Tohban Report 2014-07-09
From RHESSI Wiki
|Start Date:||2 Jul 2014|
|End Date:||9 Jul 2014|
|Tohban:||Lindsay Glesener (Vice Tohban: Säm Krucker)|
|Next Tohban:||Me again|
|List all reports|
The Sun was very quiet for most of the week, but activity has picked up a bit, with 2 M flares yesterday.
We continued to anneal the Ge detectors. The intent was to anneal for 10 days at a temperature of 100 deg C. As described below, we didn't stay at full temperature for that entire time due to a couple more anomalies.
2014-Jul-6: Another cryocooler anomaly occurred, similar in character to the one that happened a week earlier. The cold-tip temperatures rose at the same time as the current decreased (only slightly, this time) and accelerations increased. Based on the experience last week, the heater setpoint was dropped by 30 degrees, during the first pass for which the anomaly was apparent. This lowers the temperature of the coldplate and will keep the cold tip from becoming too warm (which could cause damage to it). After conferencing of the operations team, tohban, and other RHESSI scientists, it was decided to try to "unbind" the cooler piston and displacer by taking two actions: first, the cryocooler power was increased for about a minute. No obvious change in cold tip temperature was apparent. Second, the cryocooler power was turned off for several minutes. During this time, the cold tip temperature began to obviously rise, so the power was turned back on. By the time of the next passes, the anomalous behavior had reversed itself, i.e. cold tip temperatures fell back down toward their expected values and the cryocooler acceleration/current returned to normal values. It is not clear if (a) the problem cured itself on its own, (b) the extra kick in power helped, or (c) power cycling the cooler helped. It is possible that the commanded operations had a beneficial effect, but it is also possible that the piston and displacer became unbound on their own.
2014-Jul-7: Another anomaly occurred. This one was shorter in duration than the others. Since the anomalous behavior was apparently correcting itself, no corrective action was taken. However, the heater setpoint was left at a low value (70 C) at the last pass, just in case another anomaly were to occur during the back orbits.
2014-Jul-8: No anomalies. The heater setpoint was turned up on the first pass of the day to bring the annealing temperature back up. The cold plate took about the entire day to warm back up to ~100C. (Note that annealing still occurs even when the detectors are at <100C, but higher temperatures are better.) On the last pass of the day, the heater setpoint was again set low (to 70C) to protect the cold tips on the back orbits.
2014-Jul-9: No anomalies. Once again, the heater setpoint was turned up on the first pass of the day. This day brought us to the end of the scheduled warm phase of the anneal. Even though we had not remained constantly at 100C for the entire annealing period, it was decided to end the warm phase as scheduled. (Annealing at 70-100C isn't as good as 100C, but reversal of radiation damage still occurs.) The heater was turned off on the last pass of the day to start the cooldown.