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The electric double layer in argon helicon plasma by using floating electrostatic probe and local optical emission spectroscopy under different external magnetic field was investigated. Results show that electrons generated in the plasma source can be magnetized by the magnetic field and transported by the gradient of diverging magnetic field in the diffusion chamber, giving rise to the hollowed distribution of electron temperature. The electron temperature on axis has a sudden decrease, leading to the sudden decrease of plasma density as well as the plasma potential, forming a double layer structure. The position of double layer moves along with the position of diverging magnetic field, and the potential drop increases along with the strength of magnetic field. The structure of the external magnetic field plays the decisive factor for the double layer in helicon plasma.

The double-layer approach (DLA) possesses superior features for the analysis of static electromagnetic problems. In this article, dealing with the magnetostatic analysis, we introduce two kinds of double layers: the first one on the surface of the magnetic body and the second one on the cut-surface within the exciting current loop. From the double layers on the cut-surface, we were able to derive a novel, unified exciting potential, which facilitates the treatment of any magnetostatic problem, including multiply connected problems. Furthermore, in this article, we use for the first time DLA for the analysis of magnetic forces acting on the magnetic bodies. The law of action and reaction provides a self-check function within DLA, enabling thus the simple and reliable tool for the confirmation if the computed results are adequate and accurate. This improved, DLA-based approach for the force analysis together with the introduced “action-reaction” principle for the self-checking of the force calculation are, to the authors' best knowledge, not known in the scientific community so far. Finally, we would like to emphasize that the presented DLA enables accurate, self-checked, generic analysis of the real-world devices, providing advanced treatment of both geometrical singularities (edges, corners) and materials used (high permeability, nonlinearities).

The plasma on a magnetic field line in the downward current region of the aurora is simulated using a Vlasov model. It is found that an electric field parallel to the magnetic fields is supported by a double layer moving toward higher altitude. The double layer accelerates electrons upward, and these electrons give rise to plasma waves and electron phase-space holes through beam–plasma interaction. The double layer is disrupted when reaching altitudes of 1–2 Earth radii where the Langmuir condition no longer can be satisfied due to the diminishing density of electrons coming up from the ionosphere. During the disruption the potential drop is in part carried by the electron holes. The disruption creates favourable conditions for double layer formation near the ionosphere and double layers form anew in that region. The process repeats itself with a period of approximately 1 min. This period is determined by how far the double layer can reach before being disrupted: a higher disruption altitude corresponds to a longer repetition period. The disruption altitude is, in turn, found to increase with ionospheric density and to decrease with total voltage. The current displays oscillations around a mean value. The period of the oscillations is the same as the recurrence period of the double layer formations. The oscillation amplitude increases with increasing voltage, whereas the mean value of the current is independent of voltage in the 100 to 800 V range covered by our simulations. Instead, the mean value of the current is determined by the electron density at the ionospheric boundary.

This investigation is composed of an observational part, plus a new theoretical model interpreting the related exhibited satellite datasets through an entirely new approach concerning the substorm's ultimate excitation mechanism. First, we present a few representative case studies showing the Bz component of the magnetic field to develop quasi-periodic negative deflections with periodicities ranging from T=15 to 60s in the central plasma sheet (CPS) with persistent tailward plasma flows. The wave activity of Bz is much lower outside the CPS, while occasionally almost a monochromatic response is identified. In certain cases, a profound change of frequency is evident and happens most probably due to the Doppler-effect; there is a relation between the plasma velocity enhancement and the increase of frequency. When comparing the amplitude of Bz deflections to the lobe magnetic field, one plausibly may infer that the deflections reflect the very dynamics of the source itself. Therefore, we put forward the concept about "a pulsating source", and more specifically, we adopt the pulsating "twin Double Layer (DL) structure" as the ultimate mechanism converting magnetic energy to kinetic. The DL acts either as a resistor or a capacitor and the twin-DL structure approximately behaves in a way similar to the cardiac cycle with repeated, rhythmic contractions and expansions. The contraction phase represents the abrupt local thinning of the plasma sheet (PS) that terminates explosively, heating the plasma and accelerating energetic particles. The expansion phase corresponds to a local distention of the source, which also terminates explosively. The DLs are oppositely polarized depending on the range of Rc whether it fulfills the condition rgi ≤ Rc < 9 rgi or rge < Rc < rgi, where rgi (rge) and Rc are the ion (electron) gyro-radius and the curvature radius of the local magnetic field, respectively. In more detail, the "akis structure", as it was earlier introduced by Sarafopoulos [1, 2] and further elaborated in this work, repetitively forms DLs that undergo a transition from depolarization to repolarization in each of the consecutive cycles. The collapse of the dissipation region (leading to local dipolarization) seems to occur when rge < Rc < 9rge. Large scale Boström's type II field aligned currents (FACs) flow and neutralize the net charges produced by "charge separation processes" within the twin-DL structure; thus the whole structure principally operates (under favorable conditions) like a huge resonant RLC-type circuit. Actually the pulsating source is an integral part of that huge (resonating) circuit, wherein even the ionosphere obviously plays its vital role imposing a positive feedback. The author of this study believes that Faraday's law can be experimentally validated with his suggested model more reliably than with the alternative X-type magnetic reconnection model incorporating the concept of "magnetic diffusion". The presently proposed "akis structure" embedded in the whole magnetotail's current system is presumably a precious structure with novel features. The source will probably be triggered at that place in which the condition for resonance is satisfied, while the resonance dramatically increases the rate of energy conversion, that is the efficiency of the source.

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.

After the theory of dynamic double layers in laser-produced plasmas arrived at several significant results in agreement with measurement, including particle acceleration, a clarification was given to the paper by Bryant et al. (1992) negating such acceleration. The discrepancy seems to be in the definition of static double layers in contradiction with dynamic double layers that are created in laser-induced plasma. We present here new results on the acceleration of electrons in a laser-irradiated plasma by double layer mechanisms. A simple analytical example is given.

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.

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 laser-driven acceleration of proton beams from a double-layer cone target, comprised of a cone shaped high-Z material target with a low density proton layer, is investigated via two-dimensional fully relativistic electro-magnetic particle-in-cell simulations. The dependence of the inside diameter (ID) of the tip size of a double-layer cone target on proton beam characteristics is demonstrated. Our results show that the peak energy of proton beams significantly increases and the divergence angle decreases with decreasing ID size. This can be explained by the combined effects of a stronger laser field that is focused inside the cone target and a larger laser interaction area by reducing the ID size.

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 thermal performance of a sunspace attached to a living room located in Amman-Jordan has been investigated. Six configurations that differ by the ratio of glazed surface area to opaque surfaces area are studied. A novel configuration that utilizes an inclined front surface is thermally investigated. The effect of orientation of the sunspace, opaque wall and floor absorption coefficients and number of glass layers on the thermal performance is evaluated. Results show that the sunspace reduces the heating load during the winter, while it creates a serious overheating problem during summer. The contribution of reducing heating requirements increases with increasing the ratio of glazed surface to opaque surface area. Also, the optimal contribution was obtained when the sunspace was oriented to the south. Two passive cooling techniques are proposed and evaluated to overcome the summer overheating problem. Additionally, a passive heating technique is proposed to minimize the thermal losses during winter nights. Internal shading and night ventilation successfully minimize the overheating problem. Employing the three passive techniques with sunspace, results show that as high as 42% reductions in annual heating and cooling load can be achieved. Utilizing an inclined front surface with double layer of glass can further reduce heating and cooling load requirements.

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.

An enhanced long-distance transport of periodic electron beams in an advanced double layer cone-channel target is investigated using two-dimensional particle-in-cell simulations. The target consists of a cone attached to a double-layer hollow channel with a near-critical-density inner layer. The periodic electron beams are generated by the combination of ponderomotive force and longitudinal laser electric field. Then a stable electron propagation is achieved in the double-layer channel over a much longer distance without evident divergency, compared with a normal cone-channel target. Detailed simulations show that the much better long-distance collimation and guidance of energetic electrons is attributed to the much stronger electromagnetic fields at the inner wall surfaces. Furthermore, a continuous electron acceleration is obtained by the more intense laser electric fields and extended electron acceleration length in the channel. Our investigation shows that by employing this advanced target, both the forward-going electron energy flux in the channel and the energy coupling efficiency from laser to electrons are about threefold increased in comparison with the normal case.

Using a Vlasov code for simulating fully nonlinear behavior of a plasma driven by an applied potential drop, it is shown that fast solitary potential pulses in the form of electron holes are a common feature of the high potential side of a strong double layer. Temporal and spatial features of the electron holes seen in the simulations are compared against the measurements from FAST. The evolution of the electron beam accelerated by a double layer and that of the plasma on its high potential side generate the suitable conditions for nearly continuously creating fast moving electron holes.

The aim of this work is to investigate the effect of anti-reflection coating to improve the performance of silicon solar cell. The reflectance for different anti-reflection coating materials (SLARC and DLARC) were calculated numerically as well as on online source of PV Education. The parameters of such materials are used in PC1D simulator to study the performance of solar cells. It was found that DLARC has considerable effect on the performance of solar cell as compare to SLARC. Further, it was observed that the photovoltaic efficiency and short circuit current is significantly high for SiO2/TiO2 DLARC.

The axial position of a magnetic-field gradient has been varied for capacitive discharges in the linear plasma device VINETA. For low magnetic fields (), double layers have been observed to form predominantly at the interface between the source and the plasma chamber. In particular, the double-layer position is independent of the position of the magnetic-field gradient. However, shifting the axial location of the magnetic-field gradient leads to a global change of the plasma potential and the strength of the double layer. For higher magnetic fields the position of the double layer can be disentangled from the position of both the diameter interchange and the magnetic-field gradient.

This comment aims at clarifying some points in the very recent work of Chauhan et al. who presented an experimental study of a fireball (FB) configuration in a magnetized plasma, similar to R. L. Stenzel et al., Plasma Sources Sci. Technol. 21, 015012 (2012).

The uniform side-on emission of second harmonic radiation has recently been measured from the corona of a laser irradiated plasma with large electron density gradients. A theoretical model has been developed to study the internal electric fields and double layers in such strongly inhomogeneous plasmas. The analytical model shows immediately a density-independent second harmonic term which reproduces very closely the measured intensity of the second harmonic. A detailed numerical evaluation of the term, for a plasma with a linear density profile (permitting Airy solutions), results in a net intensity with small spatial variation but also with both long and short wavelength periodicities exactly as measured. The observed vanishing of the periodicity, when broad band laser sources are used, can then immediately be explained from integration of the standing-wave like oscillations.

Recently J.N. Munday and F. Capasso [Phys. Rev. A {\bf 75}, 060102(R) (2007); arXiv:0705.3793] claimed that they have performed a precision measurement of the Casimir force between a sphere and a plate coated with Au, both immersed in ethanol. The measurement results were claimed to be consistent with the Lifshitz theory. We demonstrate that the calculation of the Casimir force between the smooth bodies following the authors prescription has a discrepancy up to 25% with respect to authors result. We show also that the attractive electrostatic force only due to the surface potential differences was underestimated by a factor of 590 and the charge double layer interaction was not taken into account. All this leads to the conclusion that the results of this experiment are in fact uncertain., Comment: 5 pages, 1 figure, submitted to Physical Review A; corrections are made in accordance to referee's suggestions

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.

Observations in steady-state plasmas confirm predictions that formation of a current-free double layer in a plasma expanding into a chamber of larger diameter is accompanied by an increase in ionization upstream of the double layer. The upstream plasma density increases sharply at the same driving frequency at which a double layer appears. For driving frequencies at which no double layer appears, large electrostatic instabilities are observed. Time-resolved measurements in pulsed discharges indicate that the double layer initially forms for all driving frequencies. However, for particularly strong double layers, instabilities appear early in the discharge and the double layer collapses.

The interaction between high power ion beam and the double-layer target system consisting of Ti film and Al substrate was simulated by TRIM Code. The evolution of energy distribution in the double-layer target irradiated by high power ion beam (HPIB) was obtained. Using the deposited energy in the target as the thermal source term in the nonlinear thermal conduction equations, finite differential method was used to solve the equations. And one-dimensional spatial and temporal evolution of the temperature of the Ti/Al double-layer target irradiated by HPIB during a pulse was obtained. The effect of the ion beam current density on the phase state of the film substrate interface was analyzed. The results show that both Ti and Al are melted at the interface when the ion beam current density is between 100 and 200 A·cm-2.

A negative potential barrier on the low-potential side of a moving double layer gives rise to a current limitation in a collisionless plasma terminated by a positively biased cold collector plate in a $Q$ machine. The double layer is produced in front of the plasma source and moves toward the collector during the limitation. When the double layer arrives at the collector, the barrier dissolves and the current increases, causing a rise in potential along the whole plasma column. The double layer then reforms at the source.

Investigations of double layer dynamics are performed in a Q-machine plasma by applying a positive step potential to a cold end-plate collector. The double layer created at the grounded plasma source just after the pulse is applied propagates towards the collector with the plasma flow speed. Large oscillations occur in the plasma current which is related to a recurring formation and propagation of the double layer. The current is limited during the propagation by a growing negative potential dip formed on the low-potential tail. Similar phenomena appear on the low-potential tail of the stationary double layer formed by applying a potential difference between two plasma sources.

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.

We review the discussions of the Third International Symposium on Double Layers in Laboratory and Space Plasmas. This symposium was held at Marshall Space Flight Center in Huntsville, Alabama, March 17-19, 1986. The symposium emphasized the applications of double layers in various astrophysical settings. Although the proceedings of the symposium will be published elsewhere, we give the main points of all of the discussions in this report. We also pass along a resolution which was adopted at the symposium to standardize the electrical circuit symbol for a double 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.