This morning, Jeff and I once again got up way too early to fill the cryostat. I had set my alarm to wake up at 5AM, but I figured I could sleep a little longer and set the countdown timer on my phone for 10 minutes more and went back to sleep. Luckily I woke up about 25 minutes later, at which point I realized that I accidentally set my timer to count down for 10 hours. Oops. It ended up working out fine; I got up and woke Jeff up and we headed to the high bay, where we found that the cryostat boiloff had slowed during the night and we had plenty of helium left.
We filled anyway, and over the course of the day the boiloff dropped even further, down to 2.6 liters per hour as of the last measurement. For reference, last time we cooled it down, the cryostat boiled off roughly 0.5 liters per hour. Fun fact: Liquid helium costs about $4/liter in Minnesota, and probably more here in NM because it has to be delivered from Texas. We have already currently used nearly 900 liters of liquid helium just to get the cryostat to this point; we will probably go through another 700-1000 liters by the time we get to fly. So figure at least $6400 in liquid helium alone. Science is expensive.
I spent most of the day trying to get our liquid helium level sensor to work. I fixed the issue I had yesterday, but it still wasn't working. Later, I discovered that the power supply I was using to run the level sensor was acting funny, meaning we won't have a level sensor unless we use a different power supply (something I'll look into tomorrow).
Ilan and Matt spent the day continuing to debug the low-temperature thermometer readout electronics, while Hannes and the McGilligans looked at SQUIDs and worked on detector software. Jeff and Ilan worked on idiot-proofing the half-wave plate commanding, and Jeff had the HWP spinning at roughly 2 Hz by the end of the day today.
The ACS team of Michele, Daniel, and Joy was able to get the gondola pointing using the magnetometer for feedback (Britt is back in New York for a long weekend). They had been trying to do this for the past couple of days, but the magnetometer was giving funny readings. They finally figured out that the floor of the high bay is somehow interfering with the earth's magnetic field (possibly the steel re-bar in the floor), and so by raising the magnetometer up to the top of the gondola they were able to get sensible readings and move the gondola back and forth.
All in all, a pretty productive Easter Sunday for the EBEX crew in New Mexico. And to think, some people took the whole weekend off.