The Large Hadron Collider, a particle accelerator in Switzerland that opened to much fanfare last week, has been shut down for at least two months due to a helium leak.
Although this accident represents a setback in groundbreaking research to understand the basic structure of the Universe, scientists are not concerned about the long-term implications of the damage.
The leak occurred at the connection between two adjacent magnets when they heated up. Powerful electrical currents that drive the magnets melted the wires as the temperature rose unexpectedly.
Particle beams consisting of fast-moving protons are accelerated in the LHC and then collided at near-light speeds. The magnets lining the collider's tunnel produce a strong magnetic field to control the path of the beam.
To achieve such field strengths, the electric currents through the coils of these giant solenoids are very high. It is necessary to cool the magnets close to absolute zero, the lowest possible temperature, to produce these fields.
At such low temperatures, the metals used in the electromagnets become superconducting, bringing their electrical resistance close to zero and dramatically increasing the strength of the magnetic fields.
This is where the helium comes into play ?- liquid helium is a powerful coolant. Other large superconducting magnets operate at four degrees Kelvin, just four degrees above absolute zero. The magnets of the LHC go down even further to 1.9 Kelvin.
"Those two degrees make a surprisingly big difference," particle physicist and Hopkins professor Barry Blumenfeld said. The Tevatron at Fermilab, a particle accelerator in Illinois with which Hopkins is affiliated, went down to four degrees Kelvin over two decades ago.
The difficult part in fixing the LHC now is not simply exchanging the few broken tunnel wall elements or magnets, but rather the process of heating up or cooling down the entire structure. "One could think of this as in Scuba diving: You want to go up and down very slowly," Blumenfeld said.
A too-rapid change in temperature could cause the structural elements to burst. Although the actual repairs might last for only a few days, the process of heating and cooling will take about two months.
"The LHC is enormously complicated and is in fact the most advanced research instrument on the surface of the planet. Assuming [you can] push a button and it will turn immediately, well you can hope for it..."
Despite the setback, Blumenfeld and his colleagues are happy the LHC was able to run at all when they initially turned it on.
Although the LHC is primarily a physics research instrument, it is also a piece of engineering art. A few hundred million electronics channels and entire halls filled with computers represent one of the most complex engineering endeavors in history. The fact that a lot of the technology used in the LHC is at the cutting edge of its field is stunning enough.
Unfortunately, the LHC was already planned to go offline in December because of the cold alpine weather, and the two months of repairs will run into that time. Blumenfeld, who spent an entire decade in Geneva as a Columbia grad student and postdoctoral fellow, recalls those "critical days" each winter.
Blumenfeld is still hopeful for at least a preliminary run of the collider before the place shuts down for the winter. "Maybe they push a little bit for the special occasion. I'd certainly like a few collisions."
