Results from the Heavy Ions In Space (HIIS) experiment on the ionic charge state of solar energetic particles
- George Mason Univ., Fairfax, VA (United States)
It has long been known that low-energy solar energetic particles (SEP`s) are partially-ionized. For example, in large, so-called `gradual` solar energetic particle events, at approximately 1 MeV/nucleon the measured mean ionic charge state, Q, of Fe ions is 14.1 +/- 0.2, corresponding to a plasma temperature of approximately 2 MK in the coronal or solar-wind source material. Recent studies, which have greatly clarified the origin of solar energetic particles and their relation to solar flares, suggest that ions in these SEP events are accelerated not at a flare site, but by shocks propagating through relatively low-density regions in the interplanetary medium. As a result, the partially-ionized states observed at low energies are expected to continue to higher energies. However, up to now there have been no high-energy measurements of ionic charge states to confirm this notion. The authors report here HIIS observations of Fe-group ions at 50-600 MeV/nucleon, at energies and fluences which cannot be explained by fully-ionized galactic cosmic rays, even in the presence of severe geomagnetic cutoff suppression. Above approximately 200 MeV/nucleon, all features of our data -- fluence, energy spectrum, elemental composition, and arrival directions -- can be explained by the large SEP events of October 1989, provided that the mean ionic charge state at these high energies is comparable to the measured value at approximately 1 MeV/nucleon. By comparing the HIIS observations with measurements in interplanetary space in October 1989, the authors determine the mean ionic charge state of SEP Fe ions at approximately 200-600 MeV/nucleon to be Q = 13.4 plus or minus 1.0, in good agreement with the observed value at approximately 1 MeV/nucleon. The source of the ions below approximately 200 MeV/nucleon is not yet clear.
- Research Organization:
- NASA Langley Research Center, Hampton, VA (United States)
- OSTI ID:
- 42738
- Report Number(s):
- N-95-23796; NASA-CP-3275-PT-1; L-17430A-PT-1; NAS-1.55:3275-PT-1; CONF-9311137-; CNN: NASA ORDER W-18409; TRN: 9523808
- Resource Relation:
- Conference: 3. long duration exposure flight (LDEF) symposium, Williamsburg, VA (United States), 8-12 Nov 1993; Other Information: PBD: Feb 1995; Related Information: Is Part Of LDEF: 69 Months in Space. Third Post-Retrieval Symposium, part 1; Levine, A.S.; PB: [10] p.
- Country of Publication:
- United States
- Language:
- English
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