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Khurana et al. 1987
Khurana, K.K., Kivelson, M.G., Armstrong, T.P. and Walker, R.J. (1987). Voids in Jovian magnetosphere revisited: Evidence of spacecraft charging. Journal of Geophysical Research 92: doi: 10.1029/JA080i012p13399. issn: 0148-0227.

As Voyager 2 moved inward toward Jupiter in the vicinity of Ganymede's orbit, the low-energy ion and electron fluxes recorded by the Plasma Science Experiment (PLS) intermittently fell to very low levels. The low fluxes, which lasted for times of the order of 10 min and recurred over an 8-hour interval, have been called ''voids.'' Early interpretations associated the voids with Ganymede wake effects. Further analysis has demonstrated that the location and extent of the voids are inconsistent with such an interpretation. In this study, we have reexamined the PLS data in conjunction with data from the magnetic field experiment and the low-energy charged particle experiment (LECP) in the relevant interval. The LECP data showed that the PLS voids were accompanied by large enhancements of the flux of energetic electrons and ions. No systematic signatures were found in the magnetic data. We suggest that increased energetic electron fluxes in the void regions intermittently charged the spacecraft negatively to values between a few kV and tens of kV. For a realistic phase space distribution of cold and hot particles in the Jovian magnetosphere, spacecraft charging can produce dropouts in the measured cold ion and electron fluxes and enhancements in the measured fluxes of hot particles consistent with the observations. Spacecraft charging would not produce a signature detectable by the flux gate magnetometer. We propose that the plasma density in the nominal voids is not exceptionally low and that the near-Ganymede anomalies arose from an unusual combination of enhanced fluxes of ~10 to ~100 keV electron in a low-density plasma environment. Further work is needed to explain why this phenomenon occurred intermittently and only over a limited portion of the Voyager trajectory. ¿ American Geophysical Union 1987

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