LHC now colder than deep space

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The LHC tunnel

(PhysOrg.com) -- The LHC (Large Hadron Collider) is once again colder than deep space as it is prepared for experiments to resume in late November.

The LHC's eight sectors have all been cooled to 1.9 kelvin (-271 C, or -456 F) using cryogenic lines containing liquid helium. This operating temperature is colder than conditions in deep space, which is estimated to be 2.7 K. Zero K is the lowest temperature possible.

The magnets that bend particle beams around the LHC need to be this cold because at these low temperatures they become superconductors, channeling electric current with almost no power loss, and with zero resistance.

In the LHC experiments, two beams of protons will be fired in opposite directions through the ring between the magnets. They will reach close to the speed of light, and smash into one another at four collision points. The collisions are predicted to produce thousands of particles, which will be studied by the scientists, The results are expected to shed new light on the nature of the universe and its beginnings.

A magnet problem dubbed a "quench" in September 2008 resulted in the LHC particle accelerator being shut down after a tonne of liquid helium leaked into the LHC tunnel. The facility had to be warmed up to allow for the approximately $40 million in repairs to be carried out.

Now the LHC ring is cooled again magnet powering tests can be carried out. In the commissioning process the magnets are powered with gradually increasing current until the operating current of 6 kA is reached. This current is needed to guide the particle beams, which will travel at a nominal energy of 3.5 TeV.

CERN will also carry out thorough tests of components of the new quench protection system before the particle collision experiments can begin. The system comprises hundreds of new detectors designed to detect any splice malfunctions at a sufficiently early stage for the machine to be protected. The new system should prevent further incidents like the one that shut down the LHC last year.

A low intensity beam test involving parts of the collider could be carried out before November, while particle collision experiments with low intensity beams are expected in late November. If these are successful, the energy of the beams will be increased, with high energy collisions scheduled for December or January.

Director of communications with CERN, James Gillies said the high-energy collisions would require delicate operation of the accelerator. He likened the relative distances in the operation to firing knitting needles across the Atlantic and making them smash into each other half way across.

The LHC is the most powerful particle accelerator ever built. Its magnets are lined end to end in a circular tunnel 27 km in circumference, buried 50 to 175 meters underground beneath the border between Switzerland and France. Operated by CERN (European Organization for Nuclear Research) at Geneva, the facility is designed to recreate conditions immediately following the Big Bang.

More information:

• CERN bulletin: http://cdsweb.cern.ch/journal/article?issue=43/2009&name=CERNBulletin&category=News%20Articles&number=3&ln=en

• 3 Questions: Steven Nahn on the elusive Higgs boson

© 2009 PhysOrg.com

   

• Bob_Kob - Oct 20, 2009
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  Is it very well insulated or just cooled down constantly?
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• jselin - Oct 20, 2009
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  Is it very well insulated or just cooled down constantly?

  
  The extent of the former determines the ongoing cost of the latter. I'd expect it's well insulated.
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• Alexa - Oct 20, 2009
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  It's well insulated, nevertheless refrigeration power equivalent to over 140 kW at 4.5 K must be distributed around the 27 km ring. The total inventory of liquid helium is about 700,000 liters (about 120 tonnes), which is about 1% of the total annual helium production worldwide. At today's prices the entire inventory is worth over $6m, every year about 25% of the helium inventory is lost due to leaks. While this might seem a lot, it is better than previous CERN accelerators such as the LEP, some of which lost their entire inventory over the course of a year.
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• physpuppy - Oct 20, 2009
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  As Alexa stated, it needs to be insulated - vacuum at the very least. Other instruments make use of helium at these temperatures, for example at 2K :
  http://www.bruker...ech.html
  
  The above instrument (Nuclear Magnetic Resonance, technique is the "grandfather" of MRI ) uses vacuum insulation followed by a layer of liquid nitrogen at 77K to reduce the thermal gradient and which is then surrounded by another vacuum chamber and radiation reflecting material (such as mylar). At least this is what is found at lower field strengths where the cooling helium can be at 4K, perhaps some more sophisticated insulation tricks are used to keep at at the more chilly 2K.
  
  I wonder if the LHC uses a liquid nitrogen layer as well?
  
  
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• Mr_Man - Oct 21, 2009
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  As Alexa stated, it needs to be insulated - vacuum at the very least. Other instruments make use of helium at these temperatures, for example at 2K :
  http://www.bruker...ech.html
  
  The above instrument (Nuclear Magnetic Resonance, technique is the "grandfather" of MRI ) uses vacuum insulation followed by a layer of liquid nitrogen at 77K to reduce the thermal gradient and which is then surrounded by another vacuum chamber and radiation reflecting material (such as mylar). At least this is what is found at lower field strengths where the cooling helium can be at 4K, perhaps some more sophisticated insulation tricks are used to keep at at the more chilly 2K.
  
  I wonder if the LHC uses a liquid nitrogen layer as well?
  
  

  
  
  Liquid Nitrogen freezes at -321 F / -196 C so they are already at a temperature where the Nitrogen would have frozen into a solid.
  
  Liquid Helium will stay at a liquid even at near absolute zero unless under great pressures.
  
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• Daein - Oct 21, 2009
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  What bugs me is that when the machine was shut down last year they said what broke was a common failure in accelerators, but they had to warm it up so it would take much more to fix this one. Well what if this problem crops up again? No science for another year and another 40 million dollar fix?
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• Doug_Huffman - Oct 22, 2009
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  Note that Helium is produced by 'mining' and that the National Helium Reserve disestablishment was to begin in 2005 due to overwhelming debt. As the US sinks to banana 'republic' status.
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