Ion Density Ratio Research Articles

Dual Ion Species Plasma Expansion from Isotopically Layered Cryogenic Targets.

A dual ion species plasma expansion scheme from a novel target structure is introduced, in which a nanometer-thick layer of pure deuterium exists as a buffer species at the target-vacuum interface of a hydrogen plasma. Modeling shows that by controlling the deuterium layer thickness, a composite H^{+}/D^{+} ion beam can be produced by target normal sheath acceleration (TNSA), with an adjustable ratio of ion densities, as high energy proton acceleration is suppressed by the acceleration of a spectrally peaked deuteron beam. Particle in cell modeling shows that a (4.3±0.7) MeV per nucleon deuteron beam is accelerated, in a directional cone of half angle 9°. Experimentally, this was investigated using state of the art cryogenic targetry and a spectrally peaked deuteron beam of (3.4±0.7) MeV per nucleon was measured in a cone of half angle 7°-9°, while maintaining a significant TNSA proton component.

Oblique Interaction of Dust-ion Acoustic Solitons with Superthermal Electrons in a Magnetized Plasma

The oblique interaction between two dust-ion acoustic (DIA) solitons travelling in the opposite direction, in a collisionless magnetized plasma composed of dynamic ions, static dust (positive/negative) charged particles and interialess kappa distributed electrons is investigated. By employing extended Poincare–Lighthill–Kuo (PLK) method, Korteweg–de Vries (KdV) equations are derived for the right and left moving low amplitude DIA solitons. Their trajectories and corresponding phase shifts before and after their interaction are also obtained. It is found that in negatively charged dusty plasma above the critical dust charged to ion density ratio the positive polarity pulse is formed, while below the critical dust charged density ratio the negative polarity pulse of DIA soliton exist. However it is found that only positive polarity pulse of DIA solitons exist for the positively charged dust particles case in a magnetized nonthermal plasma. The nonlinearity coefficient in the KdV equation vanishes for the ne...

Breaking of a Langmuir wave in cold electron–positron–ion plasmas

The space–time evolution of a given density perturbation in cold homogeneous electron–positron–ion plasma is investigated with an assumption of infinitely massive ions by employing a numerical calculation method. The phase-mixing time and wave-breaking time can be effectively distinguished with this method. It is found that an increase of the ratio of equilibrium ion density to equilibrium electron density can attenuate plasma oscillations, leading to a delay in wave breaking. The dependence of the phase-mixing and wave-breaking times on the amplitude of the initial perturbation is also discussed.

Dust ion acoustic freak waves in a plasma with two temperature electrons featuring Tsallis distribution

We present an investigation for the nonlinear dust ion acoustic wave modulation in a plasma composed of charged dust grains, two temperature (cold and hot) nonextensive electrons and ions. For this purpose, the multiscale reductive perturbation technique is used to obtain a nonlinear Schrödinger equation. The critical wave number, which indicates where the modulational instability sets in, has been determined precisely for various regimes. The influence of plasma background nonextensivity on the growth rate of modulational instability is discussed. The modulated wavepackets in the form of either bright or dark type envelope solitons may exist. Formation of rogue waves from bright envelope solitons is also discussed. The investigation indicates that the structural characteristics of these envelope excitations (width, amplitude) are significantly affected by nonextensivity, dust concentration, cold electron–ion density ratio and temperature ratio.

The ion streaming effect on Weibel instability in the relativistic dense plasma

The Weibel instability plays an important role in stopping hot electrons and energy deposition mechanism in fast ignition of inertial fusion process. In this paper, the ion Weibel instability in counter propagating electron‐ion plasmas is investigate. The obtained results show that the growth rate of Weibel instability will be decreased about 40% with the anisotropy velocity as vxe = 2vze = 20; the ion density ratio, b = n0i1/n0i2, and density gradient, are increasing 50 and 90% respectively. The ion streaming in density gradient of dense plasma leads to increasing the Weibel instability growth rate and its amplification through ion streaming in the large wavenumber. The maximum unstable wavenumber has been decreased with decreasing the ion beam density ratio. For fixed ion density ratio, increasing 90% of the density gradient in the near of fuel plasma corona leads to reducing growth rate and unstable wavenumber about 43 and 42% respectively.

Non-thermal effects of electrons on stopbands of fast ion-acoustic solitons

The occurrence of a stopband which is a forbidden range in soliton speeds was recently reported to occur for fast ion-acoustic solitons in a model with cold ions, warm adiabatic ions, and Boltzmann electrons (Nsengiyumva et al., Phys. Plasmas 21, 102301 (2014)). The stopband occurs as a direct consequence of the existence of two solutions for the soliton speed which coincides with the warm ion density limit and is restricted to a certain range of cold to warm ion density ratios. In this study, we investigate the effects of the presence of non-thermal electrons on stopbands through adopting a Cairns and kappa distribution for the electrons. Our results reveal that increasing non-thermal electron effects based on a Cairns (kappa) distribution has the effect of reducing (increasing) the width of the stopband. The stopband obtained for two-temperature Boltzmann electrons increases in width for increasing cool electron density and hot to cool electron temperature.

Nonlinear ion acoustic ring solitons in a multicomponent plasma with superthermal electrons: Propagation and collision

In this paper, the propagation and the collision of ion acoustic ring solitons (IARSs) in a multicomponent plasma with superthermal electrons are theoretically investigated by employing an extended Poincaré–Lighthill–Kuo method. For the generic case, the dynamics and collisions of IARSs are studied via cylindrical Korteweg-de Vries (cKdV) equations and phase shift equations. It is found physically that both positive and negative polarity IARSs can propagate and collide, which usually leads to a time delay in propagation occurring during the collision, as compared to a single ion acoustic soliton (IARS) without collisions in the same physical model. Moreover, at a critical value of the negative ion-to-positive ion concentration, modified cylindrical Korteweg-de Vries (mcKdV) equations and their corresponding phase shifts have been derived. In general, it is observed that the trajectories of IARSs after collisions are significantly modified due to the influence of negative ion-to-positive ion density ratio, negative ion-to-positive ion mass ratio, the superthermal electron parameter, and the positions of IARSs. The numerical results are applied to the Earth's ionosphere, such as the D and F regions. The present investigation will be helpful in understanding the properties of the Earth's ionosphere containing positive and negative ions with superthermal electrons.

Dust ion-acoustic cnoidal waves in a plasma with two temperature superthermal electrons

An investigation of dust ion-acoustic (DIA) cnoidal waves in unmagnetized collisionless plasma consisting of two temperature superthermal electrons, inertial warm ions, and negatively charged dust grains is presented. Reductive perturbation technique has been used to derive the modified Korteweg-de Vries (mKdV) equation for the study of nonlinear periodic waves. Further, applying the Sagdeev potential approach, energy balance equation is derived. Using the expression for Sagdeev potential in expanded form, the cnoidal wave solution is determined. Both positive and negative potential (compressive and rarefactive) nonlinear DIA cnoidal structures are observed. The effects of parameters like the number density of cold electrons, superthermality of hot and cold electrons, ions to hot electrons temperature ratio, and dust to ion density ratio on the characteristics of DIA cnoidal waves are analyzed.

Equatorial ionospheric plasma drifts and O+ concentration enhancements associated with disturbance dynamo during the 2015 St. Patrick's Day magnetic storm

AbstractDisturbance dynamo is an important dynamic process during magnetic storms. However, very few direct observations of dynamo‐induced plasma drifts and ion composition changes in the equatorial ionosphere are available. In this study, we use measurements of the Defense Meteorological Satellite Program (DMSP) satellites to identify the characteristics of the disturbance dynamo process in the topside equatorial ionosphere near dawn during the magnetic storm with a minimum Dst of −223 nT on 17 March 2015. Data from four DMSP satellites with equatorial crossings at 0245, 0430, 0630, and 0730 LT are available for this case. The dynamo process was first observed in the postmidnight sector 3–4.7 h after the beginning of the storm main phase and lasted for 31 h, covering the second storm intensification and the initial 20 h of the recovery phase. The dynamo vertical ion drift was upward (up to 150–200 m s−1) in the postmidnight sector and downward (up to ~80 m s−1) in the early morning sector. The dynamo zonal ion drift was westward at these locations and reached ~100 m s−1. The dynamo process caused large enhancements of the O+ concentration (the ratio of the oxygen ion density to the total ion density) at the altitude of 840 km near dawn. The O+ concentration increased from below 60% during the prestorm period to 80–90% during the storm time. More specifically, the O+ density was increased, and the H+ density was decreased. The variations of the O+ concentration were well correlated with the vertical ion drift.

Relativistic wave-breaking limit of electrostatic waves in cold electron-positron-ion plasmas

A one-dimensional nonlinear propagation of relativistically strong electrostatic waves in cold electron-positron-ion (EPI) plasmas has been analyzed. The motion of all the three species, namely, electron, positron, and ion has been treated to be relativistic. The maximum permissible electric field amplitude − so called “wave-breaking limit” of such an electrostatic wave before wave-breaking has been derived, showing its dependence on the relativistic Lorentz factor associated with the phase velocity of the plasma wave, on the electron/positron to ion mass ratio, and on the ratio of equilibrium ion density to equilibrium electron/positron density.

Dissociative recombination of molecular ions in the He–Ne plasma. Partial rate constants of atoms formation in the 2p 53d and 2p 54d configurations

A spectroscopic study of population processes was carried out for states of the neon atom of the 2p53d configuration in the discharge afterglow in helium with a small admixture of neon ([Ne]/[He] ≈ 10–5) at a pressure of 38 Torr. Based on the comparative analysis of time dependences of the spectral line intensities of the Ne I 2p53d → 2p53d and 2p54d → 2p53d transitions and ratio of ion densities [Ne2+ ]/[HeNe+], it has been found that the formation of excited Ne(2p53d) atoms in the afterglow caused by two dissociative recombination processes: HeNe+ + e → Ne(2p53d) + Ne and Ne2+ + e → Ne(2p53d) + Ne. Distributions of population fluxes of the 2p53d levels \(\Gamma _{3{d_t}}^{HeN{e^ + }}\) and \(\Gamma _{3{d_t}}^{Ne_2^ + }\)—were obtained for each of these processes.

Measurement of radial profiles of density ratio of helium to hydrogen ion using charge exchange spectroscopy with two-wavelength spectrometer.

Radial profiles of density ratio of helium to hydrogen ions are measured using the charge exchange spectroscopy technique with the two-wavelength spectrometer system in the large helical device. The two-wavelength spectrometer system consists of a dichroic mirror box, a spectrometer with two grating and two camera lenses, and one CCD detector. The dichroic mirror box is used to divide the light of one fiber from the plasma to two fibers, one for HeII (λ = 468.6 nm) and the other for H(α) (λ = 656.3 nm), that are connected to the entrance slit of the spectrometer to eliminate the interference between the HeII and the H(α) spectra on the CCD. This system provides a simultaneous measurement of helium and hydrogen ion density ratio at 8 exact same locations (8 spatial channels) with a time resolution of >40 ms in the wide range of the density ratio of 0.05-5.

Some aspects of the double layer structure in magnetized electronegative plasmas with q-nonextensive electrons

In this paper, the double layer (DL) structure in a magnetized electronegative plasma consisting of ions and nonextensive electrons is studied by using the reductive perturbation method. The basic set of fluid equations is reduced to the extended Korteweg–de Vries equation. It is shown that around the critical density, DL structures coexist. The effects of negative to positive ion density ratio (β), nonextensive index (q), the angle between the directions of the wave propagation vector and the external magnetic field (lz), and positive (negative) ion gyrofrequency (Ω±) and positive to negative ion mass ratio (Q) on DL structure are discussed.

Dust acoustic shock waves in arbitrarily charged dusty plasma with low and high temperature non-thermal ions

Using the well-known reductive perturbation technique, the three-dimensional (3D) Burgers equation and modified 3D Burgers equation have been derived for a plasma system comprising of non-thermal ions, Maxwellian electrons, and negatively charged fluctuating dust particles. The salient features of nonlinear propagation of shock waves in such plasmas have been investigated in detail. The different temperature non-thermal ions and Maxwellian electrons are found to play an important role in the shock waves solution. The analytical solution of the 3D Burgers equation and modified 3D Burgers equation ratifying the propagation of dust acoustic shock waves are derived using the well-known tanh method. On increasing the population of non-thermal ions, an enhancement in the amplitude of shock waves is seen for negatively charged dust particles. A striking dependence of amplitude and width of shock waves on the ratio of ion temperatures and densities are also reported. Finally we introduced a new stretching coordinate and perturbation for the nth-order nonlinear 3D Burgers equation and its solution by the use of the tanh method. We found that, due to higher nonlinearity, the amplitude of shock waves decreases while width remains constant for all plasma parameters considered in the present investigation. The features accounted here could be relevant in the case of different space and astrophysical plasmas and laboratory dusty plasma for negatively charged dust fluctuation.

Head-on collision of two ion-acoustic solitary waves in plasmas with electrons described by Tsallis distribution

The problem of the head-on collision of two ion-acoustic solitary waves (IASWs) is addressed in electronegative plasmas with a nonextensive electron velocity distribution. Our plasma model is inspired from the experimental studies of Ichiki et al. (2001). Using the extended Poincare–Lighthill–Kuo (PLK) perturbation method, the phase shifts of the head-on collision are obtained. Analytical and numerical results reveal that the magnitude of the phase shift of the IASWs depends sensitively on the number density ratios μ and υ, the mass ratio σ as well as the nonextensive parameter q. For a given mass ratio σ≃0.27 (Ar+−SF6−), the magnitude of the phase shift increases with an increase of the nonextensive parameter q. An increase of the electron-to-positive ion density ratio μ lowers the phase shift, a trend which is much perceptible for q>1. As σ increases [σ≃0.89 (Xe+−SF6−)], the phase shift becomes larger.

Ion thermal effects on slow mode solitary waves in plasmas with two adiabatic ion species

Using both the Sagdeev and Korteweg-de Vries (KdV) methods, ion thermal effects on slow mode ion acoustic solitons and double layers are investigated in a plasma with two adiabatic positive ion species. It is found that reducing the gap between the two ion thermal speeds by increasing the relative temperature of the cool ions increases the typical soliton/double layer speeds for all values of the ion-ion density ratio and reduces the range in the density ratio that supports double layers. The effect of increasing the relative cool ion temperature on the soliton/double layer amplitudes depends on the relative densities. For lower values of the ion density ratio, an increase in cool ion temperature leads to a significant decrease in soliton/double layer amplitude, so one may find that solitons of all permissible speeds lie within the range of KdV theory.

Nonlinear dynamics of ion acoustic waves in quantum pair-ion plasmas

The nonlinear properties of the ion acoustic waves (IAWs) in a three-component quantum plasma comprising electrons, and positive and negative ions are investigated analytically and numerically by employing the quantum hydrodynamic (QHD) model. The Sagdeev pseudopotential technique is applied to obtain the small-amplitude soliton solution. The effects of the quantum parameter$H$, positive to negative ion density ratio${\it\beta}$and Mach number on the nonlinear structures are investigated. It is found that these factors can significantly modify the properties of the IAWs. The existence of quasi-periodic and chaotic oscillations in the system is established. Switching from quasi-periodic to chaotic is possible with the variation of Mach number or quantum parameter$H$.

Effect of the Divertor Leg Length on the Population of Molecular Ions in the Divertor Simulator TPD-SheetIV

In TPD-SheetIV, a simulation experiment on a long leg divertor configuration has been conducted and hydrogen molecular ion formation in detached plasma was observed. Improvements to the simulation geometry used in DEGAS 2 allowed us to study the effect of leg length on neutral transport. This paper also describes a simple ion balance equation and the ion density ratios obtained with it. From these data, it is shown that a long leg divertor enhances molecular ion density in the divertor, which might enhance molecular assisted recombination.

Bulk plasma fragmentation in a C4F8 inductively coupled plasma: A hybrid modeling study

A hybrid model is used to investigate the fragmentation of C4F8 inductive discharges. Indeed, the resulting reactive species are crucial for the optimization of the Si-based etching process, since they determine the mechanisms of fluorination, polymerization, and sputtering. In this paper, we present the dissociation degree, the density ratio of F vs. CxFy (i.e., fluorocarbon (fc) neutrals), the neutral vs. positive ion density ratio, details on the neutral and ion components, and fractions of various fc neutrals (or ions) in the total fc neutral (or ion) density in a C4F8 inductively coupled plasma source, as well as the effect of pressure and power on these results. To analyze the fragmentation behavior, the electron density and temperature and electron energy probability function (EEPF) are investigated. Moreover, the main electron-impact generation sources for all considered neutrals and ions are determined from the complicated C4F8 reaction set used in the model. The C4F8 plasma fragmentation is explained, taking into account many factors, such as the EEPF characteristics, the dominance of primary and secondary processes, and the thresholds of dissociation and ionization. The simulation results are compared with experiments from literature, and reasonable agreement is obtained. Some discrepancies are observed, which can probably be attributed to the simplified polymer surface kinetics assumed in the model.

Auroral electrostatic solitons and supersolitons in a magnetized nonthermal plasma

Exploiting the spacecraft measurements in the auroral region, finite amplitude nonlinear low frequency electrostatic solitons and supersolitons in a magnetized plasma consisting of cold ions fluid, Boltzmann protons, and nonthermal hot electrons are studied by applying a pseudo-potential technique. The localized solution of the nonlinear structures is obtained through the charge neutrality condition. Further numerical investigation shows the existence of supersoliton solutions at supersonic Mach numbers regime. The amplitude of ion-acoustic structures decreased with an increase in nonthermal electrons and ion density ratio. For the plasma parameters relevant to the auroral zone of the Earth's magnetosphere, the electric field amplitude of supersolitons is found to be about 9 mV/m, which is in agreement with satellite observations.