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Genesis Solar Wind Concentrator: Computer Simulations of Performance Under Solar Wind Conditions
Abstract and Figures
The design and operation of the Genesis Solar-Wind Concentrator relies heavily on computer simulations. The computer model is described here, as well as the solar wind conditions used as simulation inputs, including oxygen charge state, velocity, thermal, and angular distributions. The simulation included effects such as ion backscattering losses, which also affect the mass fractionation of the instrument. Calculations were performed for oxygen, the principal element of interest, as well as for H and He. Ion fluences and oxygen mass fractionation are determined as a function of radius on the target. The results were used to verify that the instrument was indeed meeting its requirements, and will help prepare for distribution of the target samples upon return of the instrument to earth. The actual instrumental fractionation will be determined at that time by comparing solar-wind neon isotope ratios measured in passive collectors with neon in the Concentrator target, and by using a model similar to the one described here to extrapolate the instrumental fractionation to oxygen isotopes.
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... With the rise of NSs came the opportunity to increase the complexity and detail of thought experiments, such as how to design meteorological field measurements (e.g., Eddy, 1974; 75 Gehrke et al., 2019;Cortina and Calaf, 2017). More frequently, however, these NSs were reserved for applications where real-world tests would have been impractical or impossible (e.g., Wiens et al., 2003). These NSs centered on prescribing and propagating a-priori knowledge, i.e. creating "data from knowledge". ...
The observing system design of multi-disciplinary field measurements involves a variety of considerations on logistics, safety, and science objectives. Typically, this is done based on investigator intuition and designs of prior field measurements. However, there is potential for considerable increase in efficiency, safety, and scientific success by integrating numerical simulations in the design process. Here, we present a novel approach to observing system simulation experiments that aids surface-atmosphere synthesis at the interface of meso- and microscale meteorology. We used this approach to optimize the Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors 2019 (CHEESEHEAD19).During pre-field simulation experiments, we considered the placement of 20 eddy-covariance flux towers, operations for 72 hours of low-altitude flux aircraft measurements, and integration of various remote sensing data products. High-resolution Large Eddy Simulations generated a super-sample of virtual ground, airborne, and satellite observations to explore two specific design hypotheses. We then analyzed these virtual observations through Environmental Response Functions to yield an optimal aircraft flight strategy for augmenting a stratified random flux tower network in combination with satellite retrievals.We demonstrate how this novel approach doubled CHEESEHEAD19’s ability to explore energy balance closure and spatial patterning science objectives while substantially simplifying logistics. Owing to its extensibility, the approach lends itself to optimize observing system designs also for natural climate solutions, emission inventory validation, urban air quality, industry leak detection and multi-species applications, among other use cases.
... Using these new data, they have refined their estimate of the solar wind composition to (2.18 ± 0.02) ·10 )3 ()407 ± 7&, 2r), from which they derive a composition for the Sun of (2.27 ± 0.03) · 10 )3 ()382 ± 8&). A potential problem with measurements of the concentrator target or the gold cross is that the concentrator introduces a significant mass-dependent fractionation of the solar wind (Wiens et al. 2003; Marty et al. 2010; McKeegan et al. 2010). An instrumental mass fractionation curve for Ne in the #60001 target measured by Heber et al. (2011b) has been used as a basis for handling instrumental mass fractionation. ...
We have measured the isotopic composition and fluence of solar-wind
nitrogen in a diamond-like-carbon collector from the Genesis B/C array.
The B and C collector arrays on the Genesis spacecraft passively
collected bulk solar wind for the entire collection period, and there is
no need to correct data for instrumental fractionation during
collection, unlike data from the Genesis “Concentrator.”
This work validates isotopic measurements from the concentrator by Marty
et al. (2010, 2011); nitrogen in the solar wind is depleted in
15N relative to nitrogen in the Earth's atmosphere.
Specifically, our array data yield values for
15N/14N of (2.17 ± 0.37) ×
10-3 and (2.12 ± 0.34) × 10-3,
depending on data-reduction technique. This result contradicts
preliminary results reported for previous measurements on B/C array
materials by Pepin et al. (2009), so the discrepancy between Marty et
al. (2010, 2011) and Pepin et al. (2009) was not due to fractionation of
solar wind by the concentrator. Our measured value of
15N/14N in the solar wind shows that the Sun, and
by extension the solar nebula, lie at the
low-15N/14N end of the range of nitrogen isotopic
compositions observed in the solar system. A global process (or
combination of processes) must have operated in interstellar space
and/or during the earliest stages of solar system formation to increase
the 15N/14N ratio of the solar system solids. We
also report a preliminary Genesis solar-wind nitrogen fluence of (2.57
± 0.42) × 1012 cm-2. This value is
higher than that derived by backside profiling of a Genesis silicon
collector (Heber et al. 2011a).
The NASA Genesis solar-wind (SW) mission was the first to return to Earth from beyond the Moon, delivering SW ions collected in high-purity substrates (e.g., Si wafers) over 887 days (2001–2004) to study the composition of the Sun. Separate arrays collected different types of SW, and an ion Concentrator increased fluences to a small target. The capsule’s landing was marred by a parachute deployment failure. The samples were still retrieved and analyzed, principally by noble gas and secondary ion mass spectrometry (SIMS). The analyses revealed that solar oxygen and nitrogen are isotopically lighter than the terrestrial planets due to solar-nebula photochemical self-shielding. Solar noble gases are confirmed as well represented in the lunar regolith. Isotopic compositions of solid elements provide constraints on theories of SW acceleration. Genesis has also measured with unprecedented accuracy the abundances of many elements, clarifying SW fractionation and contributing to a better understanding of solar abundances.
The observing system design of multi-disciplinary field measurements involves a variety of considerations on logistics, safety, and science objectives. Typically, this is done based on investigator intuition and designs of prior field measurements. However, there is potential for considerable increase in efficiency, safety, and scientific success by integrating numerical simulations in the design process. Here, we present a novel approach to observing system simulation experiments that aids surface-atmosphere synthesis at the interface of meso- and microscale meteorology. We used this approach to optimize the Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors 2019 (CHEESEHEAD19).
During pre-field simulation experiments, we considered the placement of 20 eddy-covariance flux towers, operations for 72 hours of low-altitude flux aircraft measurements, and integration of various remote sensing data products. High-resolution Large Eddy Simulations generated a super-sample of virtual ground, airborne, and satellite observations to explore two specific design hypotheses. We then analyzed these virtual observations through Environmental Response Functions to yield an optimal aircraft flight strategy for augmenting a stratified random flux tower network in combination with satellite retrievals.
We demonstrate how this novel approach doubled CHEESEHEAD19’s ability to explore energy balance closure and spatial patterning science objectives while substantially simplifying logistics. Owing to its extensibility, the approach lends itself to optimize observing system designs also for natural climate solutions, emission inventory validation, urban air quality, industry leak detection and multi-species applications, among other use cases.
The Genesis Discovery mission returned solar matter in the form of the solar wind with the goal of obtaining precise solar isotopic abundances (for the first time) and greatly improved elemental abundances. Measurements of the light noble gases in regime samples demonstrate that isotopes are fractionated in the solar wind relative to the solar photosphere. Theory is required for correction. Measurement of the solar wind O and N isotopes shows that these are very different from any inner solar system materials. The solar O isotopic composition is consistent with photochemical self-shielding. For unknown reasons, the solar N isotopic composition is much lighter than essentially all other known solar system materials, except the atmosphere of Jupiter. Ne depth profiling on Genesis materials has demonstrated that Ne isotopic variations in lunar samples are due to isotopic fractionation during implantation without appealing to higher energy solar particles. Genesis provides a precise measurement of the isotopic differences of Ar between the solar wind and the terrestrial atmosphere. The Genesis isotopic compositions of Kr and Xe agree with data from lunar ilmenite separates, showing that lunar processes have not affected the ilmenite data and that solar wind composition has not changed on 100 Ma time scales. Relative to Genesis solar wind, ArKrXe in Q (the chondrite noble gas carrier) and the terrestrial atmosphere show relatively large light isotope depletions.
The Ne isotopic composition measured in the concentrator target will be
used correct the instrumental mass fractionation induced by the
concentration process to obtain the definitive oxygen isotopic
composition of the solar wind.
We describe the Genesis mission solar-wind sample collection period and the solar wind conditions at the L1 point during this 2.3-year period. In order to relate the solar wind samples to solar composition, the conditions under which the samples were collected must be understood in the context of the long-term solar wind. We find that the state of the solar wind was typical of conditions over the past four solar cycles. However, Genesis spent a relatively large fraction of the time in coronal-hole flow as compared to what might have been expected for the declining phase of the solar cycle. Data from the Solar Wind Ion Composition Spectrometer (SWICS) on the Advanced Composition Explorer (ACE) are used to determine the effectiveness of the Genesis solar-wind regime selection algorithm. The data collected by SWICS confirm that the Genesis algorithm successfully separated and collected solar wind regimes having distinct solar origins, particularly in the case of the coronal hole sample. The SWICS data also demonstrate that the different regimes are elementally fractionated. When compared with Ulysses composition data from the previous solar cycle, we find a similar degree of fractionation between regimes as well as fractionation relative to the average photospheric composition.
The Genesis solar wind samples are under long-term curation at NASA Johnson Space Center so that as sample analysis techniques evolve, pristine solar wind samples will be available to the scientific community in the decades to come. This article and a companion paper (Wiens et al. 2013, this issue) provide post-flight information necessary for the analysis of the Genesis array and foil solar wind samples and the Genesis solar wind ion concentrator samples, and thus serve to complement the Space Science Review volume, The Genesis Mission (v. 105, 2003).
We describe improvements to Genesis Solar Wind Concentrator computer simulation, compare results to analyses made on the Concentrator target, and use these to predict the utility of the Concentrator target for analyses of other elements and isotopes.
Neon was analysed along the radius of one arm of the Genesis concentrator gold cross. 20Ne amounts are in agreement with predicted values. The reproducibility of 20Ne/22Ne is about 0.1%. But fractionation is different as predicted for O isotopes.
The solar wind (SW) concentrator, a key instrument onboard the
Genesis mission, was designed to provide larger fluences of implanted SW
for precise isotope analyses of oxygen and nitrogen [1]. SW ions in the mass
range 4–28 amu were accelerated and focused on a “concentrator target” by
an electrostatic mirror. This concentration process caused some instrumental
mass fractionation of the implanted SW ions as function of the radial position
on the target. Correction of this fractionation will be based on a combination
of the measured radial fractionation of Ne isotopes with results of simulations
of the implantation process using the actual performance of the concentrator
and the SW conditions during exposure. Here we present He and Ne
abundance and Ne isotopic composition data along one arm of the gold cross
that framed the 4 concentrator subtargets.
The Genesis Discovery mission will return samples of solar matter for analysis of isotopic and elemental compositions in terrestrial
laboratories. This is accomplished by exposing ultra-pure materials to the solar wind at the L1 Lagrangian point and returning
the materials to Earth. Solar wind collection will continue until April 2004 with Earth return in Sept. 2004. The general
science objectives of Genesis are to (1) to obtain solar isotopic abundances to the level of precision required for the interpretation
of planetary science data, (2) to significantly improve knowledge of solar elemental abundances, (3) to measure the composition
of the different solar wind regimes, and (4) to provide a reservoir of solar matter to serve the needs of planetary science
in the 21st century. The Genesis flight system is a sun-pointed spinner, consisting of a spacecraft deck and a sample return
capsule (SRC). The SRC houses a canister which contains the collector materials. The lid of the SRC and a cover to the canister
were opened to begin solar wind collection on November 30, 2001. To obtain samples of O and N ions of higher fluence relative
to background levels in the target materials, an electrostatic mirror (‘concentrator’) is used which focuses the incoming
ions over a diameter of about 20 cm onto a 6 cm diameter set of target materials. Solar wind electron and ion monitors (electrostatic
analyzers) determine the solar wind regime present at the spacecraft and control the deployment of separate arrays of collector
materials to provide the independent regime samples.
The primary goal of the Genesis Mission is to collect solar wind ions and, from their analysis, establish key isotopic ratios
that will help constrain models of solar nebula formation and evolution. The ratios of primary interest include 17O/16O and 18O/16O to ±0.1%, 15N/14N to ±1%, and the Li, Be, and B elemental and isotopic abundances. The required accuracies in N and O ratios cannot be achieved
without concentrating the solar wind and implanting it into low-background target materials that are returned to Earth for
analysis. The Genesis Concentrator is designed to concentrate the heavy ion flux from the solar wind by an average factor
of at least 20 and implant it into a target of ultra-pure, well-characterized materials. High-transparency grids held at high
voltages are used near the aperture to reject >90% of the protons, avoiding damage to the target. Another set of grids and
applied voltages are used to accelerate and focus the remaining ions to implant into the target. The design uses an energy-independent
parabolic ion mirror to focus ions onto a 6.2 cm diameter target of materials selected to contain levels of O and other elements
of interest established and documented to be below 10% of the levels expected from the concentrated solar wind. To optimize
the concentration of the ions, voltages are constantly adjusted based on real-time solar wind speed and temperature measurements
from the Genesis ion monitor. Construction of the Concentrator required new developments in ion optics; materials; and instrument
testing and handling.
Genesis (NASA Discovery Mission #5) is a sample return mission. Collectors comprised of ultra-high purity materials will be exposed to the solar wind and then returned to Earth for laboratory analysis. There is a suite of fifteen types of ultra-pure materials distributed among several locations. Most of the materials are mounted on deployable panels (‘collector arrays’), with some as targets in the focal spot of an electrostatic mirror (the ‘concentrator’). Other materials are strategically placed on the spacecraft as additional targets of opportunity to maximize the area for solar-wind collection.
Most of the collection area consists of hexagonal collectors in the arrays; approximately half are silicon, the rest are for solar-wind components not retained and/or not easily measured in silicon. There are a variety of materials both in collector arrays and elsewhere targeted for the analyses of specific solar-wind components.
Engineering and science factors drove the selection process. Engineering required testing of physical properties such as the ability to withstand shaking on launch and thermal cycling during deployment. Science constraints included bulk purity, surface and interface cleanliness, retentiveness with respect to individual solar-wind components, and availability.
A detailed report of material parameters planned as a resource for choosing materials for study will be published on a Genesis website, and will be updated as additional information is obtained. Some material is already linked to the Genesis plasma data website (genesis.lanl.gov). Genesis should provide a reservoir of materials for allocation to the scientific community throughout the 21st Century.
The Genesis Ion Monitor (GIM) and the Genesis Electron Monitor (GEM) provide 3-dimensional plasma measurements of the solar
wind for the Genesis mission. These measurements are used onboard to determine the type of plasma that is flowing past the
spacecraft and to configure the solar wind sample collection subsystems in real-time. Both GIM and GEM employ spherical-section
electrostatic analyzers followed by channel electron multiplier (CEM) arrays for detection and angle and energy/charge analysis
of incident ions and electrons. GIM is of a new design specific to Genesis mission requirements whereas the GEM sensor is
an almost exact copy of the plasma electron sensors currently flying on the ACE and Ulysses spacecraft, albeit with new electronics
and programming. Ions are detected at forty log-spaced energy levels between ∼ 1 eV and 14 keV by eight CEM detectors, while
electrons with energies between ∼ 1 eV and 1.4 keV are measured at twenty log-spaced energy levels using seven CEMs. The spin
of the spacecraft is used to sweep the fan-shaped fields-of-view of both instruments across all areas of the sky of interest,
with ion measurements being taken forty times per spin and samples of the electron population being taken twenty four times
per spin. Complete ion and electron energy spectra are measured every ∼ 2.5 min (four spins of the spacecraft) with adequate
energy and angular resolution to determine fully 3-dimensional ion and electron distribution functions. The GIM and GEM plasma
measurements are principally used to enable the operational solar wind sample collection goals of the Genesis mission but
they also provide a potentially very useful data set for studies of solar wind phenomena, especially if combined with other
solar wind data sets from ACE, WIND, SOHO and Ulysses for multi-spacecraft investigations.
Density dependent ionization equilibria for carbon, oxygen and neon ions in the optically thin solar atmosphere are calculated.
All relevant processes are included and the results are expected to be accurate to ~ 40 per cent. Excepting for the neutral
and first ionized ions in each case, the results are applicable to the ionization equilibrium in any thermal plasma where
the ionization is maintained by the free electrons. Fractional ion abundances on incorporating a chromosphere and corona model
are also presented.
A comprehensive and self-consistent set of new atomic data for photoionization cross sections, σ_PI, and total unified recombination rate coefficients, α_R(T), of oxygen ions are obtained. The calculations are carried out in the close coupling approximation employing the R-matrix method. The unified treatment of total recombination includes both the radiative and dielectronic processes. The analysis of astrophysical
spectra and ionization balance requires atomic data for all ionization stages of an element, and the accuracy depends on the self-consistency and completeness of data. In the present work the criterion of self-consistency between the rates for the inverse processes of photoionization and recombination is satisfied in an ab initio manner by employing an identical set of eigenfunction expansions in the calculations
for both atomic processes. State-specific recombination rate coefficients are also presented for a large number of bound states. As a first application, the present α_R(T) are used to obtain ionization fractions of oxygen ions in plasmas in coronal equilibrium. Ionization fractions in photoionization equilibrium can be readily obtained by employing the present data for the total σ_PI and for α_R(T).
Abstract— The outer layers of the Sun are thought to preserve the average isotopic and chemical composition of the solar system. The solar O-isotopic composition is essentially unmeasured, though models based on variations in meteoritic materials yield several predictions. These predictions are reviewed and possible variations on these predictions are explored. In particular, the two-component mixing model of Clayton and Mayeda (1984) (slightly revised here) predicts solar compositions to lie along an extension of the calcium-aluminum-rich inclusion (CAI) 16O line between (δ18O, δ17O) = (16.4, 11.4)%0 and (12.3, 7.5)%0. Consideration of data from ordinary chondrites suggests that the range of predicted solar composition should extend to slightly lower δ18O values. The predicted solar composition is critically sensitive to the solid/gas ratio in the meteorite-forming region, which is often considered to be significantly enriched over solar composition. A factor of two solid/gas enrichment raises the predicted solar (δ18O, δ17O) values along an extension of the CAI 16O line to (33, 28)%0. The model is also sensitive to the nebular O gas phase. If conversion of most of the gaseous O from CO to H2O occurred at relatively low temperatures and was incomplete at the time of CM aqueous alteration, the predicted nebular gas composition (and hence the solar composition) would be isotopically heavier along a slope 1/2 line. The likelihood of having a single solid nebular O component is discussed. A distribution of initial solid compositions along the CAI 16O line (rather than simply as an end-member) would not significantly change the predictions above in at least one scenario. Even considering these variations within the mixing model, the predicted range of solar compositions is distinct from that expected if the meteoritic variations are due to non-mass-dependent fractionation. Thus, a measurement of the solar O composition to a precision of several permil would clearly distinguish between these theories and should clarify a number of other important issues regarding solar system formation.
Recent observations with UVCS on SOHO of high outflow velocities of O5+ at low coronal heights have spurred much discussion about the dynamics of solar wind acceleration. On the other hand, O6+ is the most abundant oxygen charge state in the solar wind, but is not observed by UVCS or by SUMER because this helium-like
ion has no emission lines falling in the wave lengths observable by these instruments. Therefore, there is considerable interest
in observing O5+ in situ in order to understand the relative importance of O5+ with respect to the much more abundant O6+. High speed streams are the prime candidates for the search for O5+ because all elements exhibit lower freezing-in temperatures in high speed streams than in the slow solar wind. The Ulysses
spacecraft was exposed to long time periods of high speed streams during its passage over the polar regions of the Sun. The
Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses is capable of resolving this rare oxygen charge state. We present
the first measurement of O5+ in the solar wind and compare these data with those of the more abundant oxygen species O6+ and O7+. We find that our observations of the oxygen charge states can be fitted with a single coronal electron temperature in the
range of 1.0 to 1.2 MK assuming collisional ionization/recombination equilibrium with an ambient Maxwellian electron gas.
A new system has been developed for calibration of space plasma analyzers, in particular ion mass spectrometers. The system provides a large‐area (∼250 cm<sup>2</sup>), highly parallel (±0.5°), and spatially uniform (±5%) beam of ions over the energy per charge range from 5 eV/charge to 100 keV/charge. Other special features include variable energy spread from ΔE∼1 eV to ∼3 keV/charge and multiple charge state ions such as He<sup>2</sup><sup>+</sup> or Xe<sup>9</sup><sup>+</sup>. Among several key ion optical elements are a high‐efficiency electron bombardment ion source capable of delivering ∼10<sup>-</sup><sup>8</sup> A, a 90° crossed electric and magnetic field mass spectrometer designed to produce either a mixed or a mass‐selected beam, and a unique beam expansion system which produces the uniform large‐area beam. The system also includes automatic beam monitoring and control via a feedback loop, as well as provisions for semiautomatic control of angle and energy analysis. Use of the calibration system during its development phases has made possible the rapid calibration of five complex satellite ion mass spectrometers already flown. Data from one of these calibrations are discussed here.
We present new data on rare ions in the solar wind. Using the Ulysses-SWICS instrument with its very low background we have searched for low-charge ions during a 6-d period of low-speed solar wind and established sensitive upper limits for many species. In the solar wind, we found He(1+)/He(2+) of less than 5 x 10 exp -4. This result and the charge state distributions of heavier elements indicate that all components of the investigated ion population went through a regular coronal expansion and experienced the typical electron temperatures of 1 to 2 million Kelvin. We argue that the virtual absence of low-charge ions demonstrates a very low level of nonsolar contamination in the source region of the solar wind sample we studied. Since this sample showed the FlP effect typical for low-speed solar wind, i.e., an enhancement in the abundances of elements with low first ionization potential, we conclude that this enhancement was caused by an ion-atom separation mechanism operating near the solar surface and not by foreign material in the corona.