The Large Hadron Collider is the most powerful particle accelerator ever built,
sending protons whipping around its tunnels at velocities near the speed of light,
and employing enormous magnets to steer those intense beams. And now silicon crystals are poised to do their part to help pilot protons around the LHC.
It’s tough to keep all those highly energetic particles in line; there’s always some
that manage to break away from the pack, creating a kind of halo that can
damage the magnets and detectors, as well as interfering with data collection
by adding to the background noise.
Physicists employ elaborate systems known as collimators to corral those wayward particles and steer them out of the beam pipe into a target that absorbs the excess energy.
Choosing the right materials with just the right properties is critical for optimal performance, especially since those subatomic particles generate a lot of heat. The LHC’s collimators are made of a carbon composite, but a few particles still manage to elude the system, and they can make several hundred trips around the ring before finally being caught.
Physicists on CERN’s UA9 collaboration think that replacing those with tiny silicon crystals could improve the reliability of the proton beams even further, by capturing errant particles more efficiently thanks to their highly ordered crystalline structure and their small size — some 300 times smaller than the collimators currently in use.
But first the UA9 scientists had to prove the crystals could withstand the massive temperatures generated within the accelerator, despite their smaller size. So they used CERN’s Super Proton Synchrotron accelerator to blast the crystals with 450 billion electron volts, and were pleased to find they didn’t melt or suffer significant damage from those high energies.
The second potential obstacle was the need to properly orient the silicon crystals, depending on the specific energy of the proton beam being used. The scientists were able to “bend” the crystals to the precise angles necessary, setting the stage to scale up their prototype silicon crystal system to the LHC when it resumes operation in 2014.
“We had two very strong technological challenges, and both have been solved this year,” UA9 spokesperson Walter Scandale told Symmetry Magazine, expressing confidence that transitioning to the LHC should occur smoothly, “with no major difficulty.”
Image: A silicon crystal in its mount. Credit: UA9 collaboration