• General Assembly Notes
• Step 1: Install the J-FET radiation shield
• Step 2:
• Step 3:
• Step 4:
• Step 5:
• Step 6:
• Step 7:
• Step 8:
• quick summary of assembly
• Making Seals
• Assembling Kevlar Supports

General Assembly Notes

• make sure all surfaces are clean.
  • use acetone or lab alcohol
  • the reason for cleanliness is to improve hold time
• put heat sink compound or N grease under joints
  • this kind of stuff is kept in the SPARO cabinet
  • heat sink compound is a very small tube of white paste
  • N grease is in a small orange tube
• use Al tape during assembly
  • this is for two purposes:
    • to cover up as many holes as possible
    • to seal joints against light leaks
  • some kinds of Al tape are good cryogenically, but some kinds of Al tape are almost totally worthless when cooled.
  • i meant to bring some of the good Al tape down, but i never did
  • i hope there is some good Al tape at Pole. I advise testing it in liquid nitrogen before using it in SPARO.
• as a default, use 10 layers of MLI between adjacent surfaces
• unless otherwise specified all screws should snugly tightened - not cranked down
• alignment cues:
  • most pieces are marked by zeros - line up all zeros
  • the charcoal pumps, optics snout, seams on shields and marked zeros all basically line up. the viper mounting interface is on the opposite of the dewar from all the previous listed reference points.
• refer to photos as you assemble
  • see photos in disassembly instructions
  • see Paolo's photos posted under "Plans"

Step 1: Install the J-FET radiation shield

• This is not necessary because you did not remove the J-FET radiation shield, right?

Step 2: Install the 4 Kelvin Shield

Note that you will want to apply a small amount of heat sink compound to the side of the 4 Kelvin cold plate between each pair of screw holes, before setting the 4 K shield down. Line the six inch slots of the 4 K shield up with the long tabs of the J-FET shield. This should line up the clearance cutouts in the rim of the 4 K shield with the gear housing for the pots heat switch and the capillary cover. (Paolo, I copied these from earlier instructions prepared by Dave Chuss and I don't know what he is referring to when he says "capillary cover". Maybe you can figure it out. If not, just ignore it.) Slide the 4 K shield down over the optical bench slowly making sure all wires taped to the 4 K surface are not pinched. Pay special attention to make sure that the long cold cables from the J-FET boxes are guided into the small cutout between the two J-FET shield slots. Using 4-40x1/4" phillips round head machine screws, fasten the 4 K shield to the edge of the cold plate.

Step 3: Install the JFET Shield Lid

Now that the 4 K shield is in place, add a small amount of heat sink compound to the edge of the JFET shield lid and carefully slide the lid in place between the JFET sheld and the 4 K shield. Using 1-72 SHCS's through the holes in the top of the JFET shield, fasten the lid to the JFET shield. Note that it may be possible to only get 2 screws in. CAUTION: USE CARE DURING THIS PROCESS IN ORDER TO AVOID BREAKING THE VERY DELICATE TENSIONED WIRES.

Step 4: Install the 4 K Shield Lid

This is by far the hardest step, because of the problem with the ruined set screw in the hwp shaft. You will have repeat the steps that you did for disassembly, but backwards. This requires tightening the hwp set screw that is inside the 4 K shield. Be sure to have the proper rotational and translational alignment so that the set screw bites down on the flat part of the shaft, not the curved part. CAUTION: USE CARE DURING THIS PROCESS TO AVOID BREAKING THE VERY DELICATE TENSIONED WIRES. Note that you will want to apply heat sink compound to the top of the inner ring of the 4 K shield before installing the lid. Note that you will want to align the "00" fiducial marks on the respected pieces. Align the holes in the lid with those in the shield and fasten the lid on with 4-40 SHCS's. Place precut Black foam pieces on each shaft where they enter the cold plate. Finally, tape seams with aluminum tape to prevent light leaks. Don't forget that there is also an electrical connection that needs to be made (hwp encoder).

Step 5: Remove "L" Brackets

Remove the four "L" brackets which connect the He-4 reservoir to the accessory ring. CAUTION: WITH THE "L" BRACKETS REMOVED, THE ONLY LATERAL SUPPORT COMES FROM THE NECK TUBE. BE CAREFUL NOT TO UNNECESSARILY JOSTLE THE DEWAR.

Step 6: Install the IVCS

Using mylar tape, cover the reservoir and 4 K shield with ten layers of MLI (superinsulation) making sure to tape it down well onto the 4 K shield lid. Once again, apply small amounts of heat sink compound to the (already mounted) bottom lid of the IVCS. Carefully slide the IVCS over the insulated dewar, making sure to line up the "00" fiducial marks. Use 4-40x1/4 phillips head screws to attach the IVCS to the bottom IVCS lid.
Fasten the kevlar support cords from the top of the 4K shield to the ring of the IVCS.
Once the kevlar is in place, line up the IVCS lid . The stainless steel pin on the 4K lid should slide into the slot on the IVCS lid. Once you are sure that everything is centered, proper tension has been placed on all of the kevlar supports and the pin and slot mechanism is in place, screw the IVCS lid down as was done in the 4K shield lid case. Finally, tape up both the top and bottom seems of the IVCS along with any unused screw holes(using aluminum tape). Note, on the short kevlar, the screws are offset- only use the center-most screw holes with the outermost screws. (This last sentence should not apply to you, Paolo, because you did not remove the Kevlar supports from any of the lids.)

Step 7: Install the OVCS

Repeat the above procedure for the OVCS.

Step 8: Install the Vacuum Jacket

Cover the OVCS with ten layers of MLI. Prepare a seal(elastomer or indium for the Assembly Ring/Vacuum Jacket junction. Slide the vacuum jacket over the assembly and attach to assembly ring using 1/4-20 SHSC's. Install kevlar supports. Prepare another seal betwee vacuum jacket and case lid and install case lid. Invert dewar and remove fill tube support.

Assembling Kevlar Supports

• Preliminary note to Paolo: You made one error in the disassembly. (Probably due to bad documentation - sorry.) When you removed the Kevlar strings last week, you removed them from the ends that attach to the rings that are on this insides of the various cylindrical shields (outer case, OVCS, and IVCS), but you should have removed them from the ends that attach to the various lids (OVCS, IVCS, and 4 K shield). If you had done this step correctly, then the outer case, OVCS, IVCS, and 4 K shield would have all ended up nicely centered when you put them back together. (There would be no way to get it wrong.) However, the way you did it has the disadvantage that when you put it together again now the centering may come out all wrong. This is because the centering depends on how many turns of the screw you use when you re-attach the anchors at the ends of the Kevlar strings back to the rings. Does this make sense? Luckily, this is not a big problem, because the centering is not really that critical. (The optics has lots of clearance as it goes through the openings in the IVCS snout, OVCS snout, and outer case snout.) So what you should do is pay attention to the centering of the four nested elements (4 K shield, IVCS, OVCS, and outer case) as you assemble it. You can correct any misalignments that you see by simply turning the screws at the point of attachment to the rings. keep adjusting until it looks good to your eye. A few mm of misalignment should not matter at all.
• The second issue to be considered is the proper tensioning of the Kevlar strings. This is adjusted by the spring. If you did not rotate the nut that controls that tension then you should not have to change this - it should come out OK. But you definitely do want the Kevlar under tension. (Otherwise - microphonics will result.) So if it seems loose, then you can adjust the nut on the spring as needed. Note that the whole system of Kevlar supports was a big disappointment to me when I first used it because it provides insufficient lateral stiffness. But this is fixed by those little stainless pins that we talked about by telephone.
• now there is the issue of the looseness of the OVCS-to- outer-case Kevlar strings that you just told me about by phone. I don't know when these got loose. I think (but am not sure) that they were fine when we assembled the dewar in 2001. One possibility is that one of these is broken. Please test all three of them by pulling on them gently but firmly. If the ends come off, then they were probably already broken and had slipped. I can tell you how to re-glue.
• finally, here are some old instructions on working with the Kevlar strings. These were written back in the old days when we used to remove the Kevlar at both ends, so this should be somewhat relevant to the present situation:
  • fasten members to outer ring
  • tighten nuts on springs to fully pre-load the springs
  • adjust the lengths of all members so that cans are basically centered. if possible, release any extra twisting of the kevlar.
  • fasten members to inner surface
  • loosen nuts on springs
  • system should now be stiff
  • make final centering adjustments by making small changes in the lengths of the members

Making Indium Seals

• wash hands well (or use clean gloves)
• clean both surfaces carefully (use solvent and q-tips)
• keep indium as clean as possible (if there's any doubt as to the cleanliness of the indium, clean it with solvent.)
• lay indium into groove
• cut to length (a diagonal cut is preferred)
• lay indium back into groove, matching cut ends carefully. freshly cut indium is sticky, so you should be able to stick ends together
• center indium in groove as well as possible
• mate surfaces
• if possible, use belleville or some other springy washer
• tighten screws very tightly. I generally use a driver with a screwdriver type handle and tighten until my hands protest.