Search

Investigates excited ion wake fields in quasineutral two component plasmas in a standard double plasma machine. Inverse relationship of the oscillating wake field to the plasma density; Dependence of the wake field amplitude on the resonance between the perturbation duration and the wake field period rather than the perturbation amplitude.

The diameter of a stem, a common origin point for streamers where the transition from the streamer to the leader takes place, has a significant effect on the simulation of streamer-to-leader transition. To measure the diameter of the stem, a schlieren system was established with the temporal and spatial resolutions of 5 μs and 70 μm, respectively. Experiments were conducted under positive lightning and switching impulses; the applied voltage, discharge current, and schlieren images were recorded synchronously. A method was proposed to measure the diameter of the stem based on the schlieren images, with which the stem diameter as a function of time was obtained. Moreover, the initial diameters of the stem under different conditions were obtained through the linear fitting. At last, a relation between the initial cross-sectional area of the stem and the discharge current was given within a certain range. [ABSTRACT FROM AUTHOR]

Self-absorption (SA) can drastically affect the emission signal which makes quantitative and, in extreme cases, qualitative investigations very challenging in laser induced plasma spectroscopy. In this study, plasma parameters are spectroscopically studied and SA in aluminum emission lines is investigated at various laser energies and gate delays. Q-switched Nd:YAG laser installed on LIBS2500plus system (1064 nm, 6 ns, 10 Hz) was used for ablation. The sample was ablated in air with different laser energies between 5 and 650 mJ, and spectra were recorded at various gate delays between 0 and 23.75 μs. Intensities of spectral lines Al I 308.2 and 309.3 nm were monitored for the range of laser energies and gate delays. The intensity of spectral lines was increased in response to the increasing laser energy. Rapid increase in intensities was observed for the first microsecond after plasma ignition. The maximum intensity of Al is observed at a gate delay of 1.25 μs. Plasma conditions are investigated on the basis of electron density and temperature in response to the change in laser energy and gate-delay. The electron temperature increased from 15 413 K to 20 200 K and the electron density from 5.0 × 1016 cm−3 to 3.5 × 1018 cm−3 with increase in laser energy from 5 to 650 mJ. The electron temperature is exponentially decreased from 26 733 K to 16 649 K and the electron density is reduced from 2.0 × 1017 cm−3 to 1.0 × 1016 cm−3 for increase in the gate delay from 0 to 23.75 μs. The self-absorption effect in resonant spectral lines of Al is estimated on the basis of SA coefficient calculated using FWHM of spectral lines. The highest values of SA coefficient are found for the lowest laser energies and longest gate delays. It states that the SA is significant when the plasma temperature is low and also, when plasma is least dense. It is fairly obvious to conclude that SA effects are least prevalent when the plasma plume is induced by high laser energies and measurements are made at short gate delays. [ABSTRACT FROM AUTHOR]

Head-on collision between ion acoustic shock waves (IASWs) and the consequences after collision are investigated considering the plasma system to be consisting of relativistic warm ions and nonextensive electrons and positrons, taking into account the effects of nonlinearity and dispersion. Two-sided KdV-Burger equations are derived employing the extended Poincar e ´ -Lighthill-Kuo method. The results reveal that the plasma parameters are responsible for the modification of the structures along with phase shifts of the shock waves. The nonlinearity effects on IASWs in a highly relativistic regime (HRR) become pronounced rather than the weakly relativistic regime (WRR). The phase shifts of IASWs are enhanced by the relativistic streaming factor and superthermality. The electrostatic IASWs become rarefactive depending on temperatures, kinematic viscosity, and superthermality in both WRR and HRR. The amplitudes of IASWs are increasing for WRR but decreasing for HRR due to increasing ion thermal velocities. Besides, the amplitudes of the solitons are detaining due to the increase in the positron concentration for the depopulation of ions. [ABSTRACT FROM AUTHOR]

In this study, we developed an analytical model for the flow field in the Huels-type arc-heated wind tunnel (L2K) of the German Aerospace Center. This flow-field model can be used to accurately reproduce the discharge behavior in the heating section and expansion in the nozzle section of L2K. It includes the radiation transport and turbulent flow as well as thermochemical nonequilibrium models, which are tightly coupled with electric field calculations. In addition, we considered the turbulent diffusion model for the mass conservation of the species and performed numerical simulations for several cases with and without the turbulent diffusion model. Computations were conducted to obtain the general characteristics of an arc-heated flow containing an arc discharge and supersonic expansion. We verified that radiation and turbulence play important roles in the transfer of heat from the high-temperature core flow to the outer cold gas in the heating section of L2K. In addition, we performed parametric studies that involved varying the degree of turbulent diffusion. The results showed that turbulent diffusion has a large influence on the formation of the arc discharge in the heating section and on the enthalpy distribution at the nozzle exit. [ABSTRACT FROM AUTHOR]

A transverse gauss shape magnetic field with wide width is proposed for collimating the fast relativistic electron beam in laser irradiating plasmas, which is highlighted by the twodimensional particle-in-cell simulations, in particular, the effects of this magnetic field on the production and transport of fast electron beam. When the axial magnetic field is also present, it is found that the energy density of fast electrons can be enhanced greatly. For example, in the presence of 30MG axial magnetic field, it is enhanced by 3-4 times when the amplitude of the applied transverse magnetic field lies within the optimal regime 200-300MG comparable to that without the transverse magnetic field. Meanwhile, the divergence angle of the electron beam can be controlled and even decreased a little due to the better sandwich structure of the overall weakening magnetic field. The study implies that the proposed transverse magnetic field is helpful to obtain the high quality electron beam which is beneficial to the fast ignition in inertial confinement fusion. [ABSTRACT FROM AUTHOR]

Propagation characteristics and interaction phenomena among the dust acoustic (DA) solitons in unmagnetized dusty plasmas are studied. The plasma is composed of negatively charged mobile dust, Boltzmann distributed electrons, and nonthermally distributed cold and hot ions. The extended Poincaré-Lighthill-Kuo method is employed to derive the two-sided Korteweg-de Vries (KdV) equations. The solutions of the KdV equations are constructed using the Hirota bilinear method both for single- and multi-solitons. The phase shifts are determined for the interactions among the two-, four-, and six-DA solitons. The effects of plasma parameters on the head-on collisions of the DA single- and multi-solitons and their corresponding phase shifts are investigated. [ABSTRACT FROM AUTHOR]

A comparative study of the interactions between nonlinear ion acoustic solitary waves (IASWs) propagating toward each other, and the electrostatic nonlinear propagation of IASWs, both for the weakly and relativistic regimes consisting of relativistic warm ions, nonthermal electrons and positrons, is carried out. Two-sided Korteweg--de Vries (KdV) equations are derived using the extended Poincar-e-Lighthill-Kuo (PLK) method to reveal the physical issues concerned. The effects of positron concentration, ion-electron temperature ratio, electron-positron temperature ratio, relativistic streaming factor, the population of electron, and positron nonthermality on the electrostatic resonances and their phase shifts are investigated for both regimes. It is found that the plasma parameters significantly modify the phase shifts, electrostatic resonances, hump-shaped electrostatic potential profiles, and the electric fields on the nonlinear propagation characteristics of IASWs. The results obtained may be useful for clarifications of interaction between IASWs in astrophysical and laboratory plasmas, especially in pulsar magnetosphere, laser produced, inertial confinement plasmas, and pulsar relativistic winds with supernova ejecta that produce nonthermal electrons, positrons and relativistic ions. Published by AIP Publishing. [ABSTRACT FROM AUTHOR]

The quantitative analysis of the standard aluminum-silicon alloy has been performed using calibration free laser induced breakdown spectroscopy (CF-LIBS). The plasma was produced using the fundamental harmonic (1064 nm) of the Nd: YAG laser and the emission spectra were recorded at 3.5 ls detector gate delay. The qualitative analysis of the emission spectra confirms the presence of Mg, Al, Si, Ti, Mn, Fe, Ni, Cu, Zn, Sn, and Pb in the alloy. The background subtracted and selfabsorption corrected emission spectra were used for the estimation of plasma temperature as 101100± K. The plasma temperature and self-absorption corrected emission lines of each element have been used for the determination of concentration of each species present in the alloy. The use of corrected emission intensities and accurate evaluation of plasma temperature yield reliable quantitative analysis up to a maximum 2.2% deviation from reference sample concentration. [ABSTRACT FROM AUTHOR]

The obliquely propagating arbitrary amplitude electrostatic wave is studied in a dense magnetized plasma having singly and doubly charged helium ions with nonrelativistic and ultrarelativistic degenerate electrons pressures. The Fermi temperature for ultrarelativistic degenerate electrons described by N. M. Vernet [(Cambridge University Press, Cambridge, 2007), p. 57] is used to define ion acoustic speed in ultra-dense plasmas. The pseudo-potential approach is used to solve the fully nonlinear set of dynamic equations for obliquely propagating electrostatic waves in a dense magnetized plasma containing helium ions. The upper and lower Mach number ranges for the existence of electrostatic solitons are found which depends on the obliqueness of the wave propagation with respect to applied magnetic field and charge number of the helium ions. It is found that only compressive (hump) soliton structures are formed in all the cases and only subsonic solitons are formed for a singly charged helium ions plasma case with nonrelativistic degenerate electrons. Both subsonic and supersonic soliton hump structures are formed for doubly charged helium ions with nonrelativistic degenerate electrons and ultrarelativistic degenerate electrons plasma case containing singly as well as doubly charged helium ions. The effect of propagation direction on the soliton amplitude and width of the electrostatic waves is also presented. The numerical plots are also shown for illustration using dense plasma parameters of a compact star (white dwarf) from literature. [ABSTRACT FROM AUTHOR]

The germanium plasma produced by the fundamental harmonics (1064 nm) of Nd:YAG laser in single and double pulse configurations have been studied spectroscopically. The plasma is characterized by measuring the electron temperature using the Boltzmann plot method for neutral and ionized species and electron number density as a function of laser irradiance, ambient pressure, and distance from the target surface. It is observed that the plasma parameters have an increasing trend with laser irradiance (9-33 GW/cm2) and with ambient pressure (8-250 mbar). However, a decreasing trend is observed along the plume length up to 4.5 mm. The electron temperature and electron number density are also determined using a double pulse configuration, and their behavior at fixed energy ratio and different interpulse delays is discussed. [ABSTRACT FROM AUTHOR]

General dispersion relation for the right hand circularly polarized waves has been derived using non-relativistic spin quantum kinetic theory. Employing the derived dispersion relation, temporal and spatial damping of the right hand circularly polarized waves are studied for both the degenerate and non-degenerate plasma regimes for two different frequency domains: (i) k||ν≫(ω+ωce),(ω+ωcg) and (ii) k||ν«(ω+ωce),(ω+ωcg). Comparison of the cold and hot plasma regimes shows that the right hand circularly polarized waνe with spin-effects exists for larger k-νalues as compared to the spinless case, before it damps completely. It is also found that the spin-effects can significantly influence the phase and group νelocities of the whistler waνes in both the degenerate and non-degenerate regimes. The results obtained are also analyzed graphically for some laboratory parameters to demonstrate the physical significance of the present work. [ABSTRACT FROM AUTHOR]

Some typical electrons trajectories around a bubble regime in intense laser plasma interaction are investigated theoretically. By considering a modification of the fields and ellipsoid bubble shape due to the presence of residual electrons in the bubble regime, we study in detail the electrons nonlinear dynamics with or without laser pulse. To examine the electron dynamical behaviors, a set of typical electrons, which locate initially at the front of the bubble, on the transverse edge and at the bottom of the bubble respectively, are chosen for study. It is found that the range of trapped electrons in the case with laser pulse is a little narrower than that without laser pulse. The partial phase portraits for electrons around the bubble are presented numerically and their characteristic behaviors are discussed theoretically. Implication of our results on the high quality electron beam generation is also discussed briefly. [ABSTRACT FROM AUTHOR]

We present spatial characteristics of the lithium fluoride plasma generated by the fundamental and second harmonic of a Nd:YAG laser. The plume emission has been recorded spatially using five spectrometers covering the spectral region from 200 nm to 720 nm. The electron density is measured from the Stark broadened line profile of the line at 610.37 nm, whereas the plasma temperature has been determined using the Boltzmann plot method including all the observed spectral lines of lithium. Both the plasma parameters; electron density and plasma temperature decrease with the increase of the distance from the target surface. The thermal conduction towards the target, the radiative cooling of the plasma, and the conversion of thermal energy into kinetic energy are the main mechanisms responsible for the spatially decrease of the plasma parameters. [ABSTRACT FROM AUTHOR]

We present new studies on the optical emission spectra of the laser produced Al 6063 alloy plasma generated by the 1064 nm Nd: YAG laser. The spectrum reveals Rydberg transitions; nd 2D3/2,5/2 → 3p 2P1/2,3/2 (n = 3 - 8), ns 2S1/2 → 3p 2P1/2,3/2 (n = 4-6), and the dominant spectral lines of the other constituent elements. We have extracted the relative abundance of the impurities using the relative intensity ratio method. Besides, we have calculated the electron temperature (∼7580 K) from the Boltzmann plot method and the electron number densities (∼1.4 × 1017/cm3) from the Stark widths of the aluminum spectral lines. The plasma parameters determined in the present work are in agreement with that reported in the literature. The molecular vibrational transitions of the AlO free radical associated with the B 2∑→X 2∑ band system have also been identified. [ABSTRACT FROM AUTHOR]

Line emission and broadband x-ray sources with x-ray energies above 10 keV have been investigated using a range of calibrated x-ray detectors for use as x-ray backlighters in high energy density (HED) experiments. The conversion efficiency of short- and long-pulse driven Mo and Ag line-emission backlighters at 17 and 22 keV was measured to investigate the crossover region between short- and long-pulse conversion efficiency. It was found that significant 17 and 22 keV line emissions were observed using a 3 ω, 1 ns long-pulse drive for Mo and Ag targets and a comparison between the measured Mo x-ray spectrum and calculations using an atomic physics code suggests that the line emission is due to thermal emission from N-like Mo atoms. Electron temperatures derived from fits to the continuum region of the x-ray spectra agree well with the Thot scaling as 100×(Iλ2)1/3. The continuum emissions from empty and 1 atm Kr-filled imploded CH shell targets were also measured for the use as broadband backlighters. [ABSTRACT FROM AUTHOR]

The fundamental mode frequency of a magnetically insulated transmission line oscillator is investigated theoretically by the equivalent circuit method, and an exact theoretical formula about the fundamental mode frequency is given. The theoretical results are compared with the simulation and experimental results, which shows that the relative error, which is calculated according to the theoretical and simulation frequencies, is less than 3%, so the validity of the theoretical formula is verified. [ABSTRACT FROM AUTHOR]

Theoretical and numerical studies are performed for the nonlinear structures (explosive, solitons, and shock) in quantum electron-positron-ion magnetoplasmas. For this purpose, the reductive perturbation method is employed to the quantum hydrodynamical equations and the Poisson equation, obtaining extended quantum Zakharov–Kuznetsov equation. The latter has been solved using the generalized expansion method to obtain a set of analytical solutions, which reflects the possibility of the propagation of various nonlinear structures. The relevance of the present investigation to the white dwarfs is highlighted. [ABSTRACT FROM AUTHOR]

In the present work, we have discussed the effects of adiabatic trapping of electrons on obliquely propagating Alfvén waves in a low β plasma. Using the two potential theory and employing the Sagdeev potential approach, we have investigated the existence of arbitrary amplitude coupled kinetic Alfvén-acoustic solitary waves in both the sub and super Alfvénic cases. The results obtained have been analyzed and presented graphically and can be applied to regions of space where the low β assumption holds true. [ABSTRACT FROM AUTHOR]

Quantum plasma oscillations are studied in a strongly magnetized, ultra-dense plasma with degenerate electrons and positrons. The dispersive role of electron and positron quantum effects on low frequency (in comparison to electron cyclotron frequency) shear electromagnetic wave is investigated by employing hydrodynamic formulation. In the presence of ions, the density balance changes, and the electromagnetic wave (with frequency lower than the ion cyclotron frequency) is shown to couple with electrostatic ion mode under certain conditions. For such low frequency waves, it is also seen that the contribution of electron and positron degeneracy pressure is dominant as compared to their diffraction effects. The results are analyzed numerically for illustrative purpose pointing out their relevance to the dense laboratory (e.g., super-intense laser-dense matter interactions) and astrophysical plasmas. [ABSTRACT FROM AUTHOR]

Investigates the reflection of modified Korteweg-de Vries solitons from the sheath in front of a negatively biased metal disk. Points of reflection for the rarefactive and compressive solitons; Magnitude of the negative bias potential that is applied to the reflector.