Radhika and I were able to connect to the temperature controller using telnet. We simply reassigned the IP address of the temp controller to fit in the IP address range of the router/network. i.e. if the router is 184.108.40.206 then the temp controller might be 220.127.116.11. This shows that the router and network are working correctly again.
I was able to connect to the router (the one on top of the switch in the rack next to the orange tool drawers) and reconfigure it using the same internal IP as found labeled and mentioned in . The router now has a different external IP that I wrote on the router (twice). The network/router and switch is now working in the lab.
Update: It turns out that the router reset itself somehow. so any settings/ port forwarding that was set up before has probably been wiped out and would need to be set up again.
SSHing into the QIL needs to be set up again.
I've attached cooldown data from 6/21-6/24. Unexplicably, the CTC-100 stopped logging temperatures at ~50 hours after the start of cooling, or around 5pm Wednesday. The red logging indicator was definitely on at 3pm Wednesday, but it was off when I checked in Thursday afternoon. It must have somehow been disabled in between. On the bright side, the temperature of the workpiece stabilized at 66K. I had checked in at 53 hrs, 62 hrs, and 64 hrs and noted the temperatures by eye (green data points on attachment 2).
The time constant for the workpiece is ~ 36.4 hrs, about the same as the previous run (tau = -40/ln(100/300)). While no improvements were made on this front (cooldown still very slow), it stabilized 6K below the previous run.
The RTD at the cold head recorded a shoot-up in temperature right at the beginning of cooldown, which makes Stephen/me think that it debonded from the cold head. This temp reading would have been informative for our model, but we will verify it's status when we open up. We can find a better bonding mechanism for the next cooldown.
[Update] I let the chamber warm up over the weekend, and brought it up to room pressure on Monday 6/28. Next steps are to open up and investigate the cold head RTD and make improvements to bonding mechanism, if necessary. We will assess any other improvements (model driven) before the next cooldown.
I accidentally powered down and restarted the TP-link safe stream router and now nothing will connect to it. Not even things that are plugged into it. I can't even connect to the router's setup screen. I have no idea how to solve this issue short of resetting the router. I don't know how it was configured before so I will not reset it because I don't know how it was configured.
I brought DAC2ADC_test.py code from the 40m to test in the QIL. I added a parser arg for the matrix root name (see attached code). I am running into the same problem as I did at the 40m where the channels seem to be locked to their values. I attached (attachment 2) the results text file that shows that for all inputs the outputs are the same. In the GDS screen the ADC is in red but I'm not sure how it got there or how to fix it.
run the test with these commands in the QIL
$ cd IanMacMillan
$ python DAC2ADC_Test.py -e 'C4:TST' -m 'cdsMuxMatrix'
One improvement that we could make to the code is have it zero out all of the matrix elements before it starts.
Background: There are currently 4 available RTDs for the large cryo chamber (henceforth named Megastat). We originally had 1 for the workpiece, 1 for the heater, 1 for the inner shield, and 1 for the outer shield. During the last sessions with the chamber open, the RTDs were moved around. Now there is 1 for the workpiece, 1 for the baseplate (bottom lid), one for the outer shield, and 1 for the cold head. These locations are marked in the diagram (attachment 9).
On Wednesday 6/16, we opened up the chamber and removed the shields and coldplate. We added foil to the inner surface of the bottom lid (attachment 10) and attached an RTD there (we forgot to take a picture). Stephen made a new foil collar, and we decided to push it against the chamber walls as a better alternative to having the foil touch the coldplate (attachment 6). We added an extra layer of aluminized mylar to wrap the copper braid, and we fed another RTD through the braid tube to be attached to the coldhead. We lastly placed the coldplate and shields back in place.
On Friday 6/18, I attached the remaining RTDs (coldhead, outer shield, workpiece). We decided to remove the aluminum foil previously covering the coldhead, due to of fear of shorting to the tube wall. I taped several pieces of mylar together to cover the coldhead and insulate it from the wall (attachments 1-3). I placed the mylar contraption into the T (attachment 4) and then closed the bottom flange. I placed back the shield lids and the main lid of the chamber (attachments 7-8). I tried to pump down, but the pressure was stabilizing on the order of 1e-1 torr. Unsure of why the pressure wasn't decreasing, I turned off the pump and left for the day.
Today 6/21, I touched base with Stephen and we realized I forgot to replace the copper gasket in the bottom flange of the T. I then unscrewed and replaced the gasket. I pumped down and the pressure reached on the order of 1e-4 torr, so I proceeded with cooling. After a few hours I could see that the cold head RTD was reading a temperature around 180K. We will extract and plot cooling data late tomorrow or Wednesday.
Lastly, a chamber diagram is attached (attachment 9). The 4 RTD locations are marked by a red 'x'. The chamber components are numbered in blue (detailed below):
3. Inner shield
4. Outer shield
5. Copper braid (wrapped with mylar)
6. Cold head
8. Baseplate (bottom lid)
RTD thoughts - we have just been using the sensors that were provided, without noticing their constraints or deficiencies.
Planning for next steps:
I was searching an I2 (Iodine) cells back to the days of the laser gyro.
I found a likely box at a very tricky location. Took the photos and returned to this tricky place.
2021/Jul The box was moved to the OMC lab (KA)
We hit another dead-end with leak hunting the IR labs dewer (we replaced screws and helicoil on the valve connection but there is still a big leak). We cleaned the flange and O-ring with isopropanal and replaced the threads with helicoil but still get the same sort of leak where we only hit 1E-2 Torr after 5 minutes of pumping and stablize around 1E-3.
After turning off the pumping station, the pressure rose quickly to 1Torr (in roughly 10 minutes or so).
[Stephen, Aidan, Wednesday 09 June]
Summary and Plan:
Troubleshooting steps taken:
Summarizing heater trends from Wednesday, 6/9. Reiterating from post , I ran the CTC-100 temp controller's auto tune routine to adjust PID coefficients for the heater. I then set the setpoint to 123K (operating temperature); the controller takes in the workpiece temperature as feedback. The heating data for this period is attached.
It took under 30 minutes for the temperature to rise from 72K (current cooling limit) to within a degree of the setpoint, 123K. The power delivered to the heater (bottom plot of first attachment) stayed below 25W, the limit we hardcoded. The workpiece temperature rises smoothly and plateaus around the setpoint, without significant overshooting. The controller holds the setpoint temperature pretty well thereafter. The second attachment is zoomed in on the workpiece temperature alone.
This run served as a test of the temperature controller's stability at the desired setpoint. Moving forward, we will continue to improve the cooling capacity of the chamber guided by our model. Once we optimize how cold we can get, we now know the heater can hold us at the desired temperature setpoint.
Code for simple heat transfer modeling can be found here: https://git.ligo.org/voyager/mariner40/-/blob/master/CryoEngineering/qil_simple_heat_transfer.ipynb
My original 1D cooldown script modeled conductive cooling along the copper braid as: Pcool = k * A/L * (T - T_set); where Pcool is the cooling power, k is the thermal conductivity of copper, A is the cross-sectional area of the braid, and L is the length of the braid. I changed the code to instead use the tabulated power vs. temperature points for the CH-104 coldhead, taken from Paco's script qil_heat_estimate.ipynb. The first figure compares the interpolated curves from the tabulated values (at 50Hz and 60Hz operation), to the original conductive transfer model (50K setpoint). The original conductive power-temp relationship is linear, which overestimates the cooling power at high temperatures. Switching to the tabulated points results in more realistic model. Moving forward, I intend to use the 50Hz interpolated curve.
The script considers radiative heating to the coldplate from the the chamber bottom (rough aluminum) and the outer shield (coated in aluminum foil). It assumes over a long period of time that the inner shield and coldplate temperatures are equal.
The second figure shows the results of this model alongside the actual coolddown data extracted from the CTC-100. It is clear that the model is not accounting for additional radiative heat sources that would explain the slower cooldown and higher final temperature. Adding in model complexity is my current focus.
Today I attempted to auto tune PID coefficients for the heater, so that we can reach and maintain a setpoint of 123K with appropriate ramp-up. The workpiece was around 72K originally. For auto tuning, I set the max power for the heater to 25W. I adjusted the lag time to 30s, and changed the setpoint to 72K so that the tuning response measured how stable the system is when being perturbed from our set point. The auto tune process ran without an error; however, by default the tuning mode switched to "step" tuning, and I am not sure why this occurred. The tuning took roughly 5 minutes to complete. The final message is attached; the adjusted parameters were:
Lag: 125.8 s
Time constant: 271.9 s
I was expecting the adjusted output to be new PID coefficients, but I noticed that the PID coefficients did seem to change after this process. To begin warmup to 123K, I changed the setpoint to 123K and let the heater do its thing (the feedback temperature is set to that of the workpiece). The heater power stabilized to around 17W, and the temperature of the workpiece reached within a degree K of the setpoint within 30 minutes. I am letting the temperature hold at 123K overnight and plan to return tomorrow morning to check on it and extract the heating data for plotting.
Quick log establishing the maximum power for our thermal actuation:
Heater: HSA25100RJ from TE, unknown sourcing. Acetone wiping cleaned off p/n and markings from body, should engrave at next opportunity, but [Attachment 1] from many months ago shows the p/n. Note that this is not the current mounting configuration - [Attachment 2] is more similar to current mounting. Anyway, according to the datasheet (now added to the QIL wiki at Documentation > Manuals) this heater is rated for 25W and has a resistance of 100Ω.
Leads: unknown, and not super important unless we had tiny hair conductor - I am not in lab presently, but it appears from our connector (Lesker FTACIR19AC) that we must have 20-24 AWG,
Carrying the 7, the current through the Heater will be 0.25 A at max actuation, and the 20-24 AWG insulated copper leads will have plenty of ampacity for this load (plus, they are cooled, so normal current capacity considerations fly out the window a bit).
Conclusion: 25W actuation will be the limit that we will apply in the CTC100 temperature actuation routine.
From first trials yesterday, the response at ~20W (at starting temperatures around 80K) appears to be on the order of 1 degree per minute, which should be just fine for actuating to maintain a +/- 1 degree constant setpoint with static thermal loads. More to follow on trials implementing temperature control.
Note that the QIL Wiki points to the DCC (which contains a budget that was helpful resources to trace these purchases), the datasheets and other documentation, and also points to the QIL Cryo Vacuum Chamber photo album, which hosts the images below.
I extracted cooldown data from the CTC100 USB around 1pm today (~50 hours of cooldown). I've attached a log plot below. The heater RTD seemed to be behaving weirdly at the beginning, but soon stabilized and cooled as expected.
I estimated the time constant for the workpiece: 50 hr/ (300K - 90K) = 0.24 hr/K = ~860 s/K
I'll be curious to see the results of Radhika's thermal model - I am suspicious of this thermal strap contact to the base plate. It would be good if we could instead make a copper mating plate:
After Thursday's work, we resumed on Friday and lifted up the coldplate to access the collar and baseplate. Stephen added metallized mylar wraps to the peek cylindrical spacers [pic 9, 10]. He took out the cylindrical collar and baseplate (previously there to minimize contact between the colplate and chamber bottom) and replaced them with a foil collar [pic 13, note this is before pushing down the foil over the PEEK spacers]. We re-inserted the coldplate.
In order to wrap/insulate the copper braid, we inserted 2 sheets of metallized mylar into the vacuum tube to surround the braid [pic 11, 14]. We cut the mylar wrapping so that it did not short to the outer shield. We also confirmed that the copper braid is not shorting to the inner shield hole (there was clearance for the shield to be lifted before hitting the braid). The mylar extends to the coldhead, which we then wrapped with aluminum foil, making sure not to short to the walls of the tube [pic 12].
We switched the foil wrapping from the inside to the outside of the outer shield, so that any radiative transfer from the inner shield to the outer shield would be absorbed as much as possible (not reflected back). We placed both shields back and bolted down the copper braid loop and workpiece. We re-attached the RTDs, then placed in both shield lids (without bolting them down) and stopped for the day.
Today I checked on the chamber setup and closed up. I started the vacuum pump and it made abnormally loud noises, indicating something was off. The percentage sign continued to flash, indicating that the pump was not reaching 80% speed. I performed 2-3 power cycles, which did not solve the issue. We will pick up to debug the issue early this week.
[update 02 June 2021]
Pumpdown and cooldown were successfully started this morning - Radhika retightened the green leak valve and pumps started just fine. We will check trends on Friday and likely will allow cooldown to proceed over the weekend.
We are both working on adding all of our photos to the photo dump at the ligo.wbridge QIL Cryostat Photo Album.
This morning I vented and opened up the chamber to add aluminum foil and other insulation. Stephen's order of mylar sheets, peet sheets, and G10 rings came in today and I picked it up from Downs.
- cut narrow rings of 0.01'' thickness peet sheet and inserted into the main hole of the inner/outer shields, to prevent shorting to the copper braid [pic 6, 2, 3]
- added foil to the inside of the outershield and outside of the inner shield, poking holes for all viewports [pics 4,5]
⁃ unclamped the copper braid from the coldplate and the RTDs from all locations (shields, heater, workpiece mount) to prepare for lining baseplate with foil [pic 7]
Tomorrow we plan to wrap the shaft of the copper braid with metallized mylar and an additional layer of foil. I left both shields outside of the chamber so that tomorrow we are ready to remove the cold plate and add foil below.
Radhika, feel welcome to post full cooling data to this entry, or to your original - up to you!
I tried Krytox around the O-ring and also tightening the screws around the valve. The leaking persists at roughly the same rate.
I tried pumping down the JPL PD chamber to test the new PD at cryo temperatures. Unfortunately, the chamber can;t get past about 6E-3 Torr with the pump on. As soon as I turned off the pump the pressure rose to around 2 Torr over 20 minutes or so.
I extricated the chamber from the pedestals, flipped it and removed the bottom plate. I cleaned the O-ring with isopropanol and wiped down the mating surface on the chamber (also with iso). I replaced the plate and tightened the screws. Then I returned the chamber to the table and reconnected it to the vacuum system. I tried pumping down once again but I saw pretty much exactly the same situation as before (pressure bottoming out around 6E-3 Torr and then rising quickly again when the pump was turned off).
I guess it's possible that the O-ring is damaged - although I couldn't see anything obivous. We didn't mess around with the viewport (when we replaced the diode a few weeks ago) so I'm hoping there is no issue there.
Instant gratification McMaster sourcing (PO S519341, submitted earlier today)
Should be able to integrate some of these items soon - they arrive Thursday, and Radhika will check to see if anything works for the setup as-is, or make requests for Stephen to cut on Friday.
future Mylar source - https://www.professionalplastics.com/MYLARFILM
- update: Radhika called Professional Plastics and they said we cannot order metallized mylar online, but we can call them back and place the order. Stephen called later and Sarah said she had to get a quote from a supplier, and will be in contact. Thickness range: 0.001-0.014 in.
future PEEK source - https://www.professionalplastics.com/PEEK_SHEET-ROD-BAR: thickness range: 0.25-2 in. (units not specified, but I assume inches).
future PEEK source - https://www.boedeker.com/Product/PEEK-Virgin-Natural: thickness range: 0.062-4 in.
exp plot tip: If you use the "grid" feature of matplotlib and plt.semilogy(), the exponentials will look like straight lines, so we can just read off the time constants with a ruler.
Also, as we talked about earlier today, we should make some analytical estimates for the various heat loads, and also put them into the model.
For protecting from radiation, all of the surfaces which are NOT shiny-polished should get wrapped in something shiny (UHV Al foil, with the shiny side out).
I suggest wrapping with foil:
I attach here a photo of the radiative shielding of a Purple Pepper Plant (PPP), to reduce the radiative coupling to the environment. This prevents the soil from drying out in the sun so fast.
Today I pulled the cyro chamber cooling data from the temperature controller. Cooling started on Friday 5/21 around 1:45pm.
The final temperatures reached at ~3:15pm today were:
outer shield: 253 K
inner shield: 168 K
heater (off): 151 K
workpiece: 150 K
The temperature curves (see attached) seem to be leveling off, so I'm not sure things will get too much colder. In the meantime I've reinserted the USB to resume temperature logging.
[Radhika, Stephen remote]
After leaving the cryocooler's compressor running overnight, Radhika found all RTDs reporting room temperature. The noises coming from the compressor were normal, and all operating conditions were consistent with QIL/2504. However, the cryocooler was silent (valve motor not starting).
It turned out that the cryocooler power cable, unplugged during installation efforts (pictured below), had not been reattached. After turning off the compressor, plugging in the power cable, and turning on the compressor, the cryocooler began making normal noises and apparently operating normally. Radhika reformatted the USB drive collecting data from the temperature controller.
Cooldown began at 1:45pm today (Friday). We will check in again on Monday.
During these troubleshooting efforts, we referred to the Cryocooler and Compressor manuals, found at the QIL Cryo Vacuum Chamber Wiki.
I've returned the Keithley Source Meter unit
- The unit (Keithley 2450?2460?)
- A power cable
- A pair of banana clips
- the transistor test fixture & triax cable/connectors
Following up from Stephen's last post. Today I completed the outstanding tasks he outlined, with the exception of connecting a com cable to record and trend cooldown from the temperature controller. For today's cooldown we are still using the usb flash drive.
The RTD connected to the workpiece (spring clamp) took some wrestling to get stable temp readout, so I had to reclamp it. Other than that, I was able to close up the radiation shields' lids and the chamber lid straight away.
I initially tried pumping down but the backing pump was very loud, not reaching full speed, and pressure wasn't decreasing. Stephen realized the KF joint on the side of the chamber was never sealed up (just wrapped in foil) --> obvious major leak. We didn't have any blanks to seal it up, so I replaced the KF port with a blank flange at the conflat joint.
Ready to pump down once more, I ran into an error message from the turbo pump but performed a power cycle and it disappeared. Pumped down and reached a millitorr before turning on cryocooler.
I plan to pop by tomorrow morning before the cryo meeting and can share consequent updates then.
Good progress toward pumping down, with a setback (impact unknown while we reach out to Karthik).
The following is the list of remaining actions before we have cooldown data:
We are both working on adding all of our photos to the photo dump at the ligo.wbridge QIL Cryostat Photo Album. We will then collaborate to add some of the most interesting images to this log!
As of last Thursday (5/13), the new vacuum tubes had been selected and bolted in. We fixed the copper braid to the cryo-cooler: the braid was folded in half, with the loose ends bolted to the cryo-cooler and the folded end fed through the vacuum tubes into the chamber. The folded loop was bolted down to the baseplate. The copper braid was pulled tight and thus has no slack. Aluminum sheets were used to wrap frayed areas of the copper braid to prevent shorting to the tube walls, though this needs to be revisited. We also still need to address shorting to the inner/outer radiation shields.
It is important to characterize the noise levels of all instruments used in the current PD testing setup. We generally expect ~5uV/rHz of ADC input noise. Verifying/correcting this value will be key to ensuring that our overall gain is enough to amplify various signals above the ADC noise floor.
I terminated the input to ADC channel 31 with a 50-ohm BNC terminator. I used diaggui to generate the resulting amplitude spectra, with 0.03 BW (attached). To convert counts to volts, I took a range of 20V divided by 2^16 counts, resulting in a scaling of 3e-4 V/count. I plan to conduct another test to confirm this value (feeding a known voltage and comparing to the output). In the meanwhile, the resulting noise level consistent with our expectation of a few uV/rHz.
Note that the back panel connectors are Triax, not the usual Coax.
Going back to a 1D heat transfer model, and matching Stephen's numbers for the area and length of the thermal strap, I confirm that the conductive power of a single strap is indeed heavily constraining the cryocooler capacity. For my simulation the peak power for a 0.5m copper strap with area 6.71e-5 m^2 is 1.06 Watts with an average of a few hundred mW during the cooldown.
The main difference with respect to Stephen's numbers is that I account for temperature dependent conductivity and heat capacity, include a radiative sink (surrounding vacuum tube at room temp), and take the strap to be made of RRR 500 Cu.
Attached is the predicted temperature at the end of the strap as a function of time when the operating point of the cryocooler is set to 123 K. Note the cooldown delay caused by the single half-meter strap (with respect to the cryocooler cold head).
Looks very clear, thanks. I guess the next thing to do is
- Updated schematic of the current PD testing setup, including noise levels for current electronics
- Table of desired measurements for new setup, with expected signal levels, accuracy, and readout values
This log investigates cooling through our current planned copper braid connection (which is standing in for an intended rigid bar linkage that is WIP)
The question is, can we get [cooling power of cryocooler] out of our baseplate through this copper braid?
Cooner Wire P/N NER 7710836 BOF (oxygen free copper)
Sumitomo CH-104 (manual from Wiki) has 77K coldhead cooling capacity of 34 W, and from the quote, 50K cooling capacity of just under 40 W.
Adequate cooling power of this setup depends on the radiative heat load and conductive losses; for our purposes, we can imagine that tens of Watts will be needed, and circle back to more precise heat budgeting.
Conductive Heat Transfer
Q = A / L * (Uint_T2 - Uint_T1)
Uint_T = the integral of thermal conductivity between T and 4K, see below table [ETP OFE Copper, W/m]. Note these are values from literature not from our copper braid's spec sheet (no such properties available from vendor).
Table of Thermal Conductivity integral values, between T and 4K. Unit = W/m. Source: Ekin, Appendix 2.1
20K = 14000, 40K = 40600, 50K = 50800, 60K = 58700, 70K = 65100, 80K = 70700, 100K = 80200, 120K = 89100, 140K = 97600
A = 6.71e-5 m^2
L = 0.5 m (estimate)
T2 = 123 K (intended workpiece temperature)
T1 = ? (coldhead temperature, unknown, we will pick a value and calculate)
Q(T1_80K) = 6.71e-5 m^2 / 0.5 m * (89100 W/m - 70700 W/m) = 2.46 W
Q(T1_20K) = 6.71e-5 m^2 / 0.5 m * (89100 W/m - 14000 W/m) = 10.07 W
It appears that the copper braid's capacity for conductive heat transfer will constrain the tens of Watts of cryocooler capacity. This is even before we consider imperfections in the clamping interfaces and similar real losses.
Fixes for this constraint might involve adding parallel linkages (increasing area) or shortening the strap length.
It would be interesting to compare this to the anticipated capacity of the flexible strap in the original design - future work.
Two sessions this week were spent working toward simplification of the cryocooler connection.
We needed to order a couple of off the shelf vacuum fittings to complete the intended design - image attached.
I purchased a set of telephoto and macro lenses for the lab. They're stored in the tool cabinet.
WIP log entry - working on getting all of our ideas down on the page, then will sort and elaborate.
We met to discuss a range of topics relating to the path ahead for the Cryo Vacuum Chamber. This reconsideration of the current state of things is necessary as the chamber needs to become the workhorse for PD characterization efforts soon, in addition to a range of other tests (large suspension tests will be conducted in a different chamber, yet to be designed)
Will sort the above into some sort of timeline (such as short term / long term).
Ruminations about the future chamber for suspension work:
Posting link to PD testing google doc here:
We put the preamp output directly into a multimeter and observed the same fluctuating behavior as the DAC channel was changed.
We're bypassing the relay to see if that makes any difference. The old relay wiring (to be bypassed) is shown in the attached diagram. That didn't do anything.
We're looking at filtering the DC output by 5kHz to see if there are any resonances at higher frequencies that might go away. Changing SR560 output for AC path to DC and setting gain to 1 on that unit. Also changing gain in FM31 filter bank from 1E-3 to 1. The results are shown in the attached time series. The channels FM30 and FM31 see the same thing. The only difference is that FM31 goes through an SR560 with a 0.03Hz pole (6dB).
Success by bypassing the DAC bias voltage. We switched to a 300mV bias voltage from a function generator. Doing that removed the causal PD voltage drift induced by changing the laser diode current set voltage (see the last time series). So the issue is some weird coupling into the DAC bias voltage.
[Aidan, Radhika, Nina]
We noticed that the DC channel readout (FM30) of the JPL A1 photodiode is drifting around. What we observe with no light on the photodiode, is the DC output drifiting around. It gets particularly bad when we apply voltage to other DAC channels.
For example, the attached plot shows the DC voltage from the photodiode as I change the set voltage to the laser diode driver. To be absolutely clear, the laser driver itself was completely powered off. I'm just varying the voltage going into the set point BNC connector on the back of it.
For reference, the set up is:
DAC (300mV bias) > relay > PD > relay > FEMTO preamp (1000x gain) > ADC channel FM30
QIL Cryo vacuum chamber cooldown was not as successful under the new configuration (radiation shielded by cylindrical outer + inner shields, cold finger thermally strapped to baseplate).
--> Karthik's Si cantilever workpiece was stable at 240 K.
--> Cold Finger was stable at 200 K - there is significant thermal loss between the cold finger and the workpiece.
--> Inner shield was stable at 250 K - seems to be somewhat decoupled from the baseplate; not very satisfied with the current state of the shielding.
Will need to re-examine some of the connections, which were not optimal (especially the improvised dog clamped strap-baseplate interface). Fabricating an adapter piece for the thermal strap which will be bolted 4x on a 2" x 2" grid. Might also look into a new thermal strap which could interface with baseplate directly.
Also will need to consider options to decouple outer shield from inner, and double check that shield orientation has no other solution (hoping there's an answer to the question, why would outer shield be coupled to baseplate?)
Data - cooldown 20210408 (CSV = raw, XLSX = Stephen's plots) in Box Folder [Voyager\MarinerBox\CryoEngineering\CSVlogs]
Description - 6 day cooldown. Layout described in QIL/2552. The radiation shields were installed and thermal strap was connected to baseplate. The cryocooler was turned on/off at the start/end of the data collection, and the in-vac heater was not powered on at all.
I posted a video tutorial of the diode replacement.
Aidan and I removed the old PD from the cryo chamber in order to start testing C3 (plan for tomorrow, 04/02).
- Brought chamber up to room pressure, disconnected readout wires and vacuum pump.
- Picked up chamber and placed it upside down on makeshift support stand (see pics).
- Unscrewed mounting plate and 2 inner insulation plates to reveal mounted PD.
- Had trouble unscrewing PD mount, since the screws were very close to the PD and we had to be careful not to slip and cause damage. Started with 2 side screws, then bottom (hardest), then top.
- Successfully removed PD and put away. Placed chamber components back in place without bolting in.
- Plan is to mount PD C3 in chamber tomorrow and begin testing.
To aid in taking photos of these diodes, I put a USB microscope on Anchal's desk - you can grab it from there. I use it with mac Photo Booth, but it should be easy to use with any camera application.
Also, I recommend buying a macro lens(es) for cell phones from Amazon or B&H. Label them with the QIL lab sticker so they don't disappear.
Karthik had completed in-chamber alignment efforts during a prior visit. In air alignment also completed following viewport move.
0) Removed lid for access to chamber.
--> posted demo video to ligo.wbridge QIL Cryostat HowTo Playlist.
1) Mounted RTDs to final positions - locations are Heater (cryo varnish+cigarette paper, pictured in IMG_8558 curing under weight of upsidedown bolt), Inner Shield (cryo varnish+cigarette paper, pictured in IMG_8559), Cold Finger (spring clamp), and Workpiece (spring clamp).
--> Final chamber layout may be viewed in IMG_8562
--> Note that Karthik's Si cantilever, mounted vertically in the right of the image, is NOT bolted down to the baseplate (just located on baseplate by dog clamps, held down via gravity). This will need to be investigated to enable workpiece cooling.
2) Installed radiation shield lids - no bolts to expedite the process and to see if there is any bulk motion during pumpdown and thermal cycling.
--> note that the lid for the outer radiation shield seems to interface with the current shield orientation perfectly; if there was a mismatch, it would point toward the inverted orientation being intended, but this seemed pretty definitive.
3) Installed the cryostat lid - final positioning and alignment made easier by teflon rails!
--> posted demo video to ligo.wbridge QIL Cryostat HowTo Playlist.
4) Pumped down - single button press to turn on pumping station.
--> note that it took about 1 hour for both gauges to reach a few mTorr.
5) Confirmed function of heater - set PID setpoint to 350 K and enabled outputs, observed temperature rise in heater RTD.
--> note that PID autotuning should be done at steady state with workpiece RTD, before enabling outputs again!
6) Turned on cryocooler - flip power lever and turn on green system switch.
--> start time was 10 am.
7) Started temperature datalogging to USB - press dull red indicator dot on upper right corner of CTC-100 once, and note that indicator is now bright red.
8) Remaining photos posted to the ligo.wbridge QIL Cryostat Photo Album
I'm attaching my rough first draft of the QIL photodiode testing schematic. Please provide comments for fixes/improvement!
1. Radiation Shields located (in TCS lab), unwrapped, fitted up.
Location in TCS Lab - IMG_8351
Removed lid and placed adjacent to chamber (cleared a little space, used 3 plastic flange covers to make nonmarring surface safe for lid and o-ring - IMG_8353
Fit up as installed - IMG_8354
Comments on the fit up - I looked at all of the apparent sources for insights into Rahul's original design intent - QIL elog 2276, DCC T1800308-v1, wiki for Cryo Vacuum Chamber. It appears that Rahul never decoupled the upper outer radiation shield from the cold plate, which seems like a strange omission. Chris and Raymond also appear to have been wrapping their heads around the intended layout, they came up with the fit up in QIL elog 2429 and sketch from QIL elog 2430. I will revisit their sketch at a future opportunity, but I went with something closer to 2429 as I was concerned about the height misalignments they described. Note that the height misalignment appears in Rahul's T1800308 CAD (see T1800308-v1 screenshot) so who knows what's "correct". I'll work on finalizing D2100310 CAD with radiation shield to capture the true current dimensions and fit up, to hopefully avoid such issues in the future.
2. Radiation Shields installed in Cryostat. Sequence was important here, as were a couple of improvised solutions to shortcomings of the existing parts.
Dog Clamps placed on bottom plate (to stand off bottom radiation shield bottom lid; not pictured, I think I placed some alumina washers on the dog clamps as well, not sure though anymore!). Also pictured are the usual PEEK legs for cold plate - IMG_8355
Bottom radiation shield bottom lid placed on dog clamps spacer, and bottom radiation shield cylinder placed on bottom lid - IMG_8356. Seems likely that the bottom radiation shield would be better configured upside-down.
Bolted cold plate down onto legs, with cold plate decoupled from bottom radiation shield - IMG_8357
Outer radiation shield installed and inner radiation shield installed (both needed to be tipped into place gingerly, but both cleared the cold finger cylinder with the flange removed. The heater also passed through the apertures successfully - IMG_8358
2x Alumina washers placed under outer radiation shield, inner radiation shield on cold plate - IMG_8374
Cold Flange reinstalled, though one of the brass SHCS was sheared - this was due to over torque, with 20 in*lb applied by mistake. Correct torque is 10 in*lb. The remaining 3 bolts were tightened to 10 in*lb. - IMG_8360
Top view of radiation shield apertures and cold plate grid - IMG_8375
Thermal strap interface to cold plate - dog clamps required due to strange spacing of clearance holes. - IMG_8376
- Unscrewed outer and inner insulation plates.
1. Viewport swap to nozzle that is not occluded by cryo shield = complete. All bolts on both Active Ion Gauge and Viewport have been torqued gradually (about a half turn at a time, around the clock dial) until the conflat seal was metal-to-metal. Periscope on damped optical rod was rotated to make room for replacement.
Before viewport swap - IMG_8487
After viewport swap - IMG_8502
2. Cryo RTD repair = complete. Two RTDs had been damaged during prior mounting efforts by me. I was able to repair the clamped RTD at the single damaged solder joint. I was able to repair the former Al-Block RTD by replacing the RTD element, and making a new direct attachment (not preloaded, not varnished to the aluminum block anymore)
Materials and set-up for solder repair - IMG_8491
Repaired Clamp-2 RTD - IMG_8494
Damaged Al-Block RTD - IMG_8492 (note short length between kapton strain relief and aluminum block was not ideal, one lead had already fractured and the second soon followed at the slightest touch)
Repaired, remounted Al-Block RTD - IMG_8495 (heater sandwiched underneath threaded adapter, clamp threaded into adapter, sandwiching RTD at top plane)
Remounted Clamp-2 RTD - IMG_8496 (RTD clamped at cold flange, strap is mounted)
Remaining Clamp-1 and Varnish RTDs are free - IMG_8497
Current readouts of CTC-100 controller, with repaired RTDs now behaving (note need to rename the Al-Block RTD) - IMG_8501
3. Next steps:
- Karthik to install clamps, align in-air relay, and confirm positition of radiation shield aperture.
- Remaining free RTDs to be mounted; current RTDs are mounted at Heater and Cold Flange, would be good to mount RTD at Work Piece/Clamp and at Outer Radiation Shield.
- Radiation shield lids to be installed (might be easiest to install Outer Radiation Shield RTD after installing lid)
- Mount lid, install bolts, pump down, turn on cryo cooler, the usual!