So what do I do?
Well, the easiest answer I've come up with to "What do you do in an Astrophysics lab?" is "Make sunglasses." Sunglasses have an anti-reflective (AR) coating that reduces reflection (of the UV rays). But this reduction in reflection is significant in Astrophysical instrumentation because it also increases the contrast of the image by eliminating stray light. That way it also maximizes transmission for a particular bandwidth.
In particular, I work on making an AR screen for a receiver cryostat that takes measurements of the Cosmic Microwave Background (CMB), leftover radiation from the Big Bang. This process involves constructing a heating plate of power resistors with customized temperature control, and eventually baking the different screen samples in a massive vacuum chamber (maybe one of the largest at Columbia). The baking of the AR screen is like a waffle-maker: you bake the material (probably some polyethylene plastic or teflon) between two of the heating plates, and hope it comes out right.
For this past week I've done quite a bit of soldering and desoldering. I desoldered the older wiring of the power resistors, and put in new 14 gauge wiring that is hopefully more or less permanent (and made legitimate with color-coded wires and heat shrink to cover the terminals). I finished soldering one of the two plates. It took a little longer because I was unfortunately using, for the most part, a soldering gun that didn't heat up very well.
Also, in deciding how to set up the resistors, I had to do some basic calculations on resistors in series and in parallel. The resistors that were previously used, and that I'll reuse anyway, were 300 ohms with a 50W capacity. There are 20 resistors in total. So the question was how to wire them up to produce a decent amount of power without tripping the circuit breaker.
Let's start with the limits of a single resistor using the power equation (1): P=(I^2)*R. We know P (50W) and we know R (300 ohms), so the max current (I) flowing through each resistor is roughly 0.41A.
(2) There are 120V coming out of the wall, and it just so happens that 120V/300Ohms is equal to 0.4A (based on Ohm's Law, V/R=I). If the voltage we want is the same across every one of the twenty resistors, then they must be wired in parallel.
(3) To check, using the power equation, 0.4A through each resistor produces about 48W of power, nearly the manufacturer's stated power limit. It's cutting it a bit close, but since the baking is done in a vacuum, we shan't be too worried about a fire breaking out.
(4) Finally, the wall socket can source out up to 15Amps, and 0.4Amps for 20 resistors requires a total of 8Amps of current, so we won't be tripping up any circuit breakers.
Nice. So the twenty resistors are set up already on the square plate in a 4x5 arrangement. Now I just had to wire and solder them in parallel using the appropriate wire gauge.
That's roughly what I've been up to this past week. I also crimped a RJ45 head on a Cat5 cable for the first time, which is a fancy way of saying I can replace the head of an ethernet cable. This was a side project, to move some servers to another room, so I had to find ethernet cables long enough to reach this other room. I missed the part about moving the server "tomorrow," so I may or may not have inadvertently unplugged the server. I mean, how was I supposed to know that Nevis Labs 40 miles away was presently running some experiments and on line with the server? Well, ten minutes later, it seemed like the phones all started ringing at the same time and some angry phone calls were coming in. Oops. My bad, guys. Blame it on the undergrad. So that was my noob move of the day.
So now for a good weekend of rest. For a good bit of the soldering, I was using lead based solder. I stopped using that and used a lead-free one after a while. But then I also realized that across the hall they were doing asbestos removal, and there were massive "Warning: Asbestos in the Area" signs posted all over the place. Yesterday, I also discovered that there were massive bricks of pure lead sitting at the foot of my work table. Either way, I must have a decent amount of lead in my system by now. So I'm probably going to detox at the beach this memorial day weekend. That's it for now.
