Subject: JEM-X2 reactivation results

Folks,

The was activated on April 2 after 26 days of down time.
The HV was on for about 5 hours at the new setting of DV=74.

The results were more or less as expected (quite dependent on
what you expected).

Figure 1.
The gain started quite low and showed the, by now familar, more
or less linear increase. In the first plot this is shown in
comparison with the start-up from orbit 170, 27 days earlier.
The data have been corrected for the different DV setting by
a factor of 1.14 per HV step to produce continous curves.
The linear increase is about 10% of the final gain per hour.
After 26 days of HV off, the gain starts out a little above 60%
of final gain. Please note, that the session of 5 hours was really
too short to reach a stable situation, but I think we got close
to the point where the curve would level out.

Figure 2.
Now it is interesting to compare to the 'good old day' before severe
aging.
Fig.2 compares the recent data with the gain in orbit 30. The data have
been corrected for the 3 step jump shortly after activation.
In orbit 30 DV was set to 80 and in orbit 179 it was set to 74.
The lower curve shows the gain from orbit corrected by the corresponding
factor of 1.14 to the power 6. In both cases data taking started about 
0.25 hour after HV on. 
We see that extrapolating back to HV on the gain is about the same.
(note that exponential decay component is just visible in the new data).
This indicates that the conditions are identical at HV on, meaning that
the plate has in some sense recovered.
However, the plate now 'ages' in about 5 hours.

Figure 3.
There is some hope seen in fig.3, showing the energy resolution derived
from
the usual source #1. Here the new data (*) are compared with orbit 30
and with
the last normal orbit 170. We see that is all three cases the initial
resolution
is about equal and inparticular orbit 30 is dominated by the rapid gain
changes
compared with the integration time. In orbit 30 the resolution then
settled at
close to 9%, whereas it landed around 13-14% in orbit 170.
In the recent data the resolution seems to settle at an intermediate
value 
around 11%.

Conclusion:
After 26 days without HV on, the charge distribution on/in the plate has
returned
to its original configuration, but time scale to return to the 'aged'
state is now
short. 

There are hints that some recovery of the energy resolution is achieved
by switching
off for some time. However, the recovery may be short lived, but the
data are inconclusive

In order to fully understand the behavior the next activation of JEM-X2
should
be for a full orbit.   


Søren