Week 1 | Week 2 | Week 3| Week 4 | Week 5| Week 6| Week 7| Week 8 | Week 9 | Final Reflections | Final Presentation
Week 8: Preparing for Presentations
As we approach the conclusion of our work this summer, Darren and I, the two NASA interns, will be presenting our work on August 1st at the center-wide intern poster session at Goddard. We will also be giving oral presentations at the American Center for Physics the following week at the closing event for the SPS internship program. To give a flavor of my work, I have included below my abstract for the presentations.
Title: Blackbody Microwave Source for Cryogenic Detector Development
Abstract: I present an evolved design for a thermally isolated blackbody source operating at 90GHz and 120GHz, frequencies of interest to Cosmic Microwave Background measurements. My lab is developing transition edge sensor bolometers for the CLASS and PIPER missions to measure the CMB polarization; the source described here is under construction for use in the 150mK test package to measure the detectors’ response to CMB light. The design is optimized to minimize heat loading into the 150mK stage by employing a Kevlar kinematic suspension and additional thermal breaks. The blackbody light is coupled to a detector by means of an electroformed waveguide, which is mated to the source by an ultraprecise ring-centered flange design; this precision is critical to maintain the vacuum gap between the heated source and the cold waveguide, which is an order of magnitude smaller than the allowable misalignment of the standard military-spec microwave flange design. The source will provide at least 50% better thermal isolation than the existing 40GHz source, as well as a smaller thermal time constant to enable faster measurement cycles.
Week 7: Counting 602000000000000000000000 Atoms
On Friday we toured NIST with Alexandra and Dr. John Suehle, her mentor. We visited so many labs that I’ve probably lost track of a few, but these are the highlights. Our first stop was in the electron microscopy suite – though the star of the show wasn’t even an SEM. For what I put down to a lab being reused from some other purpose, the walls of the antechamber and SEM space were covered in anechoic foam; however, it transpired that when people are talking in the space around the microscope, it’s possible to reconstruct the conversation based on the vibration of the sample in the image. After spending quite a while discussing the various samples the first machine could image and why most of their work starts on that one (mostly the larger working volume, as well as the option of a cryogenic stage to hold biological samples), we briefly stopped at another machine that currently holds the world resolution record at half a nanometer. Then we turned a corner and beheld a microscope whose exterior size was at least five times that of the first machine, and which as I mentioned, doesn’t even use electrons: it uses helium ions. It’s capable of imaging many exciting samples, including carbon nanotubes, which by the thinness of their walls barely interact with electrons in the SEM machines. Apparently it’s virtually a one-of-a-kind capability, and the device itself is quite rare – as if SEMs weren’t rare enough in the first place.
NIST is absolutely huge, and much bigger than even its .37 mile long central hallway would indicate: beneath almost the entire footprint of the central buildings are two or three more floors of basements, with the lowest rooms’ footings on the bedrock. This makes sense in the context of our next destination, the coordinate measuring lab.
Here they have two machines with working volumes a meter in length which can make linear, roundness and surface measurements to within 500 nanometers. To enable this accuracy, they’ve air-leveled the floor and the room temperature is maintained within a few millidegrees of 20C. We saw the temperature spike on the screen of the monitor when we walked into the room; even the lights had been designed with temperature control in mind, as the bulbs were located outside the double walls of the room, and the light passed in through waveguides.
One of the efforts underway at NIST – custodian of all measurement standards for the United States – is to find a fundamental definition of the kilogram, the last unit still based on a physical artifact. An approach to this problem is to use Avogadro’s number (the number of particles in a mole, related via carbon to the kilogram) of atoms to construct an object consistent with the fundamental definition. Silicon is the element of choice, and the idea is to grow a perfect crystal, then polish it into a precise sphere. Then, knowing the crystal lattice spacing, one can calculate the number of atoms in the measured sphere.
Next, we visited the NanoFab, where all sorts of ridiculously tiny devices are manufactured on an impressive array of equipment. I must say, however, that seeing a few more multi-million-dollar instruments in cases, class 10 cleanroom notwithstanding, wasn’t much of a shock after all the other incredible tools they have. Finally, we visited a lab attempting to sequence DNA by trapping chemical tags liberated by polymerase in pores in a bilayer membrane. They anticipate bringing the cost to fully sequence a genome down to a few tens of dollars, and the time to a couple of hours. This would significantly alter the paradigm in the medical profession, but there are of course many ethical and privacy concerns to assuage first. Who would have guessed that an organization perhaps more known for complaining about miniscule changes in a lump of platinum-iridium sealed away in a vault would be at the forefront of medicine?
Week 6: Project Progress and Goddard Tour
This week we held the NASA Goddard tour for the other SPS interns, and I made major progress on my project. Early in the week I decided to replace the hodgepodge of bits from the parts-without-a-home cabinet that had been simulating the central component of my model with a proper part. The actual component will be copper, but for my purposes, aluminum is easier to work, so I turned an aluminum rod to the right profile and added the holes for the suspension threads. As I disassembled the old model, it occurred to me I could also use actual Kevlar instead of the nylon stand-in as before. Once the bobbin was suspended in place with the Kevlar, and all the strings were tight, I tentatively prodded the bobbin to test its range of motion. It moved so little that if I closed my eyes, I couldn’t tell it wasn’t just bolted to the frame! Furthermore, my previous tests concluded the Kevlar has a working load of 31 newtons; when I measured the tension in my model, it came to 26 newtons. This is ideal because it means we are using the full available strength of the Kevlar to provide stiffness to the bobbin, and thus we are using the minimum cross-section for the stiffness. Reducing the cross-section is important because it improves the thermal isolation of the heated source and bobbin from the refrigerated base. I also realized that I would need to add an additional piece between the mounting plate and the waveguide it attaches to, which will provide another place to implement an innovation which the existing unit does not employ: placing an insulating layer of plastic between the metal parts. Now my design has two insulated breaks in addition to the Kevlar, which on its own is a 55% improvement over the existing design. I have yet to estimate the gain from the breaks, but it should be significant.
On Wednesday we brought the other ten interns to NASA Goddard for a tour and town hall with the Center Director and the Administrator of NASA. We looked around the visitor center, enjoyed a fun and science-heavy presentation with the Science on a Sphere visualization system, and then attended the Administrator’s talk. Afterwards, we met up with Dr. John Mather, Goddard’s own Nobel laureate and friend of SPS interns everywhere for a tour of the cleanroom, integration and vacuum test facilities where they’re building the James Webb Space Telescope and a number of other projects. He gave us an insider’s view of the progression of the project, delivered while we all had our noses glued to the second-story windows of the largest cleanroom in the world. Exploring the myriad spaces and running across while fleets of satellites or equipment returned from space (HST WFC2!) is an amazing way to discover how incredible our capabilities are when we put our minds to work.
Week 4: My Kevlar Gets Stuck
My main accomplishments this week comprised one material project and one conceptual breakthrough: I built a fully analogous test rig for the Kevlar strands, and I figured out an elegant way to route them. Since the Kevlar strands are the most critical component of the source assembly, it’s important to verify that they behave as expected. My test system consists of adding the proper end attachments to new samples and breaking them with the force meter.
In the final assembly, the Kevlar will suspend a central rod from a frame, holding it very precisely in place while thermally insulating it. The key point in attaching them is to ensure they don’t bend where they meet the support, so knots won’t work. The solution we employ is to glue them in place with epoxy, in such a way that they run straight out from the support towards the load. The previous test I ran used knots, but with unexpected results: even when the strand failed in the middle between the end knots, it broke consistently at about 50% of the theoretical load. The knots were having some subtle but significant effect, and testing the fibers with epoxy terminations will be important to verify they can attain their design strength. On Friday afternoon, I completed the test jig and will break the samples first thing on Monday.
How the Kevlar is routed around the structure is another important factor in the mechanical and thermal performance of the source. Previously, we had considered using four threads to hold the center rod, but I simulated the deflection in that configuration and ruled it out as too flexible. Six threads will provide complete geometrical constraint, and I have figured out how to arrange this with only three separate Kevlar segments.
On Thursday afternoon, we had a delightful reception with the Development Board at ACP, and I had the opportunity to meet a number of exceptionally interesting people. Dr. Mather was in full swing answering questions about Webb, and I even had an extended conversation with the emeritus director of NIST. It’s wonderful that so many significant people in science are specifically interested in interns like us – though they all went through their own similar experiences to get where they are.
Our meeting with the SPS Executive Committee on Friday was a bit more lighthearted – we conducted many trials of an experiment involving small-scale rubber band rockets and each other. The committee members even got involved, and we concluded they are, in fact, fun. As has been our whole summer so far, definitely including the performance of the Capitol Steps on Friday night.
Week 3: Life and Science in DC
This week has been both productive and enjoyable – it’s my favorite week thus far, and given the prospects of my project, the trend looks like it will continue. We are advancing towards a final design as we identify and quantify the parameters most critical for our project, and I’ve been doing a number of experiments to validate our assumptions.
I’ve been interacting more with many of my mentors, and I reached the point earlier this week where I started to really comprehend not just the specific recommendations from my group, but the context in which that knowledge is valuable. I’m looking forward to making more substantive and independent contributions as I continue learning.
Of late I have taken to leaving International House earlier in the morning to walk to Whole Foods for breakfast. It’s very calming to get outside early in the morning and see the city slowly waking up around you. The metro stop is only around the corner from Whole Foods’ sidewalk tables, which is a nice change from the distance to I House, close though it is. Speaking of I House, it turns out there is an organic drycleaner’s located just a couple of blocks over in the Watergate, and I dropped off some shirts there on Thursday. It’s quite the experience to go through the motions of everyday life in a place so infamous for its history – but then again, when I pause to think about it, that’s true of many places I frequent in DC. I’ve unwound the last few days by walking along the Potomac, and around the Kennedy Center. Contrary to the warnings of friends who have spent time in DC previously, the weather has been quite amenable to comfortable outdoor activity so far, and I hope it continues to be so. I tried to make it to the free nightly concert at the Kennedy Center one night this week, but the commute gets in just a bit too late. Another night, we went to the café on the roof for dinner and saw a spectacular sunset on the summer solstice.
I’ve never lived in a city with good public transit for any period of time before, and it’s one of my favorite parts of DC. As I witnessed the first few days, driving is impractical, and it’s downright fun to take the metro for a train buff like me. I’m especially lucky in that respect because the orange line, on which I commute, runs parallel to the Amtrak and MARC route from Union Station northbound. I see the Acelas going past everyday, and it always startles me how they make the metro look like it’s standing still. I even took one a couple of weeks ago, and barely had time to get comfortable before we arrived. High speed rail is the only way to travel, if you ask me.
Washington is turning out to be a much better place to live than I anticipated: it’s both exciting and relaxing depending on what one is looking for, and it’s incredibly easy to get around from one destination to another.
Week 2: Copper in the Waveguide
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.
Week 1: Any two five elevennis?
Monday the third of June was our first day at work for the summer, and everything looks quite exciting. As we’ll hopefully continue to do throughout the summer, all of us who are staying at GW walked to the metro station at 7:40, and we were at the American Center for Physics at 9 on the dot. Hopefully the delay-free timing of the metro will persist throughout the summer.
We heard from, as far as I could tell, all the SPS staff, and many of the heads of AIP’s subdivisions. It’s exciting to hear from those working in policy, journalism and all the other fields which support and augment traditional “physics.” During our lunch, consisting of just the interns and the incomparable but delightfully down-to-earth John Mather, I learned a great deal from my colleagues about their motivations and their hopes for the summer – and their varied goals have helped me expand my perspective as well.
Soon after lunch, we dispersed to our work locations: myself and Darren to Goddard, others to NIST and Capitol Hill, and some just a couple of floors up in the ACP. Upon arriving at Goddard, we were met by Dr. Lucy McFadden, Chief of University and Higher Education. As we walked towards her car to drive to our building, I noticed a bike quite similar to the Capitol Bikeshare bikes which usefully occupy many street corners in DC; Goddard has its own bikeshare program, and this bike was available. She pointed me to the water tower barely visible over the trees to the northeast, and told me to meet her there. After laboring up the final hill to the tower, traversing many parking lots, and even a stoplight on a four-lane road – all within the center – I can tell you that Goddard is big. Another useful figure is that 3000 civil servants and 7000 contractors work there at once.
Our destination was Building 34, a shiny new space peppered with overflowing whiteboards in the halls alongside academic posters and mock-ups of spacecraft hardware; the models are the most useful landmarks in a somewhat labyrinthine building. Even Lucy got turned around a bit, but everyone we encountered was nothing but helpful and eager to help us locate the offices of my and Darren’s mentors.
The team with which I will be working is young and vibrant, and this fits their project: creating the hardware to study light from the first moment the universe became transparent. The team consists of my mentor, his postdocs, an intern from the spring who is continuing, and a few others who help with semiconductor fabrication and testing.
My lab has a large cryostat which reaches 150 thousandths of a degree above absolute zero, and the blackbody source I am designing will mount inside along with a detector to reproduce the conditions in space. This is looking like a most excellent project, perfect to go along with my (physics-)fun-loving fellow interns and exciting location. Go physics!