Ion Population Research Articles

Dust-acoustic solitary and cnoidal waves in a dense magnetized dusty plasma with temperature degenerate trapped electrons and nonthermal ions

A rigorous theoretical study has been made on obliquely propagating dust-acoustic solitary waves (OPDASWs) and cnoidal waves in a dense degenerate dusty plasma medium in the presence of temperature degenerate trapped electrons and κ−nonthermal ion population. A reductive perturbation technique has been adopted to obtain the Zakharov-Kuznetsov (ZK) equation and the modified ZK (mZK) equation. The solitary wave solutions of ZK and mZK equations are obtained to analyse the characteristics of solitary waves in such a plasma. The Jacobi (cn) elliptic periodic wave solution for mZK is also derived to analyse the nature of dust acoustic travelling wave. The different plasma parameters (e.g., electron-to-dust number density via δ, ions nonthermality via κ, temperature effect of degenerate trapped electrons via T, etc.) are seen to have significant inluence on the propagation nature of OPDASWs. The applications of results may be useful to explain/understand the nature of solitary waves in different ultra-dense astrophysical environments (such as neutron stars, white dwarfs etc. [, ]) and also in experiments involve the interaction of laser and solid density plasma and inertial confinement fusion, [, ] in which the relativistic effects play major role.

Ionized particle transport in reactive HiPIMS discharge: correlation between the energy distribution functions of neutral and ionized atoms

We investigated the transport of titanium ions produced in a reactive high-power impulse magnetron sputtering device used for titanium nitride coating deposition. Time-resolved mass spectrometry measurements of ionized sputtered atoms correlated to time-resolved tuneable diode-laser induced fluorescence (TR-TDLIF) measurements of neutral sputtered atoms were used to understand transport features. Based on ion energy distributions of Ti+, we identified four populations of ions and explore their physical origins. The signals of all ion populations decrease strongly when only 1% N2 is added to the Ar/N2 gas mixture. Time resolved mass spectrometry confirms the result reported in previous work: the fast target poisoning when nitrogen is added in HiPIMS discharges. Based on the measured energy distribution functions of Ti2+, N+, N2 +, and Ar+, we discuss the production of these ions in HiPIMS discharges. The temperature of thermalized sputtered neutral atoms determined by previous TR-TDLIF measurements evidences the physical origin of an ion population with energies lower than 4 eV. According to discharge pressure, cathode voltage, and ion type, we also discuss the physical origins of high-energy ions (>4 eV).

Long Short Term Memory networks (LSTM)-Monte-Carlo simulation of soil ionization using radon

Earthquake events are usually associated with atmospheric processes variations. Some of the important events in seismic periods include the atmospheric electricity/conductivity modification, which mostly depends on the ion population in the vicinity of earthquake preparation area. Radon, together with cosmic radiation are the major ionization sources in the lower troposphere. The radon induced soil ion-pair production rate was estimated for Erzincan, a city along the North Anatolian Fault Zone, Turkey. The Long Short-Term Memory networks (LSTM's) and Monte Carlo method are proposed to account for uncertainty in estimating the ion production rate. The advantage of the LSTM model is taken to study radon anomalies during the M = 5 Girlevik earthquake, Erzincan. Radon concentration is found to increase prior to the 5.0 Girlevik earthquake. According to estimations, 23 × 109 ion-pairs m−3s−1 were generated at 1 m depth from the Earth's surface during this earthquake. The soil-ion production estimation rate due to radon and its progeny in Erzincan is at the order of 109 ion-pairs m−3s−1. When these generated ions and charged aerosols reach the surface and were added to other ionization sources, parameters such as the near surface conductivity and electric field would be modified. In addition, under pronounced conditions could favor ionospheric perturbations.

Global and local processes of thin current sheet formation during substorm growth phase

Formation of thin current sheets in Earth's magnetotail is a critical element of the magnetosphere dynamics. The configuration and stability of these thin current sheets control the onset of magnetic reconnection and particle acceleration in the magnetotail during substorms and other geomagnetic activities. In recent years, multipoint observations, kinetic and hybrid simulations have significantly improved our understanding of the structure and dynamics of thin current sheets, including their ion kinetic physics. Global hybrid simulations have also revealed many details of ion kinetics in thin current sheet physics. In this paper we review current understanding of current sheet physics and discuss our recent observational and simulation results on thin current sheet formation, emphasizing the kinetics of current sheet thinning, multi-component ion populations, the role of electron anisotropy and ion agyrotropy, and the role of the ionosphere.

Examination of stiff ion temperature gradient mode physics in simulations of DIII-D H-mode transport

A systematic evaluation of gyrokinetic and gyrofluid model predictions of ion temperature gradient (ITG) stability and transport using parameters from DIII-D high confinement mode (H-mode) plasmas has been performed. The nonlinear CGYRO code is used to make the gyrokinetic predictions, and the quasilinear TGLF model for the corresponding gyrofluid predictions. The assessments are made at three radii (normalized toroidal flux ρ tor = 0.4, 0.55, and 0.7) in three different plasma scenarios with varying levels of neutral beam heating and torque. For each of the nine cases (3 radii × 3 scenarios) considered, ITG turbulence is found to be the dominant long-wavelength instability and transport mechanism. The inclusions of both transverse magnetic fluctuations and dynamic fast beam ions are stabilizing for all cases considered, with strongest effects seen at ρ or = 0.4 where the fast ion population and normalized plasma pressure β = 2μ 0 nT/B 2 are highest. The further inclusion of parallel magnetic fluctuations does not have a meaningful impact on the ITG turbulence in these scenarios, but does destabilize (in combination with fast ions) new high-frequency instabilities at ρ tor = 0.4 in the high power scenarios. In each case the linear and nonlinear ITG critical gradients are predicted to be lower than the measured ITG scale lengths and their associated uncertainties. Inclusion of equilibrium flow shear in the transport predictions generally leads to an upshift in effective critical gradient rather than a qualitative change in the predicted stiffness, with stronger responses typically seen in the gyrokinetic predictions than in the gyrofluid results. However, in most cases these upshifted gradients still remain below the measured values and their uncertainties. Although the predicted critical gradients are below the measured gradients, both models predicted flux-matching gradients consistent with measured values in six of the nine cases considered, with no clear systematic over- or underprediction. Thus, while the experimental ion temperature profiles do not appear to be closely pinned to the ITG critical gradient, both gyrokinetic and gyrofluid models are able to accurately match the measured gradients reasonably well in most cases.

Photodetachment and Test-particle Simulation Constraints on Negative Ions in Solar System Plasmas

Abstract Negative ions have been detected in abundance in recent years by spacecraft across the solar system. These detections were, however, made by instruments not designed for this purpose and, as such, significant uncertainties remain regarding the prevalence of these unexpected plasma components. In this article, the phenomenon of photodetachment is examined, and experimentally and theoretically derived cross-sections are used to calculate photodetachment rates for a range of atomic and molecular negative ions subjected to the solar photon spectrum. These rates are applied to negative ions outflowing from Europa, Enceladus, Titan, Dione, and Rhea and their trajectories are traced to constrain source production rates and the extent to which negative ions are able to pervade the surrounding space environments. Predictions are also made for further negative ion populations in the outer solar system with Triton used as an illustrative example. This study demonstrates how, at increased heliocentric distances, negative ions can form stable ambient plasma populations and can be exploited by future missions to the outer solar system.

Density dependence of ion cyclotron emission from deuterium plasmas in the large helical device

Ion cyclotron emission (ICE) driven by perpendicular neutral beam-injected (NBI) deuterons, together with the distinctive ICE driven by tangential NBI, have been observed from heliotron–stellarator plasmas in the large helical device (LHD). Radio frequency radiation in the lower hybrid range has also been observed Saito K. et al (2018 Plasma Fusion Res. 13 3402043), with frequency dependent on plasma density. Here we focus on recent measurements of ICE from deuterium plasmas in LHD, which show substantial variation in spectral character, between otherwise similar plasmas that have different local density in the emitting region. We analyse this variation by means of first principles simulations, carried out using a particle-in-cell (PIC) kinetic approach. We show, first, that this ICE is driven by perpendicular NBI deuterons, freshly ionised near their injection point in the outer midplane edge of LHD. We find that these NBI deuterons undergo collective sub-Alfvénic relaxation, which we follow deep into the nonlinear phase of the magnetoacoustic cyclotron instability (MCI). The frequency and wavenumber dependence of the saturated amplitudes of the excited fields determine our simulated ICE spectra, and these spectra are obtained for different local densities corresponding to the different LHD ICE-emitting plasmas. The variation with density of the spectral character of the simulated ICE corresponds well with that of the observed ICE from LHD. These results from heliotron–stellarator plasmas complement recent studies of density-dependent ICE from tokamak plasmas in KSTAR Thatipamula S.G. et al (2016 Plasma Phys. Control. Fusion 58 065003); Chapman B. et al (2017 Nucl. Fusion 57 124004), where the spectra vary on sub-microsecond timescales after an ELM crash. Taken together, these results confirm the strongly spatially localised character of ICE physics, and reinforce the potential of ICE as a diagnostic of energetic ion populations and of the ambient plasma.

Dust-Acoustic Rogue Waves in an Electron-Positron-Ion-Dust Plasma Medium

In this work, the modulational instability of dust-acoustic (DA) waves (DAWs) is theoretically studied in a four-component plasma medium with electrons, positrons, ions, and negative dust grains. The nonlinear and dispersive coefficients of the nonlinear Schrödinger equation (NLSE) are used to recognize the stable and unstable parametric regimes of the DAWs. It can be seen from the numerical analysis that the amplitude of the DA rogue waves decreases with increasing populations of positrons and ions. It is also observed that the direction of the variation of the critical wave number is independent (dependent) of the sign (magnitude) of q. The applications of the outcomes from the present investigation are briefly addressed.

High Latitude Zones of GeV Heavy Ions at the Inner Edge of Jupiter's Relativistic Electron Belt

AbstractJuno has discovered signatures of a high energy heavy ion population (>100 MeV/nucleon) within the inner edge of Jupiter's relativistic electron belt. The particles were detected in narrow zones in the high‐latitude lobes of the synchrotron emission region, a location never explored by prior spacecraft (∼31°–46° magnetic latitude; radial distances 1.12–1.41 Jovian radii, M‐shells 1.5–2.37). The population was revealed by extremely high signal ionization signatures seen in images collected by Juno's Stellar Reference Unit star camera (equivalent to 0.2–0.7 MeV of deposited energy per pixel). Signature morphology indicates a population of GeV ions (Z > 1) with atomic mass as high as sulfur, although species with 2 ≤ Z ≤ 8 potentially account for all of the signatures. The detections have occurred while the spacecraft is magnetically connected to Jupiter's halo and gossamer rings, but not while it is connected to the main ring; similar to equatorial observations of GeV carbon and sulfur ions by the Galileo Probe. We find that the particles reside on magnetic drift shells that suggest they are stably trapped within Jupiter's magnetosphere. Because the cosmic ray albedo neutron decay mechanism can only produce protons and electrons, it cannot be the source of this trapped Z > 1 ion population; other galactic cosmic ray origins are suspected. Inward radial transport of tens of keV heavy ions from the outer magnetosphere is another potential source.

A novel technique for in situ calibration of the C-2W electromagnetic neutral particle analyzer utilizing machine learning.

In TAE Technologies' current experimental device, C-2W, neutral beam injection creates a large fast ion population that sustains a field-reversed configuration (FRC) plasma. Diagnosis of these fast ions is therefore critical for understanding the behavior of the FRC. Neutral Particle Analyzers (NPAs) are used to measure the energy spectrum of fast ions that charge exchange on background or beam neutrals and are lost from the plasma. To ensure correct diagnosis of the fast ion population, a calibration check of the NPAs was performed. A novel, generally applicable method for an in situ relative calibration of diagnostics on an unknown source with a small dataset was developed. The method utilizes a machine learning technique, Generalized Additive Models (GAMs), to reconstruct the diagnostic source distribution, and Stochastic Gradient Descent (SGD) to determine the NPA channel calibration factors. The results on both synthetic and experimental datasets are presented.

Protein Analysis by Electrospray-Orbital Frequency Analyzer with Charge Detection Mass Spectrometry Algorithm.

Orbital frequency analyzer (OFA) is one of the electrostatic ion trap mass analysers for FTMS, which offers ultrahigh mass resolution and high ion charge capacity. In order to analyze multiply charged proteins and other large biological particles by means of charge detection mass spectrometry, a data processing algorithm was created to suit the image charge signal of nonharmonic waveform nature. The algorithm is capable of detecting collisions between ions and residual gas molecules, to determine lifetime of ions, and to evaluate the charge and mass values for ions having lifetime above a threshold. With the filtering of the lifetime and charge value, the chemical noise from small molecules and protein fragments can be eliminated in the reconstructed spectrum, facilitating measurement of protein content at a very low concentration, down to tens of nanomolars. The standard deviation of charge measurement is between 1.1 to 1.8 e for ions with oscillation lifetimes from 1 to 0.4 s, and this in turn determines the CDMS spectrum mass peak width. It has been found that the lower voltage setting of the OFA results in a larger population of ions surviving for longer times and thus produces narrower mass peak width. While OFA is able to run multiplexed CDMS without ion motion interference, coexisting ions of the same or very close m/z can cause interference between their image charge signals, which increases the error in charge determination.

A fast tool for ICRH + NBI modelling within the EU-IM framework

Most if not all tokamak heating scenarios involve multiple ion populations being heated simultaneously. To allow the simulation of various aspects of physics dynamics determining the characteristics of operational scenarios in a flexible way, speedy yet sufficiently accurate models are needed, and they should be connected to each other via a ‘backbone’. Under the umbrella of EUROfusion's Integrated Modelling efforts, such a structure is provided. The present paper focuses on one physics aspect: auxiliary heating. After solving the wave equation or beam source equation, this requires solving a set of coupled Fokker–Planck equations for the various populations involved. The adopted modules – enabling accounting for the Coulomb collisional interaction of several non-Maxwellian (minority, majority and beam) populations – are discussed and a practical example of their use is provided: the JET ‘baseline’ scenario heating a minority of${}^3\textrm {He}$ions in a balanced D$+$T mix heated by D and T neutral beams.

Theoretical balance model of the ytterbium-doped fiber amplifier

Based on conservation laws, kinetic equations for changes in ion populations in different energy states are written down, as well as equations how optical radiation intensity (and power) is changing in the optical fiber core is sequentially derived. Physical limitations of the given approach are also considered. A comparison of the results of a numerical analysis of the formation of luminescence in the ytterbium-doped optical fiber (with different representations of the probability of “survival” of spontaneous emission photons) with experimental data is presented.

Electrostatic wave breaking limit in a cold electronegative plasma with non-Maxwellian electrons

A one-dimensional multifluid hydrodynamic model has been adopted as basis for an investigation of the role of suprathermal electrons on the wave breaking amplitude limit for electrostatic excitations propagating in an electronegative plasma. A three-component plasma is considered, consisting of two inertial cold ion populations of opposite signs, evolving against a uniform background of (non-Maxwellian) electrons. A kappa-type (non-Maxwellian) distribution function is adopted for the electrons. By employing a traveling wave approximation, the first integral for the fluid-dynamical system has been derived, in the form of a pseudo-energy balance equation, and analyzed. The effect of intrinsic plasma parameters (namely the ion density ratio, the ion mass ratio, and the superthermal index of the nonthermal electrons) on the wave breaking amplitude limit is explored, by analyzing the phase space topology of the associated pseudopotential function. Our results are relevant to particle acceleration in Space environments and to recent experiments based on plasma-based accelerator schemes, where the simultaneous presence of negative ions and nonthermal electrons may be observed.

Particle-in-cell simulations of the Cassini spacecraft’s interaction with Saturn’s ionosphere during the Grand Finale

ABSTRACT A surprising and unexpected phenomenon observed during Cassini’s Grand Finale was the spacecraft charging to positive potentials in Saturn’s ionosphere. Here, the ionospheric plasma was depleted of free electrons with negatively charged ions and dust accumulating up to over 95 per cent of the negative charge density. To further understand the spacecraft–plasma interaction, we perform a three-dimensional Particle-In-Cell study of a model Cassini spacecraft immersed in plasma representative of Saturn’s ionosphere. The simulations reveal complex interaction features such as electron wings and a highly structured wake containing spacecraft-scale vortices. The results show how a large negative ion concentration combined with a large negative to positive ion mass ratio is able to drive the spacecraft to the observed positive potentials. Despite the high electron depletions, the electron properties are found as a significant controlling factor for the spacecraft potential together with the magnetic field orientation which induces a potential gradient directed across Cassini’s asymmetric body. This study reveals the global spacecraft interaction experienced by Cassini during the Grand Finale and how this is influenced by the unexpected negative ion and dust populations.

A Magnetically Filtered Atomic Oxygen Plasma Source for Low-Earth-Orbit Simulation

A magnetically filtered oxygen plasma source has been developed and characterized for the purpose of simulating the low-Earth-orbit environment. The source uses a magnetic ring cusp geometry coupled with a transverse magnetic filter to produce a plasma stream consisting of streaming atomic oxygen ions with energy, density, and ion species composition corresponding to orbital conditions at altitudes ranging from 275 to 550 km. Plasma properties downstream of the source are dependent on the operational settings for source flow rate and discharge current. The properties are examined as a function of these operating parameters to optimize the production of ions with energy and density relevant for low-Earth-orbit satellite drag applications. At each source operational setting presented in this work, the ion energy distributions are measured 0.55 m downstream of the source using a retarding potential analyzer, and the streaming ions were shown to have most probable energies ranging from 2.8 to 7 eV or 5800 to . In addition, a Wein filter () and a residual gas analyzer are used to measure the ion species percent composition as a function of the operational conditions. Source flow rate and discharge current settings are presented that allow for the composition of atomic oxygen ions to be adjusted from 63 to 90% of the total plasma ion population.

Ion cyclotron resonance heating with shifted separatrix

Ion cyclotron resonance heating, which we refer to as ICRH-SS, with the quasilinear (QL) separatrix (i.e., the separatrix in the space of QL routes of ion acceleration) located in the region of passing particles is studied. The aim of ICRH-SS is to minimize the fraction of trapped particles (particles with small longitudinal velocities) in the population of fast ions. The basic idea of ICRH-SS—shifting the separatrix to the region of passing particles—was advanced in the paper (Kolesnichenko et al 2017 Nuclear Fusion 57 066004). In this work, new features of ICRH-SS are revealed. The 3D QL routes of the particle acceleration and effects of Coulomb collisions are studied. A QL equation for distribution function of neutral beam injection (NBI) ions, which is convenient for analysis, is derived. Conditions for QL flux prevailing over collisional flux caused by pitch scattering are obtained. Numerical simulations using the SCENIC package are carried out for a JET plasma with NBI ions that are accelerated by RF field in the core region. A JET pulse designed as a demonstration of the so called ‘three ions’ scheme, which also complies with the criteria of ICRH-SS scheme, was selected. The numerical results show that in the considered example most accelerated ions have larger longitudinal velocities and fast particle orbits are passing during ICRH-SS, whereas, ‘conventional’ ICRH (defined as ICRH with the separatrix in the region of trapped particles) produces accelerated ions with banana orbits. Numerical results also show an increase in fast ion generation and core plasma heating performance for ICRH-SS as compared to the conventional ICRH.

Shock Induced Strong Substorms and Super Substorms: Preconditions and Associated Oxygen Ion Dynamics

It is well known that the interaction between interplanetary (IP) shocks and the Earth’s magnetosphere would generate/excite various types of geomagnetic phenomena. Progresses have been made on the Earth’s magnetospheric response to solar wind forcing in recent years in the aspects associated with magnetospheric substorms. Strong substorms and super substorms could be triggered externally by sudden changes of solar wind dynamic pressures. When a strong substorms (AE > 1000 nT) or super substorms (AE > 2000 nT) occurs, singly charged oxygen ions escaped from the Earth’s ionosphere are found to be a dominated ion population in the magnetotail and in the inner magnetosphere—ring current region. The products of a strong substorms or super substorms- plasmoid, burst bulk flows are also found to contain significant oxygen ions, even substorm injections can be dominated by oxygen ions. Thus, the magnetospheric dynamic must consider the contributions from the heavy oxygen ions. Also, the IP shock induced super substorms associated electromagnetic pulses (dB/dt) would shift the energetic particle (injections) inward and accelerate existing population significantly. Extensive attempts have also been made to understand how the solar wind energy couples with the magnetosphere to excite magnetospheric substorms. The statistical analysis shows that strong substorms (AE > 1000 nT) and super substorms (AE > 2000 nT) triggered by interplanetary shocks are most likely to occur under the southward interplanetary magnetic field (IMF) and fast solar wind pre-conditions. In addition, strong substorms after the IP shock arrival are more likely to occur when IMF points toward (away from) the Sun around spring (autumn) equinox, which can be ascribed to the Russell-McPherron effect. Thus, the southward IMF precondition of an interplanetary shock and the Russell-McPherron effect can be considered as precursors of a strong substorm and/or super substorm triggered by IP shocks. Moreover, the average duration of CME sheath region which is just behind the interplanetary shock are found to be about 7 hours. This indicates that southward IMF compressed by shock could last at least 7 hours long in the downstream of the interplanetary shock (sheath region) if a southward IMF pre-condition is present, which explains why the largest substorm often occur in the CME sheath.

Conceptual design of a collimated neutron flux monitor and spectrometer for DTT

A conceptual design and performance studies for a collimated neutron flux monitor and neutron spectrometer for the Divertor Tokamak Test (DTT) facility are presented. This study is based on the single-null divertor configuration and for “Half Power” and “Full power” scenarios with 15 MW of negative-ion NBI, 29 MW of ECH and 3 MW of ICRF heating with a maximum neutron yield of 1.5×1017 s−1. Fast ion distributions (both from auxiliary heating systems and fusion born) have been simulated in TRANSP/NUBEAM and the corresponding neutron energy spectra have been calculated using DRESS. Synthetic diagnostics have been implemented to determine the neutron fluxes and spectra at the detector location. Neutron emissivity profiles, plasma position, core ion temperature and the ratio of thermal and non-thermal D ion populations can be obtained with good accuracy and time resolution.

The influence of photo-induced processes and charge transfer on carbon and oxygen in the lower solar atmosphere

ABSTRACT To predict line emission in the solar atmosphere requires models that are fundamentally different depending on whether the emission is from the chromosphere or the corona. At some point between the two regions, there must be a change between the two modelling regimes. Recent extensions to the coronal modelling for carbon and oxygen lines in the solar transition region have shown improvements in the emission of singly and doubly charged ions, along with Li-like ions. However, discrepancies still remain, particularly for singly charged ions and intercombination lines. The aim of this work is to explore additional atomic processes that could further alter the charge-state distribution and the level populations within ions, in order to resolve some of the discrepancies. To this end, excitation and ionization caused by both the radiation field and by atom–ion collisions have been included, along with recombination through charge transfer. The modelling is carried out using conditions which would be present in the quiet Sun. This allows an assessment of the part atomic processes play in changing coronal modelling, separately from dynamic and transient events taking place in the plasma. The effect the processes have on the fractional ion populations are presented, as well as the change in level populations brought about by the new excitation mechanisms. Contribution functions of selected lines from low-charge states are also shown, to demonstrate the extent to which line emission in the lower atmosphere could be affected by the new modelling.