40m QIL Cryo_Lab CTN SUS_Lab CAML OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
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ID Date Authordown Type Category Subject
  2492   Mon Apr 6 18:38:50 2020 KojiUpdateGeneralWest Bridge flooding Apr 6th

To check the status of all the labs, I went to WB. There was no ongoing water leakage in the labs.

Attachment 1: The subbasement was completely dry.

Attachment 2: Upon the lab inspection, I took PPE from the OMC lab. This was intended to prevent me to pick up anyone's anything and you to pick up my anything.

Attachment 3: The EE shop has no problem

Attachment 4: Cryo Lab. No problem.

Attachment 5: Crackle Lab. No problem, but a lot of dead cockroaches on the floor!

Attachment 6: OMC Lab. No problem.

Attachment 7: C.Ri.Me Lab. Gabriele has already checked the status in the morning. And I found no problem. Didn't bother to turn on the light.

Attachment 8: CTN Lab. No problem.

Attachment 9: QIL Lab. The floor was mostly dry. Did someone wipe the floor?

Attachment 10: Some water drip was found in front of the workbench.

Attachment 11: It comes from the ceiling.

Attachment 12: Left a trash box to catch future possible leak.

Attachment 13/14: TCS Lab. No problem found.

Attachment 15: As per Aidan's request, the instruments were moved to the North-East area of the room to avoid future possible leak.

Attachment 1: 20200406143251_IMG_9618.jpg
Attachment 2: 20200406143856_IMG_9621.jpg
Attachment 3: 20200406143932_IMG_9622.jpg
Attachment 4: 20200406144014_IMG_9623.jpg
Attachment 5: 20200406144119_IMG_9626.jpg
Attachment 6: 20200406143837_IMG_9620.jpg
Attachment 7: 20200406144413_IMG_9633.jpg
Attachment 8: 20200406144522_IMG_9635.jpg
Attachment 9: 20200406144648_IMG_9639.jpg
Attachment 10: 20200406144730_IMG_9643.jpg
Attachment 11: 20200406144752_IMG_9644.jpg
Attachment 12: 20200406144942_IMG_9645.jpg
Attachment 13: 20200406145125_IMG_9646.jpg
Attachment 14: 20200406145127_IMG_9647.jpg
Attachment 15: 20200406145347_IMG_9652.jpg
  2493   Mon Apr 6 19:01:21 2020 KojiUpdateGeneralWest Bridge flooding Apr 6th

Additional notes:

I did not see anyone in the building.

Attachment 1/2: Our labs have no sticker/paper to indicate any disinfection of the room. (Make sense)

Attachment 3: Most of the basement offices have the notes to indicate disinfection.

Attachment 4/5: Our offices have no notes.

Attachment 1: 20200406151420_IMG_9653.jpg
Attachment 2: 20200406151428_IMG_9654.jpg
Attachment 3: 20200406151459_IMG_9655.jpg
Attachment 4: 20200406151633_IMG_9656.jpg
Attachment 5: 20200406151709_IMG_9658.jpg
  2521   Fri Nov 20 18:47:42 2020 KojiSummaryGeneralPermenant exchange of TED200C(QIL) and TED200C(2umECDL)

I moved the brand new TED200C on the workbench to Crackle for 2um ECDL (permanently)
The TED200C temp controller used in the 2um PD test setup will stay there (permanently)


  2522   Fri Nov 20 18:49:43 2020 KojiSummaryGeneralInstrument loan

FEMTO DLPCA200 low noise preamp (brand new)

Keithley Source Meter 2450 (brand new) => Returned 11/23/2020

were brought to the OMC lab for temporary use.

  2526   Tue Dec 22 15:20:14 2020 KojiSummaryGeneralInstrument loan

Is the reverse bias programmable? FEMTO has a bias trimmer on it. It's useful in the usual application, but for automation, the configuration of the input becomes cumbersome.

  2572   Thu May 20 16:57:32 2021 KojiElectronicsGeneralKeithley Source Meter returned to Downs

I've returned the Keithley Source Meter unit
- The unit (Keithley 2450?2460?)
- A power cable
- A pair of banana clips
- the transistor test fixture & triax cable/connectors

Attachment 1: P_20210520_154439.jpg
Attachment 2: P_20210520_154505.jpg
Attachment 3: P_20210520_154523.jpg
  2589   Wed Jun 16 17:17:12 2021 KojiUpdateGeneralI2 cell

I was searching an I2 (Iodine) cells back to the days of the laser gyro.

I found a likely box at a very tricky location. Took the photos and returned to this tricky place.

2021/Jul The box was moved to the OMC lab (KA)

Attachment 1: P_20210616_170104.jpeg
Attachment 2: P_20210616_170038.jpeg
Attachment 3: P_20210616_170021.jpeg
  2603   Thu Jul 15 23:34:17 2021 KojiSummaryTempCtrlTemprerature Log for cooling down / warming up

[Stephen Koji Radhika]

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

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

[Stephen / Koji]

Bonding work for the prep of the preliminary suspension test

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

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

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

Next Things To Do (Attachment 3)

  • Vent the chamber
  • We will move an optical port to the opposite position of the other port.
  • A DB9 feedthru is going to be installed.
  • Suspension
    • Move the sus frame in the chamber
    • Suspend the mass
  • Sensor arrangement
    • Set up the oplev
    • Hold the OSEM at the height of the magnet
    • Set up a camera to observe the magnet-OSEM clearance
    • We improvise the DB crimping sockets so that we can electrically connect the OSEM (optional)
  • Pump down / cool down the chamber
    • The main target of the cooling is to check the cooling capability of the test mass mainly with radiative cooling.
    • An optional target is to observe the misalignment as a function of the temperature -
      • -> Oplev signals are to be connected to CDS / check if CDS is logging the data
    • Check if the OSEM/magnets survive the thermal cycle
    • If possible we can try to actuate the OSEM / check the LED/PD function at the cryo temp
Attachment 1: P_20210715_170102-1.jpg
Attachment 2: P_20210715_172218-1.jpg
Attachment 3: experiment_plan.pdf
  2605   Fri Jul 16 23:28:24 2021 KojiSummaryCryo vacuum chamberSus Test Work 07/16/2021

[Stephen Koji]

We started cooling down of the test mass.


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

OSEM wiring

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

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

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

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

Dsub feedthru in-air pinout (Mating side)

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

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

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

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

Suspension installation (Attachment 3)

- The sus frame was moved into the chamber

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

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

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

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

Oplev installation

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

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

Pumping down

- Started ~8:30PM?

DAQ setup

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

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


- Temp Logging started. Filename: temp_log_cool_down_20210716_2255.txt

- Cryocooler turned on. ~10:55PM

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

OSEM photo

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

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

Temperature log for the first 2 hours (Attachment 1)

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


Attachment 1: temp_log_cool_down_20210716_2255.pdf
  2609   Mon Jul 19 17:21:19 2021 KojiSummaryCryo vacuum chamberTemp Log 210716_2255

Temp Log on Jul 19 2021 17:20

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


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

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

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

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

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

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

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

Updated the model the latest log data with cooling prediction

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

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

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

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

Attachment 1: cooling_model.pdf
  2613   Wed Jul 21 14:53:28 2021 KojiSummaryGeneralJul 17, 2021: Canon camera / small silver tripod / macro zoom lens / LED ring light borrowed -> QIL

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

  2614   Wed Jul 21 21:05:59 2021 KojiSummaryCryo vacuum chamberTest mass cooling (2021/07/16 ~ 2021/07/21)

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

1. Temperature Trend

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

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

2. Oplev Trend (Attachment 1)

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

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

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

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

3. OSEM and the magnet

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

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

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

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

4. CTC100 logging

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

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

5. Heating

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

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

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

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

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

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

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

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

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

Also brought some power cables.

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


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

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

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

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

Can we extract any information from this "0.15"?

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

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

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

F_e is an emissivity factor.

The book explains some simple cases in P 443:

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

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

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

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

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

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

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.

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

Updated Jul 26, 2022 - 22:00


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

[Stephen Koji]

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

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

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

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

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

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

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

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

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

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

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

[Stephen Koji]

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

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

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

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

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

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


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

[Stephen Koji]

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


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

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

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

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

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

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

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

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

- The cold head cooling is faster and cooler

- The inner shield cooling is faster

- The test mass cooling is faster

Attachment 1: comparison_cold_head.pdf
Attachment 2: comparison_inner_shield.pdf
Attachment 3: comparison_test_mass.pdf
  2628   Fri Jul 30 18:18:21 2021 KojiDailyProgressCDSConnecting CTC100 to EPICS/rtcds system

[Radhika, Koji]

During the process, we corrected the channel labeling for RTD #3/#4. So  for a few first data points, the numbers for the workpiece and the outer shield were swapped.

  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
  2632   Mon Aug 2 21:51:37 2021 KojiDailyProgressCDSConnecting CTC100 to EPICS/rtcds system

The legit way to restart st.cmd is

systemctl restart CTC100
  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
  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?


  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
  2740   Mon Mar 28 18:00:43 2022 KojiSafetyCleanlinessLab flooding

Flood photo album: https://photos.app.goo.gl/BZAG8DyQzFVTfMNz6 (This link is read-only who has no access to the account)


  2743   Wed Mar 30 16:25:06 2022 KojiSafetyCleanlinessLab flooding

Muddy Waters is not new, but if the facility can fix it we'd take it.


  2826   Thu Jan 12 11:50:20 2023 KojiHowtoGeneralHow to move the large engine hoist through the narrow door

How to move the large engine hoist through the narrow door

See http://nodus.ligo.caltech.edu:8080/Mariner/122

  2871   Tue Jun 13 14:02:17 2023 KojiSummaryGeneralOrganizing subbasement storage cage

Storage organizing session Jun 13, 2023
I'm posting the log here because there is no other appropriate place to post.
JC, Shruti, Aaron, Yahonathan, and Rana worked on organizing the WB SB storage cage.

  • The left half was cleared at the beginning
  • Wire shelving was built in the cage
  • Placed the heavy vacuum stuff at the bottom, then placed the electrical instruments on the shelf. We still have a lot of space to put. Victory! (Attachment 1)
  • We have some items to be transported to the 40m, including a picomotor driver that would be used for the 40mBHR (Attachment 2)
  • We found a potential clean room table set. Bring the set to the 40m so that we can use it once the large optical table is removed. (Attachment 3)
  • The previous bottom wooden pallet was removed. We will toss it. (Attachment 4)

Action Item:
Having one or two flat/piano dollies in the cage would be great.

Attachment 1: PXL_20230613_191826685.jpg
Attachment 2: PXL_20230613_191841771.jpg
Attachment 3: PXL_20230613_191853574.jpg
Attachment 4: PXL_20230613_191903191.jpg
  1910   Mon Mar 9 18:57:21 2015 Kate, StephanieMiscSeismometerUpdated tilt-free seismometer design concept

Rana and I visited Fabrice and Matt at MIT last week to discuss our line of thinking for a tilt-free seismometer design. They've spent about 3 years working on the design, construction, and testing of their own concept, a T240 seismometer placed on a suspended platform. Tilt is filtered simply by virtue of the suspension point. They successfully measured their tilt-to-displacement transfer functions through the use of a tilt-shaker, showing measurement matches theoretical predictions. They got stuck at the point of doing a huddle test of 2 such tilt-free seismometers due to extra noise from magnetic fields in the local environment. Thus, as of yet, they haven't been able to demonstrate the displacement sensitivity. 

Warnings from Fabrice had to do with keeping the initial experimental set up simple and remotely controllable. He recommended, for instance, using two wires to hang the mass, so as to restrict one of the two longitudinal degrees of freedom. Eddy current damping is also good. He also showed us how he attached a picomotor onto the side of his mass. Driving the picomotor is his method for adjusting the location of the center of mass. The picomotor is on the right in the first photo; the second photo focuses on the wire clamping. 

In discussion including Matt, Fabrice, and Rich M. about designs, we discussed what is needed to make a pendulum with a resonance as low as around 10 mHz. This can be done with inverted pendula and Matt pointed us to a mechanical design from Virgo involving 4 legs under tension that we could look into further. Rather than having two pendula of different lengths / moments of inertia hanging side by side and measuring the relative tilt / displacement between them, we could place an inverted pendulum on top of the mass of a ~1 Hz pendulum. The suspension point of the inverted pendulum should be at the rotational axis of the main pendulum (its center of mass) and the main pendulum could be designed to have a very large moment of inertia to help in improving the bandwidth in which tilt can be measured. Furthermore, the main pendulum could have its mass distributed such that some of it is in the same plane with the inverted pendulum mass, creating a natural location to set up an interferometer for readout. 

Stephanie took our sketches and made a drawing to aid with visualization of the newest scheme.

  1911   Wed Mar 11 15:12:51 2015 Kate, StephanieMiscSeismometerUpdated tilt-free seismometer design concept

I color coded the drawing of the newest scheme so that it's easier to identify the different parts (eDrawing file attached).


Attachment 1: Seismometer2.EASM
  1913   Thu Apr 2 23:24:19 2015 Kate, StephanieMiscSeismometerDesign of low rotational freq. mass

Stephanie and I spent some time today working out a practical design for the first of two suspended masses that will make up the seismometer.

Restrictions we set included the following requirements: 

  • the mass must have a large moment of inertia
  • the top of the mass must be in the same plane as the top of the suspension cage
  • it should fit within the existing (arbitrary) size of the cage
  • the center of mass should be at (slightly below) the suspension point

We will use Bosch parts to create the frame of the mass and try to concetrate weight at the top and bottom. To do this, we'll use an optical breadboard at the bottom (it appears Zach might have an extra we could use). We can't use a breadboard at the top because the second mass will need to fit in its interior. The second mass itself can serve to add weight to the top of the first. Optics + mounts used for the readout will also add weight to the top. 

Some sketches we came up with are below. We'll need to slightly modify the existing cage to accomodate a need to move the crossbar from which the first mass will be suspended. The crossbar will sit below the top of the cage. In the bottom two right drawings, some cage parts are partially transparent to see the mass behind them. We also made a list of some hardware we will need in order to construct the mass. This includes more brackets (32 total) like the ones in the picture and some hardware (32+ pieces) that slides into the frame slots which allows 1/4-20 screws to secure pieces like optical mounts and brackets to the frame. 

Stephanie took note of some dimensions and will determine how tall the mass can be and therefore what size Bosch parts we should buy. She'll also make a model in SolidWorks to compute the total mass and moment of inertia. 

Attachment 2: drawing.svg
  1964   Thu Jul 9 00:37:35 2015 Kate, AlessandraElectronicsSeismometerPCB

I have attached some pictures of the PCB required to make digital measurement for the seismometer.

Attachment 1: IMG_1128.JPG
Attachment 2: IMG_1130.JPG
Attachment 3: IMG_1131.JPG
  1951   Fri Jun 26 18:02:17 2015 Kate, Alastair, MeganMiscSeismometerSuspension attempt

We spent the afternoon preparing the rhomboid to be suspended once more. This was done once already with two wires, but we had found the wire lengths were not equal enough to work out. This time we set up a device to carefully adjust the wire lengths. This required cutting new wires and re-clamping them in the pin vises. Unfortunately, one of the upper pin vises broke (see photo). This is one of the two that we had died so that we could screw bolts onto it. It broke at a location such that the mechanism for closing the collet around the wire no longer functions. In a spirit of pushing through to try to get the rhomboid suspended anyway, we mixed up some expoxy and glued the wire into the collet and the collet into the pin vise head. We decided we would adjust the other wire to match this particular wire's length. We prepared the other wire and slowly lowered the rhomboid. Upon letting the 2 wires fully take the weight, the second wire pulled out of its bottom pin vise. The wire didn't break, but the pin vise was simply not clamping it well enough. Upon inspection, it turns out this was the pin vise that had previously been damaged. The collet teeth don't fit together perfectly anymore, and there is indeed a gap between two of them which is most likely the cause of the malfunction. We taped the free end of the wire so it's not a hazard and are leaving the setup as is for now until we get a replacement pin vise. 

Attachment 1: IMG_0823.JPG
  1961   Mon Jul 6 19:52:28 2015 Kate, Alastair, MeganMiscSeismometerIdeas for new pin vise clamp

Last week Alastair, Megan, and I had a brainstorming session about how to design a better pin vise clamp. Alastair's suggestion was to take the route of eliminating all of the pin vise parts except for the collet. Our approach so far was to do a lot of machinig on the pin vise handle, but the result is something that's weak, easily breaks, and not very well secured. I'm attaching a picture of the white board with some of our sketches. Alastair's taking the better ideas and making a real drawing that we can review in detail and send to the machine shop. He also suggested we can try using some guitar tuning pegs to take the weight and use the collet only for the purpose of defining the bending point. 

Attachment 1: IMG_0834.JPG
  1896   Fri Jan 23 15:33:46 2015 Kate, AlastairMiscSeismometerPin vise holder, version 1

Here is the first version of a design for a mounting block for the pin vise. The concept is that the pin vise will be screwed into this aluminum block and the block will be screwed into the optical breadboard (i.e. inertial mass). We want to have the flexure point of the wire be located (ideally) at the center of mass of the system, so I computed where the center of mass would be using the estimation that both the breadboard and mounting block are solid Aluminum (density = 2.7 g/cm^3).

For the dimensions as follows:

optical breadboard = 12" x 10" x 0.5" (2655 grams)

mounting block = 2" x 2" x 1.75" (310 grams)

the center of mass would be:

R = \frac{m_1 r_1 + m_2 r_2}{m_1 + m_2} = \frac{0 + (310)*(1.125)}{2655 + 310} \approx 0.12\,\mbox{inches} \approx 3\,\mbox{mm}

below the center of mass (also geometric center) of the breadboard. I haven't yet calculated the flexure length for the wire, but the consensus between Alastair and Koji is that it won't be more than a couple mm. This means the tip of the pin vise which grasps the wire should be yet another few mm lower, or approximately co-located with the bottom surface of the breadboard. However, since the flexure point will need to be slightly above the center of mass for stability and because we will load the breadboard with some weights (i.e. mirrors for optical readout of the mass's motion and balancing weights) which will raise the center of mass, I decided to make the tip of the pin vise somewhere in the middle of the lower half of the breadboard. 

I  brought this design to the machine shop in the sub-basement of Lauritsen, but the guy I talked with there said the 1 mm thick wall of the pin vise handle is too thin to die (add threads to) with any of the machines they have. We discussed an alternate solution of tapping two holes into the side of the block and just grasping the pin vise with the force of screws. He also suggested filling the pin vise handle with aluminum to make it stronger. 

Pin vise holder


Attachment 1: SCAN7247_000.pdf
  1897   Fri Jan 23 15:46:13 2015 Kate, AlastairMiscSeismometerSteel wire for seismometer

Norna and Calum provided me with two different rolls of wire from storage that I could use for the seismometer. They're 252 um and 410 um in diameter. 

Alastair provided me with the data from a stress test they've done on the wire. He says, "Here's a typical breaking strength measurement on that music wire.  It looks to go plastic around 2.5GPa, so lets a assume that you don't want to load it more than 1GPa.  For the thinner (252um) wire that comes out to a maximum force of 50N, so approximately 5kg of weight." 


Wire strength test

  1915   Thu Apr 16 15:21:11 2015 Kate, AlastairMiscSeismometerFiber pulling lesson (belated entry)

Feb. 26, 2015

Alastair got the glass fiber pulling setup back in working order and gave me a first lesson. This is in preparation for later making fused silica fibers for suspending the main mass of the tilt-free seismometer. For the initial prototypes, we will be using steel wires instead.

This method of pulling fibers does not make use of a machine and is done by hand. We create a flame by mixing Oxygen and Hydrogen, and keep it in a stable resting place on a tabletop. Then, upon holding the two ends of a glass rod, we place the center of the rod in the hottest part of the flame and rotate the rod around its long axis to heat the entire circumference evenly. Once the center of the rod is bright white and feels fluid, we lift the rod up out of the flame and pull quickly in one even motion to the desired length. Welding glasses must be worn to protect the eyes. In my one attempt to pull a fiber, I found the dark glasses made it very difficult to be able to see whether or not I was holding the glass rod in the flame. I also found it challenging to rotate the rod without also moving it up and down. Alastair's ease of pulling a fiber demonstrates how practice makes a difference. A video is attached.

A few notes about the gas tanks and their valves:

  • Oxygen is in the green tank
  • Hydrogen is in the red tank
  • To close the regulator valve, turn knob anti-clockwise (the spring will be loose)
  • To close the cylinder valve, turn knob clockwise

The standard procedure for initiating gas flow from a tank is as follows:

  • Check that the regulator is closed
  • Open the cylinder
  • Take a reading of the pressure
  • Close the cylinder (pressure reading should not change)
  • Wait 1 min. and watch to see if pressure drops (would indicate a leak)
  • Open cylinder
  • Open regulator until gas flow sounds right

The procedure for creating the flame is as follows:

  • Turn on Hydrogen
  • Light it (Hydrogen self burns)
  • Add Oxygen until flame looks right (hottest part should be a few mm long)

And for extinguishing the flame:

  • Turn Oxygen off
  • Turn Hydrogen off
Attachment 1: IMG_0457.MOV
  1889   Wed Dec 3 18:31:15 2014 KateLab Infrastructure First tilt-free seismometer entry

Stephanie Moon, Kate Dooley

We've started getting the lab in order and some parts assembled for putting together an early prototype of a tilt-free seismometer concept. We're using the optics table furthest from the door (i.e. not Zach's) and have cleaned up a good portion of it, putting things away in cabinets. Because we need a fair amount of height for the suspension cage, we disassembled half of the upper shelf that had been used for storing electronics. Last week we ordered Bosch-Rexroth struts for building the cage (invoice is attached). They arrived today and we now have them assembled per design with the exception of one additional bar that will go across the top:

Photo of frame 

Calum and Norna are letting us borrow 2 spools of phosphate-coated steel wire (and a pair of safety glasses). These are on the optics table. 

We also ordered a 10"x10"x1" piece of Aluminum from the machine shop on campus next to the 40m to be used as our first test mass. It is unfortunately so poorly machined!

Photo of Aluminum test mass



  1891   Tue Dec 16 21:36:07 2014 KateLaser Fiber coupler work

We started working on getting some stable light from the CTN experiment fiber-coupled into the ATF lab. It's not set up and working yet, but the fiber + coupler is fixed to the seismometer table and the output immediately dumped. Please take note that the laser hazard sign is more likely now to be on at times compared to the last couple months.

  1895   Wed Jan 21 15:27:08 2015 KateMiscSeismometer1 dof seismometer noise budget

Here is the first version of a noise budget for a seismometer based on a pendulum principle. The only noise sources I include so far are thermal noise and sensor noise. I've used Chris' noise budget software, which does the loop math (using Simulink) and automatically produces nice plots. A sketch of the system which I'm modelling is shown below. The basic concept is that from a measurement of relative displacement (delta) between an inertial mass and the ground, we want to extract the motion of the ground (X). For this to work, we need to know the transfer function of ground displacement to the inertial mass motion and we need to know what the displacement-equivalent sensor noise is. From a practical standpoint, we assume that the sensors (i.e. mirrors forming an interferometer) are rigidly attached to the inertial mass and ground, respectively.

The transfer function from ground to inertial mass motion is:

\frac{x}{X} = \frac{k+i \gamma \omega}{k+i \gamma \omega - m\omega^2}

where \gamma is the force coefficient for viscous damping of the mass. 

The displacement noise of the mass due to thermal noise from viscous damping has the following power spectral density:

x_{thermal}^2(f) = \frac{k_B T \gamma}{\pi^2 f^2 (\gamma^2 + (2 \pi f m - k/2 \pi f)^2)}

For now, I have assumed that sensor noise is flat in frequency at a level of 1e-13 m/rtHz.

The simulink model is shown below. The NoiseSink block is located where we make our measurement: the relative motion between ground and the inertial mass (\delta = X -x). The Cal block is at the location of the quantity we wish to know: ground motion X. This snapshot also includes the beginnings of adding in tilt-to-displacement coupling to the model. 

The noise budget for a mass m=5 kg at room temperature with a resonant frequency of 5 Hz is shown below. Low frequencies are limited by thermal noise and high frequencies by sensor noise. The sensor noise has a dip at the resonant frequency because here the mass' motion is amplified, resulting in a higher SNR. I've added in the dashed black curve, which is a sketch of the Ringler & Hutt measurement of the STS2 noise floor. This serves as a figure of merit for our design to surpass. 

Sketch of concept
Sketch of concept


Attachment 1: Screen_Shot_2015-01-21_at_2.16.12_PM.png
Attachment 2: Screen_Shot_2015-01-21_at_2.10.05_PM.png
Attachment 3: IMG_0432.JPG
  1898   Mon Jan 26 15:58:18 2015 KateMiscSeismometerDetermining tilt/translation couplings

We want to compute the tilt/translation coupling matrices for a few potential 'tilt-free' seismometer designs to evaluate how good the designs are. We'll make a collection of calculations here for minor variations of a simple pendulum and then expand from there. Some of the basic elements that will need to be included are as follows:

  • the suspension point of the mass is *not* located at the center of mass
  • the effect of a translation of the top suspension point on the motion of the mass
  • the coupling between a tilt of the ground and displacement of the top suspension point
  • the effect of the reference point being fixed to the moving ground
  • finite wire stiffness

The first attachment shows the calculation of the equations of motion using a Lagrangian for the simplest scenario of a block suspended as a pendulum at its center of mass. In this case, there is no coupling between the angle of the pendulum and that of the mass. The second attachment shows the start of the calculation for the scenario where the mass is suspended a distance d away from its center of mass. This will result in a set of equations of motion showing the relationship between the angle of the pendulum wire and the position of the mass. 

What we will eventually be interested in is the transfer function from suspension point translation and tilt to coordinates describing the motion of the mass. We'll probably want to later represent the location of the mass as a function of x and theta rather than the currently used phi and theta. 

Attachment 1: SCAN7248_000.pdf
Attachment 2: SCAN7250_000.pdf
  1899   Thu Jan 29 15:54:26 2015 KateMiscSeismometerSeismometer work update

I've worked some more on computing equations of motion for modifications to a simple pendulum. The first attachment shows two different scenarios, on p. 1 and p. 2, respectively: 

  • top suspension point can be translated; point mass
  • top suspension point fixed; mass suspended away from center of mass

The second attachment shows the computation of the Langrangian for the first example. 

The equations of motion for both examples reduce properly to that of a simple harmonic oscillator in the limits of the suspension point not moving and the mass being suspended at its center of mass. I'm not sure yet whether the decoupled forms of the equations of motion make sense. Also, I think I need to choose to use different coordinates before I go on to combine the two scenarios. I also need to think about how to have the right variables for compting a transfer function from top point motion to mass motion.

In addition, Alastair and I have started playing with SimMechanics. We've each modeled a simple pendulum, but have more to do to figure out if we can turn it into a realistic model.

Attachment 1: SCAN7252_000.pdf
SCAN7252_000.pdf SCAN7252_000.pdf
Attachment 2: SCAN7253_000.pdf
  1901   Wed Feb 4 17:53:58 2015 KateMiscSeismometerSeismometer work update

I'm attaching 2 pages of math which finish the problems started from the main entry.

The first attachment solves the second equation of motion for the example of the block suspended away from its center of mass, and shows that it reduces properly to the SHO when the distance from suspension point to center of mass is set to 0. The second attachment continues the driven oscillator problem, which correctly uses just one equation of motion (the attempt to find an equation of motion by varying "x" in the main entry was wrong). For this example, I also take the Fourier transform and show that the transfer function from ground excitation to mass position reduces to the familiar form. 


I've worked some more on computing equations of motion for modifications to a simple pendulum. The first attachment shows two different scenarios, on p. 1 and p. 2, respectively: 

  • top suspension point can be translated; point mass
  • top suspension point fixed; mass suspended away from center of mass

The second attachment shows the computation of the Langrangian for the first example. 

The equations of motion for both examples reduce properly to that of a simple harmonic oscillator in the limits of the suspension point not moving and the mass being suspended at its center of mass. I'm not sure yet whether the decoupled forms of the equations of motion make sense. Also, I think I need to choose to use different coordinates before I go on to combine the two scenarios. I also need to think about how to have the right variables for compting a transfer function from top point motion to mass motion.

In addition, Alastair and I have started playing with SimMechanics. We've each modeled a simple pendulum, but have more to do to figure out if we can turn it into a realistic model.


Attachment 1: SCAN7270_000.pdf
Attachment 2: SCAN7271_000.pdf
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