Uninstalling the Tower

The next steps are to remove the bottom flange, each thermal stage, and then the tower. For the uninstallation process, you’ll need the tool box, the two clear plastic boxes (one for screws and one for parts), and the indium bottle with the plastic scraper.

This process will involve removing all of the screws in the bottom flange and cleaning it. Be aware that we will leave in two screws as support when we go to break the indium seal.

1. Using the silver allen wrench from the tool box (if it’s not in the tool box you must get one from the tool drawer and clean it), loosen all the screws on the bottom flange. Designate two screws that are 180 degrees from one another to be left in and remove all other screws. Check the heads of the screws to make sure they’re still okay - if they’re bad (i.e. if they look like they’re becoming stripped), we’ll need to replace them so that we don’t have difficulties in the future putting them in or taking them out.
2. When only the two screws are left, take two screws already removed and insert them into the threaded holes. These screws will be used to push the bottom flange off of the upper flange.
3. Alternate loosening the last two screws and tightening the threaded ones you entered in the last step. When the flanges are separated, be sure to support the bottom flange with your hands and unscrew the two loose screws until they’re out of the top flange. You can now pull the bottom flange away.

Before removing the stages, we try to remove as much of the indium seal as possible from the top and bottom flanges. Whatever indium is recovered we recycle by putting the scraps in the clear plastic bottle. When we run out of indium we give this to the machine shop so they can make more for us.

1. Using a pair of tweezers from the toolbox, pull off as much indium as you can WITHOUT letting the tweezers scrape against the flange AT ALL. We don’t want to introduce any dents or scratches onto the flange because it will interfere with the integrity of the seal and cause a leak.
2. Use the plastic scraper to scrape off more of the indium.
3. The scraper and tweezers will not suffice to remove all of the indium.

Once all of the indium that can possibly be removed from the flanges (using these methods) has been done, you can set aside cleaning the top flange until after the stages have been removed. It’s easier to clean the upper flange once the 4 K stage is no longer present.

There are four stages to be removed: 4 K, 600 mK, 100 mK, and 30 mK. They will be removed in the order as mentioned. Removing parts of the stages will be a delicate process and some of the components will have to be bagged and placed in the larger plastic container. Be careful when removing screws to unscrew them in as vertical of a position as possible. We can’t afford to have any screws break in their holes or have holes stripped.

The most delicate part of the 4 K stage are the SQUET cards. These are attached to the striplines and plugged into the tower. After the IR shields and heat sinks on the 4 K stage have been removed, then the SQUET cards will be removed. Note that all the screws here are brass and almost all of them have Philips heads, except for the ones that go above the SQUID flyover cable on the SQUET cards. Those require a balldriver. Be very, very careful to remove all of the screws as vertically as possible so as to not strip any holes or screws.

1. Detach the heat sinks. Be careful to support them as you do so such that the screws you pull out don’t come out at an angle.
2. Remove the small copper shields and put them in the screw box.
3. Detach the SQUID cards.
4. Remove the spool cap (note that there is only one screw holding it in and it is delicate) and any tape covering the holes around the spool cap.
5. Unscrew one FET card and detach it from the tower. Using the black plastic tool (do NOT use any metal device) in the tool box, carefully wedge it between the copper plate and the circuit board and gradually push them apart. BE CAREFUL not to push the black rubber tool against the circuit board side. Only push against the copper plate. A proper method of doing so is to go around the edges of the board and push against each corner little by little. This will help to create an even removal of the SQUET card because you need to be very careful upon the separation of the plates that none of the pins bend. Additionally, as you are taking turns at each corner of the board to press against the copper plate, be sure not to twist the stripline while doing so. You need to be very careful in handling the stripline.
6. When the SQUET card is removed from the stripline, place it in its respective ziploc bag (there is a number etched on the SQUET card and some ziploc bags have numbers on them).
7. Repeat the same process for the other SQUET cards, if there are additional ones.
8. Now remove all of the screws on the outer perimeter of the 4 K stage. These are holding the plate in place, so be sure to support it as the final screws are removed
9. Place the 4 K stage in the large ziploc bag that is marked “4 K stage” on the bottom corner.
10. Place this in the anteroom.

The 600 mK stage consists of a copper rod that’s fastened to the tower at three points.

1. Remove the Phillips head brass screw attaching the rod to the tower.
2. Remove the copper lugs attached to the ears of the tower with an M3 balldriver.
3. Remove the two screws on the copper plate that attaches to the back of the copper rod with an M3 balldriver.

There are several components to the 100 mK stage: 4 half-circular copper shields and 3 heat sinks.

1. Remove the heat sinks and place into the screw box.
2. Remove the copper tape on the shields and around the 600 mK rod.
3. Unscrew and remove the inner copper shields and place them in ziploc bag.
4. Unscrew and remove the outer copper shields and place in the same ziploc bag as above. Put this bag into the cold hardware container.

This last stage is the main point where the tower is fastened within the fridge. Thus, in removing the 30 mK stage, you are removing the tower and detector. Therefore, additional supports will need to be attached to the upper IVC to support the tower once detached from the 30 mK stage.

1. Bring the three prong stand and the bag containing the long threaded screws and circular aluminum plate into the mini clean room.
2. Remove any tape fastening the thermometer wire to the 30 mK can and unplug the thermometer. You need to make sure that when the tower is removed the thermometer doesn’t get ripped out. Additionally, if you are using tweezers to remove tape, take care not to brush the tweezers against the wire because you might damage it.
3. Attach the aluminum plate to the bottom of the upper IVC flange. There are screws in the bag to do so. Make sure that the large holes in the plate align with the holes in the top of the mini clean room so that the three prong stand can be pushed through both of them - otherwise the prongs cannot be pushed high enough to attach to the IVC.
4. Screw in the cylinder with the threaded screw at one end of it into the tower. Make sure this is very secure.
5. Insert the threaded rods down through the holes in the aluminum plate. The knobs on the rods will prevent them from falling through. Make sure the larger side of the knob is not flush with the aluminum plate.
6. Lift the stand and guide it so that the prongs move through the holes in the plate and clean tent and screw in the rods into the holes in the stand.
7. If you’ve secured all of the threaded rods properly, the stand should now be supported by the upper IVC flange. Push the stand up so that the center of the stand is almost flush against the cylindrical rod coming out of the end of the tower, and turn the knobs to keep the stand in position.
8. Using the last screw in the bag, screw it through the bottom of the stand and into the hole in the bottom of the cylinder. Make sure this is very secure.
9. Remove the screws that attach the adapter plate on the tower to the 30 mK can. The tower should no longer be attached to anything within

the fridge. The cylinder supporting the tower should not wobble, which is why the secure fastenings mentioned above were important. Tighten any attachments that seem loose.

1. Begin lowering the stand-tower combination by turning the knobs on the threaded rods counter-clockwise. MAKE SURE to push the 600 mK rod gently out of the way as the tower lowers.
2. When the stand-tower combination has been completely lowered, re- move the threaded rods, screws, and aluminum plate and put them back in the ziploc bag.
3. Place the stand with the tower in the main clean room.