IRCAL (Dis)Assembly Instructions

1. Crack vacuum
2. Flip dewar so that it rests on its handles
3. Remove 16 9/64 screws on base and dismount base.
4. Withdraw the base vertically so as not to snag the G-10 dog clutches It's nice if you leave on the waveplate/flexure metrology system bracket, which provides a mechanical reference when reinstalling it.
5. Stow the base and cover with kim wipe. The o-ring should come off with the base.
6. Remove 3/32 first radiation shield screws
7. Remove 8 G-10 tab screws, being careful not to scratch the o-ring mating surface withthe screwdriver
8. Remove 8 feed through screws. Remove the first radiation shield by lifting up on the G-10 tabs.
9. Remove 3/32 second radiation shield screws and remove the 2nd radiation shield, again lifting by the G-10 tabs.
10. You now have access to the optics

Changing Apertures

To reinstall the aperture wheel, just slide it back into position and re-attach the screws. It helps to have someone hold the mask wheel properly aligned as you screw it in. If the aperture wheel is placed where is naturally sits, the feedthroughs rub on the shroud. To prevent this, hold the aperture wheel with a stiff clockwise rotation before screwing it down.

Specifications: Aperture masks must be 0.995" in diameter, 1/16" thick. Plate scale at this focal plane is 34.3 microns/detector pixel = 454 microns/arcsec.

Changing Filters

Individual filters are most easily changed via the access hatches on the filter box. By twirling the motor drive shaft with your fingers, you can rotate the appropriate filter into the aperture. Filters are held in via small beryllium copper clips, which can be removed via a small screwdriver. (Just loosen the clips enough to rotate them out of the way. This make it far easier to get them back into place after inserting the new filter.)

In order to see the filters in position, you will have to slide the cold pupil up out of the way. **Be sure to put it back down into position when done** Doing this is a useful way to check the orientation of grisms or prisms.

The charcoal getter doesn't wear out unless it becomes contaminated. The zeolite permanently adsorbs water unless it is baked at extremely high temperatures. Given the small size of the getter charge, it pretty easy to just replace it. The charcoal is really messy, so best to leave it alone.

1. Reverse 9-4. If any screws fall down between the dewar and first radiation shield, the easiest fix is to flip the dewar and gently shake it until the screw falls back out.
2. Clean edge of dewar wall where o-ring seals with isopropyl alcohol. Clean o-ring and groove. Apply a thin coating of vacuum grease. Reseat o-ring
3. Align G-10 cubes in the dog clutches and lower the base. This step is made much easier by first aligning all the dog clutches and cubes in the same orientation, e.g. with their sides parallel to the sides of the dewar.
4. Tighten the screws 1/4 of a turn at a time, rotating one side at a time so that you uniformly apply pressure on the O-ring. If the outer dewar wall were to become tilted with respect to the dewar, the o-ring can pinch.
5. Check for positive engagement of the motor feedthroughs by confirming motor motion. You can see the aperture mask moving by looking in the window, and you should be able to feel/hear the home position engage.
6. Put back on the final outer dewar walls.
7. Connect the pumping manifold to the pump using stainless flexible hose. Include the convectron vacuum guage using a T-piece. Make sure that the o-rings are free of dust and debris. Do not over-tighten the clamps. With the dewar valve closed pump down the fore line to a few mTorr (should take no more than a minute). If the line does not pump down promptly check the seals. When the fore line is fine open the dewar valve slowly (10-20 seconds to open). Leave the dewar pumping with the valve fully open for at least two hours at < 10 mTorr. Valve off, disconnect the fore line and begin cool down.
8. To cool, use the white plastic funnel connected to the long narrow metal tube. Insert this *carefully* into the opening on top of the dewar, being careful to insert it vertically so as not to puncture the sides of the heat exchanger which are apparently quite thin. A cardboard box of the appropriate size may be used to prop the funnel up so its bottom is only about 1" inside the reservoir, which will make the fill *much* faster.

   Get LN2 from down in the basement near the CAT room. Pour the LN2 into the funnel and wait for it to drain out and boil off. Repeat this procedure until it stops boiling off inside of IRCAL; the pattern of escaping gases will change noticably at this point so it's not hard to tell when this is. You can also monitor the cooldown by connecting the temperature controller and reading out the internal thermocouples.

In order to open it safely requires two people. Place the filter wheel box horizontally on a table, with the removable side facing up. It's irregularly shaped so you will want to support it using some small flat objects like kimwipe boxes etc. One person should, by hand, hold the two pieces of the filter box together, while the other person unscrews them. Only once all of the screws are removed should the first person *slowly* release pressure on the top piece, allowing the springs to lift it up and away from the rest of the filter mechanism slowly and without everything flying apart. The top side can then be lifted off carefully by hand, exposing the wheels and other mechanisms inside. *DO NOT* unscrew the filter wheel shaft (which is the central machine screw on one side, and looks very tempting). The removable side is the other one.

Putting it back together requires a reversal of this process. In order to put the removable piece back in place, the wheels and springs have to be compressed. One trick that works well is to hold everything together by applying downward pressure through the open aperture hole onto the wheels, compressing the springs that way and allowing everything to be fit back together and screwed into place.