Feature - People behind the LHC: Mariusz Sapinski
Mariusz Sapinski is part of the Accelerators and Beams Department for the Large Hadron Collider, (LHC) where he models what happens inside a supercooled magnet hit by high-energy protons. “It has the potential to be a very violent process, leading to magnet destruction,” he said, “and requires a lot of computing power to simulate—and prevent.” The bearded, Poland-born physicist described his work on the eve of a crucial test in one of the sections of the LHC.
iSGTW: What do you do at the LHC?
MS: “I try to reconstruct on a computer the physical processes happening inside the supercooled magnets (1.9 K above absolute zero), by measuring the temperature increase inside a magnet using outside monitors. What might happen inside a supercooled magnet because of the accidental deviation of even a small part of the proton beam is a very violent process, in which all of the energy stored in the magnet is converted to heat within microseconds.”
“It’s a tricky business. You have a high-energy beam of 362 megajoules, or the energy equivalent of 90 kg of TNT, right next to something supercold. It’s like having boiling hot water contained inside a piece of ice, only our ‘water’ is 1 quadrillion times hotter, and our ice is 300 times colder.”
“And you don’t want any spillover of heat from the beam to the magnet, because if that happens, then the magnet loses its superconductivity, or ‘quenches,’ and the LHC has to shut down. Then, you have to wait for two to four hours for the magnet to cool enough to start again.”
iSGTW: What happened in the previous test?
MS: “That was a big one. Things had to be very precise, with all the optics, magnets, fields and the beam itself lined up precisely; If they are off at all, it won’t work. They had allowed several hours, and instead they got it all on the first shot. So everything lined up precisely.”
“You have a tight window in which to operate, from 1.9 to 9 K, before quenching occurs. I was happy to see that my simulations of what would happen when a beam passes through were very, very close to what happened in real life.”
From astrophysics to ATLAS
iSGTW: What will happen with the next test?
MS: “The last time was just one octant of the circle with a clockwise beam, and there are still some things that we want to tweak in terms of optics and the polarity of a magnet. This next shot will be counter-clockwise, on a different octant. And once you know that you can inject well, then you know that 10 September for a fully circulating beam can be a reality.”
iSGTW: How did you get into this?
MS: “I worked on ATLAS for my PhD, then to astrophysics for five years on a project for the space station called the Alpha Magnetic Spectrometer, which aims to measures anti-matter in space. (It’s actually being assembled here at CERN.) I am now back here at CERN, which is the most fascinating place to be for a physicist now.”
iSGTW: Is astrophysics similar to what you are doing now?
MS: “From a technical point of view, they’re quite similar, in that I’m doing simulations that reconstruct physical processes, and they both require massive computing power to predict what is happening.”
iSGTW: How did you become interested in physics?
MS: “I always loved physics. When I was 15, I read a book about quantum mechanics, and became fascinated by how the smallest element behaves completely differently from what you see in the macroworld. It's a whole other world.”
—Dan Drollette, iSGTW