Back in the fall of 2008, the Large Hadron Collider experienced a setback when a section of the liquid helium coolant exploded. Aside from the damage caused by the explosion, there was damage to the electrical system. The lack of coolant resulted in a loss of superconductivity, which caused the temperature of the conductors to rise to damaging levels — the conductors were still carrying thousands of amps of current, but their resistance had increased by several orders of magnitude. Ohm, the humanity!
To help prevent such an occurrence in the future, the LHC team has begun installing special shunts, which will help lower the resistance of the conductors at non-cryo temperatures, in order to prevent similar damage from happening again.
On 19 September 2008, during powering tests on the Large Hadron Collider (LHC), a fault occurred in a superconducting interconnection between two magnets – a dipole and a quadrupole – resulting in mechanical damage and release of helium from the magnet cold mass into the tunnel. Proper safety procedures were in force, the safety systems performed as expected, and no-one was put at risk. But the fault did delay work on the LHC by six months.
After the incident, CERN engineers decided that such interconnections should be upgraded to avoid similar electrical faults in future. As a precaution, beams in the LHC were accelerated below the LHC’s design limit for the first three years of running. Upgrading the interconnections will be one of the main activities at the LHC during its two-year shutdown, allowing the LHC to run at 7 TeV per beam when it starts up again.
There are 10,000 “splices” – superconducting connections between magnets – on the LHC. Each splice carries 13,000 amps.
In the video above, Jean-Phillipe Tock of the Technology department explains how, over the next 18 months, technicians will add an additional piece – a “shunt” – to each splice. The shunt is a low-resistance connection that forms an alternative path for a portion of the current in the event that the splice loses its superconducting state. A total of 27,000 shunts will be installed in the 27-kilometre accelerator.