1. Turn off the RGA filament and disconnect it.

2. Record the pressure and then close the angle valve and gate valve on the RGA line to isolate it from the system.

3. Turn off the backing and turbo pump and let the turbo pump spin to a stop by slowly leaking the chamber. The slower the safer.

4.Slowly open the vents on the chamber and the turbo pump. Making sure not to raise the pressure too fast.

5. Once done venting the chamber, open the lid by removing the bolts and prying the lid open with a long flat head screw driver.

6. Removed previous parts and placed them into clean bags. Place new parts inside of the chamber and group them together close to the center.

7. Place the lid back onto the chamber and tighten the bolts in a circular pattern until tightened all the way with the wrench.

8. Make sure all vents are closed and turn the backing pump back on.

9. The turbo pump can be turned back on when the pressure reaches e-1 torr.

10. Wait until the chamber reaches a pressure of e-6 torr before opening the angle and gate valve on the RGA line. After the RGA line is open and the pressure is still below e-6 torr, the RGA filament can be turned on and a leak test of the lid should be performed.

11. After the leak test shows no leaks, proceed with starting the low temp bake.

I measured the temperature of the flanges where some of the electronics will go and I found that the RGA flange was at 55C and the two full range gauges were at 65C. I also stopped bake 9 to cool down for measurement.

Leak tested each flange and weld and only found two flanges to have noticeable leaks with the electron multiplier on. These were the turbo pump flange and the RGA flange that connects to the cross. The RGA one is rather new as it has not had a measurable leak before and it was around 2 e-8. We then applied the new sealant to these two flanges as directed by the instructions on the packaging.

Then after waiting a few minutes for the sealant to dry we started the bake. We got the PID controllers set to 120 after many steps and we checked the temperature of the flanges throughout this increase. The flanges never reached 70C with the electronics still left on it. The RGA was left on as well.

Below is the data for the most recent bake. I believe the chamber is cleaner than it is actually showing as the RGA data was still getting lower while the data was being taken. I will take the data again tomorrow just in case. Still, the data shows that the chamber is basically as clean as it was before bake 10 and this means further power testing can proceed.

Helium leak tested the chamber again today to check if the sealant changed anything. The two primary target flanges from last time have improved significantly with the flange from the RGA on the cross now being below 2e-14. While the turbo pump flange was leaking at a rate of 4e-13. Much better than what it has been before.

Took more data today and the chamber and elements are showing an even lower HC level than we have gotten before. It is safe to say that the elements are not contaminated and out gassing HC into the chamber.

I ended the bake of the UHV system (that began on Monday) at 6:23 pm today by switching OFF both PID controllers. The heaters elements were run at max power (24 V DC / 200 mA per element) during this bake, and I left them powered at the same level.

At the time, the instrument readings were as follows:

• Left high-limit controller: 138 C
• Right high-limit controller: 128 C
• Left PID controller: 100 C
• Right PID controller: 100 C
• Main volume pressure: 8.17e-7 Torr
• RGA volume pressure: 4.63e-7 Torr

Summary

Following Wednesday's cleanroom cleaning [333], we proceeded to vent the vacuum chamber, remove the heater elements and their mount structure, and install the FROSTI reflectors. The reflectors are the final components to undergo RGA testing before the FROSTI prototype can be assembled. After installing the reflectors, we pumped the chamber back down and initiated a 48-hour 125 C bake.

Vacuum Vent

At ~1:00 pm, we shut off power to all eight of the FROSTI heater elements. Prior to shutoff, all were operating in vacuum at roughly 300 C. We then waited approximately 30 minutes for the elements' temperatures to fall below 50 C.

At this point, we isolated the RGA volume from the main volume by closing both gate valves, leaving the RGA volume to continue to be pumped through the bypass line. We then backfilled the main volume via the needle valve connected to one of the 2.75" ports. Once the pressures had equalized, we removed the chamber lid via our usual procedure (requiring only a small amount of flathead-screwdriver prying) and extracted the heater element assembly.

Reflector Assembly

We then removed the FROSTI reflectors from their protective packaging (for the very first time) on the cleanroom tabletop. We tested the fit of the Macor and stainless steel hardware in the reflectors' tapped holes. The Macor standoffs and bolts appear to fit perfectly. However, the 1/4-20 tapped holes for joining the two reflector halves are too shallow by ~1/4". As a temporary fix, we used some on-hand stainless steel washers (which had already been cleaned and baked) to securely fasten the two halves together. In the final assembly we will replace these with slightly shorter 1/4-20 vented bolts.

Pumpdown and Bake

The two fastened reflector halves were placed inside the chamber, sitting on top of the two mounting legs (see attached photos). We then reinstalled the lid. In order to rough the main volume, we isolated the RGA volume from the pumpline (by closing the bypass line valve), shut down the pumps, and then backfilled the pumpline via the manual vent valve on the turbo pump.

Once the pressures had equalized, we opened the 6" gate valve separating the pumpline from the main volume and powered on the roughing pump. Once the main volume pressure fell below 0.5 Torr, we powered on the turbo pump as well. The main volume pressure reached 5e-6 Torr within ~30 minutes, consistent with previous experience, and was continuing to slowly fall.

Lastly, we initiated a 125 C bake-out of the entire system following our usual procedure. We plan to run this bake for 48 hours (i.e., through the end of the day Friday).

It should be noted that we can not have the zero length reducer and the gate valve on the same arm as they both have blind tapped holes. We need to decide if we want the gate valve or not as if we do, we will need to use the 3 inch long reducer.

Important Measurements:

From the back of the flange to the back of the RGA: 25.25 in

Height from bottom of the blank to the bottom of the chamber: 2.75 in

We will be configuring the RGA line to remove the spherical cube from the system. Currently our plan for the new design is to connect a 4.5" to 2.75" Reducing Cross to the gate valve on the vacuum system. It will be orientated vertically with the turbo pump on top coming off the end will be a 90 deg elbow. On the bottom there will be a 4.5" to 2.75" Zero length reducer attached to that will be a Tee on one side the pressure sensor and the other the RGA. Connected to the elbow will be the calibrated leak. 

The only parts not readily available are the ZLR and the 2.75" gaskets

[ Luke, Cynthia, Michael, Xuesi, Anthony ]

Started work around 12:45

We vented the chamber first and once it reached atmospheric pressure we started taking apart the RGA line.

We removed the parts in this order: Calibrated leak, RGA, Pressure gauge, 2.75" Blank on Tee, 2.75" Tee, all 1.33" Blanks on the cube, 4.5" feed through port, and finally the cube. Everything went smoothly after every part was taken off we covered the ends in Aluminum foil to maintain cleanliness. 

We then started the assembly of the new line. The parts were added in this order: Reducing cross, ZLR, Tee, Cal leak, RGA, 90 deg Elbow, and Pressure sensor.

We left off the Turbo pump as of now because we weren't able to find a 1" post not in use and we didn't want to put too much weight on the cross. We also noticed that the RGA might not fit on its probes because of a slight tilt to the cross and by extension the Tee. If this ends up being a problem we might need to remove all the parts connected to the cross so that we can reposition it so that the 2.75" rotating flange is connected to the gate valve.

Ended work around 4:00

[ Luke, Jon ]

Started work at 11:00

As mentioned in my previous post the RGA was not clearing the table because of a tilt in the cross. So I removed the 90 deg elbow, loosened the bolt securing the Tee to the ZLR, and removed the cross from the gate valve. I then spun around the Tee on the bottom so that the cal leak would be pointing in the right direction and connected the rotating 2.75" flange of the cross to the gate valve. I then added the small turbo pump to the top of the cross. 

Then with the help of Dr. Richardson, we made some adjustments to how the Tee was oriented with respect to the cross and how the cross was with respect to the table. So that the cal leak and RGA would fit on the table. After that we made some changes to the bolting of the ZLR to reducing cross replacing the 2.00" bolts and nuts with 1.75" bolts and nut plates. We did face some difficulty with half of the 2.00" bolts which required a bit of torque to get them out. 

Finished work at 2:20 

Things to do:

Before we start pumping down the system again Dr. Richardson wanted two other changes to be made. To replace the 2.75" to 1.33" conical reducer with a zero length reducer. He also wants the bolts that hold the main turbo pump to be replaced with nut plates. 

I plan on starting this work on Friday (7/12) before pumping down over the weekend

Today, I borrowed a bolt extractor drill bit from the machine shop to remove some stuck bolts from the zlr. Before starting, I laid down a sheet of aluminum foil on the work table and wiped down all the tools I was going to use. I began by drilling a small pilot hole and then enlarged it with a 5/32 drill bit. However, when I attempted to use the bolt extractor, it didn't grip the bolt effectively. Our bolts were too seized, causing the extractor bit to repeatedly slip instead of gaining traction.

[Luis, Luke, Tyler]

Vacuum chamber parts were finally received and assembled. After whipping down the parts, the blank was removed from the reducing cross. Then, the zero-length reducer was attached. Lastly, we installed the T that had the argon leak and RGA. The final pump down showed signs of an improved seal since the pressure dropped quite fast. This pressure is well bellow the limit required to use the RGA, argon test leak could be performed some time next week.

[Luke, Luis, Jon, Tyler]

On the 22nd Dr. Richardson showed Luis, Tyler and I how to preform a leak test with the RGA. We did the initiall test and found a few leaks two were particuarly bad highlighted in orenge below. To try and remidy this we planned on replacing the copper gaskests on the leaking flanges. We then began taking the two problem flanges off, but seven of the eight bolts holding on the turbo pump were over tightened and had seized. So after we got them off we postponed the rest of the work to the next day.

On the 23nd Luis and I reattached the badly leaking flanges with new copper gaskets. We then preformed the Helium leak test with the RGA. As seen in the table below we weren't able to majorly changed the leaks in the two flanges.

[Luke, Tyler]

On the 27th Tyler and I ran the RGA leak test again with the electron multiplier on. These were the leaks we measured. The chamber's overall pressure was at ~6e-8 torr. 

[Luke, Luis, Cinthia, Michal, Tyler]

On the 26th Cinthia, Michal, and I took off the insolation on the vacuum chamber and re-routed it to include the new RGA volume. 

The next day Luis and I finished up the last of the flanges to be attached. We attached the Pirani gauge with a conical reducing nipple to the 2.75" port on the vacuum chamber. We then preformed the Helium leak testing, both flanges were quite low the 2.75" flange had a leak of 1.68e-10 torr and the 1.33" flange of 5.5e-12 torr. The leak on the 1.33" flange was so low it was difficult to know how much of it was real and how much was just noise.

[Luke, Tyler, Jon]

On the 3rd we set up the pid controllers for the heater tapes and after putting on the insulation we started heating them up. We first brought it to ~50C and let it stabilize, there was about a 6-7 degree difference between the RGA and the barrel temperature, with the barrel being higher. We then brought it to 60 then 70C it still maintained the slight difference between the RGA and barrel temperatures.

Here is a table of the temperatures of the flanges connected to electronics as I left it.

Notes: I removed the electronics from the pressure gauge (main volume) because while it was below the required threshold it was still quite high compared to the other flanges.

On the 5th I had tried to start baking the vacuum chamber however certain parts of the chamber were getting too hot and causing the controllers to shut off. So I turned them off so that the next day I could rearrange the temperature probes. I then on the 6th set them up so that instead of overshooting the temperature they would be a little low in places.

After being left over night the cooler parts of the vacuum chamber got much closer to the desired temperature of 120C.

Here is a table of the temperatures of the sections of the chamber. Note: After these measurements were taken the PID controllers were set to 125C.

Here is a table of temperature of the flanges that have electronics.

Other temperatures of note:

The optical table was about 38C

The cleanroom was around 33C (~91F)

I measured the temperature of the flanges and reconnected the RGA turning on its filament. I then turned off the PID controllers.

Here is a table that has the temperature of the different parts of the vacuum chamber.

[Luis, Luke}

Three RGA scans were taken. The improvement in the amount of HC in the vacuum is visible across the different measurements. Images are attached.

The following images compare the RGA scans from 9/23/24, after the first bake with the new vacuum system, with those from 3/14/24, after bake 12 with the old system.

The first image shows a graph of the raw data and includes the calibrated leak for both curves. As we can see, our new system meets LIGO standards of cleanliness.

The second graph contains the plot of the normalized data.

The following figure displays data acquired on 10/09, and it shows that we are no longer below the cleanliness standard. Also, the system's pressure went up to 1.9x10^-8 Torr (approximately 7x10^-9 Torr previously). This might be due to a leak somewhere in the system. More tests will be performed later.

[Luke, Luis, Mary, Ma]

On 10/22/24 Luke, Ma, Mary and myself ran a leak test, the results are displayed below. The overall pressure of the vacuum was 2.0e-8 and the temperature readings were 26C for the RGA and 25C for the main volume.

[Luke, Luis, Mary, Ma]

On 10/22/24 Luke, Ma, Mary and myself ran a RGA scan, the results are displayed below. The overall pressure of the vacuum was 2.0e-8 and the temperature readings were 26C for the RGA and 25C for the main volume.

As we can see, the vacuum is passing cleanliness standards again.

[Luis, Luke, Ma Michael]

The isolation test was conducted on the vacuum system. Every pump was turned off under vacuum, and pressure measurements were taken every minute for 15 minutes. The results are displayed in the sheet linked at the end of this report. The pressure of the main volume dropped very slowly.

The pressure of the RGA Volume dropped in an exponential manner. The test had to be paused at 11 minutes due to concerns about the pressure exceeding the lowest permitted level for the RGA filament.

After the ISO test was performed, we attempted to tighten the bolts of the small turbo pump on the RGA Volume. However, we noticed that the pressure had increased by nearly an order of magnitude, going from 3.27 × 10^-9 Torr to 1.45 × 10^-8 Torr when both volumes were separated. We conducted a leak test for that particular flange and found a concerning leak of 2.15 × 10^-8 Torr, which had previously been 1.9 × 10^-9 Torr. We believe the copper seal was damaged during the ISO test.

View the results sheet

Chamber temperature: 23C

Chamber Initial Pressure: ~1.8e-8 main, ~3.5e-8 rga

Did another leak test after monday's work to check how the seal was holding up initial leak was 5.5e-9. I then tried to tighten the bolts a bit more the leak rose to 1.9e-8 about a factor of 4 change.

I checked another flange to confirm that I was preforming the test properly. I measured the elbow to pressure sensor to be 2.2e-11 aproximatly what it was earlier in the month (1.9e-11). 

I ran another isolation test. It is still exponetial. Graph attached.

Thoughts:

I belive at this point that it is a knife edge issue when replacing the gasket I checked both flanges and the new gasket. The tp knife edge seemed perfectly fine, the gasket had very minor scratches, and the reducing cross had very small imperfections on its edge. 

We may want to try and use the liquid sealant or get annealed gaskets for 4.5"

[Luke, Luis]

After the gasket replacement performed on Monday (11/18/24) we let the vacuum pump down to UHV pressure for a couple days. Today (11/20/24) we measured the pressure to be 5.30*e^-9 with a temperature of 22C, and we performed a leak test and RGA Scan.

Here are the results:

1. Macor spacer (drawing: LIGO_Redesign_Macor_Spacer_Drawing_v4.pdf attached below), quantities: 40
   • No defects, damages observed
   • Parts are free from grease/ machining fluid
   • Wall thickness of 1 mm appear to provide sufficient stiffness to part
   • Images of parts: Macor_spacer_0.jpg, Macor_spacer_1.jpg
2. Macor 5-40 UNC screw (drawing: LIGO_Redesign_Macor_Screw_Drawing_v6.pdf attached below), quantities: 20
   • One screw broke, location of break: should edge between head and shaft (see image Macor_screw_5.jpg )
   • All other screws look ok, no damage observed, clean surface overall
   • Images: Macor_screw_0.jpg , Macor_screw_4.jpg

Below is the procedure we will follow to assemble the FROSTI prototype.

1. Install SS guide rods and bottom Macor spacers in bottom reflector
2. Install AlN elements on top of bottom Macor spacers
3. Install upper Macor spacers on top of AlN elements
4. Feed unterminated power and RTD leads through slots in upper reflector
5. Install upper reflector, using guide rods to slowly lower into position
6. Install vented SS bolts for reflectors; Macor bolts for heater elements
7. Remove SS guide rods
8. Bundle power and sensing cable with PEEK cable ties and SS cable mounts
9. Terminate power and sensing cable bundles with PEEK DB25M connectors

FROSTI assembly began today. After a final set of RGA scans were taken, the vacuum chamber was vented and the reflectors were removed. The chamber was then resealed and pumped down again. 

Today we completed the installation of the Macor hardware and heater elements between the two reflector halves. Tomorrow we will route, bundle, and terminate the power and sensor cables.