This is why you should always tidy up as you go along.
CERN, home to the Large Hadron Collider, has grand plans to update the world's largest particle accelerator complex in the next few years. But engineers have identified a barrier to the upgrade: there's no space for new cables in the injectors that accelerate particles before they enter the LHC.
In the past, when parts of the accelerators have been upgraded or added to, engineers would often additionally replace the cables that connected them. In the process, they would leave in place the old cables that were no longer in use. Now, a heap of obsolete cables are blocking the way to install new ones needed for the accelerator's next big upgrade. To make space, CERN engineers have set out to identify and remove the old, unused cables. All 9,000 of them.
Telling apart functioning and out-of-use cables in one of the world's biggest and most expensive experiments is a high-stakes game. Pull out the wrong cable, and at best you might have lost some data monitoring capabilities. Worst case scenario, you might yank out a crucial safety cable and the accelerator simply won't work. "That's why it's so tricky to complete this operation—because any mistake could start major trouble at the restart of the accelerator," Sébastien Evrard, the mechanical engineer leading the clean-up project, told me.
CERN wants to install new cables as part of its LHC Injectors Upgrade Project (LIU), one of the key projects scheduled for the LHC's next long shutdown in 2019. In preparation, Evrard's team of 60 is attacking the mess of cables in three of the collider's injectors: the Proton Synchrotron Booster (PS Booster), the Proton Synchrotron (PS), and the Super Proton Synchrotron (SPS). These are all part of a chain of machines that accelerate particles into the beams that eventually transfer into the LHC.
"Of course, in an ideal world we would remove the old and obsolete cables before installing new ones, but this was not the case," Evrard said. "Today, all the cable containments—the cable trays that are housing all these cables—are really crowded, and it's no longer possible to add new cables."
The engineers can only work on the machines themselves during the annual technical stop, which lasts a couple of months in winter. They started disconnecting cables in the PS Booster in December, and are now moving in on the SPS too. They won't actually remove the cables until the next technical stop at the end of this year, both because they won't have time and because they want to make extra sure they haven't disrupted the functioning of the machines before getting rid of any cables completely.
Evrard said that, on paper, the team had identified about 3,000 obsolete cables in each injector—9,000 in total. In the PS Booster itself, they have already found and disconnected 2,700 of those documented as obsolete. "So we are confident at the end of the day we will reach 8,000 cables in total that will have been prepared, that will be ready for removal next year," Evrard added.
Each cable in the PS Booster is about 50 metres long, travelling from the surface buildings at CERN's Geneva base down underground to the injector
The process of finding and removing the cables is painstaking. Evrard admitted it was "not sexy" work, and it had been difficult to motivate people to undertake the massive housekeeping task until the upcoming LIU project highlighted its necessity.
The cables they're dealing with are generally associated with control systems and safety systems, which have undergone many technological upgrades since CERN was first established in 1954. The proton synchrotron, the oldest of the three accelerators targeted in this project, was first put in operation in 1959, long before the Large Hadron Collider was built.
These old cables could have been intended for any of a myriad of tasks, such as carrying data to an accelerator or sending signals to open a valve on a vacuum system, for example. The large power supply cables are not included in the project—they're more permanent, and usually intended to work over the equipment's lifetime.
Over the years, Evrard said CERN had a "not-so-good habit" of simply leaving old cables in situ when they were replaced, and piling the new ones up top. Now, removing the old ones is not as straightforward as you might think. Each cable in the PS Booster, for instance, is about 50 metres long, travelling from the surface buildings at CERN's Geneva base down underground to the injector. "That's why we started to identify and disconnect this year and next year we will remove them," said Evrard.
The engineers started the process in June by referring to a CERN database that documents every cable's technical features, function, and location. They compiled a list of all cables thought to be associated with obsolete systems. "But of course the database is not 100 percent reliable, so it means in the second step we have to go onsite and check the correct location of all these expected obsolete cables to see if they are really obsolete or still in use," explained Evrard. "From the experience we've got in the past few weeks, we can say that about two percent of the cables that were expected to be obsolete are in fact still in use."
Before the accelerators restart at the end of February, all of the equipment will be checked and double-checked to make sure everything's in place. The epic housekeeping operations will still be far from over, however. "It is something that started this year and will resume every annual technical stop until the end of 2020," said Evrard. "It's not a one-year operation; it will last for four years in fact, because it's a huge job."
Watch more: The Large Hadron Collider Returns in the Hunt for New Physics