Light Positive Ions Research Articles

Coexistence of positive and negative polarity solitons, double layers and supersolitons in electron-positron multi-ion plasmas

In order to analyze the nonlinear propagation of arbitrary amplitude ion-acoustic waves, the Sagdeev pseudopotential formalism is used to a four-component multi-ion plasma made up of inertial light positive ions, heavy negative ions, inertialess nonextensive electrons, and positrons. At first, we derived the expression of Sagdeev Pseudopotential for our plasma model and then numerically investigated the condition for the existence of several nonlinear structures such as solitons, double layers, supersolitons, etc. Based on numerical simulation, it is observed that within a certain range of parameters, our plasma model allows compressive as well as a rarefactive soliton, flat-top soliton, double layer, and supersoliton solutions. Great emphasis is placed on the determination of the existence regions for both solitons and supersolitons in the parameter space. Also, various nonlinear structures are explored to examine the effects of various plasma properties, such as the nonextensivity parameter, Mach number, etc. The findings of the current investigations may be helpful for comprehending significant features of ion-acoustic wave structures in space plasmas such as earth's ionosphere, cometary tails, etc., and laboratory plasmas like laser-plasma interaction research.

Heavy ion–acoustic rogue waves in magnetized electron–positron multi‐ion plasmas

AbstractNon‐linear heavy ion‐acoustic waves (HIAWs) are studied in a homogeneous magnetized four‐component multi‐ion plasma composed of inertial heavy negative ions, light positive ions, and inertia‐less non‐extensive electrons and positrons. The non‐linear Schrödinger equation is derived in this model using the perturbation method. The criteria for modulational instability of HIAWs and the basic features of finite‐amplitude heavy ion acoustic rogue waves (HIARWs) are investigated. The presence of the magnetic field was found to reduce the amplitude of HIARWs and enhances the stability. It is interesting to note that increasing positive ion mass causes decreases in the amplitude and width of rogue waves, which is opposite behaviour to that demonstrated in the previous study of these waves in an unmagnetized plasma. Furthermore, it is also shown that striking parameters, such as the non‐extensive parameter, the positron number density, the electron number density, the electron temperature, and the magnetic field parameter, play an undeniable role on the stability of waves packets. The findings of the present investigation may be of wide relevance to some plasma environments, such as active galactic nuclei, pulsar magnetospheres, and other magnetic confinement systems.

HYGIENIC CHARACTERISTIC OF CONDITIONS FOR PATIENTS’ TREATMENT AT STOMATOLOGICAL HOSPITAL OF CLINICAL MULTIPROFILE MEDICAL CENTER AFTER RECONSTRUCTION

Aim. To fulfill the in-depth sanitary-and-hygienic assessment of the internal environment of stomatological hospital after its reconstruction. Materials and methods. Sanitary-and-hygienic assessment was fulfilled by means of modern devices, subjected to metrological check. Microclimate (temperature, relative humidity, air speed, temperature of guarding surfaces), aeroionization regime (light negative and positive air ions), natural and artificial light, noise load and electromagnetic radiation value were determined. The study was carried out during cold (January-February) and warm (June) periods of the year. Results. Hygienic characteristic of conditions for patients’ treatment at stomatological hospital showed the sanitary parameters to correspond to the existing standards. Conclusions. The reconstruction of stomatological hospital carried out permitted to improve the environmental parameters, contributing to effective treatment of patients.

Heavy ion-acoustic rogue waves in electron-positron multi-ion plasmas.

The nonlinear propagation of heavy-ion-acoustic (HIA) waves (HIAWs) in a four-component multi-ion plasma (containing inertial heavy negative ions and light positive ions, as well as inertialess nonextensive electrons and positrons) has been theoretically investigated. The nonlinear Schrödinger (NLS) equation is derived by employing the reductive perturbation method. It is found that the NLS equation leads to the modulational instability (MI) of HIAWs, and to the formation of HIA rogue waves (HIARWs), which are due to the effects of nonlinearity and dispersion in the propagation of HIAWs. The conditions for the MI of HIAWs and the basic properties of the generated HIARWs are identified. It is observed that the striking features (viz., instability criteria, growth rate of MI, amplitude and width of HIARWs, etc.) of the HIAWs are significantly modified by the effects of nonextensivity of electrons and positrons, the ratio of light positive ion mass to heavy negative ion mass, the ratio of electron number density to light positive ion number density, the ratio of electron temperature to positron temperature, etc. The relevancy of our present investigation to the observations in space (viz., cometary comae and earth's ionosphere) and laboratory (viz., solid-high intense laser plasma interaction experiments) plasmas is pointed out.

Effects of dust size distribution on dust negative ion acoustic solitary waves in a magnetized dusty plasma

Dust negative ion acoustic solitary waves in a magnetized multi-ion dusty plasma containing hot isothermal electron, ions (light positive ions and heavy negative ions) and extremely massive charge fluctuating dust grains are investigated by employing the reductive perturbation method. How the dust size distribution affect the height and the thickness of the nonlinear solitary wave are given. It is noted that the characteristic of the solitary waves are different with the different dust size distribution. The magnitude of the external magnetic field also affects the solitary wave form.

Higher harmonics generation by a spiraling ion beam in collisionless magnetized plasma

AbstractA spiraling ion beam propagating through a magnetized plasma cylinder containing K+ light positive ions, electrons, and C7F14− heavy negative ions drives electrostatic ion–cyclotron waves to instability via cyclotron interaction. Higher harmonics of the beam cyclotron frequency can be generated in this way. The unstable mode frequencies and growth rates of both unstable light positive ions and heavy negative ions increase with the relative density of heavy negative ions. Moreover, the growth rate of unstable modes scales as the one-third power of the beam density. The growth rate of unstable modes increases with harmonic number. The frequencies of both unstable modes also increase with magnetic fields. In addition, the real part of both unstable modes (K+ and C7F14−) increases with the beam energy and scales as almost one-half power of the beam energy.

Dust negative ion acoustic shock waves considering dust size distribution effect

A multi-ion dusty plasma containing hot isothermal electrons, ions (light positive ions and heavy negative ions), and extremely and negatively charged dust grains is studied in the present paper. The dust negative ion acoustic shock waves have been investigated by employing the reductive perturbation method. How the dust size distribution affects the height and the thickness of the nonlinear shock wave is studied. It is noted that the different dust size distribution has different shock wave form and different moving speed.

Nonlinear dust-ion-acoustic waves in a multi-ion plasma with trapped electrons

A dusty multi-ion plasma system consisting of non-isothermal (trapped) electrons, Maxwellian (isothermal) light positive ions, warm heavy negative ions and extremely massive charge fluctuating stationary dust have been considered. The dust-ion-acoustic solitary and shock waves associated with negative ion dynamics, Maxwellian (isothermal) positive ions, trapped electrons and charge fluctuating stationary dust have been investigated by employing the reductive perturbation method. The basic features of such dust-ion-acoustic solitary and shock waves have been identified. The implications of our findings in space and laboratory dusty multi-ion plasmas are discussed.

Excitation of electrostatic ion-cyclotron waves by an ion beam in a two-ion component plasma

An ion beam propagating through a magnetized plasma cylinder containing electrons, light positive potassium ions (K+), and heavy positive cesium ions (Cs+) drives electrostatic ion cyclotron (EIC) waves to instability via Cerenkov interaction. Two EIC wave modes are present, the K+ and Cs+ modes. The unstable wave frequencies and the growth rate of both the light positive ion and heavy positive ion modes increase with an increase in their relative ion concentrations. The growth rate of both the unstable modes (K+ and Cs+) scales one-third power of the beam density. The real part of the frequency of both the unstable modes (K+ and Cs+) increases with the beam energy and scales as almost one-half power of the beam energy. Numerical calculations of the growth rate and mode frequencies have been carried out for the parameters of the experiment of Suszcynsky et al. [J. Geophys. Res. 94, 8966 (1989)]. It is found that the unstable wave frequencies of both the light positive ion and heavy positive ion modes increase with the magnetic fields in accordance with the experimental observations.

Dust negative ion acoustic shock waves in a dusty multi-ion plasma with positive dust charging current

Recent analysis of Mamun et al. [Mamun et al., Phys. Lett. A 373, 2355 (2009)], who considered electrons, light positive ions, heavy negative ions, and extremely massive (few micron size) charge fluctuating dust, has been extended by positive dust charging current, i.e., considering the charging currents for positively charged dust grains. A dusty multi-ion plasma system consisting of electrons, light positive ions, negative ions, and extremely massive (few micron size) charge fluctuating stationary dust have been considered. The electrostatic shock waves associated with negative ion dynamics and dust charge fluctuation have been investigated by employing the reductive perturbation method. It has been shown that the dust charge fluctuation is a source of dissipation and is responsible for the formation of dust negative ion acoustic (DNIA) shock structures. The basic features of such DNIA shock structures have been identified. The findings of this investigation may be useful in understanding the laboratory phenomena and space dusty plasmas.

Dust charging effects on test charge potential in a multi-ion dusty plasma

The Debye–Huckel and oscillatory wake potentials caused by a test charge are studied in a multi-ion dusty plasma, whose constituents are the Boltzmann distributed electrons and light positive ions, the heavy mobile negative ions, and static but charge fluctuating dust particles. For this purpose, fluid equations are employed to obtain the dielectric constant of the dust-negative-ion acoustic wave involving the negative ions and dust charge fluctuation effects. Theoretical and numerical investigations have revealed the modification in the Debye–Huckel and wake potentials due to the effects of dust relaxation rate, dust absorption frequency, dust grain radius, and negative ion temperature. The present results should be important to form new materials in the presence of negative ions in laboratory as well as dust coagulation/agglomeration in space dusty plasmas.

Arbitrary amplitude dust ion-acoustic shock waves in a dusty plasma with positive and negative ions

Arbitrary amplitude dust ion-acoustic shock waves in a multi-ion dusty plasma (composed of electrons, light positive ions, heavy negative ions, and stationary massive dust grains) has been studied. For this purpose, the coupled Poisson and dust-charging equations, which accounts for the fluctuation of charges on static dust, have been numerically solved. The large amplitude shocks are associated with a sudden decrease in the electrostatic potential and of the dust grain charge. It is found that in the lower speed limit small amplitude shocks are formed, while in the larger speed limit large amplitude shocks are formed. It is anticipated that the profiles and amplitudes of the DIA shocks predicted here will be observed in forthcoming laboratory and space experiments.

Dust negative ion acoustic shock waves in a dusty multi-ion plasma

A dusty multi-ion plasma system containing electrons, light positive ions, heavy negative ions, and extremely massive (few micron size) charge fluctuating dust has been considered. The dust negative ion acoustic (DNIA) shock waves, which are associated with negative ion dynamics and dust charge fluctuation, have been investigated by employing the reductive perturbation method. It has been shown that the dust charge fluctuation is a source of dissipation, and is responsible for the formation of such DNIA shock structures. The basic features of such DNIA shock structures have been identified. The implications of our results in laboratory dusty multi-ion plasmas have been discussed.

Semiempirical formulae for electron-impact double-ionization cross sections of light positive ions

Electron-impact double-ionization processes of light positive ions from He- to Ne-like isoelectronic sequences, as well as of the heavy ions Arq+ (q = 1–7) and Kr q+ (q = 1–4) are considered for incident-electron energies E < 50 Ith where Ith is the threshold energy for double-electron ionization. On the basis of reliable experimental data and quantum-mechanical calculations, simple semiempirical formulae with three fitting parameters, by taking into account the contribution of direct double ionization and of inner-shell ionization processes, are obtained which describe the experimental cross sections within an accuracy of 20–30%. With this accuracy, the formulae suggested can be used for prediction of the double-ionization cross sections of positive ions with the nuclear charge Z ⩽ 26 in the electron energy range of E < 50Ith. According to the model suggested, the direct ionization cross section σdir (simultaneous ionization of two outer electrons) is scaled as I−3th against scaled electron energy E/Ith and contains only one fitting parameter. Two additional fitting parameters are obtained using the least-squares method in conjunction with numerically calculated single-electron inner-shell ionization cross sections. All fitting parameters are found to be constant for ions within a given isoelectronic sequence. The present analysis also provides a method for indirect determination of K-shell ionization cross sections for ions from Be-like to Ne-like sequences. The fluorescence yields ωK for a single K-shell vacancy in ions from Li-like to Ne-like sequences with nuclear charges 3 ⩽ Z ⩽ 26 are calculated as well.

Development of an H− ion source based on the electron cyclotron resonance plasma generator at CEA/Saclay

Electron cyclotron resonance (ECR) plasma generators have demonstrated their efficiency, reproducibility, and long lifetime for the production of light positive ions like protons or deuterons. These sources generally work in cw mode. A 2.45 GHz ECR test stand based on a pure volume H− ion production is currently under development. This negative ion source is working in pulsed mode, 1 ms at 10 Hz. The first H− ions have been observed at the beginning of 2002 with a poor efficiency. Only a few μA were produced. To avoid negative ions destruction by a nonabsorbed microwave close to the extraction aperture, a stainless steel grid was installed in the rectangular plasma chamber. As a result, the chamber is now effectively separated into two zones: the ECR plasma generator and the H− production zone. By plotting the extracted current versus the production zone length, the H− ion intensity reached more than 100 μA with the grid located 25 mm from the aperture. A voltage difference on the order of 10 V can be applied between the two parts of the plasma chamber in order to modify the electron energy entering the production zone.

Plasma charge-density ratios in a dusty plasma

It is shown that particle diffusion in the afterglow of a dusty plasma can be used to establish several properties of the active plasma. Specifically, the ratio of the average mass of light negative and positive ions, and a limit for the ratio of electron to ion charge densities can be determined. From the afterglow decay of visible particles, with and without electrode bias, the charged fraction of particles can be measured. An afterglow ambipolar-diffusion model is developed to relate this neutral fraction to the densities and masses of electrons and light ions in the active plasma. We then use this technique to analyze a silane radio-frequency plasma. In the active plasma positive charge is dominated by small SiyHn+ cations, and the negative charge by small SixHm− anions, with x and y&amp;lt;100. This analysis establishes that the electron density is less than 10% of the ion density in the operating discharge and that the anion/cation average mass ratio (x/y) is ∼6.

Noctilucent clouds and regions with polar mesospheric summer echoes studied by means of rocket‐borne electron and ion DC‐probes

During the Noctilucent Cloud Campaign from Esrange, Kiruna, Sweden in July‐August 1991, detailed in situ mesurements were performed by means of plasma probes in the TURBO rocket payload. When launched through NLC and PMSE layers, these probes indicate that the NLC layer was associated with a one kilometer thick region containing heavy positive ions. Embedded in this layer were structures only a few tens of metres in vertical extent. These structures exhibited strongly enhanced ion current and corresponding sharp decreases of electron current. The observations indicate that the structures contain enhanced densities of light positive ions as well as heavy, negative charge carriers in the form of ions or particles. VHF radar measurements from the same site showed Polar Summer Mesospheric Echoes from a layer that at first was located just above the NLC layer, but the rocket results indicate that it later merged with the NLC‐layer.

Energy distribution measurements in radio frequency plasma discharges using a cubical analyzer

A compact and inexpensive cubical energy analyzer has been developed to measure ion and electron energy distributions at the boundaries of a rf plasma. It consists of two grids parallel to the plasma boundary behind which lies a 1 cm×1 cm×1 cm cube. The absorbed current and voltage on the grids and on each face of the cube can be monitored and biased independently. A Helmholtz coil on the outside of the cube allows a 0–15 G field to be produced perpendicular to the path through the gridded apertures. The advantages over standard gridded energy analyzers include direct measurements of ion-induced secondary electrons and separation of electrons, negative ions, and heavy and light mass positive ions to different collection surfaces. Measurements of the ion and electron energy distributions at the grounded electrode of a parallel plate 13.56 MHz plasma discharges clearly show a time-varying rf sheath and a non-Maxwellian electron energy distribution. Data is presented for Ar, CH4, and H2 plasmas.

Apparatus Drawings Project. Report Number 14. Omegatron for Undergraduate Laboratory Determination of the Ratio e/m of the Proton

An omegatron, a form of cyclotron, designed for measuring the cyclotron resonance frequency of light positive ions is described. Protons, formed by the collision of electrons and residual gas molecules in the apparatus, are accelerated normal to the axis of two semicylindrical electrodes by an rf electric field. An intense uniform magnetic field, parallel to the electrode axis, causes the protons to follow spiral paths. When the frequency of the electric field is approximately 5 Mc, the magnetic field required is about 4 kgauss, uniform over a volume measuring 2.5 cm diam ×3 cm. From data obtained with this instrument, the student can compute the ratio e/m of the proton. The agreement between this computed value and the accepted modern value for e/m of the proton, is directly dependent upon the accuracy with which frequency and magnetic field strength can be measured.