Tohban Report 2015-09-30
From RHESSI Wiki
|Start Date:||23 Sep 2015|
|End Date:||30 Sep 2015|
|Next Tohban:||Juan Carlos and Hazel|
|List all reports|
Very active week! There were two active regions (12422 and 12423) that produced many C and M flares. 2423 is now just rotated off (so keep an eye out for awesome occulted events...) and 2422 is a few days away from the west limb. A Major Flare Watch was called a few days ago and is still in effect, so high activity is expected to continue.
How many GOES flares occurred? Flares above B, C, M, X class were 17 47 15 0 And how many of these are listed in the RHESSI flare list? Flares above B, C, M, X class were 10 26 9 0 And how many had EXCELLENT coverage? Flares above B, C, M, X class were 0 0 0 0 There were RHESSI flares/GOES flares 162 / 79 over the time range 23-Sep-15 30-Sep-15
The SSR is a bit high due to high solar activity, with a max of 48% and at 28% after the last pass set today.
The SSR started the week almost emptying. However, after the HV drop on D4, slow events from D4 and D6 were high enough to keep steadily increasing the SSR fill. This was even BEFORE solar activity picked up. Because of this, I proposed that it might be a good idea to disable events on D4, with the reasoning that those events aren't giving us good data and are just eating up the SSR. Because things didn't quite get bad enough that we were really in trouble, I did not implement this suggestion. Future tohbans should keep it in mind as a last resort.
The cold plate temps have come down a bit, consistent with solar fraction. CP1 = 134.7K, CP2 = 133.1K.
Brian discussed the temperature trends and the solar fraction trends. He proposes a plan whereby we violate the temperature-power curve for a short time in order to make it into the next two peaks in the sun fraction cycle, when we will presumably stay colder than now. In other words, if we're willing to bend the limits for the cryocooler for a short time (~1 month?), we might stay cold for longer. It's anticipated that we'll drop ~1 degree during the sun fraction peak.
We also discussed whether it's a good idea to anneal (consensus: at present, no) and what the criteria and parameters of an anneal might be. The idea of annealing at room temperature (which would allow us to turn the cryocooler off entirely, giving it a rest) was brought up. This may be safer for the cryocooler health, but may be less effective reversing radiation damage in the detectors.
No data gaps as of Tuesday evening.
- On Sept 23, it was decided that the last changes to the slow threshold were probably too drastic, especially considering that the fast threshold was changed at the same time. We backed the front slow threshold back down to 0x1C, which is what it had been before the last adjustment. This needs to be monitored to see how D3 operates in this state, and keep an eye on the slow rates + SSR. UPDATE Sept. 24: the D3 event rate did not significantly change with this threshold drop. Livetime is still ~90% (same as before the drop) so I think this is a stable, working condition. If more livetime is desired, the fast threshold could be raised again.
2015-266-19:24:00 /IDPUTABLE3 OFFSET=FRONTSLOWDAC 2015-266-19:24:12 /IDPLOAD VALUE=0x1C ;was 0x80
- Sept. 23 2015: Despite our best efforts, there's been no success in recovering livetime from D4. The front segment livetime is essentially 0. Since desperate times call for desperate measures, we're lowering the HV by 1000V to try and recover some performance. (This was temporarily tried last week, for an orbit, and the livetime did rise to 30%.) The detector does not seem to be anywhere near segmenting. UPDATE Sept. 24: this drop was successful in bringing the fast rates down some, from 4x10^5 to 10^5. This freed up some livetime, which is now at ~35%. However, it also allowed the slow rates to skyrocket, to about 3000. This is probably cutting into the SSR, and so now the SSR fill is gradually rising (13% min today vs ~4% min yesterday). Action should be taken to reduce the fill rate.
2015-266-19:25:51 /IHVDAC DETECTOR=4, VOLTAGE=134 (2598 V)
- It was noticed that Detector 9 ULD events had maxed out in the monitor plots again on Sept. 11. This wasn't noticed because D9 events are still off. To try and avoid/mitigate potential damage to the detector, we lowered the HV on D9 on Sept. 29 PDT (Sept. 30 03:00 UTC) from ~800V to 490V. We briefly turned on events for G9 as well. Events were then turned off
again at eclipse entry. The detector remained segmented. The events should be checked to see what the ULD rate actually was before (and after) the HV turndown.
2015-273-03:00:43 /itmon value=AFE8 (Detector 9 events on) 2015-273-03:01:09 /IHVDAC DETECTOR=9, VOLTAGE=26
- Here are plots of the D9 rear resets (proxy for leakage current) around the time of the ULD runaways in August and September. The values are not the same, with the September one being higher. In both plots, the last data point is around the time the ULDs hit max in the monitor rates.
The idea was brought up to turn OFF one or multiple detectors (both HV and preamp) in order to save power and thus cooling ability. We could try this initially with D9, since we're not taking events from this detector. But first, we should assess the data from the time when the D9 events were turned back on just prior to the HV drop on the 29th/30th.
It's about time for a spinup.
|HLAT Decimation||Rear decimation weight 6, no front decimation|
|Night time data (fronts)||+/- 4 minutes|
|Night time data (rears)||+/- 4 minutes|
|Require extra passes?||No|
|Requirement for moving pointer?||No|
|Attenuator operation||Looks ok.|
|Detector problems?||See notes above.|