Why did the 40,000 pound superconducting magnet cross the country? The full answer to this take on the old joke is complicated, but here’s the short version: Unraveling the Secrets of the Atom.
Pristine particle tracking magnets are rare enough to count on two hands. Most of these one-of-a-kind engineering feats lie at the heart of some of history’s most ambitious physics experiments, and were designed specifically to discover new facets of matter.
Such a singular instrument recently arrived at the Brookhaven National Laboratory of the United States Department of Energy (DOE). The massive electromagnet is at the heart of proposed improvements to Brookhaven’s Relativistic Heavy Ion Collider (RHIC), which shatters particles together at near the speed of light to recreate the super-hot conditions of the early universe.
RHIC, a DOE Office of Science user facility for nuclear physics and the only operational particle collider in the United States, is currently in its 15th experimental period.
“After 14 years of discovery, RHIC remains the world’s most versatile collider and our best tool for exploring the atomic nucleus,” said Berndt Mueller, who heads the Directorate of Nuclear and Particle Physics at Brookhaven. “We have a lot more to learn about the basics, and RHIC is operating more productively than ever. We are grateful to our colleagues and collaborators at SLAC for the opportunity to give a second life to this remarkable magnet at RHIC. “
The massive solenoid, a cylindrical electromagnet that generates a precise and uniform magnetic field, has already spent nearly a decade making discoveries at the SLAC National Accelerator Laboratory in California. From 1999 to 2008, he settled inside a particle detector in SLAC’s BaBar experiment, probing the puzzling asymmetry between matter and antimatter. When BaBar finished its cycle, the SLAC stored the 20 ton solenoid for use in future experiments.
Meanwhile, across the country, physicists at the Brookhaven Lab are developing upgrades to the PHENIX detector, one of RHIC’s two main experiments. Complemented by the STAR detector, the house-sized PHENIX tracks subatomic debris to explore the particles and forces that bind most visible matter in the universe. The proposed upgrade, the result of more than four years of research and development, is called sPHENIX. The purchase of the BaBar magnet significantly lowers the cost of sPHENIX, if the proposed upgrade is approved.
“PHENIX needs a powerful solenoid to see new particle signatures inside RHIC collisions,” said Brookhaven physicist David Morrison, co-spokesperson for the PHENIX collaboration. “This type of precise and powerful instrument is incredibly difficult and expensive to build. Fortunately, our colleagues at SLAC kept their solenoid in perfect condition. So we jumped up when we heard he might be available. “
The BaBar solenoid, attached to a custom heavy truck, left SLAC on January 16 and arrived at Brookhaven’s Long Island campus late on the night of February 3.
“It was quite unreal to finally see this amazing machine arrive safe and sound at the main entrance to the lab,” said John Haggerty, the Brookhaven physicist who led the acquisition of the BaBar magnet. “We were looking forward to having him here and getting down to work on the next generation of nuclear physics experiments.”
MRI of the size of an elephant
The solenoid is 3.5 meters in diameter and 3.9 meters long, like an MRI large enough to accommodate an African elephant.
“The underlying technology is similar to an MRI – both use a uniform magnetic field to scan matter and create three-dimensional maps,” Morrison said. “But as MRI scans map our bodies, this huge electromagnet tracks broken atoms.”
The solenoid consists of superconducting cables enclosed in an aluminum shell. When these cables are cooled to 4 Kelvin – the temperature of liquid helium or about -452 degrees Fahrenheit – they generate the 1.5 Tesla magnetic field needed to track the particle debris.
Much like the 2013 move of the 50-foot-wide Muon g-2 ring from Brookhaven to Fermilab – another DOE national lab – the BaBar solenoid required special care and attention on its journey. Michael Anerella and Paul Kovach of Brookhaven’s Superconducting Magnets division worked together to plan the one-of-a-kind movement. The internal mechanics are very sensitive: each component must be perfectly aligned to maintain the precision necessary in nuclear physics.
“Our initial check of the magnet, carried out at room temperature, has been completed,” said Peter Wanderer, head of the superconducting magnets division. “The magnet has passed all of these tests. The next step, testing the magnet at superconducting temperatures, will be completed at the end of the summer.”
Mapping the primordial plasma
Subatomic collisions inside RHIC’s 2.4-mile particle racetrack reach temperatures 250,000 times warmer than the center of the sun, melting protons and releasing quarks and gluons otherwise bound to the inside the core. The resulting quark-gluon plasma, known as QGP, only exists for a tiny fraction of a second, but it filled the universe microseconds after the Big Bang and reveals otherwise imperceptible aspects of the strong nuclear force.
RHIC physicists saw the first clues they created QGP at RHIC in 2001 and were the first to reveal that it behaves like a perfect liquid with virtually zero resistance in 2005.
“We still don’t know why these subatomic particles flow as a leakage liquid or the characteristics through the phase transition from normal matter to QGP,” Morrison said.
The ongoing QGP puzzle motivates the upgrade of sPHENIX.
“A strong, uniform field allows us to track charged particles and measure their momentum with great precision,” Haggerty said. “We often look to superconducting solenoid magnets to achieve this because they can produce a strong magnetic field without putting a lot of material in the way of the particles, which could scatter them and lead to measurement errors.”
The proposed sPHENIX will specialize in part in chasing jets, the rapidly flying particles formed when the quarks and gluons released cool and bind to each other. The BaBar magnet will specifically target upsilons, the bound state of a very heavy bottom quark and its antimatter twin.
“We know the exact temperatures at which three types of upsilons melt and decompose in RHIC collisions,” Morrison said. “Tracking these upsilons – what this magnet can do – helps us map the transition from primordial QGP trillion degrees to normal matter.”
Brookhaven proposes that sPHENIX be operational to track particles by 2021.
Relativistic heavy ion collider breaks record for polarized proton luminosity
Provided by the Brookhaven National Laboratory
Quote: Giant electromagnet arrives at Brookhaven Lab to map molten matter (May 1, 2015, retrieved October 19, 2021 from https://phys.org/news/2015-05-giant-electromagnet-brookhaven-lab.html
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