喷气Z箍缩内爆等离子体的雪铲模型

在喷气Z pinch内爆等离子体研究中,雪铲模型是一种常用的、比较简单的物理模型。根据实验中提供的电流波形,负载线质量和初始半径,可以通过雪铲模型来估算内爆到心的时刻。根据一维运动方程和不同构形下的解析解以及部分实验结果相结合,讨论了雪铲模型的适用范围。数值计算的内爆时间和实验（Gamble II, Double EAGLE, BLACKJACK 5）测量值符合得较好。结果表明,雪铲模型在喷气Z pinch实验的负载优化设计研究中是很有参考价值的方法。     

Characterizing passive coherent population trapping resonance in a cesium vapor cell filled with neon buffer gas

We present a pair of phase-locked lasers with a 9.2-GHz frequency difference through the injection locking of a master laser to the RF-modulation sideband of a slave diode laser. Using this laser system, a coherent population trapping (CPT) signal with a typical linewidth of ～ 182 Hz is obtained in a cesium vapor cell filled with 30 Torr (4kPa) of neon as the buffer gas. We investigate the influence of the partial pressure of the neon buffer gas on the CPT linewidth, amplitude, and frequency shift. The results may offer some references for CPT atomic clocks and CPT atomic magnetometers.     

Formation of cavities in a Z pinch plasma

Technical Physics - The spatial structure and dynamics of the plasma in a high current vacuum spark discharge are studied via pulsed shadowgraphy. The formation of cavities in the neck plasma at...     

Magnetohydrodynamic instabilities of a pinch resonant streamer microwave discharge

A pulsed freely localized resonant streamer microwave discharge in air and high-pressure hydrogen in the field of a linearly polarized standing electromagnetic wave in a two-mirror open cavity is investigated. The observed characteristic features of the discharge are treated as consequences of the sausage and wriggle instabilities of the plasma channel with a longitudinal microwave current contracted by its magnetic self-field.     

Experimental evidence of non-inverted population in a neon hollow-cathode

By the use of two step excitation from the (2p⁵ 3s)¹P₁ state of neon very large enhancements of the optogalvanic signals were obtained. This proves that no inverted population between the levels 2p_1,2,3,4,5 and ¹P₁ occurs as it was proposed in a recent paper. A new explanation of the inverted optogalvanic signals obtained for transitions originating from this ¹P₁ state is proposed.     

Measurement of instability growth in a magnetized Z pinch in the finite-Larmor-radius regime

The development of the m = 0 instability in a Z pinch was followed and the measured growth rates compared with 2D MHD simulations. Where MHD is valid, the measured growth rates agree well with simulation. Where the ions are magnetized, i.e., where the ion-cyclotron frequency is smaller than the ion-collision frequency and the ratio of the ion Larmor radius to pinch radius is of the order of 0.1, the growth rate was smaller than expected by a factor of 2.5. This is as predicted by finite-Larmor-radius theory. The product of the wave number and the pinch radius was ka approximately 2pi and was the same for all conditions. Perturbations as large as 30% of the pinch radius were observed; no nonlinear saturation was evident.     

Optogalvanic signals generated in a neon positive column discharge by resonant chopped CW radiation at 588.2 nm

The optogalvanic line profile for the 1s₅?2p₂ transition (Paschen notation) in a neon positive column discharge has shown a change in sign as a function of dye laser power for a pressure of 1.5 Torr and small currents (2–20 mA). Rate equation analysis suggests this may be due to the increase in the 1s₃ metastable density.     

铝丝阵列Z箍缩的辐射磁流体动力学过程

在拉格朗日坐标系下,建立了描述Z箍缩等离子体内爆动力学过程的一维三温辐射磁流体力学方程组,并编制了相应的拉氏程序。利用该程序对美国Sandia实验室Saturn装置上的铝丝阵列内爆实验进行了数值模拟,得到了内爆等离子体各参量的时空分布。其中内爆到心时刻、X光峰值功率、X光总能量等计算结果与实验结果基本一致。表明所建立的物理模型和编制的程序是合理和可靠的。     

用马赫贞德干涉仪测量喷气式Z箍缩等离子体密度

为了研究喷气式Z箍缩（gas-puff Z-pinch）等离子体的内爆特性,研制了一套马赫-贞德干涉系统,并在小型喷气式Z箍缩装置(充电电压23kV,放电峰值电流210kA)上进行了试验,获得了清晰的干涉图像。根据干涉图上条纹的移动数目,计算得到该装置内爆早期等离子体的平均电子密度为1017~1018/cm3。     

Realization of population inversion in a two-level system by damping field

We propose a new method for reversing the quantum state of a two-level system. From solving the time-dependent Schrödinger equation numerically, we show that by applying a classical decaying oscillatory field the state in a two-level system can be completely reversed if the parameters of the field satisfy certain conditions. The transition probability from one level to the other is calculated for different parameters and its maximum value can reach unity. By using such field with specific oscillatory frequency the Rabi oscillations between two levels in the case of applying a constant field can be suppressed and a stable manipulation of the quantum state can be performed. The estimation of such manipulation by using laser pulse acting on the states of hydrogen atom shows that the population inversion higher than 0.9 may be realized in less than 2 fs.     

Effect of the Doppler broadening on the nonlinear amplification of a polarized wave that propagates in a resonant medium without population inversion

The general nonlinear stationary theory of propagation of an elliptically polarized pulse that resonantly interacts with the 1/2-1/2 transition is developed taking into account relaxation processes. It is shown that interference of magnetic sublevels in the field of polarized radiation that optically pumps atoms results in inversionless amplification of radiation. Taking into account the Doppler broadening of spectral lines shows that there exists a certain optimal length of the resonant medium along which the radiation that emerges from the medium is maximally amplified.     

Design and characteristics of a differential Helmholtz resonant photoacoustic cell for infrared gas detection

The Helmholtz resonant photoacoustic (PA) cell is a very convenient design of PA system for air pollution monitoring based on infrared molecular absorption. A simple differential Helmholtz resonator designed for flow measurements is presented in this work. The investigation of the PA systems characteristics based on this design includes experimental study of the responsitivity both of the separate photoacoustic cell and the whole photoacoustic system applied to trace gases detection. The experimental observations are compared to the theoretical predictions. A simple arrangement to enhance the photoacoustic signal of the whole system by a factor of 2 is presented.     

Time reversal during magnetization of gas atoms by a resonant light pulse

The optically induced magnetic moment of a stationary atom is calculated as a function of time and the resonance detuning ω-ω _ba to within a constant factor having the dimensions of a magnetic moment based on the symmetry of an atom in the field of a resonant light pulse and symmetry with respect to time reversal including the initial conditions. The even dependence of the optically induced magnetic moment on ω-ω _ba for an elliptically polarized pulse with an isotropic initial state of the atom and its odd dependence on ω-ω _ba in the case of a linearly polarized pulsed with an anisotropic initial state in the atom’s alignment are shown to be consequences of symmetry with respect to time reversal and the initial conditions. This behavior is retained even after passage of the light pulse, when the resulting relaxation destroys the time reversal symmetry. The optically induced magnetization of an atomic gas is found to have analogous properties. Zh. éksp. Teor. Fiz. 112, 453–469 (August 1997)