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The dynamic behavior of large amplitude ion-acoustic double layers in a plasma is investigated in the presence of two-temperature nonextensive electrons. The effects of physical parameters, such as the temperature and concentration of positive ions on the formation and structure of double layer are discussed. It is shown that the depth of the Sagdeev potential and the amplitude of both positive and negative ion-acoustic double layers sensitively depend on the temperature and the concentration of positive ions. The obtained results are also compared with the results of a similar Maxwellian plasma with warm ions and two (cold and hot) electron species.

We report the experimental generation of highly energetic carbon ions up to 48 MeV per nucleon by shooting double-layer targets composed of well-controlled slightly underdense plasma and ultrathin foils with ultraintense femtosecond laser pulses. Particle-in-cell simulations reveal that carbon ions are ejected from the ultrathin foils due to radiation pressure and then accelerated in an enhanced sheath field established by the superponderomotive electron flow. Such a cascaded acceleration is especially suited for heavy ion acceleration with femtosecond laser pulses. The breakthrough of heavy ion energy up to many tens of $\mathrm{MeV}/\mathrm{u}$ at a high repetition rate would be able to trigger significant advances in nuclear physics, high energy density physics, and medical physics.

In the present investigation, ion-acoustic double layers in an inhomogeneous plasma consisting of Maxwellian and non-thermal distributions of electrons are studied. We have derived a modified Korteweg–de Vries (mKdV) equation for ion-acoustic double layers propagating in a collisionless inhomogeneous plasma. It is observed that the non-thermal parameters affect the amplitude and width of the double layer which further depend on the density.

Small amplitude ion-acoustic double layers in an unmagnetized and collisionless plasma consisting of cold positive ions, q-nonextensive electrons, and a cold electron beam are investigated. Small amplitude double layer solution is obtained by expanding the Sagdeev potential truncated method. The effects of entropic index q, speed and density of cold electron beam on double layer structures are discussed.

An analytical solution for time stationary weak double layers in an unmagnetized dusty plasma by using Sagdeev’s pseudopotential method is studied considering dusts with constant charge and mass. Here, the plasma consists of electrons, ions and negatively-charged micron-sized dust particles. From the study, expressions for the potential and the dust acoustic velocity of the double layer is determined.

[1] The formation and dynamic evolution of double layers which form inside the auroral cavity are studied using one- and two-dimensional electrostatic particle-in-cell simulations. Both the one- and two-dimensional simulations are confined to processes that occur in the auroral cavity and include four plasma populations: hot electrons, H+ and O+ anti-earthward ion beams and a hot H+background population. We show that double layers inside the auroral cavity can evolve nonlinearly from ion phase space holes and are supported by the cold, anti-earthward traveling O+beam. We then present two-dimensional particle-in-cell results which show that double layers in the interior of the auroral cavity can form in higher dimensions. The electric field structure in 2-D is verified as a double layer through simultaneous analysis of the parallel electric field and H+ and O+ phase space.

The pseudopotential technique is applied to a multicomponent plasma consisting of nonthermal electrons and warm positive and negative ions with drift motion with a view to studying ion-acoustic double layers. Conditions for the existence of such layers are obtained, two critical concentrations of negative ions being identified which control the formation and nature of the ion-acoustic double layers. The effects of nonthermal electrons, negative-ion concentration, and negative-ion temperature on the double layer formation and structure are also investigated. The nonthermal electrons and the negative ions are shown to contribute significantly to the excitation and structure of the double layers. The importance of the results in the context of magnetospheric and auroral plasmas is discussed.

The plane-parallel flow of the collisionless ion flux integrally neutralized by Boltzmann electrons is considered. It is shown that there is a rigid unique relation between the velocity and current density in the quasi-neutral region on the collector, which defines equilibrium conditions of the near-cathode double layer.

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.

The conditions for formation of ion acoustic weak double layer in a dusty plasma are investigated. In case of much lower value of ion-electron temperature ratio, the weak double layer is observed when the fraction of the negative charge in the plasma on the dust grain is , whereas for equal ion-electron temperature it is observed only when the fraction is . The parameter regimes of transition from compressive to rarefactive double layer are also specified.

A theoretical model is presented to investigate the double layers, associated with the kinetic Alfven waves, in a magnetized electron–positron–ion plasma with a small but finite value of β, and small-amplitude double layer solutions are obtained. The existence of small-amplitude double layers requires that the density of ions is appreciably larger than that of positrons at equilibrium. The properties of the double layers are determined by the ratio between the number densities of positrons and ions at equilibrium, the direction cosines defining the moving frame, as well as the electron to positron temperature ratio.

It is found that, by means of numerical simulations, an ion acoustic instability (v/sub d/ < v/sub te/) results in the formation of double layers in a sufficiently long system. Anomalous resistivity generated by the ion acoustic instability causes the buildup of a dc potential which in turn accelerates electrons further to enhance the original instability leading to the formation of double layers. A necessary condition required for generating a double layer is given.

The existence of small amplitude ion acoustic double layers in a plasma consisting of cold ions, a hot population of electrons and negatively charged dust particles is investigated. The effect of trapped electrons on the formation of double layers is also investigated. It is shown that both compressive and rarefactive double layers can occur.

In the contribution the preliminary results of the simulation experiment on expansion of a collisionless plasma with negative ions into a vacuum are presented. The electric field profile development in time and phase spaces for all three species are presented and discussed. Dependencies on negative ion mass are also studied. Double layer‐like potential structure is observed to form in the expanding plasma under certain conditions.

Propagation of ion-acoustic double layers has been studied in plasma consisting of warm positive- and negative-ion species with different masses, concentrations, and charge states along with electrons with two-electron temperature distributions. It is found that there exist two critical concentrations of negative ions, ${\ensuremath{\alpha}}_{R}$ and ${\ensuremath{\alpha}}_{Q}.$ One of them $({\ensuremath{\alpha}}_{R})$ generally decides the existence of the double layer, whereas the other one $({\ensuremath{\alpha}}_{Q})$ decides the nature of the double layer. It is found that the system supports ion-acoustic double layers only when the negative-ion concentration (\ensuremath{\alpha}) is greater than the critical concentration ${\ensuremath{\alpha}}_{R}.$ It is also found that below the critical concentration ${\ensuremath{\alpha}}_{Q},$ compressive double layers exist and above it rarefactive double layers exist. For some values of cold-electron concentrations (\ensuremath{\mu}) it is found that if the temperature of the negative-ion species is higher than the positive-ion species, then the system supports compressive double layers for all values of \ensuremath{\alpha} lying in the range $0l\ensuremath{\alpha}l{\ensuremath{\alpha}}_{Q}.$ The dependence of the critical concentrations on the temperatures of the two-ion species and on the concentration of cold electrons has also been investigated.

In order to achieve a high-quality, i.e., monoenergetic, intense ion beam, we propose the use of a double-layer target. The first layer, at the target front, consists of high-Z atoms, while the second (rear) layer is a thin coating of low-Z atoms. The generation of high-quality proton beams from the double-layer target, irradiated by an ultraintense laser pulse, is demonstrated with three-dimensional particle-in-cell simulations.

A theoretical study about the ion acceleration in low-energy (1010 W/cm2) laser-produced plasma is presented. Calculations have been implemented following a 1-D particle-in cell method. We describe the plasma-vacuum expansion dynamics and the ion acceleration due to the so-called double-layer formation. Observed results show that, regardless of the initial temperature and density of the plasma, postheating is needed to obtain average values of final ion kinetic energy distributions similar to the experimental results. This confirms that, with nanosecond pulsed lasers, the plasma is strongly heated by the laser pulse tail.

Undriven double layers observed in plasmas expanding along magnetic fields are the result of a sheath instability connected with the Bohm criterion. Diverging magnetic field lines cause the presheath acceleration of ions, causing a potential jump resembling that of a double layer. The process stops when it runs out of energy.

The propagation of ion acoustic double layers in a plasma containing a negative species of ions has been investigated theoretically. It has been found that this type of double layer exists when the electric potential is positive and the negative ion concentration is greater than some limiting value. It has also been shown that the double layers discussed in this paper may explain the recent observations on the auroral field lines.

The experimental results of the time evolution of a weak asymmetric ion-acoustic double layer, from a current-driven ion-acoustic instability are reported.

The spatial profile of potential in an ion sheath formed in front of a grid with a large cross-section is studied experimentally using a triple plasma device in the absence of a magnetic field. A potential double layer is established by injecting the ion beam into the ion sheath from the low potential side. The reflection of the injected ions produces a crest of the ion density, resulting in the formation of a knee on the potential profile. A relationship d varies as Delta phi 3/4 corresponding to space charge limitation is obtained where Delta phi and d are the height and the width of the potential double layer, respectively.

A one-dimensional particle-in-cell computer simulation is used to model the formation of an electrostatic double layer. The conditions for the onset of the layer formation are explored and a relation between the length of the layer and the electrostatic potential difference across is found.

Small-amplitude double layers and solitary waves containing magnetic-field-aligned electric field components have been observed for the first time in the auroral plasma between altitudes of 6000 and 8000 km in association with electron and ion velocity distributions that indicate the presence of electric fields parallel to the magnetic field. The double layers may account for a large portion of the parallel potential drop that accelerates auroral particles.

A potential double layer is formed by exciting a laminar shock wave with a step injection of ion beam in a triple plasma device. A potential jump of the double layer moving with a velocity of laminar shock wave is (1-1.4)kTe/e and the density fluctuation is 15-40%. Time resolved measurements of energy distribution function of both ions and electrons reveal that electrons are trapped and ions are reflected due to the formation of the potential double layer.

Ion acoustic double layer solutions have been obtained in a plasma in presence of a negative species of ions. It has been shown that the rarefactive double layer solutions exist when the negative ion concentration is less than a limiting value. Our theoretical result is in good agreement with the recent observation of rarefactive double layers moving from the ionosphere to the magnetosphpere of the earth.

The negative potential depression with a depth of approximately electron temperature is observed on the low potential tail of the double layer just at the moment when the electron current passing through the layer is disrupted. The depression is confirmed to serve as an electron thermal barrier and form as ion hole from phase-space measurements of electrons and ions, respectively. The depth of the depression becomes maximum when the density around the depression becomes most inhomogeneous.

The theory of propagation of modified electron acoustic double layers and solitary waves in a four-component plasma, consisting of electrons having both a “hot” and a “cold” component and positive ions at two different temperatures, has been investigated. The effect of isothermal and non-isothermal hot electrons in the formation of double layers and solitary waves has been studied. It is found that, when the hot electronic component is isothermal, there exist only rarefactive soliton solutions. However, the presence of non-isothermal hot electrons gives rise to both compressive soliton and double layer solutions.

Floating double electric probes in conjunction with optoisolators have been applied to detect strong local electric fields ( approximately=1.5 kV mm-1) in a moving double layer generated by a high-voltage straight plasma discharge. The probe current estimated from the electric signal picked up and the input impedance is found to be very much larger than the ion saturation current (convection current). The result can be explained if one supposes that these probes collect the polarisation current induced by passage of a highly polarised space-charge layer.

Experimental results are presented which demonstrate the formation of fully three dimensional double layers in a magnetized plasma. The measurements are performed in a magnetized stationary plasma column with radius 1.5 cm. Double layers are produced by introducing an electron beam with radius 0.4 cm along the magnetic field from one end of the column. The voltage drop across the double layer is found to be determined by the energy of the incoming electron beam. In general we find that the width of the double layer along the external magnetic field is determined by plasma density and beam energy, while the ion Larmor radius gives a characteristic width in the perpendicular direction. The electrons are strongly magnetized for all experimental conditions considered here.

A potential double layer is formed by injecting an ion beam into an ion-absorbing boundary with a large cross section from a low potential side in a non-magnetized plasma. An ion-density crest caused by the ion reflection is observed.