Wi-Fi and the Origins of the Universe

By Gerry Blackwell

February 26, 2007

CERN's underground experiments to recreate Big Bang conditions required a mesh network to monitor equipment the size of a building.

The Large Hadron Collider (LHC), part of the massive particle physics lab at CERN, the European Organization for Nuclear Research (and the birthplace of the Internet), will later this year host some of the most audacious scientific experiments ever conceived. And Wi-Fi will play a vital role.

In fact, Wi-Fi already has played a vital role.

The LHC includes a 27-kilometer circular tunnel 50 to 175 meters below the surface near Geneva, Switzerland, plus an underground lab the size of a small village, as well as fantastically complex and delicate detectors -- some as big as small office blocks and weighing hundreds of tons.

In the experiments, slated to begin later this year, beams of protons or heavy ions rotating around the LHC tunnel in opposite directions at close to the speed of light will collide, smashing into smaller constituents – hadrons, electrons, muons, photons. The detectors will measure the results.

The object? To recreate conditions a fraction of a second after the Big Bang that scientists believe created the universe billions of years ago, to try and work out what happened -- and also to study high-energy particle interactions and, just maybe, observe new particles and phases of matter, including the basic building blocks of the material world.

This facility is riddled with Wi-Fi networks, an estimated 300 access points in all, most from Proxim Wireless. Not only do the number of APs mean that interference is a major problem, but much of the scientific equipment also interferes. Which is why CERN’s network gurus have turned to Wi-Fi mesh technology for a number of applications, including one mind-boggling maneuver during site construction.

The requirement was to move the huge detector for the ATLAS experiment – the size of a five-story building – from the surface down a 100-meter shaft to the lab. The trick was that the incredibly fragile detector could not tilt or absorb vibration, even a tiny bit. That meant that the crane lowering it had to be controlled very precisely, based on feedback on the detector’s progress down the shaft.

The solution the project team came up with involved a unique Wi-Fi mesh network that would relay data from sensors on the detector to computers that engineers could use to calculate adjustments in crane controls, which would guide the operator.

Using mesh technology was vital for a couple of reasons, says Olaf van der Vossen, the engineer responsible for network infrastructure at CERN. One is the ability -- with dual-radio mesh access points -- to switch between using 2.4GHz and 5.8GHz spectrum to avoid interference, and the ability of the network to dynamically reroute data when the path between two access points becomes “polluted” with interference. Another crucial benefit was ease of setup.

“The [Proxim] mesh network builds itself,” van der Vossen says. “You switch it on, make sure the access points are positioned such that they can form a group, and then the mesh will form itself, even heal itself if you take one access point out. That makes it relatively simple to install and get working.”

Network designers used nine mesh access points to build the network that would guide the ATLAS detector down its shaft: six in the cavern and three others on the way down – one on the detector itself, two on the shaft. It took almost six hours to move the detector very slowly down the shaft. It arrived safe and sound at the bottom.

Why did CERN choose Proxim equipment for such a delicate application? Not even Proxim manager of international business development Robert Veenis claims that it’s because the company’s mesh technology is radically different from or superior to competing vendors’ products.

“They’ve had good experience with [Proxim] equipment, and also good experience with us helping them solve ‘funny’ problems,” Veenis explains. “They have really stretched out [our] equipment to the maximum of its capabilities.”

The mesh network equipment is still in constant use at CERN. One network is closed and dedicated to the accelerator and the ATLAS detector. Another is publicly accessible. It takes six mesh APs and a few fixed APs to cover the entire 400-by-200-meter cavern. Scientists and others in the facility also use the mesh APs to create temporary networks – such as when they need to go into the walkways alongside the LHC tunnel.

“That’s one of the big advantages of using mesh technology,” says Veenis. “It lets you very quickly create a wireless network without installing cables to connect access points to the network.”

Today, the ATLAS detector is in place, awaiting the start of the experiments. CERN recently announced that it had successfully powered up the electromagnetic system that will guide the beams around the Large Hadron Collider’s circular track. The first proton collisions are scheduled to occur in November 2007.  

ATLAS will observe and measure what happens, generating terabytes of data per second in the process. Wi-Fi isn’t quite up to moving that much data – but perhaps it will be in the future.

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