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Energetic charged particle injections at SaturnC. Paranicas1, D. G. Mitchell1, D. C. Hamilton2, S. M. Krimigis1, B. H. Mauk1, P. C. Brandt1, J. F. Carbary1, A. M. Rymer1, A. Mueller3(1) Johns Hopkins Univ/APL(2) University of Maryland(3) Max Planck/SonnensystemforschungFall AGUSan Francisco, CA16 December 2008

overview
Overview
  • For our purposes, injections are any non-azimuthally-symmetric populations that are higher in flux than ambient particles
  • Our main goal is to continue to study injection phenomena to create a picture of transport/acceleration that is appropriate to what is observed in energetic charged particle data
  • We will also show occurrence statistics of these features in the Cassini/MIMI data obtained at Saturn
picture of the transport
Picture of the transport
  • In the classical picture of interchange, flux tubes with hotter, less dense plasma move inward and take the place of flux tubes with colder, denser plasma
  • But in many instances of plasma physics, the flux tube concept breaks down.
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Injections

In this example, it appears that flux tubes filled with energetic protons are displacing the ambient particles (data from MIMI/CHEMS: All 3 telescopes included).

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This section of the previous plot includes CHEMS/Telescope-2 only, measuring particles with near 90o pitch angle (Cassini is near Saturn’s equator at this time)

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Remnants of a previous proton injection that are dispersed

This is a section of the plot including data from CHEMS/Telescope-1 only. Here it does not appear that a separate flux tube is displacing the background particles (during this time, T-1 is detecting particles with pitch angles of about 45o).

transport acceleration
Transport/acceleration
  • In CHEMS/T-2 and LEMMS, the data seem to show the spacecraft on flux tubes containing newly injected particles only
  • In telescopes 1 and 3, it appears that the spacecraft is on flux tubes that simultaneously contain new injecting distributions and older dispersed injections that join seamlessly with the surrounding medium
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A second example showing a dispersed injection detected at the same position by Cassini as new injections at lower energy

occurrence statistics
Occurrence statistics
  • To study whether the various types of injections have common properties, we surveyed the near equatorial injections observed by Cassini/MIMI
  • Here we consider only very recent injections that have not had sufficient time to disperse in energy
  • Previously, the plasma injections detected by Cassini was surveyed in this manner (e.g. Hill et al. 2005)
distribution of plasma injections
Distribution of plasma injections
  • At the plasma energies, injections appear to be initiated at all local times and longitudes
  • From Hill et al. (2005):
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While the recent injections in this survey appear to cluster around noon and midnight local time, this is also where Cassini has taken data

Proton injections by local time, Cassini coverage

discussion
Discussion
  • We are still considering mechanisms of acceleration and transport for the various injections observed by MIMI
  • This preliminary work does not suggest strong organization of recent injections by LT, longitude, or SKR longitude
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