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ID Date Author Type Category Subject
2564   Wed May 5 00:34:14 2021 ranaSummary2um PhotodiodesUpdated PD testing schematic / measurement table

Looks very clear, thanks. I guess the next thing to do is

1. ask if this will work for all the various PDs we want to test,
2. is it good enough for all our requirements, and then we
3. draw a new diagram for the new setup, incorporating what to keep and what circuit to make ourselves
2566   Mon May 10 15:38:36 2021 ranaSummary2um PhotodiodesKeithley connections

Note that the back panel connectors are Triax, not the usual Coax.

2568   Wed May 12 15:43:30 2021 AidanSummary2um PhotodiodesChamber is leaking

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.

2578   Wed May 26 18:38:25 2021 AidanSummary2um PhotodiodesChamber is leaking

I tried Krytox around the O-ring and also tightening the screws around the valve. The leaking persists at roughly the same rate.

 Quote: 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.

2586   Fri Jun 11 07:42:54 2021 StephenSummary2um PhotodiodesChamber is leaking

[Stephen, Aidan, Wednesday 09 June]

Summary and Plan:

• Poor sealing at the output valve (The Gap) needs to be resolved.
• Planning to install #4-40 helicoils today (chamber will remain sealed, will need to remove output valve and cover output orifice, then transport the chamber to the WB EE shop for redrilling of holes.)
• Meeting with Nina and Aidan this afternoon to iterate one more time.

Troubleshooting steps taken:

1. Aidan took us through the full sequence of pump down and disassembly to bring me up to speed.
2. We opened the lid and inspected the old o-ring.
1. Signs of plastic deformation and of small flecks of particulate near sealing surface - good idea to change.
3. We found new o-rings in a box from the Cryo lab, and one of these was swapped in after a good wipedown with IPA.
4. Upon pumpdown, Aidan compared behavior and found no meaningful change to rate of pumpdown or stable pressure in e-4 torr range after 10+ minutes.
1. By valving off [chamber + gauge] from pump line, it was clear that there was a leak in that volume, as within seconds the pressure rose from e-4 torr to e-2 torr, and stabilized at _(need to confirm - e0?)_ torr over ~10 minutes.
5. Attempted to squirt IPA along o-ring seals, but there was not good access to the sealing surfaces, so this was a null test
6. Looked closer at all of the chamber features, and noticed The Gap between chamber wall and chamber output valve, pictured in [Attachment 1]. Not good! But promising as a leak source.
1. Three of the four screws were found to be loose due to apparent thread damage.
7. IPA was squirted into The Gap at stable pressure of e-4 torr, but no change in pressure was noticed.
8. Longer #4-40 screw reinstallation was attempted, and I could feel a small amount of pull at the very tip of the screw, but tightening the screws led to that small pull to fail as well - need to rework.
9. The Clamp was installed and The Gap was closed [Attachment 2].
1. When isolated from the vacuum pump, the chamber pressure progressed more slowly. Within seconds, we were at e-3 torr, and over 10 minutes the pressure stabled at e-2 torr, about 30x lower pressure per Aidan's records.
Attachment 1: IMG_8865.JPG
Attachment 2: IMG_8881.JPG
2588   Fri Jun 11 16:48:31 2021 Aidan, StephenSummary2um PhotodiodesChamber is leaking

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).

 Quote: [Stephen, Aidan, Wednesday 09 June] Summary and Plan: Poor sealing at the output valve (The Gap) needs to be resolved. Planning to install #4-40 helicoils today (chamber will remain sealed, will need to remove output valve and cover output orifice, then transport the chamber to the WB EE shop for redrilling of holes.) Meeting with Nina and Aidan this afternoon to iterate one more time. Troubleshooting steps taken: Aidan took us through the full sequence of pump down and disassembly to bring me up to speed. We opened the lid and inspected the old o-ring. Signs of plastic deformation and of small flecks of particulate near sealing surface - good idea to change. We found new o-rings in a box from the Cryo lab, and one of these was swapped in after a good wipedown with IPA. Upon pumpdown, Aidan compared behavior and found no meaningful change to rate of pumpdown or stable pressure in e-4 torr range after 10+ minutes. By valving off [chamber + gauge] from pump line, it was clear that there was a leak in that volume, as within seconds the pressure rose from e-4 torr to e-2 torr, and stabilized at _(need to confirm - e0?)_ torr over ~10 minutes. Attempted to squirt IPA along o-ring seals, but there was not good access to the sealing surfaces, so this was a null test Looked closer at all of the chamber features, and noticed The Gap between chamber wall and chamber output valve, pictured in [Attachment 1]. Not good! But promising as a leak source. Three of the four screws were found to be loose due to apparent thread damage. IPA was squirted into The Gap at stable pressure of e-4 torr, but no change in pressure was noticed. Longer #4-40 screw reinstallation was attempted, and I could feel a small amount of pull at the very tip of the screw, but tightening the screws led to that small pull to fail as well - need to rework. The Clamp was installed and The Gap was closed [Attachment 2]. When isolated from the vacuum pump, the chamber pressure progressed more slowly. Within seconds, we were at e-3 torr, and over 10 minutes the pressure stabled at e-2 torr, about 30x lower pressure per Aidan's records.

Attachment 1: IMG_3002.jpg
Attachment 2: IMG_3001.jpg
2600   Fri Jul 9 10:57:58 2021 RadhikaSummaryCryo vacuum chamberCTC100 temperature extraction

I wrote a python script to extract temperature data from the CTC100 via ethernet, for monitoring cooldown/warmup of Megastat. This is intended to replace USB data extraction, which requires the user to manually insert/remove the stick and plug into a computer.

The script queries the CTC100 every ~60 seconds for the latest temperature values (the frequency can be supplied as a parameter, but default is 60s). The script writes line-by-line to a .txt file and also plot the outputted data once collection is terminated.

Here is a gitlab link to the script: https://git.ligo.org/voyager/mariner40/-/blob/master/CryoEngineering/ctc100_controller.py. It is also found on the QIL workstation at /home/controls/CTC100/ctc100_controller.py. To run from the workstation, open terminal to /home/controls (home). Then:

cd CTC100
python ctc100_controller.py --filename='tutorial'

Here, 'tutorial' stands in for the desired filename for the outputted data. The script will start pulling data and will print each line to the terminal. It will continue printing and logging the temperature values until the user hits Ctrl+C in the terminal. This will terminate the script and output the final data file. The file is saved as a .txt file in /home/controls/CTC100/data.

Attachment 1: terminal1.png
2601   Fri Jul 9 13:44:39 2021 RadhikaSummaryCryo vacuum chamber1D cooling model updates

*Takeaway*: The current 1D cooling model is getting closer to matching our observed cooling trends, mainly in the lower temperature limit. The predicted time constant is still much smaller than we are seeing in reality (by about a factor of 3), but this can potentially be improved by revising specific heat values and/or dimensional estimates for chamber components.

The model uses the known cooling power of the cold head [attachment 2] and considers radiative heat from the outer shield, baseplate (bottom lid), and mylar wrapping around braid. I increased the complexity of the script by solving a system of ODEs (for braid and coldplate temperature) simultaneously instead of assuming the temperatures are equal at all times, and solving only 1 ODE. This resulted in the model's lower temperature limit prediction matching our observed data, at ~66 K.

The model still predicts a much smaller time constant than we are seeing. This is affected by specific heat values for Cu and Al, along with dimensional estimates of the coldplate and braid (AKA how much mass is being cooled). It is possible that these values are being underestimated in the model, which would lead to the smaller time constant. Currently the model uses constant values for the specific heat of Cu and Al (room temperature). But since specific heat increases with temperature, accounting for temperature dependence would lower the specific heat values and shift the model in the opposite direction (towards an even smaller time constant). Therefore I suspect the model is underestimating the mass of the coldplate, though I am unsure if this would completely correct the discrepancy.

If the term (specific_heat * density * volume) of the coldplate (Al) is increased by a factor of 4, the model resembles the data well [attachment 3].

Attachment 1: model_vs_data_7-1.pdf
Attachment 3: model_vs_data_7-1.pdf
2603   Thu Jul 15 23:34:17 2021 KojiSummaryTempCtrlTemprerature Log for cooling down / warming up

Stephen and Radhika worked on the cooling down and warming up of the cryostat with the cold head RTD attached using a spring-loaded screw. No other configuration changes compared to QIL/2599. Here are the temperature log plots. Photos of spring clamped RTD are outstanding, but the clamp is the same as the workpiece pictured in QIL/2599/Attachment 12.

Attachment 1: temp_log_cooldown_20210709_1747.pdf
Attachment 2: temp_log_warmup_20210712_1315.pdf
2604   Thu Jul 15 23:37:53 2021 KojiSummaryCryo vacuum chamberBonding work for the prep of the preliminary suspension test

[Stephen / Koji]

Bonding work for the prep of the preliminary suspension test

- 1" sq mirror-ish polished SUS piece was bonded to a face of the silicon mass. We chose the location right next to a line on the barrel. (Attachment 1)

- The mass was flipped with two more same thickness pieces used for the spacers to keep the mass horizontal.

- A pair of an OSEM and dumbbell-magnet was brought from the 40m (courtesy by Yehonathan). The magnet was glued on the mass at the opposite position of the attached mirror because the optical ports are going to be arranged to share an axis. A piece of cryo varnish was also painted with a piece of cigarette paper at the center of the mass so that we can attach an RTD. (Attachment 2)

Next Things To Do (Attachment 3)

• Vent the chamber
• We will move an optical port to the opposite position of the other port.
• A DB9 feedthru is going to be installed.

• Suspension
• Move the sus frame in the chamber
• Suspend the mass
• Sensor arrangement
• Set up the oplev
• Hold the OSEM at the height of the magnet
• Set up a camera to observe the magnet-OSEM clearance
• We improvise the DB crimping sockets so that we can electrically connect the OSEM (optional)
• Pump down / cool down the chamber
• The main target of the cooling is to check the cooling capability of the test mass mainly with radiative cooling.
• An optional target is to observe the misalignment as a function of the temperature -
• -> Oplev signals are to be connected to CDS / check if CDS is logging the data
• Check if the OSEM/magnets survive the thermal cycle
• If possible we can try to actuate the OSEM / check the LED/PD function at the cryo temp

Attachment 1: P_20210715_170102-1.jpg
Attachment 2: P_20210715_172218-1.jpg
Attachment 3: experiment_plan.pdf
2605   Fri Jul 16 23:28:24 2021 KojiSummaryCryo vacuum chamberSus Test Work 07/16/2021

[Stephen Koji]

We started cooling down of the test mass.

Venting

- Stephen vented the chamber at 2PM. An optical port was moved to see the OSEM from the back.

OSEM wiring

- Brought DSub crimp sockets from the 40m. We picked up 3x 1m LakeShore WCT-RB-34-50 (twisted silver-plated copper, 34 AWG with Teflon insulation). The ends of the wires were dangled so that crimping is possible. A single wire resistance was measured to be ~1Ohm at room temp. (Attachment 1)

- OSEM pin out / backside view (cable going down) (Attachment 2)

|   o   o   o | | o   o   o   |                 Wire   ^ ^ ^ ^ ^ ^---PD K        ---- R3   | | | | |-----PD A        ---- B3   | | | |-------LED A       ---- B2   | | |---------LED K       ---- R2   | |-----------Coil End    ---- B1   |-------------Coil Start  ---- R1

Twisted Pair 1: (R1&B1) with 1 knot  at the feedthru side
Twisted Pair 2: (R2&B2) with 1 knot  at the feedthru side
Twisted Pair 3: (R3&B3) with 1 knot  at the feedthru side

Dsub feedthru in-air pinout (Mating side)

1  2  3  4  5
\ o  o  o  o  o /  \ o  o  o  o  /    6  7  8  9

Pin1 - Coil Start
Pin6 - Coil End
Pin2 - LED K
Pin7 - LED A
Pin3 - PD A
Pin8 - PD K

Pin1-6 R=16Ohm
Pin2-7 Diode V (with Fluke) 1.18V (Pin2 black probe / Pin7 red probe)
Pin3-8 Diode V (with Fluke) 0.7V (Pin3 red probe / Pin8 black probe)

- OSEM pin out / backside view (cable going down)

Suspension installation (Attachment 3)

- The sus frame was moved into the chamber

- We measured the test mass dimension before installation: L 3.977" D 4.054"

- The attached mirror size is 1"x1" made of SUS #8 (?)

- The mass was suspended. The height / rotation of the mass was adjusted so that the reflecting mirror is visible from the oplev window and also the OSEM magnet is visible from the OSEM window.

- The OSEM was placed on an improvised holder. (Attachment 4)

Oplev installation

- ...Just the usual oplev installation. Adjusted the alignment and the return beam hits right next to the laser aperture. This beam was picked off by a mirror and steered into a QPD. (Attachments 5/6)

- The lever arm length is ~38" (960mm) -- 9" internal / 29" external
- The oplev signal is shaking so much and occupying ~50% of the full scale. Added a lens with f=250 to make the beam bigger, but the improvement was limited.

Pumping down

- Started ~8:30PM?

DAQ setup

- Wired 3 BNC cables from the table to the DAQ rack. CHX/Y/S are connected to ADC16/1718ch.

- The real-time processes seemed dead. Looked at [QIL ELOG 2546] to bring them up. TIM/DAQ error remains, but the data stream seems alive now. Leave it as it is.

Cooling

- Temp Logging started. Filename: temp_log_cool_down_20210716_2255.txt

- Cryocooler turned on. ~10:55PM

- Confirmed the cold head temp was going down. The cold head temp is 75K at 0:30AM

OSEM photo

- An example photo was taken from the rear window. The attempt with 40m's Canon failed. Attachment 7 was taken with KA's personal compact camera with a smartphone LED torch. The gap between magnet and OSEM is highly dependent on the view axis. So this is just a reference for now.

Attachment 1: 20210716170727_IMG_0719.jpeg
Attachment 2: 20210716174712_IMG_0723.jpeg
Attachment 3: 20210716195953_IMG_0726.jpeg
Attachment 4: 20210716200005_IMG_0728.jpeg
Attachment 5: 20210716200224_IMG_0734.jpeg
Attachment 6: 20210716200112_IMG_0733.jpeg
Attachment 7: 20210716234113_IMG_0742.jpeg
2606   Sat Jul 17 00:55:41 2021 KojiSummaryCryo vacuum chamberTemp Log 210716_2255

Temperature log for the first 2 hours (Attachment 1)

I wonder why the temperatures displayed on CTC100 and the ones logged are different...?

Attachment 1: temp_log_cool_down_20210716_2255.pdf
2608   Mon Jul 19 15:57:17 2021 StephenSummaryCryo vacuum chamberTemp Log 210716_2255

Uh oh, review of the cooldown plot from the previous cooldown (QIL/2603) shows workpiece temperature of ~92 K at conclusion, while a temperature of 65K was observed in the CTC100 readout (Attachment). The logging of the warmup is consistent with the CTC100 image, as the logging started a few minutes after the warmup was started, and the warmup "5 minutes after starting" temperature of ~ 71 K is a practical temperature.

Seems to be something weird going on here, we will need to have Radhika take a look on her return (and continue taking photos of the CTC100 whenever we stop by).

 Quote: Temperature log for the first 2 hours (Attachment 1) I wonder why the temperatures displayed on CTC100 and the ones logged are different...?

2609   Mon Jul 19 17:21:19 2021 KojiSummaryCryo vacuum chamberTemp Log 210716_2255

Temp Log on Jul 19 2021 17:20

I wonder what is the heat transfer mode for the test mass right now. Radiative? or Conductive through the wires?

Attachment 1: temp_log_cool_down_20210716_2255.pdf
2610   Tue Jul 20 11:33:52 2021 KojiSummaryCryo vacuum chamberA cooling model (Temp Log 210716_2255)

A naive cooling model was applied to the cooling curve.
A wild guess:

- The table temp is the same as the test piece temp as measured on 2021/7/9
- The inner shield temp is well represented by the table temp
- The specific heat of Si is almost constant (0.71 [J/(g K)] between 300K~200K

The curve was hand-fitted by changing the emissivity of the inner shield and the silicon mass. I ended up having the same values for these to be 0.15.
Surprisingly well fitted!

Conductive cooling:
The conductive cooling through the wire does not fit the cooling curve, although the quantitative evaluation of the wire conductivity needs to be checked carefully.

Appendix:
Stephen shared attachments 2 and 3, which contain insights on the wire used to hang the Si mass. .017" diameter Music Wire from California Fine Wire, 2004 vintage, borrowed from Downs High Bay.

Attachment 1: cooling_model.pdf
Attachment 2: IMG_9390.JPG
Attachment 3: IMG_9391.JPG
2611   Tue Jul 20 17:28:30 2021 KojiSummaryCryo vacuum chamberA cooling model (Temp Log 210716_2255)

Updated the model the latest log data with cooling prediction

• The radiative cooling is expected to be the dominant cooling mode.
• It will take ~3 more days to reach 123K. We don't need to wait for it.
• For more informative temp data, we need the temperature of the inner shield and the table.

• We know the cold head temp from the measurement. For the prediction, the constant cold head temp of 65K was assumed.
• The table temp was estimated using conductive cooling model + linear empirical dependence of the conductivity on the temp
• The constant specific heat of the silicon mass (0.71 J/K/g) was assumed. This may need to be updated.
• The radiative cooling is given from Stefan–Boltzmann law with the emissivity of 0.15 for both the shield and the mass.

• The conductive cooling of the test mass was estimated using: Wire diameter 0.017" (=0.43mm), 4 wires, length of ~10cm (guess), no thermal resistance at the clamps (-> upper limit of the conductive cooling)

Radiative cooling already gives us a good agreement with the measured temp evolution for the test mass. The conductive cooling is not significant and does not change the prediction.

Updated the plot with the new data (2021/7/21 12:30PM)

Attachment 1: cooling_model.pdf
2613   Wed Jul 21 14:53:28 2021 KojiSummaryGeneralJul 17, 2021: Canon camera / small silver tripod / macro zoom lens / LED ring light borrowed -> QIL
2614   Wed Jul 21 21:05:59 2021 KojiSummaryCryo vacuum chamberTest mass cooling (2021/07/16 ~ 2021/07/21)

[Stephen and Koji for discussion / Koji for the execution]

1. Temperature Trend

See [QIL ELOG 2611] for the updated temp log and the cooling model.

Considerations for the next cycle:
-> How can we accelerate the cooling? It seems that the table cooling is conduction limited. Improve the cold head connection.
-> We want to move the RDTs
-> How can we improve radiative cooling?

2. Oplev Trend (Attachment 1)

Sum: The beam has been always on the QPD (good). See also Attachment 2

X&Y: In the first few hours the beam drifted in -X and then +X while Y had slow continuous drift in +Y. ~11hours later sudden drift in -Y and totally saturated. Also -X saturation observed @~16hrs. Again +Y drift was seen @~25hrs. The totally saturated in -X and +Y.
They may be related to the drift of various components with various cooling time scale.

Visual check: ~2mm shift in X&Y is visually observed. Attachment 2

-> How can we quantify the drift? What information do we want to extract?

3. OSEM and the magnet

The magnet is intact. And the suspension seemed still free after cooling (Attachment 3)
Significant misalignment was not visible. No visible damage by cooling was found. The coil is alive and the PD/LED are also intact. Fluke showed that they are still diodes, but their function was not checked.

The coil resistance changed from 16Ohm -> 4.2Ohm. For the 16Ohm, 2 Ohm was from the wire. Let's assume we still have 2Ohm overhead -> The coil R changed from 14->2.2. This corresponds to the coil temperature of the order of ~100K. This is not so crazy.

Some actuation current was applied to the magnet. For this test, the oplev was realigned.
First, some ~300mA current pulses were applied to the coil. The ringdown of the yaw mode was visible. Then the DC current of 100mA was applied. This didn't make visible change on the spot position but the data showed that there was a DC shift.

-> We prefer to have a softer suspension for the next test.

4. CTC100 logging

During the cooling we kept having inaccurate data logged compared with the displayed data on the screen of CTC100.
As soon as the cooling logging was stopped, telneting to CTC100 was available. So, I telnetted to the device and sent the data transfer command ("getOutput"). Surprisingly, the returned values agreed with the displayed values.
So my hypothesis is that somehow the data strings are buffered somewhere and gradually the returned values get delayed. From the behavior of the device, I imagined that the fresh telnet connection gives us the latest data and there is no buffering issue.

So I tweaked the data logging code to establish the telnet connection every time the values are asked. The connection is closed after the every data acquisition. I like this as we can also make the test connection between each data acquisition points, although I have not tried it yet. The code is in the same folder named ctc100_controller_v2.py

5. Heating

Now I thought that I did all I wanted to do this evening, so the heater was turned on at ~20:50, Jul 21. The heating power saturated at 22W, which is the set limit.

Attachment 1: oplev_trend.png
Attachment 2: 20210721201333_IMG_0765.jpeg
Attachment 3: 20210716234113_IMG_0742.jpeg
Attachment 4: Screenshot_from_2021-07-21_20-19-09.png
2615   Thu Jul 22 22:03:45 2021 KojiSummaryCryo vacuum chamberTest mass heating in progress (2021/07/21 ~ 2021/07/23)

- Temperature Log updated 2021/7/23 12:00 Heating Ended

- Assuming reaching the room temp at ~30hrs and heating power saturated at 22W: Predicted heat injection 30*3600*22 = ~2.4MJ

Update from Stephen
- Note that we can check logging accuracy against the snapshot (timestamp 20210723_1113).
If my math is correct, this would be time = 37.35 38.35 hours

Update from KA
=> The corresponding time in sec is 138060 sec
The raw data line for the corresponding time is:

138016.839614, 295.805, 306.678, 302.518, 312.401, 0.000, 0.000, -0.001, 0.621, 0.622, 1.429, 0, 0, NaN, NaN, NaN
The values on the photo 295.806, 306.677, 302.518, 312.401 ==> Well matched. Victory!

Attachment 1: IMG-9395.jpg
Attachment 2: temp_log_warmup_20210721_2052.pdf
2616   Fri Jul 23 20:53:40 2021 KojiSummaryGeneralJul 17, 2021: Canon camera / small silver tripod / macro zoom lens / LED ring light returned / ELectronics borrowed

[Returned] Brought one HAM-A coil driver (D1100687 / S2100619) and one Satellite Amplifier (D1002818 / S2100741) from the 40m

Also brought some power cables.

Brought ~1m of 0.0017" (~43um) misical wire. This will make the tension stress be 341MPa. The safety factor will be ~7.

Attachment 1: P_20210723_212158.jpg
2617   Sun Jul 25 21:45:46 2021 KojiSummaryCryo vacuum chamberAbout the radiation heat transfer model

The following radiation cooling model well explained the cooling curve of the test mass (until ~150K)

$\dot{Q}=0.15 A\,\sigma (T_{\rm SH}^4-T_{\rm TM}^4)$

where dQ/dt is the heat removed from the test mass, A is the surface area of the test mass, $\sigma$ is the Stefan-Boltzmann constant, T_SH and T_TM are the temperatures of the surrounding shield and the test mass.

Can we extract any information from this "0.15"?

I borrowed "Cryogenic Heat Transfer (2nd Ed)" by Randall F. Barron and Gregory F. Nellis (2016) from the library.
P.442 Section 8.5 Radiant Exchange between Two Gray Surfaces can be expressed by Eq 8.44

$\dot{Q} = F_e F_{1,2} \sigma A_1 (T_2^4-T_1^4)$

where T_i is the temperature of objects 1 and 2. For us, OBJ1 is the test mass and OBJ2 is the shield. A1 is the surface area of A1. F_1,2 is the view factor and is unity if all the heat from the OBJ1 hits OBJ2. (It is the case for us.)

$F_e$ is an emissivity factor.

The book explains some simple cases in P 443:

Case (a): If OBJ2 is much larger than OBJ1, $F_e = e_1$ where the e_i is the emissivity of OBJi. This means that the radiated heat from OBJ1 is absorbed or reflected by OBJ2. But this reflected heat does not come back to OBJ1. Therefore the radiative heat transfer does not depend on the emissivity of OBJ2.

Case (b): If OBJ1 and OBJ2 has the same area, $\frac{1}{F_e} = \frac{1}{e_1} + \frac{1}{e_2} -1$. The situation is symmetric and the emissivity factor is influenced by the worse emissivity between e1 and e2. (Understandable)

Case (c): For general surface are ratio,  $\frac{1}{F_e} = \frac{1}{e_1} + \left(\frac{A_1}{A_2}\right)\left(\frac{1}{e_2} -1 \right )$. OBJ2 receives the heat from OBJ1 and reradiates it. But only a part of the heat comes back to OBJ1. So the effect of e2 is diluted.

For our case, OBJ1 is the Si mass with DxH = 4in x 4in, while the shield is DxH = 444mm x 192mm. A1/A2 = 0.12.
We can solve this formula to be Fe=0.15. e1 = (0.147 e1)/(e2-0.0178).

Our inner shield has a matte aluminum surface and is expected to have an emissivity of ~0.07. This yields the emissivity of the Si test mass to be e1~0.2

How about the sensitivity of e1 on e2? d(e1)/ d(e2) = -0.95 (@e2=0.07).

Depending on the source, the emissivity of Aquadag varies from 0.5 to 1.
e.g. https://www.infrared-thermography.com/material-1.htm / https://www.mdpi.com/1996-1944/12/5/696/htm

• Assuming Aquadag's emissivity is ~1
• If only the test mass is painted, F_e increases from 0.15 to 0.39 (x2.6)
• If the inner shield is also painted, F_e increases to 1, of course. (pure black body heat transfer)
• If shield panels are placed near the test mass with the inner surface painted, again F_e is 1.
• Assuming Aquadag's emissivity is ~0.5
• If only the test mass is painted, F_e increases from 0.15 to 0.278
• If the inner shield is also painted, F_e increases to 0.47.
• If shield panels are placed near the test mass with the inner surface painted, F_e is 0.33 assuming the area ratio between the test mass and the shield panels to be unity.

It seems that painting Aquadag to the test mass is a fast, cheap, and good try.

2618   Mon Jul 26 01:30:42 2021 KojiSummaryCryo vacuum chamberPrep for the 2nd cooling of the suspension

Updated Jul 26, 2022 - 22:00

1. Reconstruct the cryostat
1. [Done] Reinstall the cryo shields and the table (Better conductivity between the inner shield and the table)
2. [Done] Reattach the RTDs (Inner Shield, Outer Shield)
-> It'd be nice to have intermediate connectors (how about MIllMax spring loaded connectors? https://www.mill-max.com/)
3. Reattach the RTD for the test mass
2. Test mass & Suspension
1. [Done] Test mass Aquadag painting (How messy is it? Is removal easy? All the surface? [QIL ELOG 2619]
2. [Done] Suspension geometry change (Higher clamping point / narrower loop distance / narrower top wire clamp distance -> Lower Pend/Yaw/Pitch resonant freq)
3. [Done] Setting up the suspension wires [QIL ELOG 2620]
4. [Done] Suspend the mass
3. Electronics (KA)
1. [Done] Coil Driver / Sat Amp (Power Cable / Signal Cables)
2. Circuit TF / Current Mon
3. [Done] DAC wiring
4. [Done] Damping loop
4. Sensors & Calibration (KA)
1. [Done] Check OSEM function
2. [Done] Check Oplev again
3. Check Oplev calibration
4. [Done] Check Coil calibration
5. Use of lens to increase the oplev range
6. Recalibrate the oplev
5. DAQ setup (KA)
1. [Done] For continuous monitoring of OSEM/OPLEV
2619   Mon Jul 26 22:49:00 2021 KojiSummaryCryo vacuum chamberAquadag painting

[Stephen Koji]

We decided to paint the silicon test mass with Aquadag to increase the emissivity of the test mass.

Stephen brought the Aquadag kit from Downs (ref. C2100169) (Attachment 1)

It's a black emulsion with viscosity like peanut butter. It is messy and smells like squid (Ammonium I think) (Attachment 2)

We first tried a scoop of Aquadag + 10 scoops of water. But this was too thin and was repelled easily by a Si wafer.
So we tried a thicker solution: a scoop of Aquadag + 4 scoops of water. (Attachment 3)

The thicker solution nicely stayed on the Si wafer (Attachment 4)

We want to leave the central area of the barrel unpainted so that we can put the suspension wire there without producing carbon powder. (Attachment 5)
1.5" from the edge were going to be painted. The central1" were masked.

The picture shows how the Si test mass was painted. The test mass was on a V-shaped part brought from the OMC lab. The faces were also painted leaving the mirror, while the place for RTD, and the magnet were not painted. (Attachment 6)

It looked messy while the painting was going, but once it started to dry, the coating looks smooth. It's not completely black, but graphite gray. (Attachment 7)

After the test mass got dry, another layer was added. (Attachment 8)

Then made it completely dry. Now the mask was removed. Nice! (Attachments 9/10)

Attachment 1: 20210726164254_IMG_0768.jpeg
Attachment 2: 20210726164530_IMG_0769.jpeg
Attachment 3: 20210726164225_IMG_0766.jpeg
Attachment 4: 20210726164957_IMG_0772.jpeg
Attachment 5: 20210726173608_IMG_0774.jpeg
Attachment 6: 20210726174523_IMG_0775.jpeg
Attachment 7: 20210726182715_IMG_0783.jpeg
Attachment 8: 20210726192042_IMG_0784.jpeg
Attachment 9: 20210726192837_IMG_0790.jpeg
Attachment 10: 20210726192853_IMG_0791.jpeg
2620   Wed Jul 28 00:59:47 2021 KojiSummaryCryo vacuum chamberThe test mass successfully suspended

[Stephen Koji]

While Stephen worked on the RTD reattachment, I worked on the suspension part.

- First of all, we found that the magnet was delaminated from the silicon mass (Attachment 1). It was bonded on the test mass again.

- The suspension frame was tweaked so that we have ~max suspension length allowed.

- The first attempt of suspending the mass with steel wires (0.0017" = 43um dia.) failed. Stephen and I went to downs and brought some reels.

- I chose the wire with a diameter of 0.0047" (= 119um) (Attachment 2). ~8x stronger! The suspension was successfully built and the mass is nicely sitting on the 4 strain releasing bars (improvised effort). (Attachments 3/4)

We can install the suspension in the chamber tomorrow (today, Wed)!

Attachment 1: P_20210727_154143.jpeg
Attachment 2: P_20210727_190356.jpeg
Attachment 3: P_20210727_190426.jpeg
Attachment 4: P_20210727_190543.jpeg
2621   Thu Jul 29 00:42:38 2021 KojiSummaryCryo vacuum chamberThe test mass successfully suspended

[Stephen Koji]

• The suspension with the test mass was installed in the chamber again
• Looking at the oplev beam, we jiggled the wire loop position to adjust the alignment approximately.
• The oplev beam was aligned more precisely.

• We intentionally kept the OSEM at the "fully-open" position, while it is still close to the magnet so that we can have some actuation.
• The coil driver was tested before closing the chamber, but it did not work.
The coil itself was still intact, and the mirror was responding to the coil current if the coil current of ~100mA was applied from a bench power supply with the current ~100mA).
So the problem was determined to be external.

• Once we were satisfied with the oplev/OSEM conditions, the inner and outer lids were closed. Then the chamber was closed.

•  Started pump down.
• Started cooling down @18:30 / started temp logging too. Log filename: temp_log_cool_down_20210728_1830.txt

The coil driver issue was resolved:

• It was necessary to take care of the enable switch. Made a DB9 short plug for this purpose.
• The output R was 1.2K (i.e. 2.4K across the + and - outputs). We needed ~10x more to see visible motion of the mass
• e.g. The internal gain of the driver is x1.1. If we connect 5VDC input across the diff input of the driver yields, +11V shows up across the outputs of the final stage.
If the R across the coil is ~100Ohm, we get ~100mA.
• Soldered 6 x  330Ohm (1/8W) in parallel to 1.2K R_out. -> This ended up 51.5Ohm x2 across the coil. Each R=330 consumes ~1/10W. ->OK

Checking the DAQ setup / damping loop

• DAQ setup
• ADC: QPD X->FM16 / Y->FM17 / S->FM18 / OSEM-> FM19
• DAC: CH11 -> Coil Driver In
• Connected FM16 and FM17 to the coil drive by setting C4:TST-cdsMuxMatrix_12_17 and C4:TST-cdsMuxMatrix_12_18 to be 1.0
• It was not obvious if the coil could damp the rigid body modes.
• Actating the magnet caused Yaw motion most. Some Pitch motion too.
• Configured FM16 and FM17 for the damping loop.
• Filter Bank #1: [Diff0.1-10]  Zero 0.1Hz / Pole 10Hz
• Filter Bank #10: [Anti Dewht]  Zero 1&200Hz / Pole 10&20Hz
• Tried various damping gain. The mass was moving too much and the proper gain for the damping was not obvious.
• So, the initial damping was obtained by shorting the coil at the coil in of the sat amp unit. (Induced current damping)
• Once the test mas got quieter, it was found that -0.01 for FM16 could damp the yaw mode. Also it was found that +0.1 for FM17 could damp the pitch mode. (But not at once as the filters were not set properly)

• TF measurement for calibration
• The beam was aligned to the QPD
• The test mass was damped by using the damping loops alternately
• Taken a swept sine measurement Filename: OSEM_TF_210729_0243.xml
Recorded the time, saved the data, and took a screenshot
• This measurement was taken @T_IS=252K / T_TM=268K @t=8hr (2:30AM), Rcoil=15.6Ohm
• Second measurement Filename: OSEM_TF_210729_2147.xml
• @T_IS=172K / T_TM = 201K @t=27.5hr (10PM), Rcoil=10Ohm
• 3rd measurement Filename: OSEM_TF_210730_1733.xml
• @T_IS=116K / T_TM = 161K @t=47hr (5:30PM), Rcoil=?
• 4th measurement Filename: OSEM_TF_210731_2052.xml
• @T_IS=72K / T_TM = 134K @t=75hr (9:30PM), Rcoil=6.0Ohm

OSEM LED/PD

• The Satellite amp brought from the 40m is used as-is.
• The initial OSEM reading was 8.8V, this corresponds to ~30000cnt.
• As the OSEM was cooled, this number was increasing. To avoid the saturation, a voltage divider made of 4x 15kOhm was attached. I didn't expect to have the input impedance of the AA filter (10K each for the diff inputs), this voltage divider actually made 18.24V across POS and NEG output to be 5.212V to the AA fiter. So the voltage division gain is not 0.5 but 0.2859.
• This made the ADC range saved, but we still have a risk of saturating the PD out. If this happens. The PD TIA gain will be reduced before warming up.
-> The TIA and whitening stages use AD822, and the diff output stage uses AD8672. AD822 can drive almost close to rail-to-rail. AD8672 can drive upto ~+/-14V.

There was not enough time for the QPD calib -> Tomorrow

2622   Thu Jul 29 13:11:17 2021 KojiSummaryCryo vacuum chamberCooling progress: Update

The current cooling curve suggests that the radiative cooling factor Fe (black body =1) increased from 0.15 to 0.5.

Update: The test mass temp is reaching 200K at ~27hrs. cf previously it took 50hrs
Update: The test mass temp is 170K at ~41.5hrs.

OSEM illumination & photodetector efficiency has been kept increasing @41.5hrs

Attachment 1: temp_log_cool_down_20210728_1830.pdf
Attachment 2: cooling_model1.pdf
Attachment 3: cooling_model2.pdf
Attachment 4: OSEM_cooling.pdf
2625   Fri Jul 30 12:22:56 2021 KojiSummaryCryo vacuum chamberCooling curve comparisons

In all aspects, the latest cooling shows the best performance thanks to better thermal connection, thermal isolation, and the black paint.

- The cold head cooling is faster and cooler

- The inner shield cooling is faster

- The test mass cooling is faster

Attachment 2: comparison_inner_shield.pdf
Attachment 3: comparison_test_mass.pdf
2629   Sun Aug 1 22:22:00 2021 KojiSummaryCryo vacuum chamberCooling update

The test mass temperature indicates 121K@100hr but there seemed a few sensor glitches for the test mass (𝛥=-4.2K) and the inner shield (𝛥=-0.43K).
So the actual test mass temperature could be 125K.

The temp was read to be 119K@114hr (Attachment 1)

There was very little cooling capability left for the test mass (Attachment 2)

The OSEM reading is now stable @12.3V (Attachment 3)

The raw temp data and the minimal plotting code are attached (Attachment 4)

Attachment 1: temp_log_cool_down_20210728_1830.pdf
Attachment 2: cooling_meas.pdf
Attachment 3: OSEM_cooling.pdf
Attachment 4: cooldown_210728.zip
2645   Sun Aug 15 00:33:15 2021 KojiSummaryCryo vacuum chamberAquadag painting on the inner shield

[Stephen Koji]

We applied Aquadag painting on the inner side of the inner shield.

• Upon the painting work, we discussed which surfaces to be painted. Basically, the surface treatment needs to be determined not by the objects but by the thermal link between the objects.
• We want to maximize the heat extraction from the test mass. This means that we want to maximize the emissivity factor between the test mass and the inner shield.
• Therefore the inner barrel surface of the inner shield was decided to be painted. The test mass was painted in the previous test.
• For the same reason, the lid of the inner shield was painted.
• It is better to paint the cold plate (table) too. But we were afraid of making it too messy. We decided to place the painted Al foil pieces on the table.

• The outer surface of the inner shield and the inner surface of the outer shield: Our outer shield is sort of isolated from the cold head and the steady-state temp is ~240K. Therefore we believe that what we want is isolation between the inner and outer shields. Therefore we didn't paint these surfaces. (note that in Mariner and beyond, the outer shield will be cooled, not isolated, and the radiative link to the outer shield would be strong by design)
• I believe that this is not the ideal condition for the inner shield. We need to model the cryo stat heat load and take a balance between the isolation and the conduction between the outer shield and the cold head so that we gain the benefit of the outer shield as a "not so hot" enclosure.

• OK, so we painted the inner barrel of the inner shield, the lid of the inner shield, and some Al foils (shiny side).
• Stephen made the Aquadag solution. The solution was 2 scoops of Aquadag concentrate + 6 scoops of water, and the adhesion/runniness test was done on a piece of aluminum foil.
• The barrel and the lid were painted twice. Attachment 1 shows the painting of the inner shield cylinder. Attachment 2 shows a typical blemish which necessitates the second coat.
• To accelerate the drying process, we brought the heat gun from the EE shop --> (update - returned to EE shop, see Attachment 3)

• We took some photos of the process. They are all dumped in the QIL Cryo Vacuum Chamber Photo Dump album in the ligo.wbridge account.
Attachment 1: IMG_9636.JPG
Attachment 2: IMG_9632.JPG
Attachment 3: IMG_9646.JPG
2675   Sun Oct 3 08:22:49 2021 AidanSummary2micronLasersStarting data taking and second test of JPL PD A1
• Output going to JPL_PD/data/A1_test2 and DAQ
• Test commenced at 8:20AM and cryo cooler started shortly afterwards
• Once trhough the loop takes about 20 minutes
• Cryocooler on at 8:42AM
2676   Wed Oct 6 13:50:18 2021 AidanSummary2micronLasersStarting data taking and second test of JPL PD A1
• Turned cryocooler off around 1317588441 (about 1:46PM)
• Restarted measurement with output going to JPL_PD/data/A1_test3
• Room is noticeably quieter without the cryocooler on.
 Quote: Output going to JPL_PD/data/A1_test2 and DAQ Test commenced at 8:20AM and cryo cooler started shortly afterwards Once trhough the loop takes about 20 minutes Cryocooler on at 8:42AM

2677   Thu Oct 7 08:07:03 2021 AidanSummary2micronLasersStarting data taking and second test of JPL PD A1
• We're at 164K as of 8AM this morning.
2678   Mon Oct 11 08:35:21 2021 AidanSummary2micronLasersStarting data taking and second test of JPL PD A1

Terminated the data taking at 8:35Am this morning. The termperature traces of the cryo chamber show a couple of discontinuities in the gradient. I don't know what the cause is,

 Quote: We're at 164K as of 8AM this morning.

Attachment 1: Screenshot_from_2021-10-11_08-36-06.png
2679   Mon Oct 18 15:25:14 2021 AidanSummary2micronLasersStarting data taking and second test of JPL PD A1

Initial running of analysis code puts the max QE at ~62 + /- 1% around 130-150K. I want to explore this temperature regime manually and see if we're saturating the PD or not.

3:30PM - Chamber is still under vacuum. Cryocooler turned back on.

Quote:

Terminated the data taking at 8:35Am this morning. The termperature traces of the cryo chamber show a couple of discontinuities in the gradient. I don't know what the cause is,

 Quote: We're at 164K as of 8AM this morning.

2691   Wed Oct 27 10:18:33 2021 Aidan, StephenSummaryCryo vacuum chamberInspection of Megastat post 408K event and pumping timeline

[Aidan]

I've attached a timeline of our inspection this afternoon along with today's pumping timeline,

Here is a brief summary of observations from previous pumping timelines. Today's pump down is consistent with previously observed timelines.

2:17PM – Assessing the impact of the 408K event in the MegaStat

Innershield reached 403K (130C)

2:24PM – Aquadag E service temperature (149C)

Maximum service temperature in air* : 300°F (149°C)

*Service temperature under vacuum conditions is significantly higher. Contact Acheson for specifics.

2:25PM – Bringing Megastat back up to air for initial inspection

2:37PM – chamber is at air

2:41PM – removing bolts

3:13PM – initial inspection looks normal. No elevated amount of black particulates found on surfaces – consistent with or less than the amount seen last time we opened.

Stephen detected faint smell different from last time (“campfire”?)

• One RTD connector did delaminate Aquadag from the inner shield

3:14PM - Stephen reattaching the RTD wiring that had delaminated. I wiped up visible particulates with isoproponal soaked wipe.

3:21PM – putting lid back on

3:30PM – lid on. Screws in finger tight

3:35PM – screws tight – ready to pump

3:40PM – pumping station on

 Time (minutes) Pressure (Torr) Notes 0 7.5E2 Pirani gauge initially 1 7.5E2 2 7.5E2 4 7.5E2 5 7.5E2 7 7.5E2 9 7.5E2 10 7.5E2 11 7.5E2 12 4.3E2 Gauge starts reading decrease 13 2.2E2 14 9.8E1 15 5.5E1 Turbo ON 16 2.9E1 17 1.6E1 Turbo at 44% 18 9.4E0 19 4.9E0 20 1.8E0 Turbo at 58% 21 3E-2 Turbo at 70% 22 1.1E-3 ION gauge readings from here. Turbo at 91% 23 7.5E-4 Turbo at 100% 24 6.3E-4 25 5.9E-4 26 5.5E-4 (Cryo-cooler normally turned on around this time) Not in this instance though 27 5.0E-4 28 4.59E-4 29 4.26E-4 30 4.05E-4

Attachment 1: IMG_5407.jpg
Attachment 2: IMG_5408.jpg
Attachment 3: IMG_5409.jpg
Attachment 4: IMG_5410.jpg
Attachment 5: IMG_5411.jpg
Attachment 6: IMG_5412.jpg
Attachment 7: IMG_5414.jpg
Attachment 8: IMG_5415.jpg
2692   Fri Nov 12 08:21:22 2021 AidanSummary2um PhotodiodesResults from JPL PD: A1-Test3

[Aidan]

Here is the analyzed data from Test 3 of the A1 JPL PD.

• HOM beam QE was performed during the warm up phase. Collimating lens was fixed and beam pointing was optimized at 100mA before each measurement. Likely that not all power was on PD but that distribution was constant throughout measurement. Therefore, good proxy for shape of QE response.
• Manual QE was performed with 25mA current, optimized collimating lens position (and thus the beam size on the PD). The data corresponds to 8.0mm between the lens mount and fiber mount. The beam pointing was optimized before each measurement at 25mA.
• QE projection scales the "HOM beam QE" result to the manual QE measurements to project out expected QE performance vs temperature

Dark current is the output from the Keithley scan - the vertical scale is correct in Amps [ignore question mark]

Dark noise spectra are included for different bias levels and at different temperatures. Stll need to add ADC noise floor for these plots.

Notes from Test 3

6-Oct-2021: done with cryocooler off and temperature increasing

PREAMP GAIN = 1E3

SR560 gain = 500

LD temp set point = 20.2kOhm

Attachment 1: A1_test3_nominal_QE.pdf
Attachment 2: A1_test3_darkcurrent.pdf
Attachment 3: A1_test3_noise_spectra_rev.pdf
2693   Fri Nov 12 10:54:55 2021 ranaSummary2um PhotodiodesResults from JPL PD: A1-Test3

IT would also be good if you could plot the RMS noise around 10 Hz and 100 Hz as a function of the bias and temperature, so we can see what the trends are. And how about post the data and scripts to the elog so we can munge data later?

2703   Thu Dec 16 17:57:15 2021 Radhika, StephenSummaryCryo vacuum chamberMegastat geometric parameters

This ELOG serves as a compilation of known/measured geometric parameters of Megastat. This is informative for thermal modeling of the system, so I wanted to create a centralized reference. A reference to these dimensions has been added to the Wiki page

Chamber specs
Outer Radius = 0.3048 m (12")
Wall thickness = .00477 m (.188")
Height = 0.3048 m (12")
Flange thickness = .0254 m (1")

Outer shield specs
Height = 0.2286 m (9") --> CAD .206 m (8.110")
Thickness = 2.90 mm (0.114") (CAD nominally 3 mm, but 9 gauge aluminum is standard)

Inner shield specs:
Height = 0.205994 m (8.11") --> CAD .192 m (7.559")
Thickness = 2.90 mm (0.114")

Cold plate specs:
Thickness = CAD .01498 m (.5897")

Test mass specs: (confirmed)
Length = 0.1016 m (4")

Copper bar specs:
Length = 0.508 m (20") --> note that center to center length is .440 m in CAD
Width1 = 0.03175 m (1.25") (bulk cross section, could be approximated accross full length)
Width2 = 0.049784 m (1.96") (cross section at cold head bolting interface)
Thickness = 0.011684 m (0.46")

Thickness = .0516 m

CAD (.EASM) is located at https://caltech.app.box.com/folder/131056505764 (File path: Voyager > Mariner > CryoEngineering). Screenshot of current state is added as Attachment 1.

CAD (source file, .sldasm - SolidWorks 2021) may be accessed via the PDM Vault (File path: llpdmpro > voyager > rnd qil cryostat)

Attachment 1: D2000310_y-003_20211222.png
2714   Fri Jan 28 10:31:15 2022 ranaSummaryTutorial videooh no, stap the units madness, aaaaahhhh!!! noooooo!!!!

2772   Wed May 25 14:32:12 2022 RadhikaSummaryEmissivity estimationList of Megastat upgrades for emissivity estimation

This post will serve as a running list of modifications for Megastat for emissivity estimation (brain dump). It is divided into categories:

Category 1: Inner shield / cold plate

We want to cover the cold plate with Aquadag, either directly or by placing aquadag-coated tiles or Al foil on top of the cold plate. It seems the latter approach is preferable, to avoid directly removing and coating the cold plate. Stephen has prepared aquadag-coated aluminum foil which we will soon assess for this purpose. If for some reason it doesn't seem to be sufficient, we will need to identify/design tiles or chunks of aluminum that we can paint with aquadag and lay on top of the cold plate. While we're coating things with aquadag, there are some spots on the inner shield that could use a touch-up.

Category 2: Suspension of sample

There are several options for suspending a 2" Si wafer or 1" optic.

This method would involve wrapping the RTD wires around the sample and somehow hanging or dangling the sample from another surface. The wire would be strain-relieved around another component, like a post, before being varnished to the sample. I will have to play around and try out various configurations to determine if this is feasible / would not strain the RTD contact. This approach would not require additional components in the chamber.

2. Insulating posts

In the case where we cannot achieve RTD lead suspension, we will need to rest the sample on support posts while minimizing conductive heat transfer through said posts. Stephen suggested using ceramic ball bearings bolted down to the cold plate. Further modeling is needed to calculate conduction through these supports. Using a bunch of tiny "pins" was also suggested, but these would need to be similarly modeled, and eventually procured.

Category 3: Heat actuation on sample

There are several options for applying heating power to the suspended sample, each with its own drawbacks.

1. Wire-wound resistor

Binding this directly to the sample will be challenging, especially if the sample is wire-suspended. The resistor will occupy a non-negligible amount of area on the sample, which is not ideal for maximum thermal coupling between the sample and the inner shield. Furthermore, since the emissivity an uncoated Si wafer is quite low (low bulk absorption given thin wafer), the emissivity of the heater body (or the varnish/epoxy) could dominate the coupling and lead to an inaccurate fit for sample emissivity.

2. Lamp source + parabolic reflector

The lamp and reflector would be placed and mounted inside the chamber and directed towards the sample. I found parabolic reflectors in the TCS lab and would need to purchase a suitable light source. Here is an example from my search: https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=7541. Its emission is broadband and could probably be modeled as a blackbody, but I would need to look into this further. I don't know how efficient the heat transfer to the sample would be, i.e. how much heating power would actually hit the sample. This would also make the control of heating power much more difficult.

3. Laser heating source

A laser could be set up outside Megastat and send its beam through one of the viewports to hit the sample. There would be some reflection from the viewport glass, but the transmission would directly heat the suspended sample without crowding the inside of the chamber. The heating power reaching the sample could more easily be determined and controlled in this method, although a laser would need to be sourced for this purpose. This would also require uncovering an additional viewport, which could contribute more heat leakage into the enclosure.

2773   Thu May 26 13:12:25 2022 RadhikaSummaryEmissivity estimationList of Megastat upgrades for emissivity estimation

I think this flashlight would work

 Quote: 2. Lamp source + parabolic reflector The lamp and reflector would be placed and mounted inside the chamber and directed towards the sample. I found parabolic reflectors in the TCS lab and would need to purchase a suitable light source. Here is an example from my search: https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=7541. Its emission is broadband and could probably be modeled as a blackbody, but I would need to look into this further. I don't know how efficient the heat transfer to the sample would be, i.e. how much heating power would actually hit the sample. This would also make the control of heating power much more difficult.
2775   Fri May 27 17:33:24 2022 RadhikaSummaryEmissivity estimationList of Megastat upgrades for emissivity estimation

Today we further discussed ideas for the enclosure, suspension/support, and heat actuation for wafers in Megastat.

Enclosure: We re-painted the inner surface of the inner shield with aquadag, including the top side of the bottom lip [Attachments 1,2]. The folded sheets of aluminum foil covering the apertures were unbolted and also painted with aquadag [Attachment 3].

Wafer support and heat actuation: Attachment 4 shows sketches and a plan forward (drawn by Stephen). The first round of upgrades includes the components underlined in blue: a baseplate to house the points of contact to the wafer, the ceramic ball bearings which will serve as the points of contact, an aquadag-painted sheet metal insert that will bolt down to the coldplate, and a mount for a Maglite mini flashlight.

We will obtain more wire-wound resistors to serve as a back-up to flashlight heating, if the need arises.

Attachment 1: IMG_3493.jpeg
Attachment 2: IMG_3494.jpeg
Attachment 3: IMG_3492.jpeg
Attachment 4: IMG_1633.jpeg
23   Tue Jan 29 12:50:00 2008 DmassThings to BuyGeneralThings to buy wiki
Temporarily located on the 40m wiki until AdhikariWiki is released.

102   Tue Nov 25 17:12:01 2008 AidanThings to BuyFiberResidual things to buy for FS

A large fraction of the equipment is already in the lab from Masha's experiment earlier in the year. The following is required for the latest design of the experiment. In the interim we can probably use the Marconi to drive AOM1.

Specifics
---------
2x Half wave plates - QWPO-1064-05-2-R10
1x Quarter wave plate - QWPO-1064-05-4-R10
3x rotation stages - New Focus 9401

General
-------
Partially transmitting retro-reflector
AOM # 2
Mode-matching lenses (possibly - might have enough downstairs)
RF photodiodes - (10-MHz InGaAs Photoreceiver (Free Space input) Model 2053-FS?)
VCO + power amp for AOM#1 - center frequency probably 77.5MHz, ~2W to AOM
Crystal oscillator + power amp for AOM#2 - probably 80MHz, ~2W to AOM
Oscillator for demod - probably 5MHz, 17dBm

What else? hmm ...
105   Wed Jan 14 11:33:58 2009 AidanThings to BuyFiberResidual things to buy for FS - QWPs, HWPs, output coupler

 Quote: A large fraction of the equipment is already in the lab from Masha's experiment earlier in the year. The following is required for the latest design of the experiment. In the interim we can probably use the Marconi to drive AOM1. Specifics --------- 2x Half wave plates - QWPO-1064-05-2-R10 1x Quarter wave plate - QWPO-1064-05-4-R10 3x rotation stages - New Focus 9401 General ------- Partially transmitting retro-reflector AOM # 2 Mode-matching lenses (possibly - might have enough downstairs) RF photodiodes - (10-MHz InGaAs Photoreceiver (Free Space input) Model 2053-FS?) VCO + power amp for AOM#1 - center frequency probably 77.5MHz, ~2W to AOM Crystal oscillator + power amp for AOM#2 - probably 80MHz, ~2W to AOM Oscillator for demod - probably 5MHz, 17dBm What else? hmm ...

Ordered the following:
2x Half wave plates - CVI - QWPO-1064-05-2-R10
1x Quarter wave plate - CVI - QWPO-1064-05-4-R10
3x rotation stages - New Focus - 9401
1x partially transmitting retro-reflector: CVI - PR1-1064-95-IF-1037 - 95% reflectance
106   Wed Jan 14 18:14:23 2009 AidanThings to BuyFiberResidual things to buy for FS - extra photodiodes

Quote:

 Quote: A large fraction of the equipment is already in the lab from Masha's experiment earlier in the year. The following is required for the latest design of the experiment. In the interim we can probably use the Marconi to drive AOM1. Specifics --------- 2x Half wave plates - QWPO-1064-05-2-R10 1x Quarter wave plate - QWPO-1064-05-4-R10 3x rotation stages - New Focus 9401 General ------- Partially transmitting retro-reflector AOM # 2 Mode-matching lenses (possibly - might have enough downstairs) RF photodiodes - (10-MHz InGaAs Photoreceiver (Free Space input) Model 2053-FS?) VCO + power amp for AOM#1 - center frequency probably 77.5MHz, ~2W to AOM Crystal oscillator + power amp for AOM#2 - probably 80MHz, ~2W to AOM Oscillator for demod - probably 5MHz, 17dBm What else? hmm ...

Ordered the following:
2x Half wave plates - CVI - QWPO-1064-05-2-R10
1x Quarter wave plate - CVI - QWPO-1064-05-4-R10
3x rotation stages - New Focus - 9401
1x partially transmitting retro-reflector: CVI - PR1-1064-95-IF-1037 - 95% reflectance

Also ordered 2x Thorlabs - PDA10CS 17MHz InGaAs photodiodes
135   Sat May 23 17:19:08 2009 AidanThings to BuyGeneralClamps, pedestals, mirror mounts, photodiodes

Unless there is another stash somewhere, we are now short of clamps (two or three are now spare), 3" pedestals (four or five spare), mirror mounts (maybe half a dozen left) and InGaAs photodiodes.

We should put together a general order for this stuff in the near future.

249   Tue Aug 11 16:38:25 2009 AidanThings to BuyGeneralOrdered mixers, splitters, LPFs and HPFs

I've ordered the following:

Mini Circuits
--------------
- ZX05-1MHW-S+ (mixers) x4
- SHP-100+ (High pass filter) x4
- SLP-1.9+ (low pass filter) x4
- ZFSC-2-1W-S+ (splitter) x2

257   Wed Aug 12 11:19:57 2009 AidanThings to BuyGeneralNew Focus Order pending ...

Going to order 15x 2.5" pedestals from New Focus. Will submit order this afternoon.

258   Wed Aug 12 14:12:22 2009 AidanThings to BuyGeneralNew Focus Order pending ...

 Quote: Going to order 15x 2.5" pedestals from New Focus. Will submit order this afternoon.

never mind.

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