Laura Lambert wrote:

Laura Lambert wrote: Laura Lambert wrote:  Tuesday, May 23, 2017, 14:42 UO2/C green was prepared May 16th, 2017. The cast peeled off the glass nicely May 17th, 2017. Initial UO2 powder used = 50.25g (Inventory R-01032A, UO2 + bottle = 876.80g before use) Graphite powder used = 10.32g Green cast dried UO2/C + organic mass = 61.70g  The green was rolled up and wrapped in a piece of graphite sheet. The Ta-target boat was wrapped with 1 long layer of heat shield and installed in evap1 today. Chamber pumped down today. Target boat will be ramped up to 520A at the rate of 0.1A/min. Vacuum limit stop at 5.0e-5 Torr, backing off at 6.0e-5 Torr. IG1 = 4.80e-6 Torr Tapped up to 30A, 0.45V Waited ~1hr, vacuum stable. IG1 = 8.3e-6 Torr Initiating auto-ramp  Wednesday, May 24, 2017, 09:26 IG1 = 5.5e-5 Torr TGHT = 64A, 0.72V Vacuum currently yo-yo-ing. Changing vacuum limits to attempt to speed up process. Vacuum limit stop at 1.0e-4 Torr, backing off at 5.0e-4 Torr. Once vacuum settles and vacuum starts to drop will adjust limits again accordingly.  Wednesday, May 24, 2017, 11:17 IG1 = 1.2e-4 Torr TGHT = 69A, 0.74V TGHT direct readout = 66A, 0.73V Thermometer attached to TP = 41.0C Room temp = 24.0C Wednesday, May 24, 2017, 13:16  Vacuum going well. Stable yo-yo-ing at current vacuum limit. TP = 41.5C, RT = 23.9C IG1 = 1.2e-4 Torr TGHT = 71A, 0.77V Increasing vacuum limit stop to 2.0e-4 Torr. Thursday, May 25, 2017, 13:03 Vacuum has stabilized. TGHT = 188A, 1.85V IG1 = 2.2e-5 Torr. Adjusting vacuum limits so when 2nd phase starts, vacuum does not spike. Vacuum limit stop at 5.0e-5 Torr, backing off at 1.0e-4 Torr.    Friday, May 26, 2017, 13:40 Everything tripped off this morning at around 4:30am This was not due to the vacuum spiking as one would expect. No power bumps according to  ISAC controls. Looking back on elogs  [see elog i.d. 145] evap1 had also tripped off during the last round of carbonizing UO2, however last time everything tripped off ~60A. For last trip off the water valve remained open and on. This time  WV1 showed yellow in the TGHT epics box, off under WV epics box, but black [open] in the WV epics box diagram [see screenshot for better understanding]. Water valves are closed - confirmed in person - water wheels not turning. Trip-off occured ~275A. Vacuum was stable at trip-off point; IG1 ~6e-6 Torr  Reason: currently unknown.        Friday, May 26, 2017, 15:43 Starting pumping down again this afternoon while trying to understand trip-off - no progress on that end. IG1 = 4.9e-6 Torr Tapped up to 40A, 0.24V Vacuum spiked to 2e-5 Torr Backed off to 35A, 0.20V Showing lower voltage output than the last round that had tripped off...but ramping is so early on/ low current, hard to tell... Vacuum stable. IG1 = 5.4e-6 Torr Target boat will be ramped up to 275A [trip-off point] at the rate of 0.1A/min. Vacuum limit stop at 5.0e-5 Torr, backing off at 6.0e-5 Torr.   TP = 37.9C, RT = 25.2C

 Monday, May 29, 2017, 08:21

Initially it looks like not enough time had been allowed for the vacuum to settle before initiating the auto-ramp resulting in the vacuum spiking and tripping off the system.

A closer look shows that is not the case.

Note: the vacuum limits were set to stop at 5.0e-5 Torr, backing off at 6.0e-5 Torr. 

The TGHT started to back off when the vacuum was ~6e-6 Torr, this is considered a good vacuum and should not have caused the system to initiate backing off yet.

Over the course of ~1min, evap1 had backed off all the way down to 0A.

At this point the vacuum was now up to ~1.75e-5 Torr and still rising.

~34min after the TGHT had reached 0A, the vacuum eventually reached 8e-4 Torr and tripped off the evaporator.

See photos attached.