Week 2: Copper in the Waveguide

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Monday, June 17, 2013


Alec Lindman

The Kennedy Center is a delightful place to unwind from the workweek, and that’s just what we did on Friday. The National Symphony Orchestra played an enjoyable program with some rather interesting cello solos, and we took it all in from our seats in the first row. While our view was somewhat limited, the music enveloped us wonderfully, and I had plenty of time to study the percussionists’ remarkable techniques involving four mallets but only two hands. Physics, even at the symphony.

This week we settled on a general form for the microwave source I am designing, & I had several discussions with other scientists who are contributing to the project. It was illuminating to meet them, having previously seen their names on the papers I have been reading for background. There’s much more to be learned from collaborating in person, no matter how well written a paper is.

I spent most of Thursday testing the tensile strength of the Kevlar threads that will thermally isolate but mechanically support the heated emitter in the microwave source. The detectors operate at a tenth of a degree above absolute zero, and the source is heated to between 3 and 20 K, so the Kevlar is essential to prevent the detectors from overheating.

Friday brought a new task that happens in every lab: cleaning day. In our case, two very long, narrow, and difficult to clean tubes were contaminated. We have a microwave spectrum analyzer on the wall, connected to liquid helium via two long vertical waveguides. Connected across the end of the two waveguides is an orthomode transducer, which separates the two polarization components of a microwave signal. We use it to send in a pulse with one polarization, which passes through unaffected, interacts with the test circuit, and returns with some composite polarization. The OMT divides the two components of the polarization and passes each back up one of the waveguides to the spectrum analyzer. Based on some spurious signals in recent tests, we concluded the OMT and/or the waveguides were contaminated.

Upon opening the waveguides, we immediately discovered tiny copper flakes throughout, probably from the manufacturing process. It took all afternoon, an ultrasonic cleaning bath, many tiny strips of chamois pulled through the waveguide with Kevlar thread, and a lot of compressed air to remove all the copper.

Our exploration of the city continues apace, with this week’s schedule including the Kennedy Center, rock climbing at one of the largest indoor gyms in the country, and an outdoor movie. We also discovered an excellent Thai restaurant right in Foggy Bottom, and determined that there are very few places to get food after 11:30 on a weeknight in Foggy Bottom. We’re starting to form a very cohesive group outside of work, and with the addition recently or soon of Dayton, Alexandra, Katherine and Fiona, I’ll finally be able to remember how many of us there are – twelve, with six at the ACP, three on Capitol Hill, two at NASA, and one at NIST.

Alec Lindman