Particle Physics Instrumentation (“Gadgeteering”)

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Simulated Black Hole event superimposed on a photo of the ATLAS detector. ATLAS Experiment © 2016 CERN

Compared to many fields of modern science, particle physics has more than its fair share of glamour. Over the last ten years media interest in the Large Hadron Collider, the discovery of the Higgs Boson, and the efforts of Brian Cox and others have transformed what was an obscure niche of nerdom into a super-trendy academic pursuit. What was once only talked about in university physics departments, has now become a topic of conversation in fashionable bars—and more importantly, in schools—around the world.

This public interest is driven by the experimental side of the subject. Journalists struggle to explain the workings of the Higgs mechanism to their readers, if they try at all, but the importance of the subject is clearly conveyed by the sheer scale of the experimental effort behind the LHC. The world’s largest particle accelerator accelerates proton beams around a 27 kilometre tunnel beneath the French-Swiss border. Yet it is not just the colossal engineering that makes it special. After all, civil engineering projects like the London Crossrail link have a similar scale, both in size and budget. It is the fact that we combine the technology and engineering to look into the fundamental mysteries of the Universe which makes particle physics special and lets our experiments inspire a sense of awe.

The beams are made to collide at four main detectors at points around the ring. The size and complexity of the ATLAS detector—a photo of which in stuck on many school classroom walls—is frequently likened to a cathedral, not just because it is on the same scale as Notre Dame in Paris, but because it represents a pinnacle of culture of our age. The work of thousands of researchers from around the world.

A puritanical theorist might feel that this focus on the instrument, rather than the science, misses the point, yet this focus is the reality of working in experimental particle physics. It is sometimes said that one percent of a typical experimentalist’s time is spent thinking about the interactions of fundamental quanta. The remaining ninety-nine percent is devoted to the more practical issues of how to test these theories: How to pump the air out of your apparatus to a pressure a million times lower than that outside, how to cool a detector to a temperature colder than outer space, and then how to feed in enough wires to measure the signal, without picking up interference from all the other electronic gadgets.

This is the job of particle physics instrumentation. Every field of research has its instruments. Astronomers have huge telescopes to catch the photons from the first galaxies. Climate scientists have satellite probes scanning the Earth in infra-red to monitor the tiniest fluctuations in temperature. Biologists have optical and electron microscopes. Particle physicists have our accelerators, which boost the energy of protons and electrons to the point where things become interesting, and particle detectors to see the results. There is also a long list of associated sensors and gadgets needed to run these experiments.

In this blog, I want to discuss the fascinating science done at particle physics experiments, but I also want to describe the instrumentation used to do it, including silicon detectors, superconducting magnetometers, scintillating crystals. I want to describe the many layers of the collider detectors, and the other experiments in underground laboratories around the world. Gadgeteering is a word I picked up in First Light—Richard Preston’s 1987 book on the astronomers working at the Hale telescope in California. Astronomy instrumentation—or gadgeteering—is an equal fascinating subject. One which I could very well have ended up working in. Instead my career led me to the post of Detector Development Scientist. Every field has its gadgeteers. If particle accelerators are the cathedrals of the modern age, then we are the craftsmen and stonemasons who built them.

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