Page 2/2 - Posted June 22, 2012
Liquid helium era may be coming to an end at South Pole
The first step in limiting the loss of liquid helium was to retrofit the old cryogenics barn, basically a plywood shell of a building, during 2000-2001 to get the three 4,000-liter Wessington dewars inside a climate-controlled environment.
“They just sat at ambient [before]. If a seal failed, game over. This was a controlled environment,” Sullivan said.
Eventually, a new cryo facility was completed during the 2005-06 summer season. About the same time, South Pole Station personnel started working with the dewar manufacturer and Cryomech, a cryo-refrigeration company, on designing and building a system to re-liquefy the helium from its gas phase.
The zero boil-off system has worked so well that the science support staff at South Pole Station is in conversation with the only other group in the U.S. Antarctic Program (USAP) that uses bulk helium to adapt a similar process. NASA’s Long Duration Balloon (LDB) facility near McMurdo Station flies in 2,000-liter liquid helium dewars as needed for launching instrument packages — basically, balloon-borne telescopes — into the stratosphere above Antarctica.
The LDB facility, however, doesn’t have the recapture system that South Pole has developed.
“Once you get the helium down there, don’t let it boil away,” Sullivan said. “The logistical cost, labor and everything is very high.”
Cost was certainly a factor in convincing the National Science Foundation (NSF) , which manages the USAP, to buy into the re-liquefecation system. For many years, Sullivan noted, the relatively low price of the bulk liquid helium and the high price of fuel required to power a closed-loop refrigeration system at the South Pole didn’t make economic sense.
Photo Credit: Daniel Luong-Van/Antarctic Photo Library
The South Pole Telescope employs a cryo-refrigeration system that doesn't require bulk helium.
Now: “It’s worth the trade-off in power to save the helium and support the science,” Sullivan said.
In addition, the heat generated by the refrigeration compressor is fed into a glycol loop. “It’s basically heating the [Cryo facility] off of the waste heat of the system,” Sullivan explained.
Experiments like the South Pole Telescope (SPT) and the newly installed South Pole Upgrades for DASI (SPUD) telescope array also employ cryo-refrigeration systems that dump excess heat into their building’s glycol loop to heat the structure.
“While our re-liquefecation system worked really well in the last few years, the overall trend in astronomy instrumentation was to move from liquid helium to the dedicated cryo-refrigerating systems serving a particular telescope,” said Vladimir Papitashvili, program director for Astrophysics and Geospace Sciences in NSF’s Office of Polar Programs .
“These systems are similar to what we used for the re-liquefecation system, but the overall cost of cooling telescopes in a new way became really attractive,” he added. “That is why the ‘liquid helium’ era for telescopes is coming to an end at South Pole.”
The Background Imaging of Cosmic Extragalactic Polarization 2 (BICEP2) telescope , an experiment looking for signs of the rapid inflation of the universe hypothesized to have happened fractions of a second after the Big Bang, is the last instrument at the South Pole to require bulk helium deliveries. This winter is its last operational season.
At its peak, the station was using 27,000 liters of liquid helium in one year. This year, the stations expects to supply about 8,000 liters.
Whether that’s the end of bulk liquid helium deliveries to the South Pole is another matter. The station compresses some of the boil-off into gas cylinders. The meteorology department launches weather balloons using the gaseous helium. NOAA also benefits by launching ozone instruments from its nearby Atmospheric Research Observatory using the compressed helium gas.