Ion Population Research Articles

Radiation influence on the plasma atomic kinetics and spectra in experiments on radiative shock waves

Radiative shocks waves are among of the most interesting astrophysical phenomena and due to their relevance, many laboratory experiments, using high-power lasers, have been performed to achieve a better understanding of them. The radiation emitted by the shock front can heat and ionize the pre-shock medium leading to the formation of radiative precursors, which are relevant in these phenomena since they absorb part of the radiation emitted by the shock front and becomes a strong source of radiation emission. The plasma in the precursor can be considered as a photoionized plasma in which the external radiation field plays a dominant role in the atomic kinetics behavior. A numerical study of the influence of the radiation field on the ion populations, radiative properties and atomic spectra of radiative precursors in radiative shocks generated in two laboratory experiments is presented. For the numerical simulations, three types of collisional-radiative models have been used. In the first one, the radiation induced processes are not included. In the second type, the radiative atomic processes induced by plasma self-absorption are considered. Finally, the radiative processes induced by both the external radiation field and the plasma self-absorption are included. The results obtained show the noticeable influence of the radiation field on the plasma properties analyzed.

A review of instrument techniques to measure magnetospheric cold electrons and ions

A review of the instruments and techniques to directly measure the full distributions of the cold-ion and cold-electron populations in the magnetosphere is presented. Relatively few studies have focused on the cold plasma populations of the magnetosphere due to difficulties associated with obtaining measurements. The cold particle populations are defined here as those with total energy approximately <100 eV which is an energy range for which measurements are difficult (regardless of species), but which often make up the bulk of the plasma density. These populations have known and suspected impacts on the structure and dynamics of the magnetosphere but to date have not yet been measured adequately. The lack of accurate measurements cold ion and electron populations through the magnetosphere makes closure of these science questions extremely difficult if not impossible. Reaching closure will require innovations in plasma spectrometers and associated techniques required to obtain high-fidelity measurements of the cold ion and electron populations in the magnetosphere. This paper seeks to review the instruments and techniques that have been used to date and present possible options for future missions.

Collision rates estimated from exact N-body simulations of a one-dimensional plasma

In a plasma, the charged particles interact via long-range forces, and this interaction causes the plasma to exhibit collective effects. If the graininess or coupling parameter g goes to zero (ideal collisionless plasma), two-body collisions are negligible, while collective effects dominate the dynamics. In contrast, when g≈1 collisions play a significant role. To study the transition between a collisionless and a collisional regime, a N-body code was developed and used in this work. The code solves exactly, in one spatial dimension, the dynamics of N infinite parallel plane sheets for both ion and electron populations. We illustrate the transition between individual and collective effects by studying two basic plasma phenomena, the two-stream instability and Langmuir waves, for different values of g. The numerical collision rates given by the N-body code increase linearly with g for both phenomena, although with proportionality factors that differ by roughly a factor of two, a discrepancy that may be accounted for by the different initial conditions. All in all, the usual collision rates published in the literature (Spitzer collisionality) appear to compare rather well with the rates observed in our simulations.

Parametric Decay Instabilities during Electron Cyclotron Resonance Heating of Fusion Plasmas, Problems and Possibilities

We review parametric decay instabilities (PDIs) expected in connection with electron cyclotron resonance heating (ECRH) of magnetically confined fusion plasmas, with a specific focus on conditions relevant for the ITER tokamak. PDIs involving upper hybrid (UH) waves are likely to occur in O-mode ECRH scenarios at ITER if electron density profiles allowing trapping of UH waves near the ECRH frequency are present. Such PDIs may occur near the plasma center in ITER full-field scenarios heated by 170 GHz O-mode ECRH and on the high-field side of half-field ITER plasmas heated by 110 GHz or 104 GHz O-mode ECRH. Additionally, 110 GHz O-mode ECRH of half-field ITER scenarios may have low ECRH absorption, due to the electron cyclotron resonance being located on the high-field side of the main plasma. This potentially allows PDIs driven by a significant amount of ECRH radiation reaching the UH resonance in X-mode to occur, as X-mode radiation can be generated by reflection of unabsorbed O-mode radiation from the high-field side wall. The occurrence of PDIs during ECRH may damage microwave diagnostics, such as the electron cyclotron emission and low-field side reflectometer systems at ITER, as well as complicate the calculation of heating and current drive characteristics. However, if PDIs are induced in a controlled manner, they may provide novel diagnostic tools and allow the generation of a moderate fast ion population in plasmas heated only by ECRH.

Characterizing the top-down sequencing of protein ions prior to mobility separation in a timsTOF.

Mass spectrometry (MS)-based proteomics workflows of intact protein ions have increasingly been utilized to study biological systems. These workflows, however, frequently result in convoluted and difficult to analyze mass spectra. Ion mobility spectrometry (IMS) is a promising tool to overcome these limitations by separating ions by their mass- and size-to-charge ratios. In this work, we further characterize a newly developed method to collisionally dissociate intact protein ions in a trapped ion mobility spectrometry (TIMS) device. Dissociation occurs prior to ion mobility separation and thus, all product ions are distributed throughout the mobility dimension, enabling facile assignment of near isobaric product ions. We demonstrate that collisional activation within a TIMS device is capable of dissociating protein ions up to 66 kDa. We also demonstrate that the ion population size within the TIMS device significantly influences the efficiency of fragmentation. Lastly, we compare CIDtims to the other modes of collisional activation available on the Bruker timsTOF and demonstrate that the mobility resolution in CIDtims enables the annotation of overlapping fragment ions and improves sequence coverage.

X-Ray Photoabsorption of Density-sensitive Metastable States in Ne vii, Fe xxii, and Fe xxiii

Metastable states of ions can be sufficiently populated in absorbing and emitting astrophysical media, enabling spectroscopic plasma-density diagnostics. Long-lived states appear in many isoelectronic sequences with an even number of electrons, and can be fed at large rates by various photonic and electronic mechanisms. Here, we experimentally investigate beryllium-like and carbon-like ions of neon and iron that have been predicted to exhibit detectable features in astrophysical soft X-ray absorption spectra. An ion population generated and excited by electron impact is subjected to highly monochromatic X-rays from a synchrotron beamline, allowing us to identify Kα transitions from metastable states. We compare their energies and natural line widths with state-of-the-art theory and benchmark level population calculations at electron densities of 1010.5 cm−3.

Inner southern magnetosphere observation of Mercury via SERENA ion sensors in BepiColombo mission

Mercury’s southern inner magnetosphere is an unexplored region as it was not observed by earlier space missions. In October 2021, BepiColombo mission has passed through this region during its first Mercury flyby. Here, we describe the observations of SERENA ion sensors nearby and inside Mercury’s magnetosphere. An intermittent high-energy signal, possibly due to an interplanetary magnetic flux rope, has been observed downstream Mercury, together with low energy solar wind. Low energy ions, possibly due to satellite outgassing, were detected outside the magnetosphere. The dayside magnetopause and bow-shock crossing were much closer to the planet than expected, signature of a highly eroded magnetosphere. Different ion populations have been observed inside the magnetosphere, like low latitude boundary layer at magnetopause inbound and partial ring current at dawn close to the planet. These observations are important for understanding the weak magnetosphere behavior so close to the Sun, revealing details never reached before.

The need for accurate measurements of thermal velocity distribution functions in the solar wind

The current state of the art thermal particle measurements in the solar wind are insufficient to address many long standing, fundamental physical processes. The solar wind is a weakly collisional ionized gas experiencing collective effects due to long-range electromagnetic forces. Unlike a collisionally mediated fluid like Earth’s atmosphere, the solar wind is not in thermodynamic or thermal equilibrium. For that reason, the solar wind exhibits multiple particle populations for each particle species. We can mostly resolve the three major electron populations (e.g., core, halo, strahl, and superhalo) in the solar wind. For the ions, we can sometimes separate the proton core from a secondary proton beam and heavier ion species like alpha-particles. However, as the solar wind becomes cold or hot, our ability to separate these becomes more difficult. Instrumental limitations have prevented us from properly resolving features within each ion population. This destroys our ability to properly examine energy budgets across transient, discontinuous phenomena (e.g., shock waves) and the evolution of the velocity distribution functions. Herein we illustrate both the limitations of current instrumentation and why higher resolutions are necessary to properly address the fundamental kinetic physics of the solar wind. This is accomplished by directly comparing to some current solar wind observations with calculations of velocity moments to illustrate the inaccuracy and incompleteness of poor resolution data.

Simulation of non-stationary neon plasma using the THERMOS toolkit

The THERMOS toolkit has been improved by adding the module for calculating the properties of non-stationary plasma. Low-density photoionized neon plasma obtained in experiments was simulated. Calculated ion populations, rates of elementary processes, and radiation spectra were compared with results obtained by other scientific groups.

What powers the wind from the black hole accretion disc in GRO J1655−40?

ABSTRACT Black hole accretion discs can produce powerful outflowing plasma (disc winds), seen as blue-shifted absorption lines in stellar and supermassive systems. These winds in quasars have an essential role in controlling galaxy formation across cosmic time, but there is no consensus on how these are physically launched. A single unique observation of a stellar-mass black hole GRO J1655−40 was used to argue that magnetic driving was the only viable mechanism and motivated unified models of magnetic winds in both binaries and quasars. The alternative, X-ray heating (thermal-radiative wind), was ruled out for the low observed luminosity by the high wind density estimated from an absorption line of a metastable level of Fe xxii. Here, we reanalyse these data using a photoionization code that includes cascades from radiative excitation as well as collisions in populating the metastable level. The cascade reduces the inferred wind density by more than an order of magnitude. The derived column is also optically thick, so the source is intrinsically more luminous than observed. We show that a thermal-radiative wind model calculated from a radiation hydrodynamic simulation matches well with the data. We revisit the previous magnetic wind solution and show that this is also optically thick, leading to a larger source luminosity. However, unlike the thermal-radiative wind, it struggles to reproduce the overall ion population at the required density. These results remove the requirement for a magnetic wind in these data and remove the basis of the self-similar unified magnetic wind models extrapolated to quasar outflows.

Storm‐Time Magnetopause: Pressure Balance

AbstractThe magnetopause is treated as a boundary where the pressure of the incoming solar wind is balanced by the pressure of the geomagnetic field and the plasma pressure inside the magnetopause is often neglected. However, published studies of pressure balance at the magnetopause reveal an excess of the magnetosheath pressure. Moreover, our survey of about 50,000 THEMIS magnetopause crossings shows that about 1% of them exhibits even larger magnetic field in the magnetosheath than in the magnetosphere. A subsequent analysis of crossings observed in the subsolar region under a southward interplanetary magnetic field shows the pressure of the dense cold ion population as an important component of the total magnetospheric pressure. This component is too cold to be registered by standard ion analyzers but its density can reach 300 cm−3. The second effect connected with a presence of cold plasma population is a reduction of the reconnection rate that slows down the transport of the magnetic flux down the tail and leads to magnetic pile‐up in the subsolar magnetosheath.

Solar Wind Impact on ENAs From Earth's Subsolar Magnetosheath

AbstractAs the solar wind (SW) crosses Earth's bow shock, it is heated and decelerated, resulting in a hot and dense magnetosheath ion population. This increases the probability of charge exchange between a magnetosheath proton and a geocoronal Hydrogen atom, which produces energetic neutral atoms (ENAs). These ENAs propagate away from the magnetosheath carrying information about the inherent properties of the progenitor plasma. In this work, ENA fluxes from the subsolar magnetosheath, observed by the Interstellar Boundary Explorer, are compared to SW conditions. These comparisons reveal that the passband‐weighted average differential flux of ENAs is strongly influenced by the SW density, and that ENA spectra flatten with increasing SW speed and temperature, and steepen with increasing SW density. In addition, there is evidence from ENA spectra for different interplanetary magnetic field configurations that most of the ENAs observed by Interstellar Boundary Explorer come from the specularly reflected proton population in the magnetosheath.

On the relation between apparent ion and total particle growth rates in the boreal forest and related chamber experiments

Abstract. The understanding of new particle formation and growth processes is critical for evaluating the role of aerosols in climate change. One of the knowledge gaps is the ion–particle interaction during the early growth process, especially in the sub-3 nm range, where direct observations are sparse. While molecular interactions would imply faster growth rates of ions compared to neutral particles, this phenomenon is not widely observed in the atmosphere. Here, we show field measurements in the boreal forest indicating a smaller apparent growth rate of the ion population compared to the total particles. We use aerosol dynamics simulations to demonstrate that this effect can be caused by the changing importance of ion-induced nucleation mechanisms during the day. We further compare these results with chamber experiments under similar conditions, where we demonstrate that this effect critically depends on the abundance of condensable vapors and the related strength of ion-induced nucleation. Our results imply that atmospheric ion growth rate measurements below 3 nm need to be evaluated very carefully as they do not represent condensational growth alone but are influenced by ion–particle population interactions.

Modeling space-resolved ion dynamics in ECR plasmas for predicting in-plasma β-decay rates

Lifetimes of radioactive nuclei are known to be affected by the level configurations of their respective atomic shells. Immersing such isotopes in environments composed of energetic charged particles such as stellar plasmas can result in β-decay rates orders of magnitude different from those measured terrestrially. Accurate knowledge of the relation between plasma parameters and nuclear decay rates are essential for reducing uncertainties in present nucleosynthesis models, and this is precisely the aim of the PANDORA experiment. Currently, experimental evidence is available for fully stripped ions in storage rings alone, but the full effect of a charge state distribution (CSD) as exists in plasmas is only modeled theoretically. PANDORA aims to be the first to verify these models by measuring the β-decay rates of select isotopes embedded in electron cyclotron resonance (ECR) plasmas. For this purpose, it is necessary to consider the spatial inhomogeneity and anisotropy of plasma ion properties as well as the non-local thermodynamic equilibrium (NLTE) nature of the system. We present here a 3D ion dynamics model combining a quasi-stationary particle-in-cell (PIC) code to track the motion of macroparticles in a pre-simulated electron cloud while simultaneously using a Monte Carlo (MC) routine to check for relevant reactions describing the ion population kinetics. The simulation scheme is robust, comprehensive, makes few assumptions about the state of the plasma, and can be extended to include more detailed physics. We describe the first results on the 3D variation of CSD of ions both confined and lost from the ECR trap, as obtained from the application of the method to light nuclei. The work culminates in some perspectives and outlooks on code optimization, with a potential to be a powerful tool not only in the application of ECR plasmas but for fundamental studies of the device itself.

Fluid simulation of dust-acoustic solitary waves in the presence of suprathermal particles: Application to the magnetosphere of Saturn

The observation of dust in the rings of Saturn by instruments on board the Voyager 1, Voyager 2, and Cassini missions triggered our interest in exploring the evolution of electrostatic dust acoustic waves (DAWs) in the Saturnian magnetospheric dusty plasma. The salient features of dust-acoustic electrostatic solitary waves have been examined by means of numerical simulations that adopted a fluid algorithm. We considered highly energetic non-Maxwellian ion and electron populations, in combination with inertial dust. The ions and electrons were modeled by kappa distributions to account for the long-tailed particle distribution featuring a strong suprathermal component. At equilibrium, the initial density perturbation in the dust density was used to trigger the evolution of DASWs propagating in non-Maxwellian dusty plasma. Our main focus is to determine the comprehensive role of the dust concentration and the suprathermal index (kappa) of the ion and electron populations in the generation and evolution of DASWs. These simulation results are thought to be relevant for (and applicable in) existing experimental data in space, especially in the magnetosphere of Saturn, but also in other planetary plasma environments that are presumably characterized by the presence of charged dust.

Loss-cone-shift maps for the Earth’s magnetosphere

Because of finite-gyroradii effects, the atmospheric loss cone for energetic particles in the magnetosphere is shifted away from the magnetic-field direction. Using the Tsyganenko T96 magnetic-field model, maps of the magnitude of the angular shift of the loss cone are created for electrons, protons, and singly-ionized oxygen in the nightside magnetosphere. When the shift exceeds about 5°–10°, stochastic scattering of particles occurs. For protons and oxygen, this loss-cone shift is quite large, even in the dipolar portions of the magnetosphere, and stochastic scattering of protons and oxygen can occur in those regions. Hence, the ring-current ion population probably exhibits a robustly shifted loss cone and stochastic scattering in the dipole magnetosphere. For electrons, large loss-cone shifts and stochastic scattering are restricted to the magnetotail near and beyond the transition region.

The dependence of Martian ion escape on solar EUV irradiance as observed by MAVEN

We analyze the planetary ion, solar wind, interplanetary magnetic field (IMF), and solar extreme ultraviolet (EUV) irradiance data from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission to quantify the variation in ion escape with solar EUV irradiance. With relatively strict constraints on the upstream solar wind and IMF conditions, we divide the planetary ion data into 4 subsets with different solar EUV conditions to estimate ion escape rates. The results show that the total ion escape rate may increase nonlinearly with solar EUV irradiance and eventually approach an asymptotic limit as EUV increases. Further analysis on different ion species, escape channels, and energy ranges show that the dependence on solar EUV varies between these different ion populations. We also find that the spatial distributions of ion density and velocity vary between high and low solar EUV conditions, which is likely caused by the variations of electromagnetic field distributions. These results suggest that as solar EUV controls the ion production and affects the ion distributions near Mars, it will in turn influence the electromagnetic field distributions and thus affect the acceleration of escaping ions. This feedback mechanism may limit the total ion escape rate as solar EUV increases under constrained solar wind and IMF conditions.

Doublet splitting of fusion alpha particle driven ion cyclotron emission

Ion cyclotron emission (ICE) originating from confined populations of fast ions in toroidal fusion plasmas is an important non-invasive, passive diagnostic for current and next-generation devices. The ability to model ICE signals accurately is an essential step towards inferring the characteristics of confined energetic alpha particles or fast neutral beam ions and background plasma. In this paper, the linear growth rates of the magnetoacoustic cyclotron instability, which is the leading explanation for ICE, are calculated in high-resolution 2D space for parameters corresponding to JET Pulse No. 26148. These calculations further highlight the origin of doublet splitting of the cyclotron harmonics and the perceived need to invoke nonlinear interactions with 1D3V particle-in-cell studies to account for lower harmonics with substantial amplitudes. The inclusion of signals of ICE from a well-resolved range of propagation angles can also account for these effects.

Radial characterization of an ion beam in a deflected magnetic nozzle

The radial characterization of an ion beam generated in a magnetically steered radio-frequency (RF) plasma source is presented. In the symmetrical magnetic nozzle (MN) configuration, radial profiles of the ion saturation current obtained with a planar Langmuir probe show a double-peaked profile. The same behaviour is confirmed by the radial measurements of the total ion current and the ion energy distribution functions (IEDFs) obtained with a retarding field energy analyzer. The IEDFs also show the presence of an ion beam centred at r = -2 cm. On the contrary, radial measurements taken with a magnetic nozzle deflected on the r - z plane exhibit a single-peaked profile with both the local ion population and the ion beam centred at r = -5 cm, in the direction of the MN orientation. It is shown that the ion beam location is changed as a result of a deflected magnetic nozzle, and that it follows the direction of increasing radial magnetic field.

Considerations for Generating Frequency Modulation Waveforms for Fourier Transform-Ion Mobility Experiments.

By casting the information regarding an ion population's mobility in the frequency domain, the coupling of time-dispersive ion mobility techniques is now imminently compatible with slower mass analyzers such as ion traps. Recent reports have detailed the continued progress toward maximizing the efficiency of the Fourier transform ion mobility-mass spectrometry (FT-IM-MS) experiments, but few reports have outlined the intersection between the practical considerations of implementation against the theoretical limits imposed by traditional signal processing techniques. One of the important concerns for Fourier-based multiplexing experiments is avoiding signal aliasing as a product of undersampled signals that may occur during data acquisition. In addition to traditional considerations such as detector sampling frequency, the limitations (i.e., maximum measurable drift time) imposed by experimental mass scan duration and the frequency sweep used for ion gate modulation must also be assessed. This work aims to connect the fundamental underpinnings of FT-IM-MS experiments and the associated experimental parameters that are encountered when coupling the comparatively fast separations in the mobility domain with the slower m/z scanning common for ion-trap mass analyzers. In addition to stating the relevant theory that applies to the FT-IM-MS experiment, this report highlights how aliased signals will manifest post Fourier transform in reconstructed arrival time distributions and calculated mobilities.