Start Time 6 1 9 . 4 3 Start Time 6 2 2 . 1 9
- 3 0
- 1 0-
0 -
1 0 -
20
-20 - 1 0 20 -20
JLVel (km/sec)
- 1 0 2 0
Figure 1-34
Bin Number
t ■ ■ I ■ t I I I I I I I I . —I—I I I I I Pitch Angle (deg)
ID CD
O O 1 0o CDO
o
turo m J* '
i i I D ■
OJ O) : CD cn r ro :
a>
a
mA ■
n id ■
"
oi ■ .t> a> :
I ' < 7A >
ii ID -
A (f> : win ■ (0 o :
O
roOJ
to o>
io -'i -o —
<n
O ro or A cn
171 &•i <x>
Ol 0>
Of <T>
cn o j
° 5
o
roO o
OJo o HEEPS Total C ounts ( KHz )
oo s o
98
T O PA Z 2 H E E P S Ra w C o u n ts
8 7
Counts (HTC), as a solid line across the data, the pitch angle look direction (solid "sine wave"), and the HEEPS Image for the accumulation bins listed on the horizontal axis. It is evident from examining the data that two ion flux peaks are seen in the panels at 496.60, 496.63, and 496.66 secs FT. Examination of the pitch angle for the two peaks reveals that the peak centered around bin number 32 has a pitch angle of ~90° while the peak centered around bin number 56 has a pitch angle of -0°. Two other points of interest from this plot The distinction between the two peaks is clearest at 496.66 because the HEEPS Total Counts has fallen to a rate at which there is no appreciable smearing of the image by the electronics. Secondly, the peak at -90° is seen to continue on in energy past the down flowing ions. This is expected because these are transversely accelerated ions (and will be discussed in the next section). The contamination from the ultraviolet emissions is also seen in the first and last two panels as that population between bins zero and sixteen.
Because this population seemed to be well behaved, a numerical fit to the data was attempted using the streaming Maxwellian:
where the parameters are the same as in the Maxwellian fit given in equation 1-29 except the term vs which is the streaming velocity and is directed along the magnetic field.
However, as was the case of the majority of superthermal tails, the down flowing ions are changing over the time period required to satisfy the numerical fit criteria. The process of numerically fitting the down flowing ions is further complicated by the presence o f either a small ambient population or transversely heated ions (discussed in the next section).
Therefore because the downflowing ions could be numerically fit, they were characterized by the streaming velocity of the peak flux for each observed distribution function. This summary is given in figure 1-36. The streaming velocity is seen to vary up to 5 km/s and has an average over the time periods o f roughly 3 km/s.
Eqn 1-34
Vs(km/s) 8
4 -
+
* + f + +
+ + + + -W- -M-+ +H- + -tt+B-HH BMHL JU wIPlT Tir
IHW U t t +-B+-4+ ++ ■ô■ + +
+ +f + 4H- +
+ •ô*■
H H f + + +
+
+ t
n ■ T r | ằ III I | II II l'| I I I I I | I II I'T]' I I II I | I T I 1 I |T I'I TT| I'l 3 5 0 4 0 0 4 5 0 5 0 0 5 5 0 6 0 0 6 5 0 7 0 0 7 5 0 800
figure 1-36
89
T ransversely Accelerated Ions. As was shown in figure 1-21, the thermal ion population changes quite dramatically as the payload entered the two most energetic arcs.
Figure 1-37 shows the phase space distribution function for an energy sweep while inside the most intense arc. A dramatic acceleration of the thermal ions in the transverse direction can readily be seen. Like the earlier reported superthermal tails, it was found that the individual transverse accelerated ion events varied on a time scale at least as small as one energy sweep (0.9218 secs). Thus once again the criteria for fitting these events to a bi- Maxwellian could not be fulfilled. Instead the distribution function was averaged over a finite pitch angle range in the perpendicular direction for each energy sweep and the characteristic perpendicular energy was found from this data. Figure 1-38 shows an example o f this process. Note, that unlike the data in which both a superthermal tail and ambient ion population is seen (figure 1-32), at this time the entire ion population has been heated in the perpendicular direction to a characteristic energy of 6.9 eV (compared to the previous ambient characteristic perpendicular energy of 0.91 eV). A summary o f the characteristic perpendicular energy is given in Figure 1-39. Outside the two intense arcs the characteristic perpendicular energy is averaged over six sweeps. In the cases of coexisting superthermal tail, the value given is that of the thermal core ions . Inside the intense arcs the characteristic perpendicular energy is for every energy sweep. Also plotted on Figure 1-39 for reference is the peak energy of the precipitating electrons.
Further inspection of the OCTO events shown in figure 1-26 revealed the coincidence of a large number of these events with the transversely accelerated ions. Because the OCTO swept to higher energies and had a larger geometry factor than the HEEPS instrument, this data is ideally suited to determining if the high energy tail portion of these ions is elevated. Figure 1-40 shows the OCTO data for four times when transversely accelerated ions were seen in both the HEEPS and the OCTO. The plots are the logarithm of the distribution function (vertical axis) versus the energy of detection (horizontal axis).
The data presented is selected from a limited pitch angle range in the perpendicular direction so that the inverse of the slope of the best fit line is simply the perpendicular temperature (kT±). The high energy tails are seen to vary between kT± = 110 to 205 eV and are distinctly elevated from the thermal portion of the distribution. A fit was not attempted in the thermal range because of the lack of coverage in energy steps at those values. It should
II V e l (k m /s e c )
TOPAZ 2
Phase Space Distribution Log (sec3 / m 6 )
Start Time 5 4 9 . 3 9
- 10-
0 -
1 0 -
20
-20 1 0 0 1 0 2 0
_L Vel (km /se c)
Figure 1-37
L og ( s e c 3 /m 6 )
91
TOPAZ 2
C h a r a c t e r i s t i c -L E n e r g y S t a r t Time 5 4 9 . 3 9 - 2
- 3
- 5
- 6
- 7
I 2 2 4
0
E n e r g y ( e V )
Figure 1-38
Eo(eV)
Energy
8 r \ ! — 1 -20
Characteristic Perpendicular Energy
6
4
2
0
3 5 0 3 0 0
2 5 0 4 0 0 4 5 0 5 0 0 5 5 0 6 0 0 6 5 0 7 0 0 7 5 0 8 0 0
Flight Time (secs) fo
Figure 1-39
Ep(keV)
93
also be noted that the data used to determine the high energy tail was over an order of magnitude higher then the one count level thus giving confidence to the calculation.
O ther Ion Observations. Other on-board observations o f thermal ions were made by the SuperThermal Ion Composition Spectrometer (STICS) provided by Marshal Space Flight Center. After the completion of the flight it was found by the team at MSFC that the STICS instrument had a geometry factor which did not allow for sampling at the pre-flight intended rate. Instead the data from the STICS must be average over a rather large time period (~20 secs). Thus the STICS data is unable to resolve any of the individual events (i.e. superthermal tail or transverse accelerated ions) seen in the HEEPS but it can give a good summary of data throughout the flight.
STICS is able to differentiate between the mass species H+, He+, 0 +, and NỢ The summary plots of these mass channels showed that: 0 + was the most abundantspecies during the flight; H+ was detected in smaller amounts then 0 + throughout the flight; He+
was hardly detected during the flight; and NO+ was found only on the down leg as the rocket passed through the f region.
The HEEPS data has shown that during the up and down legs of the flight the plasma observed is a well behaved cold rammed plasma which can be fit with a Maxwellian distribution function. During these times the STICS data can be averaged over the required time periods to produce phase space distribution plots. Furthermore Dr. Tom Moore has developed a computer routine to fit the to the Maxwellian distribution function o f equation 1-29. Figure 1-41 shows the data (individual marks) and numerical fits (solid lines) for the H+ and 0 + channels averaged over the down leg of the flight. The dashed lines in the plots are the one count level. Any data below this line is considered background noise.
Both distribution function fits show that ions are indeed simple cold rammed particles with the plasma temperatures being well in the thermal range. The STICS data was also averaged over the time periods in which the payload was in the intense arcs. While the thermal core part of this data is suspect at the very least, the STICS instrument does detect a superthermal tail in H+ channel. The fit of this superthermal tail gave kT=15 eV in the direction of steepest gradient in distribution function. This compares well to the most energetic events observed at the same time by the HEEPS. While the composition of the
Log(m*3IAn"6) log(sec*3Aô**6)
487.64 FT 490.41 FT
-3
Tail: kT -1 3 7 eV -4
-5
■6
-7
-8
50 1 0 0 150 200
0
I
-4
Tail: kT-115 eV -5
- 8
-7
-8
50 100 150 200 250 300
0
Energy Energy (eV)
546.62 FT 549.39 FT
Tafl: kT - 205 eV
■5-
300 400 500
100 2 0 0
0
-3
Tati: kT - 110 eV -4
-5
■7
150 200
1 0 0
0 50
Energy (eV) Energy (eV)
Figure 1-40
f (s e c 3 /m 6 )