In October, I drew a crude prototype of the torsional pendulum seismometer, after discussing estimated dimensions and parts with Kate (Prototype 1 Drawing.PDF) Recently, I made frame models with accurate dimensions and parts on SolidWorks. I ran through some (very slow) simulations on ANSYS for modal frequencies of the aluminum alloy frames. Our goal is to look out for any modes with a resonant frequency <100 Hz and see if there's some modification we could make to the frame to remove them.

Results: Frame with middle struts lower to the ground had highest first modal frequency of 64.318Hz. Second highest was frame with middle struts right in the middle of total height of frame with f = 64.288Hz. Lowest was middle struts higher up the frame, with f = 59.338Hz (see attached ppt)

The objective of this work is to find the frame configuration with the highest modal frequency (>100Hz) in order to provide most stable supporting structure for the seismometer.

I made multiple frame designs on SolidWorks and ran modal simulations on these drawings via ANSYS. The varied parameters of different designs include height of the horizontal structs, addition of cross bracings, presence of brackets, and struct thickness.The frames have dimensions of 3' height x 2' width x2' depth. The first six modal frequencies were considered (Fig 1). Eight different designs were evaluated (Fig 2). Their frequencies are summarized in a graph (Fig 3).

Summary of observations made:

• Having crossbeams yield 50-100Hz higher frequencies for modes 1,2,3,4.
• K crossbeams yield 10-15Hz higher frequencies than parallel crossbeams
• Thicker (60mm vs 45mm) beams yield ~10Hz higher in modes 1,2,3,4; and ~40Hz higher in modes 5,6
• Having brackets yield 13-15Hz higher in modes 1,2,3,4; and significantly more in modes 5,6

Figure 1. Six modal frequencies were taken into consideration for comparison.

Figure 2. Eight different designs were considered for comparison.

Figure 3. Different designs yielded a differing set of modal frequencies.

See attached ppt for more details.

Since modal frequencies have been calculated for different frame designs through FEA analysis, we decided to physically test the modal frequencies of the current frame in the lab.

We clamped an accelerometer onto a middle, horizontal strut of the frame. The accelerometer was connected to an amplifer, which was then connected to an oscilloscope. I banged the middle frame with my hand to give it an impulse. Without the ampifier, the amplitude of the waves was about 30mV. With the amplifier, the amplitude was on the magnitue of several volts. The oscilloscope displayed sinusoidal waves with frequencies ranging around 190-250Hz. There was also an enveloping wave with a frequency ranging around 30-50Hz. Our next plan is to transform these time domain waves into frequency domin spectra to identify modal frequencies of the frame.

Fig 1. When the frame was struct, there was a wave of 192Hz and enveloping wave of 27.8Hz (measurement made through the amplifier).

We used the signal processor to try to plot a frequency domain output of the accelerometer. The rough plot did show a noticeable peak at 73Hz and 164Hz (Fig 2). However, the signal processor is not very user friendly, and we are still trying to figure out all the settings. Hopefully we can save the file as well so that we can perform further analysis.

Fig 2. Frequency spectrum of the frame modal frequencies. The faint (lower) line is the ambient noise. The bold line is the data collected after the frame was struct with the rubber handle of a screwdriver.

Setup of the experiment are shown in Figure 3, 4.

Figure 3. The accelerometer is attached to the frame by a clamp secured by two screws. Because there is a gap in the frame, a piece of tape was used to allow more contact between the accelerometer and the frame.

Figure 4. Setup of the experiment. The frame is on the laser table, with the accelerometer mounted on the top, horizontal struct (location can vary for each test). The accelerometer is connected to an amplifier which is then connected to the oscilloscope and signal processor.

To reduce additional mass on the frame, a zip tie was used instead of the mount (Figure 5). We gathered some data, using the plastic handle of a ball driver as a source of impulse. The raw data files are attached (Vpk (log) vs Hz (linear)). The locations of testing are in Figure 6.

Figure 5. Accelerometer was attached on the frame using tape and zip tie.

Figure 6. The numbers indicate where I lightly hit the frame. The numbers correspond to raw data file name (#7,11 are ambient).

I plotted the raw data collected with the accelerometer attached to the high bar (Fig 7) and to the middle bar (Fig 8). Then I identified noticeable peaks.

Figure 7. Raw data of modal frequencies detected by an accelerometer attached to the high strut of frame.

Figure 8. Raw data of modal frequencies detected by an accelerometer attached to the middle strut of frame.

Next, Kate and I wrote a Matlab code that, given a left bound and right bound of a peak (chosen by observation), approximates a Lorentzian probability distribution in the range and fits the approximation to the raw data (using lsqfit). The function also outputs the peak frequency and the Q factor. Figure 9 displays the raw Data 8 (blue dots) and the fitted curves of identified peaks (red lines). Figure 10 displays the Data 14 and its peaks.

Figure 9. Data 8 (blue) with its fitted peaks (red).

Figure 9. Data 14 (blue) with its fitted peaks (red).

The motivation for this analysis is to observe whether the collected data are comparable to the ANSYS simulation that I previously did in order to identify the different modes present in the frame. Data 8 and Data 14 share many of the identified peak frequencies. By comparing these values with that of the simulation, many of the frequencies align with those calculated by the simulation (see attached "Peak Freq and Q factor.xlsx"). However, the collected data has so many peaks that it is difficult to discern whether the frequencies actually match the simulation frequencies or whether it's coincidence due to the large number of peaks. In order to obtain more accurate sets of data, I will fine tune the frame by adjusting each screw to its optimal roitation using a torque wrench. I will do some research online to find this optimal torque for the the type of screws used on the frame. Afterwards, the plan is to collect more data using the same procedures and compare the peak frequency values of the "better frame" with the ones I have collected here and those of the simulation.

I made a Solidworks drawing of the hanging pendulum model Kate and I discussed. To simplify the model, we didn't include the inverted pendulum. I specified the dimensions of the brass mass so that the brass mass and laser board pair had a 5kg mass at the bottom and top (each). I cut holes on the brass masses and laser boards so that the two 1mm diameter wires could be hung from above. As for specifying the materials, the downloaded laser board and struts didn't come with materials selected. So I chose "Aluminum Alloy - 1060 Alloy" for all boards, struts, and brackets. I looked up stainless steel wires on McMaster and one was "AISI 304 Steel". So I chose that for the wires. And for the masses, I chose "Brass."

Figure 1. Hanging pendulum. Origin is at the center of the middle laser board with x-axis running parallel to the shorter length, y-axis vertical, and z-axis longer length.

Under MassProperties, I found some useful properties:

Mass = 13841.72732 grams

Center of mass: ( centimeters )
    X = 0.00000
    Y = 0.01629
    Z = 0.00000

Moments of inertia: ( grams *  square centimeters )
Taken at the center of mass and aligned with the output coordinate system.
    Lxx = 14327802.07985    Lxy = 0.00002    Lxz = -0.00000
    Lyx = 0.00002    Lyy = 1189278.97915    Lyz = 0.00000
    Lzx = -0.00000    Lzy = 0.00000    Lzz = 14051480.23033

Moments of inertia: ( grams *  square centimeters )
Taken at the output coordinate system.
    Ixx = 14327805.75446    Ixy = 0.00002    Ixz = -0.00000
    Iyx = 0.00002    Iyy = 1189278.97915    Iyz = 0.00000
    Izx = -0.00000    Izy = 0.00000    Izz = 14051483.90493

Then, I used ANSYS to find the modal frequencies. The procedure I used is:
1. Select "Modal" for type of simulation
2. Import Geometry > Select the pendulum Solidworks file
3. Under "Model">"Geometry"> Change materials from library (Note: You cannot import preset materials from Solidworks. Default materials library in ANSYS is more limited. I used the pre-existing Aluminum Alloy and Brass but had to make new material called "AISI 304 Steel" and copy its mechanical properties (e.g. density, Young's modulus) from Solidworks)
4. Fixed Support > Select the circular top surfaces of the wires (the wires are fixed in space and cannot move)
5. Solve (took around 1hr)

The first modal frequency was found to be 38.44mHz and the pendulum swung in the direction of a playground swing swinging back and forth. The second frequency was 1.5063Hz in the direction of a playground swing swinging side to side.

I put together part of the rhomboid (the hanging pendulum) and added the top strut to the cage (Fig 1).

Figure 1. The rhomboid (without top board) and cage.

I've also atttached the ANSYS modal frequency simulation videos of the rhomboid with the top of the wires constrained in space (turn on repeat to play video continuously). The frequencies are as follows:

Mode 1: 38.44 mHz

Mode 2: 1.51 Hz

Mode 3: 10.15 Hz

Mode 4: 11.62 Hz

Mode 5: 12.69 Hz

Mode 6: 12.69 Hz

I've also attached the eDrawing file of the rhomboid.

We successfully suspended the rhomboid this evening. We are using only 1 wire for now and made it very bottom heavy to avoid any tipping over problems. (This was also necessary because the top breadboard does not have a hole in the middle for one wire--the locations of its holes are for the 2 wire design.) We got some good experience learning some of the limits of the pin vises, and uncovered some problems we'll face when using 2 wires. 

The first attempt to hang the rhomboid failed. The wire slipped right out of the pin vise at the bottom suspension point. This was the pin vise we had first put the wire into and we had not tightened it as much as the top pin vise. This was tightened essentially by hand. For the top pin vise, we used a pair of pliers, putting protective material between the pliers and the pin vise, to tighten the grip on the wire. The reassembly of the bottom pin vise mount was not easy. The pin vise handle did not slip into its hole easily, which was different than before. The inside of the hole appears scratched, and we cleaned it, but there was not obvious debris creating blockage. With a pair of pliers, we could force the pin vise into the hole, but this should probably be made a bit larger in the future. 

For the second (successful) attempt, we first let the bottom pin vise clamp hang freely from the wire. This allowed the wire to untwist. Its final resting place was about 45 deg from normal to the cage. We had the rhomboid supported by some boxes underneath so the topology was correct, but the rhomboid was out of the way. We then screwed the bottom clamp to the rhomboid, supported the rhomboid with our own hands, removed the boxes, and slowly lowered it until the wire supported its weight. As expected, it rotated into the 45 deg position and remained there. We have a pile of foam underneath, so that the rhomboid will fall less than an inch and onto something soft should the wire break. 

The untwisting of the wire made it clear that this aspect will pose a challenge for when we use two wires. Both wires will have to be untwisted in the same particular way so that the rhomboid sits squarely in the cage and so that neither wire is twisted in the resting position. I'm not sure yet how we'll address this problem.

We've left the rhomboid suspended. We've put a large danger sign in front of the cage to alert anyone who might enter the lab that wire is under tension and laser safety goggles must be worn.

Pictures follow:

Fig 1. Pin vise clamping onto the wire

Fig 2. Rhomboid hanging by a wire

(More pictures on ligo.wbridge@gmail.com > https://drive.google.com/drive/photos)

Kate and I suspended the rhomboid with two wires [see photo 4]. The general procedure was:

• From the previous hanging, one wire was already set up (clamped on both ends)
• Secure second wire into top pin vise. Tighten pin vise. Secure vise into holder using nuts
• Measure length of the first wire (already set up)
• Cut and secure the other end of second wire into bottom pin vise. Tighten pin vise
• Screw in the bottom vise holder onto underside of the middle breadboard
• Insert bottom pin vise into this holder
• Untwist the two wires
• Screw in the top two vise holders onto top bar of cage
• Slowly lower the rhomboid to suspend

Some key aspects include:

• Securing top pin vise into its holder using nuts
  • The relative position of top pin vise and its holder was determined by first tightening the bottom nut onto the vise. The distance between the top of the pin vise and the nut was measured and made same for the two pin vises. After slipping in the pin vise into its holder, the top nut was tightened. Photo #1 shows that the two pin vises nonetheless don't seem to be the same height.
  • TO-SOLVE: What is the most consistent and accurate way to make sure the relative positions of the top pin vise and its holder are exact? 
• Securing bottom pin vise into its holder using set screws
  •  The relative position of vise and clamp is preset since vise lip should be flush with the holder counterbore. However, because the vise had a thin, chamfered lip, it was difficult to make sure the vise was perfectly perpendicular to the holder, espeically because when we tightened the set screws, the screws pushed the pin vise around in the holder.
  • TO-SOLVE: How to make sure bottom pin vise is square with its holder? Better method than two set screws per bottom pin vise holder?
• Same length of the two wires
  • We want the wires to be of same length. One wire was already clamped on both ends from a previous hanging. We obtained a drawstring, held it next to the clamped wire, cut the string to the same length (between the tips of the pin vises on both ends), and used it as a reference length to match the second wire to be the same length
  • TO-SOLVE: Better way of making sure the two wires are of the same length?
• Tightening the pin vises to grab the wire
  • After slipping the wire into the pin vise tip, we grabbed the pin vise with two pliers with grips, held on in place, and twisted the other to tighten. We wrapped thicker kimwipes(?) around the vise in case the pliers would damage the vise. This method tightens the vise to clamp the wire securely significantly better than tightening by hand (when tightened by hand, the wire slipped out when the rhomboid was hung). We tightened the vise until the kimwipe slipped on the vise (the maximum tightness we could acheive).
  • TO-SOLVE: In the future, we want to use an adjustable vise grip with a torque wrench attached to it so that the tighteness can be measured and remain consistent for every testing. The details of attaching the torque wrench onto the vise grip and what value of torque to apply is to be determined.
• Untwisting the two wires
  • When the rhomboid is hung, we ideally want the wires to be not twisted. This time, we attached the bottom of the wires on the rhomboid (and top wires not attached to cage yet), flipped the rhomboid upside down, added mass on the top pin vise holder so that the wire was at its center of mass, and let it untwist itself (see photos 2&3). One wire was 180 degrees opposite from its desired orientation, and the other wire was about 165 to 170 degrees opposite from the desired orientation. As a result, we decided to flip the top vise holder 180 degrees (so the two wires at the top ended up farther apart than we had wanted it to be due to the asymmetry of the holder) to have the wires least twisted.
  • We came up with a better solution for next time. We would attach the top of the wire to the cage first, and let the bottom pin vise untwist itself. When untwisted, we would secure it into its holder using the set screws.
• Other TO-SOLVE's:
  • What is the best mechanism to adjust wire length once everything is set up?
    • We predict that it will be very difficult for the two wire lengths to be exactly the same, even with measurements. So after hanging the rhomboid, we plan to use a level to see whether the rhomboid is tipped. If it is tipped slightly (meaning the length of wires are not equal), we want to adjust the wire length without deconstructing everything. Adjusting the wire length at the bottom seems easier than at the top since the bottom pin vise can easily be removed by unscrewing the set screws from its holder.

Today, we tried to hang the rhomboid with the top two wires closer together (~4cm apart). First, we unclamped the bottom pin vises and rotated the top pin vise holders by 180 degrees so that the pin vises were closer together. We then let the wires with bottom pin vises attached hang freely to their untwisted state. When untwisted, it was obvious the wires wanted to be in a certain orientation (high rotational spring constant). We marked the pin vises at their untwisted states. We modified the rhomboid itself by attaching the top bread board (previously unattached). We then clamped the bottom pin vises into the bottom holders. When we let the rhomboid hang, one wire wasvisibly shorter (~1cm or so). Without letting go completely, we unclamped and clamped the longer wire pin vise, making sure to hold down the pin vise to its lowest point. When we hung the rhomboid the second time, the wires were more similar in length. Nevertheless, there was an obvious tilt to the rhomboid. We will try to balance the rhomboid tomorrow.

We also attached corner brackets to the top of the cage's four middle struts.

As we tried to balance the rhomboid, we found out that the difference in the wire lengths was the main contributor to the tipped rhomboid. Thus, we will now focus on making the wires have the same length by setting a wire clamp above the top pin vises. The idea is to extend each wire through the pin vise and top strut and hold it with a clamp made up of two plates. We can fine tune the effective length of the wire by sliding the plates up or down. When the optimal positions of the wires are found, we can then permanently secure the wires by tightening the top pin vises. The rough set up for this mechanism for one wire is shown in Figure 1.

Figure 1. We can adjust the height of the clamp using the micrometer to fine tune the effective wire length. In these photos, the clamp is incomplete; the existing platform will serve as one plate and we will need to machine the other plate. We will then attach these two using screws in order for the assembly to act as a clamp.

TO-DO:

1. Drill two holes on the top strut so that the wires can pass

2. Make a steel plate to attach to the platform (see attached CAD Drawing Wire Plate.PDF)

----------------------------------------------------------------------------------------------------------------------------

We also decided to order 6" diagonal braces to act as inner corner brackets for two opposing sides of the cage.

We will also try to attach a strut on the top side of the cage and attach 90 degree plates, on which we will attach rubber to act as stoppers.

(Updated CAD Assembly of cage + rhomboid + thermal shield to be uploaded this weekend)

I updated the cage and rhomboid CAD assembly with the latest changes. I also made a CAD of the thermal enclosure prototype. It includes aluminum panels on six sides (0/08in thickness), foam on top of the panels (1in thickness), and feet under the cage. I made some holes on the aluminum panels so that we can fasten the panels to the cage using screws. I also added corner brackets to connect the panels.

I had trouble making 3D renderings, so I took some screenshots. I may try to attempt 3D rendering again later. I've attached some photos and eDrawing files.

Updated assembly of cage with suspended rhomboid.

Thermal enclosure. Blue are aluminum panels, brown are foam.

This post will host plots and trends from this radiative cooling run (QIL/2704).

Preliminarily, it looks like the reconfiguration to remove a hardware mistake or two led to a healthier run. The comparison below clarifies the two runs:

• QIL/2702 - conductive link between inner shield and outer shield (twisted pair from an RTD lead accidentally clamped); possibly another conductive link between outer shield and baseplate (outer shield more wobbly than usual on spacers)
  • this data set should only be used to study the impact of a known conductive link between inner and outer shields.
  • this run demonstrates that there will be more effective, faster cooling if the outer shield is conductively cooled!
• QIL/2704 - resolved above mistakes!
  • this data set may be used to gain understanding of the impact of emissivity changes to the inner surface of the inner shield.
  • may be compared to QIL/2695, a run that is equivalent except with a higher emissivity inner surface of the inner shield

Run ended with cryocooler shutdown at 12:27 pm (actual duration just under 92 hours). System will warm up with pumps on for the rest of the break, unless I am inspired to come in and run one of the next intended runs discussed in QIL/2704. I did not run any heat input test for this data set, as I am not planning to come in frequently enough to monitor the heating safely.

Data:

Attachment 1 compares QIL/2704 (solid) to QIL/2702 (dashed). As expected, the outer shield temperature from the latter run stays warm since the conductive short was resolved. Due to the reduction of the inner shield's thermal load, the inner shield is able to cool faster and plateau at a colder temperature. As Stephen pointed out, however, the test mass is not cooled as efficiently compared to when the outer shield was conductively cooled.

Fitting Results:

Attachment 2 is a current model diagram of the various components being considered, and their thermal couplings. Attachment 3 plots the fitted model (dashed) over the temperature data (solid). The fit parameters were the following emissivities: aluminum foil, rough aluminum, and aquadag. Notes from the fit:

1. With the conductive shorting of the outer shield resolved, the model (which considers only radiative cooling of the OS) is well fit to the OS temperature data. 

2. The inner shield model is missing some key term(s) affecting its time constant and steady state temperature.

3. The above error propagates to the test mass model (I believe). 

Given these caveats, the fit results are as follows: aquadag e = 0.92, Al foil e = 0.04, rough Al e = 0.19. These all initially seem reasonable, and I'm happy to see that the aquadag emissivity is higher than previously estimated.

Next steps:

1. Separate the cold plate from the inner shield, and model their conductive and radiative link. Also model the radiative link between the cold plate and the test mass.

2. Cover the test mass in foil (to best of our ability) to refine the radiative link between the test mass and inner shield. Doing so will mean both elements have the same emissivity, so there is only one unknown parameter.

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).

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

2020 Sep 01, StephenA with remote assistance from RaymondR

Highlights

• Silicon Mass - Rana had dropped off the Silicon mass in the first room, so I found it when I arrived - thanks!
• Organization - It was my first time accessing the QIL lab, but everything was pretty well organized and easy to find. All tools for modifications to parts were used in the EE lab which was also well organized. Raymond helped me to figure out where to access things on a few occaisions.
• Packages - received from Downs Logistics room the Electropolished shield set, a Grainger order with deburring tool and step drill bit, and a McMaster order with a range of bolts - these have all been transported to the lab. Also transported the QIL machined parts that I had received from Machining Solutions to the lab.
  • Koji's Photodiode holders are in the QIL lab ready for pickup.
• Summary of progress
  • Assembled frame (using torque values from T1100066- #8-32 used 20 in*lb)
  • Assembled brackets to frame
  • Hung silicon mass from music wire
    • Wire is captured under #4-40 SHCS with washers ((using torque values from T1100066- #4-40 used 5 in*lb)
• Outstanding tasks and questions
  • Did the hang hold?
  • Do we want to have the layered Electropolished and Plain shields during the first installation? Or some sanded state?
  • Assembly requires oversized #8-32 washers which I wasn't able to track down from inventory - these are now on order, along with some more supplies for roughening the surface.

Full Details

• Assembly work
  • Refer to the DCC - T2000538 - for the videos capturing this assembly effort. I've snagged some screenshots which I've dropped into the attachments.
    • There is a tree catching procedures and other experiment documentation for the QIL Setup at T2000539
• Issues - there were four issues with the fabricated parts, three of which required small modifications;
  • D2000299-01 small angle rails had threaded holes where there should have been clearance holes for the interface (no issue on big angle rails)
    • modified by drill press to drill out clearance holes at same location
  • D2000308 interface cubes all were threaded only partially through.
    • No action taken, just paid attention and made sure the threads I needed were adequate. Seemed like an offset of only a turn or two, suggesting the CAM program was just a little off (this can happen with tapping, the tap is tapered and the machinist needs to thread deep enough to have the thread major diameter realized through the hole.)
  • D2000307-04 frame upper spacer had threaded holes that were not tapped all the way through.
    • I ran a tap through all of these threads.
  • D2000299-02 large angle rails had threaded holes that didn't pass all of the way through, and we happened to be inserting screws into the wrong side.
    • I ran a screw through these threads, which required a little bit more force than I would have liked, and forcing the screw provided an adequate thread.
      • Note that I anticipate that there will be an issue similar to this, with similar resolution, on the D2000299-01 small angle rails. The shield panels installed on the sides are to be installed from the inside. This can be resolved with a screw coming in from the outside.
  • There was also some inability to access certain screws with the long torque driver, especially if loosening/tightening after putting the frame together.
    • This was managed by use of an L allen key, which of course meant those joints were not torqued to spec. I'm not worried about this compromise.

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

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.

[updated with reference to data set, cleaner plot, images of chamber configuration]

StephenA, 2021.02.05

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.

Images -

1. IMG_8047 = starting conditions;
2. IMG_8119 = intermediate conditions after 5.7 hours;
3. IMG_8148 = final conditions after 96 hours;
4. IMG_8232 markup = view of RTD locations on cold flange, with annotations;
5. IMG_8225 = top view of cold flange and chamber configuration without radiation shields.

Plots -

1. cooldown_20210205_uhv_coupled_cold_flange_first_segment - shows first 5.5 hours only;
2. cooldown_20210205_uhv_coupled_cold_flange_all_time - shows all 96 hours, with data points extracted from images.

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.

2021.03.17, StephenA

1. Radiation Shields located (in TCS lab), unwrapped, fitted up.

Location in TCS Lab - IMG_8351

Removed lid and placed adjacent to chamber (cleared a little space, used 3 plastic flange covers to make nonmarring surface safe for lid and o-ring - IMG_8353

Fit up as installed - IMG_8354

Comments on the fit up - I looked at all of the apparent sources for insights into Rahul's original design intent - QIL elog 2276, DCC T1800308-v1, wiki for Cryo Vacuum Chamber. It appears that Rahul never decoupled the upper outer radiation shield from the cold plate, which seems like a strange omission. Chris and Raymond also appear to have been wrapping their heads around the intended layout, they came up with the fit up in QIL elog 2429 and sketch from QIL elog 2430. I will revisit their sketch at a future opportunity, but I went with something closer to 2429 as I was concerned about the height misalignments they described. Note that the height misalignment appears in Rahul's T1800308 CAD (see T1800308-v1 screenshot) so who knows what's "correct". I'll work on finalizing D2100310 CAD with radiation shield to capture the true current dimensions and fit up, to hopefully avoid such issues in the future.

2. Radiation Shields installed in Cryostat. Sequence was important here, as were a couple of improvised solutions to shortcomings of the existing parts.

Dog Clamps placed on bottom plate (to stand off bottom radiation shield bottom lid; not pictured, I think I placed some alumina washers on the dog clamps as well, not sure though anymore!). Also pictured are the usual PEEK legs for cold plate - IMG_8355

Bottom radiation shield bottom lid placed on dog clamps spacer, and bottom radiation shield cylinder placed on bottom lid - IMG_8356. Seems likely that the bottom radiation shield would be better configured upside-down.

Bolted cold plate down onto legs, with cold plate decoupled from bottom radiation shield - IMG_8357

Outer radiation shield installed and inner radiation shield installed (both needed to be tipped into place gingerly, but both cleared the cold finger cylinder with the flange removed. The heater also passed through the apertures successfully - IMG_8358

2x Alumina washers placed under outer radiation shield, inner radiation shield on cold plate - IMG_8374

Cold Flange reinstalled, though one of the brass SHCS was sheared - this was due to over torque, with 20 in*lb applied by mistake. Correct torque is 10 in*lb. The remaining 3 bolts were tightened to 10 in*lb. - IMG_8360

Top view of radiation shield apertures and cold plate grid - IMG_8375

Thermal strap interface to cold plate - dog clamps required due to strange spacing of clearance holes. - IMG_8376

2021.04.08, StephenA

Karthik had completed in-chamber alignment efforts during a prior visit. In air alignment also completed following viewport move.

0) Removed lid for access to chamber.

--> posted demo video to ligo.wbridge QIL Cryostat HowTo Playlist.

1) Mounted RTDs to final positions - locations are Heater (cryo varnish+cigarette paper, pictured in IMG_8558 curing under weight of upsidedown bolt), Inner Shield (cryo varnish+cigarette paper, pictured in IMG_8559), Cold Finger (spring clamp), and Workpiece (spring clamp).

--> Final chamber layout may be viewed in IMG_8562

--> Note that Karthik's Si cantilever, mounted vertically in the right of the image, is NOT bolted down to the baseplate (just located on baseplate by dog clamps, held down via gravity). This will need to be investigated to enable workpiece cooling.

2) Installed radiation shield lids - no bolts to expedite the process and to see if there is any bulk motion during pumpdown and thermal cycling.

--> note that the lid for the outer radiation shield seems to interface with the current shield orientation perfectly; if there was a mismatch, it would point toward the inverted orientation being intended, but this seemed pretty definitive.

3) Installed the cryostat lid - final positioning and alignment made easier by teflon rails!

--> posted demo video to ligo.wbridge QIL Cryostat HowTo Playlist.

4) Pumped down - single button press to turn on pumping station.

--> note that it took about 1 hour for both gauges to reach a few mTorr.

5) Confirmed function of heater - set PID setpoint to 350 K and enabled outputs, observed temperature rise in heater RTD.

--> note that PID autotuning should be done at steady state with workpiece RTD, before enabling outputs again!

6) Turned on cryocooler - flip power lever and turn on green system switch.

--> start time was 10 am.

7) Started temperature datalogging to USB - press dull red indicator dot on upper right corner of CTC-100 once, and note that indicator is now bright red.

8) Remaining photos posted to the ligo.wbridge QIL Cryostat Photo Album

2021.04.14 StephenA

QIL Cryo vacuum chamber cooldown was not as successful under the new configuration (radiation shielded by cylindrical outer + inner shields, cold finger thermally strapped to baseplate).

--> Karthik's Si cantilever workpiece was stable at 240 K.

--> Cold Finger was stable at 200 K - there is significant thermal loss between the cold finger and the workpiece.

--> Inner shield was stable at 250 K - seems to be somewhat decoupled from the baseplate; not very satisfied with the current state of the shielding.

Will need to re-examine some of the connections, which were not optimal (especially the improvised dog clamped strap-baseplate interface). Fabricating an adapter piece for the thermal strap which will be bolted 4x on a 2" x 2" grid. Might also look into a new thermal strap which could interface with baseplate directly.

Also will need to consider options to decouple outer shield from inner, and double check that shield orientation has no other solution (hoping there's an answer to the question, why would outer shield be coupled to baseplate?)

Data - cooldown 20210408 (CSV = raw, XLSX = Stephen's plots) in Box Folder [Voyager\MarinerBox\CryoEngineering\CSVlogs]

Description - 6 day cooldown. Layout described in QIL/2552. The radiation shields were installed and thermal strap was connected to baseplate. 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.

Images -

1. IMG_8570 = starting conditions;
2. IMG_8585 = final conditions after 144 hours;

Plots -

1. cooldown_20210408_first_si_workpiece_with_shields_and_straps

RadhikaB, StephenA

Two sessions this week were spent working toward simplification of the cryocooler connection.

We needed to order a couple of off the shelf vacuum fittings to complete the intended design - image attached.

Still WIP!

StephenA

This log investigates cooling through our current planned copper braid connection (which is standing in for an intended rigid bar linkage that is WIP)

The question is, can we get [cooling power of cryocooler] out of our baseplate through this copper braid?

Copper Braid

Cooner Wire P/N NER 7710836 BOF (oxygen free copper)

• AWG Size 2/0
• Circular Mil Area 132300 (conversion: .104 in^2 = 6.71e-5 m^2) - note that a 1 cm x 1 cm bar would have an area of 1e-4 m^2
• No. of Wires 5292
• Wire AWG Size 36
• Construction 7x7x108/36
• Nominal Diameter .483"
• Pounds Per MFT 433.

ref. https://www.coonerwire.com/flexible-wire-rope/

Cryocooler

Sumitomo CH-104 (manual from Wiki) has 77K coldhead cooling capacity of 34 W, and from the quote, 50K cooling capacity of just under 40 W.

Adequate cooling power of this setup depends on the radiative heat load and conductive losses; for our purposes, we can imagine that tens of Watts will be needed, and circle back to more precise heat budgeting.

Conductive Heat Transfer

Q = A / L * (Uint_T2 - Uint_T1)

Uint_T = the integral of thermal conductivity between T and 4K, see below table [ETP OFE Copper, W/m]. Note these are values from literature not from our copper braid's spec sheet (no such properties available from vendor).

Table of Thermal Conductivity integral values, between T and 4K. Unit = W/m. Source: Ekin, Appendix 2.1

               20K = 14000, 40K = 40600, 50K  = 50800, 60K = 58700, 70K = 65100, 80K = 70700, 100K = 80200, 120K = 89100, 140K = 97600

A = 6.71e-5 m^2

L = 0.5 m (estimate)

T2 = 123 K (intended workpiece temperature)

T1 = ? (coldhead temperature, unknown, we will pick a value and calculate)

Q(T1_80K) = 6.71e-5 m^2 / 0.5 m * (89100 W/m - 70700 W/m) = 2.46 W

Q(T1_20K) = 6.71e-5 m^2 / 0.5 m * (89100 W/m - 14000 W/m) = 10.07 W

Conclusion

It appears that the copper braid's capacity for conductive heat transfer will constrain the tens of Watts of cryocooler capacity. This is even before we consider imperfections in the clamping interfaces and similar real losses.

Fixes for this constraint might involve adding parallel linkages (increasing area) or shortening the strap length.

It would be interesting to compare this to the anticipated capacity of the flexible strap in the original design - future work.
 

[Radhika, Stephen]

Good progress toward pumping down, with a setback (impact unknown while we reach out to Karthik).

• Made final connection of copper braid to baseplate. With the current length, we must pull the folded-over braid completely taught. We are shorting on the aperture of the inner shield, but we appear to have clearance from the vacuum skin (checked by hand at the cryocooler joint, checked by eye at the chamber) and the outer shield. We should be able to resolve these issues with the plan for a long rigid copper bar interfacing directly to the cold head, plus a short copper rope thermal linkage.
• Completed vacuum flange connections at cryocooler and vacuum gauge on T.
  • See IMG_8743 for overview of current cryocooler connection.
• Installed Heater on workpiece holder using 2x #4-40 screws, with an indium gasket underneath. Need to check whether we adequately compressed the indium (needs a certain pressure to flow into surface microroughness), but we didn't have any flexibility in the position or bolting arrangement - something to consider for future sample holders.
• Connected RTDs at Inner Shield (cryo varnish), Outer Shield (cryo varnish), Heater (cryo varnish), and Workpiece (spring clamp). Heater RTD Kapton Tape separating soldered leads needed to be separated, as a short was found at those bare leads. Workpiece RTD connected directly to the workpiece holder since we want to witness the temperature of the sample as directly as possible, and the RTD mounted to the outside of the heater will be overly-sensitive to heat input, yielding a very different time constant from the workpiece (and an inaccurate witness to sample temperature).
  • See IMG_8745 for overview of internal configuration, including RTD positions and thermal linkage to baseplate.
• Outer and Inner radiation shields were aligned to the copper braid connection to avoid shorting, then to the optical beam path by eye.
• While making final tightening of workpiece holder, Stephen's allen key slipped, and the installed silicon cantilever was whacked and fractured. The workpiece holder will need to be registered, and the workpiece will need to be swapped out.

The following is the list of remaining actions before we have cooldown data:

1. Replace workpiece (may require removal of workpiece holder, may require removal and reconnection of RTDs
2. Check alignment of radiation shield apertures, confirming outer radiation shield is still standing on the 3x G10 spacers
3. Confirm conductivity of RTDs, both by eye and by temperature controller readout.
4. Add radiation shield lids, including bolts to inner radiation shield lid.
5. Bolt down top chamber lid, incremental torquing 1/4-turn at a time with metal-to-metal end result (to achieve full compression of o-ring).
   1. Would be good to wipe down outer surface of o-ring using a wiper and IPA, since there have been a lot of on/off moves since we last pumped down, and we could have picked up particulate introducing a leak path. Check by eye after wipe down.
6. Pump down system and confirm that we have no leaks (tightening new CF joints would be the first resolution, if there are any issues)
   1. Gauge cables to controller/readout are currently disconnected, need to reconnect.
   2. Can we collect and trend pumpdown data yet from the gauge controller? Might be worth setting this up, if the com cable is already in place as it appears to be.
7. Turn on cryocooler once vacuum pressure reaches tens of milliTorr or better (should be an hour or two).
   1. Need to start USB datalogging at temperature controller.
   2. RTD names might need updating for consistency with current mounting.
   3. Can we collect and trend pumpdown data yet from the temperature controller? Might be worth setting this up, if the com cable is already in place as it appears to be.

We are both working on adding all of our photos to the photo dump at the ligo.wbridge QIL Cryostat Photo Album. We will then collaborate to add some of the most interesting images to this log!

[Radhika, Stephen remote]

After leaving the cryocooler's compressor running overnight, Radhika found all RTDs reporting room temperature. The noises coming from the compressor were normal, and all operating conditions were consistent with QIL/2504. However, the cryocooler was silent (valve motor not starting).

It turned out that the cryocooler power cable, unplugged during installation efforts (pictured below), had not been reattached. After turning off the compressor, plugging in the power cable, and turning on the compressor, the cryocooler began making normal noises and apparently operating normally. Radhika reformatted the USB drive collecting data from the temperature controller. 

Cooldown began at 1:45pm today (Friday). We will check in again on Monday.

During these troubleshooting efforts, we referred to the Cryocooler and Compressor manuals, found at the QIL Cryo Vacuum Chamber Wiki.

• Cooldown complete as of 4:41, with part 2 of data posted to CSVlogs Box folder with file name "cooldown part 2 20210525.CSV" for Radhika's analysis.
• Resumed USB logging and started Warmup. Simply turned off cryocooler using compressor panel's green power switch, then flipped circuit breaker lever to off position.
  • Expected to be ready for opening, with warmer-than-freezing temperatures throughout, on Thursday morning.
  • Noticed a "burp" of the gauge pressure readings up to e-2 torr range immediately upon turning off cryocooler, lasting about 1 minute before gauge readings were back down to e-6 range. Interesting, and something to keep an eye on.
• Linked Active Ion Gauge (5e‐2 to 5e‐10 torr per AIG manual) to Active Pirani Gauge (atm to 7e‐3 torr per APG manual) so that the Edwards TIC controller will enable the high-vacuum AIG during pump down and disabled during venting. Prior, the AIG had to be manually enabled at suitable operating pressures. Followed instructions at Section 4.11 of the TIC controller manual. Recall that all manuals are hosted on the QIL Cryo Vacuum Chamber wiki.

Radhika, feel welcome to post full cooling data to this entry, or to your original - up to you!

Quick log establishing the maximum power for our thermal actuation:

Heater: HSA25100RJ from TE, unknown sourcing. Acetone wiping cleaned off p/n and markings from body, should engrave at next opportunity, but [Attachment 1] from many months ago shows the p/n. Note that this is not the current mounting configuration - [Attachment 2] is more similar to current mounting. Anyway, according to the datasheet (now added to the QIL wiki at Documentation > Manuals) this heater is rated for 25W and has a resistance of 100Ω.

Leads: unknown, and not super important unless we had tiny hair conductor - I am not in lab presently, but it appears from our connector (Lesker FTACIR19AC) that we must have 20-24 AWG,

Carrying the 7, the current through the Heater will be 0.25 A at max actuation, and the 20-24 AWG insulated copper leads will have plenty of ampacity for this load (plus, they are cooled, so normal current capacity considerations fly out the window a bit).

Conclusion: 25W actuation will be the limit that we will apply in the CTC100 temperature actuation routine.

From first trials yesterday, the response at ~20W (at starting temperatures around 80K) appears to be on the order of 1 degree per minute, which should be just fine for actuating to maintain a +/-  1 degree constant setpoint with static thermal loads. More to follow on trials implementing temperature control.

Note that the QIL Wiki points to the DCC (which contains a budget that was helpful resources to trace these purchases), the datasheets and other documentation, and also points to the QIL Cryo Vacuum Chamber photo album, which hosts the images below.

[Stephen, Aidan, Wednesday 09 June]

Summary and Plan:

• Poor sealing at the output valve (The Gap) needs to be resolved.
• Planning to install #4-40 helicoils today (chamber will remain sealed, will need to remove output valve and cover output orifice, then transport the chamber to the WB EE shop for redrilling of holes.)
• Meeting with Nina and Aidan this afternoon to iterate one more time.

Troubleshooting steps taken:

1. Aidan took us through the full sequence of pump down and disassembly to bring me up to speed.
2. We opened the lid and inspected the old o-ring.
   1. Signs of plastic deformation and of small flecks of particulate near sealing surface - good idea to change.
3. We found new o-rings in a box from the Cryo lab, and one of these was swapped in after a good wipedown with IPA.
4. Upon pumpdown, Aidan compared behavior and found no meaningful change to rate of pumpdown or stable pressure in e-4 torr range after 10+ minutes.
   1. By valving off [chamber + gauge] from pump line, it was clear that there was a leak in that volume, as within seconds the pressure rose from e-4 torr to e-2 torr, and stabilized at _(need to confirm - e0?)_ torr over ~10 minutes.
5. Attempted to squirt IPA along o-ring seals, but there was not good access to the sealing surfaces, so this was a null test
6. Looked closer at all of the chamber features, and noticed The Gap between chamber wall and chamber output valve, pictured in [Attachment 1]. Not good! But promising as a leak source.
   1. Three of the four screws were found to be loose due to apparent thread damage.
7. IPA was squirted into The Gap at stable pressure of e-4 torr, but no change in pressure was noticed.
8. Longer #4-40 screw reinstallation was attempted, and I could feel a small amount of pull at the very tip of the screw, but tightening the screws led to that small pull to fail as well - need to rework.
9. The Clamp was installed and The Gap was closed [Attachment 2].
   1. When isolated from the vacuum pump, the chamber pressure progressed more slowly. Within seconds, we were at e-3 torr, and over 10 minutes the pressure stabled at e-2 torr, about 30x lower pressure per Aidan's records.

RTD thoughts - we have just been using the sensors that were provided, without noticing their constraints or deficiencies.

• our RTD p/n is 615-1123-ND (Digikey), which is a Littlefuse PPG102A6 platinum RTD and has an apparent temperature range of -200 °C (73 K) to + 600 °C. The primary data sheet does not have a Resistance vs Temperature curve, simply presenting the slope of the temperature dependence in a parameter "Temperature Coefficient of Resistance" (TCR), but a table is available in an auxiliary document called "RT Chart". An image of this chart is attached below.
• we have not violated that 73 K lower limit yet, but we are about to as we mount an RTD directly to the coldhead. Let's see how that RTD on the coldhead will withstand the lower temperatures.
• the CTC100 manual indicates that any arbitrary calibration curve may be input, but there are a number of sensors' calibration curves built in - it might be a good idea to make our next sensor decision based on that list.
• there is a Lakeshore guide and category page for temperature sensor selection - reconfiguring our 4 RTDs would cost over a kilobuck through Lakeshore, but perhaps we can learn general ideas from the guide as well.
  • it seems that switching to their Cernox line would be helpful in terms of packaging options, and would be the most accurate.
  • their line of silicon diodes would be suitable and has flexible packaging as well.
  • their platinum RTDs also have low temperature range and would be suitable. Packaging is cylindrical, so might be best to pursue the aluminum housing with a bolt hole.

Planning for next steps:

• for now, it seems that we could get by with our generic and 73 K limited RTDs, and this option is tempting as it requires no additional effort.
• if we decide we really want to have reliable sensing down to sub-50 K temperatures, we should move to one of the Lakeshore product lines (hopefully one which the CTC100 is configured with a calibration curve for) for about a kilobuck.
• we should engage in more serious sensor design before Mariner, regardless of whether we take any action now.
  • as a starting point, the Lakeshore catalog and appendices (ref. product info page) and other resources should be absorbed, for considerations like thermal anchoring, lead length, benefits of 4-lead wiring, polyimide leads causing less conduction to the sensor than teflon, phosphor bronze having lower thermal conduction than copper, etc. Most of these topics are gathered from Appendix C.

Radhika and I started discussing in detail the items needed to transfer the 2um PD setup into the Cryo Vacuum Chamber.

1) Electrical

To interface with the PD setup, it seems that we will need want to use the feedthrough already in use on the IRLabs cryostat. This square-flanged feedthrough appears to host the in-vacuum cabling. The in-air cabling would ideally also be reused.

• Detoronics Hermeic Sealed Connectors (DT02H-18-*PN) http://www.hselectronics.com/pdf/Detoronics-Hermetic-Connectors.pdf (see page 14, ref. QIL/2460)

To implement this, we will need to modify a blank 2.75" conflat flange (in hand in QIL boxes on wire shelf) with a the following features:

• through bore, 1.18 diameter on center.
• a 4x #4-40 tapped hole square bolt pattern, 1.062" spacing on center.
• preferably, a hand-polished o-ring sealing area.

I will take care of this part through the PMA shop.

2) Optical

The Cryo Vacuum Chamber windows are Thorlabs VPCHW42‐C (ref. D2000310-v1). The broadband AR coating is rated for 1050-1700 nm (here's the data sheet), with a steep climb in AR coating reflectance. There is also fused silica substrate transmission to worry about. Perhaps the easiest way to proceed would be to repeat Koji's Transmission test (ref. QIL/2458) for the windows already in use on the Cryo Vacuum Chamber, and see if we can accept ~10% loss (or more).

Else, perhaps we scavange the IRLabs cryostat and create another custom blank CF modification?

Or buy a new, suitable window with CF interface? (<---- preferred option)

Brief summaries of the last week's progress and the coming week's plans (plots will be posted soon!):

- progress Friday 09 July: Opened the cryostat up at the cold head, and attached an RTD to the cold head with a spring clamp (instead of relying purely on the cryo varnish).

- progress Monday 12 July: Found 65 K workpiece temp and 63 K cold head temp. RTD was apparently held successfully by spring clamp, and we will continue to collect cold head temperature in future runs. Warmup was started, with old data collection completed (cooldown_20210709) and new data collection commenced (warmup_2021_07_12). Note that warmup started at 1:14 pm, and it took me ~ 5 minutes to stop and restart the script to changeover to the warmup data collection.

- table plan Wednesday 15 July: Complete in-air optical layout. Make one flat face of Si mass reflective.

- chamber plan Thursday 16 July: Open up main volume and drop in frame with Si mass. Connect RTDs. Start cooldown. Confirm cooldown is going ok (optical alignment, especially), and revert if necessary before things get too cold.

- table plan Friday 16 July: Maybe measure stuff, maybe better to wait till coming week and use controlled heating to hit different temperature setpoints.

Uh oh, review of the cooldown plot from the previous cooldown (QIL/2603) shows workpiece temperature of ~92 K at conclusion, while a temperature of 65K was observed in the CTC100 readout (Attachment). The logging of the warmup is consistent with the CTC100 image, as the logging started a few minutes after the warmup was started, and the warmup "5 minutes after starting" temperature of ~ 71 K is a practical temperature.

Seems to be something weird going on here, we will need to have Radhika take a look on her return (and continue taking photos of the CTC100 whenever we stop by).

(Aidan, Stephen, Koji)

Building off of QIL/2597 after more thorough discussion in Mariner meeting today. Aidan and I will confirm details today and make moves toward installation of PDs next week.

Necessary capabilities (note: no need to scavange anything from the IRLabs dewar):

 - Cold temperatures = ready (via conductive mounting we have seen workpiece ~ 80 K, workpiece heating and CTC100 temp control is demonstrated)

 - Optical interface = ready (existing 1700 nm AR-coated window will be used at 2 micron, input power will just be calibrated with a power meter)

 - Electrical interface = almost ready, pending cabling (the cryo vacuum chamber has RTDs instrumented, so we just need the leads for the PDs, and we can create Cu twisted pair leads with in-vac crimp/solder sockets a la Koji's OSEM cabling) (also need in-air cabling with DB9 plug - trivial)

Improvements in advance of PD testing:

 - RTD cabling and Heater cabling (in vacuum) should be split with in-vac pins and insulated with PTFE tube - Koji has the magic material recommendations

Desired improvements (not necessarily in advance of PD testing):

 - Cu solid linkage (being fabricated).

 - Inner radiation shield should be clamped well to cold plate (consistent with most recent trial, but do we want better/more clamps?).

 - RTD mounting option on shields without cryo varnish (new threaded hole, new clamps).

 - RTDs consistent with planned Mariner RTDs (ref. QIL/2590).

 - Heater mounting should be directly to the workpiece via an improved clamp on the 2" x 2" grid (rather than on unused Si cantilever workpiece holder).

With Test Mass RTD at 119K, and with all of Koji's trials completed, I started the warmup this afternoon.

 - Cryocooler off at 12:41

 - Heater on at 13:05 (forgot to complete this task durming my initial visit).

Anticipated warmup duration of ~ 1 day, as improvements to cooldown (higher emissivity test mass, better conduction to inner shield) should also improve the efficiency of our active warming, which took a bit more than 30 hours last time (ref QIL/2615).

Actions on my to-do list, before we are able to pump down for Aaron and Shruti’s Si Cantilever Q measurement:

0. Confirm Aaron has completed cantilever mounting and is happy with shield alignment.
 - if needed, might have to rotate shields and/or clamp down workpiece holder.
[Done 2021.08.07] 1. Solder on new RTD, then mount RTD and heater to workpiece holder.
2. Verify electrical continuity of RTDs and heater.
3. Close up (shield lids, chamber lids).
4. (anytime, optional) complete RTD and Heater disconnection junctions with in-vac crimped pins.
[Koji indicated these were likely scavanged from DB connector kits, Stephen ordered more] - crimped plug pins were in 40m lab parts tower, but didn’t see any receptacle pins in the vicinity.

[update - Aaron indicated interest in deferring 1 week to establish more permanent setup. Likely to reattach outer shield RTD to cantilever clamp, allowing two different workpiece sensors] Planning to complete items on this list Friday, by Mariner meeting timeslot at the latest.We are in good shape to pump down Friday early afternoon, and for Aaron to collect data via controlled warmup on Monday/Tuesday (could run through Wednesday, if needed).  

Actions on my to-do list, once we are warm and up to air, before Aidan and I are able to run the JPL PD test. This list complements the optical setup tasks and data acquisition setup tasks that are also mentioned by Aidan in this thread.

Update 23 August - using this list to [comment on details] and highlight items which are still outstanding instead of duplicating in a daily progress log entry :)

0. Remove Aaron and Shruti’s Si cantilever clamp, and return to them for safekeeping [I set the clamp aside, need to coordinate return of cantilever to with Aaron!]
1. Solder a connector equivalent to the testpiece (ref. QIL/2465) but with the cryo wire, In-Ag solder on the connector end, and crimped plug pins on the free end. The crimped plug pins interface the with receptacle pins of the existing leads, which are connected to in-vac side of DB9 feedthrough).
 - need to locate some In-Ag solder! [done, and checked connectivity - used standard lead-tin solder following Rana's recommendation (ref. QIL/2418) born out by Koji's testing (ref. QIL/2462 and QIL/2465)]
2. Confirm which PD holder will be most useful for this effort (Koji’s newly machined holders might be useful?) and mount to cold baseplate. If using the tombstone from the IRLabs dewar, which is likely shorter than the beam height, it sounds like we would need to mount it on a pedestal or post. [Aidan used Koji's taller PD mount from the same purchase (ref. QIL/2459). The beam height required no modification, nice!]
3. Mount RTD to PD holder, likely with cryovarnish (unless there is a lucky extra hole for a screw/clamping post). [Radhika and Aidan's G2100807 demo shows the problem with the prior lug, not super stable mounting for the RTD as the same hole is being used to host two screws. Instead, I retrofitted the upper screw from the mount's retaining ring to host one of the trusty spring clamps, see Attachment 1. I checked for clipping or connector interference throughout, and found none.]
4. Mount heater to ___ (TBD, ideally on PD holder but possibly on cold baseplate nearby). [dog-clamped the heater to the baseplate, directly adjacent to the mount - see overview images in Attachment 2 and Attachment 3. We may go through some PID growing pains with this configuration, and we also need to learn whether the 22 W heater power locally applied can overcome the cryocooler's  ~50 W cooling power at our operating temperatures (ref. Radhika's QIL/2585). Might be necessary to intermittently power cycle the cryocooler.]
5. Confirm alignment of shields and PD. [aligned both shields, clamped inner shield, but could reposition if there is an issue.]
6. Verify electrical continuity of PD cable, RTDs, and heater. [note need to add indium and finalize clamping of PD holder, also note routing of pins to be connected to PD connector per Koji's QIL/2605 as described in Attachment 3]
7. Close up (shield lids, chamber lid). [note that in particular, the covering up (with foil sheets) of unused shield apertures is still WIP but wasn't originally mentioned!]
8. (anytime, optional) complete RTD and Heater disconnection junctions with in-vac crimped pins. [done, with mounting isolation achieved by kapton tape as ptfe tubing has not yet arrived. Attachment 4 shows one example, from the inner shield.]
 - crimped plug pins were in 40m lab parts tower, but didn’t see any receptacle pins in the vicinity. [ordered a few hundred new socket pins, I should share some with the 40m parts tower]

Pending Aaron and Shruti’s measurements, it is likely that heater-assisted warmup will occur starting Tuesday, in time for Wednesday/Thursday access. Friday 13th August could be the start of the cool down if everything goes to plan. [Nothing goes well on Friday the 13th. Aaron and Shruti do not need in-vacuum measurements anytime soon. The current plan is for cooldown to begin Tuesday and, if everything goes to plan, we will collect data through the week, then likely swap out the PDs on Monday for another run next week. The next experiment slated for the QIL Vacuum Cryostat is another Si mass radiative cooling run w/ black paint on inner surfaces of inner shield.]
 

[Aidan, Stephen]

Worked toward aligning and characterizing beam on PD. Will complete next session.

Log:

Some difficulty aligning to the 2um beam, which is sensed by a thermal card. Aidan intends to upgrade with a fiber coupled visible laser, which could then be swapped interchangably for alignment.

The 1" mirror at the top of the periscope doesn't make sense, given larger apertures in shields and viewport. We looked for a nearby 2" replacement but did not have luck. Ended up swapping back in the gold-coated 2" mirror, even though it is thin enough to be a pain to mount.

Instrumented connector pins to DB9 pins using the following translation (ref Aidan's drawing for connector / PD pinout, ref drawing from QIL/2639)

            DB9   - 1 6 2 7 3 8 

    Connector - 2 3 4 5 6 7

[Aidan, Stephen]

After Aidan validated that model inputs were creating physical parameter changes, we proceeded with some last few checks before closing up. Notes:

 - Aidan set up a helpful script turning laser power on and off, and strip tool to follow PD and monitor PD signals. A strip tool chart was used to confirm that there was no loss of functionality or alignment during pump down.

 - Checked Heater function and Workpiece RTD response - all good.

 - Confirmed alignment by steering at periscope output mirror and watching PD voltage.

At this point Aidan gave a green light for pumpdown prep, and to start pumpdown and start cooldown. Notes:

 - Stephen disconnected the PD connector accidentally while trying to add strain relief (the irony is palpable). Reattachment of connector didn't seem to affect any signal levels.

 - During installation of radiation shield lids, shields became misaligned and PD signal fell (presumably due to clipping). Recovered previous signal levels by realligning outer shield.

 - Double checked that everything seemed good to go, no issues!

 - Timeline of pumpdown and cooldown:

     17:32 - Pumpdown started.

     17:47 - Turbo spin up started (pump station delay parameter).

     17:55 - Pressure dropped below 1 mTorr, so I started cryocooler.

     18:05 - Healthy so far - Pressure had come down half a decade more, and Coldhead RTD was reading 235 K.

Monday I completed the vent that Aidan had started by turning off the cryocooler. During the afternoon I turned off the pumps, unbolted the chamber lid, and removed the radiation shield lids.

Next, Aidan was going to run some characterization measurements and determine whether to swap the diode or repeat with A1.

Pump down sequence executed tonight; Aidan plans to automate data collection during cooldown and warmup both, and the script will be activated early in the coming week.

- Carbon paint flakes (mentioned by Aidan in QIL/2667) were either picked up or scrubbed by IPA wipe, except the biggest, which were nudged near the closest 1/4-20 hole and picked up with tweezers for removal. There are still some small flakes of paint as there was less benefit to cleaning flakes closer to the PD or lens, and I opted not to risk any bumps. Aidan was correct, some areas of inner shield ID wall have flaked, but it seems the main location of delaminated paint is on the wrinkly foil excess covering the rim of the shield, an accidental paint location.

- While adding the lids, I monitored the PD outputs using Aidan's strip tool kindly left running. I never noticed any clipping in the trends - should I have been more skeptical?

- While adding the lids, I forgot to monitor the RTD outputs to the CTC100 controller, and the outer shield ended up shorting and ceasing to read any temperature. Didn't notice until I had turned on the roughing pump! Had to reopen and fix the short. Good reminder.

- Turbo came on at 12:07 am on 03 October at a pressure of 30 Torr - the setting is actually a timer and not a gauge reading.

Started a new run this afternoon, with the following goals:

   1) confirm that the first run (QIL/2695) went smoothly, by performing a visual inspection in the chamber while setting up for the first run.

      - kapton tape affixing inner shield RTD lead junctions to inner shield had fallen. These junctions were simply hanging - not ideal, but apparently not too harmful. Not likely to impact temperatures, in my opinion, but could have led to shorts or glitches in data.

      - all RTDs appeared to be fixed and well-contacted to surfaces

      - Everything seemed to be in good shape with the copper bar, no apparent issues

   2) obtain a second run with similar configuration, now that the rigid copper bar linkage has been implemented.

   3) vary a single important parameter relative to the first run, namely the inner surface emissivity of the inner shield, so that the impact of that parameter may be observed.

      - Added Aluminum foil (matte side visible) to the inner shield inner surfaces (lid and cylinder, both). Anywhere there was previously black Aquadag, there is now matte aluminum foil.

      - Kept the same apertures for viewport access and for electrical and thermal connection passthrough, basically attempted to achieve identical shield coverage.

      - There is one small sliver of black aquadag visible at the location of the electrical leads, but I didn't worry about patching that small area.

Run Details:

   - Pumps on at  ~3:40 pm

   - Cooling started at 4:13 pm (pressure ~6 mTorr, rapidly falling with turbo pump spinning up from ~70% to ~85% over a 1 minute interval). Coldhead RTD is responsive.

   - All photos will be posted to the QIL Cryo Vacuum Chamber photo album.

   - Note from check in on Monday afternoon, ~ 69 hours after start: everything looks good, and the workpiece temperature (~127 K) seems to reflect the emissivity change.

I opened the QIL cryostat today for a health check and visual inspection before the next run. Because I saw a couple of interesting issues, I decided to redo the same run with more attention to detail on the closeout. I'm worried the outer shield may have been linked to the inner shield and baseplate enough to affect comparability with the prior run.

issues with this  run, requiring redo:

• RTD wire for outer shield was clamped under lid of inner shield - this might have created a conductive link between the inner shield and the outer shield
• outer shield was more wobbly than usual, and could have possibly been off of the three spacers - this might have created a conductive link between the outer shield and the baseplate

run details:

• pumping started at 3:45 pm
• turbo started with 15 minute delay at 20 torr
• cryocooler started at 4:15 pm with active ion gauge pressure at 3 e-4 torr.

And since I didn't get to implement any of the intended next runs, here are some notes on other future runs of interest:

• Si mass covered with Al foil (matte side facing out) - interested in making the emissivity of the test mass equal to that of the inner shield in the new config, for modeling.
  • (of course, this emissivity equivalence would be an approximation, as there is a large area of the test mass which is bare silicon)
• outer shield clamped/resting on baseplate - this is predicted by Koji to be the most efficient cooling configuration.
• shielding attached to structure holding Si mass (electropolished aluminum, aquadag aluminum, bare aluminum surfaces are all available.

As discussed during the 07 Jan 2022 meeting, the next cryostat run will seek the fastest radiative cooling through the following configuration choices:

• eliminate radiation leak apertures
• maximize emissivity of test mass volume
• improve conductivity to outer shield

Actions completed 14 Jan 2022

• Vent
• Cover up aperture to viewport with foil (on both shields).
• Remove foil from inner shield inner surface.
• Place outer shield directly onto cold plate (no clamping force).
  • A bit unsatisfying, because the outer shield is not flat relative to the cold plate, but the shield is resting quite firmly with only a slight wobble when pressed. As with any plane-plane contact, there are a limited number of true points of contact, and the contact area is increased somewhat by foil that is folded around the outer shield or the cold plate.
    • I would estimate the contact area at ~5% of the total area of the bottom flange.
  • 2x G10 spacer washers were dropped into the lower volume whild making this switch.
  • Note that bottom lid of outer shield is still not conductively cooled, and therefore will be approximately room temperature.
• Tidy up aluminum foil collar around bottom lid of outer shield.
• Tidy up mylar shield around conductive link after inner shield
• Pump down, cool down.
  • Pump down started at ~15:35.
  • Cool down started at 16:10.