I pumped the chamber down and added LN2 today. The pressure was slowly rising - it was about 20m Torr in the chamber when I added the LN2. Per Raymond's instructions, I added about a third of a container of LN2. This got the temperature down to about 89K (when I had 20W running in the heater). It stayed there for about 25-30 minutes.
I turned off the heater and left the LN2 to boil off. You could see the cloud coming out of the top (the plume height would increase proportionally to the heat in the heater).
Eventually the LN2 evaporated and the shield temperature started to increase back to room temperature. As of this post it is 282K (which took about 5 hours).
The PD thermistor is not currently registering. However, the temperature of the PD can be inferred from the shield temperature (see aLOG 2517).
The rate of increase in temperature was much faster than the previous test - see second time series. I wonder if the thermal mass of the shields in the Feb 2020 test was cooled down a lot more due to 5 hours at 80K in that test - thus reducing the overall ambient load on the inner shield ...
I pumped the small vacuum volume down but the pressure started rising as soon as I turned off the vacuum pump. Closing the main valve to the pump and the valve to the chamber did little to change the leak rate. So the main leak seems to be from the volume around the pressure gauge - best guess, the section and O-ring that I connected to the chamber yesterday.
Vacuum pressure was recorded from vacuum gauge to text file in Python (using pyserial). Haven't got this into EPICS just yet.
Link to ligo.wbridge QIL Cryostat HowTo Playlist Cryostat on youtube - not super user-friendly as of yet, but populated with a couple of videos so far.
Link to ligo.wbridge QIL Cryostat Photo Album on google photos - not well curated, currently just a dump.
I recorded a 15 minute overview that describes the JPL PD set up and how to operate it. I'm in the process of embellishing the operation procedure (previous version can be found here: eLOG 2476).
I measured the power incident on the cryo chamber viewport and the reference PD reading to calibrate the incident power. Data is attached. Power meter head = S148C.
I ran the bright PD test on the photodiode currenlty in the vacuum chamber. The test was run at air and room temperature. I aligned the 2um laser onto the PD using the piezo mirror and the readout from the preamp. I then switched to the Keithley and ran the bright scan with the "runsweep.py" script. I actually ran the scan at multiple laser diode current settings by varying the control voltage into the diode driver. The change in response wrt control voltage looks linear but I need to run an analysis on it.
The data is stored in /home/controls/JPL_PD/data/20210303_bright_scans
is the x-axis in units of seconds? I think if we are clever, we should be able to look at a couple of the thermal time constants and figure out where the heat leaks are.
[updated with reference to data set, cleaner plot, images of chamber configuration]
Data - cooldown 20210205 (CSV = raw, XLSX = Stephen's plots) in Box Folder [Voyager\MarinerBox\CryoEngineering\CSVlogs]
Description - 5.5 hour cooldown with data, which was then allowed to continue for a total of 96 hours (but data collection failed for the long stretch, except for a snapshot of the final state). The cold flange was below 100 K after 6 hours, and leveled off at about 80 K. The vacuum pressure was steady at 3 microTorr throughout, via a roughing line connecting the external and internal volumes (mitigated losses in external connection volume, with no areas dramatically cold to touch). The cold flange was radiating to room temperature surroundings, as the radiation shields were not installed. The cryocooler was turned on/off at the start/end of the data collection, and the in-vac heater was not powered on at all.
StephenA, RaymondR remotely assisting (off payroll haha)
It seems that we won't likely receive the intended hand-off resources (especially of note is that Raymond can't seem to find the videos he made, wherein he guides through operations of the vacuum system and cryocooler). Raymond has been kind enough to support via Zoom as needed so that things can progress with some sort of guidance.
I'll stay on top of the lessons learned and dump these, along with photos and other resources in the log. I'll also make weekly visits with the intent of making continued progress.
1) What is the current state of the QIL Chamber?
- Raymond left the vacuum line shorting the "external volume" with the cross, cryocooler, etc. directly to the "main volume" because the losses between the "external volume" and the feedthrough entering the chamber were too large. The system was down in the e-5 torr range. Ref IMG_8019, with flex hose connecting bottom of 4-way cross to side of chamber.
- To implement this vacuum arrangement, there was a key component put aside on the table - IMG_8024 is a T which connects the roughing line to both the external volume and the main volume, using the flex line from IMG_8019 and the components pictured in IMG_8020.
- The copper feedthrough has all clamps attached, such that temperature measurements are being made on the adapter copper rod, which has a bolt pattern for thermal straps. Sensor names reflect current locations.
- We inspected everything (cryocooler connections, vacuum gauges, temperature logging), and pronounced it "ready to go" at the end of my work day.
2) What did I learn today?
- Cryocooler has only one setting, and temperature control must be engineered at the output using thermal contact, emissivity, etc.
- Formatting of USB is the main error that can befall the CTC100 datalogger. If the red dot in the upper right corner of the screen does not light up bright when it is tapped (this starts datalogging), then there is something wrong. Easy enough to test by removing the USB when the red dot is dim (datalogging paused) and checking whether there are log contents.
- Raymond's focus with the QIL chamber had been on answering the question, "can we cool down the cryocooler's connection (copper linkage which passes into the chamber) adequately?" He had never successfully obtained a cooldown that was below 150 K, and the primary limitation appeared to be related to high pressures in the "external volume".
3) What are we up to next?
- The next time I come in, I will be turning on the cryocooler and datalogging first thing, and I will hopefully have cooldown trends to share in the log.
- If those trends are > 150 K, I was advised that the next thing to do would be to bring the "external volume" out of the equation, and directly attach the cryocooler to the copper feedthrough linkage. This would be one way to demonstrate the least-lossy, best case scenario.
- If < 150 K, I am told that Karthik may be ready to move in for some measurements. If not, I would be interested in dropping in the suspended, shielded Silicon dummy (currently standing by) and seeing if we can measure a successful (< 150 K) cooldown on the Si mass.
4) Can we increase the height of the chamber?
I've shared lots of images related to the question of extending the height of the chamber. Here are my thoughts:
- Raw measurements - Ceiling = 0", Crane ~ -12", Crane hook ~ -16", Chamber Lid ~ -26", Chamber Base ~ -40", Table ~ -43".
--> Not much space above the surface of lid, currently about 10" of range for a possible extension.
--> Actual useable range is less, due to real world limitations such as the height of lifting straps, interference with the angled crane arm, etc.
- It would require a clever solution to increase the crane height (spacer at base? extended height model?) or lower the lid height wrt the crane (position on lower table? lower the table on its leveling feet?) to buy a few more inches.
- Current allowed object height ~8" (could be extended to about 10" with modified PEEK spacers at base); would we benefit greatly from having a ~16" allowed object height? Or do we need to get more height out of this update?
- I need to follow up with my request for quote of an extension of ~10" height.
Mid afternoon I moved some equipment to QIL for making Q measurements of cantilevers, which Karthik is planning to do in the IR labs cryostat. See cryo elog for more information, photos attached to show location of equipment in QIL.
This morning I rolled the AG4395A from Adaptive Optics lab (labeled QIL, IP = 10.0.1.64) for use in Crackle. Will return after end using.
doesn't seem so, but they sell this one:
which has a USB interface and pretty good voltage noise spectrum
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.
I was thinking about getting this new current pre-amp from NF:
It seems to have a good noise performance and has a built in low pass filter and also a remote interface.
The FEMTO seems less fancy, but their noise performance is actually 2-3x better.
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.
I have a python script for communication with the Met One 227a particle counter, but it appears like I am not receiving a response from the device. I swapped out a few serial-USB cables, but this did not fix the issue. I suspect I am making an unsound assumption about the communication protocol so I am going back to basics and reading more on RS232 and ASCII commands.
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)
Here's the python code I used to control this.
I incorrectly used the Move to Limit command ('1MV-3': axis 1, MoVe, negative direction, speed 3', where the speeds are given in the manual, see Section 4.7 in particular). Once this command is issued, the stage will keep moving until it receives the stop command. The JOG command would be more appropriate.
I confirmed a smooth change in the PD output as the beam translated across it.
I installed the Agilis mirror before the lens and cryo-chamber. Used the USB interface to align the beam onto the PD. So we can control the alignment remotely now (or once I’ve properly connected the USB cable instead of today’s janky test connection).
I installed the Agilis mirror before the lens and cryo-chamber. Used the USB interface to align the beam onto the PD. So we can control the alignment remotely now (or once I’ve properly connected the USB cable instead of today’s janky test connection).
An issue was raised with last calculation about the fact that our sensing of PDH signal isn't ideal and in the real world there is scattering, clipping extra adding excess noise in the PDH loop. This noise primarily comes by the intensity noise imparted on promptly reflected light from the cavity via various shaking optics etc on the table before it goes to the PDH reflection RF photodiode.
This noise's coupling to the PDH loop is identical to how shot noise of light couples into the PDH loop i.e.:
Looks like the temperature difference between the PD and the shield is relatively small. Even the transients when the heater is applied are order 5K.
This means that, for quick purposes, the shield RTD is a good proxy for the PD temperature.
The attached data is the difference between PD and shield RTD from circa 5th-6th February 2020.
Okay - all the steps in the procedure of eLOG 2476 have been verified as working - with the exception of the RTDs in the chamber.
With regards to taking dark noise spectra at different biases and temperatures, looks like Raymond took spectra with biases of [50, 100, 200, 400, 600, 1000]mV. If no objections, I’ll stick to that number of measurements.
I’m a bit pushed for time with other stuff. I wonder if the shield RTD is sufficient to run tests on the system? I’ll go back through the data and see how reproducible the relationship between shield temperature and PD temperature is. If it is reliable then in the interests of time, I’m going to forgo re-installing the extra RTDs in the chamber just now.
I have a preliminary calculation to post here. This does not include noise sources from cavity fluctuations and main frequency noise. But it gives some idea about shot noise and frequency noise of AUX laser conttribution to the noise in calibration.
Embellished Chris's PD MEDM screen a bit to illustrate controls in a diagram. The representation of the RELAY SWITCH between the Keithley and the SR560 is a bit off - I think the transimpedance amplifier is switched out as well.
Also - Keithley bright PD sweep output is attached.
Quick update, more detailed update to follow.
Still to do:
If we use ECDL for auxiliary frequency in 40m and hope to stabilize it up to 1 MHz with digital compensation of PZT, it is important to take into account any phase effect of the nearby FSR at 3.97 MHz. This should ideally be included in the Input Mode Cleaner loop considerations as well. These effects would be more prominent in longer cavities like aLIGO and LISA where FSR is very low and should we attempt to stabilize a laser lock beyond cavity's FSR.
I did a no assumptions calculation for getting a general transfer function fo PDH error signal in units of [W/Hz] assuming 1 W of incident power. This calculation would soon be uploaded here. I'll put down here primary results.
For incident field on a Fabry-Perot cavity (with fsr of ), reflected electric field transfer function (unitless) is given by:
Then, PDH error signal for a modulation frequency of at a modulation index of , in units of [W/Hz] (i.e. error signal power per Hz of error in laser frequency from cavity resonance) is given by:
after demodulation and low pass filtering. Note this transfer function is a complex quantity as it carries phase information of the transfer function too. The real signal is obtained by multiplying this signal at with and taking the real value of the product.
Having done this, we can see how in the real PDH error signal, there is a low pass at cavity pole, given by and a notch every fsr. The notch creates a zig-zag in the phase of the tranfer function and has a HWHM same as cavity pole. After this point, I just fitted a ZPK model to the transfer function to obtain a empirically derived model for PDH error signal transfer function. Apart from the cavity pole, this model needs to have resonance and antiresonance features present at each FSR with resonance having a linewidth of cavity pole while anti-resonance having a linewdth of . Here's how the ZPK model would look like:
I've attached my notebook where I did the fitting analysis and the overlap plot of real PDH error signal TF and the modelled approximation.
would be easier to achieve there with higher laser powers and higher cavity finesse.
But I haven't attempted that here as we do not know our NPRO PZT's resonance features yet.
I don't know why it would be easier to have higher finesse with longer arms. Something about beam size???
The NPRO PZT TF's are all in the 40m elog - there are many measurements of TF made over the past 10 years. Its like Raiders of the Lost Ark - you have to believe its there while searching.
Following up on the last post, here I presented a near back of the envelope calculation of how different choices of AUX cavity finesse and laser source for mariner would affect the prospects of calibration scheme.
As mentioned in the last elog post, here I considered using an NPRO seeded auxiliary laser source (converted to 1418nm by whatever method), ECDL based on ANU design with a modified PDH loop and same ECDl with a digital compensation of PZT resonances. I have taken the residual frequnecy noise of these lasers as the dominant noise source in the calibration scheme. Craig and Gautam in their proposal for SoCal wanted the AUX laser to be locked to the arm cavity in a PDH shot noise limited way. That would be necessary for 4km interferometers and would be easier to achieve there with higher laser powers and higher cavity finesse.
Here I considered three cases. First assumes about 3% transmittance of 1418nm in ITM and ETM HR coatings for mariner. This gives a finesse of about 100 and a cavity pole of 18.9 kHz. I believe this is the existing case at 40m. Next we consider transmittance of 0.5% and 0.05% (500 ppm) of 1418nm in ITM and ETM HR coatings for mairner. These cases give finesse of 625 and 6.28k respectively with cavity poles at 3 kHz and 299 Hz respectively.
Page 1: Consideres the case of finesse of 100. The green dashed line shows the amount of drive strength (in m) required at different frequencies if we use ECDL with PZT resonance compensation, to get an SNR of 1000 in 100s of integration time.
Page 2: Same as above but for Finesse of 625.
Page 3: Same as bove but for Finesse of 6280.
Page 4: Comparison of different finesse cases for the ECDL with PZT compensation option. Dashed curves represent requried drive strength (in m) for different cases.
Page 5: Same as above but for NPRO seeded auxiliary laser.
Note: For the NPRO seeded auxiliary laser, we have assumed that the noise of conversion to 1418 nm is similar to noise due to SHG process which is not dominant. There would be an effect of multiplying with a factor ranging form 1-1.5 due to frequency conversion but I have ignored it here for simiplicity. Also, NPRO case is limited in bandwidth due to PZT resonances. We might be able to get away with them using digital compensation like the case study for ECDL. But I haven't attempted that here as we do not know our NPRO PZT's resonance features yet.
We can use Thorlabs SAF1450S2 gain chip to generate 1418 nm light using an ECDL design similar to the one described in Kapasi et al. Optics Express Vol. 28, Issue 3, pp. 3280-3288 (2020) (ANU 2um ECDL design).
I have contacted Disha and Johannes to get the actual measured data for the PZT transfer function of this ECDL design. Fig.5b in their paper plots the transfer function of the PZT. Since, in ECDL PZT directly changes the cavity length, it has a more powerful actuation strength (2 orders of magnitude more) with actuation of 560 MHz.V upto 1 kHz. It however had a very low pole at 1 kHz and two mechanical resonance-antiresonance pairs near 1 kHz and 2 kHz. I modeled a transfer function by eye using Fig.5b of the paper. Page 1 in the attached pdf shows this modelled transfer function.
Next, we need to change the PDH loop for the auxiliary laser lock with the 40m cavity since the PZT has changed. I modelled one from scratch. This simple analog loop's performance is shown in orange in pages 2-5. This loop seemed stable from all the metrics I know, viz: phase margin of about 55 degrees (Page 2), no strong peak in close loop transfer function (page 3), and no remanant oscillations in time domain response (page 4).
I also modeled a similar loop but with digital compensation of the resonance-antiresonance features. This loop is plotted in green on pages 2-5. Both these loops have 300 kHz of bandwidth just by using PZT. I beleive this could be increased but I have not taken into account any saturation of PZT.
From Fig.4. of the paper gives a frequency noise estimate for free running ECDL. They mentioned that a roll-off below 10 Hz was due to their thermal feedback to remain in linear range of their frequency noise emasruement method. I modeled the noise of ECDL hence by
where the flicker noise contribution is similar to NPRO noise but ECDL has a white noise of 15 Hz/rtHz due to natural linewidth of spontaneous emission or Schawlow-Townes linewidth (with several broadening factors). I think this is an inherent limitation of ECDLs.
Page 5 shows both unsuppressed and suppressed frequency noise estimate for ECDL with the loops mentioned above and current values of NPRO noise are also plotted for comparison.
Came into lab today, with two main goals:
1) Bring Downs equipment for vibration measurements of cryo cooler during next operation
--> DONE, see photo
2) Assemble shields, with two layer scheme using electropolished and mill finish panels.
--> issue: the electropolished shield set was only partially shipped out in Ticket 15101 - unfortunately there was a misinterpretation by Logistics personnel regarding which parts to ship, due to the formatting of the ticket page. I will coordinate shipment of the balance of the panels to the vendor Able Electropolishing for completion of PO S479514
I entered QIL just before Wed Sep 23 00:27:51 2020 to check out and photograph the sprinklers, spent about 20 min looking around the lab and drawing inspiration for in cryo. Wore shoe covers and gloves, touched nothing, sanitized doors after.
HEPA filters on top of the WOPO table have been turned to High (earlier were at Low).
2020 Sep 01, StephenA with remote assistance from RaymondR
Cryopump is up and running. Initial attempts to run the cooler were stymied by an open circuit in the cold head to compressor connection caused by one of the two accessory port fuses (right, circled in attachment 1). The compressor would run but the valve motor wouldn't start in the cooler itself. I extended the spring in the fuse housing (attachment 2) and it seems to have fixed the problem, as now the valve motor starts at the same time the compressor is turned on. Attachment 1 also shows the highly technical cord management procedure done to reduce the trip hazard caused by the compressor power plug.
User manual recommendations*:
*Manuals for both the compressor and the cryocooler are linked on the West Bridge wiki manuals page
The diaphragm pump was turned on earlier this week after finally closing up this external adapter tank. Out of an overabundance of caution the tank and cryocooler are supported by the skycrane and a number of posts to prevent it walking off the foam resting pad once the cryocooler is switched on.
All temperature sensors agree with each other within 0.1 K at room temperature
Used the 19-pin MIL feedthrough to run 4 platinum RTD's and a 25 Ω 100 W resistive heater to the cold head. Attachment 1 is the wiring diagram for the feedthrough and the D-sub connector to the CTC-100 temperature sensor. Attachment 2 shows the three RTDs placed on the cold head. It also shows the thermal anchoring of all lead wires. Attachment 3 shows the RTD attached to the cooler below the cold head using cigarette paper and cryo varnish (stored in the flammables cabinet in QIL).
The Al block is a premade PT-RTD integrated mounting setup, which was placed on some indium sheet bits and clamped down with a screw and belleville washer. The other two cold head sensors are pressure fit to the cold head by a spring loaded mini dog clamps, and one of the two has some indium underneath the RTD to see if there is any value in doing so going forward with these mounting springs. The glued sensor was attached by painting a thin layer of cryo varnish on the cooler, adding a strip of cig paper, layer of varnish, press in sensor, another strip of paper, paint over all of it with a last thin layer of varnish that reaches beyond the bounds of the paper strips.
Picked up the prototype shield panels from Hamilton Metalcraft 7/22 and brought them to QIL. All of the parts are wrapped by part number and in a bin (see attached photo). There are 6 sets of shield panels, but 2 full sets were removed for coating vendors. One full set is as follows (20 parts total):
All component #'s are preceded by 'D2000298-'. 031, 032, and 033 are 03 panels but with hole variations, same goes for 131, 132, and 133 with respect to panel 13
Alex dropped off the new round of 2um PD's, they're on the north table accompanied by his data sheet.
First day back (7/15) found the particle board trim w/ powerstrip on the QIL workbench had collapsed. Re-glued and added 4 screws to the middle board where vertical boards from the shelves extended low enough. See attached photos for before, during, and after looks.
Copper parts picked up July 23rd and brought to QIL, now only waiting on PO# S477874 and the pirani gauge from Koji's bulk JPL order
Torque driver set for QIL setup bolted joints, with range 15 in*oz - 50 in*lb, p/n WIHA 5HYL9, is on order from Grainger, with anticipated delivery in the week of July 20th. Refer to PO S477925. *update* Tracking Number UPS 1Z19W9330321365493
Cryo connection copper parts PO S475316 will be finished early next week by the machine shop in Torrance, I'll bring them to campus or to Raymond's place (TBD).
I've updated the PSOMA optical layout. I still have some questions on locking, and there are a few additional configurations that we could try. In particular:
Each of these configurations also has a couple different ways to pickoff an LO for homodyne readout. Shruti and I enumerated these configurations on a zoom whiteboard a couple weeks ago, and I've attached them (the zip contains png).
Chris also mentioned last week that we may run into a frequency-dependent loss in the critically coupled cavity configurations. The pdf I've attached shows a configuration that I think is a minimal modification of the Mach-Zehnder amplifier described in PSOMA. One of the ring cavities is replaced with a tunable steering mirror, and the LO is picked off before the pump reaches the MZ.
In the new diagram, I'm thinking about controlling the following degrees of freedom:
Some things I'm unsure about:
Shruti and I are now tracking our work on git issues in the PSOMA repo.
Attachment 1 contains the SR785 dark noise measurements at number of PD reverse bias voltages from 77-295K with filenaming convention:
[PD]_drkspec_[date]_[temp]_[input V]_[scan freq]_[FEMTO gain]_[date]_.txt
It also contains the keithley sweeps for QE calculations.
I'm still working out what is wrong with the QE data and how to effectively process the dark noise versus temperature.
I put together two PSOMA layouts, one for a bowtie cavity and one for a ring cavity configuration.
I expect there are a number of problems with the layout as I've drawn it, and I note a number of these in the bowtie diagram. Among these
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.
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.
West Bridge flooding Apr 6th due to rain in the night
Looks like the first responder was Calum. The attached photos were sent from him.
Last Friday, I found the HEPA units on the squeezer table were not on. I turned them on at "SLOW".