Updated the model the latest log data with cooling prediction

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

• We know the cold head temp from the measurement. For the prediction, the constant cold head temp of 65K was assumed.
• The table temp was estimated using conductive cooling model + linear empirical dependence of the conductivity on the temp
• The constant specific heat of the silicon mass (0.71 J/K/g) was assumed. This may need to be updated.
• The radiative cooling is given from Stefan–Boltzmann law with the emissivity of 0.15 for both the shield and the mass.
   
• The conductive cooling of the test mass was estimated using: Wire diameter 0.017" (=0.43mm), 4 wires, length of ~10cm (guess), no thermal resistance at the clamps (-> upper limit of the conductive cooling)

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

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

See https://nodus.ligo.caltech.edu:8081/40m/16250

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

1. Temperature Trend

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

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

2. Oplev Trend (Attachment 1)

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

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

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

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

3. OSEM and the magnet

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

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

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

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

4. CTC100 logging

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

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

5. Heating

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

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

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

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

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

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

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

Also brought some power cables.

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

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

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

Can we extract any information from this "0.15"?

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

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

is an emissivity factor.

The book explains some simple cases in P 443:

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

Case (b): If OBJ1 and OBJ2 has the same area, . The situation is symmetric and the emissivity factor is influenced by the worse emissivity between e1 and e2. (Understandable)

Case (c): For general surface are ratio,  . OBJ2 receives the heat from OBJ1 and reradiates it. But only a part of the heat comes back to OBJ1. So the effect of e2 is diluted.

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

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

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

Can Aquadag increase the radiative heat transfer?

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

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

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

Updated Jul 26, 2022 - 22:00

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

[Stephen Koji]

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

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

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

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

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

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

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

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

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

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

[Stephen Koji]

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

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

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

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

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

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

[Stephen Koji]

Road to cooling down

• The suspension with the test mass was installed in the chamber again
• Looking at the oplev beam, we jiggled the wire loop position to adjust the alignment approximately.
• The oplev beam was aligned more precisely.
   
• We intentionally kept the OSEM at the "fully-open" position, while it is still close to the magnet so that we can have some actuation.
• The coil driver was tested before closing the chamber, but it did not work.
  The coil itself was still intact, and the mirror was responding to the coil current if the coil current of ~100mA was applied from a bench power supply with the current ~100mA).
  So the problem was determined to be external.
   
• Once we were satisfied with the oplev/OSEM conditions, the inner and outer lids were closed. Then the chamber was closed.
   
•  Started pump down.
• Started cooling down @18:30 / started temp logging too. Log filename: temp_log_cool_down_20210728_1830.txt

The photos were uploaded to Google Photo of WB labs.

The coil driver issue was resolved:

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

Checking the DAQ setup / damping loop

• DAQ setup
  • ADC: QPD X->FM16 / Y->FM17 / S->FM18 / OSEM-> FM19
  • DAC: CH11 -> Coil Driver In
• Connected FM16 and FM17 to the coil drive by setting C4:TST-cdsMuxMatrix_12_17 and C4:TST-cdsMuxMatrix_12_18 to be 1.0
• It was not obvious if the coil could damp the rigid body modes.
  • Actating the magnet caused Yaw motion most. Some Pitch motion too.
  • Configured FM16 and FM17 for the damping loop.
    • Filter Bank #1: [Diff0.1-10]  Zero 0.1Hz / Pole 10Hz
    • Filter Bank #10: [Anti Dewht]  Zero 1&200Hz / Pole 10&20Hz
  • Tried various damping gain. The mass was moving too much and the proper gain for the damping was not obvious.
  • So, the initial damping was obtained by shorting the coil at the coil in of the sat amp unit. (Induced current damping)
  • Once the test mas got quieter, it was found that -0.01 for FM16 could damp the yaw mode. Also it was found that +0.1 for FM17 could damp the pitch mode. (But not at once as the filters were not set properly)
     
• TF measurement for calibration
  • The beam was aligned to the QPD
  • The test mass was damped by using the damping loops alternately 
  • Taken a swept sine measurement Filename: OSEM_TF_210729_0243.xml
    Recorded the time, saved the data, and took a screenshot
    • This measurement was taken @T_IS=252K / T_TM=268K @t=8hr (2:30AM), Rcoil=15.6Ohm
  • Second measurement Filename: OSEM_TF_210729_2147.xml
    • @T_IS=172K / T_TM = 201K @t=27.5hr (10PM), Rcoil=10Ohm
  • 3rd measurement Filename: OSEM_TF_210730_1733.xml
    • @T_IS=116K / T_TM = 161K @t=47hr (5:30PM), Rcoil=?
  • 4th measurement Filename: OSEM_TF_210731_2052.xml
    • @T_IS=72K / T_TM = 134K @t=75hr (9:30PM), Rcoil=6.0Ohm

OSEM LED/PD

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

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

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

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

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

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

- The cold head cooling is faster and cooler

- The inner shield cooling is faster

- The test mass cooling is faster

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)

[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.

• Output going to JPL_PD/data/A1_test2 and DAQ
• Test commenced at 8:20AM and cryo cooler started shortly afterwards
• Once trhough the loop takes about 20 minutes
• Cryocooler on at 8:42AM

• Turned cryocooler off around 1317588441 (about 1:46PM)
• Restarted measurement with output going to JPL_PD/data/A1_test3
• Room is noticeably quieter without the cryocooler on.

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

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

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

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

[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.

• https://nodus.ligo.caltech.edu:8081/QIL/2674. Turbo comes on after 15 minutes. Roughing pump gets to 30 Torr at this time
• https://nodus.ligo.caltech.edu:8081/QIL/2654
  • t = 0m: pump ON
  • t = 15m: Turbo ON (~30 Torr) [Turbo automatically on at 15m]. Reading at approximately 15-16m
  • t = 23m: 1mTorr
  • t = 33m: 0.3-0.5mTorr
• https://nodus.ligo.caltech.edu:8081/QIL/2288
  • t = 6 hours, 8.2E-6 Torr

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

Coldhead reached 363K (90C)

Innershield reached 403K (130C)

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

https://www.laddresearch.com/index.php/lanotattachments/download/file/id/40/store/1/

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

[Aidan]

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

Note about the QE measurement: 

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

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

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

Notes from Test 3

~/JPL_PD/data/A1_test3/README

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

PREAMP GAIN = 1E3

SR560 gain = 500

LD temp set point = 20.2kOhm

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

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
   Outer Radius = 0.2794 m (11")--> CAD .265 m (10.433")
   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:
   Outer Radius = 0.244983 m (9.645") --> CAD .225 m (8.858")
   Height = 0.205994 m (8.11") --> CAD .192 m (7.559")
   Thickness = 2.90 mm (0.114")

Cold plate specs:
   Radius = CAD .254 m (10")
   Thickness = CAD .01498 m (.5897")

Test mass specs: (confirmed)
   Radius = 0.0508 m (2")
   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")

Coldhead specs:
   Radius = 0.03175 m (1.25")
   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)

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.

1. RTD lead suspension

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. 

I think this flashlight would work

[Stephen, Radhika]

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.

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

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

I've ordered the following:

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

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

 never mind.

75$ Spectrum Analyzer

Shannon Sankar has done testing at MIT of the G&H HR mirrors. The results are good. I'm attaching a PDF of the result here.

Oh, very good. This is like a magic mirror such that we can use either P or S, from 0 deg to 45 deg.

In our latest design, we have flat input mirrors (2" diameter) and curved corner mirrors (1" dia). We have been thinking of using the:

              Suprema SN100-F2K                                      or the SL51BCH (also from Newport)

The SL series shown here is for 2" optics and is available today (its 10 weeks for knobs). The Suprema is only available for 1" optics and is in stock.

Since the Suprema is ~5x cheaper, I think we should get the left handed and right handed of that kind now. But its worth considering the SL since it might be more stable.

I think Koji has some actual data of the long term stability of some mounts ------

we have one of the 2" SL mirror mounts in the ATF, so we can have a look if the size is not too big. it's huge compared to other 2" mirror mounts.
We also have several 2" Ultima mirror mounts in the old Miller Lab (2 knobs). Maybe they are good enough for first tests...

 I've ordered six right and six left handed Suprema 1" mounts.

**edit** I've also now ordered two of the SL51BCH mounts.  We'll just have to cope with hex actuators to save the 10week wait.

 Also ordered some solid core wire from Jameco and a couple of solderless breadboards.

 In true CVI fashion they don't have any of the mirrors that we want.  I'm not actually certain what they keep in their warehouse but it certainly isn't optics.

Delivery time is going to be 4weeks (make that more like 6) for both the output mirror (another 2" diameter BS1- 99%) and the beam splitter for the Mach Zehnder (2" BS1 50%).  I'm going to put through the order for them now.

Edit - That's the order through Techmart now (5/18).

We wasted some time today looking around for the IR viewer. We found that it had been taken into the TCS lab with no notice left about it being borrowed.

This is unacceptable and the second time this has happened. The next time anyone from the TCS lab tries to borrow equipment, refuse.

Tell whomever it is to come and talk to me if they have a problem with this policy.

One possible vacuum chamber solution for the Gyro is to use long tubes for the Gyro arms and then to have a small chamber with ports at each corner.

I looked a little at using stock MDC vacuum parts for this; its not out of the question.

For the tubes, we could use something like their NW50 Kwik-Flange nipple. It has an OD of 2" and a length of 6.5". Its $63.

For the corners, we can use one of their '5-way crosses' like the 406002. Its basically 5 flanges welded onto a shell. Depending on the size its ~$250 ea.

I would prefer to get one long tube for each arm, rather than stick a bunch of short ones together, so I'll get a quote from MDC on a custom job.

Uncoated quartz viewports are ~$250 ea. I expect that we will want AR coated and angled viewports. Maybe $400 ea then.

So the total cost, without pumps would be ~5k$.

We're not looking for super high-vacuum though are we?  Maybe we can get away with borrowing the small turbo pumping station from the suspensions lab to pump it down and then we can just valve it off.

Also, we have the cylinder head for a tank of helium now so we should order in a tank to try that (the tanks get delivered really fast so that shouldn't be a problem).  Of course we'll at least need windows before doing that.

I've asked Gina to check on the CVI W2 window order.  The order went in on 22nd July and CVI said that they had them in stock.

 I think that's right - we won't need any better than 1 mTorr. As long as there is no huge leak, we should be fine. It would be handy to have a (EPICS trendable) gauge on the system so that we can know if its leaking.

The system's total volume will be ~20 liters. So we need the leak rate to be below ~1e-6 Torr-liters / hour. A suggestion from Mike Z is to use the usual flexi-hosing from Norcal instead of the rigid nipple type of tube

I was talking about before. flexi hose link ..... I think we can use the 2" ID, 24" long tubes and make up for the difference in the length in the corner chambers. The length of each side of the gyro should be 29.5" with a 100 MHz FSR.

 I realised that I had not bought a vacuum gauge for the gyro system.  The simplest solution seemed to be to use a wide-range gauge so we don't need to worry about damaging the gauge if the pressure creeps up too high.  I've ordered a combination gauge from Kurt Lesker that gives atmosphere down to 1e-9 Torr with an analogue output so we can hook it up to a DAQ channel.

 I finished purchasing all the components for the PDH2 today, including the RF stuff from MiniCircuits and CoilCraft, SMA/SMP adapters and miscellaneous switches/LEDs/pots/etc from DigiKey, Allied and Mouser. I also ordered 6 NIM front panels from FrontPanel Express to go with the 6 boards that were ordered (in production now) form Sunstone last week. Lead times will vary I suppose, but everything I ordered was in stock.

• VWR While sticky mat (Large 25"x45") / VWR 18888-216 (30 layers x 8 sheets) -> delivered
• VWR While sticky mat (Small 24"x36") / VWR 21992-042 (60 layers x 4 sheets) -> delivered
   
• Thorlabs 8-32 screw kit / Thorlabs HW-KIT1 -> ordered newport equivalent
• Pedestal Shims - Newport -> ordered (one kit and 10 additional pieces of PS-0.25, PS0.125)

SP-0.25-S-10	0.5" dia. 1/4in thick bag of 10 ($20.99)
SP-0.125-S-10	0.5" dia. 1/8in thick bag of 10 ($20.99)
SP-0.063-S-10	0.5" dia. 1/16in thick bag of 10 ($19.99)
SP-0.031-S-10	0.5" dia. 1/32in thick bag of 10 ($19.99)

PS-0.25		1" dia. 1/4in thick 1 ea. ($6.99)
PS-0.125	1" dia. 1/8in thick 1 ea. ($6.99)
PS-0.063	1" dia. 1/16in thick 1 ea. ($5.99)
PS-0.031	1" dia. 1/32in thick 1 ea. ($5.99)

Also you have a kit:
SP-KT ($199.99)
This contains
	5x PS-0.25
	5x PS-0.125
	5x PS-0.063
	5x PS-0.031
	10x SP-0.25-S-10
	10x SP-0.125-S-10
	10x SP-0.063-S-10
	10x SP-0.031-S-10

The kit is slightly more expensive than the individual ones.
Maybe due to the plastic case???