Ionization Stages Research Articles

An Updated Formalism for Line-driven Radiative Acceleration and Implications for Stellar Mass Loss

Abstract Radiation contributes to the acceleration of large-scale flows in various astrophysical environments because of strong opacity in the spectral lines. Quantification of the associated force is crucial to understanding these line-driven flows, and a large number of lines (due to the full set of elements and ionization stages) must be taken into account. Here we provide new calculations of the dimensionless line strengths and associated opacity-dependent force multipliers for an updated list of approximately 4.5 million spectral lines compiled from the NIST, CHIANTI, CMFGEN, and TOPbase databases. To maintain generality of application to different environments, we assume local thermodynamic equilibrium, illumination by a Planck function, and the Sobolev approximation. We compute the line forces in a two-dimensional grid of temperatures (i.e., values between 5200 and 70,000 K) and densities (varying over 11 orders of magnitude). Historically, the force multiplier function has been described by a power-law function of optical depth. We revisit this assumption by fitting alternate functions that include saturation to a constant value (Gayley’s Q ¯ parameter) in the optically thin limit. This alternate form is a better fit than the power-law form, and we use it to calculate example mass-loss rates for massive main-sequence stars. Because the power-law force multiplier does not continue to arbitrarily small optical depths, we find a sharp decrease, or quenching, of line-driven winds for stars with effective temperatures less than about 15,000 K.

Performance of decoupled electroaerodynamic thrusters

Solid-state aerodynamic devices, which use electroaerodynamics (EAD) to produce a propulsive force, have the potential to make drones and airplanes significantly quieter and may provide benefits in sustainability and manufacturability. In these devices, ions are accelerated between two electrodes by an electric field, colliding with neutral air molecules and producing an ionic wind and a thrust force. The authors' previous work showed that a “decoupled” device architecture, which separates the ionization and ion acceleration processes, can increase thrust density and thrust-to-power compared to the prevailing corona-discharge-based EAD architecture, which uses a single DC potential for both processes. However, the discharge characteristics of this decoupled architecture have not been previously determined. Here, we experimentally characterize a decoupled EAD thruster with a wire-to-wire dielectric barrier discharge (DBD) ion source: an AC voltage drives the DBD, which ionizes neutral air molecules at the emitting electrode, while a separate DC voltage accelerates ions toward the collecting electrode. We determine the discharge characteristics (i.e., the DC-current-to-DC-voltage relationship) of this decoupled thruster as well as a model for the interaction between the ionization and acceleration stages: we find that the former takes the same functional form as the analytical solution for space-charge limited current in a thin collisional ion channel, whereas the latter is determined primarily by the power draw of the DBD ionization stage. We present a complete model for the thrust and power draw of decoupled EAD thrusters, enabling their quantitative design and optimization for use in aircraft propulsion and other applications.

Down-the-barrel observations of a multi-phase quasar outflow at high redshift

We present ultraviolet to near infrared spectroscopic observations of the quasar SDSS J001514+184212 and its proximate molecular absorber atz = 2.631. The [O III] emission line of the quasar is composed of a broad (FWHM∼ 1600 km s−1), spatially unresolved component, blueshifted by about 600 km s−1from a narrow, spatially-resolved component (FWHM∼ 650 km s−1). The wide, blueshifted, unresolved component is consistent with the presence of outflowing gas in the nuclear region. The narrow component can be further decomposed into a blue and a red blob with a velocity width of several hundred km s−1each, seen ∼5 pkpc on opposite spatial locations from the nuclear continuum emission, indicating outflows on galactic scales. The presence of ionised gas on kpc scales is also seen from a weak C IVemission component, detected in the trough of a saturated C IVabsorption that removes the strong nuclear emission from the quasar. Towards the nuclear emission, we observe absorption lines from atomic species in various ionisation and excitation stages and confirm the presence of strong H2lines originally detected in the SDSS spectrum. The overall absorption profile is very wide, spread over ∼600 km s−1, and it roughly matches the velocities of the narrow blue [O III] blob. From a detailed investigation of the chemical and physical conditions in the absorbing gas, we infer densities of aboutnH ∼ 104 − 105cm−3in the cold (T ∼ 100 K) H2-bearing gas, which we find to be located at ∼10 kpc distances from the central UV source. We conjecture that we are witnessing different manifestations of a same AGN-driven multi-phase outflow, where approaching gas is intercepted by the line of sight to the nucleus. We corroborate this picture by modelling the scattering of Ly-αphotons from the central source through the outflowing gas, reproducing the peculiar Ly-αabsorption-emission profile, with a damped Ly-αabsorption in which red-peaked, spatially offset, and extended Ly-αemission is seen. Our observations open up a new way to investigate quasar outflows at high redshift and shed light on the complex issue of AGN feedback.

A simplified method of calculating electronic energy level populations in nonequilibrium plasmas

<sec> In order to investigate the radiative properties of plasma in non local thermodynamic equilibrium (NLTE), it is of great importance to determine energy level populations, which are often obtained by the so-called collisional-radiative (CR) model. As is well known, the CR model is accurate but computationally costly, and thus it is difficult to be applied to engineering calculations for such as complex three-dimensional plasmas.</sec> <sec> In this work, a bound-state characteristic temperature (BCT) method is proposed, which can be used to calculate quickly the energy level populations in non-equilibrium plasmas. In this method, we assume that for each kind of ionization stage, the bound-state population is Boltzmannian at a certain characteristic temperature. The assumed characteristic temperature is related to the degree of none-equilibrium and may be different from the electronic temperature of the plasma. Based on a modified Saha equation, the assumed characteristic temperature can be calculated easily, and then the energy level populations are obtained conveniently. Five cases of non-equilibrium neon plasma at variable electronic temperatures and densities are investigated and compared with the results from a CR model. Good agreement is found between them if the degree of non-equilibrium is not very large. It shows that the present method is effective and at least 3000 times faster in computation time than the CR model. The method is very useful in engineering applications.</sec>

Photon leaking or very hard ionizing radiation? Unveiling the nature of He II-emitters using the softness diagram

Aims. Star-forming galaxies with nebular He II emission contain very energetic ionizing sources of radiation, which can be considered as analogs to the major contributors of the reionization of the Universe in early epochs. It is therefore of great importance to provide a reliable absolute scale for the equivalent effective temperature (T*) for these sources. Methods. We study a sample of local (z < 0.2) star-forming galaxies showing optical nebular He II emission using the so-called softness diagrams, involving emission lines of two elements in two consecutive stages of ionization (e.g., [S II]/[S III] vs. [O II]/[O III]). We use for the first time the He I/He II ratio in these diagrams in order to explore the higher range of T* expected in these objects, and to investigate the role of possible mechanisms driving the distribution of galaxy points in these diagrams. We build grids of photoionization models covering different black-body temperatures, model cluster atmospheres, and density-bounded geometries to explain the conditions observed in the sample. Results. We verified that the use of the softness diagrams including the emission-line ratio He I/He II combined with black-body photoionization models can provide an absolute scale of T* for these objects. The application of a Bayesian-like code indicates T* in the range 50−80 kK for the sample of galaxies, with a mean value higher than 60 kK. The average of these high temperature values can only be reproduced using cluster model populations with nearly metal-free stars, although such ionizing sources cannot explain either the highest T* values, beyond 1σ, or the dispersion observed in the softness diagrams. According to our photoionization models, most sample galaxies could be affected to some extent by ionizing photon leaking, presenting a mean photon absorption fraction of 26% or higher depending on the metallicity assumed for the ionizing cluster. The entire range of He I/He II, [S II]/[S III], and [O II]/[O III] ratios for these HeII-emitting galaxies is reproduced with our models, combining nearly metal-free ionizing clusters and photon leaking under different density-bounded conditions.

Spatiotemporally resolved optical emission spectroscopy and harmonic generation in Cu plasmas

Laser-induced ablation plasmas of Cu generated by nanosecond 1064 nm pulses have been examined as media for third harmonic generation of a nanosecond driving pulse. A narrow window of ablation fluences where third harmonic generation is optimized has been identified in a region around twice the ablation threshold. A detailed analysis of the features of the Cu plasma across this critical fluence window, through spatially and temporally resolved optical emission spectroscopy, has been used to assess critical plasma parameters such as temperature, electron density, and abundance of Cu species in different ionization stages. This description has been correlated with the conditions for optimum low-order harmonic generation in the Cu plasma.

Physical conditions of five O vi absorption systems towards PG 1522+101

ABSTRACT We present the analysis of five O vi absorbers identified across a redshift path of z ∼ (0.6−1.3) towards the background quasar PG 1522+101 with information on five consecutive ionization stages of oxygen from O ii to O vi. The combined HST and Keck spectra cover UV, redshifted extreme-UV, and optical transitions from a multitude of ions spanning ionization energies in the range of ∼(13−300) eV. Low-ionization (C ii, O ii, Si ii, Mg ii) and very high-ionization species (Ne viii, Mg x) are non-detections in all the absorbers. Three of the absorbers have coverage of He i, in one of which it is a >3σ detection. The kinematic structures of these absorbers are extracted from C iv detected in HIRES spectra. The farthest absorber in our sample also contains the detections of Ne v and Ne vi. Assuming co-spatial absorbing components, the ionization models show the medium to be multiphased with small-scale density–temperature inhomogeneities that are sometimes kinematically unresolved. In two of the absorbers, there is an explicit indication of the presence of a warm gas phase (T ≳ 105 K) traced by O vi. In the remaining absorbers, the column densities of the ions are consistent with a non-uniform photoionized medium. The subsolar [C/O] relative abundances inferred for the absorbers point at enrichment from massive Type II supernovae. Despite metal enrichment, the inferred wide range for [O/H] ∼ [−2.1, +0.2] amongst the absorbers along with their anticorrelation with the observed H i suggest poor small-scale mixing of metals with hydrogen in the regions surrounding galaxies and the IGM.

Inevitable consequences of ion–neutral damping of intermediate MHD waves in Sun-like stars

ABSTRACT In the context of the solar atmosphere, we re-examine the role of neutral and ionized species in dissipating the ordered energy of intermediate-mode MHD waves into heat. We solve conservation equations for the hydrodynamics and for hydrogen and helium ionization stages, along closed tubes of magnetic field. First, we examine the evolution of coronal plasma under conditions where coronal heating has abruptly ceased. We find that cool (<105K) structures are formed lasting for several hours. MHD waves of modest amplitude can heat the plasma through ion–neutral collisions with sufficient energy rates to support the plasma against gravity. Then we examine a calculation starting from a cooler atmosphere. The calculation shows that warm (>104) K long (> several Mm) tubes of plasma arise by the same mechanism. We speculate on the relevance of these solutions to observe properties of the Sun and similar stars whose atmospheres are permeated with emerging magnetic fields and stirred by convection. Perhaps this elementary process might help to explain the presence of ‘cool loops’ in the solar transition region and the production of broad components of transition region lines. The production of ionized hydrogen from such a simple and perhaps inevitable mechanism may be an important step towards finding the more complex mechanisms needed to generate coronae with temperatures in excess of 106K, independent of a star’s metallicity.

High-resolution X-ray spectroscopy of the stellar wind in Vela X-1 during a flare

Context. We present a ~130 ks observation of the prototypical wind-accreting, high-mass X-ray binary Vela X-1 collected with XMM-Newton at orbital phases between 0.12 and 0.28. A strong flare took place during the observation that allows us to investigate the reaction of the clumpy stellar wind to the increased X-ray irradiation. Aims. To examine the wind’s reaction to the flare, we performed both time-averaged and time-resolved analyses of the RGS spectrum and examined potential spectral changes. Methods. We focused on the high-resolution XMM-Newton RGS spectra and divided the observation into pre-flare, flare, and post-flare phases. We modeled the time-averaged and time-resolved spectra with phenomenological components and with the self-consistent photoionization models calculated via CLOUDY and XSTAR in the pre-flare phase, where strong emission lines due to resonant transitions of highly ionized ions are seen. Results. In the spectra, we find emission lines corresponding to K-shell transitions in highly charged ions of oxygen, neon, magnesium, and silicon as well as radiative recombination continua (RRC) of oxygen. Additionally, we observe potential absorption lines of magnesium at a lower ionization stage and features identified as iron L lines. The CLOUDY and XSTAR photoionization models provide contradictory results, either pointing towards uncertainties in theory or possibly a more complex multi-phase plasma, or both. Conclusions. We are able to demonstrate the existence of a plethora of variable narrow features, including the firm detection of oxygen lines and RRC that RGS enables to observe in this source for the first time. We show that Vela X-1 is an ideal source for future high-resolution missions, such as XRISM and Athena.

NLTE spectral analysis of the intermediate helium-rich subdwarf B star CPD−20°1123

ABSTRACT Subdwarf B (sdB) stars are core helium-burning stars with stratified atmospheres. Their atmospheres are dominated by hydrogen (H) while the helium (He) and metal abundances are shaped by an interplay of gravitational settling and radiative levitation. However, a small fraction of these show spectra dominated by He i absorption lines. In between these groups of He-deficient and extreme He-rich sdBs, some are found to have intermediate surface He abundances. These objects are proposed to be young ‘normal’ (He-deficient) sdBs for which the dynamical stratification of the atmosphere is still ongoing. We present an analysis of the optical spectrum of such an intermediate He-rich sdB, namely CPD−20°1123, by means of non-local thermodynamic equilibrium (NLTE) stellar atmosphere models. It has a He-to-H number ratio of He/H = 0.13 ± 0.05 and its effective temperature of $\mbox{$T_\mathrm{eff}$} = 25\, 500 \pm 1000 \, \mathrm{K}$ together with a surface gravity of $\log \, (g$ / cm s−2) = 5.3 ± 0.3 places the star close to the high-temperature edge until which it may be justified to use LTE model atmospheres. This work states a test of the Tübingen NLTE Model Atmosphere Package for this temperature regime. We present the first application of revised, elaborated model atoms of low ionization stages of light metals usable with this atmosphere code.

Spectroscopic analysis of N-intrashell transitions in Rb-like to Ni-like Yb ions

Extreme ultraviolet spectra of highly-charged ytterbium ions produced in an electron beam ion trap at the National Institute of Standards and Technology were observed with a flat-field grazing incidence spectrometer in the wavelength region of about 4 nm–20 nm. The measured spectra were interpreted through detailed analysis by collisional-radiative modeling of the non-Maxwellian EBIT plasma. Seventy-nine new spectral lines due to intrashell (Δn = 0, n = 4) electric–dipole, magnetic–dipole, and electric–quadrupole transitions were identified in Rb-like Yb33+ through Ni-like Yb42+ ions. The effects of strong configuration interaction within the n = 4 complex on the measured spectra are discussed for a number of ionization stages.

Current Status and Developments of the Atomic Database on Rare-Earths at Mons University (DREAM)

The main purpose of the Database on Rare Earths At Mons University (DREAM) is to provide the scientific community with updated spectroscopic parameters related to lanthanide atoms (Z = 57–71) in their lowest ionization stages. The radiative parameters (oscillator strengths and transitions probabilities) listed in the database have been obtained over the past 20 years by the Atomic Physics and Astrophysics group of Mons University, Belgium, thanks to a systematic and extensive use of the pseudo-relativistic Hartree-Fock (HFR) method modified for taking core-polarization and core-penetration effects into account. Most of these theoretical results have been validated by the good agreement obtained when comparing computed radiative lifetimes and accurate experimental values measured by the time-resolved laser-induced fluorescence technique. In the present paper, we report on the current status and developments of the database that gathers radiative parameters for more than 72,000 spectral lines in neutral, singly-, doubly-, and triply-ionized lanthanides.

NLTE for APOGEE: simultaneous multi-element NLTE radiative transfer

Context.Relaxing the assumption of local thermodynamic equilibrium (LTE) in modelling stellar spectra is a necessary step to determine chemical abundances to better than about 10% in late-type stars.Aims.We describe our multi-element (Na, Mg, K, and Ca) non-LTE (NLTE) calculations, which can be applied to the APOGEE survey.Methods.The new version ofTLUSTYallows for the calculation of restricted NLTE in cool stars using pre-calculated opacity tables. We demonstrate thatTLUSTYgives consistent results withMULTI, a well-tested code for NLTE in cool stars. We usedTLUSTYto perform LTE and a series of NLTE calculations that simultaneously used all combinations of one, two, three and four of the elements in NLTE.Results.We take into account that departures from LTE in one element can affect others through changes in the opacities of Na, Mg, K, and Ca. We find that atomic Mg, which provides strong UV opacity and exhibits significant departures from LTE in the low-energy states, can affect the NLTE populations of Ca, leading to abundance corrections as large as 0.07 dex. The differences in the derived abundances between the single-element and the multi-element cases can exceed those between the single-element NLTE determinations and an LTE analysis. We therefore caution that this is not always a second-order effect. Based on detailed tests for three stars with reliable atmospheric parameters (Arcturus, Procyon, and the Sun), we conclude that our NLTE calculations provide abundance corrections that can in the optical amount to 0.1, 0.2, and 0.7 dex for Ca, Na and K, but LTE is a good approximation for Mg. In theH-band, NLTE corrections are much smaller and always lower than 0.1 dex. The derived NLTE abundances in the optical and in the IR are consistent. In all three stars, NLTE line profiles fit the observations better than the LTE counterparts for all four elements.Conclusions.The atomic elements in ionisation stages where over-ionisation is an important NLTE mechanism are likely affected by departures from LTE in Mg. Particular care must be taken with the collisions that are adopted for high-lying levels when NLTE profiles of lines in theH-band are calculated. The derived NLTE corrections in the optical and in theH-band differ, but the derived NLTE abundances are consistent between the two spectral regions.

Electrostatic precipitator for fine and ultrafine particle removal from indoor air environments

An electrostatic precipitator was evaluated to reduce nanometric and micron-sized particles in indoor air environments. This process consists in a negative air ionizer assisted by a parallel-plate collector. The ionization stage contained four or eight corona needles, which were supplied by a negative high-voltage DC. The collection stage was designed in a plate-to-plate configuration, of which the plates are alternately connected to a high-voltage DC supply and the ground. Fractional efficiency (expressed in number) was investigated using NaCl ultrafine particles and atmospheric aerosol according to different geometric, environmental and operating parameters (concentration, relative humidity, collector and ionizer voltage, collector length, number of needles, and airflow rates). The results are discussed according to particle size. Under optimized conditions (eight needles, 20 cm collector length, −7 kV ionization voltage, 5 kV collection voltage, 1 m/s air velocity), the process revealed high performance levels. The efficiency of particles of 10–25 nm in diameter was 94%, between 30 and 300 nm the efficiency was 99%, while in the most penetrating particle size, the efficiency was 96%, with an ozone concentration at the outlet of the process less than 5 ppbv. This process generated a very low ozone concentration, which is an essential challenge for indoor air treatment. The results confirmed the existence of the partial charging regime for particles less than a few tens of nanometers for which the efficiency was lower. For these particles, the collection conditions (collection time and voltage) had no influence on the efficiency. For larger particles, both the parameters of the charging phase (ion concentration, charging time) and the parameters of the collection phase (collection time and voltage) had a significant influence on the collection efficiency.

Collisional-radiative modeling of the 5p−5s spectrum of W xiv–W xvi ions

The wavelength and rate of the $5p-5s$ transition of W XIV - W XVI ions have been calculated by the relativistic configuration interaction (RCI) method with the implementation of Flexible Atomic code (FAC). A reasonable collisional-radiative model (CRM) has been constructed to simulate the $5p - 5s$ transition spectrum of W XIV - W XVI ions which had been observed in electron beam ion trap (EBIT) device. The results are in reasonable agreement with the available experimental and theoretical data, and might be applied to identify the controversial spectra. The confusion on the assignment of the ionization stage are solved in the present work.

Non-local thermodynamic equilibrium line formation for Si i–ii–iii in A–B stars and the origin of Si ii emission lines in ι Her

ABSTRACT A comprehensive model atom was developed for Si i–ii–iii using the most up-to-date atomic data available so far. Based on non-local thermodynamic equilibrium (NLTE) line formation for Si i, Si ii and Si iii and high-resolution observed spectra, we determined the NLTE abundances for a sample of nine unevolved A9–B3 type stars with well-determined atmospheric parameters. For each star, NLTE reduces the line-to-line scatter for Si ii substantially compared with the LTE case and leads to consistent mean abundances from lines of different ionization stages. In the hottest star of our sample, ι Her, Si ii is subject to overionization that drives emission in the lines arising from the high-excitation doublet levels. Our NLTE calculations reproduced 10 emission lines of Si ii observed in ι Her. The same overionization effect leads to greatly weakened Si ii lines, which are observed in absorption in ι Her. Large positive NLTE abundance corrections (up to 0.98 dex for 5055 Å) were useful for achieving consistent mean abundances from lines of the two ionization stages, Si ii and Si iii. It was found that NLTE effects are overestimated for the Si ii 6347, 6371 Å doublet in ι Her, while the new model atom works well for cooler stars. At this stage, we failed to understand this problem. We computed a grid of the NLTE abundance corrections for lines of Si i, Si ii and Si iii in model atmospheres with effective temperatures and surface gravities characteristic of unevolved A–B type stars.

Newly Improved Ionization Corrections for the Neutral Interstellar Medium: Enabling Accurate Abundance Determinations in Star-forming Galaxies throughout the Universe*

Abstract Studies measuring the chemical abundances of the neutral gas in star-forming galaxies (SFGs) require ionization correction factors (ICFs) to accurately measure their metal contents. In the work presented here, we calculate newly improved ICFs for a sample of SFGs. These new corrections include both the contaminating ionized gas along the line of sight ( ) and unaccounted for higher ionization stages in the neutral gas ( ). We make use of recently acquired spectroscopic observations taken with the Cosmic Origins Spectrograph on board Hubble to measure column densities for Fe ii and Fe iii. Using the Fe iii/Fe ii ratios as well as other physical properties (i.e., log[ ], N(H i), T, and Z), we generate ad hoc photoionization models with CLOUDY to quantify the corrections required for each of the targets. We identify a luminosity threshold of log[ ] ∼ 40.75 erg s−1 above which the values for nitrogen are relatively higher ( −0.7) than those for the rest of the elements ( ). This behavior indicates that, for the high UV luminosity objects, N ii is found in non-negligible quantities in the neutral gas, making these corrections critical for determining the true abundances in the interstellar medium. In addition, we calculate ICFs from a uniform grid of models covering a wide range of physical properties typically observed in studies of SFGs and extragalactic H ii regions. We provide the community with tabulated ICF values for the neutral gas abundances measured from a variety of environments and applicable to chemical studies of the high-redshift universe.

Finite-difference time-domain modeling of multi-stage soil ionization with residual resistivities—Part I: Theoretical background and the proposed FDTD formulation

In this first part of the paper, a Finite-Difference Time-Domain (FDTD) model for multi-stage soil ionization with residual resistivities is proposed to obtain realistic transient responses of grounding systems subjected to high intensity currents. Four phases of soil ionization process are modeled: non-ionization (linear soil representation), presparking (first stage of ionization), sparking (second stage of ionization) and deionization. Mechanisms identified experimentally in literature for water ionization explain presparking and sparking phases of soil ionization. Weak ionization in clusters of gas bubbles produced due to high current flows explains the presparking phase. The sparking phase is governed by ionization of aqueous solutions in soil. A mathematical function is defined to represent the rise of electrical conductivity over time for each point in the soil FDTD lattice during sparking phase. Additionally, effects associated with limited production of free charges over time and their increasing reduction of mobility are considered by means of residual resistivities in presparking and sparking phases. Due to the complex nature of the phenomenon, which involves various physical processes, comprehensive theoretical background is also provided in part I. The second part of the paper presents numerical validation cases for the proposed FDTD soil ionization model.

Observational constraints on the origin of the elements

The abundance ratios of manganese to iron in late-type stars across a wide metallicity range place tight constraints on the astrophysical production sites of Fe-group elements. In this work, we investigate the chemical evolution of Mn in the Milky Way galaxy using high-resolution spectroscopic observations of stars in the Galactic disc and halo stars, as well as a sample of globular clusters. Our analysis shows that local thermodynamic equilibrium (LTE) leads to a strong imbalance in the ionisation equilibrium of Mn I and Mn II lines. Mn I produces systematically (up to 0.6 dex) lower abundances compared to the Mn II lines. Non-LTE (NLTE) radiative transfer satisfies the ionisation equilibrium across the entire metallicity range, of −3 ≲ [Fe/H] ≲ −1, leading to consistent abundances from both ionisation stages of the element. We compare the NLTE abundances with Galactic Chemical Evolution models computed using different sources of type Ia and type II supernova (SN Ia and SN II) yields. We find that a good fit to our observations can be obtained by assuming that a significant (∼75%) fraction of SNe Ia stem from a sub-Chandrasekhar (sub-Mch) channel. While this fraction is larger than that found in earlier studies (∼50%), we note that we still require ∼25% near-Mch SNe Ia to obtain solar [Mn/Fe] at [Fe/H] = 0. Our new data also suggest higher SN II Mn yields at low metallicity than typically assumed in the literature.

Experimental characterization of ID-Hall, a double stage Hall thruster with an inductive ionization stage

We present experimental results on the characterization of ID-Hall, a double stage Hall thruster with an inductively coupled magnetized ionization stage. This first experimental prototype of ID-Hall operates in a low power regime, typically below 400 W. The purpose of this work is not only to study the properties of ID-Hall and provide directions for optimization but also, and more generally, to study the relevance of the double stage concept with respect to important physical issues such as current oscillations and anomalous electron transport. We present experimental measurements of the current–voltage characteristics, extracted ion beam current (Faraday cup measurements), and ion energy and angular distribution functions (RPA measurements) in single and double stage regimes of operation, as a function of DC voltage and RF power. The results demonstrate that ions can be extracted from the inductive RF ionization stage even under conditions where the applied DC voltage is not sufficient to ionize the gas flow, i.e., ID-Hall can indeed operate in a double stage regime. At intermediate voltages, the overshoot observed in the current–voltage characteristics of single stage thrusters disappears in double stage operation, indicating a decrease in anomalous electron transport. Time-resolved and time-averaged ion energy distribution measurements show a coupling between ion energy, breathing mode oscillations, and the magnetic configuration of ID-Hall.