Ion Mass Ratio Research Articles

Virtual anode as a source of low-frequency oscillations of a high-current electron beam

The research into the transportation of a relativistic electron beam with an above-critical current in the cylindrical drift chamber in the presence of an ion stream is described. The theoretical analysis of the electron-ion formation dynamics is based on a particle-in-cell (PIC) method. It shows that at a joint injection of a supercritical electron beam and a low-energy low-current ion beam in the drift chamber a virtual anode may appear along with an electron virtual cathode. This virtual anode pulsates periodically. Numerical results obtained for hydrogen and nitrogen ions show that the ratio of pulsation frequencies is in inverse proportion to the ion mass ratio. Oscillations of a virtual anode result in a time modulation of electron and ion currents at the same frequency at the drift chamber output.

Observation of ion-acoustic waves in two-ion-species plasmas

Coexistence of two modes of ion-acoustic waves in two-ion-species plasmas is investigated both theoretically and experimentally. Two ions are combinations of H2, He, Ne, Ar and Xe. The boundary of existence of two modes in the plane of an electron–ion temperature ratio and heavy–light ion mass ratio is obtained from the two-species ion-acoustic dispersion relation with a real frequency and a complex wavenumber. The boundary is given approximately by Te/Ti = 2Mh/Ml, where Te and Ti are temperatures of electrons and ions, respectively, and Mh and Ml are masses of heavy and light ions, respectively. The experiment is perfomed with a double-plasma device. Ion-acoustic waves are transmitted by applying a sinusoidal pulse to the anode of the source plasma. A single mode is observed for Ne–Ar, He–Ne, Ne–Xe and Ar–Xe plasmas and two modes are detected for H2–Ar, H2–Ne and He–Ar plasmas.

Rapid oxidation of sulfide mine tailings by reaction with potassium ferrate

The chemistry of sulfide mine tailings treated with potassium ferrate (K 2FeO 4) in aqueous slurry has been investigated. The reaction system is believed to parallel a geochemical oxidation in which ferrate ion replaces oxygen. This chemical system utilized in a pipeline (as a plug flow reactor) may have application eliminating the potential for tailings to leach acid while recovering the metal from the tailings. Elemental analyses were performed using an ICP spectrometer for the aqueous phase extract of the treated tailings; and an SEM-EDX for the tailing solids. Solids were analyzed before and after treatments were applied. ICP shows that as the mass ratio of ferrate ion to tailings increases, the concentration of metals in the extract solution increases; while EDX indicates a corresponding decrease in sulfur content of the tailing solids. The extraction of metal and reduction in sulfide content is significant. The kinetic timeframe is on the order of minutes.

I–V characteristics of the Langmuir probe in flowing afterglow plasmas

The specific features of the probe I–V characteristics in flowing-afterglow plasmas are studied experimentally and in theory. As it was found at a probe potential equal to the plasma one, V=0, an electron concentration in a probe vicinity (and a probe current) is decreased due to a predominant outflow of the electrons into an electrical circuit of the probe from the probe vicinity. The expression allowing one to reconstruct the undisturbed-by-probe electron concentration from only experimental data is derived. The reconstructed values of the electron concentration enable one to find from the experiments the semiempiric expressions allowing to describe quantitatively the behavior of the probe I–V characteristics at the electron-attracting as well as at the ion-attracting potential, respectively. The expressions found (both for electron-attracting and ion-attracting potential) include the “separating length,” which merely is the Langmuir length with a factor equal to the square root of the electron mass over the ion mass ratio for two-component plasma. The intermediate part of the probe I–V characteristics is discovered for probes operating with afterglow plasmas. This intermediate part is described in terms of the experimental parameter L0 having a dimension of the length (presumably electron-orbital length). The value of the parameter L0 does not depend on plasma parameters to within the ranges of plasma parameter variations for experimentally investigated plasmas as it was found. The experiments were performed with two cylindrical probes of 10 and 25 μm diam and ∼3 mm lengths in the experimentally investigated ranges of the afterglow plasma parameters: 105 cm−3<n<1010 cm−3, 0.017 eV<kT<0.3 eV, and 0.5 Torr⩽p⩽2 Torr of He gas pressure (corresponding to 950 μm⩾λTe⩾240 μm electron mean-free path) with (or without) Ar addition.

Dust acoustic solitary waves and double layers in a dusty plasma with an arbitrary streaming ion beam

The effects of variable dust charge, dust temperature and an arbitrary streaming ion beam on small amplitude dust acoustic waves are investigated. It is found that both compressive and rarefactive solitons as well as double layers exist. There exists a critical ion beam velocity below which the ion beam is unable to generate solitons. Korteweg–de Vries (KdV) equations with third and fourth-order nonlinearity at the critical values are derived and the properties of dust acoustic solitary waves are discussed. In the vicinity of the critical values, KdV-type with mixed nonlinearity is obtained. The quite dense positive ion, the dust temperature, the ion beam density, mass ratio and temperature govern the existence of dust acoustic waves. The findings of this investigation may be useful in understanding laboratory plasma phenomena and astrophysical situations.

Modified Korteweg de Vries (MKdV) and Korteweg de Vries (KdV) Solitons in a Warm Plasma with Negative Ions and Electrons' Drift Motion

In this investigation, both compressive and rarefactive Korteweg de Vries (KdV) solitons of high amplitude are shown to exist in a warm plasma under the influence of electrons' drift motion for different values of Q ′ (= m j / m i , negative to positive ion mass ratio) greater or less than one. But these KdV solitons of high amplitude are noticed in the plasma for negligible temperature α (= T i / T e , ion to electron temperature ratio → 0) for Q ′ 1 in an upper range of v e ′ ≥45 when temperature is small. On the other hand, for concentration of heavier population of negative ions ( Q ′ >1) in the warm plasma, MKdV solitons of small but significant amplitude are established to exist even in a new range (45≤ v e ′ ≤60).

Experimental observation of dominant propagation of the ion-acoustic slow mode in a negative ion plasma and its application

Different characteristics of ion acoustic waves were experimentally observed in two types of Xe+–F− double plasmas at different electron temperatures. For the lower electron temperature (around 0.15 eV), the slow mode, which had been considered not to dominate the wave propagation, was found to be dominant rather than the fast mode, which was observed to be dominant for the higher electron temperature (around 1.5 eV). According to the previous numerical investigation [Phys. Plasmas 8, 4275 (2001)], the new wave characteristic appeared when the ratio of negative ion mass to positive ion mass and to the ratio of electron temperature to ion temperature are lower than certain critical values. Further, a method of evaluating both the positive ion temperature and the negative ion temperature in a negative ion plasma by observing the dominant slow mode is described. Using this method, the positive and negative ion temperatures in the former plasma were estimated to be 0.075 eV at the highest and 0.1 eV at the lowest, respectively.

Extension of the Harris magnetic field model to obtain exact, two‐dimensional, self‐consistent X point structures

Harris [1962] developed a one‐dimensional current sheet model in a magnetic field that was self‐consistent with a collisionless Maxwellian plasma. This model has served as a starting point for many current sheet studies. Kan [1973] showed how this approach could be extended to two dimensions, but there has been little further application of this extension to magnetospheric problems. We have followed Kan's technique and give exact analytic expressions for plasma and magnetic field structures in the vicinity of a two‐dimensional magnetic X point. The plasma is Maxwellian with arbitrary electron to ion mass ratio, but in the present stage of work the flow is constrained to be perpendicular to the plane containing the X point. The model is flexible in that it contains parameters that should allow it to be adapted to particular observational geometries and to be extended further using perturbation techniques to higher dimensions.

Atomic mass of6Liusing a Penning-ion-trap mass spectrometer

The atomic mass of 6 Li has been measured using a Penning-ion-trap mass spectrometer to he 6.015 122 795(16) u. The fractional measurement uncertainty of ′2.7×10 - 9 represents a 30-fold improvement over that of the accepted published value. External ion sources were used to create ions outside the cryogenic (4 K) environment of the Penning trap and an ion-transport beamline was used to deliver ions into the trap for measurement. The ion mass ratios of 6Li+:12C2+ and 6 Li + :D + 3 were measured using this apparatus and the atomic mass of neutral 6 Li was derived from these ratios. A measurement of the He + :D + 2 mass ratio with a fractional uncertainty of ′ 1. 1× 10 - 9 and differing from the accepted published value by a fractional amount -0.6×10 - 9 is also reported.

A Landau fluid model for electromagnetic plasma microturbulence

A fluid model is developed for the description of microturbulence and transport in magnetized, long mean-free-path plasmas. The model incorporates both electrostatic and magnetic fluctuations, as well as finite Larmor radius and kinetic effects. Multispecies Landau fluid equations are derived from moments of the electromagnetic gyrokinetic equation, using fluid closures which model kinetic effects. A reduced description of electron dynamics, appropriate for the study of microturbulence on characteristic ion drift and Alfvén scales, is derived via an expansion in the electron to ion mass ratio. The reduced electron equations incorporate curvature, ∇B, and linear and nonlinear E×B drift effects, needed to model the electron contribution to the drive and damping of ion gyroradius scale instabilities in tokamaks. The Landau fluid model is linearly benchmarked against gyrokinetic codes, and found to reproduce the toroidal finite beta ion temperature gradient and kinetic ballooning instabilities.

A fluid–kinetic hybrid electron model for electromagnetic simulations

A fluid–kinetic hybrid electron model for electromagnetic simulations of finite-β plasmas is developed based on an expansion of the electron response using the electron–ion mass ratio as a small parameter. (Here β is the ratio of plasma pressure to magnetic pressure.) The model accurately recovers low frequency plasma dielectric responses and faithfully preserves nonlinear kinetic effects (e.g., phase space trapping). Maximum numerical efficiency is achieved by overcoming the electron Courant condition and suppressing high frequency modes. This method is most useful for nonlinear kinetic (particle-in-cell or Vlasov) simulations of electromagnetic microturbulence and Alfvénic instabilities in magnetized plasmas.

Three-dimensional simulations of ion thruster beam neutralization

Motivated by the recently revived interest in electric propulsion, the neutralization regime of an ion thruster is investigated by means of a three-dimensional particle-in-cell simulation. Electrons enter the simulation box with a half-Maxwellian velocity distribution, while the ions are injected with a uniform bulk velocity. Focus is put on the dynamics of the electrons, and the actual electron to ion mass ratio of 1:250 000 is used. The injection velocity ratio η≔ve0th/vi0 between electron thermal velocity and ion bulk velocity turned out to be a crucial parameter for the electron dynamics within the plasma beam: For η<1.7 a moving electrostatic shock forms with a potential jump of a few kTe0/e. Downstream of the shock front, the electron plasma becomes fully Maxwellian and drifts with the ion bulk velocity. For η>1.7, the electrons still obtain a drift velocity roughly equal to vi0 within a few electron inertia lengths behind the emitting plane. However, a shock front does not form, and the electron velocity distribution does not become Maxwellian. On the basis of a tentative model, in which the plasma beam is regarded as a self-similarly expanding electron diode, the shock front can be identified with a kind of virtual cathode and the dependence of the shock velocity on the beam cross section can be explained.

Omegatron ion mass spectrometer for the Alcator C-mod tokamak

A new ion mass spectrometry probe that operates at high magnetic field (∼8 T) has been recently commissioned on the Alcator C-Mod tokamak. The probe combines an omegatron E(t)×B ion mass spectrometer and a retarding field energy analyzer. The probe samples the plasma in the far scrape-off layer, on flux surfaces between 25 and 50 millimeters from the separatrix. Radio-frequency (rf) power is used to collect ions with resonant cyclotron frequency on the side walls of an rf cavity. Scanning the frequency results in a spectrum ordered by the ratio of ion mass to charge, M/Z. Resonances are presently resolved for 1⩽M/Z<12 down to signal levels as low as 5×10−4 times that of the bulk plasma species. Well-resolved resonances have widths within a factor of two of theoretical values obtained from particle orbit theory. Absolute impurity fluxes and individual impurity charge state temperatures are quantified by varying the applied rf power and recording the change of the amplitude of the resonant ion current. The design of the hardware and electronics design is described, the principles of operation are discussed, and initial experimental results are presented. Sources of noise which presently limit the sensitivity of the device are also discussed along with techniques to improve the signal–to–noise ratio.

Nonlinear hybrid Boltzmann–particle-in-cell acceleration algorithm

Kinetic simulation of plasmas in which equilibrium occurs over ion time scales poses a computational challenge due to disparity with electron time scales. Hybrid electrostatic particle-in-cell (PIC) algorithms are presented in which most of the electrons reach thermodynamic equilibrium [Maxwell–Boltzmann (MB) distribution function] each time step. Conservation of charge enables convergence of the nonlinear Poisson equation. Energy conservation is used to determine the temperature of the Boltzmann species. This article first develops an algorithm where all the electrons have a MB energy distribution, either with a full MB distribution or with a truncation of the high energy tail. Second, high energy PIC electrons are added to the truncated distribution so that high energy electrons are modeled kinetically by PIC and low energy electrons (the majority) are modeled by the MB distribution. Collisions for PIC electrons are included via a Monte Carlo model, while for the MB electrons, the distributions are integrated with energy dependent cross sections. The MB model is not constrained by the electron time scale which decreases the required computer time by about the square root of the mass ratio of ion to electron. However, the hybrid boundary conditions are more complex and the simulation is not quite self-consistent. Comparison between full PIC and the PIC–MB hybrid is made for simulations of photo-ionized sustained discharges and current-driven dc discharges.

Optimization and performance of a rapid gas chromatography–mass spectrometry analysis for methylmalonic acid determination in serum and plasma

We have developed a rapid and sensitive GC–MS assay for methylmalonic acid determination in serum and plasma utilizing an anion exchange solid-phase extraction and trimethylsilyl derivatization. Each step of the procedure was optimized by the experimental design methods to assure the assay reliable performance. The limit of detection and limit of quantitation were 0.025 and 0.1 μmol/l. The total coefficient of variation for the method was 9.8, 4.4, and 4.6% at the concentration of 0.2, 3.1, and 6.2 μmol/l methylmalonic acid concentration, respectively. The assay are linear up to 9.0 μmol/l, and showed good correlation with a reference method. The method has proven to be reliable in routine production, producing clean chromatography, unique ion fragments, and consistent ion mass ratio.

Energy distribution of light ions backscattered from a solid in the single-collision approximation

The backscattering of light ions bombarding solid target has been investigated with the single-collision model, which assumes two straight line trajectories between the surface and the point of a wide-angle collision. This model allows to obtain the energy and angular distributions of backscattered ions in explicit form. Previous analytical theories considered the case when the probability of the scattering event is small and the ratio of the free path length λ 0 to the total inelastic range R T is large. In the present work, we obtained analytical solution for arbitrary values of the ratio λ 0/ R T. The solution holds for the case of normal ion incidence on the target surface and atom to ion mass ratios M 2/ M 1>1. It is shown that for moderate ratios λ 0/ R T the energy distribution of backscattered ions, integrated over all ejection angles, can have a maximum which was absent in the case of λ 0/ R T≫1. The results of the theory are confirmed by comparison with experimental and computer simulation data.

Analysis of gabapentin in serum and plasma by solid-phase extraction and gas chromatography-mass spectrometry for therapeutic drug monitoring.

A simple method for the determination of gabapentin (Neurontin) is described. The method uses solid-phase extraction by disk column and derivatization followed by gas chromatographic-mass spectrometric analysis. The single-step derivatization with MTBSTFA produces a t-BDMS derivative of both the carboxylic and amine moieties of the molecule. Each step of the procedure was optimized to assure reliable performance of the method. The assay limit of detection was 0.1 microg/mL with a linear range from 1.0 to 35 microg/mL. Within-run (n = 3) and between-run (n = 40) coefficients of variation were less than 8.2 and 15.9%, respectively. The method has proven reliable in routine production for more than a year, producing clean chromatography with unique ion fragments, consistent ion mass ratios, and no interferences. Statistical analysis of the gabapentin concentrations measured in 1020 random specimens over a 2-month period showed a mean concentration of 6.07 microg/mL with a standard deviation of 5.28.

A comparative study of modified Korteweg–de Vries (MKdV) and Korteweg–de Vries (KdV) solitons in plasmas with negative ions under the influence of electrons’ drift motion

In the plasma under consideration, the existence of modified Korteweg–de Vries (MKdV) solitons has been established for different values of electrons’ drift velocities νe′ and of Q′ (=mj/mi, negative to positive ion mass ratio). The amplitudes of the MKdV solitons are found to be much smaller (<1) than those of the corresponding amplitudes (>1) of the KdV solitons for Q′<0.6 when νe′=10. Unlike the existence of both compressive and rarefactive KdV solitons with two unaccountable regions of νe′, there is found to exist only compressive MKdV solitons of small amplitudes in the lower but entire range of νe′ for U=1.09, 1.12, and 1.15 when Q′=0.4. It is noteworthy to mention that, the width of the KdV soliton does not depend on Q′, i.e., on the concentration of negative ions whereas that of the MKdV soliton depends on Q′.

Ion-acoustic solitons and shocks in negative ion-beam relativistic plasma

We have analyzed the formation of solitons in a beam plasma system consisting of warm relativistic negative ions. The subsequent destruction of the nonlinearity of Korteweg-deVries equation near the critical density of negative ions and evolution of the shock wave are discussed in detail. The physical attributes of the ion-acoustic solitary wave and shocks are depicted graphically for the plasmas having (H/sup +/, Cl/sup -/) ions, (H/sup +/, O/sup -/) ions, (H/sup +/, SF/sub 5//sup -/) ions, (He/sup +/, Cl/sup -/) ions. It is found that mass ratio of negative ions and positive ions, relativistic effect and negative ion concentration have important contribution on the formation of solitons and shocks in the plasma.

Effect of Boundary, Electron Inertia and Streaming on LargeAmplitude Waves in a Relativistic Plasma

Nonlineaer wave propagation in a relativistic bounded plasma isanalysed through the pseudopotential approach by taking into accountthe streaming of electrons, and electron inertia. The finite geometryis seen to effect both the forward moving and reflected modes ofpropagation. Its dependence on the electron–ion mass ratio isalso critically analysed. In the second part of the paper we study theformation of solitons through the pseudopotential approach. Thevariation of the form of the pseudopotential is studied with respectto the radius of the bounding system, the electron–ion massratio, and the streaming velocity u0. It isobserved that the finite geometry and electron inertia significantlyaffect the solitary wave formation.