FDTD方法分析高功率微波对大气的电离与击穿

应用麦克斯韦方程和电子流体方程,利用时域有限差分方法(FDTD)计算模拟了高功率微波(HPM)对大气的电离与击穿;该方法用瞬时电场代替等效电场,时刻更新大气电离击穿过程中的电离频率和碰撞频率,消除了近似解析法未考虑大气电离击穿过程中电场幅度衰减而引起的误差,计算得到击穿阈值大小随海拔高度的变化趋势与文献所得的变化趋势相吻合,其值略大于近似解析解;并通过仿真计算分析了HPM脉冲幅值、脉宽以及海拔高度等参数对大气击穿的影响。     

FDTD方法分析高功率微波对大气的电离与击穿

 应用麦克斯韦方程和电子流体方程,利用时域有限差分方法(FDTD)计算模拟了高功率微波(HPM)对大气的电离与击穿;该方法用瞬时电场代替等效电场,时刻更新大气电离击穿过程中的电离频率和碰撞频率,消除了近似解析法未考虑大气电离击穿过程中电场幅度衰减而引起的误差,计算得到击穿阈值大小随海拔高度的变化趋势与文献所得的变化趋势相吻合,其值略大于近似解析解;并通过仿真计算分析了HPM脉冲幅值、脉宽以及海拔高度等参数对大气击穿的影响。     

The Ulam problem and the ionization of Rydberg atoms by microwave radiation

We study the Ulam problem for long times (several million collisions) by numerical methods. We show that in the diffusion regime, which is valid for moderate times, this problem is mathematically equivalent to the problem of the diffusive ionization of atomic Rydberg states by microwave radiation. It is concluded that the diffusion regime sets in only for a very small number of initial conditions (field phases). It is theorized that the analogy between the two problems can be extrapolated to times longer than the diffusion time. We show in the Ulam problem that after the diffusional buildup of energy has finished, the quasistationary regime does not continue indefinitely: after several million particle-wall collisions the energy rapidly drops to zero. On the basis of this extrapolation we examine the possibility that an electron which has reached the continuous spectrum will not fly off to infinity (ionization), but will return to bound Rydberg states of the atoms (if the field acts for a sufficiently long time). This can make the diffusive ionization probability much lower than the value given by the known estimates. Zh. éksp. Teor. Fiz. 114, 37–45 (July 1998)     

Enhancement and control of H2 dissociative ionization by femtosecond VUV laser pulses

We report ab initio calculations of H2 ionization by VUV/fs 10(12) W/cm2 laser pulses including correlation and all electronic and vibrational degrees of freedom (DOF). Inclusion of the nuclear DOF leads to a substantial increase of resonance enhanced multiphoton ionization. By varying pulse duration, it is possible to control the ratio of dissociative to nondissociative ionization as well as the final H+(2) vibrational distribution. For pulses longer than 10 fs and proportional to omega>0.46 a.u., dissociative ionization entirely dominates, which is a very unusual situation in photoionization studies.     

Long-time limit of a quasicontinuum model

We calculate the long-time averages of populations in a system consisting of a discrete state coupled to a flat quasicontinuum by summing for each level the squares of the residues of the Fourier-transformed probebility amplitudes. We find that the long-time limit and the continuum limit may be interchanged.     

Near-classical noise enhancement of microwave ionization of Rydberg atoms

The ionization of the highly excited hydrogen atom in a strong external microwave field is a classically chaotic, near-classical quantum system for microwave frequencies somewhat below the initial Kepler electron orbit frequency. The addition of microwave noise is found to reduce the sinewave microwave field needed for ionization, modifying the near-classical fast process responsible for the microwave energy absorption. A classical numerical calculation based upon a many-frequency model of the noise qualitatively reproduces the observed noise enhancement.     

Enhancement of optically reconstructed images from microwave holograms

Simultaneous viewing of a number of identical microwave holograms produces, under specified conditions, enhanced optical images. This mode of operation is demonstrated for elementary microwave and synthetic holograms.     

Enhancement of the electric field threshold for microwave breakdown by crossed magnetic field

The enhancement of breakdown threshold is of benefit to the high power microwave transmission. We propose a magnetic field in the transverse direction to the electric field to enhance the breakdown threshold. A theory of electric field threshold with crossed magnetic field for short pulse is developed, and verified by particle-in-cell/Monte Carlo collision (PIC/MCC) simulations. The result shows that the crossed magnetic field can enhance the breakdown threshold significantly.     

Instabilities of electron-hole plasma under impact ionization and microwave emission

The nonlinear stage of the evolution of electron—hole plasma instabilities in semiconductors under impact ionization (static differential conductivity σ_d > 0) is considered for the case of spatially uniform pertubations of density and electric field. If the differential mobility of carriers μ _d > 0, the instability arises only with allowance for the retardation of the process of impact ionization (linear theory of this effect was developed by M. Toda [4]). When μ _d < 0, the instability may appear in the absence of the retardation. Both these instabilities exhibit oscillating form and are due to h.f. negative dynamic differential conductivity. We determine time sweeps of the electric field under condition of fixed current for the case n-InSb at T = 77 K. The amplitude and the frequency (f>10¹⁰Hz) of the oscillations are evaluated and the conditions, when the shape of E(t)-oscillations is essentially non-harmonic, are determined. Microwave emission observed in semiconductors under impact ionization may have resulted from the instabilities at hand.     

微波输入功率引起a-C∶F薄膜交联结构的增强

使用C2H2和CHF3的混合气体,在改变微波功率的条件下,利用微波电子回旋共振等离子体增强化学气相沉积方法制备了氟化非晶碳薄膜(aC∶F).薄膜的傅里叶变换红外光谱分析结果表明:薄膜中的CC与C—F键含量的比值随功率的增加而相应地增大;借助于紫外可见光谱分析发现,薄膜的光学带隙随功率的增大而减小.由此推断微波输入功率的提高有助于增强薄膜的交联结构.aC∶F薄膜的交流电导与x射线光电子能谱进一步证实了这种增强效应 关键词： 氟化非晶碳薄膜 傅里叶变换红外光谱 x射线光电子能谱     

Controlled suppression of ionization of Rydberg atoms in a microwave field

A computational procedure for controlling the stochastic ionization of one-dimensional single electron Rydberg atoms in the correspondence principle regime is developed. Using our procedure it is possible to suppress excitation and ionization of the one-dimensional Rydberg atom even in strong microwave fields for which ionization would otherwise be instantaneous.     

Coherent microwave rayleigh scattering from resonance-enhanced multiphoton ionization in argon

Multiphoton ionization and electron recombination processes are studied in argon using coherent microwave Rayleigh scattering from a localized, resonance-enhanced multiphoton ionization produced plasma. A time dependent one-dimensional plasma dynamic model is developed to predict the time evolution of the microwave scattering from the plasma. Experimental results of the argon ionization spectrum and electron recombination rates are in good agreement with the model predictions.     

高功率微波大气传输电离过程的物理研究

指出平面1维近似不符合在远场处微波单位面积能流与传输距离平方成反比的规律。给出了束流1维近似下微波大气传输的基本方程组。详细研究了微波电离大气的特性和相似律。估计了平面1维近似下和束流1维近似下的尾蚀,指出当无量纲电离电子数不太小时,两者可能有很大差别。     

高功率微波大气传输电离过程的物理研究

 指出平面1维近似不符合在远场处微波单位面积能流与传输距离平方成反比的规律。给出了束流1维近似下微波大气传输的基本方程组。详细研究了微波电离大气的特性和相似律。估计了平面1维近似下和束流1维近似下的尾蚀,指出当无量纲电离电子数不太小时,两者可能有很大差别。     

Enhancement of the molecular nitrogen dissociation and ionization levels by argon mixture in flue nitrogen plasma

In this work, the nitrogen molecular dissociation and ionization levels in Ar/N₂ flue plasma are evaluated as functions of plasma parameters such as Ar mixture quantity and N₂ flux in order to obtain the best condition for various applications such as thin film deposition and material surface modification. This plasma is operated at 10 kV and the nitrogen dissociation rate is determined by analyzing the optical emission of the nitrogen band. For different operating conditions, the dissociation rate [N] of N₂ molecules was enhanced, as the mixture quantity of Ar increased from 0.06 m³/h to 0.9 m³/h and the max of enhancement factor is 4.3. This factor becomes bigger when the N₂ flux becomes bigger. Moreover, the molecular nitrogen ionization density is calculated from the current intensity of the plasma. The ionization density was also enhanced, as the mixture quantity of Ar increased from 0.1 m³/h to 1.5 m³/h, under three different voltages. The max of enhancement factor of 1.96 is much smaller than the factor of the dissociation rate. These results are discussed in terms of the kinetics of the electrons, nitrogen ions, atoms and molecules.     

Quantum suppression of microwave ionization of Rydberg atoms at high scaled frequency

Microwave ionization of Rydberg atoms is well described as the onset of classical chaos when the microwave frequency omega is less than the Kepler frequency 1/n(3). However, when omega>1/n(3), i.e., at high scaled frequency Omega=omegan(3)>1, classical ionization is predicted to be suppressed by quantum interference, an analogue to Anderson localization in a solid. Using 17.55 GHz microwave fields we have observed the ionization of Sr Rydberg atoms in the regime 1相似文献   

Thermal ionization instability of an air discharge plasma in a microwave field

Results are presented from experimental studies of the initial stage of an air discharge initiated in a linearly polarized quasi-optical microwave beam. The discharge was excited at an air pressure at which the electron-neutral collision frequency in the discharge plasma was considerably higher than the circular frequency of the electromagnetic field and at a microwave field amplitude close to the threshold field for air breakdown. The experiments revealed relatively bright plasma channels stretched along the microwave electric field. The development rate of these channels and their characteristic transverse dimensions are estimated. A comparison of the experimental data and theoretical estimates indicates that the channels observed arise due to the onset of thermal ionization instability in the microwave discharge plasma.