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2810   Sun Nov 27 15:13:42 2022 ranaDailyProgressEmissivity estimationAlumina samples

On their web page (https://www.masterbond.com/properties/thermally-conductive-epoxy-adhesives), they have one with Aluminum Nitride that's twice as conductive. Is that useful to get?

In order to get the strong cooling from the test mass, do we need a more conductive epoxy? (I found this related paper on low temp epoxies).

I exchanged emails with someone at MasterBond about the thermal conductivity of this epoxy. They said they do not expect the thermal conductivity to drop significantly from its room temperature value (1.44 W/m*K) until about 30K. They were confident the value would stay above 1 W/m*K in the 77-123K range. However, they didn't provide any data or qualitative measure of this.

2808   Thu Nov 10 09:29:30 2022 JCSafetyLab MonitoringMinor flooding 11/7

On Monday Nov 7, Koji found a puddle of water in the beside the lab’s toolbox. I contacted facilities to check this out and find the source of the issue.

Plumbing from facilities came today at 8:00 am. After moving the toolbox aside and checking the pipe, there is a very evident crack running down the side. This pipe is running from the first floor level. Steve from plumbing began to poke around to see if he could where the pipe was coming from and found that the source is a kitchen sink on the first floor. The sink has been labelled “Out of Order”, so the leaking should stop soon.

Plumbing will contact the carpenters today to see if try to get this done next week. Radhika and I will cover electronics with tarps and use other tarps as curtains the block off the lab area while plumbing is fixing this issue. I will provide updates with the dates soon.

Attachment 1: 0F498FED-37FF-4F95-9C94-89156AB628FC.jpg
2807   Mon Nov 7 15:20:30 2022 RadhikaSafetyLab MonitoringMinor flooding 11/7

Today Koji noticed a water puddle along the south wall of QIL (265B). Photos attached. I lifted the cables from the main rack off the ground, and JC contacted Facilities.

Attachment 1: IMG_3875.jpeg
Attachment 2: IMG_3879.jpeg
Attachment 3: IMG_3876.jpeg

We met today to discuss the design of the aluminum insert for the cold plate. [Diagram to come]

For a setup with an elevated base plate (sample mount), Stephen suggested having an inner aluminum disk on standoffs and an outer ring that would extend to the wall of the inner shield. The raised outer ring would eliminate the need to align tapped holes with the coldplate, and it wouldn't interfere with any components currently bolted down to the cold plate (dog clamps, cold finger flange). The outer ring would also have a slit to fit around the copper bar/flexible strap. The inner disk would first be bolted down according to the base plate's position, and the outer ring's slit would be aligned with the copper bar/strap. Having 2 elements provides an extra degree of freedom for alignment.

We took the following measurements inside the chamber:

- height from cold plate to copper flange: 35.7 mm (min height of outer ring)
- width of copper bar: 32 mm (min width of slit)
- length of copper bar within inner shield: 117.2 mm (min length of slit)
- dist from tip of copper bar to opposide inner shield wall: 333 mm
- from above 2 measurements, max radius of inner disk [centered w.r.t inner shield]: 107.9 mm

*We forgot to take a measurement of the smallest inner shield diameter, to inform max diameter of outer ring. I'll add this soon.*

Attachment 1: Measurements_11_7_22.PNG

Here is a promising epoxy for bonding an alumina strip to a Si wafer (full data sheet in Attachment 1):

- High thermal conductivity: 1.4423 W/mK (at RT)
- Temperature range: 4K to +400F; withstands thermal cycling
- Low thermal expansion: ~20e-6 K-1
- Low outgassing
- Can cure at ambient temperatures

Ekin recommends silver-based epoxies for high thermal conductivity and high electrical conductivity [Attachment 2].

Attachment 1: EP21TCHT-1.pdf
Attachment 2: Screen_Shot_2022-11-04_at_17.59.16.png

We met today to regroup and plan out next steps for Megastat:

1. Design and machine/order aluminum sheet to cover cold plate. Thick enough to not bulge, thin enough to be somewhat maneuverable around cold strap.

2. Thoroughly clean Megastat.

3. Paint aluminum sheet with aquadag, install onto cold plate.

4. Replace cold head RTD with newly-ordered (calibrated) PT100.

5. Cool down with alumina strip, on existing mount w/ ceramic ball bearings.

I'm documenting new 75x75mm alumina strip samples brought to the QIL by Chris. We have 5 strips 120um thick [Attachments 1, 2] and another 5 strips 40um thick [Attachments 3,4].

I've modeled cooldowns in Megastat's current configuration for the two strip thicknesses [Attachments 1, 2]. For both, the strip is modeled sitting atop 3 ceramic ball bearings, as in the Si wafer setup.

An important note is that the emissivities of these strips is much lower (effectively transparent) than typically quoted for alumina ceramic, due to how thin they are (emissivity proportional to bulk absorption, dependant on bulk thickness). This means the 120um and 40um strips also likely have different effective emissivities. Bulk transmission decays exponentially as exp(-c*z) for some c, so the effective emissivity of the 40um strip is likely much much smaller than that of the 120um strip. The model doesn't consider this dependence analytically - I've made a guess for emissivity of 0.02 for the 120um strip, and 0.005 for the 40um strip. Despite these low values, the plots still show significant cooling of the samples because their mass is very tiny.

This analysis could be improved by deriving an analytic model of alumina emissivity as a function of sample thickness.

Attachment 1: IMG_3813.jpeg
Attachment 2: IMG_3816.jpeg
Attachment 3: IMG_3814.jpeg
Attachment 4: IMG_3815.jpeg
Attachment 5: alumina_wafer_120um_cooldown.pdf
Attachment 6: alumina_wafer_40um_cooldown.pdf
2802   Fri Sep 16 16:29:28 2022 RadhikaDailyProgressCryo vacuum chamberProgress - Heaters, RTDs, Maglite

I torqued down the toothed washer and bolt holding the ground wire to the Maglite body and locally flattened the aluminum, securing the electrical connection. With the Maglite wired up, I connected a Tenma power supply to a mini breadboard and attached the Maglite leads [Attachment 1]. At 3V, 0.38A flowed through the incandescent bulb [Attachment 2].

Next steps:

- I will wire a current-limiting circuit to protect the bulb.

- Normally the Maglite batteries press up against an internal component to complete the flashlight circuit. Since we’ve cut off the body and of course have no batteries, I plan to use vacuum/cryo-safe epoxy to hold it in place (or use some spring mechanism to apply pressure to that component).

- The head of bolt used to connect the ground wire to the aluminum body sticks out and interferes with screwing on the flashlight's reflector. I will need to cut away some of the metal to allow the piece to screw in all the way.

Once these steps are complete, we need to address the feedthrough for the maglite leads into Megastat. Then it will be ready to be mounted inside the chamber and used for wafer heat actuation.

Attachment 1: IMG_3756.jpeg
Attachment 2: IMG_3759.jpeg
2801   Fri Sep 9 12:10:29 2022 RadhikaDailyProgressCryo vacuum chamberProgress - Heaters, RTDs, Maglite

I acquired internal tooth lock washers to bolt down the ground wire to the aluminum maglite body, but I soon recognized that the curvature of the aluminum does not allow for flush contact of a washer or nut. Attachment 1 shows a 4-40 screw and nut relative to the maglite body.

I am continuing to search for the best way to get electrical contact, given these constraints and the issues with soldering in the last ELOG

Attachment 1: IMG_3745.PNG
2800   Tue Aug 23 22:23:06 2022 awadeUpdateWOPOInstalling 1811 PDs

I recall at one point we had one of these NF1811 with a broken power suply pin.  It was from a limited production run with the smaller micro 3-pin power connectors. Maybe check yours is not that one.

Long story short it still responded with only the positive rail but DC will gave a bad photovoltaic mode response and the AC had a large unstable oscillation that was only viewable on a high speed scope (if I recall right higher than the 125 MHz nominal bandwidth).  I would check the power-in pins aren't bent/broken and also check the AC out on a higher speed scope (i.e. >=500 MHz).

We performed a calibration procedure on the newly ordered RTDs for Megastat, in LN2 and ice water. We noted that these are 1kohm RTDs at 0C, as opposed to the 100ohm RTDs previously calibrated that are inside the chamber. We chose to calibrate 6 RTDs and labeled them alphabetically starting with G.

The first calibration point was taken at the boiling point of LN2. We dispensed the LN2 into a dewar and dipped each RTD just below the surface of the liquid. Since the temperature right below the surface is 77K with relatively high accuracy, we only took 1 measurement of each RTD resistance. The results are tabulated below:

 RTD LN2 measurement 1 (ohms) G 196.8 H 197.0 I 196.9 J 196.4 K 197.2 L 197.1

The second calibration point was the melting point of ice. We created an ice bath by filling a beaker with crushed ice and adding deionized water until 1/2" below the surface of the ice. We let this equilibriate for a few minutes and then proceeded to dip each RTD and record its resistance. When we started this process, we realized we had not let the system equilibriate for long enough, since the temperature of the water was dropping with every measurement. The water surrounding the ice had not yet been cooled sufficiently. We scrapped the first set of resistances, but the 2 rounds of valid measurements are tabulated below. The multimeter was overloaded when set to display the resistance in ohms, so we had to display kohms and thus lost a significant figure.

 RTD H2O measurement 1 (kohms) H2O measurement 2 (kohms) G 0.990 0.990 H 0.992 0.989 I 0.991 0.992 J 0.992 0.993 K 0.992 0.993 L 0.992 0.991

RTD G was dropped and lost after calibration, but we calibrated more than we needed in anticipation of an accident like this.

2798   Tue Aug 2 11:37:19 2022 RadhikaDailyProgressCryo vacuum chamberProgress - Heaters, RTDs, Maglite

- RTD calibration with Clare scheduled for Wed 8/3 morning.

- A heater will be bolted down to the cold plate for the next cooldown (to aid in chamber warmup).

- For the maglite, I took the wire intended for ground and wrapped it through the drilled hole and around [Attachment 1]. When I applied solder, it bonded to the wire but made no contact with the Maglite aluminum surface. The near-instant oxidation of the aluminum still prevents the solder from bonding to it. Previously when we tried scratching the surface and immediately using mineral oil (vaseline) to prevent oxidation, the solder joint still did not form due to the layer of oil. So I am not convinced that applying vaseline will help this joint with the drilled hole - I am in favor of considering an alternative connection. In addition, the wrapped wire does not allow the maglite shaft to slide completely into the "head", and thus the bulb does not make it through the opening of the reflector.

 Quote: Update to QIL/2795: RTDs (Digi-key P/N 615-1123-ND) brought to lab (see pic). Heaters (Digi-key P/N A102128-ND) brought to lab (see pic). Maglite hole drilled; remains to be seen whether than improves solderability, but we could also look at a lug / ring connector as an alternative connection.

Attachment 1: IMG_3704.jpeg
2797   Fri Jul 29 14:27:43 2022 StephenDailyProgressCryo vacuum chamberProgress - Heaters, RTDs, Maglite

Update to QIL/2795:

• RTDs (Digi-key P/N 615-1123-ND) brought to lab (see pic).
• Heaters (Digi-key P/N A102128-ND) brought to lab (see pic).
• Maglite hole drilled; remains to be seen whether than improves solderability, but we could also look at a lug / ring connector as an alternative connection.
2796   Wed Jul 20 15:55:41 2022 YehonathanUpdateWOPOInstalling 1811 PDs

{Yehonathan, Paco}

We comfirmed that the DC ouput of one of the 1811s is bad. We set out to measure the AC response of the PDs.

For this, we decided to use the current modulation on the Diabolo laser which is rated to have 0.1 A/V and a bandwidth of 5kHz. We calibrated the current to optical power by swiping the current and measuring the power at the homodyne PDs using a power meter. The laser power before the 1064nm PZT mirror was measured to be 5mW.

Attachment shows the measurement and a linear fit with slope=0.97 mW/A.

We drove the current modulator using a sine wave from a function generator with 1kHz 0.5Vpp. When we looked on the PD AC signal port in the Oscilloscope we saw 2 Vpp 12Mhz signal. We passed the signal with a low pass filter but again we saw mostly noise.

We took the PDs to the 40m PD test stand but we accidently fried Jenne's laser.

Next, we should just use the Moku network analyzer instead of the scope to measure the response in the QIL using the Diabolo current modulator.

Attachment 1: Diabolo_Current_Power_at_PDs.png

We started a cooldown on Thursday with an undoped Si wafer in Megastat [2794]. The chamber does not have the Maglite flashlight installed, due to struggles with soldering the ground wire to the aluminum surface of the flashlight. We decided to pivot to drilling a hole in the aluminum, wrapping the ground wire through and around, and then applying solder to the joint. This will be completed by next week.

• Order new RTDs [done]
• Order new heater to aid in chamber warmup (not for actuating on wafer) [Stephen]
• Calibrate new RTDs in an ice bath and LN2 bath [Hiya, Clare]
• Finalize aluminum sheet design [Stephen]
• Finalize baseplate design [Stephen]
• Drill hole in Maglite to solder ground wire [Stephen, if time]
• Continue optimal excitation analysis [Hiya]
• Finalize final report abstract [Hiya]
• Continue MCMC model development [Clare]

These tasks will ideally lead up to a Si wafer cooldown next week with optimal heat excitation and with an RTD re-installed on the cold head, and potentially with the finalized baseplate and aquadag-coated Al sheet on the cold plate. It is with this cooldown that we can start to estimate the sample’s emissivity, first with least-squares fitting and eventually with MCMC analysis.

2794   Thu Jul 14 18:15:41 2022 RadhikaDailyProgressEmissivity estimationUndoped Si wafer cooldown in Megastat

On Thursday 7/14 we started a cooldown of an undoped Si wafer in Megastat. Our goals were to swap out the glass wafer from the previous cooldown for the new undoped Si wafer, to verify that there is sufficient radiative coupling between thin Si and the inner shield. This way we ensure that our cooldown data can be fit for the wafer's emissivity.

When we opened up the chamber, we noticed some of the aquadag-coated foil was touching the bottom face of the glass wafer [bottom edge of wafer in Attachment 1]. This is a potential conductive short, and analyzing the cooldown data will reveal how significant the conduction was. We also noticed several aquadag flakes on the ceramic ball bearings/wafer [Attachment 1]. Stephen pointed out ways to improve the clamping of one end of the base plate to the cold plate, given that the hole spacings of the two did not line up (explained in 2792). We mapped out a new bolting/clamping approach for the baseplate using metal spacers instead of folded Al foil [Attachment 2]. We applied grease to the bottom surface of the baseplate and then bolted/clamped it down to the cold plate [Attachment 3].

We removed the glass wafer and debonded the varnish from the RTD. We then re-varnished this RTD to the undoped Si wafer [Attachment 4] and placed it on top of the ceramic ball bearings on the bolted/clamped baseplate [Attachment 5].

Lastly, we trimmed off excess aquadag-coated Al foil to ensure there would be no future shorting to the wafer. We then verified all RTDs were responsive and closed up the chamber.

The vacuum pump was turned on at 5:35pm, and the cryocooler was turned on at 6pm.

Attachment 1: IMG_3665.jpeg
Attachment 2: IMG_3669.jpeg
Attachment 3: IMG_3673.jpeg
Attachment 4: IMG_3671.jpeg
Attachment 5: IMG_3676.jpeg
2793   Tue Jul 5 17:40:14 2022 RadhikaDailyProgressEmissivity estimationGlass wafer cooldown with ceramic ball bearings

The cryocooler was switched off on Tue 7/5 at 11:45am.

2792   Tue Jul 5 11:58:01 2022 RadhikaDailyProgressEmissivity estimationGlass wafer cooldown with ceramic ball bearings

On Thursday 6/30 we worked towards a cooldown with a glass wafer rested on ceramic ball bearing supports. We used a glass wafer for this cooldown because it has a higher emissivity than a Si wafer, and therefore could be more easily validate our cryostat setup.

The procedure went as follows:

1. RTD preparation [Attachments 1, 2]

- Re-soldered the leads of the 3 RTDs we previously calibrated (2791)

- Bonded RTDs to the inner shield, outer shield, and glass wafer with varnish

RTD C --> wafer
RTD E --> outer shield
RTD F --> inner shield

*Note that we did not have any RTDs left to clamp to the coldhead

2. Wafer support structure [Attachments 3, 4]

- Applied grease to the bottom of the baseplate and bolted it down to the cold plate using 2 screws and a dog clamp. The hole spacings on the cold plate and base plate did not align align along the longer axis of the baseplate, so we needed the dog clamp to hold down one end. To get the dog clamp elevated to the right height, we folded a piece of aluminum foil until it was tall enough to rest the dog clamp flush on top of the base plate.

- Rested 3 ceramic ball bearings and wafer on top (*The ball bearings created enough clearance between the dog clamp and the wafer)

We closed up the chamber and started the vacuum pump [Attachments 5, 6], but soon after I realized the wafer RTD was glitching/shorting. I turned off the pump and re-opened the chamber, and upon inspection noticed that a few of the RTD lead pins were fraying. I replaced these pins and left for the day.

On Friday I verified that all RTDs were operating properly and closed up the chamber. The vacuum pump was started at 3:10pm and the cryocooler was switched on at 4:10pm on 7/1.

Attachment 1: IMG_3622.jpeg
Attachment 2: IMG_3626.jpeg
Attachment 3: IMG_3614.jpeg
Attachment 4: IMG_3624.jpeg
Attachment 5: IMG_3623.jpeg
Attachment 6: IMG_3629.jpeg
2791   Wed Jun 29 09:39:01 2022 Clare NelleDailyProgressEmissivity testingRTD Calibration Day 2

We debonded the RTDs from the chamber using isopropanol and acetone, then soaked the RTDs in isopropanol for about 15 minutes to remove residue. We then took resistance measurements in ice water detailed below:

Ice Water Calibration Measurements (completed 28-06-2022):

1) Prepared ice water bath by filling beaker with crushed ice and then water to one half inch below the ice surface. Let the ice bath sit for about 1 minute.

2) All six RTDs were measured (labeled A-F). For each RTD, the resistance in the ice water bath was measured by swirling the RTD held by the DMM leads in the water until the DMM readout stabilized.

3) These measurements were repeated in the reverse direction (Started with RTD F).

*Note: in the process of ice bath calibration, RTD D broke.

 RTD Trial 1 ($\Omega$) Trial 2 ($\Omega$) A 100.2 100.15 B 100.15 100.3 C 100.1 100.1 D X X E 100.1 100.1 F 100.1 100.1

Liquid Nitrogen Calibration Measurements (completed 30-06-2022):

Procedure: We clipped the DMM leads to the RTDs and taped the two clips together. This is very secure - good method for the future. We dipped the taped clips with the RTD into the LN2, and swirled under the liquid surface until the DMM readout stabilized. We only took one set of measurements because we are very confident of the boiling point of N2.

*Note: RTD A broke. This is because we spread the RTD wires out to put into the aligator clips, making them very prone to snapping when we move them. This means that we do not have an RTD on the cold head.

Results (ohms):

A: X

B: 19.8

C:18.2

E:18.5

F:19.8

Attachment 1: ice_bath_calibration.xlsx

Here I analyze potential gains from using LN2 to kick off a Megastat cooldown, and transition to a cryocooler to cool under 77K. I've removed the heat loads in the system by modeling an empty chamber (no wafer) and no exposed apertures in the inner shield. I've also modeled the flexible strap is a solid copper element, for an ideal cooldown scenario.

Attachment 1 is a reminder of the cooldown of the cold head of the cryocooler. The cooling power of the cryocooler is a function of the temperature at the cold head, and this is tabulated in its manual. The cold head reaches 77K at ~3.8 hours from past data. This provides an upper limit on gains from using LN2 - if the cold head is cooled to 77K instantly, its cooldown curve will be shifted to the left by 3.8 hours, and thus the system will reach steady state 3.8 hours faster. In reality, there would be a time constant for the cold head to reach 77K due to the LN2-copper interaction, and the mass/heat capacity of the cold head.

Attachment 2 is a plot from Ekin which shows the heat transfer rate (Qdot) per m^2, for the boundary between LN2 and a solid. The different curves correspond for different $\Delta T$ between the LN2 and cold head, and for a majority of the cooling from RT, we will use the curves for $\Delta T$ ~ 100K. These have lower heat transfer because film boiling is occurring, and a layer of film "insulates" the surface of the solid from the 77K bath. These curves vary in the diameter of the contact area, and we use the bottom curve corresponding to D >= 1.0 cm. Once $\Delta T$ reaches 10K, the heat transfer rate jumps up to the nucleate boiling curves. We use the one corresponding to 1atm of pressure.

Attachment 2: thermal_transfer_rate_LN2.png

Here I analyze potential gains from using LN2 to kick off a Megastat cooldown, and transition to a cryocooler to cool under 77K.

2788   Thu Jun 23 11:56:21 2022 JCElectronicsGeneralEquipment

[JC, Paco]

I took the Moku and iPad from QIL over to 40m for PLL Measurement at the 40m. (SURF)

2787   Tue Jun 21 11:00:57 2022 RadhikaDailyProgressEmissivity estimationThermal conduction through ceramic ball bearings

Here I summarize the analysis of thermal conduction through 3 ceramic ball bearings supporting a test wafer in Megastat. I considered a baseplate or housing for the ceramic ball bearings at the temperature of the cold plate, the 3 ceramic ball bearings themselves, and the wafer seated on top. This pathway can be broken down into the following components:

1. Thermal resistance across joint from Al baseplate to ball bearing

2. Thermal resistance of bulk of ball bearing

3. Thermal resistance across joint from ball bearing to wafer

These resistances in series can be summed, and there exist 3 of these pathways in parallel (1 for each bearing) and the net resistance can then be found using the corresponding formula.

Attachment 1 is a plot of the thermal conductance of alumina ceramic (Al2O3), and it was taken from from this paper. The peak value of 99% Al2O3 agrees with what is listed in the ceramic ball bearing spec sheet: 28 W/mK. I've used these tabulated values to obtain component 2 above.

Attachment 2 is a plot of the thermal conductances across various joints, taken from Ekin. I could not find data for the conductance across Al--Al2O3 pressure joints or Al2O3--Si pressure joints, but I have used the value corresponding to a stainless steel--stainless steel pressure joint as a conservative upper bound. (*When I was calculating non-negligible conduction last Friday, I had forgotten to update the joint conductance value from an Al--Al pressure joint (orange box in Attachment 2). This greatly overestimated the joint conduction, and the ceramic joints should be a few orders of magnitude below this.)

The results of this modeling show that the maximum cooling power delivered via conductive contact is below 7e-5 W. Compared to the 6e-3 W of radiative cooling power (~1%), this is negligible. Attachment 3 shows the nominal difference in wafer cooldown - the solid and dashed orange curves are barely distinguishable (T difference of ~0.2K at steady state - RTD uncertainty is +- 0.15K). We should proceed with this design plan for emissivity testing in Megastat.

Attachment 1: 1-s2.0-S027288421100229X-gr4.jpg
Attachment 2: thermal_conductance_joints.png
Attachment 3: wafer_cooldown_model_ball_bearings.pdf
2786   Tue Jun 21 10:35:15 2022 Clare NelleDailyProgressEmissivity estimationRTD Calibration

RTD Calibration Plan Developed on 16-06-2022:

1. Prepare an ice bath and liquid nitrogen bath to calibrate the RTD.

1. Ice bath: fill cup (?) with ice. Fill with water until 2 inches below the top of the ice. Let sit for 2 minutes before calibration.

2. We will use a DMM to measure the resistance across the leads. Right now, we are thinking that we will connect the leads to the resistor using alligator clips or solder them together.

3. Use linear fit to calibrate the RTD value as a function of resistance using these two reference values.

4. Repeat for all three RTDs

-----------------------------------

1. Q: What is the tolerance of the resistor?

1. 100 ohm +/- .06%. Means that our calculation if done correctly will be between 99.4 → 100.6 ohms in the ice bath. Our RTD is class A, which has tolerance +/- .15 degrees. Pt-100 SHOULD be 100 ohms at 0C – the temp changes linearly.

From the plot, it seems like the slop is ~50 Ohms / 120 K. So a difference of 5 K corresponds to ~2 Ohms.

It could be that your measurement of the resistance is off slightly due to the lead resistances, etc. Are you using a 3-wire or 4-wire probe?

You can get a higher accuracy relative calibration by dunking all the RTDs together in ice water and then in boiling water.

https://us.flukecal.com/literature/articles-and-education/temperature-calibration/application-notes/how-calibrate-rtd-or-pla

I looked closer at the RTDs, and they are all PT100s with the same resistance-temperature curve [Attachment 1]. So we might need to re-calibrate them.

The chamber is currently warming up, and I plan to cool down again on Monday to a) obtain data for the entire cooldown and b) see if this inner shield behavior is repeated.

Attachment 1: hmfile_hash_88f68a98.png

I encountered several puzzles in the data from this cooldown (Attachment 1):

1. Due to residual challenges with getting the Megastat SLOW channels recorded to frames (after flood), we've been using a USB to extract data form the CTC100. However, only ~48 hours of cooldown were recorded on the drive - we lost data from the rest of the cooldown. I'm hoping this is due to storage limits on the USB, and if so I will decrease the sampling rate of the CTC100 and/or source a USB with larger storage. Of course this is a temporary solution, and efforts would be better spent on getting data recorded in frames. For now, since every component had reached steady state (except the test mass), most parameters can theoretically still be inferred from the data we obtained. (Note that data logging started a bit after the cryocooler was switched on.)

2. The inner shield appears to have reached a steady-state temperature lower than that of the cold head. This is bizzare, and non-physical - the cold head should be the component supplying cooling power to the rest of the system. Our current Megastat model would not predict such behavior under any choice of parameters. I replaced the inner shield RTD before this cooldown, so I am hoping the new RTD has a different calibration curve than what the CTC100 was expecting. If this is the case, I should be able to use the data to undo the existing calibration and obtain correctly-calibrated temperature for the inner shield. It is worth noting that the new RTD accurately measured room temperature, so if this theory is correct then the calibration error only exists at low temperatures.

Attachment 1: MS_cooldown_2022-06-02_data.pdf
2782   Thu Jun 9 10:27:01 2022 RadhikaDailyProgress2um PhotodiodesPD testing plan in CAML lab

On Tuesday 6/7 we met to discuss next steps for getting PD testing up and running in CAML (cryo auxiliary mariner lab). Here is a rough 2-month plan:

Step 0 [1 week]: Get CAML workstation running and confirm connection to EPICS/CDS.

- Organize BNC cables coming in from QIL and connect to the PD testing table.

Step 1 [1 week]: Outline desired measurements and sketch diagram of electronics/components.

- Decide how we want these component organized; i.e. how many boxes, number of inputs/outputs per box.

Step 2 [2 weeks]: Implement desired setup.

Step 3 [2 weeks]: Replicate QE measurements on JPL PDs

- Tweak setup as necessary

Step 4 [2 weeks]: Test MCT detectors

The cryocooler was turned off 6/8 at 11am.

2780   Tue Jun 7 11:50:09 2022 RadhikaDailyProgressEmissivity estimationFastest cooldown + power budgets for 2" Si wafer cooldown in Megastat

I've modeled the theoretical "best" achievable configuration in Megastat, replacing the flexible strap with a solid copper element, and leaving all but one aperture open in the inner shield [Attachment 1]. In this configuration, the wafer can reach 123K in ~20 hours.

- The difference in time constant between the copper bar end and cold head (purple and blue curves) is due to the thermal resistance across the bar and 2 joints, plus realistic radiative losses from bar.

- The difference in time constant between the cold plate and copper bar end (brown/green and purple) is the thermal resistance across the additional solid copper finger and 2 joints.

- The stead-state temperature difference between the inner shield and the wafer (orange and green) is maintained by heat leaking from 1 aperture in the shield. (We've closed up 4, but best case there will need to be 1 open for the copper bar and leads.

Attachment 2 shows power budgeting of heating and cooling power delivered to various components: 1. copper bar, 2. cold plate, 3. inner shield, 4. Si wafer. The points of intersection of the heating and cooling power curves correspond to the steady-state temperature for each component, which can be verified by Attachment 1. The total heat load on the copper bar and cold plate is just over 70W.

The ideal model shows that there are two areas of potential gains:

1) Optimizing the flexible strap or replacing it with a solid copper connection can reduce the time constant between the cold plate and copper bar.
2) Reducing to effectively 1 exposed aperture in the inner shield, by covering more of the opening around the copper bar and/or around the RTD leads.

Analyzing the most recent cooldown data will hopefully validate the efforts of closing up apertures and painting the entire wafer enclosure with aquadag.

Attachment 1: wafer_cooldown_model_ideal.pdf
Attachment 2: power_budget_ideal.pdf
2779   Mon Jun 6 14:05:08 2022 AidanElectronicsPurchasesReturn me to WB265B: Location of Thorlabs S130C (silicon photodiode 5mW/500mW settings)

[Aidan]

I bought a new photodiode for the West Bridge Labs. It will be housed in the QIL (WB265B) in the central cupboards. There is a QR code on it linking to this page.

Attachment 1: S130C_calibration.pdf
Attachment 2: IMG_9289.jpg
Attachment 3: IMG_9287.jpg

This entry describes efforts towards the most recent Megastat cooldown with:

1.) the inner shield repainted with aquadag and pieces of foil covering the apertures,

2.) aquadag-painted aluminum foil lining the cold plate,

3.) the original test mass and suspension used in previous cooldowns.

Because of the lead time for ordering/fabricating components for wafer supports, we proceeded to use the previous test mass. This way, the improvements made to the chamber can be quantified by comparing the test mass cooldown to past cooldown data.

On Tuesday 5/31, Hiya and I coated the outside surface of the inner shield with Al foil (previously removed for hole tapping / aquadag repainting -  see 2775). We inserted the inner shield into the chamber and cut a circular piece of aquadag-coated Al foil to cover the cold plate [Attachments 1, 2]. A slit was cut in the piece of foil in order to pass it over the copper bar and flexible strap. Then, the foil was lightly rested over the bulk created by the flexible strap and its flange [Attachment 3]. We poked holes in the foil in order to bolt down dog clamps for securing the inner shield; then we tightened these dog clamps all around [Attachment 4].

After completing this, we realized we hadn't applied grease to the bottom lip of the inner shield, for maximizing thermal conductance across the cold plate <--> inner shield joint. We also noticed that the inner shield RTD, previously removed for hole tapping / aquadag repainting, was glitching and read an unphysical temperature value. We wrapped up for the day and made note of these items to address next time.

On Wednesday 6/1, Stephen and I picked up with removing the inner shield and aquadag foil. We applied grease to the bottom lip of the inner shield, in the same manner as previous setups. Stephen noticed that the solder joints of the inner shield RTD (that was glitching) had debonded, and so we re-soldered those joints. We re-inserted the inner shield and aquadag foil and bolted the components down. We placed the suspension frame with the test mass back inside the chamber and connected all RTDs [Attachemnt 5]. Since the heater from previous runs had been damaged, we wrapped the exposed leads with kapton tape and proceeded without a heater. Lastly, a piece of foil was placed under the copper bar opening to cover the cut-out area of the inner shield [Attachment 6].

I closed up the chamber and pumped down on Thursday 6/2 at 2:20pm. The cryocooler was switched on at 2:55pm.

Attachment 1: IMG_3501.jpeg
Attachment 2: IMG_3500.jpeg
Attachment 3: IMG_3507.jpeg
Attachment 4: IMG_3503.jpeg
Attachment 5: IMG_3509.jpeg
Attachment 6: IMG_3512.jpeg
2777   Thu Jun 2 10:28:26 2022 YehonathanUpdateWOPOInstalling 1811 PDs

[Shruti, Yehonathan]

We took newport 1811 PDs, one from CTN lab (suspicious) and one from (I forgot) for their high gain and low dark noise.

The detector diameter is small 0.3mm, but our focusing is sufficient:

The mode field diameter of the PM980 fiber is ~ 6.6um. The beam is collimated by a Thorlabs F240APC-1064 with f = 8.07mm and focused with an f = 30mm lens. It means that the diameter at the focus should be roughly 6.6um*30/8.07 = 0.024mm which is well within the PD active area.

We place the PDs at the focal point of the lens at the BHD readout. The impinging optical power was set to be ~ 0.6mW at each port. In one of the PDs, we measure the DC response with a scope to be ~ 5.5 V/0.6 mW ~ 9e3 V/W. According to the specs, the DC monitor as a response of 1e4 V/A while the responsivity of the PD itself is ~ 0.8 A/W at 1064nm so the overall responsivity is ~ 8e3 V/W.

However, the second PD's DC response was bonkers: we measured it to be ten times less. The AC response might still be OK since it is a different port but we haven't measured it yet.

2776   Tue May 31 17:53:07 2022 ranaDailyProgressEmissivity estimationSi wafer emissivity testing

that's a good start, but we want the cooldown to be fast, so what we would need from the model is for you to change some parameters and find out what kind of possible physical changes we can make to make the cooldown fast. i.e. change some parameters and see what configurations would give a fast cooldown, and then we can discuss which of those is the easiest.

 Quote: [WIP] I modeled the cooldown of a 2" Si wafer in Megastat with cooling from a) the existing cryocooler and b) LN2. The only difference between the two models is the temperature that the cold end of the copper bar "sees" - in the cryo-cooler case, I've used cold head temperature data from a previous cooldown; in the LN2 case, I've used 77K. In Attachment 1, the cryo-cooler models are solid lines and the LN2 models are dashed.  It is clear from the plot that the cold head gets ~30K colder than LN2 at 77K. This explains the discrepancy between the inner shield models for the two cases at steady state. While the initial temperature rates of change are greater in the LN2 case, the cold head crosses the 77K line in roughly 5 hours.

Does the true cold-head temperature follow the model? Or is it less good than the model?

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

I modeled the cooldown of a 2" Si wafer in Megastat with cooling from a) the existing cryocooler and b) LN2. The only difference between the two models is the temperature that the cold end of the copper bar "sees" - in the cryo-cooler case, I've used cold head temperature data from a previous cooldown; in the LN2 case, I've used 77K. In Attachment 1, the cryo-cooler models are solid lines and the LN2 models are dashed.

It is clear from the plot that the cold head gets ~30K colder than LN2 at 77K. This explains the discrepancy between the inner shield models for the two cases at steady state. While the initial temperature rates of change are greater in the LN2 case, the cold head crosses the 77K line in roughly 5 hours.

 Quote: I've modeled the cooldown of a 2" diameter and 4" diameter Si wafer in Attachments 1 and 2, using the current Megastat model and previous cold head temperature data. The model includes heat leaking into the inner shield enclosure from an aperture, which we currently observe in Megastat cooldowns. (Note how the wafer cools down much faster than the current test mass, due to the very tiny volume.) The analytic equation for radiative heat transfer in a 2-surface enclosure (formed by the inner shield and Si wafer) is: $R = \frac{1-e_{Si}}{A_{Si}*e_{Si}} + \frac{1-e_{IS}}{A_{IS}*e_{IS}} + \frac{1}{A_{Si}*F_{Si \rightarrow IS}}$ $P_{Si \rightarrow IS} = \frac{\sigma (T_{Si}^4 - T_{IS}^4)}{R}$ This is dependent on properties of inner shield / cold plate, and as such the accuracy of wafer emissivity measurements will be limited by our uncertainty on the inner shield and cold plate emissivities.  As the ratio $\frac{A_{Si}}{A_{IS}}$ approaches 0, the above equation simplifies to: $P_{Si \rightarrow IS} = A_{Si} e_{Si} \sigma (T_{Si}^4 - T_{IS}^4)$. The terms related to the surrounding surface (inner shield) drop out of the equation, and so the smaller the ratio of areas, the less of an impact the inner shield / cold plate emissivities will have on the cooldown. Thus we should seek to minimize the ratio of areas to minimize the uncertainty on eSi. On the other hand, in this low area ratio limit, the thermal power transfer between the wafer and surrounding inner shield is proportional to the area of the wafer. As the attachments show, the 4" diameter wafer gets colder than the 2". This should be taken into account when determining in what temperature range we would like to fit the wafer emissivity. Larger wafer ---> colder. Do we care about emissivity measurements < 123K? If not, the 2" wafer gets us there.

Attachment 1: cryocooler_vs_LN2_wafer.pdf
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.
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.

2771   Fri May 20 11:08:16 2022 RadhikaDailyProgressEmissivity estimationMegastat Inner Shield for emissivity estimation

The results from tapping are in the previous entry, and it seemed to work well. As for the emissivity of the inner surface, it would definitely be better to have it black but I wasn't sure how feasible it would be to coat the coldplate. If this is something we can consider, I won't remove the aquadag from the shield.

 Quote: I'd recommend drilling a through hole and using a nut, rather than tapping as I suggested earlier. The shield is not thick enough to have many 4-40 threads. Is it better to have the inner shield inner surface low or high emissivity? \Depending on the effect on the MCMC uncertainties, we may want to make everything black, including the cold plate. i.e. we could mount something like black aquadag tiles on the cold plate.

2770   Wed May 18 21:53:31 2022 ranaDailyProgressEmissivity estimationMegastat Inner Shield for emissivity estimation

I'd recommend drilling a through hole and using a nut, rather than tapping as I suggested earlier. The shield is not thick enough to have many 4-40 threads.

Is it better to have the inner shield inner surface low or high emissivity? \Depending on the effect on the MCMC uncertainties, we may want to make everything black, including the cold plate. i.e. we could mount something like black aquadag tiles on the cold plate.

2769   Wed May 18 09:42:34 2022 RadhikaDailyProgressEmissivity estimationMegastat Inner Shield for emissivity estimation

In order to avoid having to order a new inner shield for emissivity estimation in Megastat (see [2768]), we decided to tap 4 holes around each unused aperture (4) in the inner shield. We used 4-40 screws to secure folded sheets of aluminum foil into each aperture, as seen in Attachments 1-2. (These pieces can be bolted on either the outside or inside surface of the shield, but it is shown here bolted to the outside for clarity.) Attachments 3-4 show a piece of folded foil prepared to conceal the gap created by the slit (cut so that the shield could slide over the copper bar). This can be bolted in every time the inner shield is inserted in the chamber. Lastly, we left open the aperture used for passing though the RTD leads, although eventually we can devise a similar foil block with a narrow opening for the leads to pass through.

The state of the test mass / heater from the last cooldown can be seen in Attachment 5. It looks like the heater "fried" and the internal resistive element came out from the brass casing [Attachment 6]. There were lots of flakes of burnt cigarette paper on the cold plate [Attachment 7] and on the test mass [Attachment 8]. I'll need to investigate this further and make sure the heater still works; otherwise we will need to source a new one.

I took out the suspension frame and cleaned up the coldplate [Attachment 9]. Inevitably some of the Aquadag flakes rubbed into the coldplate, but most of it was removed.

Additionally, the simplest model for determining the emissivity of a suspended sample requires that the entire surface surrounding the sample be of the same emissivity. This way, the surrounding surface can be treated as one component that completely encloses the sample (as opposed to 2 or more surfaces with different emissivities partially enclosing the sample). The cold plate surface is rough aluminum, and so I would like to remove the Aquadag coating from the inner surface of the inner shield to restore it to rough aluminum as well.

Attachment 1: IMG_3463.jpeg
Attachment 2: IMG_3468.jpeg
Attachment 3: IMG_3464.jpeg
Attachment 4: IMG_3469.jpeg
Attachment 5: IMG_3369.jpeg
Attachment 6: IMG_3472.jpeg
Attachment 7: IMG_3459.jpeg
Attachment 8: IMG_3476.jpeg
Attachment 9: IMG_3475.jpeg
2768   Fri May 13 09:12:14 2022 RadhikaDailyProgressEmissivity estimationPlan towards MCMC emissivity estimation

I've now used the following model of heat transfer between a suspended Si sample (1), inner shield (2), and aperture heat leak (3) in Megastat:

$m_1Cp_{Si}(T_1)\frac{dT_1}{dt} = \sigma A_1[\frac{(T_2^4-T_1^4)}{\frac{1}{\epsilon_1} + \frac{A_1}{A_2}(\frac{1}{\epsilon_2} - 1)} + \frac{(T_3^4-T_1^4)}{\frac{1}{\epsilon_1} + \frac{A_1}{A_{leak}}(\frac{1}{\epsilon_3} - 1) + \frac{1}{F_{leak}} -1}]$,

where the first term is the heat transfer from the inner shield to the sample, and the second term is the heat transfer from an aperture opening to the sample. Note that the second term contains the geometric view factor Fleak, which is dependent on the radii of and separation between the 2 surfaces. (This parameter is also implicit in the first term, but because we approximate the inner shield as nearly completely surrounding the sample, we set this to 1.)

Once again I simulated typical/expected values for the emissivities of silicon and rough aluminum:

$\epsilon_{Si}(T) = (2.3*10^{-3})T + 0.12$, for the sample,

$\epsilon_{Al}(T) = (1.5*10^{-4})T + 0.03$, for the inner shield and outer shield (source of heat leaks).

I further parametrized both Aleak and Fleak in terms of rleak, in the assumption of circular aperture openings. This reduced the number of parameters to consider to 4 (e1, e2, e3, rleak).

As before, I simulated T1 using these emissivities, previous inner shield T data, and the above model. I numerically evaluated dT1/dt from the simulated T1 data.

The resulting evaluations for e1 using the dimensions of a large, cylindrical test mass (like the one we've been cooling in Megastat) can be found in Attachment 1. The uncertainty bounds from e2 and rleak were found by evaluating partial derivatives of e1 with respect to those parameters. (The uncertainty bound from e3 was not even resolvable on the plot, so I excluded it as it is a negligible source of e1 error.) This process is mathematically equivalent to evaluating the 2x2 Fisher matrices formed by e1 and e2, e1 and e3, and e1 and rleak.

The resulting uncertainties can be summarized by:

10% e2 uncertainty --> 15.7% euncertainty
10% e3 uncertainty --> 0.3% e1 uncertainty
20% rleak error --> 3.2% e1 uncertainty
All 3 uncertainties --> 16.5% e1 uncertainty

where I have used reasonable guesses for our uncertainties in these parameters. This tells us that in the high mass/area sample case, the uncertainty in the emissivity of the inner shield is our largest source of potential error in e1 determination, even with heat leaks into the system. This makes sense qualitatively, since the first term in the model dominates and view factor from heat leak apertures is small.

Attachment 2 shows the same analysis but using dimensions of a thin, 2" wafer. The resulting uncertainties can be summarized by:

10% e2 uncertainty --> 1.3% euncertainty
10% e3 uncertainty --> 2.0% e1 uncertainty
20% rleak error --> 42% e1 uncertainty
All 3 uncertainties --> 42% e1 uncertainty

This tells us that in the low mass/area case, the uncertainty of the size of the heat leak is the largest contributor to error in e1 evaluation. Now, the first term in the model no longer dominates, and heat leaks play a non-negligible roll in the cooldown of a wafer.

I next verified these results by simulating my own form of MC, aka defining a prior distribution on e2 and rleak and observing the posterior on e1. I specified the prior on eas a 2-dimensional gaussian (m vs. b) with standard deviations of 1e-4 and 1e-2, respectively. I specified the prior on rleak also as a gaussian with standard deviation 1e-2. The results for both the high mass/area case and low mass/area case can be found in Attachments 3 and 4. These serve to verify the previous error analysis and create groundwork for MCMC analysis.

To design our experimental setup with this analysis in mind, I propose contacting the company/manufacturer of the shields and requesting an inner shield with only 1 or 2 apertures. (1 for the copper linkage to pass through, and maybe 1 for the RTD feed through if they can't be passed in through the first aperture). This can be the inner shield used when we have no use for the optical viewports, AKA for emissivity testing. Since minimizing uncertainty in the emissivity of the inner shield is in our best interest especially in the high mass case, this might also be a good opportunity to specify the roughness/polishing level of the inner shield that we have the best model for. (We could still paint the inner surface of the inner shield with Aquadag, but my only concern with this is not fully being able to quantify Aquadag emissivity vs. temperature.)

Attachment 1: e1_eval_uncertainty_TM.pdf
Attachment 2: e1_eval_uncertainty_wafer.pdf
Attachment 3: e1_posterior_TM.pdf
Attachment 4: e1_posterior_wafer.pdf
2767   Wed May 11 15:53:06 2022 AidanLab InfrastructureCleanlinessCeiling tile replacement - Day 2

Tiles are replaced.

 Quote: Henry from the Carpentry Shop has started replacing ceiling tiles. They need to be cut to fit each location. There was a lot of set up getting equipment across to Bridge before lunch so not that much progress was made replacing tiles in QIL and TCS Labs. Expect work will speed up as we find our groove.

Attachment 1: IMG_8806.jpg
Attachment 2: IMG_8807.jpg
Attachment 3: IMG_8803.jpg
2766   Tue May 10 14:27:26 2022 AidanLab InfrastructureCleanlinessCeiling tile replacement - Day 1

Henry from the Carpentry Shop has started replacing ceiling tiles. They need to be cut to fit each location. There was a lot of set up getting equipment across to Bridge before lunch so not that much progress was made replacing tiles in QIL and TCS Labs. Expect work will speed up as we find our groove.

Attachment 1: IMG_8782.jpg
Draft   Mon May 9 09:45:17 2022 StephenDailyProgress2um PhotodiodesRecovery of IR Labs dewar WIP

The Helium leak testing setup from the 40m Bake Lab was transported to WB B265B and setup.

The connection to the cryostat was made to the intrinsic KF25 flex tube of the leak tester, at the location of the KF25 - KF40 adapter.

Leak testing found a strong Helium signature at one location of the bottom end cap o-ring seal. The location has been marked in black marker.

Forensics should continue, first with a

At this time, there is no reason to suspect that

2764   Thu Apr 28 14:12:20 2022 YehonathanUpdateWOPOStill figuring out the readout electronics and fixing of some stuff

{Shruti, Yehonathan}

We went to the e-shop to investigate the PD circuits. Completely confused about the behavior of the PDs we decide to gain some sanity by testing a sample AD829 on a breadboard with resistors and capacitors similar to those in the design of the PD circuits shown here. The PD is replaced by a voltage source and a 2kOhm resistor such that 0db gain is expected. We first measure the TF of the opamp with the Moku just with the resistors (attachment 1) then with the compensation capacitors.

We tried powering the opamp with shorting V- to ground like we did in the WOPO lab (for some reason this was how it was connected) and got garbage results (attachment 3).

We then turned to retesting the PD circuits with a proper powering scheme. However, connecting +/-5V and ground from a power supply resulted in the output of the PD circuit being ~ -2V even when the PD is taken out which might suggest that the opamps have really gone bad.

Attachment 1: JustTIR.pdf
Attachment 2: TIR_WithCapacitors.pdf
Attachment 3: OnlyV_plus.pdf
2763   Thu Apr 28 11:39:24 2022 JCElectronicsGeneralNetwork

I checked the internet in the TCS/MD Lab and it is running great and the switch is runing properly.

Attachment 1: IMG_0671.jpeg
2762   Mon Apr 25 11:08:35 2022 YehonathanUpdateWOPOStill figuring out the readout electronics and fixing of some stuff

{Shruti, Yehonathan}

We realized that the PD amp circuit only requires a 5V DC supply so we try that. One of the PD had the right response, although only after cycling the input impedance from 50ohm to 1Mohm which is weird. The other one (which produces the negative signal) was complete bonkers.

We remove the home-built PDs and put 2 Thorlabs PDs (forgot the model) with a bad dark current but a decent response and high saturation current. With these PDs we are limited by the PD noise to about 1.25db od squeezing when 30mW LO is detected on each PD without using electronic amplifiers. Attachment 1 shows the different noise spectra we measured.

We maximize the coupling efficiency before boosting the LO power. For some reason, the coupling between the LO fiber and fiber BS deteriorated but there was no apparent dirt on them upon inspection. We crank up the power and measure PD outputs using the Moku oscilloscope. The PD signals were subtracted digitally, but now we were not able to get the shot noise even after fine-tuning the gains. What went wrong? maybe it's because the PDs have separate power supplies?

Details later...

Some analysis in this notebook

2761   Fri Apr 22 13:58:09 2022 RadhikaDailyProgressEmissivity estimationPlan towards MCMC emissivity estimation

I've used the following model of heat transfer between a suspended Si sample (1) and the inner shield (2) in Megastat:

$m_1 C_p(T_1)\frac{dT_1}{dt} = \frac{\sigma A_1 (T_2^4 - T_1^4)}{\frac{1}{\epsilon_1(T_1)} + \frac{A_1}{A_2}(\frac{1}{\epsilon_2(T_2)}-1)}$, where I have not assumed that A1/A2 << 1.

For this analysis, I simulated temperature data of a sample using models of e1 and e2. I simulated e1 and e2 as linear in T:

$\epsilon_1(T) = 0.0025*T$

$\epsilon_2(T) = 0.00075*T + 0.13$, and generated test mass temperature data using these emissivity models and inner shield temperature data from a previous cooldown. My goal was to determine how uncertainty in the emissivity of the inner shield and heat capacity of silicon would propagate to the calculated emissivity of the sample.

I back-calculated the emissivity of the sample using a procedure similar to this paper: https://www.sciencedirect.com/science/article/pii/S0017931019361289?via=ihub. To summarize, I used a Savitzky-Golay (SG) filter in scipy to calculate dTdt from the temperature of the sample, and rearranged the model above to solve for e1.

The uncertainty of e1 can be found by:

$\Delta\epsilon_1^2 = \sum_i (\frac{\partial \epsilon_1}{\partial x_i} \Delta x_i)^2$.

I considered Cp_Si and e2 as uncertain parameters of interest, and assumed we do not have significant uncertainty on the geometric parameters such as the areas of the inner shield or the sample, or mass of sample.

The results from this analysis are:

10% uncertainty on emissivity of inner shield ---> 3% uncertainty on emissivity of sample
10% uncertainty on heat capacity of silicon ---> 12% uncertainty on emissivity of sample

Plots of these uncertainties can be found in Attachments 1 and 2.

Next steps are to add an additional radiative heating term to the model (more realistic given what we see in MS) and repeat this analysis, adding uncertain parameters such as size of heat leak. Transfering this analysis to MCMC is also in progress.

Attachment 1: e_uncertainty_eIS.pdf
Attachment 2: e_uncertainty_CpSi.pdf
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