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

Willis, M.J. and Burchell, Mark J. and Cole, Mike J. (2004) Influence of impact ionisation detection methods on determination of dust particle flux in space. Planetary and Space Science, 52 (8). pp. 711-725. ISSN 0032-0633. (The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided)

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Results are presented for a series of experiments investigating effects which call influence the interpretation of data from ionisation-based dust detectors carried oil 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 0degrees (normal incidence) to 80degrees (glancing incidence). Little or no variation was observed at angles up to 60degrees, but at 80degrees 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 oil to an aluminium target Lit various angles, and the impact ionisation signal on a nearby gold target was measured. It was found that ionisation signals were observed oil the gold target, and that these were very similar in appearance to those observed in direct impacts. The effect of reduction in particle charge oil 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 I-IONISATION = 1.67 x 10(-9) Q(PARTICLE)(0.35) (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. lonisation 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 all example, the influence of oblique incidence, side-wall impacts and particle charge effects oil 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 call affect the interpretation of data from instruments deployed in space.

Item Type: Article
Uncontrolled keywords: cosmic dusts; impact ionisation; micrometeoroids; detectors
Subjects: Q Science
Divisions: Faculties > Science Technology and Medical Studies > School of Physical Sciences > Centre for Astrophysics and Planetary Sciences
Depositing User: Mark Burchell
Date Deposited: 09 Sep 2008 14:51
Last Modified: 14 May 2014 15:19
Resource URI: (The current URI for this page, for reference purposes)
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