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1.
Experiments are described which show that the reflection coefficient for ion acoustic waves (IAW) from the sheath at a grid is affected by an HF electric field with a frequency fHF≲5fpi(fpi =ion plasma frequency). For peak-to-peak amplitudes of the HF voltage drop across the sheath Φ0kB Te/e and fHF>f pi, the energy distribution of the ions passing through the grid develops a hot tail and the reflected wave suffers enhanced Landau damping. If Φ0kBTe/e and fHF<fpi, a large-amplitude IAW is excited at the grid; a well-defined ion beam is formed; and local growth of the reflected wave is observed. Test waves launched from the grid show the same propagation characteristics as the reflected waves  相似文献   

2.
A simple calculation of a free-electron laser in the Compton regime that uses a dielectric-lined waveguide is presented. The introduction of a dielectric lining in a free-electron laser considerably reduces the requirements on beam voltage for generating a given frequency ω1=k0c/(1 - vb η/c), where k0 is the wiggler wave period η is the effective index of refraction (1<η<√ϵ) and ϵ is the permittivity. The system supports electromagnetic waves whose Poynting flux is largely concentrated in the dielectric; hence the electron beam is required to propagate close to the dielectric lining. The mode structure and dispersion behavior of the guiding system without the beam are discussed. a thin annular beam is introduced, and a perturbation theory is used to obtain the frequency and growth rate of radiation  相似文献   

3.
An expression for the spatial dependence of the electric potential in a collisionless and source-free planar plasma sheath is presented. This expression is derived by analogy with Child's law and approaches Child's law asymptotically as the potential drop φW across the sheath becomes large, |eφW/kTe|>104. Here k is Boltzmann's constant, Te is the electron temperature, and e is the electronic charge. Comparison with numerical solutions of the model equations indicates that the sheath thickness and potential variation predicted by this improved Child's law are accurate for |eφW/kTe|>10. In contrast, the authors find that Child's law is accurate only when |e φW/kTe|>104  相似文献   

4.
The relativistic harmonic content of large-amplitude electromagnetic waves propagating in underdense plasmas is investigated. The steady-state harmonic content of nonlinear linearly polarized waves is calculated for both the very underdense (wp/w 0)≪1 and critical density (wp/w0)≃1 limits. For weak nonlinearities, eE0/mcω0<1, the nonlinear source term for the third harmonic is derived for arbitrary wp/w0. Arguments are given for extending these results for arbitrary wave amplitudes. It is also shown that the use of the variable x-ct and the quasi-static approximation leads to errors in both magnitude and sign when calculating the third harmonic. In the absence of damping or density gradients the third harmonic's amplitude is found to oscillate between zero and twice the steady-state value. Preliminary PIC simulation results are presented. The simulation results are in basic agreement with the uniform plasma predictions for the third-harmonic amplitude. However, the higher harmonics are orders of magnitude larger than expected and the presence of density ramps significantly modifies the results  相似文献   

5.
A general theory is developed for self-consistent calculations of mode competition in a gyrotron with nonfixed axial structure of the RF field for arbitrary cyclotron harmonics. The theory is applied to the gyrotron operating at the Kernforschungszentrum Karlsruhe with a frequency of 150 GHz. The formalism presented allows a self-consistent calculation of mode competition for the operating and parasitic modes at the cyclotron resonance at arbitrary harmonics. Specific calculations are carried out for the cases n0=1, n1 =2 and n0=2, n1=1. It is emphasized that the formalism considered applies only to the case in which the azimuthal orthogonality condition is satisfied: n0m1n1 m0. There are circumstances when this condition is not satisfied  相似文献   

6.
A 30-A, 3-mm-diameter, wall-stabilized argon arc with 1% hydrogen is examined spectrometrically at pressures of 0.1-10 bar. Values of Tg, and Texa diverge as pressure decreases below 5 bar (ne⩽1×1017 cm-3) at r=0. Texβ is 20-40% larger than the other temperatures. The results are dependent on the transition probability scale used  相似文献   

7.
A three-wave free-electron laser (FEL) was operated with a powerful 8.4-GHz electromagnetic pump wave replacing the usual magnetostatic wiggler. The presence of a uniform axial magnetic field B0 produced cyclotron-harmonic idler waves. Peaks in the emission spectrum corresponding to cyclotron harmonics were observed covering a frequency range from 16.5 to 130 GHz. The frequency spectrum of this novel FEL mechanism was tuned continuously by the variation of B0  相似文献   

8.
蒋世明 《物理学报》2015,64(18):184601-184601
当介电高弹聚合物薄膜被施以面内等双轴预拉伸后, 受到厚度方向的电压作用时, 薄膜在力场和电场共同作用下产生大变形. 电场采用Maxwell应力分析, 力场采用橡胶弹性模型分析. 拟合这类变形的常用橡胶弹性模型主要有Neo-Hookean, Arruda-Boyce, Gent等模型. 这些模型对实验数据的定量拟合存在不同程度的偏差. 通过对实验数据的分析, 结合数学方法, 提出了一个新的自由能函数模型. 通过该模型对VHB4905介电高弹聚合物薄膜的多组等双轴预拉伸电力耦合实验进行拟合, 并以Neo-Hookean, Gent模型作为对照, 结果与实验数据拟合很好, 比对照模型的偏差明显缩小.  相似文献   

9.
For pt.I see ibid., vol.16, no.3, p.368-73, June 1988. Methods of increasing, by a factor greater than five, the neutron yield/short Y n from D-D fusion reactions in a plasma focus (PF) enhance both the D+-ion acceleration to energy values E d>1-8 MeV and the ion confinement in the pinch region. Nuclear activation of C and N in the (doped) filling gas of the discharge chamber and of solid targets of C and BN bombarded by the ion beam in the direction of the electrode axis (0°) confirms earlier determination of the energy spectrum of the trapped ions (dφt/dE∝φ0tE -m) and of the ejected beam (dφb/dE∝φ0bE d-m, m=2.5±0.5 for 0.1 MeV≲E≲3 MeV). A Thomson (parabola) spectrometer with nanosecond time resolution determines the time of emission t( E) of the beam at 0°. Ion acceleration and trapping occur within the small (filamentary) elements of the magnetic fine structure of the pinch, which can be dispersed on a relatively large confinement volume after the pinch disintegration. It has been found that φtb≳10-103 for Ed≳1 MeV, depending on Yn  相似文献   

10.
D2 temperature-programmed desorption (TPD) was used to probe the structure of the Si(011)-(16 × 2) surface. Deuterium was adsorbed at 200°C to coverages θD ranging up to complete saturation (approximately 1.1 ML) and the sample heated at 5°C s−1. TPD spectra exhibited three second-order desorption peaks labelled β2, β*1 and β1 centered at 430, 520 and 550°C. Of the proposed models for the Si(011)-(16 × 2) reconstruction, the present TPD results as a function of θD provide support for the adatom/dimer model with the β2 peak assigned to D2 desorption from the dihydride phase, while the β*1 and β1 peaks arise from adatom and surface-atom monohydride phases.  相似文献   

11.
A major goal of current X-ray laser research is the achievement of gain in the 23.3-43.7 Å wavelength region, known as the `water window'. Silicon is the lowest atomic number element for which all the heliumlike 3-2 transitions lie in this region. The authors examine the fundamental kinetics of recombination lasing in this species, and conclude that the Si XIII 1s3d1D 2-1s2p1P1 line at 39.1 Å is an attractive candidate for recombination-pumped lasing. Attainment of gain in this line is somewhat more energetically favorable than for the hydrogenic Al XIII 3-2 transitions, but radiative trapping may be somewhat more troublesome than for H-like Al  相似文献   

12.
S.C. Wilks et al. (1988) showed that when an infinite expanse of gas, carrying a linearly polarized electromagnetic wave, is instantly ionized, the initial wave is frequency upshifted. This phenomenon of frequency upconversion through flash ionization gives rise to steady-state transmitted and reflected electromagnetic waves and to a time-independent magnetic field. The case in which the final state of ionization is achieved not instantly but in a finite turn-on time, 0⩽tt 0, which is followed by the steady state, is studied. It is shown that the electric field is obtained from the one-dimensional Helmholtz equation, d2F(t)/dt2 02g(t)F( t)=0, if electrons are born at rest when they are created during ionization. As a result, the instantaneous frequency of the upshifted radiation is ω(t)=√g(t). The electric field can be solved exactly for specific choices of g(t). It is solved using WKB approximations for arbitrary g(t). The magnetic field is then found by integrating Faraday's law. It is found that the steady-state electric field amplitude depends on the steady-state value o f g(t) but does not depend on the ionization time t0. Conversely, the static magnetic field amplitude decreases with increasing turn-on time  相似文献   

13.
邢伟  孙金锋  施德恒  朱遵略 《物理学报》2018,67(19):193101-193101
利用考虑Davidson修正的内收缩多参考组态相互作用(icMRCI+Q)方法结合相关一致基组aug-ccpV6Z计算了AlH~+离子前两个离解极限对应的5个Λ-S态和10个?态的势能曲线.为了提高势能曲线的可靠性和精确性,计算中考虑了自旋轨道耦合效应、芯电子价电子相关和标量相对论修正以及将势能外推至完全基组极限.基于得到的势能曲线,获得了束缚和准束缚的4个Λ-S态和8个?态的光谱常数和振动能级,与已有的实验结果符合.计算了2(1/2)→X~2Σ_(1/2)~+和A~2Π_(3/2)→X~2Σ_(1/2)~+跃迁的跃迁偶极距.利用计算的精确的势能曲线和跃迁偶极矩,获得了2(1/2)~(第一势阱)(υ′=0, 1)→X~2Σ_(1/2)~+(υ′′)和A~2Π_(3/2)(υ′=0, 1)→X~2Σ_(1/2)~+(υ′′)跃迁的高度对角化分布的Franck-Condon因子(f_(00)和f_(11))和大的振动分支比;预测了2(1/2)~(第一势阱)(υ′=0, 1)和A~2Π_(3/2)(υ′=0, 1)态短的自发辐射寿命和窄的辐射宽度,这适合于AlH~+离子的快速激光致冷.所需的3束激光冷却波长都在紫外区域.这些结果表明了激光冷却AlH~+离子的可行性.此外,评估了自旋轨道耦合效应对光谱常数、振动能级和激光冷却AlH~+离子的影响.  相似文献   

14.
A modified fractal growth model based on the deposition, diffusion, and aggregation (DDA) with cluster rotation is presented to simulate two-dimensional fractal aggregation on liquid surfaces. The mobility (including diffusion and rotation) of clusters is related to its mass, which is given by Dm=D0 sD and θm0sθ, respectively. We concentrate on revealing the details of the influence of deposition flux F, cluster diffusion factor γD and cluster rotation factor γθ on the dynamics of fractal aggregation on liquid surfaces. It is shown that the morphologies of clusters and values of cluster density and fractal dimension depend dramatically on the deposition flux and migration factors of clusters.  相似文献   

15.
Theoretical and experimental investigations of the folded waveguide launcher as proposed for use in the ion-cyclotron range of frequencies (ICRF) heating of tokamak plasmas are presented. Theoretical results include an analysis of the folded waveguide using Ritz's method to obtain various field quantities. The cutoff wavenumbers from this analysis are within 10% of those calculated using an unfolded equivalent rectangular waveguide model. Measurements of cavity resonances for a scale-model ICRF-folded waveguide with a cutoff frequency of 2.4 GHz also agree closely with those calculated using an unfolded equivalent model. An unfolded equivalent waveguide model is used to evaluate the properties of an inductive strip placed in the folded waveguide. Applying variational analyses provides upper and lower bounds to the reflection magnitude |S11| that are in good agreement with measured values. Polarizing plates (which have been proposed to increase the on-axis directivity of the radiated power) are modeled using an unfolded equivalent waveguide. A variational analysis is used to determine an upper-bound value of |S11| in air due to a polarizing plate inside a matched folded waveguide. Measured values are found to be within 3% of the calculated values, with |S11|>0.95 for frequencies between 2.5 and 4.5 GHz  相似文献   

16.
The parasitic oscillation of the TE°21 gyrotron backward-wave (gyro BW) mode is observed in a low-Q, 8 GHz TE°011, gyrotron. At low power (PBW<5 kW), the oscillation of the gyro BW mode, simultaneously with the gyrotron mode, results in a maximum TE°011, mode efficiency of less than 0.25. The parasitic oscillation is suppressed by operating the gyrotron with a negative magnetic field gradient along the electron beam, which allows the maximum efficiency to reach 0.40 and the output power to be multiplied by a factor varying from 1.4 to 1.7. The optimum efficiency curve of the TE°011 mode indicates that the low-Q cavity behaves as a much higher Qdiff cavity. Excessive values of magnetic field gradient and α favor the TE°012 , longitudinal mode, which oscillates in place of the TE°011 mode and limits its maximum output power. This competitive process is responsible for the high-Q-like behavior of the optimum efficiency curve  相似文献   

17.
Validity conditions for complete and partial local thermodynamic equilibrium (CLTE and PLTE) of homogeneous, time-dependent, and optically thin plasmas are derived. For Cu I, electron densities of ne⩾(5×1022-5×1023 ) m-3 are required for the establishment of CLTE. For Cu I and Cu II, ne⩾(5×1021-5×1021 -5×1022) m-3 is necessary for PLTE (for electron temperatures of 1-2 eV). Application to low-current copper vapor arcs in vacuum shows that CLTE can be expected for r<200-600 μm (r=distance from the cathode spot). A further limitation follows for temperatures of 2 eV or higher if diffusion effects are taken into consideration. Consequently, the use of the LTE formulas in plasma spectroscopy of low-current vacuum arcs is very limited  相似文献   

18.
Particle simulation in a one-dimensional bounded system is used to examine the formation of acoustic double layers in the presence of two ion species. Double-layer formation depends critically on the details of the distribution functions of the supporting ion populations, and their relative drifts with respect to the electrons. The effect of having two ion components, an H+ and an O+ beam, on double-layer evolution from ion acoustic turbulence driven by an electron drift relative to the H+ beam of ≈0.5u e, where uue is the electron thermal speed, is examined. The ratio of ion drifts is taken to be consistent with acceleration by a quasi-static auroral potential drop (i.e. V H/VO=√MO/ MH=4.0). Acoustic double layers form in either ion species on the time scale τ≈100ωps-1, where ωps is the ion plasma frequency for species `s' and s=H or O, and for drifts relative to the electrons lower than that required for double layer formation in simulations of single ion component plasma  相似文献   

19.
The universal crossover behavior of Lyapunov exponents in transition from conservative limit to dissipative limit of dynamical system is studied. We discover numerically and prove analytically that for homogeneous dissipative two-dimensional maps, along the equal dissipation line in parameter space, two Lyapunov exponents λ1 and λ2 of periodic orbits possess a plateau structure, and around this exponent plateau value, there is a strict symmetrical relation between λ1 and λ2 no matter whether the orbit is periodic, quasiperiodic, or chaotic.The method calculating stable window and Lyapunov exponent plateau widths is given. For Hénon map and 2-dimensional circle map, the analytical and numerical results of plateau structure of Lyapunov exponents for period-1,2 and 3 orbits are presented.  相似文献   

20.
We point out that the compact exponential operator V≡exp[-i(λ1Q22P2)/2] (where λ1, λ2 are real;P and Q are momentum and coordinate operators, respectively;the units of h=m=ω=l is taken, m and ω are harmonic oscillator's mass and'frequency, respectively) is a generalized single-mode squeeze operator which can generate mixed squeezing and rotating transformations. The decomposition of V as a product of a squeeze operator and a rotating operator is derived through the technique of integration within an ordered product.The fluctuation in quadrature phases for the squeezed vacuum state generated by V is analyzed.  相似文献   

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