共查询到20条相似文献,搜索用时 46 毫秒
1.
E. Z. Gusakov A. Yu. Popov M. A. Irzak 《Journal of Experimental and Theoretical Physics》2016,123(4):723-734
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. 相似文献
2.
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. 相似文献
3.
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. 相似文献
4.
The experimental conditions have been analyzed for a significant reduction of the threshold of the reflective parametric decay
instabilities under electron cyclotron resonance heating (ECRH) of a plasma in magnetic devices in the absence of the upper
hybrid resonance for the pump wave. The role of the nonmonotonic profile of the plasma density near the O point of the magnetic
island, which allows for the localization of ion Bernstein waves in the direction of the density gradient and the suppression
of convective losses from the decay region has been discussed. It has been shown that the threshold of the instability of
the induced backscattering near the local maximum of the density profile is decreased by four orders of magnitude and is easily
exceeded in present-day ECRH experiments at a power of several hundred kilowatts. 相似文献
5.
The saturation level of the low-threshold parametric two-plasmon instability of the extraordinary pump wave decay to two upper hybrid plasmons is analyzed under conditions when the only efficient saturation mechanism is the pump depletion. A closed system of differential equations describing both the instability excitation and saturation is derived. The system is solved numerically and an analytic expression is obtained for the anomalous absorption coefficient of the pump wave caused by the development of this instability. The saturation level of the two-plasmon decay instability and the related anomalous absorption efficiency are estimated from data obtained in experiments on the electron cyclotron resonance heating of the plasma by an extraordinary wave in the TEXTOR tokamak. 相似文献
6.
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
7.
Hadi Al Janabi A. Kumar A. Sharma R.P. Tripathi Y.K. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1994,22(1):65-70
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 相似文献
8.
9.
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. 相似文献
10.
Kumar A. Sugawa M. Isobe S. Sharma R.P. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1995,23(6):980-986
In the present paper, the parametric decay instability of an extraordinary electromagnetic wave (X-wave) into an electron Bernstein wave (EBW) and an electrostatic whistler wave (W-wave) has been studied. Expressions are derived for homogeneous threshold, growth rate, and convective threshold for this instability. The relevance of the present parametric process has been pointed out to explain the generation of whistler mode radiations in the SL-2 experiment, ionospheric modification experiment, in the polar cusp region of the magnetosphere, as well as during intense electron cyclotron resonance heating in the MTX tokamak 相似文献
11.
The parametric decay process in inhomogeneous layers existing near the plasma boundaries or in front of antennas and probes in a plasma has been investigated. The linear enhancement of the pump field near ω = ωp, the threshold fieldstrength, the wavenumber selection rules and the influence of spontaneous low frequency fluctuations are discussed in detail using a one-dimensional model of the inhomogeneous plasma capacitor. According to this model the instabilities appear in the layers with maximum linear transformation and (linear) absorption. In addition, a strong nonlinear part of absorption in the presence of the instability has been observed. The level of the spontaneous low frequency fluctuations influences strongly the spectrum of the parametrically excited ion waves. The experiments show a redistribution of the transferred ion acoustic wave energy over the whole wave continuum up to ωpi, if a sufficient strong spontaneous fluctuation level exists in the plasma. It is impossible, however, to excite ion acoustic turbulence by the decay of the high frequency pump field under the present conditions. The conditions for the linear field enhancement are disturbed by the action of the ponderomotive forces changing the density profile near the critical point before reaching the strong pump amplitude being necessary for the excitation of a cascade of decay processes. 相似文献
12.
《中国物理快报》2016,(8)
The parametric decay instabilities(PDIs)of ion Bernstein wave with different input power levels are investigated via particie-in-cell simulation.It is found that the number of decay channels increases with the input power.Resonant mode-mode couplings dominate for a low input power.With increasing the input power,the nonresonant PDIs appear to dissipate the energy of the injected wave and give rise to edge ion heating.The generated child waves coupie with each other as well as the injected wave and/or act as a pump wave to excite new decay channels.As a result,the frequency spectrum is broadened with the increase of the input power. 相似文献
13.
We consider nonlinear interactions between intense circularly polarized electromagnetic (CPEM) waves and electron plasma oscillations (EPOs) in a dense quantum plasma, taking into account the electron density response in the presence of the relativistic ponderomotive force and mass increase in the CPEM wave fields. The dynamics of the CPEM waves and EPOs is governed by the two coupled nonlinear Schr?dinger equations and Poisson's equation. The nonlinear equations admit the modulational instability of an intense CPEM pump wave against EPOs, leading to the formation and trapping of localized CPEM wave pipes in the electron density hole that is associated with a positive potential distribution in our dense plasma. The relevance of our investigation to the next generation intense laser-solid density plasma interaction experiments is discussed. 相似文献
14.
黄林 《核聚变与等离子体物理》1985,(1)
本文研究了外pump电场E_0在离子束-等离子体系统中所激发的静电低频参量不稳定性。导出了这种低频波的一般色散关系,并用数值方法分析了一维质子束-等离子体系统的参量不稳定性的激发过程。结果表明:离子束对等离子体中参量不稳定性的激发有极重要的影响。当没有离子束时,只能激发一种模式的波;一旦将离子束引入等离子体中,就可以在系统中激发两个波长较长的低频波。 相似文献
15.
The resonant parametric decay of a Langmuir wave into a backward propagating Langmuir wave and an ion acoustic (IA) wave is studied in a cylindrical dusty plasma. The analysis shows that the frequency of the IA mode decreases with the parameter δc (where δc is the ratio of the ion density to the electron density) for negatively charged dust grains. The growth rate of the resonance decay instability (RDI) and the threshold required for its onset also decrease with δc and are strongly dependent on the electron to ion temperature ratio for both positively and negatively charged dust grains. The results obtained also illustrate the dependence of the threshold of the resonance decay instability (μth) on the plasma cylinder radius. 相似文献
16.
S. M. Grach 《Radiophysics and Quantum Electronics》1999,42(7):572-588
We consider effects related to acceleration of electrons by high-frequency plasma turbulence in the ionospheric F-region modified
by powerful radio waves. The threshold of avalanche growth of the number of accelerated particles due to additional ionization
is determined for pump-wave frequencies far from the multiple cyclotron resonance. The steady-state density of the accelerated
electrons is found for the above pump-frequency values taking into account both turbulent trapping in the accelerating layer
due to scattering of plasma waves and the return of electrons to this layer due to collisions. If the pump wave frequency
is close to the multiple cyclotron resonance, fast electron distribution with significant transverse anisotropy is formed.
Relaxation of this distribution due to collisions with charged particles outside the accelerating layer leads to the appearance
of a maximum over transverse velocities in the tail of the distribution function. We propose a generation mechanism for the
broad upshifted maximum feature in the spectrum of stimulated electromagnetic emission, which is related to the cyclotron
instability of the accelerated electrons. The instability occurs in the double-resonance region in which the pump frequency
is close to both the upper-hybrid and multiple-cyclotron frequency.
Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika,
Vol. 42, No. 7, pp. 651–669, July 1999. 相似文献
17.
18.
Maekawa T Kobayashi T Yamaguchi S Yoshinaga K Igami H Uchida M Tanaka H Asakawa M Terumichi Y 《Physical review letters》2001,86(17):3783-3786
Extraordinary (X) waves are perpendicularly injected for electron Bernstein (B) wave heating into an Ohmically heated plasma from the inboard side in the WT-3 tokamak. Measurements show that absorption does not take place at the electron cyclotron resonance layer nor the upper hybrid resonance layer, but does happen midway between them. This is consistent with the ray tracing prediction, i.e., the poloidal field and poloidal inhomogeneity of toroidal field lead the B waves to have a large parallel refractive index N( parallel) (>1), and the B waves are damped away via the Doppler-shifted cyclotron resonance. 相似文献
19.
Experimental evidence of parametric excitation, by an intense external H.F. field, of an electron surface mode and an ion wave is presented. The pumping electromagnetic energy density is equal to or slightly larger than the thermal energy density of the electrons. The value of fpc/f0 (electron plasma frequency/external field frequency) is that for an electron surface wave. Depending on the pressure and field intensity, this decay instability can lead to three types of low frequency oscillations, with frequencies close to the ion plasma frequency. Two of these are described by Aliev and Silin's intense field theory: one is the volume ion plasma oscillation and the other a surface ion plasma oscillation. The third corresponds to no known ion eigenmode. Several other features of the theory by Aliev and co-workers are also confirmed experimentally, such as the harmonic excitation of the instability (nf0 ≈ fpe/√2, where n is an integer), the instability amplitude as a function of fpe/f0 (above threshold conditions), the value of the mismatch parameter as a function of field strength and ion mass, and the existence of a fine structure corresponding to the symmetric and antisymmetric electron surface oscillations. Even at high pump field strengths, the decay products are nearly monochromatic i.e. the plasma does not become turbulent. 相似文献
20.
We present the results of numerical modeling of the effect of amplification of coherent bichromatic radiation due to its cyclotron parametric interaction with a modulated ensemble of electrons in the absence of partial synchronism of waves and particles. The numerical results agree with the analytical conclusions. We find that under certain conditions, the developing parametric instability is accompanied by “driving” of the wave frequencies to the resonance with the particles, which results in significant “peaking” of the instability. 相似文献