Theory of Parametric Instabilities and Harmonic Generation in Tonks-Dattner Resonances

Onedimensional fluid theory of Tonks-Dattner resonances in inhomogeneous, bounded plasmas is extended to stronger exciting electric fields. The relation of parametric instabilities and harmonic generation with Tonks-Dattner resonances will be worked out in a more direct way than in previous work. Electric field thresholds and growth rates for parametric instabilities will be obtained from theory of homogeneous Mathieu equation. Stationary excitation at the driving frequency and its harmonics follows from a particular solution of an inhomogeneous Mathieu equation.     

Parametric excitation of magnetic electron drift vortex modes by Langmuir waves

A new multi-dimensional parametric interaction coupling Langmuir waves with magnetic electron drift vortex modes is presented. A general dispersion relation for the parametric instabilities is derived, and the growth rates of the decay and modulational instabilities are obtained. The present instabilities can be the source of large-scale magnetic fields near the critical surface of a laser-produced plasma.     

国内典型地区地面大气中子能谱测量与仿真

基于多球能谱仪开展了广州、兰州和拉萨等地区的大气中子能谱和通量测量,获取了大气中子能谱的典型特征。测量结果表明：不同地区的大气中子通量受海拔高度的影响明显,地面大气中子通量随着海拔的增加而增加。此外,基于蒙特卡罗仿真工具也可以模拟初级宇宙射线粒子在地球大气层中的核反应过程,从而计算获取大气中子能谱。大气中子能谱测量数据与仿真数据吻合良好。     

啁啾展宽激光脉冲的有限带宽效应对参量不稳定性及超热电子的抑制

若驱动激光的相干时间小于不稳定性增长时间,则有可能直接控制参量不稳定性。研究了有限带宽的啁啾展宽脉冲对等离子体晚区参量不稳定性及超热电子的抑制效果,给出解析分析及用ＰＩＣ程序数值模拟结果,考察了电子一离子磁拦对超热电子的影响。     

Secondary transverse instabilities in optical parametric oscillators

We investigate the effect of coupling between diffraction and walk-off on secondary instabilities in nondegenerate optical parametric oscillators. We show that traveling waves that propagate in the walk-off direction, which are generated at the onset of absolute instability, experience Eckhaus and zigzag phase instabilities. Each of these secondary instabilities splits into absolute and convective instabilities that modify the Eckhaus and zigzag instability boundaries. As a consequence, the stability domain of modulated traveling waves is enlarged and may coexist with uniform steady states. The predictions are consistent with the numerical solutions of the optical parametric oscillator model.     

Parametric instabilities and their control in advanced interferometer gravitational-wave detectors

A detailed simulation of Advanced LIGO test mass optical cavities shows that parametric instabilities will excite 7 acoustic modes in each fused silica test mass, with parametric gain R up to 7 and only 1 acoustic mode with R approximately 2 for alternative sapphire test masses. Fine-tuning of the test mass radii of curvature causes the instabilities to sweep through various modes with R as high as approximately 2000. Sapphire test mass cavities can be tuned to completely eliminate instabilities using thermal g-factor tuning. In the case of fused silica test mass, instabilities can be minimized but not eliminated.     

Parametric instabilities in quantum plasmas with electron exchange-correlation effects

Parametric instabilities induced by the nonlinear interaction between high frequency quantum Langmuir waves and low frequency quantum ion-acoustic waves in quantum plasmas with the electron exchange-correlation effects are presented.By using the quantum hydrodynamic equations with the electron exchange-correlation correction,we obtain an effective quantum Zaharov model,which is then used to derive the modified dispersion relations and the growth rates of the decay and four-wave instabilities.The influences of the electron exchange-correlation effects and the quantum effects on the existence of quantum Langmuir waves and the parametric instabilities are discussed in detail.It is shown that the electron exchange-correlation effects and quantum effects are strongly coupled.The quantum Langmuir wave can propagate in quantum plasmas only when the electron exchange-correlation effects and the quantum effects satisfy a certain condition.The electron exchange-correlation effects tend to enhance the parametric instabilities,while quantum effects suppress the instabilities.     

Parametric decay instabilities of lower hybrid wave into electromagnetic wave

The parametric decay instabilities of lower hybrid wave into electromagnetic modes are investigated in homogenous magnetized plasma. The resonant decay instabilities and the oscillating two stream instabilities are studied numerically in detail.     

激光(I=1014-1015wcm-2,λ=1.06μm)等离子体参量不稳定性加热

本文利用一维半粒子云网格(Cloud-in-Ccll)程序,对激光打靶中的参量不稳定性引起的湍流加热进行了数值模拟研究。得到的线性增长率和理论预估合理地符合;还得到了非线性加热率、受热电子的速度分布、波纹临界密度面和离子坑等物理图象。对这些结果进行了分析和讨论。     

Comparison of parametric instabilities for different test mass materials in advanced gravitational wave interferometers

Following the recognition that parametric instabilities can significantly compromise the performance of advanced laser interferometer gravitational wave detectors, we compare the performance of three different test mass configurations: all fused silica test masses, all sapphire test masses and fused silica inboard test masses with sapphire end test masses. We show that the configuration with sapphire end test masses offers the opportunity for thermal tuning on a time scale comparable to the ring up time of oscillatory instabilities. This approach may enable significant reduction of parametric gain.     

Analytical investigation on unstable vibrations of single-mesh gear systems with velocity-modulated time-varying stiffness

Time-varying mesh stiffness parametrically excites gear systems and causes severe vibrations and instabilities. Taking speed fluctuations into account, the time-varying mesh stiffness is frequency modulated, and more complex instabilities might arise. Considering two different speed fluctuation models, parametric instability associated with velocity-modulated time-varying stiffness is analytically investigated using a typical single-mesh gear system model. Closed-form approximations are obtained by perturbation analysis, and verified by numerical analysis. The effects of the amplitude of the mesh stiffness variation, the characteristics of speed fluctuations and damping on parametric instability are systematically examined.     

On parametric absorption in laser plasma

A theory for the nonlinear saturation of convective parametric instabilities in inhomogeneous plasmas is proposed. The role of parametric processes in laser light absorption in a dense plasma corona is discussed on the basis of this theory.     

A gas target for the study of laser-induced parametric instabilities in plasmas

A hydrogen gas target is described which has been irradiated with a high intensity CO₂ laser beam to study parametric instabilities. Such a target, with n ? n_c, provides considerable flexibility and optical access for detailed diagnostics. Preliminary measurements are reported on stimulated Brillouin (and Compton) scattering, 2-plasmon decay and second harmonic generation, in addition to interferometric and enhanced Thomson scattering measurements, which illustrate the versatility of this target for detailed investigation of parametric instabilities.     

Decay and modulation instabilities of beat waves in a plasma

Summary A large-amplitude beat wave excited at the beat frequency of two copropagating laser beams is extremely unstable and suffers strong three- and fourwave parametric instabilities with large growth rates. The relativistic effects are seen to be negligible on both the decay and modulation instabilities. However, the growth rates of these instabilities are sensitive functions of the plasma parameters. The authors of this paper have agreed to not receive the proofs for correction.     

Modification of pattern formation in doubly resonant second-harmonic generation by competing parametric oscillation

We analyze pattern formation in doubly resonant intracavity second-harmonic generation in the presence of competing nondegenerate parametric downconversion. We show that for positive cavity detuning of the fundamental frequency the threshold for parametric oscillation is lower than that of transverse, pattern forming instabilities. The parametric oscillation strongly modifies the pattern dynamics found previously in a simplified analysis that neglects parametric instability [Phys. Rev. E 56, 4803 (1997)]. Stationary and dynamic patterns in the presence of parametric oscillation are found numerically.     

A wide bandwidth,high power laser source for plasma interaction studies

Wide spectral emission (50 Å FWHM) from a resonator comprising two Nd doped glass rods in the same cavity has been obtained. The realization is mainly devoted to the study of parametric instabilities in laser plasmas. Further developments and applications are discussed.     

Threshold Fields of Parametric Instabilities

The threshold electric fields of parametric decay instabilities in a magnetized plasma have been derived. Consideration is given to a unified presentation of a number of basic processes of particular interest.     

Parametrically excited helicopter ground resonance dynamics with high blade asymmetries

The present work is aimed at verifying the influence of high asymmetries in the variation of in-plane lead-lag stiffness of one blade on the ground resonance phenomenon in helicopters. The periodical equations of motions are analyzed by using Floquet's Theory (FM) and the boundaries of instabilities predicted. The stability chart obtained as a function of asymmetry parameters and rotor speed reveals a complex evolution of critical zones and the existence of bifurcation points at low rotor speed values. Additionally, it is known that when treated as parametric excitations; periodic terms may cause parametric resonances in dynamic systems, some of which can become unstable. Therefore, the helicopter is later considered as a parametrically excited system and the equations are treated analytically by applying the Method of Multiple Scales (MMS). A stability analysis is used to verify the existence of unstable parametric resonances with first and second-order sets of equations. The results are compared and validated with those obtained by Floquet's Theory. Moreover, an explanation is given for the presence of unstable motion at low rotor speeds due to parametric instabilities of the second order.     

Spectra of Stimulated Electromagnetic Emission of the Ionosphere Sweeping of the Pump Wave Frequency Near Gyroharmonics. II. Discussion of the Results

Alternative mechanisms of generation of the stimulated electromagnetic emission (SEE) excited in the ionosphere by high-power radio waves are analyzed on the basis of measurements of the SEE spectra obtained during the pump-wave frequency sweeping near the forth (n = 4) and fifth (n = 5) harmonics of the electron gyrofrequency nf_ce [1] and their comparison with the existing physical models. A method for determination of the magnetic field strength and plasma density near the double-resonance region in the ionosphere is developed. It is shown that the generation of the broad upshifted maximum (BUM) feature in the SEE spectrum should occur several kilometers below the double-resonance altitude. A role of high-frequency plasma modes and small-scale magnetic field-aligned irregularities, excited under ionosphere pumping by a high-power radio wave, in the formation of SEE spectra is demonstrated. It is shown that the difference in the emission intensities for f₀ ≲ nf_ce and f₀ > nf_ce is related to different regions (altitudes) at which the plasma waves exist in these cases. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 7, pp. 553–570, July 2008.