The ion-composition of the plasma produced by impacts of fast dust particles

doi:10.1016/0032-0633(77)90017-4

Planetary and Space Science

Volume 25, Issue 2, February 1977, Pages 135-147

https://doi.org/10.1016/0032-0633(77)90017-4 Get rights and content

Abstract

The composition of the impact plasma produced by fast dust particles (v > 1 km/sec) hitting an Au or W target was measured both with a model of the HELIOS micrometeoroid experiment (low electric field at the target) and a high field detector. The plasma composition and the total plasma charge depend strongly on the impact velocity and the electric field strength at the target. Spectra of 9 different projectile-target combinations were analysed. Two types of spectra could be observed, depending on the projectile material. (1) Spectra of metals and hard dielectrics (Mohs' hardness ⩾ 5). Particle constituents of low ionisation energy (e · u ⩾ 7eV, e.g. Na, K, Al) dominate the spectra of these materials at impact velocities below 10 km/sec. At higher speed the relative intensities change and new ions with higher ionisation energies appear. (2) Spectra of soft dielectrics (Mohs' hardness < 3). Below 9 km/sec these materials produced less total charge than did the others. The highest masses were detected at 74 amu. The relative abundance of ions with low ionization energies such as Li, Na, K, etc. is comparatively small. Negative ions were also observed in the impact plasma. Their total number was found to be approximately 3–6% of that of the positive ions at 6 km/sec particle speed.

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Cited by (51)

A cosmic dust detection suite for the deep space Gateway
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At low impact speeds there is surface ionization, whereas at higher speeds there is complete volume ionisation. There are also velocity thresholds for partial or full ionization of different elemental species, and this is illustrated for example by Dahlmann et al., 1977, or Ratcliff et al., 1997a; 1997b. A step forward in understanding this was the wide-spread adoption of the use of non-metal projectiles in laboratory impact experiments (the particles are accelerated electrostatically, so are coated with thin overlayers of either metal or conducting polymers).
The decade of the 2020s promises to be when humanity returns to space beyond Earth orbit, with several nations trying to place astronauts on the Moon, before going further into deep space. As part of such a programme, NASA and partner organisations, propose to build a Deep Space Gateway in lunar orbit by the mid-2020s. This would be visited regularly and offer a platform for science as well as for human activity. Payloads that can be mounted externally on the Gateway offer the chance to, amongst other scientific goals, monitor and observe the dust flux in the vicinity of the Moon. This paper looks at relevant technologies to measure dust which will impact the exposed surface at high speed. Flux estimates and a model payload of detectors are described. It is predicted that the flux is sufficient to permit studies of cometary vs. asteroidal dust and their composition, and to sample interstellar dust streams. This may also be the last opportunity to measure the natural dust flux near the Moon before the current, relatively pristine environment, is contaminated by debris, as humanity’s interest in the Moon generates increased activity in that vicinity in coming decades.
Trajectory measurements for individual dust particles on the colorado dust accelerator
2018, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Citation Excerpt :
Micrometeorite impacts by interstellar dust on the sub-micrometer to micrometer size scale, whether on the surface of an airless body or space-borne instruments, are useful phenomena for extracting information on a particle’s characteristics (e.g. chemical composition, size, and trajectory) as well as on the environment in which it is found (e.g. dust flux) [1]. Dust particles in space typically impact at hypervelocities leading to a plasma produced by the ionization of both the impactor and the impact surface material [2]. Space-borne instruments based on some form of impact target use impact ionization for in situ measurements.
The Dust Coordinate Sensor (DCS) is a dual detector instrument located on the beamline of the 3 MV hypervelocity dust accelerator at the University of Colorado Institute for Modeling Plasma, Atmospheres and Cosmic Dust (IMPACT). This instrument non-destructively measures the three-dimensional trajectories of charged, hypervelocity (3–8 km/s), micron-sized dust particles in flight by utilizing the image charge induced on grids of wire electrodes. Where previous peak detection was typically limited to dust particles carrying charges $> \sim 100$ fC, new signal processing techniques developed for DCS allow for effective trajectory measurements on particles carrying charges as small as 6 fC. The new signal processing also effectively eliminates false signal detections completely. The position measurements are matched by timestamp to the charge and velocity for each launched dust particle. Verification of the system was performed with independent impact location measurements on a target placed in the beamline. These measurements agree to within 1 mm² of the predicted locations using DCS trajectories. This study demonstrates the capability of the instrument including new processing methods. Precise trajectory measurement along the beamline enables new options for instrument calibration, scientific experiments, and improvement of the accelerator performance.
Impact ionisation mass spectrometry of platinum-coated olivine and magnesite-dominated cosmic dust analogues
2018, Planetary and Space Science
Impact ionisation mass spectrometry enables the composition of cosmic dust grains to be determined in situ by spacecraft-based instrumentation. The proportion of molecular ions in the impact plasma is a function of the impact velocity, making laboratory calibration vital for the interpretation of the mass spectra, particularly at the low velocities typical of lunar or asteroid encounters. Here we present an analysis of laboratory impact ionisation mass spectra from primarily low (<15 km s⁻¹) velocity impacts of both olivine and magnesite-dominated particles onto the SUrface Dust Mass Analyzer (SUDA) laboratory mass spectrometer.
The cation mass spectra show characteristic peaks due to their constituent elements, with Mg, Al, Si, C, Ca, O and Fe frequently present. Contaminant species from the conductive coating process (B, Na, K, C, Pt) also occur, at varying frequencies. Possible saponite or talc inclusions in the magnesite particles are revealed by the presence of Si, Fe, Ca and Al in the magnesite mass spectra. Magnesium is clearly present at the lowest impact velocities (3 km s⁻¹), at which alkali metals were presumed to dominate. Peaks attributed to very minor amounts of water or hydroxyl present in the grains are also seen at low velocities in both cation and anion mass spectra, demonstrating the feasibility of impact ionisation mass spectrometry in identifying hydrated or hydrous minerals, during very low velocity encounters or with very low abundances of water or hydroxy groups, in the impinging grains.
Velocity thresholds for the reliable identification of the major elements within the magnesite and olivine cation spectra are presented. Additionally, relative sensitivity factors for Mg (5.1), Fe (1.5) and O (0.6) with respect to Si, in the olivine particles, at impact speeds >19 km s⁻¹, were found to be very similar to those previously determined for orthopyroxene-dominated particles, despite different target and projectile materials. This confirms that quantitative analyses of mineral dust grain composition in space is viable despite initially poorly-constrained mineralogy.
Detection of meteoric smoke particles in the mesosphere by a rocket-borne mass spectrometer
2014, Journal of Atmospheric and Solar-Terrestrial Physics
Citation Excerpt :
A possible source of spurious signals is secondary charge generation analogous to that seen from the impact of the icy NLC particles that can be tens of nanometers in radius (Havnes and Næsheim, 2007; Kassa et al., 2012). However, laboratory experiments with accelerators for nanometer-scale particles with compositions similar to MSPs have shown the absence of charge generation for these smaller particles moving at velocities typical of sounding rockets (Dalmann et al., 1977). The payloads carried four Colorado Dust Detectors (CDD) (Robertson et al., 2004; Amyx et al., 2008) spaced 90° apart around the periphery of the forward bulkhead, Fig. 1.
In October 2011, two CHAMPS (Charge And Mass of meteoric smoke ParticleS) sounding rockets were launched into the polar mesosphere, each carrying an electrostatic multichannel mass analyzer for charged meteoric smoke particles (MSPs) that operated from 60 to 100 km and returned data on the number density of the charged MSPs in several ranges of mass. The payloads also carried Faraday rotation antennas and an array of plasma probes for determining electron and ion densities and the payload charging potential, thus providing a comprehensive picture of the distribution of charges over a wide range of altitudes that can be compared with models for the vertical distribution of MSPs and for the distribution of charge. The launches were from the Andøya Rocket Range, Norway, following the end of the noctilucent cloud season to avoid detection of ice. A night launch (11 October 21:50 UT) and a day launch (13 October 13:50 UT) helped to elucidate the role of solar ultraviolet in determining the charge state of the particles. The night data show a distinct change in the charge state of MSPs at the D-region ledge (~78 km) below which the density of free electrons is greatly reduced. Above the ledge, negative MSPs are detected at up to 92 km, have number densities reaching ~200 cm⁻³, and positive MSPs are absent. Below the ledge, positive and negative MSPs are about equally abundant, each with densities of ~2000 cm⁻³ at 70 km and with slightly lower densities at 60 km. The MSPs are seen predominantly in mass bins spanning 500–2000 amu and 2000–8000 amu, with more massive particles (radii above ~1.2 nm assuming a smoke particle density of 2 g/cm³) having number densities below the detection threshold (10 cm⁻³) and less massive particles being indistinguishable from ions. The daytime launch data show positive MSPs present only below the ledge and their number density is reduced to below 300 cm⁻³. The daytime data show negative MSPs both above and below the D-region ledge and their number density is also reduced, perhaps as a consequence of photodetachment. Modeling of the charge state of the MSPs shows that the total number density of MSPs, charged and uncharged, is approximately 20,000 cm⁻³ below the ledge and the model reproduces the absence of positive MSPs above the ledge.
On the application of a linear time-of-flight mass spectrometer for the investigation of hypervelocity impacts of micron and sub-micron sized dust particles
2013, Planetary and Space Science
Citation Excerpt :
The generated charge signals are then amplified and recorded. With suitable charge detectors and instrument geometry, impact ionization sensors can act as highly sensitive time-of-flight (TOF) mass spectrometers (Dalmann et al., 1977). The advantages of such detectors are their simplicity and the possibility of simultaneous measurements of the dynamical properties of the particle and its chemical composition, as well as the reduction of noise because of coincidence detection.
Impact physics plays an important role in a variety of fields such as investigation of matter at extreme pressures and temperatures, shock waves in solid bodies or planetology and cosmic dust research. The processes of interest are the generation of impact plasma, neutrals, secondary ejecta, and electromagnetic (EM) radiation. The generation of charge during impacts provides one of the most sensitive methods for the detection and characterization of dust particles in space. To relate the measured values resulting from hypervelocity impact experiments with the impact parameters (speed, mass, composition) a comprehensive set of experiments is needed with well known experimental conditions, and a wide variety of diagnostic tools. For such experiments dust particles are accelerated to hypervelocity speeds in the laboratory with an electrostatic accelerator.
In the present contribution, linear time-of flight (TOF) mass spectrometry is used to investigate the thermodynamical properties, e.g. the velocity distribution, of the ions within an impact plasma. Furthermore, the dependence of the plasma properties on the impact parameters is studied for different dust and target material combinations to investigate the constraints for the validity of impact ionization models. These studies provide new insights into the physics of hypervelocity impacts and the short timescale high-pressure states of matter, they also lead to the development of new and optimization of existing instrument concepts for the detection and characterization of cosmic dust in space.
Application and calibration of a simple position detector for a dust accelerator
2013, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
A newly developed position sensitive detector was implemented in the beam line of the Heidelberg dust accelerator. By charge induction, the detector enables the position of a dust particle to be determined without affecting its motion. The detector consists of four pairs of parallel plates, connected to a single common charge amplifier. The charge induced on the plates varies as a function of the dust particle trajectory, producing simple, easily interpreted signals. Using a segmented target installed in the beam line for a second independent measure of the trajectory, the position detector has been calibrated, allowing the detector signal to be mapped to a dust particle position. The resulting calibration curve indicates that the detector's position accuracy is approximately 0.14 mm, based on an average SNR of 700 for dust particles passing through the centre of the detector. The minimum dust charge for reliable detection was found to be about 1.1 fC. A detector simulation was used to produce a calibration curve that confirms the experimental results.

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Planetary and Space Science

Abstract

References (17)

Surf. Sci.

Vacuum

Earth Planet. Sci. Lett.

Appl. Phys.

Space Res. XIII

J. Phys. E. Scientif. Instr.

Z. Naturf. (A)

Rev. Sci. Instr.

Cited by (51)

A cosmic dust detection suite for the deep space Gateway

Trajectory measurements for individual dust particles on the colorado dust accelerator

Impact ionisation mass spectrometry of platinum-coated olivine and magnesite-dominated cosmic dust analogues

Detection of meteoric smoke particles in the mesosphere by a rocket-borne mass spectrometer

On the application of a linear time-of-flight mass spectrometer for the investigation of hypervelocity impacts of micron and sub-micron sized dust particles

Application and calibration of a simple position detector for a dust accelerator