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Influence of impact ionisation detection methods on determination of dust particle flux in space

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Title: Influence of impact ionisation detection methods on determination of dust particle flux in space
Authors: Willis, M.J.1, Burchell, M.J.1 m.j.burchell@kent.ac.uk, Cole, M.J.1, McDonnell, J.A.M.2
Source: Planetary & Space Science. Jul2004, Vol. 52 Issue 8, p711-725. 15p.
Subjects: Dust, Iron, Research, Gold, Space sciences
Abstract: Results are presented for a series of experiments investigating effects which can influence the interpretation of data from ionisation-based dust detectors carried on spacecraft. First, the variation of the impact ionisation yield with angle of impact was studied for impacts of iron microparticles onto gold at speeds of 1–75 km s-1. The angle of incidence was from 0° (normal incidence) to 80° (glancing incidence). Little or no variation was observed at angles up to 60°, but at 80° the total impact ionisation signal was around an order of magnitude lower than at smaller angles. In addition, the fast rising component of the ionisation signal rise time showed no variation with impact angle, but the total signal rise time showed a steady decrease. The effect of secondary impact ionisation resulting from particle impacts on detector side walls was also studied. Iron microparticles were fired on to an aluminium target at various angles, and the impact ionisation signal on a nearby gold target was measured. It was found that ionisation signals were observed on the gold target, and that these were very similar in appearance to those observed in direct impacts.The effect of reduction in particle charge on an impact ionisation signal was investigated. Iron microparticles were fired on to a gold target after passing through a thin film which reduced the charge which was used to accelerate them. It was found that there was a measurable drop in ionisation signal in the reduced-charge case. The empirical relation IIONISATION=1.67×10-9QPARTICLE0.35 (units of C) was found. This implies there is a component in the observed ionisation signal that is not related to the impact. To test this, charged tungsten carbide particles were dropped at very low velocity onto a replica of a dust detector used in space whilst placed in a vacuum chamber. Ionisation signals were frequently recorded by the detector. It was concluded that this signal originated from the incident particle charge.In the final section of work, as an example, the influence of oblique incidence, side-wall impacts and particle charge effects on data collected by the Gorid dust detector in Earth orbit were investigated. Corrections were applied to the mass and velocity distributions derived from Gorid data. In extremis, oblique incidence effects were found to shift the mass distribution down by an order of magnitude, and the velocity distribution up by a factor of two to three. If all the data had come from unrecognised side-wall impacts, the mass distribution would be shifted downwards to lower masses by three orders of magnitude, and the velocity distribution upwards by a factor of five. Possible particle charge effects were found to shift the mass distribution down by 30%, and did not alter the velocity distribution.Overall we have investigated a variety of impact-related phenomena and conclude that these can affect the interpretation of data from instruments deployed in space. [Copyright &y& Elsevier]
Copyright of Planetary & Space Science is the property of Pergamon Press - An Imprint of Elsevier Science and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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DbLabel: Engineering Source
An: 13064611
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PubTypeId: academicJournal
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  Data: Influence of impact ionisation detection methods on determination of dust particle flux in space
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  Data: <searchLink fieldCode="AR" term="%22Willis%2C+M%2EJ%2E%22">Willis, M.J.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Burchell%2C+M%2EJ%2E%22">Burchell, M.J.</searchLink><relatesTo>1</relatesTo><i> m.j.burchell@kent.ac.uk</i><br /><searchLink fieldCode="AR" term="%22Cole%2C+M%2EJ%2E%22">Cole, M.J.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22McDonnell%2C+J%2EA%2EM%2E%22">McDonnell, J.A.M.</searchLink><relatesTo>2</relatesTo>
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  Data: <searchLink fieldCode="JN" term="%22Planetary+%26+Space+Science%22">Planetary & Space Science</searchLink>. Jul2004, Vol. 52 Issue 8, p711-725. 15p.
– Name: Subject
  Label: Subjects
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  Data: <searchLink fieldCode="DE" term="%22Dust%22">Dust</searchLink><br /><searchLink fieldCode="DE" term="%22Iron%22">Iron</searchLink><br /><searchLink fieldCode="DE" term="%22Research%22">Research</searchLink><br /><searchLink fieldCode="DE" term="%22Gold%22">Gold</searchLink><br /><searchLink fieldCode="DE" term="%22Space+sciences%22">Space sciences</searchLink>
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  Data: Results are presented for a series of experiments investigating effects which can influence the interpretation of data from ionisation-based dust detectors carried on spacecraft. First, the variation of the impact ionisation yield with angle of impact was studied for impacts of iron microparticles onto gold at speeds of 1–<f>75 km s-1</f>. The angle of incidence was from <f>0°</f> (normal incidence) to <f>80°</f> (glancing incidence). Little or no variation was observed at angles up to <f>60°</f>, but at <f>80°</f> the total impact ionisation signal was around an order of magnitude lower than at smaller angles. In addition, the fast rising component of the ionisation signal rise time showed no variation with impact angle, but the total signal rise time showed a steady decrease. The effect of secondary impact ionisation resulting from particle impacts on detector side walls was also studied. Iron microparticles were fired on to an aluminium target at various angles, and the impact ionisation signal on a nearby gold target was measured. It was found that ionisation signals were observed on the gold target, and that these were very similar in appearance to those observed in direct impacts.The effect of reduction in particle charge on an impact ionisation signal was investigated. Iron microparticles were fired on to a gold target after passing through a thin film which reduced the charge which was used to accelerate them. It was found that there was a measurable drop in ionisation signal in the reduced-charge case. The empirical relation <f>IIONISATION=1.67×10-9QPARTICLE0.35</f> (units of C) was found. This implies there is a component in the observed ionisation signal that is not related to the impact. To test this, charged tungsten carbide particles were dropped at very low velocity onto a replica of a dust detector used in space whilst placed in a vacuum chamber. Ionisation signals were frequently recorded by the detector. It was concluded that this signal originated from the incident particle charge.In the final section of work, as an example, the influence of oblique incidence, side-wall impacts and particle charge effects on data collected by the Gorid dust detector in Earth orbit were investigated. Corrections were applied to the mass and velocity distributions derived from Gorid data. In extremis, oblique incidence effects were found to shift the mass distribution down by an order of magnitude, and the velocity distribution up by a factor of two to three. If all the data had come from unrecognised side-wall impacts, the mass distribution would be shifted downwards to lower masses by three orders of magnitude, and the velocity distribution upwards by a factor of five. Possible particle charge effects were found to shift the mass distribution down by 30%, and did not alter the velocity distribution.Overall we have investigated a variety of impact-related phenomena and conclude that these can affect the interpretation of data from instruments deployed in space. [Copyright &y& Elsevier]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Planetary & Space Science is the property of Pergamon Press - An Imprint of Elsevier Science and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1016/j.pss.2004.01.001
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      – Code: eng
        Text: English
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      Pagination:
        PageCount: 15
        StartPage: 711
    Subjects:
      – SubjectFull: Dust
        Type: general
      – SubjectFull: Iron
        Type: general
      – SubjectFull: Research
        Type: general
      – SubjectFull: Gold
        Type: general
      – SubjectFull: Space sciences
        Type: general
    Titles:
      – TitleFull: Influence of impact ionisation detection methods on determination of dust particle flux in space
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            NameFull: Cole, M.J.
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              Text: Jul2004
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              Y: 2004
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