Theory of weak modified electron acoustic double layers

Summary We have obtained the double-layer solutions for the small-amplitude modified electron acoustic waves propagating in a plasma having one ion and two electron components. No DLs solutions are found to exist when the temperature of the free and trapped particles is considered to be the same for all the species. However, when the effects of the reflected hot electrons are considered, DL solutions are found to exist.

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Riassunto Si sono ottenute soluzioni del doppio strato per onde acustiche modificate dall’elettrone di piccola ampiezza, che si propagano in un plasma avente una componente ionica e 2 componenti elettroniche. Si trova che non esistono soluzioni DL quando la temperatura delle particelle libere e intrappolate si considera stessa per tutte le specie. Tuttavia si trova che le soluzioni DL esistono quando si considerano gli effetti degli elettroni caldi riflessi.

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Резюме Мы получили решения для двойных слоев в случае акустических волн с малой амплитудой, распространяющихся в плазме, имеющей одну ионную и две электронные компоненты. Показано, что не существуют решения для двойных слоев, когда температура свободных и захваченных частиц является одинаковой для всех компонент. Однако, когда учитывается влияние отраженных горячих электронов, решения для двойных слоев существуют.

     

Weak electron acoustic double layers in a multicomponent plasma

Formation of electron acoustic double layers in a magneto-plasma with two ion species is investigated. The existence of double layers propagating almost perpendicular to the magnetic field in a plasma with two distinct ion species and cold electron is discussed.     

弱耦合封闭声腔的声辐射模态理论与计算

有源结构声控制是耦合封闭声腔的声辐射控制的有效方法。在此前的研究中有学者提出了\     

Theory and calculation for acoustic radiation mode of weak coupled enclosure

Active structural acoustic control(ASAC)is an efficient method in acoustic radiation control of coupled enclosure.In the past research of ASAC,the concept of "acoustic radiation mode(ARM)of coupled enclosure"was proposed,which was a set of basis functions of structural mode amplitude.However,there was an incompatibility with the ARM definition in free space radiation case which was a set of basic functions of normal velocity or pressure on the vibrating surface.Also,there was severe inconvenience for application as structural modes were required while accurate and useful structural modes were difficult to be extracted in practice.To overcome these problems,by analogy to ARM theory of free space,the acoustic potential energy was expressed in quadratic form of normal velocity on coupling surface and ARM of coupled enclosure was redefined.Furthermore,theoretic derivation showed that ARM of coupled enclosure could be replaced simply by corresponding acoustic mode projection of enclosure when the coupling surface was discretized into equal size elements.Therefore,the ARM theory of coupled enclosure which was consistent with that of free space and convenient for application was formed.Finally,numerical calculation was performed and the results proved that the presented theory was very efficient in ARM calculation of coupled enclosure and ASAC.     

Electrostatic double layers in a warm negative ion plasma with nonextensive electrons

The electrostatic double layer (DL) structures are studied in negative ion plasma with nonextensive electrons q-distribution. The extended Korteweg–de Vries (EKdV) equation is derived using a reductive perturbation method. It is found that both fast (compressive) and slow (rarefactive) ion acoustic (IA) DLs can propagate in such type of plasmas. The effects of various plasma physical parameters; such as nonextensivity of electrons, presence of negative ions, temperature of both positive and negative ions and different mass ratios of positive to negative ions on the formation of DL structures are discussed in detail with numerical illustrations.     

Moving double layers

Using a triple-plasma device, moving double layers have been produced by abruptly increasing the plasma density in the region of the double layers. Propagation velocities up to 3.5 c_s have been achieved with their velocity scaling as $\text{ν ～ (2e ×}\text{δ?}\text{T}{}_{\mathrm{<mtext>e</mtext>}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{c}{}_{\mathrm{<mtext>S</mtext>}}$.     

Large-amplitude double layers in a dusty plasma with an arbitrary streaming ion beam

Formation of large-amplitude double layers in a dusty plasma whose constituents are electrons, ions, warm dust grains and positive ion beam are studied using Sagdeev’s pseudopotential technique. Existence of double layers is investigated. It is found that both the temperature of dust particles and ion beam temperature play significant roles in determining the region of the existence of double layers.     

Potential double layers in double plasma device

Results of the investigation on the formation of double layers in double plasma device are presented. By appropriate modifications in the biasing conditions, we have been able to obtain both weak (eΔφ<10KT _e ) and strong double layers (eΔφ>10kT _e ) in the device. Unlike previous experiments, we have not been limited to potential jumps equal to ionisation potential of the neutral gas. A detailed investigation has been carried out to find out why earlier experiments in similar devices were limited to only weak double layers. We have also investigated the phenomenon of the so-called psuedo-double layers and have shown that they are potential jumps over the thickness of the order of Debye length and precede plasma expanding with velocity many times the ion-acoustic velocity. They do not represent metastable states of the plasma as suggested by earlier investigators.     

Ion acoustic double layers in the vicinity of the critical velocity in a weakly relativistic plasma

Ion acoustic double layers in the vicinity of the critical velocity in a weakly relativistic plasma are found for the first time from a mixed form of the KdV and mKdV equations by the reductive perturbation method. It is shown to yield compressive and rarefactive double-layer profiles under certain conditions.     

Fake double layers in double plasma devices

The double layer like potential jumps have been observed in a double plasma device. They do not correspond to a switching of plasma potential from one metastable state to another but are caused by the ionisation of a very minute amount of the gas that inevitably leaks into the system during the probe movement.     

Magnetoexcitons in unbalanced double layers

We study theoretically correlations of electrons and holes in unbalanced double-layer electronic systems in strong magnetic fields. Calculations are made using the exact diagonalization and the variational wave function. The ground state of an electron–hole pair in quantized cyclotron orbits possesses an in-plane electric dipole moment, when an electron and a hole are in different Landau orbits with different radii. The resulting attractive interactions between pairs creates the possibility of novel states.     

Hemispherical ion acoustic solitons

Hemispherical solitons are studied experimentally using a double-plasma device provided with a hemispherical dividing screen. Their properties are compared with those of spherical solitons and differ appreciably. Auxiliary pulses appear behind the soliton, each propagating faster than the soliton but eventually approaching the soliton speed     

Acoustic double layers in multispecies plasma

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 uu_e 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/V_O=√M_O/ M_H=4.0). Acoustic double layers form in either ion species on the time scale τ≈100ω_ps^-1, where ω_ps 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     

Theory of the spectral acoustic phonon emission intensity of hot 2D electrons in quantized n-inversion layers

The spectral acoustic phonon emission intensity of the hot quasi two-dimensional electron gas (2DEG) in quantized n-Si (GaAs) inversion layers is calculated as a function of the phonon angular frequency w at different values of the carrier temperature T_e and density N_s. In the long wave length limit (ℏw ⪡ k_BT_e) the emission intensity increases ∝ w^s(w^s+1) for bulk- (surface-) modes where s = 3 for the unscreened acoustic deformation potential coupling. At w ≈ v_j2k_F (v_j: sound velocity of the phonon mode j, k_F: radius of the Fermi-circle) the emission intensity reaches a maximum whose position is shifted to higher w-values if N_s increases. For given values of N_s, T_e, T (lattice temperature) and ϑ (emission angle) the emission intensity maximum of the n-GaAs inversion layer is found to be about one order of magnitude smaller than the intensity maximum of the n-Si inversion layer.