Long Shutdown 1

LHC shuts down: 2-year maintenance period begins

16 February 2013

The news on the CERN website posted 18 February 2013:

On Saturday at 8.25am the shift crew in the CERN Control Centre extracted the beams from the Large Hadron Collider (LHC) for the last time before the machine's first Long Shutdown. The following message marked the event on LHC Page 1: "No beam for a while. Access required: Time estimate ~2 years."

January's proton-lead run was followed last week by four days of proton-proton collisions at 1.38 TeV. Final proton collisions in the LHC took place on Thursday at 7.24am, but beams were kept in the machine for 48 hours for "quench tests" on the magnets.

A quench is when a superconducting magnet fails to maintain a superconducting state, and therefore stops operating correctly. This can happen if a tiny amount of the beam is off orbit and deposits energy in the magnets. The tests aimed to establish what beam loss is actually required to quench the magnets.

The LHC now enters its two-year shutdown, which will see a hive of maintenance activity on all of CERN's accelerators. Work on the LHC will include the consolidation of more than 10,000 interconnections between magnets. The entire ventilation system for the 628-metre circumference Proton Synchrotron will be replaced, as will over 100 kilometres of cables on the Super Proton Synchrotron.

It's going to be a busy shutdown.

Long Shutdown 1

27,000th electrical shunt in place on the LHC

5 May 2014

From the CERN website, posted 5 May 2014:

Since April last year, the Superconducting Magnets And Circuits Consolidation (SMACC) team has been strengthening the electrical connections of the superconducting circuits on the Large Hadron Collider (LHC). Last week they installed the last of 27,000 electrical shunts to consolidate "splices" – connections between superconducting magnets – on the accelerator.

Each of the LHC's 10,000 splices carries a hefty 13,000 amps. A shunt is a low-resistance connection that provides an alternative path for a portion of the current in the event that a splice loses its superconducting state.

On 19 September 2008, during powering tests on the LHC, a fault occurred in one of the splices, 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 operation of the accelerator by six months. The new shunts make such a fault unlikely to happen again.

To install a shunt the SMACC team first has to open the area around the interconnection they want to work on. They slide the custom-built metallic bellows out of the way and remove the thermal shielding inside, revealing a series of metallic pipes linking the magnets to each other. One set of these pipes – the "M-lines" – must then be cut open to access the splices between the superconducting cables. The team opened up the last of the M lines in February and has been at work ever since adding the shunts.

Check out some more of the main LHC consolidations

Long Shutdown 1

Cooling down: The LHC is filled with liquid helium at 4K

17 December 2014

From the CERN website, posted 17 December 2014:

Last week the cryogenics team at CERN finished filling the arc sections of the Large Hadron Collider (LHC) with liquid helium. The helium, which is injected into magnetsthat steer particle beams around the 27-kilometre accelerator, cools the machine to below 4 degrees kelvin (-269.15°C).

The process of filling the LHC is an important milestone on the road to restarting theaccelerator at higher energy, though it will still take many weeks to cool the entire accelerator to its nominal operating temperature of 1.9 K (-271.3°C).

The electromagnets that steer particle beams around the LHC must be kept cold enough to operate in a superconducting state – the temperature at which electricity can pass through a material without losing energy to resistance. The niobium-titanium wires that form the coils of the LHC’s superconducting magnets are therefore maintained at 1.9 K by a closed liquid-helium circuit. This is colder than the average temperature – 2.7 K – in outer space.

Some 1232 dipole magnets will produce a magnetic field of 8.33 tesla to keep particle beams on course around the LHC's 27-kilometre ring. A current of 11,850 amps in the magnet coils is needed to reach magnetic fields of this amplitude. The use of superconducting materials has proved to be the best – and most cost-effective – way to avoid overheating the coils.

Find out more:

Long Shutdown 1

First LHC sector up to full energy

26 February 2015

From the CERN website, posted 9 December 2014: 

Target energy achieved ! On Tuesday 9 December at 2.18 p.m., a key milestone in the restart of the world’s largest and most powerful particle accelerator was passed. Sector 6-7 of the Large Hadron Collider has been commissioned to a beam energy of 6.5 TeV. The 154 superconducting dipole magnets which make up this sector – corresponding to one eighth of the accelerator – were powered to a current of around 11,000 amps! These currents (about a thousand times greater than in your average household appliance) are needed to generate sufficiently high magnetic fields to bend the trajectory of particles with an energy of 6.5 TeV. It’s at this unprecedented beam energy that the LHC will restart next spring with the aim of producing collisions with a total energy of 13 TeV.

From 2010 to 2013, the LHC ran at beam energies of up to 4 TeV. This first run produced a rich harvest of results in hitherto uncharted areas of physics and, in particular, led to the discovery of the famous Higgs boson. But the LHC was designed to operate at even higher energies and, to achieve this, the machine was shut down for almost two years for the main magnet circuits to be consolidated. This involved reinforcing 1,700 magnet interconnections, including more than 10,000 superconducting splices. So the commissioning of the modified sectors of the accelerator with the higher-intensity currents needed to reach 6.5 TeV beams is a key milestone in the restart process.

Like top athletes, the LHC magnets have to undergo a strenuous training programme to reach the required energy. The magnets are superconducting, which means that when they are cooled down current passes through them with zero electrical resistance. During training, the current is gradually increased and as it circulates inside the magnet coils the forces generated can cause tiny movements, which can in turn cause the magnets to “quench”,  i.e. suddenly return to a non-superconducting state. When this occurs, the circuit is switched off and its energy is absorbed by huge resistors.

The magnets in all the other sectors will undergo similar training before being ready for 6.5 TeV operation. Many other tests will follow before beams can circulate in the LHC once more, next spring.


Long Shutdown 1

Testing the injection lines on the LHC

26 February 2015

From the CERN website, posted 24 November 2014:

Over the weekend, proton beams came knocking on the Large Hadron Collider's (LHC) door. Shooting from the Super Proton Synchrotron (SPS) and into the two LHC injection lines, the proton beams were stopped just short of entering the accelerator. 

Although the actual physics run will not start until 2015, the LHC Operations team used these tests to check their control systems, beam instrumentation, transfer line alignment, perform the first optics measurements and to spot possible bottle necks in the beam trajectory. Furthermore, the ALICE and LHCb experiments could calibrate their detectors.

"These initial tests are a milestone for the whole accelerator chain," says Reyes Alemany Fernandez, the engineer in charge of the LHC. "Not only was this the first time the injection lines have seen beams in over a year, it was also our first opportunity to test the LHC's operation system. We successfully commissioned the LHC's injection and ejection magnets, all without beam in the machine itself."

Just before entering the LHC, the beams were stopped by 21.6 tonnes of graphite, aluminium and copper "beam dumps" that absorb the accelerated particles. Offshoot particles - primarily muons - generated during the dump were in turn used to calibrate ALICE and LHCb. "The experiments where given the precise timing of each beam dump, which allowed them to tune their detectors and trigger to the LHC clock," says Verena Kain, SPS supervisor. 

Following these successful extraction tests, the Operations team return to their preparations for the next run of the LHC. The first LHC tests with beams are scheduled for February 2015.

Read more: "The proton beam knocks at the LHC door– Update by the LHCb experiment collaboration

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