共查询到20条相似文献,搜索用时 531 毫秒
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Rosenbluth等人曾建议在托卡马克外侧产生少量高能香蕉粒子就可以稳定气球模,使托卡马克过渡到第二稳定区运行。本文就设计了一种用电子迴旋共振加热(简称ECRH)在反应堆托卡马克中产生这样的高能电子的方法:在托卡马克外侧,主要沿小环θ方向射入一束具有有限N∥和某一合适频率ω的射频波,使波束主要在一个磁面附近的窄层内传播,利用高次谐频接力式加热把处于分布函数尾部的少量电子变成这样的高能电子。用各向异性弱相对论介电系数理论作数值计算发现,当N∥和ω取适当值时,寻常模和异常模都有明显的加热作用。
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一种同步回旋激射不稳定性对电磁波的直接放大 总被引:2,自引:0,他引:2
本文讨论了一种同步回旋激射不稳定性对电磁波的直接放大,它基于少量在速度空间具有空心分布的中等相对论性高能电子束与本底等离子体中本征电磁模的共振相互作用。主要关心的是的参数区域(ω_e为电子等离子体频率,Ω_e为电子回旋频率)。计算表明,若电子束的单能性很高,则不稳定性增长率比同样参数下由动力效应计算得出的增长率高若干个数量级,且最大增长率处在2ω_e附近。 相似文献
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本文对高β等离子体中槽纹模低杂漂移不稳定性从迴旋动力论出发作了较系统的研究,考虑了密度梯度、电子的温度梯度以及磁场梯度漂移的共振效应,解析结果与数值计算取得了完全一致的结论。发现,当温度梯度方向与密度梯度方向相反时,与温度梯度有关的电子的磁漂移共振起不稳定作用,使模的增长率比温度均匀时明显增大;而当方向相同时,温度梯度效应加强电子磁漂移共振的稳定作用,减少模的增长率。在两种情形中随着β值的增大,模的增长率都会减小,而且最大增长率向长波方向移动。电子温度各向异性对模的性质没有影响。
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束—等离子体放电中低频等离子体波的非稳定性研究 总被引:1,自引:1,他引:0
刘祖黎 《核聚变与等离子体物理》1990,10(4):209-215
本文采用非中性冷等离子体模型,研究了沿磁场入射的电子束和等离子体相互作用引起的低频等离子体波的非稳定性。计算表明,在束-等离子体放电情况下,振动频率和增长率都随电子束密度增加而增加,当束电流一定时,它们随l增加而略有增加。l=1时其频率数量级与离子迴旋频率相同。l≥3时,振动频率几乎不随k_z变化,其振动频率和增长率数量级与低混杂振荡频率相同,实质是低混杂漂移非稳定性。理论结果与实验一致。 相似文献
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本文讨论了具有简单结构磁层顶中的低混杂漂移不稳定性,假定在磁层顶中磁场方向是相互平行的,电子与离子的密度处处相等,总压力为一常数,采用1971年Alpers建立的分布函数做为零级分布,计算了下混杂漂移不稳定性的增长率和饱和时相应的反常电阻,计算表明,当磁层顶厚度接近两个质子迴旋半径时,低混杂漂移不稳定性的增长率约为0.26ωLH(ωLH为低混杂频率),反常电阻率为10-5sec,随着磁层顶厚度成倍增加,反常电阻率以指数形式下降。
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This paper presents an analytical and numerical investigation of an intense circularly polarized wave propagating along the static magnetic field parallel to oscillating magnetic field in magnetoactive plasma. In the relativistic regime such a magnetic field is created by pulse itself. The authors have studied different regimes of propagation with relativistic electron mass effect for magnetized plasma. An appropriate expression for dielectric tensor in relativistic magnetoactive plasma has been evaluated under paraxial theory. Two modes of propagation as extraordinary and ordinary exist; because of the relativistic effect, ultra-strong magnetic fields are generated which significantly influence the propagation of laser beam in plasma. The nature of propagation is characterized through the critical-divider curves in the normalized beam width with power plane For given values of normalized density (ωp/ω) and magnetic field (ωc/ω) the regions are namely steady divergence (SD), oscillatory divergence (OD) and self-focusing (SF). Numerical computations are performed for typical parameters of relativistic laser-plasma interaction: magnetic field B = 10-100 MG; intensity I = 1016 to 1020 W/cm2; laser frequency ω = 1.1 × 1015 s−1; cyclotron frequency ωc = 1.7 × 1013 s−1; electron density ne = 2.18 × 1020 cm−3. From the calculations, we confirm that a circularly polarized wave can propagate in different regimes for both the modes, and explicitly indicating enhancement in wave propagation, beam focusing/self-guiding and penetration of E-mode in presence of magnetic field. 相似文献
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Chen K.-R. Katsouleas T.C. Dawson J.M. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1990,18(5):837-841
The amplification mechanism of the ion-channel laser (ICL) in the low-gain regime is studied. In this concept, a relativistic electron beam is injected into a plasma whose density is comparable to or lower than the beam's density. The head of the electron beam pushes out the plasma electrons, leaving an ion channel. The ion-focusing force causes the electrons to oscillate (betatron oscillations) about the axis and plays a role similar to the magnetic field in a cyclotron autoresonance maser (CARM). Radiation can be produced with wave frequencies from microwaves to X-rays depending on the beam energy and plasma density: ω~2γ3/2ωpe, where γ is the Lorentz factor of the beam and ωpe is the plasma frequency. Transverse (relativistic) bunching and axial (conventional) bunching are the amplification mechanisms in ICLs; only the latter effect operates in free-electron lasers. The competition of these two bunching mechanisms depends on beam velocity ν0z; their dependences on ν0z cancel for the cyclotron autoresonance masers. A linear theory is developed to study the physical mechanisms, and a PIC (particle-in-cell) simulation code is used to verify the theory. The mechanism is examined as a possible explanation for experimentally observed millimeter radiation from relativistic electron beams interacting with plasmas 相似文献
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Zongjun Shi Ziqiang Yang Zheng Liang 《International Journal of Infrared and Millimeter Waves》2003,24(11):1823-1831
The dispersion characteristics of plasma–loaded free-electron laser has been analyzed using linear fluid model. The device under consideration consists of the cylindrical metallic waveguide, completely filled with background plasma and a relativistic electron beam which passes through a helical wiggler magnetic field. The result predicts that reasonable plasma density tends to improve the growth rate of the low-frequency optical wave of FEL and causes an shiftup in the operating frequency, However it has little effect on the growth rate of the high-frequency wave. In the plasma–loaded FEL, for the FEL oscillator, it may be tuned by varying the plasma density; and for the FEL amplifier, the wider frequency bandwidth is gained. A critical density n
c
p for the background plasma density is found. 相似文献
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We examine here the effects of plasmas and beam slippage on the gain of an optical klystron (OK) free electron laser (FEL) device under the influence of a weak guiding magnetic field and background plasma. The beam energy spread decreases with background plasma density nop and increases with beam plasma density nob. The maximum gain (Gmax) scales proportional to . The beam slippage phase Δψ scales directly to five power of relativistic factor γ0 and one half power to nob. 相似文献
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Leonhard Kellerer 《Zeitschrift für Physik A Hadrons and Nuclei》1970,239(2):147-161
The theory of light scattering in plasmas containing a magnetic field yields the special case of modulated scattering spectra. The modulation frequency is governed by the field in the plasma and is equal to the electron cyclotron frequency. In this investigation magnetic fields in a plasma were determined by a laser scattering experiment. The experimental data were: electron densityn e=1016cm?3, electron temperatureT e=3.2 eV, scattering angle θ=90 °, scattering parameter α=0.6, and a maximum field in the plasma of 125 kG. The spectrum measured at the maximum magnetic field was modulated with 3.6 × 1011 Hz. In scattering experiments with a field reduced by about 20% the observed modulation frequency was 2.8 × 1011 Hz. A thermal spectrum with a smooth profile was found when no field was present in the plasma. Applying the theory of cyclotron modulated spectra one obtains from the scattering experiment magnetic fields of 128, 100, and 0 kG. Within the experimental accuracy these values agree well with the fields determined by means of magnetic probes. Other possible interpretations of the measured deviations from thermal spectra (modulation with the plasma frequency or additional cold electron components in the plasma) are discussed, but they afford no explanation. This experiment has domonstrated that magnetic fields in plasmas can be measured locally and almost without disturbance by means of light scattering. 相似文献
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本文分析沿外磁场方向的等离子体川流激发回旋不稳定性的尼奎斯特图.阐述包含变量ns(川流等离子体的电子密度),n0(静止等离子体的电子密度),B(外磁场强度),k(波数),v(川流速度)与T(体系温度)的不稳定性判据的计算方法。具体算出氢等离子体的定量结果。为探讨不稳定区域的特征,还分析了有两支川流时的回旋与静电不稳定性。
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R. El-Bahi M. N. Rhimi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,57(3):365-374
An analytic linear theory of the electron dynamics in a three-dimensional helical wiggler free electron laser (FEL) with
axial magnetic field is presented. Orbits are obtained by perturbing the steady state-trajectories in order to determine the
characteristic frequencies Ω± of the FEL. The effect of the self-fields on electron dynamics is studied and modified
steady-state orbits and their stabilities have been analysed considering variation of electron energy and density. Among the
features
encountered is that in both group-I and group-II, one of the characteristic frequencies may have either signs affecting then
the
stability of the motion, while in group-II operation a repulsion of the frequencies at a pseudocrossing leads to highly perturbed
trajectories when the wiggler frequency is approximately half the cyclotron frequency. Self-fields effects can significantly
impair
the stability of the electron orbits. For group-I orbits, they are more important for higher wiggler frequencies and lower
beam energies.
For group-II orbits, they remain less important for higher wiggler frequencies and lower beam energies before reaching the
inversion
zone, then they behave as for group-I orbits. It should be remarked that self-fields shift the inversion zone towards higher
cyclotron
frequencies the thing that is obtained by either decreasing the wiggler frequency or increasing the beam energy. It is shown
that the
axial velocity-induced self-magnetic field has a diamagnetic effect for both groups orbits, while the wiggler-induced self-magnetic
field has a diamagnetic effect for group-I orbits and a paramagnetic effect for group-II orbits. The paramagnetic and diamagnetic
effects are more important for higher beam energies and densities. 相似文献
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Dispersion properties of plasma waves with frequencies close to the upper hybrid frequency u and the multiple electron cyclotron frequency nBe (double resonance) are considered for an inhomogeneous plasma with opposite gradients of the electron density and magnetic field magnitude. We show that a region of possible solutions of the dispersion relation decreases in real space as well as in wave vector space as of the wave frequency approaches double resonance. The results are applied to an interpretation of experiments on ionospheric modification by high-power radio waves with frequencies close to nBe.Radiophysical Research Institute, Nizhny Novgorod, Russia. Swedish Institute of Space Physics, Uppsala Division, Sweden. Swedish Institute of Space Physics, Kiruna Division, Sweden. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 5, pp. 617–633, May, 1994. 相似文献
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We consider generation of electromagnetic radiation at the electron cyclotron harmonics by energetic-electron beams having the mean momentum parallel, transverse, or oblique to the external magnetic field. This process is most efficient if the characteristic transverse momentum is sufficiently large. The radiation spectrum of the beam moving exactly along the magnetic field is closest to the equidistant one. The angle between the direction of the maximum emission and the magnetic field varies from 70° for the field-aligned beam to 90° for the beam whose characteristic momentum is transverse to the magnetic field. In fairly strong magnetic fields, i.e., for Be >pe, where Be and pe are the electron cyclotron and plasma frequencies, respectively, the radiation is maximum at low cyclotron harmonics and the second harmonic dominates. In the weaker fields (Be < pe), higher harmonics, up to fifth or sixth, are generated. Both wave modes are generated, but generation of the ordinary waves is far less efficient than that of the extraordinary waves under the same conditions. 相似文献
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Investigation of the diocotron instability of an infinitely wide sheet electron beam by using the macroscopic cold-fluid model theory 下载免费PDF全文
This paper investigates the diocotron instability of an infinitely wide relativistic sheet electron beam in conducting walls propagating through a uniform magnetic field by using the macroscopic cold-fluid model theory. Assuming low-frequency perturbations with long axial wavelengths, the eigenvalue equation and the dispersion relation are acquired for a sheet electron beam with sharp boundary profile and uniform density. The results presented in this paper has developed the use of the macroscopic cold-fluid model theory by extending the parameter of the electron cyclotron frequency ωc to a wider usage range, which is restricted to be much larger than the plasma frequency ωp in the previous research work. Theoretical analyses and numerical calculations indicate that the transport of the sheet electron beam will be completely stabilized by augmenting the normalized beam thickness to a conductor gap larger than a threshold λb, which is greatly dependent on the parameter ωc/ωp. The larger ωc/ωp is, the smaller λb will be needed. Moreover, the system parameters, including the wave number kx of the perturbations and the relativistic mass factor γb, will also influence the growth rate of diocotron instability obviously. 相似文献