Ion Production Rate Research Articles

Solar cycle variation of interstellar neutral He, Ne, O density and pick-up ions along the Earth's orbit

We simulated the modulation of the interstellar neutral (ISN) He, Ne, and O density and pick-up ion (PUI) production rate and count rate along the Earth's orbit over the solar cycle from 2002 to 2013 to verify if solar cycle-related effects may modify the inferred ecliptic longitude of the ISN inflow direction. We adopted the classical PUI model with isotropic distribution function and adiabatic cooling, modified by time- and heliolatitude-dependent ionization rates and non-zero injection speed of PUIs. We found that the ionization losses have a noticeable effect on the derivation of the ISN inflow longitude based on the Gaussian fit to the crescent and cone peak locations. We conclude that the non-zero radial velocity of the ISN flow and the energy range of the PUI distribution function that is accumulated are of importance for a precise reproduction of the PUI count rate along the Earth orbit. However, the temporal and latitudinal variations of the ionization in the heliosphere, and particularly their variation on the solar cycle time-scale, may significantly modify the shape of PUI cone and crescent and also their peak positions from year to year and thus bias by a few degrees the derived longitude of the ISN gas inflow direction.

Transport and chemical loss rates in Saturn's inner plasma disk

AbstractThe Kronian moon Enceladus is constantly feeding its surrounding with new gas and dust, from cryovolcanoes located in its south polar region. Through photoionization and impact ionization of these neutrals, a plasma disk is created, which mainly contains hydrogen ions and water group ions. This paper investigates the importance of ion loss by outward radial transport and ion loss by dissociative recombination, which is the dominant chemical loss process in the inner plasma disk. We use plasma densities derived from several years of measurements by the Cassini Radio and Plasma Wave Science electric field power spectral density and Langmuir probe to calculate the total flux tube content NL2. Our calculation shows that NL2 agrees well with earlier estimates within dipole L shell 8. We also show that loss by transport dominates chemical loss between L shells 4 and 10. Using extrapolation of available measurements, we extend the study to include L shells 2.5 to 4. The results indicate that loss by transport dominates chemical loss also between L shells 2.5 and 4. The loss rate by transport is around five times larger at L shell 5, and the difference increases as L7.7 beyond L = 5, for the net ion population. Chemical loss may still be important for the structure of the plasma disk in the region closest to Enceladus (around ±0.5 RS) at 3.95 RS (1 RS = Saturn's equatorial radius = 60,268 km), since the transport and chemical loss rates only differ by a factor of ∼2 in this region. We also derive the total plasma content of the plasma disk between L shells 4 and 10 to be 1.9 × 1033 ions and the total ion source rate for the same region to be 5.8 × 1027 s−1. The estimated equatorial ion production rate P ranges from 2.6 × 10−5 cm−3 s−1 (at L = 10) to 1.1 × 10−4 cm−3 s−1 (at L = 4.8). The net mass loading rate is derived to be 123 kg/s for L shells 4 to 10.

Simple and compact nozzle design for laser vaporization sources

We have developed and implemented a compact transparent nozzle for use in laser vaporization sources. This nozzle eliminates the need for an ablation aperture, allowing for a more intense molecular beam. We use this nozzle to prepare a molecular beam of aluminum monohydride (AlH) suitable for ion trap loading of AlH+ via photoionization in ultra-high vacuum. We demonstrate stable AlH production over hour time scales using a liquid ablation target. The long-term stability, low heat load and fast ion production rate of this source are well-suited to molecular ion experiments employing destructive state readout schemes requiring frequent trap reloading.

The characterization and optimization of NIO1 ion source extraction aperture using a 3D particle-in-cell code.

The geometry of a single aperture in the extraction grid plays a relevant role for the optimization of negative ion transport and extraction probability in a hybrid negative ion source. For this reason, a three-dimensional particle-in-cell/Monte Carlo collision model of the extraction region around the single aperture including part of the source and part of the acceleration (up to the extraction grid (EG) middle) regions has been developed for the new aperture design prepared for negative ion optimization 1 source. Results have shown that the dimension of the flat and chamfered parts and the slope of the latter in front of the source region maximize the product of production rate and extraction probability (allowing the best EG field penetration) of surface-produced negative ions. The negative ion density in the plane yz has been reported.

Numerical model of electron cyclotron resonance ion source

Important features of Electron Cyclotron Resonance Ion Source (ECRIS) operation are accurately reproduced with a numerical code. The code uses the particle-in-cell technique to model a dynamics of ions in ECRIS plasma. It is shown that gas dynamical ion confinement mechanism is sufficient to provide the ion production rates in ECRIS close to the experimentally observed values. Extracted ion currents are calculated and compared to the experiment for few sources. Changes in the extracted ion currents are obtained with varying the gas flow into the source chamber and the microwave power. Empirical scaling laws for ECRIS design are studied and the underlying physical effects are discussed.

Access of energetic particles to Titan׳s exobase: A study of Cassini׳s T9 flyby

We study how the local electromagnetic disturbances introduced by Titan affect the ionization rates of the atmosphere. For this, we model the precipitation of energetic particles, specifically hydrogen and oxygen ions with energies between 1keV and 1MeV, into Titan׳s exobase for the specific magnetospheric configuration of the T9 flyby. For the study, a particle tracing software package is used which consists of an integration of the single particle Lorentz force equation using a 4th order Runge–Kutta numerical method. For the electromagnetic disturbances, the output of the A.I.K.E.F. hybrid code (kinetic ions, fluid electrons) is used, allowing the possibility of analyzing the disturbances and asymmetries in the access of energetic particles originated by their large gyroradii. By combining these methods, 2D maps showing the access of each set of particles were produced. We show that the access of different particles is largely dominated by their gyroradii, with the complexity of the maps increasing with decreasing gyroradius, due to the larger effect that local disturbances introduced by the presence of the moon have in the trajectory of the particles with lower energies. We also show that for particles with gyroradii much larger than the moon׳s radius, simpler descriptions of the electromagnetic environment can reproduce similar results to those obtained when using the full hybrid simulation description, with simple north–south fields being sufficient to reproduce the hybrid code results for O+ ions with energies larger than 10keV but not enough to reproduce those for H+ ions at any of the energies covered in the present study. Finally, by combining the maps created with upstream plasma flow measurements by the MIMI/CHEMS instrument, we are able to estimate normalized fluxes arriving at different selected positions of the moon׳s exobase. We then use these fluxes to calculate energy deposition and non-dissociative N2 ionization rates for precipitating O+ and H+ ions and find differences in the ion production rates of up to almost 80% at the selected positions. All these results combined show that the electromagnetic field disturbances present in the vicinity of Titan significantly affect the contribution of energetic ions to local ionization profiles.

Detections of lunar exospheric ions by the LADEE neutral mass spectrometer

AbstractThe Lunar Atmosphere and Dust Environment Explorer (LADEE) Neutral Mass Spectrometer (NMS), operating in ion mode, provides sensitive detections of ions from the lunar exosphere. By analyzing ion‐mode data from the entire mission, utilizing Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) plasma and magnetic field measurements to organize NMS data and eliminate background sources, we identify highly significant detections of lunar ions at mass per charge of 2, 4, 12, 20, 28, 39, and 40, moderately significant detections at 14 and 23, and weak detections at 24, 25, and 36. Unlike many previous observations of Moon‐derived ions, an outward pointing viewing geometry ensures that these ions originate from the exosphere, rather than directly from the surface. For species with known neutral distributions, inferred ion production rates appear consistent with expectations for both magnitude and spatial distribution, assuming photoionization as the predominant source mechanism. Unexpected signals at mass per charge 12 and 28 suggest the presence of a significant exospheric population of carbon‐bearing molecules.

Experimental investigation of ion–ion recombination under atmospheric conditions

Abstract. We present the results of laboratory measurements of the ion–ion recombination coefficient at different temperatures, relative humidities and concentrations of ozone and sulfur dioxide. The experiments were carried out using the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at CERN, the walls of which are made of conductive material, making it possible to measure small ions. We produced ions in the chamber using a 3.5 GeV c−1 beam of positively charged pions (π+) generated by the CERN Proton Synchrotron (PS). When the PS was switched off, galactic cosmic rays were the only ionization source in the chamber. The range of the ion production rate varied from 2 to 100 cm−3 s−1, covering the typical range of ionization throughout the troposphere. The temperature ranged from −55 to 20 °C, the relative humidity (RH) from 0 to 70 %, the SO2 concentration from 0 to 40 ppb, and the ozone concentration from 200 to 700 ppb. The best agreement of the retrieved ion–ion recombination coefficient with the commonly used literature value of 1.6 × 10−6 cm3 s−1 was found at a temperature of 5 °C and a RH of 40 % (1.5 ± 0.6) × 10−6 cm3 s−1. At 20 °C and 40 % RH, the retrieved ion–ion recombination coefficient was instead (2.3 ± 0.7) × 10−6 cm3 s−1. We observed no dependency of the ion–ion recombination coefficient on ozone concentration and a weak variation with sulfur dioxide concentration. However, we observed a more than fourfold increase in the ion–ion recombination coefficient with decreasing temperature. We compared our results with three different models and found an overall agreement for temperatures above 0 °C, but a disagreement at lower temperatures. We observed a strong increase in the recombination coefficient for decreasing relative humidities, which has not been reported previously.

Influence of local ionization on ionospheric densities in Titan's upper atmosphere

AbstractTitan has the most chemically complex ionosphere of the solar system. The main sources of ions on the dayside are ionization by EUV solar radiation and on the nightside include ionization by precipitated electrons from Saturn's magnetosphere and transport of ions from the dayside, but many questions remain open. How well do models predict local ionization rates? How strongly do the ionization processes drive the ionospheric densities locally? To address these questions, we have carried out an analysis of ion densities from the Ion and Neutral Mass Spectrometer (INMS) from 16 close flybys of Titan's upper atmosphere. Using a simple chemical model applied to the INMS data set, we have calculated the ion production rates and local ionization frequencies associated with primary ions and . We find that on the dayside the solar energy deposition model overestimates the INMS‐derived production rates by a factor of 2. On the nightside, however, the model driven by suprathermal electron intensities from the Cassini Plasma Spectrometer Electron Spectrometer sometimes agrees and other times underestimates the INMS‐derived production rates by a factor of up to 2–3. We find that below 1200 km, all ion number densities correlate with the local ionization frequency, although the correlation is significantly stronger for short‐lived ions than long‐lived ions. Furthermore, we find that, for a given N2 local ionization frequency, has higher densities on the dayside than on the nightside. We explain that this is due to CH4 being more efficiently ionized by solar photons than by magnetospheric electrons for a given amount of N2 ionization.

Photocatalytic Degradation of the Azo Dye Acid Red 14 in Nanosized TiO2 Suspension under Simulated Solar Light

The degradation and mineralization of azo dye acid red 14 by Titanium dioxide (TiO2) photocatalysis under simulated solar light was studied at lab scale. The characteristics (such as phase features, specific surface area, bandgap energy, etc.) of nanosized TiO2 were investigated in detail. The color removal rate, decrease rate of total organic carbon, and production rate of sulfate ions in aqueous solution were determined. Acid red 14 could be decolorized and mineralized efficiently with nanosized TiO2 under simulated solar light. Acidic or neutral conditions were beneficial to the decolorization of acid red 14 aqueous solutions. Acid red 14 was nearly 100% mineralized after 60 min irradiation by simulated solar light under certain experimental conditions. The photocatalytic degradation efficiency increased with increasing the irradiation intensity of solar simulated light. TiO2 dosage, pH value of aqueous solution, and initial concentration of acid red 14, had significant influences on the decolorization efficiency. It is feasible to use photocatalysis with nanosized TiO2 under simulated solar light to efficiently degrade and mineralize acid red 14. The high photocatalytic efficiency of TiO2 under simulated solar light might be related to its lower bandgap energy and the relatively higher fraction of anatase phase.

Limited impact of escaping photoelectrons on the terrestrial polar wind flux in the polar cap

AbstractA statistical analysis using a long‐term (over one solar cycle) photoelectron data set obtained by the Fast Auroral SnapshoT satellite demonstrates that photoelectron outflows has little impact on the polar wind ion flux. This result implies that it is the source region of H+ ions in the topside ionosphere and not the photoelectron flux that controls the terrestrial polar wind flux. The polar wind ion flux, estimated from electron outflow does not change with increasing net photoelectron production due to increasing solar activity. The magnitude of a self‐created field‐aligned potential drop is likely determined so as to equilibrate electron fluxes with ion fluxes regulated by a net production rate of H+ ions. The result suggests that the polar wind H+ ion flux from magnetized terrestrial planets, including Earth‐like exoplanets, can be estimated once the composition and temperature of its atmosphere, which determine the net ion production rate, are known.

Extracted Current, Bias Voltage, and Ion Production of Cathodic Hollow-Cathode-Driven Plasma Contactors

Plasma properties on extracted electron current–bias voltage characteristics are presented for three selected plasma contactor configurations: a hollow-cathode-only concept, a motive discharge chamber concept, and a passive discharge chamber concept. Measurements were used to demonstrate how one could achieve low impedance performance without being affected by space plasma properties or by consuming significant propellant mass and power. A one-dimensional model was applied to describe the plasma expansion process that occurs downstream of a cathodic contactor. The model matched well with experimental trends and indicated that the plasma ion production rate within and nearby the plasma contactor dominated the emission-bias behavior of the devices. High ion production rate at a given total mass flow resulted in high propellant utilization and low discharge loss. However, plasma potential measurements showed that an anode sheath limited the maximum propellant unitization to less than and led to a foldback in discharge loss curves. The anode sheath and foldback resulted in poor agreement with zero-dimensional energy balance models that do not model this process. Finally, it was found that the passive discharge chamber concept resulted in the lowest energy cost and a larger clamping extracted current compared with the hollow-cathode-only concept.

Detailed characterization of DC electric field effects on small non-premixed flames

When drawn from a flame by an electric field, ion and electron collisions with neutral gas molecules influence flame shape, combustion intensity, soot formation, and the ion production rate. We describe these behaviors as they relate to the voltage–current relationship of a coflowing non-premixed methane/air flame. Simultaneous measurements of CH∗ chemiluminescence and ion current confirm a scaling relationship between these properties at saturation conditions. Separate mechanisms, depending on polarity, adequately explain additional current measured beyond saturation. Finally, flame oscillations observed at the transition to saturation ion current under certain flow conditions suggest a competition between two forces. The reason for this behavior is not clear; however, plausible mechanisms are identified.

Interhemispheric asymmetry of the equatorial ionization anomaly in solstices observed by COSMIC during 2007–2012

AbstractThe ionospheric radio occultation measurements from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites during 2007–2012 are utilized to analyze variations of the hemispheric asymmetry in the equatorial ionization anomaly (EIA) in solstice seasons. A hemispheric asymmetry index (Ah) is introduced to quantitatively characterize the relative interhemispheric asymmetry or north‐south differences of the EIA crests. The seasonal, solar activity, and longitudinal dependences of the hemispheric asymmetry are investigated during these low to moderately high solar activity levels. Our main findings are as follows: (1) The transition of stronger crest from the winter to summer hemispheres generally took place during noon to afternoon hours (~11:00–14:00 LT), whereas the change of the EIA hemispheric asymmetry pattern toward a stronger summer crest actually started 2–3 h earlier. (2) Remarkable differences were observed in the EIA hemispheric asymmetry between June and December solstices. In June solstice, the transition from stronger winter to summer crests occurred later, and consequently, the duration with stronger winter crest lasted longer during the morning period. (3) In the afternoon hours, the magnitudes of relative interhemispheric asymmetry of EIA crests were obviously anticorrelated with the solar activity, while in the morning hours their solar activity dependence was weak. (4) Interhemispheric asymmetry of the crests and its transition time varied with longitudes. It is also found that the longitudinal and seasonal variations of the change rate of Ah was generally consistent with the corresponding variations of hemispheric asymmetry in ion production rate. Our results indicate that the photochemical process may also play a role in the EIA hemispheric asymmetry, in addition to the important contribution from the transequatorial neutral wind and equatorial fountain effects.

An empirical approach to modeling ion production rates in Titan's ionosphere I: Ion production rates on the dayside and globally

AbstractTitan's ionosphere is created when solar photons, energetic magnetospheric electrons or ions, and cosmic rays ionize the neutral atmosphere. Electron densities generated by current theoretical models are much larger than densities measured by instruments on board the Cassini orbiter. This model density overabundance must result either from overproduction or from insufficient loss of ions. This is the first of two papers that examines ion production rates in Titan's ionosphere, for the dayside and nightside ionosphere, respectively. The first (current) paper focuses on dayside ion production rates which are computed using solar ionization sources (photoionization and electron impact ionization by photoelectrons) between 1000 and 1400 km. In addition to theoretical ion production rates, empirical ion production rates are derived from CH4, CH3+, and CH4+ densities measured by the INMS (Ion Neutral Mass Spectrometer) for many Titan passes. The modeled and empirical production rate profiles from measured densities of N2+ and CH4+ are found to be in good agreement (to within 20%) for solar zenith angles between 15 and 90°. This suggests that the overabundance of electrons in theoretical models of Titan's dayside ionosphere is not due to overproduction but to insufficient ion losses.

An empirical approach to modeling ion production rates in Titan's ionosphere II: Ion production rates on the nightside

AbstractIonization of neutrals by precipitating electrons and ions is the main source of Titan's nightside ionosphere. This paper has two goals: (1) characterization of the role of electron impact ionization on the nightside ionosphere for different magnetospheric conditions and (2) presentation of empirical ion production rates determined using densities measured by the Cassini Ion and Neutral Mass Spectrometer on the nightside. The ionosphere between 1000 and 1400 km is emphasized. We adopt electron fluxes measured by the Cassini Plasma Spectrometer‐Electron Spectrometer and the Magnetospheric Imaging Instrument as classified by Rymer et al. (2009). The current paper follows an earlier paper (Paper I), in which we investigated sources of Titan's dayside ionosphere and demonstrated that the photoionization process is well understood. The current paper (Paper II) demonstrates that modeled and empirical ionization rates on the nightside are in agreement with an electron precipitation source above 1100 km. Ion production rate profiles appropriate for different Saturnian magnetospheric conditions, as outlined by Rymer et al., are constructed for various magnetic field topologies. Empirical production rate profiles are generated for deep nightside flybys of Titan. The results also suggest that at lower altitudes (below 1100 km) another source, such as ion precipitation, is probably needed.

Theoretical study of lower ionospheric response to solar flares: sluggishness of D-region and peak time delay

The rates of ion production and loss processes in the lower ionosphere during solar and other astronomical ionizing events vary with height. This variations influence the time lags of the response in different ionospheric layers. Very Low Frequency (VLF) signals reflected from any of these layers follow this time lag or delay during a transient cosmic events. One of the easiest ways to study this property is to observe the shift in the peak of VLF signal amplitude with respect to the peak of solar flares. We numerically model to find ion densities and resulting VLF signal perturbations during some solar flares. We clearly find from the model that the delay in the peak of the electron densities (with respect to peak of the ionizing event) in the lower ionosphere varies from height to height. The result also depends on the properties of events, such as peak intensity and sharpness. We investigate analytically how the delay of electron density peak should depend on height varying chemical rate parameters as well as the nature of transient events. Our capability is demonstrated using three classes (namely, X, M and C) of solar flares. The work is a step forward in our goal to employ ionosphere as a natural detector for astronomical observations.

Predictions of the effects of Mars's encounter with comet C/2013 A1 (Siding Spring) upon metal species in its ionosphere

AbstractThe infall of dust from the coma of comet C/2013 A1 (Siding Spring) and its subsequent ablation in the atmosphere of Mars has the potential to affect the abundances of metal species in the atmosphere and ionosphere. We develop relationships between properties of the dust population in the coma and densities of metal species in the atmosphere and ionosphere. These can be used to predict the abundances of metal species in the atmosphere and ionosphere during the encounter. Given postencounter observations of the atmosphere and ionosphere, they can also be used to infer relevant cometary properties. Although current predictions suggest that the influx of cometary dust will be comparable to the sporadic background, the higher entry speed involved, which leads to a greater production rate of ions during ablation, means that metal ion abundances may be enhanced during and after the encounter.

Study on the phase relation between ion current signal and combustion phase in an HCCI combustion engine

Ion sensing is a promising approach for cycle resolved combustion phasing in HCCI engines. This paper investigates the fundamental processes affecting the phase difference (Pdelta) between ion current signal phase Ion50 and combustion phase CA50 based on 2 numerical models. One model is used to explore fluid dynamic effects on an HCCI engine. The other model, a 10-zone model, is used to primarily explore the affecting mechanism on Pdelta. Both numerical analysis and experimental results of the ionization process indicate that Pdelta is affected by both flame ionization and fuel heat release process. For fuels with similar octane number (ON), such as gasoline (ON=97) and ethanol (ON=107), both the combustion phase CA50 and the ion current signal phase Ion50 retard when the equivalence ratio Φ decreases. However, the CA50 for ethanol fuel retards moderately compared with the gasoline case since the CA50 for ethanol fuel is more sensitive to intake temperature Tin rather than Φ. Then larger Pdelta values can be seen in ethanol fueled HCCI engine under lower Φ conditions. For the fuels with different widely octane number, such as gasoline and diesel (ON=0), their combustion boundary conditions are different in HCCI engines, they produce ions at a different ratio. For diesel fuel, the ion production rate is much lower due to the lower intake temperature and higher compression ratio. Under low Φ conditions, the ion current signal cannot be observed at the beginning of ion concentration increase in diesel fueled HCCI engines, and the Ion50 appears much later compared with the gasoline fueled HCCI engine. As a result, the values of Pdelta increase significantly in the diesel fueled HCCI engine.

Influence of hadron and atmospheric models on computation of cosmic ray ionization in the atmosphere—Extension to heavy nuclei

In the last few years an essential progress in development of physical models for cosmic ray induced ionization in the atmosphere is achieved. The majority of these models are full target, i.e. based on Monte Carlo simulation of an electromagnetic-muon-nucleon cascade in the atmosphere. Basically, the contribution of proton nuclei is highlighted, i.e. the contribution of primary cosmic ray α-particles and heavy nuclei to the atmospheric ionization is neglected or scaled to protons. The development of cosmic ray induced atmospheric cascade is sensitive to the energy and mass of the primary cosmic ray particle. The largest uncertainties in Monte Carlo simulations of a cascade in the Earth atmosphere are due to assumed hadron interaction models, the so-called hadron generators. In the work presented here we compare the ionization yield functions Y for primary cosmic ray nuclei, such as α-particles, Oxygen and Iron nuclei, assuming different hadron interaction models. The computations are fulfilled with the CORSIKA 6.9 code using GHEISHA 2002, FLUKA 2011, UrQMD hadron generators for energy below 80GeV/nucleon and QGSJET II for energy above 80GeV/nucleon. The observed difference between hadron generators is widely discussed. The influence of different atmospheric parametrizations, namely US standard atmosphere, US standard atmosphere winter and summer profiles on ion production rate is studied. Assuming realistic primary cosmic ray mass composition, the ion production rate is obtained at several rigidity cut-offs – from 1GV (high latitudes) to 15GV (equatorial latitudes) using various hadron generators. The computations are compared with experimental data. A conclusion concerning the consistency of the hadron generators is stated.