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| Titel |
Plasma gradient effects on double-probe measurements in the magnetosphere |
| VerfasserIn |
H. Laakso  , T. L. Aggson, R. F. Pfaff |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 13, no. 2 ; Nr. 13, no. 2, S.130-146 |
| Datensatznummer |
250011743
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| Publikation (Nr.) |
 copernicus.org/angeo-13-130-1995.pdf |
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| Zusammenfassung |
| The effects on double-probe electric field
measurements induced by electron density and temperature gradients are
investigated. We show that on some occasions such gradients may lead to marked
spurious electric fields if the probes are assumed to lie at the same probe
potential with respect to the plasma. The use of a proper bias current will
decrease the magnitude of such an error. When the probes are near the plasma
potential, the magnitude of these error signals, ∆E, can vary
as ∆E ~ Te(∆ne/ne)+0.5∆Te,
where Te is the electron temperature, ∆ne/ne
the relative electron density variation between the two sensors, and
∆Te the electron temperature difference
between the two sensors. This not only implies that the error signals will
increase linearly with the density variations but also that such signatures grow
with Te, i.e., such effects are 10 times larger in a
10-eV plasma than in a 1-eV plasma. This type of error is independent of the
probe separation distance provided the gradient scale length is much larger than
this distance. The largest errors occur when the probes are near to the plasma
potential. At larger positive probe potentials with respect to the plasma
potential, the error becomes smaller if the probes are biased, as is usually the
case with spherical double-probe experiments in the tenuous magnetospheric
plasmas. The crossing of a plasma boundary (like the plasmapause or
magnetopause) yields an error signal of a single peak. During the crossing of a
small structure (e.g., a double layer) the error signal appears as a bipolar
signature. Our analysis shows that errors in double-probe measurements caused by
plasma gradients are not significant at large scale (»1 km) plasma boundaries,
and may only be important in cases where small-scale (<1 km), internal
gradient structures exist. Bias currents tailored for each plasma parameter
regime (i.e., variable bias current) would o1q1improve the double-probe response
to gradient effects considerably. |
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