Ion Production Rate Research Articles

Inferring thermospheric composition from ionogram profiles: a calibration with the TIMED spacecraft

Abstract. We present a method for augmenting spacecraft measurements of thermospheric composition with quantitative estimates of daytime thermospheric composition below 200 km, inferred from ionospheric data, for which there is a global network of ground-based stations. Measurements of thermospheric composition via ground-based instrumentation are challenging to make, and so details about this important region of the upper atmosphere are currently sparse. The visibility of the F1 peak in ionospheric soundings from ground-based instrumentation is a sensitive function of thermospheric composition. The ionospheric profile in the transition region between F1 and F2 peaks can be expressed by the “G” factor, a function of ion production rate and loss rates via ion–atom interchange reactions and dissociative recombination of molecular ions. This in turn can be expressed as the square of the ratio of ions lost via these processes. We compare estimates of the G factor obtained from ionograms recorded at Kwajalein (9∘ N, 167.2∘ E) for 25 times during which the Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) spacecraft recorded approximately co-located measurements of the neutral thermosphere. We find a linear relationship between G and the molecular-to-atomic composition ratio, with a gradient of 2.55±0.40. Alternatively, using hmF1 values obtained by ionogram inversion, this gradient was found to be 4.75±0.4. Further, accounting for equal ionisation in molecular and atomic species yielded a gradient of 4.20±0.8. This relationship has potential for using ground-based ionospheric measurements to infer quantitative variations in the composition of the neutral thermosphere via a relatively simple model. This has applications in understanding long-term change and the efficacy of the upper atmosphere on satellite drag.

Nonuniform Electric Field-Enhanced In-Source Declustering in High-Pressure Photoionization/Photoionization-Induced Chemical Ionization Mass Spectrometry for Operando Catalytic Reaction Monitoring.

Photoionization mass spectrometry (PI-MS) is a powerful and highly sensitive analytical technique for online monitoring of volatile organic compounds (VOCs). However, due to the large difference of PI cross sections for different compounds and the limitation of photon energy, the ability of lamp-based PI-MS for detection of compounds with low PI cross sections and high ionization energies (IEs) is insufficient. Although the ion production rate can be improved by elevating the ion source pressure, the problem of generating plenty of cluster ions, such as [MH]+·(H2O)n (n = 1 and 2) and [M2]+, needs be solved. In this work, we developed a new nonuniform electric field high-pressure photoionization/photoionization-induced chemical ionization (NEF-HPPI/PICI) source with the abilities of both HPPI and PICI, which was accomplished through ion-molecule reactions with high-intensity H3O+ reactant ions generated by photoelectron ionization (PEI) of water molecules. By establishing a nonuniform electric field in a three-zone ionization region to enhance in-source declustering and using 99.999% helium as the carrier gas, not only the formation of cluster ions was significantly diminished, but the ion transmission efficiency was also improved. Consequently, the main characteristic ion for each analyte both in HPPI and PICI occupied more than 80%, especially [HCOOH·H]+ with a yield ratio of 99.2% for formic acid. The analytical capacity of this system was demonstrated by operando monitoring the hydrocarbons and oxygenated VOC products during the methanol-to-olefins and methane conversion catalytic reaction processes, exhibiting wide potential applications in process monitoring, reaction mechanism research, and online quality control.

THE SIMULATION OF VIBRATIONAL POPULATIONS OF ELECTRONICALLY EXCITED N2 IN TITAN’S UPPER ATMOSPHERE DURING PRECIPITATIONS OF HIGH-ENERGETIC PARTICLES

We study the electronic kinetics of singlet molecular nitrogen in Titan’s upper atmosphere during precipitations of high-energetic particles. Both radiative processes and processes of electron excitation energy transfer during inelastic collisions with N2 and CH4 molecules were considered in the calculation of vibrational populations of electronically excited singlet states a'1Σu–, a1Πg, w1Δu of molecular nitrogen in the upper atmosphere of Titan. It is shown that the calculated volume emission intensities of the Lyman-Birge-Hopfield bands correlate with the profiles of the ion production rate in the atmosphere of Titan during the considered cases of electron precipitation for considered interval of the energies 30-1000 eV of magnetospheric electrons. This fact is explained by the negligible contribution of collisional processes to the vibrational populations a1Πg(v'=0-6) in the considered range of heights above 900 km.

Theoretical investigation of the negative ionization of hydrogen particles on metal surfaces with low work function

This work addresses the negative ionization of hydrogen particles on low work function metal surfaces, which is an important process for the field of the surface plasma negative ion beams sources. We present the theoretical model for the computer calculation of the negative ionization probability which takes into account the component of atom/ion velocity, parallel to the surface. The calculated negative ionization probability of hydrogen quantitatively fits to the experimental data in the wide range of ion exit energies. The theoretical estimation shows, that for the low work function converter surfaces (φ ∼ 1.5 eV) the negative ionization probability of hydrogen can be enhanced up to 30% if the hydrogen has velocity component parallel to the surface ∼0.05 a.u. (∼60 eV). Therefore, the H- ion production rate can be increased for a negative ion source configuration that implements the oblique exit angle of hydrogen.

Directly quantifying multiple interacting influences on plant competition.

When plants compete what influences that interaction? To answer this we measured belowground competition directly, as the simultaneous capture of soil ammonium and nitrate by co-existing herbaceous perennials, Dactylis glomerata and Plantago lanceolata, under the influence of: species identity; N uptake and biomass of focal and neighbour plants; location (benign lowland versus harsher upland site); N availability (low or high N fertilizer); N ion, ammonium or nitrate production (mineralisation) rate, and competition type (intra- or interspecific), as direct effects or pairwise interactions in linear models. We also measured biomass as an indirect proxy for competition. Only three factors influenced both competitive N uptake and biomass production: focal species identity, N ion and the interaction between N ion and neighbour N uptake. Location had little effect on N uptake but a strong influence on biomass production. N uptake increased linearly with biomass only in isolated plants. Our results support the view that measuring resource capture or biomass production tells you different things about how competitors interact with one another and their environment, and that biomass is a longer-term integrative proxy for the outcomes of multiple separate interactions-such as competition for N-occurring between plants.

Elevated pressure increases the effect of electric fields on ionic wind in methane premixed jet flames

Electric fields are useful for enhancing stability limits of flames, increasing the overall burning rate and reducing soot emissions. The electric body force has been known as a key element behind the aforementioned augmentation, and recent studies have provided clear picture for the resulted flow modification. In this study, we investigate the effects of pressure on an ionic wind by applying transverse electric fields to methane premixed jet flames in a pressurized chamber up to 2 atm. We investigated the voltage-current response by varying the pressure, the equivalence ratio of the mixture, and the flow rate. We found that the saturated current for lean and stoichiometric mixtures was not affected by the pressure, while the saturated current of rich premixed flames changed significantly. We developed a model to predict the voltage-current behavior and the ion-production rate, which we validated using experimental results. Based on our flow field measurements, we found that elevated pressure conditions enhanced ionic wind-driven mass transport. These results support the use of electric fields in a high-pressure environment.

A RT-LAMP based hydrogen ion selective electrode sensing for effective detection HIV-1 RNA with high-sensitivity

Development of a simple, sensitive and specific method for HIV-1 assay is demanded. In some emergency situations, a portable reverse transcription loop-mediated isothermal amplification (RT-LAMP) platform is necessary. A novel hydrogen ion-selective RT-LAMP (H+-RT-LAMP) sensor was developed for highly sensitive HIV-1 using hydrogen ion concentration as a signal producing compound. The H+-RT-LAMP sensor was based on screen-printed with carbon-doped graphene conductive layer, carbon nanotubes (CNTs) solid electrolyte layer, and reference electrode KCl functional layer, which provided superior electrical signals, high sensitivity and stability for HIV-1 detection. The rate of hydrogen ion production was related to the viral load (VL) during the amplification of HIV-1. The sensitive HIV-1 RNA detection range was achieved from 0 copies/μL to 105 copies/μL. The proposed H+-RT-LAMP sensor was applied to detect HIV-1 RNA in real human serum. 57 samples were detected and satisfactory results were obtained. Compared with commercial instruments, the detection results of H+-RT-LAMP sensor demonstrated a perfect concordance rate of 96.5 %, and the limit of detection (LOD) for the clinical samples was 10 copies per tube. Time to get the result is from 10 min to 25 min. Therefore, the proposed H+-RT-LAMP sensor was particularly suitable as a point-of-care device for the on-site detection of HIV-1.

Ionization effect in the Earth’s atmosphere during the sequence of October–November 2003 Halloween GLE events

The effect of precipitating high-energy particles on atmospheric physics and chemistry is extensively studied over the last decade. In majority of the existing models, the precipitating particles induced ionization plays an essential role. For such effects, it is necessary to possess enhanced increase in ion production, specifically during the winter period. In this study, we focus on highly penetrating particles — cosmic rays. The galactic cosmic rays are the main source of ionization in the Earth’s stratosphere and troposphere. On the other hand, the atmospheric ionization may be significantly enhanced during strong solar energetic particle events, mainly over the polar caps. A specific interest is paid to the most energetic solar proton events leading to counting rate enhancement of ground-based detectors, namely the so-called ground level enhancements (GLEs). During solar cycle 23, several strong ground level enhancements were observed. A sequence of three GLEs was observed in October–November 2003, the Halloween events. Here, on the basis of 3-D Monte Carlo model, we computed the energetic particles induced atmospheric ionization, explicitly considering the contribution of cosmic rays with galactic and solar origin. The ion production rates were computed as a function of the altitude above sea level using reconstructed solar energetic particles spectra. The 24 h and event averaged ionization effects relative to the average due to galactic cosmic rays were also computed.

Simultaneous kinetic-potentiometric determination of levodopa and carbidopa using multivariate calibration methods

Partial least squares (PLS) and principle component regression (PCR) multivariate calibration methods were applied to the simultaneous determination of carbidopa and levodopa using kinetic data from novel potentiometry methods. These methods were based on the rate of chloride ion production in the reaction of carbidopa and levodopa with N-chlorosuccinimide (NCS) which was monitored by a chloride ion-selective electrode. The experimental data shows suitability of ion-selective electrodes (ISEs) to be used as detectors not only for the direct determination of chloride ion but also for simultaneous kinetic-potentiometric analysis using chemometric methods. These methods are based on the differences observed in the production rate of chloride ions. The results show that simultaneous determination of carbidopa and levodopa can be performed in their concentration ranges of 1.0-14.0 and 0.5-25.0 μg/mL, respectively. The total relative standard errors for applying PCR and PLS methods to 9 synthetic samples in the concentration range of 2.0-13.0 μg/mL for carbidopa and 1.0-18.0 μg/mL for levodopa were 4.81 and 4.29, respectively. The effects of certain additives used as excipients upon the reaction rate were determined to assess selectivity of the method. Both methods (PLS and PCR) were validated using a set of synthetic sample mixtures and then were successfully applied to the determination of carbidopa and levodopa in several commercially available mixture formulations. The recoveries were satisfactory and comparable to those obtained by applying the reference Pharmacopoeia method of high performance liquid chromatography.

Mid-latitude convective boundary-layer electricity: A study by large-eddy simulation

This paper reports the first investigations of the mid-latitude convective boundary layer (CBL) electricity above the homogeneous land surface using a large-eddy simulation (LES). Our approach uses LES together with a subgrid kinematic model for relative dispersion of scalar to calculate Lagrangian trajectories of notional particles carrying radioactive nuclei, small atmospheric ions, and charged aerosol particles. This technique opens up new possibilities for quantifying the influence of various environmental conditions on the formation of the electrical state of the undisturbed lower atmosphere. We examine the altitude distribution of principal atmospheric electrical quantities in the CBL and lower free weakly stable atmosphere without clouds depending on surface turbulent heat flux, geostrophic wind speed, mixed-layer height, ionospheric potential, and various ion production rates due to cosmic rays and radioactive gases.

Mapping of Magnetic Field of SPIDER by a Three-Axis Automatic Positioning System

SPIDER is the prototype of the ion source of the neutral beam injector (NBI) for ITER, and is currently in operation at the Neutral Beam Test Facility (NBTF), Consorzio RFX, Padova, Italy. The magnetic field is important in SPIDER and, in general, in negative ion sources. It is required for filtering the fast electrons in the plasma source (magnetic filter field), thus for enhancing the negative ion production rate, and for suppressing the coextracted electrons in the accelerator (electron suppression field). In order to measure and map the magnetic field in SPIDER, a positioning system has been designed and realized, then applied with success during 2018. A three-axis system holds a Hall probe, and can be controlled manually or remotely by a graphical user interface. Once the three-axis system is installed on SPIDER, it can be programed to automatically move through the 1280 accelerator apertures and acquire magnetic field profiles. The development of this programable system allowed saving a considerable amount of time. This article describes the design and the realization of the magnetic field mapping system, along with the results of the measuring campaigns carried out in 2018 and the comparison with numerical models.

Towards prediction of the rates of antihydrogen positive ion production in collision of antihydrogen with excited positronium

We present a 4-body calculation of scattering between an antihydrogen atom () and a positronium (Ps) aiming at the prediction of cross sections for the production of antihydrogen positive ions . The antihydrogen positive ions are expected to be a useful source of ultra-cold anti-atoms for the test of matter-antimatter gravity. We convert the Schrödinger equation to a set of coupled integro-differential equations that involve intermediate states which facilitate the internal region description of the scattering wavefunction. They are solved using a compact finite difference method. Our framework is extended to scattering between an excited Ps and H. Cross sections of the reactions, Ps (1s/2s/3s) , in s-wave collisions, are calculated. It is found that the reactions originating from Ps (1s/2s) + produce with a constant cross section within 0.05 eV above the threshold while the reaction cross section from Ps (3s) decreases as the collision energy increases in the same energy interval. Just above the threshold, the cross section of production from Ps (3s) + in s-wave collision is 7.8 times larger than that from Ps (1s) + in s-wave and 2.3 times larger than that from Ps (2s) + in s-wave. The near-threshold de-excitation reaction from Ps (3s) + occurs more rapidly than the production.

Towards prediction of the rates of antihydrogen positive ion production in antihydrogen-excited positronium reaction

SynopsisWe present the 4-body calculation of the antihydrogen-positronium scattering aiming at the prediction of cross sections for the production of antihydrogen positive ions. The latter are expected to be a useful source of ultra-cold atoms for the test of matter-antimatter gravity. We convert the Schrödinger equation to a set of coupled integro-differential equations that involve intermediate states and are solved using the compact finite difference method. We will present the investigation of the rearrangement reaction between the ground-state antihydrogen atom and the excited positronium.

Modeling of Diffuse Aurora due to Precipitation of H+‐H and SEP Electrons in the Nighttime Atmosphere of Mars: Monte Carlo Simulation and MAVEN Observation

AbstractThe nighttime limb intensity of diffuse auroral emission of CO2+ (B2Σu+ ‐ X2πg) Ultraviolet Doublet (UVD) is observed in the northern hemisphere of Mars during 17–21 December 2014 from Imaging Ultraviolet Spectrograph instrument onboard Mars Atmosphere and Volatile Evolution. We have used hybrid model and four‐dimensional yield spectrum approach based on Monte Carlo simulation to calculate the ionization rate, limb intensity, and ion and electron densities of diffuse aurora due to precipitation of solar energetic particle and proton‐hydrogen (H+‐H) fluxes in the nighttime ionosphere of Mars. It is found that the production rates of atmospheric ions (CO2+, N2+, and O+) are dominant in the upper ionosphere at about 100–150 km due to impact of H+‐H. The solar energetic particle formed auroral ionosphere (CO2+, NO+, and O+) in the middle ionosphere between 50 and 100 km due to precipitation of monoenergetic electrons of energies 25 to 100 keV. The simulated limb intensities of CO2+UVD due to impact of H+‐H and auroral electrons are compared with Imaging Ultraviolet Spectrograph observations. Our model results are overestimating the observations, but 100 keV electrons deposited maximum energy around 75 km, closer to the observed altitude of the maximum emission. The densities of upper ionosphere (O2+, NO+, and CO2+) due to impact of H+‐H are smaller by one to two orders of magnitude than that produced by auroral electrons in the middle ionosphere.

The dayside ionosphere of Mars: Comparing a one-dimensional photochemical model with MAVEN Deep Dip campaign observations

A one dimensional photochemical model for the dayside ionosphere of Mars has been developed for calculating the density profiles of ions and electrons under steady state photochemical equilibrium condition. The study focuses on the Deep Dip campaigns of the Mars Atmosphere and Volatile EvolutioN mission (MAVEN) and used the in-situ measurements of neutral density profiles, solar flux and electron temperatures from instruments onboard MAVEN as input to the model. An energy deposition model is employed for calculating the attenuated photon flux and photoelectron flux at different altitudes in the ionosphere. The Analytical Yield Spectrum approach is used for calculating the photoelectron fluxes. Volume production rates of major primary ions, CO2+, CO+, O+, C+, N2+, and N+, due to photon and photoelectron impact are calculated and used as input to the model in which ion-neutral chemistry in the dayside ionosphere is simulated. The modeled ion profiles are compared with the ion mode observations of Neutral Gas Ion Mass Spectrometer (NGIMS) and electron density estimates from Langmuir Probe and Waves (LPW). The model could reproduce the observed structure of the major ion profiles O2+, CO2+, and electron density reasonably well. However, when the magnitudes are compared, the modeled values are roughly a factor of 2 larger than observation. By reducing the neutral CO2 density, the model outputs and the observed ion profiles and electron density profile can become closer. The model also calculated the densities of 11 other ions, viz. N+, C+, O+, NO+, N2H+, HCO+, N2+, CO+, OCOH+, HNO+, and OH+. Profiles of each of these ions are compared with the NGIMS observations during the respective orbits and are discussed in detail. Such a comparison for the deep dip periods is reported for the first time, which showcases the level of the current understanding of the ion chemistry in the Martian ionosphere.

Development of microwave plasma proton transfer reaction mass spectrometry (MWP-PTR-MS) for on-line monitoring of volatile organic compounds: Design, characterization and performance evaluation

Proton transfer reaction mass spectrometry (PTR-MS) is a revolutionary on-line VOCs monitoring method. In this study, a new microwave plasma-based proton transfer reaction mass spectrometry (MWP-PTR-MS) is developed. The MWP consists of a surfatron type resonator and a cooperative ion extraction device to achieve high efficiency production of hydronium ions. Non-local thermodynamic equilibrium water plasma is generated in a quartz tube at 200 Pa with 2.45 GHz microwave. Characters of MWP, such as emission spectroscopy, input power, dirty ion suppressing and ion extraction, are explored systematically. With the same test platform, MWP has a 7-fold increment of hydronium ion production rate than glow discharge source. The counts rate of hydronium ion is 8 × 106 cps with abundance of NO+ and O2+ is less than 0.4% and 5% respectively. The performance of MWP-PTR-MS is validated by analysis of several chemicals and demonstration application is conducted. The instrument showed good linearity above 99% in the range of 4.5 × 10−11 to 4.5 × 10−9 mol/L. Benefited from the character of surface wave and 2.45 GHz microwave, MWP has high potential in improving the performance and reliability of current PTR-MS.

Promotion of activation ability of N vacancies to N2 molecules on sulfur-doped graphitic carbon nitride with outstanding photocatalytic nitrogen fixation ability

Nitrogen vacancies and sulfur co-doped g-C3N4 with outstanding N2 photofixation ability was synthesized via dielectric barrier discharge plasma treatment. X-ray diffraction, ultraviolet–visible spectroscopy, N2 adsorption, scanning electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, and temperature-programmed desorption were used to characterize the as-prepared catalyst. The results showed that plasma treatment cannot change the morphology of the as-prepared catalyst but introduces nitrogen vacancies and sulfur into g-C3N4 lattice simultaneously. The as-prepared co-doped g-C3N4 displays an ammonium ion production rate as high as 6.2 mg·L−1·h−1·gcat−1, which is 2.3 and 25.8 times higher than that of individual N-vacancy-doped g-C3N4 and neat g-C3N4, respectively, as well as showing good catalytic stability. Experimental and density functional theory calculation results indicate that, compared with individual N vacancy doping, the introduction of sulfur can promote the activation ability of N vacancies to N2 molecules, leading to promoted N2 photofixation performance.

In-Situ Synthesis of Highly Efficient Direct Z-Scheme Cu3P/g-C3N4 Heterojunction Photocatalyst for N2 Photofixation

In this work, a highly efficient p-type Cu3P/[Formula: see text]-type g-C3N4 heterojunction photocatalyst was synthesized in situ. XRD, UV–Vis, N2 adsorption, TEM, XPS, PL, and EIS are used to characterize the as-prepared catalysts. The results show that Cu3P nanoparticles are highly dispersed onto the g-C3N4 surface, which obviously promotes the separation rate of electrons and holes. The charge transfer between Cu3P and g-C3N4 follows the “Z-scheme” mechanism. The as-prepared Cu3P/g-C3N4 heterojunction photocatalyst displays the ammonium ion production rate of 7.5[Formula: see text]mg[Formula: see text]L[Formula: see text][Formula: see text]h[Formula: see text][Formula: see text]g[Formula: see text], which is 28.8 times higher than that of neat g-C3N4, as well as good catalytic stability. The possible reaction mechanism is proposed.

A NanoSIMS 50 L Investigation into Improving the Precision and Accuracy of the 235U/238U Ratio Determination by Using the Molecular 235U16O and 238U16O Secondary Ions

A NanoSIMS 50 L was used to study the relationship between the 235U/238U atomic and 235U16O/238U16O molecular uranium isotope ratios determined from a variety of uranium compounds (UO2, UO2F2, UO3, UO2(NO3)2·6(H2O), and UF4) and silicates (NIST-610 glass and the Plesovice zircon reference materials, both containing µg/g uranium). Because there is typically a greater abundance of 235U16O+ and 238U16O+ molecular secondary ions than 235U+ and 238U+ atomic ions when uranium-bearing materials are sputtered with an oxygen primary ion beam, the goal was to understand whether use of 235U16O/238U16O has the potential for improved accuracy and precision when compared to the 235U/238U ratio. The UO2 and silicate reference materials showed the greatest potential for improved accuracy and precision through use of the 235U16O/238U16O ratio as compared to the 235U/238U ratio. For the UO2, which was investigated at a variety of primary beam currents, and the silicate reference materials, which were only investigated using a single primary beam current, this improvement was especially pronounced at low 235U+ count rates. In contrast, comparison of the 235U16O/238U16O ratio versus the 235U/238U ratio from the other uranium compounds clearly indicates that the 235U16O/238U16O ratio results in worse precision and accuracy. This behavior is based on the observation that the atomic (235U+ and 238U+) to molecular (235U16O+ and 238U16O+) secondary ion production rates remain internally consistent within the UO2 and silicate reference materials, whereas it is highly variable in the other uranium compounds. Efforts to understand the origin of this behavior suggest that irregular sample surface topography, and/or molecular interferences arising from the manner in which the UO2F2, UO3, UO2(NO3)2·6(H2O), and UF4 were prepared, may be a major contributing factor to the inconsistent relationship between the observed atomic and molecular secondary ion yields. Overall, the results suggest that for certain bulk compositions, use of the 235U16O/238U16O may be a viable approach to improving the precision and accuracy in situations where a relatively low 235U+ count rate is expected.

Heavy Ion Composition of Mercury's Magnetosphere

AbstractWe modeled the exospheric densities for sputtering and thermal desorption in detail for the time period of the first MESSENGER flyby of Mercury. From the exospheric densities we calculate ion production rates. These ions will be transported to the location of MESSENGER if they are produced on magnetic field lines connecting the cusp with the downwind side. From these ions we produce mass spectra that we compared with the Fast Imaging Plasma Spectrometer measurements performed during this flyby. We find good qualitative agreement between the modeled and the measured ion mass spectrum. We find that sputtering is a major process to contribute to the population of planetary ions in the magnetosphere because of the large scale height of the exospheric particles and the resulting long flight times. In addition, thermal desorption of Na contributes significant amounts to the magnetospheric ion population. From the volatile species we can identify He, OH, H2O, and Ne in the measured mass spectrum. However, for most of the volatile species the reported upper limits must be reduced by 2–3 orders of magnitude to be compatible to the measured ion spectrum.