40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
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ID Date Author Type Category Subjectup
  35   Fri Oct 1 13:24:40 2021 AidanGeneralDesign specsTM Barrel coating emissivity

I have to question whether this passes a sanity test. Surely in the case of Stack 2, the 10um thick Ta2O5 will absorb the majority of the incident radiation before it reaches the SiO2 layer beneath. It should at least be similar to just absorption in Ta2O5 with some Fresnel reflection from the AIr-Ta2O5 interface.

For example, at around 18um, K~2, so the amplitude attenuation factor in a 10um thick layer is 160,000x or a gain of 6E-6. So whatever is under the Ta2O5 layer should be irrelevant - there is negligible reflection.

Quote:

[Paco, Nina, Aidan]

We ran our stack emissivity calculation on different AR stacks to try and make a decision for the TM barrel coatings. This code has yet to be validated by cross checking against tmm as suggested by Chris. The proposed layer structures by Aidan and Nina are:

  1. *| Air || SiO2 x 800 nm || Ta2O5 x 5 um || Silicon |*
  2. *| Air || Ta2O5 x 10 um || Sio2 x 20 nm || Silicon |*
  3. *| Air || SiO2 x 100 nm || TiO2 x 1 um || Silicon |*

Attachments # 1-3 show the emissivity curves for these simple dielectric stacks. Attachment #4 shows the extinction coefficient data used for the three different materials. The next step is to validate these results with tmm, but so far it looks like TiO2 might be a good absorbing film option.

 

  36   Fri Oct 1 14:11:23 2021 PacoGeneralDesign specsTM Barrel coating emissivity

Agree with this. Quickly running tmm on the same "stacks" gave the Attachment #1-3. (Ignore the vertical axis units... will post corrected plots) and extend the wavelength range to 100 um.

Attachment 1: stack_1.pdf
stack_1.pdf
Attachment 2: stack_2.pdf
stack_2.pdf
Attachment 3: stack_3.pdf
stack_3.pdf
  53   Thu Jun 16 14:04:30 2022 JuanGeneralSuspensionTable for Mariner Suspension Cryo

Today we looked at possible locations for where we will be setting up Mariner Suspension and Cryo chamber. The first option was the far left table in the CAML lab but it seems that there is going to be an issue with height clearance, so we have come up with another solution which takes a table from Koji's lab which is 3'x4' ft and moving it into CAML lab in the back right of the lab. To move the table we may need to call facilities to help us because we will most likely need to take the table apart to get it out of the lab. The aisle space in Koji's lab is about 43 inches, but the doorway, which is the tightest space, is 35 inches.

After we have set up the table in CAML we are planning on moving the Chamber in DOPO-lab to CAML. We plan to use skyhook with has a load limit of 500lbs/227kg this should be more than enough to move the chamber. We still need to get the wheeled base for skyhook we are in the works in doing so. 

Also, We want to remove the previous setup from the chamber and leave it at DOPO-lab. Stephen is going to figure out how to keep it clean (sort of). Besides these transportation logistics, I am also working on the electronics as an immediate task and the electrical arrangement in the chamber.

to do list
        - Check the table height
        - Check the chamber height (base/cap)
        - Check how much the chamber cap needs to be lifted (so that we can remove it)
        - Is the weight capacity sufficient?

 

  54   Thu Jun 16 19:43:36 2022 KojiGeneralSuspensionTable for Mariner Suspension Cryo

- B246/QIL Skyhook

  • Find the base of Skyhook. It should be in the storage room (B246). Stephen contacted Chub for lab access. Done
  • Assemble Skyhook with the base and check the stability/safety/capacity/height/etc

- DOPO

  • Ask Paco to move the delicate instruments from the table. Done
  • Bring Skyhook to DOPO. The chamber seems already vented.
  • Find the way to place the cap on the floor safely and cleanly. => Stephen
     
  • Open the cap and then remove the crackle interferometer. Wrap it with something and place it somewhere in the room. How? => Stephen
     
  • Move the base to a dolly or something. Then put a cap on the base. => It'd be better to ask Caltech Transp for the chamber transportation.
  • Do we have to temporarily remove the laser safety curtain?

- OMC Lab

  • We probably need to separate the optical table and the base. Ask Caltech Transp to check how the work should be done.
  • Do we have to temporarily move anything on the way?
  • The table can be rolled out to the corridor and then rolled in to the CAML.

- CAML

  • Remove the grey rack and push the desk to the East.
  • Place the optical table.
  • Place the rack close to the table.
  55   Thu Jun 23 21:11:03 2022 KojiGeneralSuspensionTable for Mariner Suspension Cryo

Table moving effort in the OMC lab: See https://nodus.ligo.caltech.edu:8081/OMC_Lab/412

 

  16   Tue Jun 22 22:28:09 2021 KojiGeneralDesign specsTest Mass wedge design

The ETM wedge of 0.5deg will allow us to separate the AR reflections. We will be OK with the ITM wedge of 0.5deg too. 0.36 deg for ITM is also OK, but not for the ETM.


- Attachment 1 shows the deflection of the 2128mn and 1418nm beams by the test mass wedge. Here, the wedge angle of 1deg was assumed as a reference. For the other wedge angle, simply multiply the new number (in deg) to the indicated values for the displacement and angle.

- Attachment 2 shows the simplified layout of the test masses for the calculation of the wedge angle. Here the ITM and ETM are supposed to be placed at the center of the in-vacuum tables. Considering the presence of the cryo baffles, we need to isolate the pick-off beam on the BS table. There we can place a black glass (or similar) beam dump to kill the AR reflection. For the ETM trans, the propagation length will be too short for in-vacuum dumping of the AR reflection. We will need to place a beam baffle on the transmon table.

- I've assumed the cavity parameter of L=38m and RoC(ETM)=57m (This yields the Rayleigh range zR=27m). The waist radii (i.e. beam radii at the ITM) for the 2128nm and 1418nm beams are 4.3mm and 3.5mm, while the beam radii at the ETM are 7.4mm and 6.0mm, respectively,

- Attachment 3: Our requirement is that the AR reflection of the ALS (1418nm) beam can be dumped without clipping the main beam.
If we assume the wedge angle of 0.5deg, the opening of the main and AR beams will be (2.462+4.462)*0.5 = 3.46 deg. Assuming the distance from the ETM to the in-air trans baffle is 45" (=1.14m), the separation of the beams will become 69mm. The attached figure shows how big the separation is compared with the beam sizes. I declare that the separation is quite comfortable. As the main and AR beams are distributed on both sides of the optic (i.e. left and right), I suppose that the beams are not clipped by the optical window of the chamber. But this should be checked.
Note that the 6w size for the 2128nm beam is 44mm. Therefore, the first lens for the beam shrinkage needs to be 3" in dia, and even 3" 45deg BS/mirrors are to be used after some amount of beam shrinkage.

- Attachment 4 (Lower): If we assume the same ITM wedge angle of 0.5deg as the ETM, both the POX/POY and the AR beams will have a separation of ~100mm. This is about the maximum acceptable separation to place the POX/POY optics without taking too much space on the BS chamber.

- Attachment 4 (Upper): Just as a trial, the minimum ITM wedge angle of 0.36deg was checked, this gives us the PO beam ~3" separated from the main beam. This is still comfortable to deal with these multiple beams from the ITM/

Attachment 1: wedge.pdf
wedge.pdf
Attachment 2: Layout.pdf
Layout.pdf
Attachment 3: ETM.pdf
ETM.pdf
Attachment 4: ITM.pdf
ITM.pdf
  20   Fri Aug 6 04:34:43 2021 KojiGeneralGeneralTheoretical Cooling Time Limit

I was thinking about how fast we can cool the test mass. No matter how we improve the emissivity of the test mass and the cryostat, there is a theoretical limitation. I wanted to calculate it as a reference to know how good the cooling is in an experiment.

We have a Si test mass of 300K in a blackbody cryostat with a 0K shield. How fast can we cool the test mass?

m\,C_p(t)\,T'(t) = -\epsilon\,\sigma A\,[T(t)^4 - 0^4]

T(0) = T_0

Then assume the specific heat is linear as

C_p(t) = c_{p0} T(t)

The actual Cp follows a nonlinear function (cf Debye model), but this is not a too bad assumption down to ~100K.

Then the differential equation can be analytically solved:

T(t) = T_0 \left( 1 + t/t_0 \right )^{-1/2},

where the characteristic time of t0 is

t_0 = \frac{m c_{p0}}{2\,\epsilon\,\sigma A\,T_0^2 }.

Here T_0 is the initial temperature, cp0 is the slope of the specific heat (Cp(T_0) = c_p0 T_0). epsilon is the emissivity of the test mass, sigma is Stefan Boltzmann constant, A is the radiating surface area, and m is the mass of the test mass.

Up to the characteristic time, the cooling is slow. Then the temperature falls sqrt(t) after that.

As the surface-volume ratio m/A becomes bigger for a larger mass, in general, the cooling of the bigger mass requires more time.

For the QIL 4" mass, Mariner 150mm mass, and the Voyager 450mm mass, t0 is 3.8hr, 5.6hr, and 33.7hr respectively.

  • If the emissivity is not 1, just the cooling time is expanded by that factor. (i.e. The emissivity of 0.5 takes x2 more time to cool)
  • And if the shields are not cooled fast or have a finite temperature in the end, of course, the cooling will require more time.
  • 1.25 t0 and 8 t0 tell us how long it takes to reach 200K and 100K.

This is the fundamental limit for radiation cooling. Thus, we have to use conductive cooling if we want to accelerate the cooling further more than this curve.

Attachment 1: cooling_curves.pdf
cooling_curves.pdf
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