Saturation time and growth rate of parametrically excited ion acoustic waves

The amplitude evolution of parametrically excited ion acoustic waves is shown. The instabilities are generated by a strong electric field applied to a krypton plasma column.     

Directivity pattern of parametrically generated acoustic waves

Summary The generation of down-converted frequency waves in the nonlinear propagation of acoustic waves is examined, in order to investigate the effects produced by the finiteness of the medium or of the media of interaction. Oscillations of the directivity patternsvs. the width of the media of interaction are set in evidence and related to resonance conditions of the medium cavity. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Dynamics of counterpropagating waves in parametrically driven systems: dispersion vs. advection

The dynamics of parametrically driven counterpropagating waves in a one-dimensional extended nearly conservative annular system are described by two coupled, damped, parametrically driven nonlinear Schrödinger (NLS) equations with opposite transport terms due to the group velocity, and small dispersion. The system is characterized by two length scales defined by a balance between (a) forcing and dispersion (the dispersive scale), and (b) forcing and advection at the group velocity (the transport scale). Both are large compared to the basic wavelength of the pattern. The dispersive scale plays an important role in the structure of solutions arising from secondary instabilities of frequency-locked spatially uniform standing waves (SW), and manifests itself both in traveling pulses or fronts and in extended spatio-temporal chaos, depending on the signs of the dispersion coefficient and nonlinearity.     

声表面波驱动的非接触式转动马达

在研究摩擦力驱动的接触式转动马达的基础上,本文研制了一种由声表面波驱动的非接触式转动马达。这种马达的定子选用128°YX-LiNbO₃晶体,在晶体表面光刻两对叉指换能器,由叉指换能器在定子表面激发两列平行而反向传播的声表面波。定子表面铺一层流体,转子就浮在流体表面。当定子表面有两列平行而反向的声表面波传播时,流体层中就会产生平行而反向的声流,这种黏性流体的声流运动就会驱动转子运动。实验上测定了马达的角速度随驱动电压、流体层厚度以及流体运动黏性系数变化的结果。同时,我们也发现,在相同工作频率下,非接触式转动马达的阈值电压远小于接触式。     

On collisionless damping of ion acoustic waves

Exact theoretical treatments show that the damping of ion acoustic waves in collisionless plasmas does not vanish when the derivative of the undisturbed distribution function at the phase velocity equals zero.     

Chaos in the parametrically driven sine-Gordon system

The appearance of chaos in the parametrically driven sine-Gordon equation is studied analytically. The chaotic behavior of breathers under the action of the periodic parametrical perturbations is found.     

Effect of nonthermal ion distribution and dust temperature on nonlinear dust acoustic solitary waves

The effects of nonthermal ion distribution and finite dust temperature are incorporated in the investigation of nonlinear dust acoustic waves in an unmagnetized dusty plasma. Sagdeev pseudopotential method which takes into account the full nonlinearity of plasma equations, is used here to study solitary wave solutions. Possibility of co-existence of refractive and compressive solitons as a function of Mach number, dust temperature and concentration of nonthermal ions, is considered. For the fixed value of nonthermal ions, it is found that the effect of increase in dust temperature is to reduce the range of co-existence of compressive and refractive solitons. Particular concentration of nonthermal ions results in disappearance of refractive solitons while the decrease in dust temperature, at this concentration restores the lost refractive solitons.     

Electron current driven ion acoustic standing wave instability

By means of a positively biased grid an electron current driven instability is excited in a single ended Q-machine. The instability shows the behaviour of a half standing ion acoustic wave with nodes at the hot plate and the grid. For high grid biases an increased plasma temperature is found.     

Radiation of ion acoustic waves in a dispersive positiveion-negative ion plasma

Experimental results that illustrate some properties of the radiation of a longitudinal ion acoustic wave launched from a solid metal disk antenna inserted in a dispersive positive-ion-negative-ion plasma are presented. The negative ions replace the free electrons in the plasma and increase the electron Debye length, hence increasing the dispersion of the plasma. It is observed that the radiation of waves in a dispersive media is significantly more complicated than in a nondispersive media. It is not possible to draw one universal radiation pattern for the radiation of the waves in this case, since so many frequency components are present in the wave and they change as the wave evolves     

Trapped electron in ion acoustic waves and solitons

Experimental evidence of trapped electrons in ions acoustic nonlinear waves and solitons propagating in a stable plasma is reported. Agreement between theory and experiment was found for the dependency of the energy of the trapped electrons versus wave amplitude.     

Harmonic ion acoustic waves in stimulated Brillouin scattering

Ion acoustic harmonic generation is a heavy damping mechanism of stimulated Brillouin scattering. The theory of first harmonic ion wave production is extended to frequencies four times the fundamental. Besides, the corresponding set of 6 differential equations is solved numerically for the steady state, and spatial solutions of the ion wave amplitudes are obtained. By varying typical parameters of laser plasma interaction experiments some characteristics properties are gained which might be of use for comparison with experiments.     

Single-electron transport driven by surface acoustic waves in quasi-one-dimensional channel

Fourier grid Hamiltonian method is applied to calculate the quantized acoustoelectric current induced by surface acoustic wave (SAW) in a quasi-one-dimensional channel defined in a GaAsAl_xGa_1−xAs heterostructure by split gate. Using simple models for the electrostatic potential barrier and piezoelectric potential, we obtain the first quantized plateau. Moreover, the role of the parameter β, defined as a ratio of piezoelectric potential amplitude to the effective height of electrostatic potential barrier induced by split gate, is also examined during the calculations of the instantaneous ground state energies and the single-electron tunneling probabilities. The flatness of the plateau is also discussed.     

Propagation of solitary ion acoustic waves in inhomogeneous plasmas

A WKB solution for the propagation of a solitary ion acoustic wave in a plasma with a density gradient is obtained.     

Theoretical simulation of a rotary motor driven by surface acoustic waves

A simulation model for theoretically studying the operation behavior of a rotary motor driven by surface acoustic waves (SAWs) is proposed. According to the model, some simulation results are obtained as follows: (1) as the rotor is excited by the SAWs, the motor experiences two phases, i.e., the acceleration phase and the steady phase; (2) the normal vibration amplitude A of SAWs has a very weak effect on the acceleration in the first phase but an enhancing effect on the steady velocity of the rotary motor; (3) as the number of the contact points between the rotor and the stator increases, the motor rotates more steadily; (4) as the rotor radius becomes smaller, both the acceleration and the steady angular velocity become greater. These features are in agreement with the experimental results.     

On the effect of fractional statistics on quantum ion acoustic waves

In this paper, I study the effect of a small deviation from the Fermi–Dirac statistics on the quantum ion acoustic waves. For this purpose, a quantum hydrodynamic model is developed based on the Polychronakos statistics, which allows for a smooth interpolation between the Fermi and Bose limits, passing through the case of classical particles. The model includes the effect of pressure as well as quantum diffraction effects through the Bohm potential. The equation of state for electrons obeying fractional statistics is obtained and the effect of fractional statistics on the kinetic energy and the coupling parameter is analyzed. Through the model, the effect of fractional statistics on the quantum ion acoustic waves is highlighted, exploring both linear and weakly nonlinear regimes. It is found that fractional statistics enhance the amplitude and diminish the width of the quantum ion acoustic waves. Furthermore, it is shown that a small deviation from the Fermi–Dirac statistics can modify the type structures, from bright to dark soliton. All known results of fully degenerate and non-degenerate cases are reproduced in the proper limits.