not radiated in case (i), while in case (ii) the second harmonics are radiated equally from the plasma boundaries atx=0 andx=d. For a rarefied plasma, the second harmonics are radiated with equal amplitudes in both cases. 相似文献
4.
Tseitlin M Eaton SS Eaton GR 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,209(2):277-281
Selection of the amplitude of magnetic field modulation for continuous wave electron paramagnetic resonance (EPR) often is a trade-off between sensitivity and resolution. Increasing the modulation amplitude improves the signal-to-noise ratio, S/N, at the expense of broadening the signal. Combining information from multiple harmonics of the field-modulated signal is proposed as a method to obtain the first derivative spectrum with minimal broadening and improved signal-to-noise. The harmonics are obtained by digital phase-sensitive detection of the signal at the modulation frequency and its integer multiples. Reconstruction of the first-derivative EPR line is done in the Fourier conjugate domain where each harmonic can be represented as the product of the Fourier transform of the 1st derivative signal with an analytical function. The analytical function for each harmonic can be viewed as a filter. The Fourier transform of the 1st derivative spectrum can be calculated from all available harmonics by solving an optimization problem with the goal of maximizing the S/N. Inverse Fourier transformation of the result produces the 1st derivative EPR line in the magnetic field domain. The use of modulation amplitude greater than linewidth improves the S/N, but does not broaden the reconstructed spectrum. The method works for an arbitrary EPR line shape, but is limited to the case when magnetization instantaneously follows the modulation field, which is known as the adiabatic approximation. 相似文献
5.
Experimental conditions under which the low-threshold absolute parametric decay instability of an electromagnetic wave with extraordinary polarization at the electron cyclotron resonance heating of a plasma at the second harmonic resonance in toroidal devices are analyzed. A new mechanism is proposed for the localization of a daughter electrostatic wave in the toroidal direction in the region of a high-power pump beam. This mechanism, along with the two-dimensional localization of the daughter wave because of a nonmonotonic radial profile of the plasma density and the poloidal inhomogeneity of the magnetic field, can be responsible for the parametric excitation of a three-dimensional cavity for this wave and, as a result, low-threshold absolute decay instability of the pump wave. 相似文献
6.
Nusinovich G.S. Li H. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1992,20(3):170-175
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, 相似文献
7.
The frequency dependence of the coefficient of interband magnetoabsorption of a weak electromagnetic wave propagating in a constant electric field and in a field of resonant laser radiation at a frequency equal to the cyclotron frequency (infrared magnetic resonance) is calculated. The specific features observed in interband absorption of the electromagnetic wave in a uniform electric field are considered for the case in which the frequency of laser radiation is equal to the confinement frequency in a parabolic quantum well (infrared quantum-well resonance). 相似文献
8.
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. 相似文献
9.
10.
Bhimsen K. Shivamoggi 《International Journal of Theoretical Physics》1992,31(12):2121-2141
This paper gives a further discussion of the analytical properties of both discrete and continuous Alfven wave spectra in an incompressible as well as compressible plasma. Although the continuous MHD modes produced by a well-behaved initial perturbation decay according to a power law, some singular solutions exist and are found to behave differently. In particular, it is possible to exhibit the existence of a new continuous mode which decays exponentially, and not as an inverse power of time, and this exponential damping is not the consequence of a continuous variation of the magnetic field. Even the set of discrete magnetohydrodynamic modes is shown to be empty unless certain conditions are satisfied. Next, we consider resistive modes and give explicit solutions for them which are valid in the neighborhood of the Alfven resonance layer and discuss their implications for plasma heating schemes. Finally, we study discrete and continuous Alfven wave spectra in a compressible plasma and discuss how they behave differently from those in an incompressible plasma. In particular, we show that though compressibility of the plasma is responsible for the slow mode continuum, strong compressibility will eliminate it. The discrete modes in a compressible plasma undergo an exponential damping even in an ideal plasma if the compressibility is strong. 相似文献
11.
We show that dynamical localization of electrons in a thin semiconductor superlattice irradiated by a TM electromagnetic wave can lead to the formation of multistable states of the high-frequency field, which is accompanied by significant distortions of the reflection characteristics of superlattices. This effect is caused by the phenomenon of nonlinear plasma resonance and the related significant increase in the component of an alternating electric field, parallel to the superlattice axis, in the case where the real part of the corresponding component of the tensor of nonlinear dielectric permittivity becomes zero. It is found that the generation efficiency of odd harmonics of the radiation increases considerably under resonance conditions. 相似文献
12.
The spectral composition of a relativistically strong uniform nonlinear electromagnetic wave in a transparent collisionless plasma is analyzed. The vortex and potential components of the wave field are shown to contain only odd and even harmonics, respectively; in a transparent plasma, the wave remains quasi-monochromatic, since the intensities of the harmonics decrease exponentially with increasing harmonic number. An equation that includes diffraction effects is derived to describe the propagation of wavepackets. The results obtained are compared with experimental data. 相似文献
13.
LIU Ke 《声学学报:英文版》1994,(4)
I.IntroductionInrecentyears,theresearchworkonnonlinearacousticshasbeendcvelopedrapid1ybe-causethehigh-intensitysoundismoreandmoreimportantincontcmporarytechnology.Aerodynamicnoiseemittedbyrockctorjetengines,noisetestofairframcs,u1trasonicpro-cessing,andothcrs,a1linvo1vefinitc-amplitudesoundwavesand,mostlystandingwaves.Athcoryofonc-dimensiona1finitc-amp1itudestandingwavesinlosslessmediahasbeenproposedbyMAAonthebasisofthcfundamenta1principlesofhydrodynamics['l,inwhichformulasofstcadywavcformsa… 相似文献
14.
Measured axial distributions of harmonic components of the electric field of the torch discharge in argon at different frequencies
of the fundamental harmonic are presented. It is found that the fourth electromagnetic field harmonic decays in the resonance
manner. 相似文献
15.
Effects of self-fields on dispersion relation and growth rate in two-stream electromagnetically pumped free electron laser with axial guide magnetic field
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A theory for a two-stream free-electron laser (FEL) with an electromagnetic wiggler (EMW) and axial guide magnetic field is developed. In the analysis, the effects of self-fields are taken into account. The growth rate is derived. The characteristics of the growth rate are studied numerically. The dependence of the normalized wave number, which corresponds to the maximum growth rate, on the cyclotron frequency is presented. The comparisons between the normalized maximum growth rate and its corresponding wave number normalized by employing the axial magnetic field, for the cases with and without self-fields in the two-stream FEL are studied numerically. 相似文献
16.
Gahl J.M. Ishihara O. Hagler M.O. Kristiansen M. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1989,17(3):520-523
Experimental observation of current drive by asymmetrical heating of ions in the Texas Tech Tokamak suggests that penetration of the fast Alfven wave near the fundamental ion-cyclotron resonance is restricted. A numerical study of the warm plasma dispersion relation near the ion-cyclotron resonance does indeed show this effect. The data reveal that, as the wave approaches the resonant layer from the high or low field side of the torus, it first passes through a region where asymmetrical heating takes place and the wave energy is absorbed by ions moving with high velocity parallel to the magnetic field 相似文献
17.
Lee Kai Fong 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1975,3(3):122-125
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. 相似文献
18.
分析了磁重联对晕等离子体加速和能量平衡过程的影响。分析表明晕等离子体向轴心的加速过程分为两个阶段:第一阶段晕等离子体在磁压或热压(依赖于丝数)作用下向轴心运动;第二阶段晕等离子体由于磁重联过程被加速到阿尔芬速度,并到达轴心形成先驱等离子体。估算表明重联层的厚度与离子的惯性长度具有相同的数量级,电流片内电子运动和离子的运动是解耦合的。在内爆滞止阶段电荷分离产生强的径向电场,这个电场将磁能转化为等离子体轴向(z方向)动能,内爆动能和轴向动能共同转化为X射线辐射能,以此解释了X射线能量大于内爆动能这一观测结果。分析了磁重联电磁脉冲的性质,对于1 MA驱动条件,电磁脉冲的总能量可达kJ量级。 相似文献
19.
E. M. Boldyrev 《Technical Physics》1997,42(2):206-211
The solutions of the equations of motion of a charged particle in an external electromagnetic field consisting of a superposition
of a constant uniform magnetic field and the field of a circularly polarized electromagnetic plane wave are presented as solutions
of the Cauchy problem. The resonance case is studied.
Zh. Tekh. Fiz. 67, 94–99 (February 1997) 相似文献