DESCRIPTION |
Instrument Overview
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This instrument detects the electric charges
contained in the plasma cloud generated by a solid
particle impacting on a gold target. The principle
of this technique is similar to that adopted for the
impact plasma detectors of SP-2. The magnitude of
the positive and negative charges is proportional to
the mass of the particle Q=Am, where A= 10**3C/s for
an impact velocity of 78 km/s. The SP-1 system
includes two similar detectors. Each unit is made up
of a base plate (1) covered by a gold target (2) at
zero potential, perpendicular to the dust flow, and
an array of strip collectors (4). The collectors are
parallel to the dust flow; they are mounted on an
insulator (3) and their edge is protected from
impacts by a shield (5) connected electrically to the
structure. Adjacent collectors are biased at
potentials of 30 V, with opposite polarities. The
two sets of electrodes in each detector detect a
positive and a negative current pulse, which are
analysed and recorded by the electronics unit. The
entrance to one detector is covered by a plastic
foil, to obtain additional information on density
and/or calibration factor. The characteristic
parameters of SP-1 are given in Table 8.
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Table 8. Dust Particle Impact Plasma Detector characteristics
Target material Gold (0.1 mm)
Toil sensor area 160 cm**2, one sensor covered with 0.6 and
2 micro m thick plastic foil
on Vegas-1 and 2, resp.
Impact charge range 3x10**-14 -10**-8 C
Estimated mass range 3x10**-17 -10**-11 g
Integration time 2 s (high data rate)
2.5 min (low data rate)
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REFERENCES |
Reinhard, R and B. Battrick (eds), 'Space Missions to Halley's Comet', European
Space Agency ESA SP-1066, ESA Pub Div, Moordwijk, Netherlands, 1986.
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