| 1. |
- Karlsson, Tomas, et al.
(författare)
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Rosetta measurements of lower hybrid frequency range electric field oscillations in the plasma environment of comet 67P
- 2017
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 44:4, s. 1641-1651
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Tidskriftsartikel (refereegranskat)abstract
- Electric field measurements from cometary environments are very rare but can provide important information on how plasma waves help fashion the plasma environment. The long dwelling time of the Rosetta spacecraft close to comet 67P/Churyumov-Gerasimenko promises to improve this state. We here present the first electric field measurements from 67P, performed by the Rosetta dual Langmuir probe instrument LAP. Measurements of the electric field from cometocentric distances of 149 and 348 km are presented together with estimates of plasma density changes. Persistent wave activity around the local H2O+ lower hybrid frequency is observed, with the largest amplitudes observed at sharp plasma gradients. We demonstrate that the necessary requirements for the lower hybrid drift instability to be operating are fulfilled. We suggest that lower hybrid waves are responsible for the creation of a warm electron population, the origins of which have been unknown so far, by heating ambient electrons in the magnetic field-parallel direction.
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| 2. |
- Khotyaintsev, Yuri V., et al.
(författare)
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In-flight calibration of double-probe DC electric field measurements on Cluster
- 2014
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Ingår i: Geoscientific Instrumentation, Methods and Data Systems. - : Copernicus GmbH. - 2193-0856 .- 2193-0864. ; 4:1, s. 85-107
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Tidskriftsartikel (refereegranskat)abstract
- Double-probe electric field instrument with long wire booms is one of the most popular techniques for in situ measurement of DC and AC electric fields in plasmas on spinning spacecraft platforms, which have been employed on a large number of space missions. Here we present an overview of the calibration procedure used for the EFW instrument on Cluster, which involves spin fits of the data and correction of several offsets. We also describe the procedure for the offset determination and present results for the long-term evolution of the offsets.
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| 3. |
- Khotyaintsev, Yuri V., et al.
(författare)
-
In-flight calibration of double-probe electric field measurements on Cluster
- 2014
-
Ingår i: Geoscientific Instrumentation, Methods and Data Systems. - : European Geosciences Union (EGU). - 2193-0856 .- 2193-0864. ; 3:2, s. 143-151
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Tidskriftsartikel (refereegranskat)abstract
- Double-probe electric field instrument with long wire booms is one of the most popular techniques for in situ measurement of electric fields in plasmas on spinning spacecraft platforms, which have been employed on a large number of space missions. Here we present an overview of the calibration procedure used for the Electric Field and Wave (EFW) instrument on Cluster, which involves spin fits of the data and correction of several offsets. We also describe the procedure for the offset determination and present results for the long-term evolution of the offsets.
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| 4. |
- Torkar, Klaus, et al.
(författare)
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Long-Term Study of Active Spacecraft Potential Control
- 2008
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 36:5, s. 2294-2300
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Tidskriftsartikel (refereegranskat)abstract
- Emitters based on the liquid metal ion source principle have been operating on the Cluster spacecraft between 2000 and 2004, in order to control the spacecraft potential. The resulting reduction of positive spacecraft potential reduces perturbations to the plasma measurements on board. Ion currents up to 40 [LA have been applied, which reduced the energy band in which photoelectrons disturb the plasma electron measurements to values close to the lower detection limit of the instrument. The experience with this method, meanwhile, covers both the maximum and minimum of the present solar cycle and allows one to study the variations of photoemission and other long-term trends and their effects on the measurements. A long-term trend of the controlled spacecraft potential is indeed observed. In addition, it appears that reconstruction of the uncontrolled spacecraft potential from the controlled one is possible if certain conditions are fulfilled. Spacecraft potential control can thereby improve the plasma measurements while still allowing one to estimate the total plasma density from the residual potential.
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