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ID Date Author Type Category Subject
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
2630   Mon Aug 2 13:25:32 2021 StephenDailyProgressCryo vacuum chamberWarmup started 02 August

With Test Mass RTD at 119K, and with all of Koji's trials completed, I started the warmup this afternoon.

- Cryocooler off at 12:41

- Heater on at 13:05 (forgot to complete this task durming my initial visit).

Anticipated warmup duration of ~ 1 day, as improvements to cooldown (higher emissivity test mass, better conduction to inner shield) should also improve the efficiency of our active warming, which took a bit more than 30 hours last time (ref QIL/2615).

2633   Tue Aug 3 23:56:00 2021 KojiDailyProgressCryo vacuum chamberWarmup started 02 August

- Confirmed the heating stopped in the evening -> The heater was deactivated @~23:00

- Made some measurements and checks - the oplev spot was approximately on the center of the QPD before warming up. Now it is ~4mm above the center (note that the QPD size is 0.5" in dia) (Attachment 2). This corresponds to ~2mrad misalignment.

- Dismantled the OSEM electronics and power supply from the table. The electronics were salvaged into the OMC lab -> to be returned to the 40m.

- A 2" Al mirror package was brought to the OPLEV periscope so that the gold mirror (too thin) can be replaced. (Attachment 1)

Attachment 1: P_20210804_000247.jpg
Attachment 2: P_20210803_235421.jpg
2634   Wed Aug 4 18:55:58 2021 aaronDailyProgressCryo vacuum chamberloading cantilevers into megastat

This afternoon I met with Aidan and Stephen about near-term plans for the megastat. Aidan and I got familiar with the various viewports, and identified that if we want to set up another window for laser access we would need to move the existing window to the viewport 60 deg clockwise from its current location (at the SE corner of the chamber). We also noted that there is a single instrument RTD currently available (plus three others monitoring each heat shield and the cold head), so setting up two separate measurements each requiring temperature readout simultaneously would require opening up the electrical feedthrough and wiring up another RTD.

This week, I will be installing a clamped cantilever into the existing op lev setup in the cryostat. We will then pumpdown the chamber on Friday, and cool down over the weekend. At the beginning of next week, I will make some Q measurements of the clamped cantilever around 123K, then warm back up so Aidan can set up PD testing at the end of next week or early the following.

Today, I pulled a moderately smooth cantilever from cryo, and brough it over to QIL to clamp it. I hadn't used this clamp before, and found that the cantilevers Zach was producing in 2018 are larger than the slot in the clamp that was in the megastat. Since the clamping screws are not centered around the cantilever itself, one end of the clamp is touching steel on steel and the other is slightly open. I found in the elog that Zach was using a spare, broken off cantilever piece to balance the clamp. Later, he updated the clamp design and used an alignment jig to set the cantilever in the clamp. I will bring these items from cryo lab and install them in the megastat tomorrow.

Attachments:

1. clamp before any changes
2. View of the indium foil below the clamp
3. Two cantilevers from cryo, I used the one on the left
4. The uneven clamping job. Following my first attempt at clamping, I opened the clamp fully and noticed (and removed) Si particulate on the clamping surfaces. This uneven clamp is damaging the cantilever, and/or the cantilever's edges are shedding.
5. Showing that the clamped cantilever is somewhat too high for the megastat window. The cantilevers Zach was using with this clamp were shorter, and we do have some remaining in the cryo lab.
6. Overview of the megastat before covering with foil

Attachment 1: IMG_0390.jpeg
Attachment 2: IMG_0393.jpeg
Attachment 3: IMG_0399.jpeg
Attachment 4: IMG_0408.jpeg
Attachment 5: IMG_0412.jpeg
Attachment 6: IMG_0413.jpeg
2636   Thu Aug 5 11:53:26 2021 RadhikaDailyProgressCryo vacuum chamberCooldown model fitting for MS

I've used the following model for cooling of the coldplate and testmass in Megastat:

$P_{coldplate} = c \frac{\kappa A}{l}(T_{coldhead} - T_{coldplate}) + F_e(bp, cp) A_{coldplate} \sigma (T_{baseplate}^4 - T_{coldplate}^4)$,

where $F_e(bp, cp) = \frac{e_{bp} e_{cp}}{e_{bp} + e_{cp} - e_{bp}e_{cp}}$, and e_cp and e_bp are the emissivities of the coldplate and baseplate, respectively. The first term is conductive cooling of the cold plate via copper braid, and the second term is radiative heating of the coldplate from the baseplate (roughly room temp). In the model, the coefficient c is the fit parameter.

$P_{testmass} = Fe(is, tm) A_{testmass} \sigma (T_{innershield}^4 - T_{testmass}^4)$,

where $\frac{1}{F_e(is, tm)} = \frac{1}{e_{is}} + (\frac{1}{e_{tm}} - 1)\frac{A_{tm}}{A_{is}}$ and e_is and e_tm are the emissivities of the inner shield and test mass, respectively. This equation considers radiative cooling of the test mass from the surrounding inner shield. Here, the fit parameter is e_tm.

Attachment 1 (top plot) shows the results of the fitting. For conductive cooling of the coldplate, the best fit parameter is c=0.62. This means that 62% of the calculated conductive cooling power is actually being delivered to cool the coldplate, according to this model. Another way to look at it is that the constant factors (A, l of copper braid) that are used in the model need a correction of 0.62. Regardless, the model predicts a plateau temperature a few degrees cooler than the data shows. This means there must be a heat source we are not considering that delivers extra heating power at lower temperatures.

The testmass cooldown best fit parameter is e_tm = 1. I supplied bounds on e_tm from 0 to 1, since it is an emissivity value; the fit hits the upper limit. This is consistent with Koji's result that the calculated test mass emissivity is over 1. It is not clear why/how the test mass is cooled so quickly, since the black paint realistically has an emissivity between 0.5-1. Just like for the coldplate, the current model predicts a plateau temperature lower than what the data shows.

The bottom plot of Attachment 1 shows the difference between the fits and the data. The coldplate model does fairly well at high temperatures, but starts to break down around 100K. Then, other effects must be kicking in that we are failing to consider.

Next I plan to simplify further and model cooling power as a polynomial of T, and fit for its coefficients. Hopefully this can give insight into the temperature dependence of cooldown curve.

Attachment 1: model_fit_v_data.pdf
2638   Thu Aug 5 14:12:36 2021 StephenDailyProgressCryo vacuum chamberloading cantilevers into megastat (and actions toward pumping down)

Actions on my to-do list, before we are able to pump down for Aaron and Shruti’s Si Cantilever Q measurement:

0. Confirm Aaron has completed cantilever mounting and is happy with shield alignment.
- if needed, might have to rotate shields and/or clamp down workpiece holder.
[Done 2021.08.07] 1. Solder on new RTD, then mount RTD and heater to workpiece holder.
2. Verify electrical continuity of RTDs and heater.
3. Close up (shield lids, chamber lids).
4. (anytime, optional) complete RTD and Heater disconnection junctions with in-vac crimped pins.
[Koji indicated these were likely scavanged from DB connector kits, Stephen ordered more] - crimped plug pins were in 40m lab parts tower, but didn’t see any receptacle pins in the vicinity.

[update - Aaron indicated interest in deferring 1 week to establish more permanent setup. Likely to reattach outer shield RTD to cantilever clamp, allowing two different workpiece sensors] Planning to complete items on this list Friday, by Mariner meeting timeslot at the latest.We are in good shape to pump down Friday early afternoon, and for Aaron to collect data via controlled warmup on Monday/Tuesday (could run through Wednesday, if needed).

2641   Wed Aug 11 14:58:47 2021 RadhikaDailyProgressCryo vacuum chamberCooldown model fitting for MS

I've made simplifications to the testmass cooling model. Assuming 2 possible cooling mechanisms, radiative and conductive, the ODE must be a function of only $(T_{coldplate}^4 - T_{testmass}^4)$ and $(T_{coldplate} - T_{testmass})$. If conductive cooling/heating of the testmass is treated as negligible, as we previously assumed, then:

$\ddot{Q}_{testmass} \approx {\color{Blue} a} \sigma (T_{coldplate}^4 - T_{testmass}^4)$, where a is the fit parameter. I include $\sigma$ in the equation because it would appear as a constant in any radiative transfer model. I use the measured coldplate/inner shield temperature data for $T_{coldplate}$. Note that $\frac{dT}{dt} = \frac{\ddot{Q}}{Cp*m}$, and here and throughout I use a temperature-dependent $Cp_{Si}(T)$.

The best fit parameter is a = 0.014, and the result of this fit can be seen in Attachment 1. The disagreement between the best-fit model and data suggest that cooling is not only dependent on $(T_{coldplate}^4 - T_{testmass}^4)$, i.e. it cannot be radiative alone. I added back a conductive heating/cooling component:

$\ddot{Q}_{testmass} = {\color{Red} a} \sigma (T_{coldplate}^4 - T_{testmass}^4) + {\color{Red} b}(T_{coldplate} - T_{testmass})$, where a and b are the parameters of the fit.

The result of the fit can be seen in Attachment 2. The best fit parameters [a, b] = [0.022, -0.0042]. This model matches the data much better than the purely radiative model, but the negative sign on b is non-physical (I think) since $(T_{coldplate} - T_{testmass})$ should always be < 0, so the sign of the conductive term should also be < 0. I'm not sure how to interpret this result, but it almost seems like there is conductive heating to the test mass even though physically this shouldn't be the case.

2642   Wed Aug 11 18:00:19 2021 KojiDailyProgressCryo vacuum chamberCooldown model fitting for MS

How about incorporating radiative and conductive terms from the object at 300K?

2643   Fri Aug 13 15:14:14 2021 RadhikaDailyProgressCryo vacuum chamberCooldown model fitting for MS

Per Koji's suggestion, I added two terms to the expression for test mass cooling power for radiative/conductive cooling from 295K (see 2641):

$P_{radiative,295K} = {\color{Green} c} \sigma (295^4 - T_{testmass}^4)$;  $P_{conductive,295K} = {\color{Green} d} (295 - T_{testmass})$.

I added 0 as a lower bound for fitting a, b, c, and d. The best fit for d came out to be neglible (on the order of 10-17): conductive heating from room temperature can be ignored. The best-fit parameters for [a, b, c] came out to:  [0.025, 0.003, 0.001]. The result can be seen in Attachment 1.

This fit would imply that there is some radiative heating of the test mass from room temperature, in addition to expected radiative/conductive cooling from the inner shield / coldplate. It is worth investigating what might be causing this, and if nothing can be determined then the model needs to be revisited.

 Quote: How about incorporating radiative and conductive terms from the object at 300K?

2644   Fri Aug 13 21:01:42 2021 RadhikaDailyProgressCryo vacuum chamberCooldown model fitting for MS

Wow, nice fit!

How is this c compared to the 300K exposure from the open aperture for the oplev beam?
We tried to cover all the ports but one. A naive assumption is that we have this opening with this aperture size, but the heat leakage could be more than that.
e.g. the aperture allows angled infrared to come into the chamber and the inner shield reflects the hot radiation inside (and a part of it reaches the test mass).

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
2647   Thu Aug 19 14:34:10 2021 RadhikaDailyProgressCryo vacuum chamberCooldown model fitting for MS

Building on [2643], I realized that the conductive cooling term proportional to $(T_{coldplate} - T_{testmass})$ was also negligible. I added back in physical parameters for the 2 radiative terms (one from the cold plate, one from 295K) and used the emissivities of the test mass and inner shield as fit parameters:

$F_e = (\frac{1}{e_{tm}} + (\frac{1}{e_{is}} - 1) \frac{A_{testmass}}{A_{innershield}})^{-1}$

$P_{rad} = F_e A_{testmass} \sigma (T_{coldplate}^4 - T_{testmass}^4)$

$F_{e295} = (\frac{1}{e_{tm}} + (\frac{1}{e_{is}} - 1) \frac{A_{testmass}}{A_{aperture}})^{-1}$

$P_{rad295} = F_{e295} A_{testmass} \sigma (295^4 - T_{testmass}^4)$

I used Koji’s input to model radiative heating from 295K. I approximated the radius of the aperture (from which room temperature could be exposed) to be 3cm, and assumed radiative heat is emitted from this circle.

The result of this fit can be seen in Attachment 1: [e_testmass, e_innershield] = [0.59736291, 0.20177643]. This would imply that Aquadag has an emissivity of about 0.6, and that the emissivity of rough aluminum is much higher than expected at 0.2.

I then used these parameters to model the cooldown, given: 1. both the test mass and inner shield surfaces are painted in Aquadag; 2. only the inner shield surface is painted in Aquadag. These models are shown in Attachment 2.

Painting the inner shield in addition to the test mass would yield marginal improvement, as expected. However, painting the inner shield while removing Aquadag from the test mass would, according to this model, weaken the coupling further compared to the reverse case. This makes sense, since in Fe the effect of the inner shield’s emissivity is scaled by the ratio $\frac{A_{testmass}}{A_{innershield}}$, which is quite small. Increasing the emissivity of the test mass therefore makes more of a difference in the coupling.

Attachment 1: model_fit_tm_painted.pdf
Attachment 2: models_painted.pdf
2648   Fri Aug 20 13:44:58 2021 ranaDailyProgressCryo vacuum chamberCooldown model fitting for MS

I think the asymptotic temperature in the model is missing the data. i.e. the steady state temperature should match up, but the recorded data terminates too soon. Probably should figure out what the missing term is.

Can you post the covariance matrix of your fit so that we can see what the fractional errors are on the physical parameters? (i.e. construct the fit function so that physical parameters which are unknown are the fit parameters.)

2649   Fri Aug 20 14:05:45 2021 RadhikaDailyProgressCryo vacuum chamberCooldown model fitting for MS

The fit parameters are 1. the emissivity of the test mass and 2. the emissivity of the inner shield. Turning on absolute_sigma=True, the covariance matrix is:

[[4.40872002e-07 1.98911860e-07]
[1.98911860e-07 1.50052351e-07]].

Interpreting this, the standard deviation $\sigma$ of the parameters is:

e_innershield (rough Al): 0.00038737.

As discussed in today's meeting, these values much lower than expected. I'll look more into how scipy.curve_fit calculates these values, and will use the fitting script discussed to better quantify the error.

2665   Tue Sep 14 15:17:03 2021 StephenDailyProgressCryo vacuum chamberChamber up to air, lids removed

Monday I completed the vent that Aidan had started by turning off the cryocooler. During the afternoon I turned off the pumps, unbolted the chamber lid, and removed the radiation shield lids.

Next, Aidan was going to run some characterization measurements and determine whether to swap the diode or repeat with A1.

2666   Tue Sep 14 15:58:51 2021 RadhikaDailyProgressCryo vacuum chamberCold plate cooling limited by copper braid

Koji asked me to calculate the thermal resistance between the cold head and cold plate from Megastat cooldown data, to compare to the theoretical thermal resistance of the copper braid. This way we can determine if cold plate cooling is limited by the braid itself or by the contact(s) between the braid and cold head / cold plate.

After folding the copper braid in half, its cross-sectional area is 1.34e-4 m2 (source here) and I estimated its length to be 30 cm. I used a room-temperature value for the thermal conductivity of copper, for simplicity (~400 W/m*K). The "theoretical" thermal resistance of the copper braid should therefore be 5.57 K/W.

I used existing cooldown data from the cold head and cold plate to fit the thermal resistance between the two. I ignored effects from room temperature and simply modeled conductive cooling from the cold head to the cold plate. The result of the fit was a thermal resistance of 5.75 K/W, obtained from data. This value is pretty consistent with the calculation above, implying that the cold plate cooling is hitting the physical limits of the copper braid.

If the copper strap were instead a solid bar with the same nominal diameter (0.483"), the thermal resistance would drop to 3.15 K/W (a factor of 0.57 in cooldown time).

2667   Wed Sep 15 08:22:32 2021 AidanDailyProgressCryo vacuum chamberCONTAMINATION: Black paint flecks throughout chamber

I was setting up for some characterization measurements of the JPL PD and I noticed that there are flecks of black paint all through the chamber. There were a couple of visible bare sections on the wall of the inner shield where paint had been removed.

 Quote: Monday I completed the vent that Aidan had started by turning off the cryocooler. During the afternoon I turned off the pumps, unbolted the chamber lid, and removed the radiation shield lids. Next, Aidan was going to run some characterization measurements and determine whether to swap the diode or repeat with A1.

Attachment 1: IMG_4686.jpg
Attachment 2: IMG_4687.jpg
Attachment 3: IMG_4689.jpg
Attachment 4: IMG_4690.jpg
2674   Sat Oct 2 23:57:50 2021 StephenDailyProgressCryo vacuum chamberChamber pumping down, carbon paint flakes cleaned up

Pump down sequence executed tonight; Aidan plans to automate data collection during cooldown and warmup both, and the script will be activated early in the coming week.

- Carbon paint flakes (mentioned by Aidan in QIL/2667) were either picked up or scrubbed by IPA wipe, except the biggest, which were nudged near the closest 1/4-20 hole and picked up with tweezers for removal. There are still some small flakes of paint as there was less benefit to cleaning flakes closer to the PD or lens, and I opted not to risk any bumps. Aidan was correct, some areas of inner shield ID wall have flaked, but it seems the main location of delaminated paint is on the wrinkly foil excess covering the rim of the shield, an accidental paint location.

- While adding the lids, I monitored the PD outputs using Aidan's strip tool kindly left running. I never noticed any clipping in the trends - should I have been more skeptical?

- While adding the lids, I forgot to monitor the RTD outputs to the CTC100 controller, and the outer shield ended up shorting and ceasing to read any temperature. Didn't notice until I had turned on the roughing pump! Had to reopen and fix the short. Good reminder.

- Turbo came on at 12:07 am on 03 October at a pressure of 30 Torr - the setting is actually a timer and not a gauge reading.

2687   Mon Oct 25 16:13:47 2021 AidanUpdateCryo vacuum chamberHeater left on - chamber got warm

The cryocooler was switched off last Thursday to do testing on the JPL_PD. I turned the heater back on during this testing and neglected to turn it off when I finished at the end of the day. As a result, the workpiece reached ~400K over the weekend.

We are now allowing it to slowly cool down.

The CTC100 has a feature to specify an upper limit on temperature and then shut off the heater if that temperature is exceeded. We should engage this going forward.

Attachment 1: Screenshot_from_2021-10-25_16-19-39.png
2689   Tue Oct 26 07:32:52 2021 AidanUpdateCryo vacuum chamberHeater left on - chamber got warm

We're at 300K as of 7AM this morning.

 Quote: The cryocooler was switched off last Thursday to do testing on the JPL_PD. I turned the heater back on during this testing and neglected to turn it off when I finished at the end of the day. As a result, the workpiece reached ~400K over the weekend. We are now allowing it to slowly cool down. The CTC100 has a feature to specify an upper limit on temperature and then shut off the heater if that temperature is exceeded. We should engage this going forward.

2690   Tue Oct 26 08:43:38 2021 AidanUpdateCryo vacuum chamberCTC100 temperature alarm and heater shutoff

Instructions on how to enable the alarm and heater shut off for the CTC100.

Status: This reports the status of the alarm. If LATCH is enabled, this must be manually set to OFF once it has been enabled.

Mode: Set to "Level"

Latch: Optional to set to "YES" if desired.

Output: Set to "Heater"

Max: Set to desired maximum temperature.

The attached photos show:

• the menu where the settings are ALARM entered
• the main display just before the alarm is enabled (at 300.350K with a 1s delay)
• the main display just after the alarm is enabled - note that the Heater Output has been set to 0W.
Attachment 1: Screenshot_from_2021-10-26_08-42-57.png
Attachment 2: IMG_5371.jpg
Attachment 3: IMG_5396.jpg
Attachment 4: IMG_5401.jpg
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

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2694   Fri Nov 12 14:21:32 2021 Stephen, RadhikaDailyProgressCryo vacuum chamberUpgrade to Rigid Copper Bar, and assorted transitions from PD testing

This post describes upgrade efforts from 10 - 16 November, with the following goals:

- introducing a solid copper bar thermal linkage

- shifting the setup away from PD testing

- preparing for the next test (radiative cooling of Si)

Here are some highlights of the effort:

• While removing the shields we found contaminants had plated near the line of sight surfaces at the optical window and the electrical feedthrough [Attachment 1]. The film was removed by IPA wipe [Attachment 2] and was not evident in any other location (presumably these were the cold surfaces in line of sight, so they received the most contaminant, but there may be a thinner deposition throughout!).
• In order to install the copper rod, we needed to cut out slots in the outer shield and inner shield. We used a reciprocating saw and held the piece stiffly on a table [Attachment 3] [Attachment 4].
• We tried to use large snips, but that failed to provide enough cutting force, especially where it was necessary to use the tip to access into the flanged corner. We also damaged a few of the electrical leads to the feedthrough (formerly used to wire the OSEMs) - this will require attention at next opportunity.
• The copper rod itself was found to have a few issues:
• Outer surfaces were somewhat tarnished and greasy, so an 80 grit aluminum oxide paper was used to clean up all surfaces [Attachment 5]. The surfaces were then wiped with IPA using Alpha wipes.
• Slot width was matching the long thermal strap instead of the short thermal strap, so a drill press was used to add cut away the correct areas of one pair of holes [Attachment 6]. Later, this modification required larger washers in the stack under the bolt head.
• The cold head had a larger OD than designed, so we were unable to use the corner holes to mount the RTD. There was not enough space at the corners to host the nut or washer. Instead one of the bolt pattern holes was used to host the RTD stack [Attachment 7]
• The installation of the copper rod required the following steps:
• We documented the previous state of the table [Attachment 8].
• We removed the inner shield, the outer shield, and the old thermal linkage.
• To access the cold head side of the linkage, we had to remove the lower conflat of the T.
• We installed a 6" conflat flange, double faced with 4" bore (Lesker p/n DFF600X400), between the cryocooler and the T. This spacer raised the bottom face of the cold head to the correct height, so that the rigid copper bar runs approximately through the center of the shield apertures.
• This required an order of new bolts with 3" length, to squeeze the three flanges (cryocooler, spacer, T) that are now stacked together.
• We bolted the rigid copper bar to the coldhead, yawing the cryocooler to match the conflat bolt hole orientation while also pointing the copper bar down the axis of the arm.
• This used new vented screws (UC Components p/n C-412-A) which are also silver plated, except in the location borrowed for the RTD stack as mentioned above [Attachment 7]. The RTD stack included a nut to adjust spring compression independently from screw threading.
• Apiezon N thermal grease was applied on both surfaces to improve thermal conductivity across this joint.
• We initially forgot to reinstall the mylar sheet radiation shielding that had been removed from the area around the cold head and around the linkage. This required that we reopen the bottom conflat to install the coldhead mitten, and that we pitch the aluminum shields away from the rigid bar to allow the mylar sheet to be inserted from the inside.
• We found that the coldhead RTD had failed during intial mounting efforts, and a new RTD (actually one that had been desoldered from the setup previously, removed from the workpiece on 2021.08.07 but found to have no issue) was soldered and attached to the cold head, under the spring clamp.
• Each shield was reinstalled, including:
• The newly cut slots were used to pass shields over the rigid copper bar.
• Electrical cabling was threaded through the usual apertures.
• The outer shield was positioned on the G10 spacers.
• Rough alignment was completed based on clearance from the rigid copper bar, and line of sight to optical window.
• Final touchups were implemented:
• Aluminum foil covered unused outer shield apertures.
• A small aluminum foil panel was placed underneath the rigid copper bar, to cover the slot in the inner shield.
• Final clamping of the inner shield and the heater (with indium gasket) were completed.
• Thermal strap was used to link the cold baseplate to the rigid copper bar, with a bolted joint at the copper bar and a dog clamp joint at the baseplate. Apiezon N grease was applied to all contact faces.

The rest of the installation effort is captured in the next log post QIL/2695, to partition the items relevant to the radiative cooling of the silicon mass.

The photos here (and others) are posted to the QIL Cryo Vacuum Chamber photo album.

Attachment 1: IMG_0352.JPG
Attachment 2: IMG_0353.JPG
Attachment 3: IMG_0371.JPG
Attachment 4: IMG_0370.JPG
Attachment 5: IMG_0343.JPG
Attachment 6: IMG_0351.JPG
Attachment 7: IMG_0358.JPG
Attachment 8: IMG_0346.JPG
Attachment 9: IMG_2734.jpeg
Attachment 10: IMG_2740.jpeg
2695   Fri Nov 12 14:31:38 2021 Stephen, RadhikaDailyProgressCryo vacuum chamberRadiative Cooling of Si Mass, with better shield emissivity

In this phase, we are working toward improving our setup with a rigid copper bar, and obtaining a new data point for our radiative cooling thermal models for a suspended silicon mass. Since the past cooling runs of a silicon test mass did not yet incorporate aquadag-painted shields, we wanted to obtain a new data point in the model (in other words, we painted the shields in QIL/2645, but the next test was a PD measurement, so this is the first silicon test mass measurment after shields were painted). The improvement to the thermal linkage, now using a rigid copper bar with higher conductivity (ref. QIL/2666), is a second variable being changed simultaneously in the spirit of improving the cooldown time.

Refer to the prior post (QIL/2694) for the bulk of the blow-by-blow of configuring the chamber to use the rigid copper bar linkage. This post will describe the mounting of the Si mass, and the pump down and cool down.

• The silicon mass with Aquadag barrel was dropped into the existing frame, with the previous wire arrangement and with no particular requirement on position or orientation (just best effort centering and leveling). Adjustments were done chamberside as access was easier.
• The frame was lifted into the chamber, with the hanging mass supported by auxiliary fingers, and placed in an available area. Since conductive cooling was not a dominant mode of heat transfer in this setup (ref. QIL/2647), clamping to the baseplate was simply a single dog clamp on each foot of the frame.
• The cigarette paper was cryovarnished to the surface in the bare central position. Once the cryovarnish was set, the RTD was cryovarnished to the cigarette paper pad. No  strain relief or thermal anchoring considerations were implemented. RTD continuity was verified.
• Lids were bolted down and shields were finalized (avoiding shorting to copper bar, making sure foil drapes covering apertures were well positioned, etc.
• Vacuum pumps on at ~3 pm, cryocooler on at 3:30 pm. At 4 pm, things are still looking good!

Closeout photos will be posted to the QIL Cryo Vacuum Chamber photo album.

Attachment 1: IMG_2738.jpeg
Attachment 2: IMG_2741.jpeg
Attachment 3: IMG_2742.jpeg
Attachment 4: IMG_2745.jpeg
Attachment 5: IMG_2747.jpeg
2697   Fri Nov 19 14:01:40 2021 Stephen, RadhikaDailyProgressCryo vacuum chamberRadiative Cooling of Si Mass, with better shield emissivity

[WIP]

11/16 was the first Megastat cooldown after exchanging the copper braid linkage for a copper bar. Attachment 1 compares the cooldown trends for the test mass, inner and outer shields, and cold head. The solid curves are the new cooldown trends (copper bar), and the faded dashed curves are the previous cooldown trends (copper braid).

Immediate observations:

- The coldhead has a reduced heat load, and interestingly a second time constant governs cooldown from ~2-35 hours.

- The inner shield time constant is reduced significantly, but the inner shield experiences a slightly greater heat load at steady state.

- The test mass cooling is improved as expected, given inner shield cooldown.

- The coupling between the outer shield and inner shield has increased, resulting in greater cooling of the outer shield. This could explain the added heat load to the inner shield.

Attachment 1: comp_cooldown_728_cooldown_1116.pdf
2698   Fri Dec 3 09:31:40 2021 RadhikaDailyProgressCryo vacuum chamberTransitioning MS cooldown fitting to MCMC scheme

This week I have been working towards a Markov-chain Monte Carlo (MCMC) approach for fitting Megastat cooldown data and obtaining estimates on various emissivity values. I started with a simple model, only simulating the radiative cooling from the inner shield to the test mass. I supply the test mass and inner shield temperature data, and the emissivity of Aquadag (coating both the TM and inner surface of IS) as the only fit parameter. I am using Stan for the modeling, and Attachment 1 is a copy of my stan model.

The results of the simple model are in Attachment 2. The emissivity of Aquadag is estimated as a gaussian centered around 0.7. I am still determining whether this result is "real", or if the simulation is simply returning my prior. I will look into this more before adding complexity to the model.

Attachment 1: MS.stan
functions {

real coupling(real e_inner, real e_outer, real A_inner, real A_outer) {

real E;
E = e_inner*e_outer / (e_outer + (A_inner/A_outer)*(e_inner - e_inner*e_outer));
return E;
}

real Cp_Si(real T) {

... 66 more lines ...
Attachment 2: stan_blackcoat_fit.pdf
2699   Sun Dec 5 17:33:50 2021 ranaDailyProgressCryo vacuum chamberTransitioning MS cooldown fitting to MCMC scheme

thats looking good

You should try to use either the corner or getdist packages to plot the 'corner' plots commonly used when showing correlated posteriors (cf. https://emcee.readthedocs.io/en/v2.2.1/user/line/) so that we can see what's up with the other uncertainties

 Quote: This week I have been working towards a Markov-chain Monte Carlo (MCMC) approach for fitting Megastat cooldown data and obtaining estimates on various emissivity values. I started with a simple model, only simulating the radiative cooling from the inner shield to the test mass. I supply the test mass and inner shield temperature data, and the emissivity of Aquadag (coating both the TM and inner surface of IS) as the only fit parameter. I am using Stan for the modeling, and Attachment 1 is a copy of my stan model. The results of the simple model are in Attachment 2. The emissivity of Aquadag is estimated as a gaussian centered around 0.7. I am still determining whether this result is "real", or if the simulation is simply returning my prior. I will look into this more before adding complexity to the model.

2701   Fri Dec 10 15:58:57 2021 StephenDailyProgressCryo vacuum chamberRadiative Cooling of Si Mass, with worse inner shield inner surface emissivity

Started a new run this afternoon, with the following goals:

1) confirm that the first run (QIL/2695) went smoothly, by performing a visual inspection in the chamber while setting up for the first run.

- kapton tape affixing inner shield RTD lead junctions to inner shield had fallen. These junctions were simply hanging - not ideal, but apparently not too harmful. Not likely to impact temperatures, in my opinion, but could have led to shorts or glitches in data.

- all RTDs appeared to be fixed and well-contacted to surfaces

- Everything seemed to be in good shape with the copper bar, no apparent issues

2) obtain a second run with similar configuration, now that the rigid copper bar linkage has been implemented.

3) vary a single important parameter relative to the first run, namely the inner surface emissivity of the inner shield, so that the impact of that parameter may be observed.

- Added Aluminum foil (matte side visible) to the inner shield inner surfaces (lid and cylinder, both). Anywhere there was previously black Aquadag, there is now matte aluminum foil.

- Kept the same apertures for viewport access and for electrical and thermal connection passthrough, basically attempted to achieve identical shield coverage.

- There is one small sliver of black aquadag visible at the location of the electrical leads, but I didn't worry about patching that small area.

Run Details:

- Pumps on at  ~3:40 pm

- Cooling started at 4:13 pm (pressure ~6 mTorr, rapidly falling with turbo pump spinning up from ~70% to ~85% over a 1 minute interval). Coldhead RTD is responsive.

- All photos will be posted to the QIL Cryo Vacuum Chamber photo album.

- Note from check in on Monday afternoon, ~ 69 hours after start: everything looks good, and the workpiece temperature (~127 K) seems to reflect the emissivity change.

2702   Thu Dec 16 15:54:44 2021 Stephen, RadhikaDailyProgressCryo vacuum chamberRadiative Cooling of Si Mass, with worse inner shield inner surface emissivity - CTC100 temperature control success

This post will host plots and trends from this radiative cooling run. At a glance, the tuned CTC100 PI control was able to control the workpiece steady state temperature in this radiative cooling test within .005 K.

Run description: At 4 pm Wednesday, the workpiece temperature was at steady state from the QIL/2701 cooldown, a little less than 120 K. From 4pm Wednesday thru 5pm Thursday (25 hours) the CTC100 controller was actuating on the workpiece RTD temperature (cryovarnished to the suspended Si mass) using the resistive heater (dog clamped to baseplate with indium foil gasket). The conductive heating of the cold plate, and therefore the inner shield, led to radiative heating capacity (via ΔT)  that actuated on the temperature of the suspended test mass. As found in QIL/2643, the suspended Si mass is well isolated from conduction to the cold plate.

Before the run, the CTC100 PID controller was allowed to autotune using a long lag (600 s) and a moderate acutation step (10 W). After autotuning, the D term was still 0, which seemed fine.

Data: Attachment 1 plots cooldown curves for all RTDs during this run. Attachment 2 compares this run's test mass and inner shield temperature curves to those from the previous run (Aquadag on inner surface of inner shield). The expected result of this change (coating inner surface of inner shield with Al foil) is a weakened radiative coupling between the inner shield and test mass, leading to less effective cooling of the test mass.

Initial observations from data:

1) The cold head temperature curve again suggests 2 time constants, and cooldown is identical.

2) The inner shield's cooldown is roughly unchanged.

3) The outer shield's temperature drops significantly more, indicating a stronger coupling to the inner shield. We will check for a conductive short the next time we open up.

4) The test mass's cooldown matches expectations (weaker radiative coupling).

[WIP - The data will be fitted and discussed]. More detailed analysis from fit to come, including from heater runs.

Attachment 1: cooldown_12-10_all.pdf
Attachment 2: cooldown_12-10_vs_11-16.pdf
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
2704   Tue Dec 21 15:33:39 2021 StephenDailyProgressCryo vacuum chamberRadiative Cooling of Si Mass, with worse inner shield inner surface emissivity - next run repeating

I opened the QIL cryostat today for a health check and visual inspection before the next run. Because I saw a couple of interesting issues, I decided to redo the same run with more attention to detail on the closeout. I'm worried the outer shield may have been linked to the inner shield and baseplate enough to affect comparability with the prior run.

issues with this  run, requiring redo:

• RTD wire for outer shield was clamped under lid of inner shield - this might have created a conductive link between the inner shield and the outer shield
• outer shield was more wobbly than usual, and could have possibly been off of the three spacers - this might have created a conductive link between the outer shield and the baseplate

run details:

• pumping started at 3:45 pm
• turbo started with 15 minute delay at 20 torr
• cryocooler started at 4:15 pm with active ion gauge pressure at 3 e-4 torr.

And since I didn't get to implement any of the intended next runs, here are some notes on other future runs of interest:

• Si mass covered with Al foil (matte side facing out) - interested in making the emissivity of the test mass equal to that of the inner shield in the new config, for modeling.
• (of course, this emissivity equivalence would be an approximation, as there is a large area of the test mass which is bare silicon)
• outer shield clamped/resting on baseplate - this is predicted by Koji to be the most efficient cooling configuration.
• shielding attached to structure holding Si mass (electropolished aluminum, aquadag aluminum, bare aluminum surfaces are all available.
2706   Fri Jan 7 14:54:58 2022 StephenDailyProgressCryo vacuum chamberFastest Radiative Cooling run started 14 Jan

As discussed during the 07 Jan 2022 meeting, the next cryostat run will seek the fastest radiative cooling through the following configuration choices:

• maximize emissivity of test mass volume
• improve conductivity to outer shield

Actions completed 14 Jan 2022

• Vent
• Cover up aperture to viewport with foil (on both shields).
• Remove foil from inner shield inner surface.
• Place outer shield directly onto cold plate (no clamping force).
• A bit unsatisfying, because the outer shield is not flat relative to the cold plate, but the shield is resting quite firmly with only a slight wobble when pressed. As with any plane-plane contact, there are a limited number of true points of contact, and the contact area is increased somewhat by foil that is folded around the outer shield or the cold plate.
• I would estimate the contact area at ~5% of the total area of the bottom flange.
• 2x G10 spacer washers were dropped into the lower volume whild making this switch.
• Note that bottom lid of outer shield is still not conductively cooled, and therefore will be approximately room temperature.
• Tidy up aluminum foil collar around bottom lid of outer shield.
• Tidy up mylar shield around conductive link after inner shield
• Pump down, cool down.
• Pump down started at ~15:35.
• Cool down started at 16:10.
2708   Tue Jan 18 16:11:35 2022 StephenDailyProgressCryo vacuum chamberStatus of Fastest Radiative Cooling run started 14 Jan

I ended the first cooldown of the run at 12:49 today, approximately 92 hours after it had started. Workpiece temperature was 100 K - more data and model fitting will reveal more insights on the results.

I started a 5 W injection through the heater (dog-clamped to baseplate with indium gasket), which I intend to leave running until steady state temperature is reached, at least overnight. This power level will not present a risk to the system, so I feel comfortable with this static power input even though it is not interlocked.

Update after 25 hours [ATTACHMENT 1]

The 5 W heating of the shields has not quite leveled off yet, and the workpiece temperature resumed falling, showing the temperature had not yet reached a steady state. I will leave 5 W on until I see a steady state, then I will plan to turn off 5 W and allow the workpiece trend to level off fully. Summary:

• with no heater input, after 90+ hours the workpiece was slowly cooling at a rate of ~ 1 K per 6 hours, and the inner shield temperature was stable at about 76 K.
• with 5W heater input, after about 25 hours the workpiece is (still) slowly cooling at a rate of ~ 1 K per 18 hours, and the inner shield temperature is about 88 K and slowly rising about 0.1 K per 7 hours

See attachment 1 for data viewer screenshot which reflects the above summary.

Update after 145 hours [ATTACHMENT 2]

Continued injecting 5 W for the whole weekend. Over the last 24 hours, the workpiece temperature seems to have leveled off into a new cooling rate, while both shields alternated between heating and cooling. I think this can be described as a steady-enough state that I'm ending the cooldown.

Now, I'll let the chamber come up to temperature with the help of the 5 W load.

Attachment 1: 5w_input_qil_cryostat_20220119.png
Attachment 2: 5w_input_121_to_145_hours_qil_cryostat_20220124.png
2709   Fri Jan 21 13:28:48 2022 RadhikaDailyProgressCryo vacuum chamberHeat transfer between grease joints and pressure joints

I took a deep dive into Ekin 2.6 to understand heat tranfer between various joint types, specifically pressure joints and grease joints. This was motivated by the fact that modeling of the cold plate and inner shield temperatures seemed to be missing some key physics.

Heat conductance through grease joints is dependent on the contact area of the surfaces:

$\frac{\dot{q}}{\Delta T} = \frac{\dot{q}}{\Delta T}(1 cm^2) \frac{A}{1 cm^2}$, where $\frac{\dot{q}}{\Delta T}$ = the heat conductance. The heat conductance of a grease contact with area 1 cm2 can be found in Attachment 1, indicated by the region between the blue and red boxes (our temperature range).

Heat conductance through pressure joints is dependent on the force holding the surfaces in contact:

$\frac{\dot{q}}{\Delta T} = \frac{\dot{q}}{\Delta T}(50kgf) \frac{F}{50kgf}$, where the heat conductance of a pressure contact with force of 50kgf is found in Attachment 1, indicated by the orange box. (Megastat pressure contacts are between the cold plate and shields, so the Al-Al contact was referenced.)

[Added] Heat conductance through varnish joints are similar to grease joints, in that the conductance scales with contact area of the joint. (It follows the same formula as above for grease joints.) The heat conductance of a varnished contact with area 1 cm2 can be found in Attachment 1, and note that it is higher than that of greased contacts.

My efforts this week went into incorporating these heat links into the model. This required splitting up components into various parts (verging on a finite-element approach), since every joint is considered in addition to the elements themselves. A few notes:

1. For now, I assume the force between the inner shield and cold plate is 50 kg, for simplicity. Therefore, the heat conductance being used for this pressure joint is 4.5 W/K (from chart), and I am using this constant value across temperatures until a better estimation can be found.

2. For the grease joints, I estimate the heat conductance at 1 cm2 to be ~ 1 W/K, for the 50-300K range.

3. The contact between the outer shield and cold plate is not actually uniformly touching, as noted in 2706. I am not sure how to estimate the actual force between the surfaces, so I will add this as a fit parameter in the model.

The new model with this incorporation still needs some adequate debugging, but I felt these were vital steps to ensure we get realistic answers regarding cooling power of the copper bar vs. LN2. Once I feel the model can be trusted, I will follow up with analysis of the new optimized cooldown.

Attachment 1: thermal_conductance_joints.png
2710   Fri Jan 21 17:32:40 2022 ranaDailyProgressCryo vacuum chamberHeat transfer between grease joints and pressure joints

Is there a units issue? 50 kg is a mass, but not a force.

2711   Tue Jan 25 10:24:14 2022 ranaDailyProgressCryo vacuum chamberHeat transfer between grease joints and pressure joints

For one surface resting on another, the force of the contact is the grativational force of the top surface. There's an implicit factor of $g$ that cancels out from the ratio, so it becomes a ratio of masses. The heat conductance listed for a 50 kg Al-Al pressure joint is interpreted as the heat conductance for a force of $50g$.

 Quote: Is there a units issue? 50 kg is a mass, but not a force.

2712   Tue Jan 25 13:15:40 2022 ranaDailyProgressCryo vacuum chamberHeat transfer between grease joints and pressure joints

I think its least confusing to just replace 50 kg g with 500 N. Writing 50 g can be misleading, it seems like 50 grams.

2713   Tue Jan 25 14:01:27 2022 StephenDailyProgressCryo vacuum chamberHeat transfer between grease joints and pressure joints

There's also a convention to write "50 kgf" to designate "kilograms of force" (implying the same conversion Rana describes, multiplying by g). I see kgf enough in the mechanical engineering world that I wouldn't have been confounded, so I wanted to pass that along.

 Quote: I think its least confusing to just replace 50 kg g with 500 N. Writing 50 g can be misleading, it seems like 50 grams.

2717   Mon Feb 7 11:57:38 2022 StephenDailyProgressCryo vacuum chamberDoubled Thermal Linkage Capacity run started 11 Feb 2022

The double copper bar configuration pictured in Attachment 1 has been implemented. We completed the updates within work sessions on Thursday and Friday. Here's a pseudo-log:

• Removed all items from coldplate to make space for thermal linkage.
• Prepared thermal linkage for installation.
• ref. QIL/2694 for all preparations made.
• Removed thermal linkage to allow for regreasing
• Discovered a single brass #4 washer sandwiched between coldhead and rigid copper bar (likely lost during efforts to install an RTD during intitial thermal linkage install); thermal grease was mostly indented at brass washer and at area opposite location of brass washer, suggesting non-uniform contact.
• Applied Apiezon N thermal grease at joints: [coldhead - top copper bar], [top copper bar - bottom copper bar, near coldhead], [top copper bar - bottom copper bar, near thermal strap].
• Sandwiched together top and bottom copper bars, to insert simultaneously.
• Angled top and bottom copper bars to pass below coldhead, and overall passing the two bars in together went smoothly.
• Bolted both copper bars into coldhead using long (1.25") 4-40 bolts threaded into coldhead. Access was from bottom port below cryocooler. Torqued using short arm of allen key (no access for long arm).
• Borrowed one bolt location for RTD spring clamp mount. Confirmed continuity of coldhead RTD.
• Repaired pins damaged in removal, and inserted sheaths intended to replace the previous scheme and hopefully prevent pin and socket damage. More detail later :).
• Installed shields.
• Applied new Apiezon N thermal grease to bottom flange of inner shield.
• Re-clamped inner shield to cold plate using a dog clamp array.
• Placed outer shield in contact with outer shield; rocking percieved when pressing on one quadrant of the annulus.
• Confirmed continuity of shield RTDs.
• Installed test mass, still with heater mounted to planar surface as in QIL/2715.
• Confirmed suspension wires were contacting bare silicon OD surface in middle.
• Confirmed continuity of heater and of workpiece RTD.
• Closed up, pumped down, cooled down.
• Roughing pump on at ~4:20 pm
• Turbo on with no issues after 15 minute programmed delay
• Cooling started at 5:15 pm, pressure was a few E-4 torr; no need to wait so long, that was just when we got around to it.

All images are (or soon to be) posted to the QIL Photo Dump.

2720   Tue Feb 15 11:59:22 2022 RadhikaDailyProgressCryo vacuum chamberDoubled Thermal Linkage Capacity run started 11 Feb 2022

*Note: The RTD spring-clamped to the cold head gave spazzy readings for this cooldown, so the last cooldown's cold head temperature data was used instead for reference.

Looking at the data, there are some initial noteworthy observations:

The outer shield's conductive coupling to the copper bar / cold plate is much higher than previous cooldowns. Attachment 2 shows that the outer shield gets colder than the test mass, and around the 82 hr mark their temperatures cross.
We hoped to see a reduction by about a half in cooldown time for the 02/11 run, after effectively doubling the cross-sectional area of the copper bar. However, the data does not show x2 improvement, as seen in Attachment 1.

It could be that somehow the resistances of re-bolted joints increased significantly to compensate the lowered resistance of the bar, but this doesn't seem too likely. The more likely answer is the model overestimated the original resistance of the bulk of the copper bar relative to other components/joints in the chain. This means more work needs to be done, and hopefully a more realistic model will also resolve the discrepancy in early cooldown of the inner shield data.

Attachment 2 shows the best fit for the new cooldown.

Attachment 1: Cu_bar_comparison.pdf
Attachment 2: cooldown_0211_all.pdf
2721   Tue Feb 15 16:54:27 2022 ranaDailyProgressCryo vacuum chamberDoubled Thermal Linkage Capacity run started 11 Feb 2022

I've been assuming that the inner shield can be treated as a point mass, but perhaps the thinness make a significant delay between the temperature of the cold plate and the inner shield during the initial cooldown.

Could you model the cold shield to estimate what the temperature gradient would look like during the rapid cooldown? Not full 3D, but something approximate that takes into account the conductivity, thinness, and heat capacity.

2722   Wed Feb 16 11:35:18 2022 StephenDailyProgressCryo vacuum chamberDoubled Thermal Linkage Capacity run started 11 Feb 2022

The heater was turned on on Wed, 2/16 at 11:30am, with control setpoint 123K. The lower power limit was verified to be 0W.

The cryocooler was turned off on Thu, 2/17 at 12pm. The heater control setpoint was changed to 295K for warmup. The plan is to address the wacky cold head RTD on Monday.

2724   Thu Feb 24 10:44:06 2022 RadhikaDailyProgressCryo vacuum chamberDouble copper bar cooldown rerun started 02/23

The goals for this cooldown are:

1) Securely re-attach the RTD to the cold head, to fix wacky readings.
2) Reduce thermal conductance between the outer shield and cold plate (/copper bar), to prevent the outer shield from cooling below 200K.
2a) Stabilize the outer shield so that its contact area with the cold plate is consistent run-to-run. ([Note] Follow-up to an in-person comment from Rana: the positioning of the shields does not leave space for any clamps to secure the outer shield to the cold plate.)

On Tuesday 2/22, we opened up the bottom conflat of the T to check on the RTD spring-clamped to the cold head. I re-inserted the RTD and tightened the nut further than last run, and it seemed much more secure [Attachment 1]. I re-inserted the mylar "cap" covering the cold head [Attachment 2].

In the chamber body, we carefully passed the RTD leads through the inner shield and outer shield apertures to remove the outer shield. We did this without having to unclamp/remove the inner shield or any components inside, to preserve consistency with the last cooldown. A few pins were damaged in this process (from inner shield).

Once the outer shield was removed, we used kapton tape to secure strips of peek sheets to its bottom rim [Attachments 3,4]. The strips were taped at 2 points along the rim associated with the most wobble, with hopes of stabilizing the shield as much as possible.

On 2/23 I repaired the pins previously damaged. I also added kapton tape labels to the socket leads, corresponding to the shapes found on the RTD leads (semi-circle example in Attachment 5). This way it will be much easier to match the right pins and sockets in the future.

I then bolted up the chamber (close-out pictures can be found on the QIL Google photo dump). The vacuum pump was turned on at 5:45pm, and the cryocooler was turned on at 7:08pm.

Attachment 1: IMG_3095.jpg
Attachment 2: IMG_3096.jpg
Attachment 3: IMG_3083.jpg
Attachment 4: IMG_3087.jpg
Attachment 5: IMG_3092.jpg
2726   Tue Mar 1 15:59:34 2022 RadhikaDailyProgressCryo vacuum chamberDouble copper bar cooldown rerun started 02/23

The heater was turned on on Tue, 3/1 at 4pm, with control setpoint 123K.

*UPDATE: After checking a few hours later, I noticed the test mass temperature hadn't risen, and the heater power was reading nan. When I initially turned the heater on, I watched the power ramp up to 22W (max power limit) and the test mass temperature start to rise. I wonder if somehow the lead pins shorted after it was turned on. For now I have turned the heater output off and will check on this after warmup.

The cryocooler was turned off at 5:45pm.

2729   Fri Mar 4 13:18:09 2022 RadhikaDailyProgressCryo vacuum chamberDouble copper bar cooldown rerun started 02/23

Analysis of 02/24 cooldown data

Attachment 1 shows the cooldown data for this run. Attachment 2 compares this run to the previous 02/11 run, where in between insulating peek sheets were taped to 2 locations along the bottom rim of the outer shield.

Observations:

1. The inner shield, outer shield, and test mass all cool slightly faster initially in this run (02/24) compared to 02/11. This effect is seen until ~35 hrs, after which:

2. The outer shield starts to warm up and re-equilibriate. It seems the radiative heating from the chamber strongly kicked in once the outer shield was sufficiently cold.

The best fit for the data can be seen in Attachment 3. Note the addition of the copper bar model, which considers radiative heating from the chamber at RT.

1. The outer shield is still getting quite cold, so we have to consider increasing the insulation from peek sheets (either adding more layers or additional points of contact), or another approach altogether.

2. There are still obscure effects at play in early cooldown that the model is not considering. I have gone back to the drawing board and am trying to fit the raw inner shield data to a sum of exponential terms, in hopes of narrowing down the cooling mechanisms that could be affecting data.

Next steps:

- Check on the heater leads during next opening and perform tests to ensure test mass is warming up

- Devise insulation solutions for outer shield to decrease system heat load

- Consider using indium foil to increase thermal conductance between joints along cooling pathway

Attachment 1: 02-24_cooldown_data.pdf
Attachment 2: 02-24_cooldown_data_comparison.pdf
Attachment 3: cooldown_0224_bestfit.pdf
2730   Thu Mar 10 16:21:11 2022 RadhikaDailyProgressCryo vacuum chamberInsulated outer shield cooldown started 3/10

Our goal for this week's cooldown was to tape peek sheets fully around the outer shield lip, to leave no bare aluminum contact area with the cold plate. Secondly, we wanted to diagnose and mend the issue preventing the heater from outputting any power. The full procedure was:

1. We allowed the chamber to vent, unbolted the chamber lid and outer/inner shield lids.

2. We noticed that the solder joints between the heater body and its leads had debonded [Attachment 1].

a. The suspension frame was taken out of the chamber and the test mass was removed from the frame.

b. In doing so, we noticed that the varnish joining 1. the heater to cigarette paper and 2. cigarette paper to Si was debonding in certain areas, likely due to Aquadag not being fully removed from the test mass in the area of contact [Attachment 2].

3. We wrapped the copper leads a few times around the heater "wings" and re-applied solder [Attachments 3, 4].

4. We cleaned off aquadag from a greater area on the test mass and applied varnish to re-bond the heater [Attachments 5, 6].

a. We let the varnish cure for ~2 days with a small weight on top.

5. The outer shield was removed from the chamber (without unbolting/removing the inner shield), and a single layer of peek sheet was taped the whole way around the bottom lip [Attachment 7].

6. We re-inserted the outer shield and passed the RTDs back through.

a. We reattached a few RTD lead pins/sockets that had broken off in handling.

7. Lastly, we placed the test mass back into the suspension and into the chamber.

8. Close out [Attachments 8, 9]

The vacuum pump was engaged and the cryocooler was turned on at ~3:30PM.

Attachment 1: 82E812D8-946F-4F93-95C2-A62EC189A1E5_1_105_c.jpeg
Attachment 2: CFDD543D-17FB-4F49-A62B-090A15E47821_1_105_c.jpeg
Attachment 3: B5D683AC-986A-49B9-A1C3-379851C877E5_1_105_c.jpeg
Attachment 4: E06C8191-8A7F-4917-A97A-80F9F38BA614.jpeg
Attachment 6: IMG_3160.jpeg
Attachment 7: C8A0E8EB-EB18-4B76-BF0D-6A67A4831C77_1_105_c.jpeg
Attachment 8: IMG_3167.jpeg
Attachment 9: IMG_3168.jpeg
2732   Mon Mar 14 14:04:54 2022 RadhikaDailyProgressCryo vacuum chamberInsulated outer shield cooldown started 3/10

The heater was turned on at 2:05PM 3/14, with a setpoint of 123K.
The cryocooler was turned off at 10:50AM 3/15, and the heater setpoint was raised to 275K to aid in warmup.

Today I opened up Megstat to add indium in between the copper bar joints, with the hopes of speeding up cooldown and informing the thermal model.

Outline of procedure:

• Disconnected RTD pins/sockets and removed suspension from chamber (with test mass)
• Removed inner shield and outer shield from chamber
• Cleaned up residual grease/aquadag from cold plate
• Opened up bottom conflat of the T to access ends of the 2 copper bars
• Unbolted copper bars and removed from chamber [Attachment 1]
• Gave copper bars a good wipe down with isopropyl to remove old grease
• Placed 2 indium gaskets previously prepared by Stephen between joints of the two bars [Attachments 2, 3, 4]
• Fed the bars back through the chamber tube and placed additional indium gasket between top bar and cold head
• Placed last indium gasket between flexible strap and bottom copper bar in chamber body
• Bolted up the copper bars, passed through 2 sheets of aluminized mylar to insulate copper bars [Attachment 5]
• Resecured the cold head RTD with spring clamp, inserted mylar "cap" around cold heat [Attachments 6, 7]
• Touched up shields
• Reapplied grease to bottom lip of inner shield
• Added some more kapton tape to secure peek sheets to bottom lip of outer shield
• Reinserted shields, bolted down inner shield
• Reinserted suspension frame with test mass [Attachment 8]
• Reconnected RTDs and closed up

The roughing pump was turned on at 7:20pm, followed by the cryocooler at 7:50pm.

Attachment 1: IMG_3191.jpeg
Attachment 2: IMG_3197.jpeg
Attachment 3: IMG_3194.jpeg
Attachment 4: IMG_3195.jpeg
Attachment 5: IMG_3206.jpeg
Attachment 6: IMG_3204.jpeg
Attachment 7: IMG_3205.jpeg
Attachment 8: IMG_3210.jpeg

The data from this cooldown is attached (labeled 03/19 - UTC time), compared to the run started on 03/10. In between these 2 cooldowns, the greased joints were replaced with indium joints on both sides of the copper bars (cold head to copper bar, copper bar to flexible strap).

Observations:
1. The outer shield is in weaker conductive contact with the cold plate than before. Due to the resting of the outer shield (no clamping), the amount of contact is expected to vary run to run.
2. The cold head seems to be experiencing a larger heat load than compared to the previous run. The inner shield does get slightly colder, but this could be attributed to less cooling power being diverted to the outer shield. It is unclear what additional elements could be receiving this extra cooling power.
3. The steady-state temperature difference between the cold head and inner shield is much smaller than in previous runs (23K to 10K). Since this offset is determined by steady-state heat loads along the conductive pathway to the inner shield, it isn't immediately clear why this would have decreased
4. The test mass cooldown trend stays nearly identical to the previous run, despite the aforementioned differences. This seems to confirm that there is some heat leaking from the outer shield to the test mass, which balances the extra cooling power from the inner shield.

Efforts to update the model (indium links) and analyze these runs is ongoing. Accurate analysis rests on understanding points 2 and 3. above, since the current model predicts a much larger steady-state offset between the cold head and inner shield.

I plan to devote some time to this analysis before planning another Megastat cooldown.

Attachment 1: cooldown_0319_vs_0310.pdf
2737   Sat Mar 26 12:49:18 2022 StephenDailyProgressCryo vacuum chamberWarmup started, issue with steady state heating

25 March 2022 (Friday) at 21:00, went to QIL to start warmup.

- Cryocooler was turned off at 21:21

- Heater output was disabled - it seemed there was an issue, and therefore I opted for passive warmup only.

Heater Issue Troubleshooting

Symptom: Heater Output was enabled but reporting only .35 W and "Err" indicator.

Symptom: When output was disabled, a fan noise was terminated. When output was reenabled, the same fan kicked back on. The fan was driving much harder than I had ever heard it before.

Symptom: The output indicated .35 W but the test mass temperature was 66 K. Past heater power for steady state at 120 K was on the order of 1 W.

Per CTC 100 manual:

- pg 9 (100W heater outputs) indicates: "If the temperature of either PCB exceeds 60°C, the CTC100 automatically shuts off the corresponding output" which was not the case.

--> Apparently not an overtemperature situation.

- pg 9 (Hardware faults) indicates a list of error conditions which are accompanied by pop up windows.

--> This error had no pop up window, not quite sure what to make of that except that the controller doesn't think our issue is something it can identify.

- pg 29 (The system fan) notes that "The main system processor reads the desired fan speed from each I/O card and sets the fan to the fastest requested speed".

--> Suggests that the louder fan noise may have indicated higher temperature condition, even if not an over tempearature condition.

- pg 41 (Numeric) describes that in the typical numerical view of the data channels, the message "Err" that I saw on the heater channel indicates "an internal error has occurred".

--> No explanation of what an "internal error" is, but in this case I suspect it could reflect that the heater output is not coupled the input Workpiece temperature.

Best Guess: the symptoms and the lack of any apparent controller-identified fault suggests that the heater may have debonded. I didn't look at temperature history, so I'm not sure if there was a point where the heater was bonded to the test mass during this run.

Next Steps: We should open up and investigate.

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