Basically, they repeated our specs and showed the coating performances for HR/AR for 10deg P and PR/AR for 45deg P. There is no RoC measurement by the vendor.
Nevertheless, their RoC (paper) specs should be compared with our request.
I have rebuilt the MCMC simulation in an OOP fashion and incorporated Lance/Pytickle functionality into it. The usage of the MCMC now is much less messy, hopefully.
I made an example that calculates the closed-loop noise-coupling from SRCL sensing and displacement to DARM in A+. I used the control filters that Kevin defined in his controls example.
The resulting noise budget is in attachment 1. The code is in the 40m/bhd git.
I also investigated why aLIGO simulations behave so different than the A+ simulation (See few previous elogs in this thread). That is why aLIGO results are much less variable, and the simulations in aLIGO barely pass the validity checks, while A+ simulations almost always pass.
The way I check for the validity of a kat model is by scanning all the DOFs and checking that the corresponding sensing RFPDs demodulated signals cross zero. Attachment 2 shows these scanning for 3 such RFPDS for 3 cases:
A+ model with maxtem = 2
ALigo model with maxtem = 2
ALigo model with maxtem = 'off'
It seems like the scanning curves for A+ and ALigo with no HOMs are well behaved and look like normal PDH signals, while the ALigo with maxtem = 2 curves look funky. I believe that the aLIGO+HOMS curves indicate that the IFO is not really in a good locking point. All the IFO lockings were done by using the locking methods straight out of the PyKat package.
Cool. Can you give us Bode plots of the open loop gain for each of the 5 length control loops?
I spent a few hours monkeying around with the control filters. They are totally made up and also it's my first time trying to design control filters.
The OLTFs of the different length controls are shown in attachment 1.
The open-loop couplings of the DOFS to DARM are shown in attachment 2.
Note that in Lance/Pytickle the convention is that CLTFs are 1/(1 - G). Where G is the OLTF.
I dived into the alog to make the OLTFs in the MC_controls example more realistic. I was mainly inspired by these entries:
and Evan's and Dennis's Theses.
Attachment 1 shows the new OLTFs. I tried to make them go like 1/f around the UGF and fall as quickly as possible at higher frequencies. I didn't do more advanced stability checks.
I also noticed that imbalances and detunings in the MC simulation can change the plants significantly. Especially DARM, CARM, and sometimes PRCL. I added the option to fix some OLTFs throughout the simulation. At every iteration, the simulation computes the required control filter to fix the selected OLTFs such that it will match the OLTFs in the undetuned and balanced IFO.
I have taken transfer functions and noise measurements of the two HAM-A coil driver boxes D1100687 #S2100027 and #S2100028. All transfer functions look as expected. I'm not sure about the noise measurements. If anyone sees flaw in my measurement method, please let me know. I'm not sure why in some channels I got 10Hz harmoni peaks in the noise. That was very strange. Also let me know if my current noise estimate is wrong.
I took transfer function and noise measurement of satellite amplifier box's photodiode transimpedance circuit. For the measurement, I created a makeshift connector to convert backside DB25 into DB9 with the 4 channels for PDA input. The output was taken in differential form at the front PD Output port. To feed current to the circuit, I put in 12 kOhm resistors in series at the inputs, so the V/V transfer function measured was multiplied by 12 kOhm to get the transimpedance of the circuit.
Edit Wed Feb 10 15:14:13 2021 :
THE NOISE MEASUREMENT WAS WRONG HERE. SEE 40m/15799.
I took some steps to reduce the coupling of 60 Hz harmonics in noise measurement. The box was transferred to the floor instead of on top of another instrument. Measurement was immediately converted into single-ended using SR560 in battery mode with a gain of 10. All of the setups was covered in aluminum foil to increase isolation.
I did the recommended modifications on of the boards with serial number S2100028. These included:
I took transfer function measurements with same method as in 40m/15774 and I'm presenting it here to ensure the modifications are correct and if I should proceed to the next board as well. I didn't have the data used to make plots in here but I think the poles and zeros have landed in the right spot. I'll wait for comments until tomorrow to proceed with changes in the other board as well. I'll do noise measurements tomorrow.
Looks fine to me visually but the verdict can only be made once the z:p locations are quantitatively confirmed, and the noise tests pass. It would be interesting to see what kind of time-domain transient (in N of force) switching on the de-whitening introduces, i guess best done interferometrically.
I'll wait for comments until tomorrow to proceed with changes in the other board as well. I'll do noise measurements tomorrow.
I fitted zeros and poles in the measured transfer function of D1100687 S2100027 and got zeros at 130 Hz and 234 Hz and poles at 10Hz and 2845 Hz. These values are different from the aimed values in this doc, particularly the 234Hz zero which was aimed at 530 Hz in the doc.
I also took the noise measurement using the same method as described in 40m/15780. The noise in Acquisition mode seems to have gone up in 10 Hz - 500 Hz region compared to the measurement in 40m/15780 before the modifications.
All channels are consistent with each other.
Edit Mon Feb 1 12:24:14 2021:
Added zero model prediction after the changes. The measurements match with the predictions.
Edit Wed Feb 3 16:46:59 2021:
Added zero modeled noise in the noise spectrum curves. The acquisition mode curves are in agreement with the model. The noise in Run mode is weirdly lower than predicted by zero.
I have made the modifications on the other board D1100687 S2100028 as well. The measurements were taken as mentioned in 40m/15784. All conclusions remain the same as 40m/15784. The attached zip file contains all measurement data, before and after the modifications.
Edit Wed Feb 3 16:44:51 2021 :
I set up a working area on the table next to the south flow bench (see attachment). I also brought in a rolling table for some extra space.
I covered all the working surfaces with a foil from the big roll between 1x3 and 1x4.
I took the SOSs, SOS parts and the OSEMS from the MC2 table to the working area.
I cleaned some LN Allen keys with isopropanol and put them on the working table, please don't take them.
You can remove the components of the optical table enclosure (black ones) and use the optical table as your working area too.
I have made modifications recommended in this doc. The changes made are:
I took transfer function measurements, fitted them with zeros and poles and plotted it against the zero model of the circuit. The zeros and poles we intended to shift are matching well with 3Hz zero and 30 Hz pole. The later pole at 1500 Hz is at a higher value from what is predicted by zero.
I also took noise measurements and they are in good agreement with the noise predicted by zero.
I gathered all the components I could find from the SOS towers and the cleanroom and put it all on the table next to the flow bench (See attachment).
I combed through the cleanroom cabinet for SOS parts but didn't find all the parts listed in the procurement spreadsheet. I did find some extra items that were not listed.
This table compares the quantities in the spreadsheet to the quantities collected on the table. Green rows are items I found more than in the procurement spreedsheet while red rows are items I found less.
As suggested, I wrapped the satellite amplifier box D10028128 S2100029 in blanket and foam and took very low frequency spectrum starting from 32 mHz to 3 Hz. The results are attached along with stiched high frequency measurements from 40m/15793.
THIS MEASUREMENT WAS WRONG. SEE 40m/15799.
I measured the output DC voltage of the satellite amplifier box at PDMon port when the PDA input was shorted and got following offsets:
However, I think I'm making a mistake while measuring this offset as well as all the noise measurements of this satellite amplifier box so far. Since it is a current input, transimpedance circuit, the noise of the circuit should be measured with open input, not closed. Infact, by shorting the PDA input, I'm giving DC path to input bias current of AD833 transimpedance amplifier to create this huge DC offset. This won't be the case when a photodiode is connected at the input which is a capacitor and hence no DC path is allowed. So my issue of offset was bogus and past two noise measurements in 40m/15797 and 40m/15793 are wrong.
Why not just do this test with the dummy suspension box and CDS system? I think Rich's claim was that the intrinsic LED RIN was dominant over any drive current noise but we can at least measure the quadrature sum of the two (which is after all the relevant quantity in terms of what performance we can realize) and compare to a model.
Testing the satellite amp i.e. PD driver
- To test the noise of the PD transimpedance amps: Leave the PD input open (do not short the terminal goes to the PD)
- To test the current noise of the LED drivers: Short the output with an appropriate Rs to have the nominal current.
- To test the overall noise level together with the LED/PD pair: Connect the dummy OSEM module.
Testing the coil drivers
- Short the output with an appropriate Rs.
Here is a proper measurement for PD transimpedance amplifier circuit in the Satellite amplifier box D1002818 S2100029. The input from rear DB25 connector was left open and measurement was taken with AC coupling with correction by the AC coupling transfer function (Zero at 0, pole at 160 mHz). I have calculated the input referred displacement noise by calculating the conversion factor of OSEM in A/m. From 40m/12470, old conversion factor of OSEM to output of sat amplifier was 1.6 V/mm. then, the transimpedance was 39.2 kOhm, so that must mean a conversion factor of 1.6e3/39.2 A/m. This I scaled with increased drive current by factor of 35/25 as mentioned in this document. The final conversion factor turned out to be around 57 mA / m. If someone finds error in this, please let me know.
There is excess noise in the low-frequency region below 5-6 Hz. If people think I should make a measurement of amplified noise to go further away from the instrument noise floor, let me know.
I expect that a single OSEM channel can't be better than 1e-10 m/rHz above 5 Hz, so probably something wrong in the calibration. 1.6 V/mm seems right to me, so could be some place else.
Gautam pointed out that there are extra Sm-Co magnets stored in the clean optics cabinet.
I took the magnet box out and put it on the rolling table next to south flow bench. The box contains 3 envelopes with magnets.
They are labelled as following:
FLUX 94 - 50 parts
FLUX 93 - 10 parts
FLUX 95 - 40 parts
(What is FLUX??)
The box also contains some procurement documents.
The clean and bake dcc says :
1. Ultrasonic clean in methanol for 10 minutes
2. Bake in vacuum at 177 C° for 96 hours
Should we go ahead with the C&B?
The curie temp of SmCo seems about x2 (in K) of the one for NdFeB. i.e. 600K vs 1000K. So I believe 177degC = 450K is not an issue. Just make sure the curie temp, referring the specific property for the magnets from this company. (You already know the company from the procurement doc). It'd be great if you upload the doc on the 40m wiki.
Also, the magnets are nickel-plated. I guess that doesn't matter for the baking (Curie temp of 355 °C)?
A summary of things that need to be fabricated/purchased/done:
Stephen and I discussed the nominal heights of the BHD platform components.
I've brought 4 DO-32L-PE cards from WB for BHD upgrade for Jon.
In the cleanroom, I opened the nickel-plated SmCo magnet box to take a closer look. I handled the magnets with tweezers. I wrapped the tips of the tweezers with some Kapton tape to prevent scratching and magnetization.
I put some magnets on a razor blade and took some close-up pictures of the face of the magnets on both sides. Most of them look like attachment 1.
Some have worn off plating on the edges. The most serious case is shown in attachment 2. Maybe it doesn't matter if we are going to sand them?
I measure the magnetic flux of the magnets by just attaching the gaussmeter flat head to the face of the magnet and move it around until the maximum value is reached.
For envelope #1 out of 3 the values are: (The magnet ordering is in attachment 3):
Going to continue tomorrow with the rest of the magnets. I left the magnet box and the gaussmeter under the flow bench in the cleanroom.
Continuing with envelope number 2
I think I have to redo envelope 1 tomorrow.
Redoing magnet measurement of envelope 1:
Moving on to inspect and measure envelope 3 (the last one):
I measure some of the dowel pins we got from Mcmaster with a caliper.
One small pin is 0.093" in diameter and 0.376" in length. The other sampled small pin has the same dimensions.
One big pin is 0.187" in diameter and 0.505" in length. The other is 0.187" in diameter and 0.506" in length.
The dowels meet our requirements.
We got some dumbells from Re-Source Manufacturing (see attached). I picked 3 in random and measured their dimensions:
1. 0.0760" in diameter, 0.0860" in length
2. 0.0760" in diameter, 0.0860" in length
3. 0.0760" in diameter, 0.0865" in length
In accordance with the Schematics.
Today I assembled the skeleton of 6 towers, without clamps and sensor assembly (attachment 1).
Some of the side plates have this weird hole that doesn't fit any of the suspension blocks (attachment 2). I didn't notice when I counted the parts and now there are exactly enough side plates to assemble 7 towers.
Also found that one of the stiffener plates has a broken threading.
We will need more parts to go beyond the necessary 7 SOSs. I will do the recounting later.
Things to do next:
1. Find the capped spring plungers and send them to C&B.
2. Assemble the clamps onto the suspension blocks.
3. Push some Viton tips into the vented screws we got to make safety stops.
4. more C&B: Magnets, dumbells, dowel pins, OSEMs.
5. Push clean dowel pins into the last suspension block.
6. Assemble 7th Tower.
7. Assemble safety stops and clamps.
8. Glue magnets to dumbells.
Today, I screwed the plungers on the sensor plates and installed them on the Towers. I also installed the wire clamps on the suspension blocks (attachment).
I ran into problems in 2 separate suspension blocks: one had a dowel pin that was slightly too fat for the wire clamp. In another, the tapped holes were too short so that the 4-40 screws couldn't be screwed all the way.
I found a "vice" in the cleanroom (attachment 1). I used it to push dowel pins into the last suspension block using some alcohol as a lubricant.
I then assembled the 7th and last suspension tower (attachment 2).
Things that need to be done:
1. Push Viton tips into vented screws and assemble the earthquake stops.
2. Glue magnets to dumbells.
Differential misalignment of the OMCs
40m BHD will employ two OMCs on the BHD platform. We will have two SOSs for each of the LO and AS beams. The challenge here is that the input beam must optimally couple to the OMCs simultaneously. This is not easy as we won't have independent actuators for each OMC. e.g. The alignment of the LO beam can be optimally adjusted to the OMC1, but this, in general, does not mean the beam is optimally aligned to the OMC2.
When a beam with the matched mode to an optical cavity has a misalignment, the power coupling C can be reduced from the unity as
where is the waist radius, is the divergence angle defined as , and are the beam lateral translation and rotation at the waist position.
The waist size of the OMC is 500um. Therefore = 500um and = 0.68 mrad. If we require C to be better than 0.995 according to the design requirement document (T1900761). This corresponds to (only) to be 35um and (only) to be 48urad. These numbers are quite tough to be realized without post-installation adjustment. Moreover, the OMCs themselves have individual differences in the beam axis. So no matter how we set the mechanical precision of the OMC installation, we will introduce a maximum of 1mm and ~5mrad uncertainty of the optical axis.
Suppose we adjust the incident beam to the OMC placed at the transmission side of the BHD BS. The reflected beam at the BS can be steered by picomotors. The distance from the BS to the OMC waist is 12.7" (322mm) according to the drawing.
So we can absorb the misalignment mode of (, ) = (0.322 , ). This is a bit unfortunate. 0.322m is about 1/2 of the rayleigh range. Therefore, this actuation is still angle-dominated but a bit of translation is still coupled.
If we enable to use the third picomotor on the BHD BS mount, we can introduce the translation of the beam in the horiz direction. This is not too huge therefore we still want to prepare the method to align the OMC in the horiz direction.
The difficult problem is the vertical alignment. This requires the vertical displacement of the OMC. And we will not have the option to lower the OMC. Therefore if the OMC2 is too high, we have to raise the OMC1 so that the resulting beam is aligned to the OMC2. i.e. we need to maintain the method to raise both OMCs. (... or swap the OMCs). From the images of the OMC beam spots, we'll probably be able to analyze the intracavity axes of the OMCs. So we can always place the OMC with a higher optical axis at the transmission side of the BHD BS.
I tried to push the clean Viton tips into the vented screws just to find out that the vented holes are too small. We need to drill 0.1" diameter holes about 0.1" deep into these screws and clean them again.
Can you just cut the viton tips smaller? If you cut it to have some wedge (or say, taper), it can get stuck with the vent hole.
Stephen and I discussed the in-vacuum OMC wiring.
- One of the OMCs has already been completed. (Blue)
- The other OMC is still being built. It means that these cables need to be built. (Pink)
- However, the cables for the former OMC should also be replaced because the cable harness needs to be replaced from the metal one to the PEEK one.
- The replacement of the harness can be done by releasing the Glenair Mighty Mouse connectors from the harness. (This probably requires a special tool)
- The link to the harness photo is here: https://photos.app.goo.gl/3XsUKaDePbxbmWdY7
- We want to combine the signals for the two OMCs into three DB25s. (Green)
- These cables are custom and need to be designed.
- The three standard aLIGO-style cables are going to be used. (Yellow)
- The cable stand here should be the aLIGO style.
Today I glued some magnets to dumbells.
First, I took 6 magnets (the maximum I can glue in one go) and divided them into 3 north and 3 south. Each triplet on a different razor (attachment 1).
I put the gluing fixture I found on top of these magnets so that each of the magnets sits in a hole in the fixture. I close the fixture but not all the way so that the dumbells get in easily (attachment 2).
I prepared EP-30 glue according to this dcc. I tested the mixture by putting some of it in the small toaster oven in the cleanroom for 15min at 200 degrees F.
The first two batches came out sticky and soft. I discarded the glue cartridge and opened a new one. The oven test results with the new cartridge were much better: smooth and hard surface. I picked up some glue with a needle and applied it to the surface of 6 dumbells I prepared in advance. I dropped the dumbells with the glue facing down into the magnet holes in the fixtures (attachment 3). I tightened the fixture and put some weight on it. I let it cure over the weekend.
I also pushed cut Viton tips that Jordan cleaned into the vented screws. While screwing small EQ stops into the lower clamps I found some problems. 4 of the lower clamps need rethreading. This is quite urgent because without those 4 clamps we don't have enough SOS towers. Moreover, I found that the screws that we bought from UC components to hold the lower clamps on the SOS towers were silver plated. This is a mistake in the SOS schematics (part 23) - they should be SS.
Then, can we replace the four small EQ stops at the bottom (barrel surface) with two 1/4-20 EQ stops? This will require drilling the bottom EQ stop holders (two per SOS).
According to the schematics, the distance between the original EQ tap holes is 0.5". Given that the original tap holes' diameter is 0.13" there is enough room for a 1/4" drill.
On Thursday, I glued another set of 6 dumbells+magnets using the same method as before. I made sure that dumbells are pressed onto the magnets.
I came in today to check the gluing situation. The situation looks much better than before. It seems like the glue is stable against small forces (magnetic etc.). I checked the assemblies under a microscope.
It seems like I used excessive amounts of glue (attachment 1,2). The surfaces of the dumbells were also contaminated (attachment 3). I cleaned the dumbells' surfaces using acetone and IPO (attachment 4) and scratched some of the glue residues from the sides of the assemblies.
Next time, I will make a shallow bath of glue to obtain precise amounts using a needle.
I glued a sample assembly on a metal bracket using epoxy. Once it cures I will hang a weight on the dumbell to test the gluing strength.
I glued another batch of 6 magnet+dumbell assemblies. I will take a look at them under the microscope once they are cured.
I also hanged a weight of ~150g from a sample dumbell made in the previous batch (attachments) to test the magnet+dumbell bonding strength.
The bonding test passed - the weight still hangs from the dumbell. Unfortunately, I broke the bond trying to release the assembly from the bracket. I made another batch of 6 dumbell+magnet.
I used some of the leftover epoxy to bond an assembly from the previous batch to a bracket so I can test it.
Jordan has made 1/4" tap holes in the lower EQ stop holders (attachment). The 1/4" stops (schematics) fit nicely in them. Also, they are about the same length as the small EQ stops, so they can be used.
However, counting all the 1/4"-3/4" vented screws we have shows that we are missing 2 screws to cover all the 7 SOSs. We can either:
1. Order new vented screws.
2. Use 2 old (stained but clean) EQ stops.
3. Screw holes into existing 1/4"-3/4" screws and clean them.
4. Use small EQ stops for one SOS.
Also, I found a mistake in the schematics of the SOS tower. The 4-40 screws used to hold the lower EQ stop holders should be SS and not silver plated as noted. I'll have to find some (28) spares in the cleanroom or order new ones.
1 or 2. The stained ones are just fine. If you find the vented 1/4-20 screws in the clean room, you can use them.
For the 28 screws, yeah find some spares in the clean room (faster), otherwise just order.
After receiving two new tubes of EP-30 I resumed the gluing activities. I made a spreadsheet to track the assemblies that have been made, their position on the metal sheet in the cleanroom, their magnetic field, and the batch number.
I made another batch of 6 magnets yesterday (4th batch), the assembly from the 2nd batch is currently being tested for bonding strength.
One thing that we overlooked in calculating the amount of glue needed is that in addition to the minimum 8gr of EP-30 needed for every gluing session, there is also 4gr of EP-30 wasted on the mixing tube. So that means 12gr of EP-30 are used in every gluing session. We need 5 more batches so at least 60gr of EP-30 is needed. Luckily, we bought two tubes of 50gr each.