Abstract
The instrument ASPOC (Active Spacecraft Potential Control) controls the electric potential of the Cluster spacecraft by means of an ion beam. This modification of the charge balance improves the plasma measurements on board. Beneficial effects have also been observed for the electric field measurements by double probes (EFW). Comprehensive knowledge about the status of the instruments including the ion beam current is necessary to correctly interpret spacecraft potential data. This paper provides an overview of the instrument modes and the parameters contained in the ASPOC data sets in the Cluster Active Archive. A few examples illustrate the relation between instrument modes and data.
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Notes
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Operating mode, including emitter start-up status and cleaning: In both of these states the beam current deviates significantly from the nominal current
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Emitter identification and emitter module identification: Each instrument carries eight emitters bundled into two modules with a common high voltage system within a module. Both emitters and modules may exhibit individual characteristics and performance, which may have an effect on the value and temporal behaviour of the beam current
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Anomaly flags: These flags give the reason for an anomaly, for example failure of ignition of an emitter
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Ion beam energy: The voltage applied to the emitter is equivalent to the energy of the ions in the beam
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Total ion source current: The current delivered by the high voltage supply into the emitter will be higher than the emitted current if internal losses are present
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Heater current: The current drawn by the heater element associated with an emitter
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Heater voltage: The voltage applied to the heater element associated with an emitter. Voltage and current together can be used to calculate not only the electrical power but also the temperature of the heater element. From this temperature, the temperature of the emitter tip can be derived
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Temperature of the ion source module: This parameter contains the ambient temperature of the emitter module. The temperature of the emitter tip shows a strong dependence on the heater temperature, but also some influence of this ion source module temperature
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Raw spacecraft potential received on board from EFW: This parameter mirrors the spacecraft potential data delivered by the instrument EFW to ASPOC on board the spacecraft. It differs from the EFW data product in the archive with respect to timing
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Mean quality level during time span
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Minimum quality level during time span
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Maximum quality level during time span
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Comment; a textual description associated with the average quality level value
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Acknowledgements
The authors would like to thank many teams for their valuable efforts: the CAA team for building the archive, the ASPOC team for building the instruments, the EFW and PEACE teams for good co-operation during the project, and ESOC and JSOC for operational support.
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Torkar, K., Jeszenszky, H. (2010). ASPOC Data Products in the Cluster Active Archive. In: Laakso, H., Taylor, M., Escoubet, C. (eds) The Cluster Active Archive. Astrophysics and Space Science Proceedings. Springer, Dordrecht. https://doi.org/10.1007/978-90-481-3499-1_2
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