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  Gold Foil Collector

The Genesis gold foil is a bulk solar wind collector, integrating fluences from all three of the wind regimes. Pyrolytic extraction of small foil samples at Minnesota yielded He fluences, corrected for backscatter, in good agreement with measurements by on-board spacecraft instruments, and He/Ne elemental ratios close to those implanted in collector foils deployed on the lunar surface during the Apollo missions. Isotopic distributions of He, Ne and Ar are under study. Pyrolysis to temperatures above the gold melting point generates nitrogen blanks large enough to obscure the solar-wind nitrogen component. An alternative technique for nitrogen and noble gas extraction, by room-temperature amalgamation of the gold foil surface, will be discussed. Ne and Ar releases in preliminary tests of this technique on small foil samples were close to 100% of the amounts expected from the high-temperature pyrolysis yields, indicating that amalgamation quantitatively liberates gases from several hundred angstroms deep in the gold, beyond the implantation depth of most of the solar wind. Present work is focused on two problems currently interfering with accurate nitrogen measurements at the required picogram to sub-picogram levels: a higher than expected blank likely due to tiny air bubbles rolled into the gold sheet during fabrication, and the presence of a refractory hydrocarbon film on Genesis collector surfaces (the "brown stain") that, if left in place on the foil, shields the underlying gold from mercury attack. We have found, however, that the film is efficiently removed within tens of seconds by oxygen plasma ashing. Potential nitrogen contaminants introduced during the crash of the sample return canister are inert in amalgamation, and so are not hazards to the measurements.

Reference: Schlutter, D. J., Pepin, R. O., Extraction of Solar Wind Nitrogen and Noble Gases From the Genesis Gold Foil Collector

Gold Foil being cleaned
Pre-launch Gold Foil
Gold foil collector being cleaned at JSC during assembly of canister pre-launch
Gold foil pre-launch


  Solar Wind Concentrator

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 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.

Concentrator closeup
Section of concentrator target
Recovered concentrator target
Concentrator target post return
Section of concentrator target post return
Recovered concentrator target post return


  Wafers and Collectors

Solar Wind Collector (small)
Hexagonal collector
array used to capture bulk solar wind
To successfully capture raw solar wind, Genesis flew a million miles away, outside Earth's magnetic field, which alters the particles, and hovered in its own orbit for 29 months. Scientists grappled with several challenges while pondering ways to keep the samples pristine during and after collection. First off, they had to find a proper way to collect and transport the samples. The largest collector consists of five bicycle-tire-sized collector arrays, each loaded with 54 or 55 hexagonal wafers measuring about 4 inches (10 centimeters) in diameter. These wafers consist of 15 different high-purity materials including aluminum, sapphire, silicon, germanium, gold and diamond-like amorphous carbon — all chosen for their durability, purity, cleanliness, retentiveness and ease of analysis.
Team member is bunny suit holding a vial of wafers
JSC Curation Team member displays some of the silicon wafer fragments collected

Each collector array was assigned to catch various types of solar wind. Genesis's goal was to collect billions of atoms of solar particles heavier than hyrogen, equivalent to "a few grains of salt," according to Genesis Principal Investigator Dr. Donald Burnett of the California Institute of Technology.

Closeup of 10 wafer fragments in a transparent dish
Assortment of recovered fragments recovered in Utah

Once the solar wind particles were collected, the wafers had to be able to retain them while warming under the Sun's rays. Each type of wafer will retain different solar wind elements. Sapphire was used because it can retain sodium under these conditions. Silicon, which comprises approximately half of the materials used in the collector arrays, does not retain sodium but does retain many other elements, including the important rock-forming element magnesium.

Geometry was also used to enhance researchers' ability to analyze the sample. By making some of the collector materials thin and mounting them on a rigid, inert structure (e.g. silicon on sapphire), the effects of impurities in the collector material were minimized by only analyzing the thin layer.


  Ion and Electron Monitors

There are two solar wind spectrometers on-board the Genesis spacecraft: the Genesis Ion Monitor (GIM) and the Genesis Electron Monitor (GEM). The primary purpose of these spectrometers is to enable the collection of appropriate samples of the solar wind by the Genesis sample collectors. This involves determining the type of solar wind that is flowing past the spacecraft, adjusting high-voltages in the Concentrator for the current conditions and deploying the appropriate Collector Array for the type of solar wind present, all in realtime. The secondary function of the Monitors is to obtain high-quality solar wind data that can be used for various scientific studies. Interested parties are referred to the detailed instrument description paper by Barraclough et al. (2003), listed on the publications page.

  The Genesis Ion Monitor (GIM)

The Genesis Ion Monitor (small)
Genesis Ion
Monitor (GIM)

GIM consists of a 120° spherical-section electrostatic analyzer (ESA) followed by an array of eight channel electron multipliers (CEMs) for energy and angle analysis of incoming ions. The ESA is negatively biased by a high-voltage power supply that steps across a number of voltage levels to build up an energy spectrum of the plasma population. The GIM is basically an E/q analyzer but does have a mass analysis capability in this instance due to the similar flow velocities of all ions in the solar wind beam. The energy range of the instrument is ~100 eV to 14 keV, with a resolution of 5.2%, but only a small fraction of this range is used at any one time. Onboard software tracks the solar wind flow speed and autonomously adjusts the energy range that is scanned to keep it centered on the beam.

GIM has a field-of-view (FOV) that is ~3.0° in azimuth by ~26° in polar angle and one of the narrow edges of the FOV is aligned such that it slightly overlaps the spacecraft rotational axis. Given this configuration, during one spin of the spacecraft GIM sweeps out a circle on the sky that is ~24° in radius with the center of the circle being coincident with the average solar wind flow direction at 1 AU. During each spin, GIM steps forty times across ten individual energy steps and this process is repeated for four spins of the spacecraft with the energy steps being varied for each spin. These four spins comprise a complete data cycle and require approximately 2.5 minutes to complete. Thus GIM acquires a complete measurement of the ion distribution function every 2.5 minutes. The data product consists of ion counts for eight polar angle and forty azimuthal angles and forty energy levels.

 The Genesis Electron Monitor (GEM)

The Genesis Electron Monitor (small)
Genesis Electron Monitor (GEM)

The GEM sensor head is almost an identical copy of the electron spectrometers that are currently flying on ACE (SWEPAM-E) and on Ulysses (BAM-E) but the electronics are of a new design. Basically, GEM consists of a 120° ESA that is backed by an array of seven CEMs for energy-angle analysis of incident plasma electrons. The energy range of the instrument is 1 to 1400 eV, the energy resolution is ~14%, and the FOV is ~12° in azimuth (this varies somewhat with polar angle) by ~150° in polar angle. The center of the FOV is centered along a normal to the spacecraft spin axis and consequently the FOV sweeps out approximately 94% of the sky during each spin. Data acquisition of the GEM is synchronized with that of the GIM and also takes four spins of the spacecraft to execute. A complete data matrix for the GEM consists of electron counts for seven polar angles and twenty four azimuthal angles and twenty energy levels.

Both the GEM and GIM were in continuous operation since shortly after launch in August 2001 until August 4, 2004, a month before sample re-entry. button
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Curator: Aimee Meyer
Updated: November 2009

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