[Jon, Cao]
1. Re-routing of cables
We re-routed the connections between the turbo pump and its fan to the controller. Instead of going through the side of the server rack, they are now routed along the the cable tray and came down from the top of the server rack.
2. Planning for vacuum assembly re-configuration
While preparing for our first pump-down, we notices that RGA pump line gate valve, at its fully closed position, is higher than the height of the chamber lid. The full range gauge attached to the RGA line, while not that high, can also cause obstruction during removal/ installation of the vacuum lid. The calibrated leak, eventhough is now running within the perimeter of the optical table, it stills introduce weak points that are susceptible to damage if personnel installing chamber lid may lean onto it. Thus we made a few suggested modification to the vacuum chamber assembly:
- Move the entire RGA arm to the mirrored CF port, where the Up-to-Air valve is at
- Move the Up-to-Air valve to the calibrated leak port
- Move the calibrated Ar leak the main chamber full-range gauge port
- Move the full-range gauge to the RGA line port
3. First test pump-down
- With all valves closed, we started scroll pump, pump line quickly got down to 6.08 mbar from atmospheric 1000 mbar (measured by Pirani gauge, channel 3 on controller )
- We open Lesker angled valve and let the RGA arm pumped down, Pirani gauge read 6.3 mbar while the full-range guage on RGA line reads 4.9 mbar ( channel 1 on controller )
- We open the pump line gate to expose the pump to the main volume, all gaugues readout immediate rise back up 1000 mbar. After 3 minutes, we started to see channel 3 slowly dropped down. A minute later channel 1 and 2 (main body) also dropped down. The slow pressure dropping speed and 6.3 mbar measured earlier got us suspected that there is some large leaks
- We proceed to tighten all the ports as the vacuum is pumped down. In particular, we found that large feedthrough port still required a lot of tightening up
- As we tighten up all the ports, after 40 minutes, the gauges are now
- Channel 1 : RGA line full-range gauge: 2.55E-1 mbar
- Channel 2 : Main chamber full-range gauge: 2.60E-1 mbar
- Channel 3 : Pump line Pirani gauge: 2.94E-1 mbar
Compare this to the scroll pump manual , Table 1, page 3, the ultimate pressure of the scroll pump is 2.5E-1 Torr (3.3E-1 mbar), we thus managed to achieve scroll pump ultimate pressure
- Turn on turbo pump : Change turbo pump controller from REMOTE to FRONT PANEL mode by pressing both "COUNTERS" and "MEASURE" buttons at the same time, select "MODE=FRONT"
- Shorting interlock pin: since we do not have an interlock signal for the controller, use the provided DB-9 connector that has pin 3 and 8 shorted and connect this to the P1 IN connection at the rear of the controller (see attachment 1 )
- Press "START" on the controller to start the turbo pump
- The pressure readout from the gauges quickly dropped down. After 3 minutes, the Pirani range is maxed out at 0.5E-3 mbar. After 20 minutes, we recorded the following values:
- Channel 1 : RGA line full-range gauge: 1.50E-5 mbar
- Channel 2 : Main chamber full-range gauge: 1.89E-5 mbar
- Channel 3 : Pump line Pirani gauge: 5.0E-4 mbar
This is Medium vacuum , we want to further reduce this by 2 orders of magnitude. However, we can run RGA test + helium leak test at this pressure
- Turn off turbo pump, wait for 10 minutes, turn off scroll pump, open Up-to-Air valve, all pressure gauges indicated pressure returned back to atmospheric pressure
3. To-do actions
- Run RGA test to get information about contamination status of vacuum
- Implement suggested changes in section 2
- Check and modify suspected poor connection: Pirani gauge on pump line. A gap can be seen between connection. There's no good way to tighten it with the screw. Maybe use threaded pin + hex bolt?
- Controller communications
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