Saturday, June 30, 2012

Day 34, 6/30/2012 -- more of the same

Today was more of the same -- After refilling the cryostat's helium, Jeff and I did more polarized Ebert-Fastie scans (at both 150 and 250 GHz), the Columbia crew did more painting of ACS bits in preparation for environmental testing in the CSBF Bemco test chamber, and the Kevins did more work characterizing the array. The Kevins, in particular, have switched to a somewhat later shift in order to get some quality time with the array when we aren't taking receiver calibration data. KyleH started doing some setup work for the sun sensors, pictures of which can be seen in today's album.

As a bonus, I took a short video of the EBEX HWP motor spinning. Ok, it's not that exciting, and the white balance is off, but it's only 8 seconds so it's not much of a commitment:


Friday, June 29, 2012

Day 33, 6/29/2012 -- More scans, more paint

Today Jeff and I set up the Ebert-Fastie to do scans to map the phase response of the EBEX achromatic HWP. Unlike regular single plate HWPs, which are tuned to a specific frequency and its multiples, the EBEX AHWP is a stack of 5 birefringent plates oriented in such a way as to increase their bandwidth. The penalty for this is that the so-called 'phase response' is no longer a simple function -- for a given input polarization angle, the output polarization angle varies slightly as a function of frequency. We need to know this effect in order to properly analyze our data, and so by putting a polarizing grid at the output of the Ebert-Fastie and rotating the HWP, we can map the phase response of the HWP to polarized light as a function of frequency. After a few fits and starts, we managed to get the scans going by the early afternoon and have three full scans in the can with more to come tomorrow.

On the gondola side, Michele managed to get the elevation actuator completely disassembled and proceeded to degrease the various parts in the ultrasonic cleaner. Britt, Andrei, and KyleH started the process of painting various gondola bits that weren't powdercoated, and Chappy, Joy, and Seth continued their software work which results in an impressive amount of clacking on keyboards but doesn't make for very interesting blog posts.

Kate and Kyle left today; Kyle will be returning next week after a short break from Texas.


Thursday, June 28, 2012

Day 32, 6/28/2012 -- The gondola returns

Today was another full day in the high bay. The big news is that the gondola has returned from powdercoating wearing its new outfit of lustrous white powdercoat. Britt and Michele spent some time this afternoon removing the masking from the holes we didn't want coated. In other gondola news, KyleH and Andrei worked on the triangle's shock absorption system on the BTS (which is intended to prevent the triangle from crashing down into the telescope on termination and landing). Michele also started disassembling our spare elevation actuator in order to degrease it and then regrease it with low-temperature grease (we use Dow-Corning Molykote33 Light, an aviation grease).

On the receiver side, we started getting set up to do polarized spectral response measurements to map out the HWP's phase response as a function of frequency. So, the HWP was ungripped, I helped Jeff make some electrical isolation pieces to isolate the motor from the cryostat, and the HWP was set spinning. It was at that point that we found the HWP position encoder readout boards weren't really reading out anything at all. After a few hours of troubleshooting, Jeff installed a spare ADC board (the so-called "mezzanine" boards of the DfMUX system) and everything worked again. We have some theories as to why the other mezzanines didn't work that we'll be investigating here. Now that everything is working again we hope to take some data tomorrow.

Kyle spent most of the day working on getting mirror alignment targets ready for eventual mirror installation and alignment on the gondola. Both he and Kate are leaving tomorrow, so he just wanted to tie up some loose ends before going back to MN. I forgot to mention in the last post that that, in addition to the gondola crew, Franky was replaced by Kevin a bit over a week ago, and a postdoc from McGill (also named Kevin, hereby known on the blog as KevinB) arrived yesterday. Kevin and KevinB spent a fair fraction of today setting up a new computer, christened 'hepburn' after the UMN group's recent theme of dead actor/actress computer names (joining monroe, mcqueen, and lamarr), that we bought for bolo streaming/visualization work.


Wednesday, June 27, 2012

Day 31, 6/27/2012 -- ...And we're back!

Yes, I have returned to Palestine, so the blog will now resume! In my absence, many things have changed: The cryostat has been running fully cold, and fridge cycles are going smashingly well (getting cold, lasting a long time). The bolo gang has been hard at work getting the detectors up and running, doing characterization, and getting detectors tuned so that we can take calibration data. Over the past few days, the team has started taking spectral response data with our Ebert-Fastie monochromator, getting nice results in all bands.

In addition, the gondola team (Britt, Michele, Joy, and Chappy from Columbia, and Andrei and KyleH from Brown) has arrived. They have set up their lab area on the north end of the high bay and have the flight computers and attitude control system (ACS) running on the bench. The gondola itself is off being powdercoated by a local vendor, and the baffle-triangle support (BTS) structure is assembled in the other high bay, awaiting its eventual mylar wrapping which will serve to shield the experiment from the sun while at float.

I showed up today after a very early flight, so it'll take me a little while to catch up on the goings-on here. Suffice to say that things are progressing nicely!


Wednesday, June 13, 2012

Day 16, 6/12/2012 -- Cooling

The cryostat continues to cool as it boils off helium at a copious rate. After 4 fills today (at ~150L of helium used apiece), the boiloff is now settling down -- the overnight fill should last for about 10-12 hours. The optics box was at about 65K in the evening; once it reaches about 40K the cooling rate increases and cools to near 10K relatively quickly. At that point, the fridges are cycled to cool the optics box and focal planes the rest of the way to 4K (and below).

This will be my last EBEX blog update for a while. I'm returning to Minnesota while Kate is coming here to help with detector work and calibration measurements for the next few weeks. I will take over Kate's job in MN of testing new detector wafers. I'll likely be back in Texas toward the end of June.

No pictures today, as everything in the high bay is pretty copacetic at the moment.

Monday, June 11, 2012

Day 15, 6/11/2012 -- Of Helium and Half-wave Plates

Unlike yesterday (which was so slow that I spent the afternoon at the apartment and didn't bother taking any pictures or posting), today was a virtual whirlwind of activity.

First, we were joined by Shaul, back from his sabbatical in Israel, and ready to PI the heck out of the project. Second was Ilan, who is stopping by Palestine (also from Israel) for a few days on his way to a conference in Hawaii. But most importantly, we were joined by our most adored visitor: liquid helium. Inside the EBEX cryostat.

This morning started by pumping the small bit (~5" out of 28" filled on Saturday) of remaining liquid nitrogen in the helium tank into the nitrogen tank. Then, we started the helium transfer, which went smoothly. Now starts the arduous task of refilling the cryostat every ~6 hours until the boiloff starts do decrease -- and at 250L for the first fill and 150L per subsequent fill, now you understand why we had 2000L of liquid helium sitting around the high bay the past few days! We refilled once this afternoon around 4PM, Kyle and Ilan are filling again at ~9:30PM, and Jeff and I get the early morning shift at 3AM. After the first day, then the helium starts lasting longer -- 8 hours, then 12 hours, then a whole day, and soon thereafter reaches its steady-state hold time of ~14 days. Of course, that's when we start cycling fridges and doing detector work.

The other big success of the day was that the half-wave plate was successfully ungripped and rotated, which is sometimes a bit harrowing. But not this time!


Saturday, June 9, 2012

Day 13, 6/9/2012 -- Nitrogen

Today's big event was flipping the cryostat over and starting the cooldown process. After flipping, we first unloaded a whole 160L dewar's worth of liquid nitrogen (minus boiloff over the past week or so) into the nitrogen tank. The next 160L dewar's contents went into the helium tank. A third was then emptied, and a fair amount from a fourth was then used to finish filling the LN2 tank. The helium tank was left with about 28" worth of helium, or about 90 liters of its full 130L volume. Most of this will boil off over the next ~2 days as the cryostat cools down, after which the remainder will be pumped into the LN2 tank in preparation for the helium fill.

Aside from that...a pretty slow day. I did some administrative stuff for our upcoming Antarctica trip while Kyle helped Franky with some clock cables (erroneously referred to as "timing cables" in the last post) to help debug some issues with the DfMUX clock distribution.


Friday, June 8, 2012

Day 12, 6/8/2012 -- Break

Today was a bit of a change for us -- we all went in to the high bay at the normal time, but the UMN crew had very little to do as we wait for the cryostat to pump out. After taking care of a few odds and ends, the three of us (Jeff, Kyle, and myself) left the high bay while Franky and KyleH stayed to continue working on DfMUX board stuff.

We dropped Kyle off at the Redlands so he could do laundry and chill out while Jeff and I took a day trip to Tyler. Like last year, we visited the Caldwell Zoo, a modest but well-curated zoo in the heart of Tyler. While their lions and giraffes seemed to be MIA today, we got to see some fairly active white tigers and a number of other interesting beasts. After the zoo we headed to the downtown Tyler area which is surprisingly cute, with a reasonable number of shops and whatnot surrounding a central square. On the way back out from Tyler, we stopped at one of the ubiquitous roadside barbecue joints and got our brisket on.


Thursday, June 7, 2012

Day 11, 6/7/2012 -- leak free!

Today we switched out the cryostat roughing pumps for turbo pumps in order to go to the next stage in the cryostat pumpout process. After that, Jeff and Kyle installed the SQUID controller boards onto the bottom of the (inverted) cryostat. We also gave an update on our progress on our weekly collaboration telecon -- all before lunch!

After lunch, Jeff and I headed over to the rigging shop to finish our aerial lift, forklift, and fall protection safety courses, which took basically the entire rest of the afternoon. During that time, Kyle gave a tour of our experiment to a group of about 50 10th-grade girls who were visiting CSBF as part of a summer engineering camp at UT Tyler.

After Jeff and I returned from our training session, we found Kyle working on a new timing cable to synchronize the timestamps across all of our bolometer readout boards while Franky and KyleH finished up the last tasks necessary to complete the heatsinking of said readout boards. At the end of the day, the cryostat was pumped down low enough to allow us to leak-check -- and no leaks were found! We will leak check again tomorrow after having allowed the cryostat to pump out even further, but we anticipate no further problems delaying us from cooling the cryostat this weekend.

Also, here's the news clip from KLTV that aired yesterday:

And today's pictures:

Wednesday, June 6, 2012

Day 10, 6/6/2012 -- Pumpin', Pumpin'

The cryostat is closed! We did the last measurements and installed the optics stack filters and window in the morning, Jeff ran the last of the half-wave-plate checks before noon, we installed the instrument around noon, installed SQUIDs and connected cables in the afternoon, and got the shells closed early evening. Right now the roughing pumps are humming away.

During the afternoon, we were visited by a news correspondent from KLTV, a local TV station based out of nearby Tyler, TX. The correspondent chatted with us, took some video of us working on the instrument, and sat down with me for an interview where she, of course, asked about the truck saga as well as the science behind what we're trying to accomplish with EBEX. It was fun, and I'll add a link to the online video when I have it.

Pictures from today:

Tuesday, June 5, 2012

Day 9, 6/5/2012 -- More alignment!

Today we managed to finish the last of the true cryostat alignment tasks (what remains is measuring reference positions to be used in later analysis) -- aligning the uppermost lens in our optical system (the so-called "field lens" which is mounted separately from the other lenses. After finishing that alignment, we removed the instrument (whose sole purpose in the field lens alignment operation was to provide a set of reference points to align to) and Jeff spent the rest of the afternoon installing the HWP system. Tomorrow we plan on re-installing the instrument for the final time, installing SQUIDs, connecting cables, and closing up radiation shields before flipping the cryostat for one last time to make the final reference measurements and install the optics stack filters and window. So close!

In other news, we got a shipment of liquid helium today -- 1000 liters! That should last us at least a few days...

In other other news, today marks the beginning of the transit of Venus across the face of the Sun. The next opportunity to observe this is in 105 years, so don't miss the chance! Check with your local university astronomy department; I'm sure they will have some public viewings arranged (don't look directly at the Sun!!). Here's one of my pictures, taken through shade 10 welding glass:


Monday, June 4, 2012

Day 8, 6/4/2012 -- Getting closer to closing

Today was another productive day in the high bay. Jeff and I started out by taking some CMM measurements of the half-wave plate system outside the cryostat to figure out reference positions for things like the optical encoder photodiodes. We then put the whole system in the cryostat to make some measurements of the HWP mount relative to the cryostat but then realized we went out of order -- we had to take those measurements first, without the HWP in the system, otherwise our reference points are obscured by the rotating part of the assembly. So, out it came, the rotor was removed from the HWP table, and the table was then reinstalled into the cryostat to do the measurements. Then the HWP table was removed, the HWP rotor reinstalled, and the first set of measurements we did was re-done.

I divided up my time by helping Kyle finish the assembly of the instrument. We first installed all the 1 Kelvin shielding on the optics box, a process which involves copious amounts of aluminum foil tape. Then, once that was done, the sub-Kelvin fridges were finally mounted to the cold plate and their heatsinking installed. Kyle did some final wire checks and the instrument was finally done!

Next comes more alignment -- this process involves installing the instrument into the cryostat and aligning the final lens which lives in the cryostat optics stack (the silver cylindrical protrusion atop the big blue cylinder of the cryostat). Then, we remove the instrument, the HWP system goes in for the final time, then the instrument goes back in for the final time, then we install SQUIDs and connect cables, close up the bottom of the cryostat, flip the cryostat over, make some final measurements with the CMM, put the window back on, make more measurements, and then...pump! Sounds like a piece of cake, right?


Sunday, June 3, 2012

Day 7, 6/3/2012 -- Alignment

Optics alignment is one of the dreaded tasks in closing up the EBEX cryostat. The procedure relies on using an articulated measuring arm to measure various locating points on the various optical components and then trying to adjust the positions and angles of these components so they meet our specifications. More often than not, this goes relatively smoothly. But sometimes...well, sometimes it doesn't. And when it doesn't it's possible to spend hours running in circles, chasing a seemingly unattainable tail.

Thankfully, today was mostly the former. After having set up the arm yesterday, Kyle and I started the task of actually doing the measurements and adjusting the optics. After a few false starts (due to tooling balls that had shifted in their holes and flex in the arm's mounting, both easily fixed), we managed to get nice, predictable results for the first three lenses we aligned. The last component, the polarizing grid, gave us some problems with some strange behavior when we tried to adjust it, but eventually it, too, succumbed to its inexorable, inevitable, aligned fate. This took up most of the day for myself and Kyle. During some stretches while Kyle was puzzling over confusing data, I was able to finish assembling our 77K optical filter stack, which helps prevent infrared radiation from penetrating into the depths of the cryostat and shortening our liquid helium hold time.

Today also marked the arrival of a new addition to the EBEX high bay personnel -- another Kyle, this one a grad student from collaborator Brown University, arrived in Palestine late last night and met us at the high bay in the morning. Due to the obvious potential for confusion between Kyle and, uh, Kyle, I shall dub the new Kyle as KyleH. KyleH's arrival was fortuitous, as Franky was starting to get bogged down with both doing the heatsinking of the DfMUX boards as well as testing them. So Franky put KyleH to work gluing heatsinks while he focused on testing. Jeff's day was spent finishing up some HWP hardware and then working with Seth from Columbia on getting HWP system commanding through our flight control software working. Which, seemingly, it now does!


Saturday, June 2, 2012

Day 6, 6/2/2012 -- Saturday in the high bay

Those familiar with this blog will recall that weekends don't really exist for us when we're in the field -- every day is a high bay day, and today is no exception. Kyle continued assembling the instrument, working in particular on mounting the other focal plane, while Jeff continued work on the HWP subsystem. Franky kept plugging away at DfMUX board heatsinking and setting up the readout system, and I finished up refitting the o-rings in the double window system and flight-readying some cables that were decidedly not flight ready before (no strain reliefs, no chafe protection). I also ended up machining some parts for Jeff -- new mounts for the LEDs and photodiodes used in the optical encoder system for the HWP:

By the end of the day, we reached a point where we are ready to install and start aligning optics in the instrument and start installing HWP system components into the cryostat. Not bad progress for a "weekend".


Friday, June 1, 2012

Day 5, 6/1/2012 -- That's more like it

Today was much the same as yesterday: Kyle worked mostly on getting the focal planes ready to be installed into the instrument, Jeff worked on half-wave-plate parts and some changes to flight computer code (with remote help from Seth at Columbia), and Franky continued to work on DfMUX heatsinking. I ran some errands in the morning (to buy some ladders to replace the ones taken) and in the afternoon started work on refitting the o-rings on the EBEX double window system.

I probably haven't mentioned the double window before at all in any previous editions of the EBEX in Flight blog. In the past, EBEX has used a single thick but rather absorptive window due to the huge amount of pressure trying to force the window inwards into the cryostat. The double window, as the name implies, has two windows -- a thick one for ground operations in order to resist the relative pressure between outside and inside the cryostat and a much thinner window for use at float altitude where the pressure differential is much smaller. While we don't plan on using the sliding functionality until we actually fly from Antarctica, this year's Palestine integration will mark the first time the double window will actually be installed on the cryostat (previous testing was with the system in isolation) and will give us the first opportunity to figure out whatever new challenges come from adding this new system.