Researchers at the ALPHA experiment at CERN made major news today with the announcement that they’ve trapped antimatter atoms for 1,000 seconds. That’s more than 16 minutes and 5,000 times longer than their last published record of two tenths of a second.
The ALPHA magnet being wound at Brookhaven
The new feat will allow scientists to study the properties of antimatter in detail, which could help them understand why the universe is made only of matter even though the Big Bang should have created equal amounts of matter and antimatter.
These studies have been made possible, in part, by a bottle-like, anti matter-catching device called a minimum magnetic field trap. At the heart of the trap is an octupole (eight-magnetic-pole) magnet that was fabricated at Brookhaven Lab in 2006.
Several special features of the coil design and a unique machine used to wind it contributed to the success of this magnet. For example, the magnet generates a very pure octupole field, which keeps the antimatter away from the walls of the trap, preventing them from annihilating.
Antiprotons and positrons are brought into the ALPHA trap from opposite ends and held there by electric and magnetic fields. Brought together, they form antiatoms neutral in charge but with a magnetic moment. If their energy is low enough they can be held by the octupole and mirror fields of the Minimum Magnetic Field Trap.
To figure out how many antiprotons were in the trap, the scientists “quench,” or abruptly switch off the superconducting magnet, releasing the antimatter. The anti-atom’s subsequent annihilation into particles called pions is recorded by a three-layer silicon vertex detector similar to those used in high-energy experiments like Fermilab’s Tevatron and the Large Hadron Collider.
But the pions must travel through the magnets of the trap before reaching the silicon. To prevent the particles from scattering multiple times during their journey to the detector, Brookhaven physicists and engineers had to figure out how limit the amount of material used in the magnet. A specially developed 3D winding machine allowed the researchers to build the magnet directly onto the outside of the ALPHA vacuum chamber. The result is a magnet that looks far different from the bulky, steel-surrounded instrumentation in most particle colliders. In fact, only the superconducting cables are metal.
–Kendra Snyder, BNL Media & Communications
