Day 16, 04/14/2011 -- G.I. Joe kung fu gripper

Today, we again attacked the problem of the HWP not rotating. We tried a few different things, like hitting the suspect gripper with tons of current and tilting the cryostat to different angles. Still, despite our best efforts, we have yet to find a solution. We do feel we have a better idea of which gripper is not working, and there are some things we can try tomorrow when we go in.

Franky has finished setting up the BROs; tomorrow we plan on connecting cables and cycling the fridges so we can start doing detector work.

Pictures:
https://picasaweb.google.com/asad137/EBEXInPalestine20110414

Day 15, 04/13/2011 -- Something is rotten in the state of Texas

Rotten is perhaps too strong a word. Basically, when you do experimental physics, things often don't work. It's part of the simultaneous charm and frustration of doing new things.

In this case, we are having trouble with the "grippers", a set of three motor-controlled jaws that hold the half-wave-plate in place as the cryostat cools down. Despite repeated testing in another cryostat and Jeff's careful assembly, we have yet to succeed in opening the grippers and releasing the HWP. We still have a few things to try tomorrow, so hope is far from lost. Even if the HWP isn't free to rotate, we still have plenty of other tests that need to be done, both without and eventually with the gondola, so we are forging ahead.

While the UMN crew tackled the gripper problem, Franky kept himself busy with continuing to assemble and populate the BROs. At this point, we're just waiting for the detectors to be cold enough that we can start connecting cables and doing the baseline checkout tests.

After Jeff and I went in at 4:30 AM for a helium transfer, the boiloff rate is now slowing down and will likely last through the night -- a good sign that we are close to being able to run the fridges and detectors.

Pictures:
https://picasaweb.google.com/asad137/EBEXInPalestine20110413

Day 14, 04/12/2011 -- At last, helium.

With the arrival of Franky from McGill yesterday, today he set about setting up the bolometer readout crates (hereafter: BROs). After first assembling the final crate, he identified and fixed a power issue related to a bent pin that caused us to damage 2 (very expensive) readout boards back in Minnesota. The main problem he and Kyle were having was failure to communicate -- no, not because of his Quebecois accent, but because they were having network problems between the computers and the BROs. In the end it turned out to be something misconfigured in one of our network switches, but it took a half day to figure out what the problem was and how to fix it.
In the meantime, Kyle, Jeff, and I started thinking about some of the upcoming calibration experiments -- how to mount a source on the water tower and be able to aim it, how to suspend a styrofoam bucket with LN2 above the cryostat window, etc. One of the outcomes of this discussion was a nice little mount based on a benchtop optical mount, a spare hexapod clevis, and a piece of scrap aluminum. This mount, an inverted altitude-azimuth mount destined for holding our millimeter-wave source atop the water tower, will allow us to map the beams of the telescope once the gondola gets here.

But the main advance of the day was helium, and lots of it. We finally got our gas regulator from Minnesota and could proceed with cooling down the cryostat with liquid helium. After pumping out most of the LN2 from the helium tank and then boiling off the little that remained with warm nitrogen gas, we then proceeded to transfer liquid helium out of one of the large 500L storage dewars we ordered. In the end we used about 250L of helium to cool and completely fill the EBEX cryostat's 130L helium tank. Because the optics box and focal planes inside are isolated from the 4K cryostat shell, they still need to cool down, and as they do, they boil off massive amounts of liquid helium. Thus, for the next few days, we'll be doing multiple fills a day, at all hours of the day or night -- Jeff and I are scheduled for a fill at about 3AM, and there will probably be another stupidly early/late fill tomorrow as well. Ah, the joys of having a big cryostat!

Pictures, again, finally:
https://picasaweb.google.com/asad137/EBEXInPalestine20110412

Day 13, 04/11/11 -- This Blog Entry Intentionally Left Blank

Day 12, 04/10/11 -- Tippecanoe and Tyler Too

Today was a slow day. With the cryostat filled with liquid nitrogen and the internals slowly cooling, there's not much that requires immediate attention. Since it's Sunday we went into the high bay only for a short period of time today -- long enough to check the liquid nitrogen levels (and refill as needed) and for Jeff to open and close the internal mechanical heatswitch to try and optimize its thermal contact.

We then drove to Tyler, TX to see what it was all about. A city of over 80,000 people, we figured it must have something worthwhile, right? Turns out we were right: Jeff found that they have a zoo and a historical aircraft and aviation museum. We went to the Caldwell Zoo first, and were treated with a surprisingly nicely maintained and well-curated zoo, with all manner of big cats (lions, white tigers, leopards, and cheetahs), a couple of black bears, and some large mammals from both the US and Africa (rhinos, giraffes, and elephants) along with the requisite reptile area (which focused mostly on species native to the area) and a nice contingent of water and tropical birds.

The aviation museum was also quite a find. Located at the Tyler airport, they have a nice collection of aviation-related memorabilia from the entire history of the US armed forces as well as a nice collection of real (but mostly engineless) aircraft sitting on the tarmac (an F-101, F-105, F-111, and an F-4 Phantom come to mind immediately out of the 10 or so aircraft they had). They also had knowledgeable and helpful docents on hand to answer questions about the aircraft, which was a nice bonus. And all for $5! Highly recommended if you're ever in Tyler.

The only pictures from today are some cell phone pictures of pelicans, so I'm not going to bother. Tomorrow we're back in the high bay, and are planning our first of many liquid helium transfers!

Day 11, 04/09/11 -- The Birth of Cool

We spent a half day in the high bay today getting the cryostat ready to cool with liquid nitrogen. Jeff and I worked on getting electronics boards mounted to the bottom of the cryostat as well as connecting their cables inside the metallic 'can' that sits at the bottom of the cryostat. Kyle meanwhile worked on getting the cryostat housekeeping (temperature sensors, heaters, and current monitors) up and running.

After installing cables and the RF can, we flipped the cryostat upright to begin the cooldown. The liquid nitrogen tank obviously holds liquid nitrogen, but we pre-cool the liquid helium tank with liquid nitrogen as well. Liquid nitrogen has a much higher heat capacity and is much less expensive than liquid helium, so we use LN2 to get us from 300K to 77K first, and then fill with LHe. That process went quite smoothly despite (or perhaps because?) the cryogen vendor gave us high pressure (250 psi!) LN2 tanks instead of the 22psi ones we requested. At any rate, it worked, and Kyle got the housekeeping system up and running after some minor wiring tweaks to account for some changes inside the cryostat.

After leaving the high bay, Kyle headed back to our lodgings while Jeff and I decided to take a bike ride. It turns out that not only is the Palestine area quite pretty as we've noticed since being here, with lots of trees and green fields, but the Texas drivers were surprisingly accommodating of two guys riding skinny-tired bikes on the farm roads and state highways. On the smaller roads, drivers without fail gave us a wide berth, and we were not once honked at from someone behind us (one guy in town coming the opposite way honked at us for some unknown reason...or perhaps he was honking at someone else). Also, Palestine's hills are surprisingly painful for someone (me) who hasn't done any real riding since last October in Minneapolis (which is largely flat). Still, the 14 miles we did today was a good start -- hopefully we'll have a chance to do some longer rides in the future.

The few pictures today were taken with my cell phone, as my DSLR's memory card was left in the apartment. Sorry.
https://picasaweb.google.com/asad137/EBEXInPalestine20110409

Day 10, 04/08/11 -- Leak free

Whoops, sorry for the late update.

Because we had a late night on Thursday and have been working pretty much all day every day, we took our first (mostly) day off. The only thing we did in the high bay was leak-checking the cryostat. This was somewhat complicated by the fact that we forgot to bring an inert gas regulator with us to Palestine. We managed to borrow one from the other science group (CREAM) that is in the high bay adjacent to ours.

Planning to attach cables, flip the cryostat, and fill with LN2 today.

No photos from Friday because there wasn't anything interesting to take pictures of...

Day 9, 04/07/11 -- Closing Time

After a long day, we got the cryostat closed and pumping! It's late and I want to go to bed so no detailed update tonight, but everything went pretty smoothly. Hopefully it won't have a leak -- fingers crossed!

Pictures:
https://picasaweb.google.com/asad137/EBEXInPalestine20110407

Day 8 , 04/06/11 -- Just talkin' 'bout shaft

Another day, another few steps closer to getting the cryostat closed and pumping. We pulled the instrument out of the cryostat for the final time so that Jeff could finish installing the parts for the half-wave-plate assembly.

Jeff spent a large fraction of the day inside the cryostat. We had a little scare early in the day as Jeff was installing part of the HWP drive shaft assembly -- it got dropped on the floor, bending two of the flexible bellows in the process. After a brief moment of panic, Jeff realized he actually had spares for the parts in his parts bin, so after a quick replacement we were back on our way. After that, the wiring for the HWP system was installed and tested. The last piece of the puzzle was measuring positions of the angle encoder components on the HWP assembly so we can later infer the HWP's angle relative to the rest of the cryostat and, by extension, the sky.

I spent much of the day working on getting our optical filter, made of porous Teflon, ready to mount. This filter, which helps protect the 1 Kelvin optics from the thermal radiation from the relatively warm (~30K) rotating HWP, is a new addition for this cryostat run.

Kyle spent a lot of the day working on getting our computer network set up, which he did with the help of Milligan back in Minnesota and the CSBF networking person. He also started getting our vacuum leak checker, which arrived today from Minnesota, set up. Kyle and I both helped Jeff where we could, as he had the most difficult work for today.

Pictures:
https://picasaweb.google.com/asad137/EBEXInPalestine20110406

Day 7, 04/05/11 -- Tape'n'tape

Today was a productive day in the high bay. Jeff started installing the half-wave-plate motor driveshaft assembly and made a lot of progress in putting together the 'table' assembly that holds the entire HWP system.

Kyle and I measured the polarizing grid orientation relative to the rest of the optics and then we started installing the shielding that protects the detectors from seeing relatively warm 4.2K radiation from the cryostat walls.

This process involves a lot of tape. Aluminum foil tape, to be precise. Sure, the shielding is screwed down, but all of the little gaps between parts need to be closed off with tape. It's a pretty tedious job, as there are a lot of seams, and some of the seams are tough to reach or have non-trivial geometry that makes them difficult to cover with tape. Still, we do our best, and the process takes a few hours to do well.

Once the instrument was all taped up, we got the CSBF guys to come in and crane the instrument over and into the cryostat. Once we got it in place, Kyle spent the rest of the day aligning the last optical element in the cryostat, the so-called "field" lens. In the meantime, I helped Jeff as much as I could, doing little things that needed to be done while he fussed with tiny bearings for the driveshaft assembly.

Tomorrow will be devoted mostly to HWP system installation (finishing the driveshaft, installing/connecting wires, and then installing the HWP system itself). The hope is we can close up and start pumping on the cryostat on Thursday.

Pictures:
https://picasaweb.google.com/asad137/EBEXInPalestine20110405