The LHC: the world’s purest diamond and my 50 micron contribution to a 17 mile tunnel

With the recent news of the successful startup of the large hadron collider (LHC) at CERN, I’m reminded that I actually worked on a small piece of it back in the late 1990s, in one of my former lives as a graduate student at Ohio State University.  The LHC is the new, big, expensive, high energy particle accelerator, a 17 mile long tunnel that will accelerate particles to very high speeds, ultimately making collisions which will  mimic the conditions of the early universe just after the big bang. 

My own tiny piece of the project involved making tracking devices to detect the particles ejected from these high energy collisions. These tracking devices consist of a thin slab of insulating or semiconducting material, with a grid of tiny metal wires running horizontally on one side and vertically on the other.  When a high energy particle comes tearing through, it ionizes atoms in the material, creating small voltages on the nearby wires.  By monitoring the voltages on all of the wires, scientists can measure the precise x-y location of the high energy particle.  The actual detector at the end of the 17 mile long tunnel consists of many thousands of these devices, arranged in a sphere surrounding the area where the collision occurs.  By accurately tracking all of the particles ejected from a collision, scientists can work backwards to understand the physics of the collision itself.

In an accelerator as powerful as the large hadron collider, the spray of ejected particles would basically shred ordinary tracking devices, which are normally made of silicon.  I worked briefly with the RD42 collaboration to help develop tracking devices made of diamond, which is much less susceptible to radiation damage.  As part of the project, the group helped develop very high purity synthetic diamonds made by a chemical vapor deposition (CVD) technique.  The chemical and electrical purity of these diamonds easily surpasses that of any naturally occurring diamond on the earth, and at one point I actually held in my hand what at the time was the most perfect diamond the world had ever seen.  (It looked like a small piece of glass, about a centimeter square, maybe a couple of millimeters thick.) 

I helped the group to perform the lithography required to pattern the diamond’s surfaces with a dense array of 50 micron gold wires, about the thickness of a human hair.  (It was a fairly standard application of existing lithography technology, made only slightly trickier by the roughness and optical properties of the diamond surface.)  Interestingly, I never set out to be a high energy physicist, and initially I didn’t have anything to do with the group working on the LHC at Ohio State University.  At the time, I was actually using lithography to attach electrodes to tiny superconducting crystals for a completely unrelated experiment; I just happened to be the local expert there when the LHC group needed some help to prepare for some upcoming “beam time” at another accelerator.  I took time away from my normal Ph.D. work to help them out, and it ended up being a very interesting and ultimately successful collaboration.

The moral of the story, for those of you who like that sort of thing, is to pay attention to what your colleagues are working on, even if it seems unrelated to what you’re doing.  There may be connections to your own work that aren’t so obvious.  The LHC is a huge project, and many thousands of people have contributed to it; I sometimes wonder how many of those are accidental contributors like me.  Accidental or not, I’m proud to have played even a tiny technical part in the experiment, and I look forward to the new physics it will tell us.

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Matt Trawick holds a B.A. from Oberlin College and a Ph.D. from Ohio State University. He was a postdoctoral fellow and later a lecturer at Princeton University before coming to the University of Richmond as an assistant professor in 2004. His research interests include block copolymers, nanotechnology, and atomic force microscopy.

One thought on “The LHC: the world’s purest diamond and my 50 micron contribution to a 17 mile tunnel”

  1. And now diamonds are the key to next-gen supercomputers, which in turn can be used to build even bigger colliders.

    Science Daily — “Diamond sheets filled with holes could be the key to the next generation of supercomputers. Scientists in California have used commercially available technology to pattern large sheets of diamonds with tiny, nitrogen-filled holes. The nitrogen-vacancy diamonds, as the sheets are called by scientists, could store millions of times more information than current silicon-based systems and process that information dozens of times faster.”

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