Saturday, December 27, 2014

Focal Plane Installed

We finally completed the installation of BICEP-3’s focal plane the day after Christmas.  The optics (two lenses) in our camera cast a magnified image of the sky onto this place, which we stuff full of detectors. 

Assembling this has been my main task (as well as three other peoples’) for the past couple weeks since I arrived.  There's a couple of us at work above.  Those nine boxes (or “modules”) each contain 64 pixels.  Because they are delicate and we did not want them to get held up in New Zealand customs, I had to “hand-carry” them down here, taking them as carry-on in a hard-case that looks like something out of a cold-war spy movie.  It's customary to give goofy nicknames to important hardware, and we're considering naming each of the nine modules after a Supreme Court justice (can you think of any other things that come in sets of nine?)

You’ll notice that there’s room for another 12 around the edge, and next year we’ll bring down another 11 (we don’t have enough wires in the camera to read out the last one).  For now, however, we will just have nine.  (I suppose when we add the others, we'll either have to change our nickname scheme or call it "packing the court").  The next immediate steps from here are to add lenses in front of the detectors and insulation around them so we can cool them to -450F.  We hope to be cooling down in the next couple days.

Those detectors need to be made even colder than the lenses, and we keep them cold by having successive “stages” at progressively lower stages, kind of like how one dresses in layers on a cold day to more easily stay at a different (albeit warmer) temperature.  You can see the final stages of that here

We call this structure "the wedding cake" (another goofy nickname) because of it's stacked multiple stages.  Here's a couple of us having some fun with that name during installation.

The installation wasn't all smooth sailing.  You can see the clips in the top picture that I had to improvise and machine last minute to hold the filters in place.  I also had to open one of the detector boxes and re-wire it to avoid some electrical cross-shorts.  You can see me threading the "wire-bonder" machine below that I used to make these fixes:

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