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Title: Hybrid simulations of positively and negatively charged pickup ions and cyclotron wave generation at Europa

In the vicinity of Europa, Galileo observed bursty Alfvén-cyclotron wave power at the gyrofrequencies of a number of species including K +, math formula, Na +, and Cl +, indicating the localised pickup of these species. Additional evidence for the presence of Chlorine was the occurrence of both left-hand (LH) and right-hand (RH) polarised transverse wave power near the Cl + gyrofrequency, thought to be due to the pickup of both Cl + and the easily formed Chlorine anion, Cl . To test this hypothesis we use one-dimensional hybrid (kinetic ion, massless fluid electron) simulations for both positive and negative pickup ions and self-consistently reproduce the growth of both LH and RH Alfvén-cyclotron waves in agreement with linear theory. We show how the simultaneous generation of LH and RH waves can result in non-gyrotropic ion distributions and increased wave amplitudes, and how even trace quantities of negative pickup ions are able to generate an observable RH signal. Here, through comparing simulated and observed wave amplitudes, we are able to place the first constraints on the densities of Chlorine pickup ions in localised regions at Europa.
Authors:
 [1] ; ORCiD logo [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [1]
  1. Univ. College London (UCL), London (United Kingdom). Mullard Space Science Lab. (MSSL); Univ. College London (UCL), Birkbeck (United Kingdom). Centre for Planetary Sciences
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Univ. of California, Los Angeles, CA (United States). Inst. of Geophysics and Planetary Physics
  4. Space Science Inst., Boulder, CO (United States)
  5. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Space Science Inst., Boulder, CO (United States)
  6. Austrian Academy of Sciences, Graz (Austria). Space Research Inst.
Publication Date:
Report Number(s):
LA-UR-17-24957
Journal ID: ISSN 2169-9380
Grant/Contract Number:
AC52-06NA25396; NAS5-01072; NNX16AM98G
Type:
Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Space Physics
Additional Journal Information:
Journal Volume: 122; Journal Issue: 10; Journal ID: ISSN 2169-9380
Publisher:
American Geophysical Union
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE Laboratory Directed Research and Development (LDRD) Program; National Aeronautics and Space Administration (NASA)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Heliospheric and Magnetospheric Physics
OSTI Identifier:
1394982