Transcript Document

Equatorially-confined warm
trapped ions at 3-5 RE
M. Yamauchi
Where?
~4 RE, confined near the equator (Cluster perigee)
Species? H+ and He+ of 20 eV ~ keV (CIS energy range)
Energy? Pancake-like trapped ions (cf. Olsen et al., 1987)
In this work: First time to examine features for > 50 eV
New results: ring-like Ion distribution + temporal change
Van-Allen radiation belt
Cluster satellites
Contamination
Contamination from radiation
belt MeV particles is always a
problem at perigee (equator)
for Cluster.
The contamination is near
90° pitch angle at perigee.
But we can yet identify....
AE=small
AE=quiet
Equatorial trapped 100 eV H+
divide by
sectors
1
SC motion
2
4
5
8 7
spin axis
equator
H+ & He+ signatures
Only in the  direction
Confined near equator
Ring distribution or
Heated distribution?
equator
Flattened gyrotropic distribution.
difficult to check “ring vs hot”
dist fn ~ exp[-(v-u0)2/T] dv3
~ E1/2 exp[-(√E-√E0)2/T] dE
flux ~ E exp[-(√E-√E0)2/T] dE
energy flux (JE)
~ E2 exp[-(√E-√E0)2/T] dE
check SC-1
HIA covers low energy
1.00E+11
1.00E+10
1.00E+09
1.00E+08
1.00E+07
1.00E+06
1.00E+05
1.0
para(H 1278)
perp(He 45)
10.0
100.0
perp(H 45)
para(ion 1278)
1000.0
para(He 1278)
perp(ion 45)
difficult due to contamination
statistics (only 2001-2002)
The observation probability ~ 35-45%
(more in noon/dusk than night-dawn)
statistics (continued)
He+ energy : Selected all “intense” H+ signature (> 3·106 keV
cm-2s-1str-1keV-1) in traversals when He+ channel is not
severely contaminated.  Total 29 traversals.
* He+ energy >> H+ energy : 10 events
* He+ energy ~ H+ energy : 6 (H+ contamination?)
* Without He+ signature : 13 events
Energy ratio between He+ and H+ varies (new!)
Dominated by H+ with variable content of He+ (mostly < 5%)
multi-spacecraft
equator
Energy-time dispersion
(new!)
Appearing in 40 min (new!)
equator
equator
The energy time dispersion indicates a drift from a remote
source (magnetic drift = energy dependent).
The difference in the drift speed between 150 eV ions and 30
eV ions ~0.04 MLT/h at 4 RE.
At 17 MLT, drift takes about 3 min (time lag in the dispersion
in SC-3) to travel 0.04 MLT.
 Drift time is expected to be 1 hour.
 Agrees with the sudden appearance in 40 min.
statistics (continued)
Energy-time dispersion: out of the same 29 events, 5
events is with clear dispersion (not often)
Summary
(1) Non-thermal ring distribution rather than pancake distribution.
(2) Energy ratio of the ring between He+ and H+ = 1~10.
(3) Some events show energy-time dispersion, indicating the drift.
(4) The time scale of the development ~ 1 h.
(5) Pitch angle ~ 90° for also > 30 eV.
(6) Observation probability at 4~4.5 RE is ~ 40-45% in noon and
dusk sectors and about 20-25% in the night-to-dawn sector.
(7) Dominated by tens eV H+ with variable content of He+. The
He+/H+ ratio is much less than 5% for the majority of the cases.
(8) Co-located with wave-defined equator
Future work
composition & wave
(1) He+ is sometimes seen, but normally less that 5% of H+
(2) (n+(1/2))fce wave is accompanied