A little more than 1 year ago, the Muon g–2 (pronounced “g minus two”) storage ring set out on an epic journey. Beginning at Brookhaven National Laboratory in Upton, New York, it traveled 5000 kilometers down the Atlantic coast, up three rivers, and across several highways to reach its new home at Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois. The ring is a key part of an experiment to measure a property called magnetic moment in muons, much heavier subatomic-particle relatives of electrons. Scientists saw tantalizing hints of new physics during Muon g–2’s first run at Brookhaven from 1999 to 2001. But to be sure, they need to run the experiment again with Fermilab’s more powerful muon beam—which is why they moved the 15-meter-wide ring halfway across the country by truck and barge. Science talks to Chris Polly, Muon g–2’s project manager, about some highlights of the trip and what’s in store for the ring at its new home. For more about Muon g–2’s journey, check out the slideshow above.
Q: What’s happened at Fermilab since the ring arrived last year?
A: Since the ring got here, we’ve been constructing the new home for the magnet. It needs a building with very special temperature and floor stability requirements, and there wasn’t any place here that would accommodate it. After the ring was successfully transported, the work to construct the experimental hall got going at 100%.
Just last week, we rolled the magnet out once again. We had [hauling company] Emmert International come out and help us with the final leg of the journey. They brought it out on Saturday morning around 8 o’clock and towed the ring about a mile to the new building.
Then, of course, they needed to get it into the building. We were clever enough to remember to design a hole big enough for it to fit through. There’s no door that you could possibly make that would accommodate it, since it’s 50 feet [15 meters] wide. It kind of looked like a giant CD player, when the whole ring just went sliding into the side of the building on a rail system. Inside, it still looks like the ring is levitating, because it’s on some scaffolding as they slowly lower it down to the experimental floor, which is about 16 feet [5 meters] below ground level.
Q: What was the hardest part of the moving process?
A: From my perspective, one of the hard parts was finding the right vendor for the job: a transportation company that could safely move this magnet and would have the political skills necessary for all the hurdles when it comes to trying to move a 50-foot-wide thing through areas where nothing that wide has ever been transported before. That was quite a task, but Emmert International was fantastic to work with. In fact, we’re going to meet their crew at the bar in about 2 hours for a beer.
Q: What was the scariest moment?
A: When the barge was coming up Cape Hatteras, there was a storm blowing up and the wave data started getting bigger, and bigger, and bigger. And we’re like, “Oh, man.” Cape Hatteras is well known as a shipping graveyard. So we made the decision to pull up into Norfolk and wait out the storm before we continued.
Q: The most exciting?
A: Truly the most exciting moment by far was the reception the ring received when it arrived at Fermilab. We invited the public to come out and see it when it arrived. Three thousand people showed up. The lab eventually had to close the gates because there wasn’t any more room. To have the ring roll down by Fermilab’s reflecting ponds, and a crowd of 3000 people cheering—I don’t know how we’ll ever rival that moment in a science experiment, it was just amazing.
Q: The ring is so delicate. Do you know yet if all its systems survived the journey?
A: We’ve done all the tests we can on the ring while it’s warm and not hooked up to a cryogenic plant. You can measure the electrical resistances, put a voltage on it, make sure it’s not leaking current, check the piping systems that will hold liquid helium to make sure they’re intact. We’ve done all those basic tests and everything looks good so far.
But this is a superconducting magnet, and for it to operate, it has to be cooled down to liquid helium temperatures. That’s the name of the game for the next 6 months. We will be rapidly trying to build the superconducting systems and connect the cryogenic wires and get the power supply operational so we can do the ultimate test, which is to cool and power the magnet.
Q: When will the experiment start running?
A: You can get it cold in about 6 or 7 months. But it’s not just good enough to have a strong enough magnetic field. It also has to be an extremely uniform magnetic field. So after the magnet is powered, that immediately begins a phase where we spend 9 months to a year iteratively changing little pieces of steel, adding little pieces of wire with currents flowing through them, where we effectively try to “shim” the magnetic field—applying corrections to make it very, very uniform.
And then you still have to be able to see the muons somehow. They’re not visible to the naked eye or anything—it takes a very sophisticated set of detectors and electronics and a data acquisition system. There’s a lot to the experiment beyond just the magnet. So all those systems are being prepared.
By the time that’s all done, that’s still about 2, 2-and-a-half years from where we are today. The current start date is March 2017, but we’re hoping there are a few tricks we can play along the way that might make it go a little faster. Of course, you never know—it’s science.