Plasma jets from conventional non-transferred arc plasma devices are usually operated in turbulent flows at atmospheric pressure. In this paper, a novel non-transferred arc plasma device with multiple cathodes is introduced to produce long, laminar plasma jets at atmospheric pressure. A pure helium atmosphere is used to produce a laminar plasma jet with a maximum length of >60 cm. The influence of gas components, arc currents, anode nozzle diameter, and gas flow rate on the jet characteristics is experimentally studied. The results reveal that the length of the plasma jet increases with increasing helium content and arc current but decreases with increasing nozzle diameter. As the gas flow rate increases, the length of the plasma jet initially increases and then decreases. Accordingly, the plasma jet is transformed from a laminar state to a transitional state and finally to a turbulent state. Furthermore, the anode arc root behaviours corresponding to different plasma jet flows are studied. In conclusion, the multiple stationary arc roots that exist on the anode just inside the nozzle entrance are favourable for the generation of a laminar plasma jet in this device.

]]>The formation of a plasma sheath in front of a negative wall emitting secondary electron is studied by a one-dimensional fluid model. The model takes into account the effect of the ion temperature. With the secondary electron emission (SEE) coefficient obtained by integrating over the Maxwellian electron velocity distribution for various materials such as Be, C, Mo, and W, it is found that the wall potential depends strongly on the ion temperature and the wall material. Before the occurrence of the space-charge-limited (SCL) emission, the wall potential decreases with increasing ion temperature. The variation of the sheath potential caused by SEE affects the sheath energy transmission and impurity sputtering yield. If SEE is below SCL emission, the energy transmission coefficient always varies with the wall materials as a result of the effect of SEE, and it increases as the ion temperature is increased. By comparison of with and without SEE, it is found that sputtering yields have pronounced differences for low ion temperatures but are almost the same for high ion temperatures.

]]>An absolutely straightforward study is presented to characterize the space-charge limited region in a planar diode with non-zero uniform initial velocity which brings about Liu's result. Unlike Liu's work, our approach is free of mathematical intricacies. In addition to its great simplicity, the presented method gives a good physical insight about the problem. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this paper, a two dimensional Particle In Cell-Monte Carlo Collision simulation scheme is used to examine the THz generation via the interaction of high intensity ultra-short laser pulses with an underdense molecular hydrogen plasma slab. The influences of plasma density, laser pulse duration and its intensity on the induced plasma current density and the subsequent effects on the generated THz signal characteristics are studied. It is observed that the induced current density in the plasma medium and THz spectral intensity are increased at the higher laser pulse intensities, laser pulse durations and plasma densities. Moreover, the generated THz electric field amplitude is reduced at the higher laser pulse durations. A wider frequency range for the generated THz signal is shown at the lower laser pulse durations and higher plasma densities. Additionally, it is found that the induced current density in hydrogen plasma medium is the dominant factor influencing the generation of THz pulse radiation. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The global nonlinear gravito-electrostatic eigen-fluctuation behaviors in large-scale non-uniform complex astroclouds in quasi-neutral hydrodynamic equilibrium are methodologically analyzed. Its composition includes warm lighter electrons, ions; and massive bi-polar multi-dust grains (inertial) with partial ionization sourced, via plasma-contact electrification, in the cloud plasma background. The multi-fluidic viscous drag effects are conjointly encompassed. The naturalistic equilibrium inhomogeneities, gradient forces and nonlinear convective dynamics are considered without any recourse to the Jeans swindle against the traditional perspective. An inho-mogeneous multiscale analytical method is meticulously applied to derive a new conjugated non-integrable coupled (via zeroth-order factors) pair of variable-coefficient inhomogeneous Korteweg de-Vries Burger (*i* -KdVB) equations containing unique form of non-uniform linear self-consistent gradient-driven sinks. A numerical illustrative scheme is procedurally constructed to examine the canonical fluctuations. It is seen that the eigenspectrum coevolves as *electrostatic rarefactive damped oscillatory shock-like structures* and *self-gravitational compressive damped oscillatory shock-like patterns*. The irregular damping nature is attributable to the *i* -KdVB sinks. The aperiodicity in the hybrid rapid small downstream wavetrains is speculated to be deep-rooted in the quasi-linear gravito-electrostatic interplay. The phase-evolutionary dynamics grow as atypical *non-chaotic fixed-point attractors*. We, finally, indicate tentative astronomical applications relevant in large-scale cosmic structure formation aboard facts and faults. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A new ignition method of the spark gap based on plasma ejection is proposed in this paper, as the conventional trigatron spark gap performs poorly under the low working coefficient (the ratio of the charging voltage to the self-breakdown voltage) in air. The plasma is generated by the capillary discharge, which has high pressure, high temperature and high velocity. The capillary discharge device is placed inside the low voltage electrode. As long as the triggering signal is sent to the device, a column of the plasma flow is ejected in axial direction and develops rapidly towards the high voltage electrode. Subsequently, the gap is broken down and a high resistive channel is formed, where the thermal ionization takes place and the arc across the whole gap is generated and develops into a well conductive channel. The process of the thermal ionization of the high resistive channel varies with the change of the spark gap distance. The breakdown delay and the delay jitter of the spark gap increase with the spark gap distance, as both parameters are mainly determined by the developing process of the plasma ejection. The characteristics of the plasma flow determine the possibility of the breakdown of the spark gap under the low working coefficient. The ignition method based on capillary plasma ejection has been proved by the preliminary experiments, which indicate that under the gap length of 8 cm and the working coefficient of less than 3%, the effective ignition is still achievable.

Map of specific power deposited by a 70 keV monoenergetic electron beam into the real target shape at time 10.2 ns of the SI scheme.

Figure 4c of the paper by S. Rezaei et al.

Excitation of highly charged ions in plasmas under the action of ultrashort electromagnetic pulses is investigated theoretically in the frame of perturbation theory. The study is based on analytical expression for probability of bound-bound transition which is derived for Gaussian pulse and Doppler broadening of spectral line shape of the transition. Electronic transitions from the ground state of hydrogen-like ions are considered with account for fine splitting of upper energy levels. The main attention is paid to the dependence of the excitation probability on pulse duration for various ion charges and carrier frequencies of the pulse. The results obtained are of interest for plasma diagnostics based on ion excitation from ground state by ultrashort pulses. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Discharge current voltage (IV) curves are directly measured at the target of a high impulse power magnetron sputtering (HiPIMS) plasma for the target materials aluminium, chromium, titanium and copper. These discharge IV curves have been correlated with ICCD camera images of the plasma torus. A clear connection between the change in the discharge IV curve slopes at specific currents and the appearance of localized ionization zones, so-called spokes, in a HiPIMS plasma is identified. These spokes appear above typical target current densities of 2 A/cm^{2}. The slope of the discharge IV curves, at current densities when spokes are formed, depends on the mass of the target atoms with a higher plasma conductivity for higher mass target materials. This is explained by the momentum transfer from the sputter wind to the argon background gas, which leads to higher plasma densities for heavier target materials. The change in the VI curve slope can be used to identify the spokes regime for HiPIMS plasmas, as being mandatory for deposition of good quality materials by HiPIMS. Consequently, the discharge IV curve slope monitoring can be regarded an essential control approach of any industrial HiPIMS process, where discharge IV curves are much easier accessible compared to more complex diagnostics such as time and space resolved ICCD camera measurements. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The nonlinear properties of two dimensional low-frequency electrostatic excitations of charged dust particles (or defects) are studied in a collisionless, unmagnetized dusty plasma. A fully ionized three-component model plasma consisting of kappa distributed electrons, Maxwellian ions, and negatively charged massive dust grains is considered. In this regard, the well known reductive perturbation technique is used to the hydrodynamical equations and the Poisson equation, obtaining the cylindrical Kadomtsev–Petviashvili (CKP) equation. A parametric investigation indicates that the structural characteristics of these nonlinear excitations (width, amplitude) are significantly affected by the plasma nonthermality as well as by the relevant plasma parameters, such as dust concentration and dust temperature. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The nonlinear dynamics of a circularly polarized laser pulse propagating in magnetized plasma contains hot nonextensive *q* -distributed electrons and ions is studied theoretically. A nonlinear equation which describes the dynamics of the slowly varying amplitude electromagnetic wave is obtained using the relativistic two-fluids model. Some nonlinear phenomena include modulational instability, self-focusing, soliton formation, and longitudinal and transversal evolutions of laser pulse in nonextensive plasma medium are investigated. Results show that the nonextensivity of particles can substantially change the nonlinearity of medium. The external magnetic field enhances the modulation instability growth rate of right-hand polarization wave but for the left-hand polarization the growth rate decreases. The spot size of the laser pulse is strongly affected by the plasma nonextensivity. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The electrostatic fluid accelerator (EFA) generates ionic wind with a simple structure that barely obstructs the free air stream or produce excessive noise. This paper presents the velocity characteristics of an EFA under a high speed free air stream to simulate an EFA-powered propulsor. The results show that when the EFA generates identical velocity to the free air stream, the EFA contributes 25% of the resultant velocity. When the EFA is replaced by a rotary fan that generates identical velocity to the free air stream, the fan contributes only 13.4% of the resultant velocity. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The most accurate models of the capillary Z-pinches used for excitation of soft X-ray lasers and photolithography XUV sources currently are based on the magnetohydrodynamics theory (MHD). The output of MHD-based models greatly depends on details in the mathematical description, such as initial and boundary conditions, approximations of plasma parameters, etc. Small experimental groups who develop soft X-ray/XUV sources often use the simplest Z-pinch models for analysis of their experimental results, despite of these models are inconsistent with the MHD equations. In the present study, keeping only the essential terms in the MHD equations, we obtained a simplified MHD model of cylindrically symmetric capillary Z-pinch. The model gives accurate results compared to experiments with argon plasmas, and provides simple analysis of temporal evolution of main plasma parameters. The results clarify the influence of viscosity, heat flux and approximations of plasma conductivity on the dynamics of capillary Z-pinch plasmas. The model can be useful for researchers, especially experimentalists, who develop the soft X-ray/XUV sources. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

An apparatus was designed for generating plasma in ethanol solution. The plasma was generated on the top of the electrode by applying microwave radiation of 2.45 GHz. The results showed that ignition power decreased with increasing temperature of ethanol solution. However, ignition power increased with increasing pressure and point electrode radius of curvature. Plasma and bubbles were generated periodically in the same manner. The electron temperature of the plasma increased with increasing power, while it decreased with increasing pressure. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Shock ignition as an alternative scheme of the laser fusion has the potential of achieving efficient implosion. However, hot electrons produced in result of ignitor-corona interaction may penetrate deep into the fuel making the compression less effective. Transport and energy deposition of hot electron beam into the dense pre compressed of HiPER target by means of Monte Carlo approach are discussed considering the influence of real density and electron beam characteristics. The target parameters before igniting the hot spot have been extracted from a fluid code and used as the initial profile for Monte Carlo simulations. In comparison with simplified step like density profile, electrons penetrate slightly deeper in the case of real shaped density profile. In addition, deposition zone of a broad spectrum electron beam is wider while, monoenergetic electrons depose their energy locally resulting more maximum energy deposition value. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A simple Semi-Analytical method used to fit the experimentally recorded current of the closed switch discharge circuit into the free running under damped LC oscillator model and the arc plasma conductivity, electron density of the plasma and efficiency of the spark gap switch energy transfer have been driven from the model by some simple calculations. The charging voltage, switch pressure and the spark gap has been changed between 6 to 15 kV, 1 to 1.5 bar and 1.4 or 2.8 mm, respectively. The obtained values for plasma conductivity and electron density of plasma are (5-25)(Ω mm)^{–1}, (0.5–3.5)·10^{24}m^{–3}, respectively. The efficiency of the switch is plotted Vs. Pd and E/P which in both cases the peak value has been about 80 present.