Tuesday, February 3, 2015

The 2014/2015 ARIANNA field season - part 2

This is part 2 of the post by Joulien Tatar about the 2014-2015 (really, 2014) field season, with more photos by Chris Persichilli.

Including a few stormy days that kept us in our tents, we installed four new stations in about a week.  There were three stations already installed from previous years so technically we were done with the hexagonal station array construction.  However, given that we were ahead of schedule, we decided to unbury two of the three pre-existing stations in order to upgrade their hardware and conduct some performance studies.  One of the stations was left completely unhampered with it for a third consecutive season to continue studying long term system performance.  Then disaster struck - we ran out of good coffee!  For an avid coffee drinker, like myself, this was a nightmare.  The panic subsided after a desperate scramble turned up a can of instant coffee stashed away in one of the food boxes...phew...

Most of our remaining time on site was devoted to station calibration and ice studies.  Both involved using a pulser, which generates a very short pulse, connected to a LPDA that transmits the pulse.  For the station calibrations, the stations' own antennas and electronics were used to digitize the transmitted pulse.  We managed to collect a large amount of station calibration data for a multitude of different transmitting antenna locations and tine orientations relative to the configuration of the stations' receiving antennas.  Since the received signal was fully propagated through the full electronics chain, as a neutrino signal would, these calibration studies will ultimately help quantify how well we can reconstruct the point in the sky the neutrino arrived from.

ARIANNA is in Antarctica because it needs vast amounts of high quality ice to act as a neutrino target and signal propagation medium.  When using the ice nature has pre-made, we are in a sense stuck with what we've got.  We can't change the ice properties, so have to fully understand them in order to accurately predict the shape of the neutrino signal we should expect.  That is the main purpose of the ice studies.  The idea is simple.  We transmit a well understood and reproducible pulse (with pulser and a LPDA) and study what we receive (with an oscilloscope and another LPDA).  The received signal has propagated down through the ice-sheet, reflected off the ice-water interface and then gone back up to the surface.  Thus, if we deconvolve the effect of the electronics and antenna from the received signal, any differences with the transmitted signal are due to properties of the ice.  To study the uniformity of the ice properties in the vicinity of the stations we repeated the same procedure of transmitting and receiving the signal but changed the location.  Then the received signals at the different locations can be compared and contrasted to look for ice difference.  Since we made the setup portable, we were able to move it at a number of different random locations away from camp.  These studies will confirm previous ice measurements establish the degree of uniformity of the properties of the ice at the ARIANNA site.

With our hard drives full of interesting data and the stations running great, it was time to break down camp and get back to McMurdo to take a hot shower that we had all felt desperate for.  Two days before our scheduled helo pick-up, a wolfer flew in to help us take the camp down.  With her help we made a berm of wooden crates full of equipment that is wintering over.  Everything was cleaned, packed and ready for the day of our departure, except our personal sleep tents.  On the day of the flight we took down the personal tents in time for a 3pm departure.  Unfortunately, the helo that was supposed to pick us up had mechanical issues and was grounded for the day.  That caused the helo schedule to fall behind.  We ended up being picked up around 9pm.  Luckily, that day was almost windless and sunny so spending the time outside wasn't a problem.  It was a good opportunity to reflect on our season, enjoy the scenic Transantarctic Mountains, and take lots of pictures.

 Many showers later, all of our stations are running great, and sending high-quality data we are in the process of analyzing.  The race to get ready for the next season has started and preparations for the 2015-2016 season are well on their way.  While preparing for another deployment, we are also hard at work analyzing data and summarizing physics results from the data we collected in a number of papers the ARIANNA collaboration will publish in the not so distant future, so stay tuned!

The 2014/2015 ARIANNA field season

The ARIANNA 7-station hexagonal array is now complete, thanks to an outstanding field season!  I didn't get to go on this, but here is a guest post from Joulien Tatar, who did.  The photos are by Chris Persichilli:

This was the last season for ARIANNA R&D work in Antarctica and it was a great one.  We successfully accomplished all of the tasks we had hoped to do this year and more.  ARIANNA is now ready to transition from the R&D phase by scaling up to the full array of ~1500 stations in an effort to detect cosmogenic neutrinos.

The deployment team this season (2014-2015) consisted of 5 physicists from UC Irvine:  Steve Barwick (PI), Corey Reed (Project Scientist: i.e. glorified postdoc :), James Walker (grad student), Chris Persichilli (grad student) and myself Joulien Tatar (postdoc).  Needless to say all of us were really excited to be going to Antarctica.  Chris and James were even more so since this was their first trip down. 

Even though preparation for the following season always begins as soon as we get back from the previous deployment, getting to Antarctica is much simpler than one would think.  NSF has excellent subcontractors who take care of the whole process (plane tickets, luggage, hotels, clothing, etc) of getting us safely to McMurdo, the main USAP base, and then back home.

Before flying with a USAP cargo plane (actually a US Air Force C-17) to McMurdo from Christchurch, New Zealand, we spent a couple of days going through safety briefings and getting appropriate clothing for the weather in Antarctica.  In between our scheduled tasks, we had time to explore Christchurch.  Steve was heartbroken.  He was last in Christchurch before the earthquake.  Most of the historic structures, charming coffee shops, lively bars and restaurants he used to frequent are gone.  However, I saw Christchurch come a long way from the rubbles it was in when I first visited in Nov. 2011, eight months after the major tremor.  Then, Downtown, where most of the structural damage took place, was completely fenced off and guarded by military personnel.  There was destruction everywhere you looked.  Now most of downtown has been rebuilt.  New businesses are opening throughout the city.  People have come back and things seem to be back to normal.  There is rarely chatter about the earthquake any more.

After a couple of days in Christchurch, we left for McMurdo.  Sometimes, the head winds are too high or the weather in McMurdo is poor for landing so the plane has to turn back.  This time we were fortunate to make it to McMurdo on our first try.  We spent about a week in McMurdo.  We had more briefings and training to go through while waiting for all of our cargo, shipped by boat, to make its way to McMurdo so we can leave for our field camp.  The station this year was at maximum capacity.  Many projects that were supposed to take place during the 2013-2014 season were delayed a year due of the government shutdown.  As a result, this year the USAP had to catch up and provide support for more projects than typical.

It took 6 helicopter flights to fly all of the components for the new stations and the rest of our electronics equipment.  Two wilderness first responders (wolfers) went to the ARIANNA site (in Moore's Bay on the Ross Ice Shelf) a day ahead of us to set up camp.  This was great because it allowed us to make every day count by starting work as soon as we arrived at camp.

Not long after we flew to the field camp, the wolfers went back to McMurdo.  The five of us, physicists, were alone on a remote Antarctic ice-sheet fully prepared to fend for ourselves and each other.  This is the first season we have camped without a wolfer.  The important help we were accustomed to getting from them was now all on us.  We had to make sure we always had melted snow for water, cleaned the two common tents (kitchen tent and science tent), check-in with McMurdo daily, cook, etc etc...

Cooking was one of the most time consuming and difficult chores we had.  We would each rotate to cook and clean for a day.  So one person would cook for everyone once every five days, which was not too bad.  Cooking in a small tent with a very limited amount of spices and ingredients (all provided to us from McMurdo) requires a certain amount of ingenuity it turns out we all possess.  The food we made was delectable and we managed not to burn down the tent.  We wrote down our food recipes so they can be used by the deployment team for years to come. :)

Our primary science objective was to have seven stations up and running and collecting high quality data.  That effort began by assembling station components that we did not ship pre-assembled.  The most time-consuming part of the assembly process was the power tower.  It consisted of putting together two ~10' triangular metal segments, mounting a 100W solar panel, and attaching two communication antennas.  It is as simple as it sounds and it took less than an hour to do.  Everything else (battery, antennas, electronics box with DAQ) came pre-assembled.  Once we had all of the components laid out and thoroughly tested, we were ready to take them to their final installation location.  Each station was placed at a corner of a hexagon and has a spacing of ~1km from the center of the hexagon where the seventh station (and our base camp) was located.  The transportation of the station was almost effortless, since we were given a sled we could load everything into and pull it with a snowmobile.  At a station's site we would first install the power tower and then dig four vertically oriented triangular slots to place the antennas in.  Digging these ~6' deep and 2' wide holes with a shovel was the most labor intensive and time consuming (1 hour) process of the station installation.  Once the holes were dug, we placed the Log-periodic Dipole Antennas (LPDA) in them, connected the various cables (power, communication, and LPDA) to the electronics box we placed at the base of the power tower, and had data streaming all the way back to our UC Irvine data server!  It took us less than 4 hours to install a station.  If we started installation a bit after breakfast, the station would be up and running before it was time for lunch.

To be continued in part 2...