The role magnets play in physics research is a critical one, helping guide the trajectory of particle beams that allow for high-speed collisions and groundbreaking discoveries. But not all magnets are create equal, with some quicker to generate the required magnetic fields than others. Physicists at the Fermi National Particle Accelerator Laboratory have developed one that outstrips all before it in this regard, and used it to demonstrate what they describe as the world’s fastest ramping rates for particle accelerator magnets.
Magnetic fields inside devices like the Large Hadron Collider (LHC), the world's most powerful particle accelerator, help keep the particles on track as they whizz around the circular chamber at close to the speed of light. The higher the energies at play, the stronger the magnetic fields needed to keep the experiments running, with the LHC calling for magnetic fields of around eight tesla.
But the superconducting magnets responsible for generating this field take around 20 minutes to reach that level, gently ramping up at a rate of around 0.006 tesla per second. Particle accelerators that use magnets with copper conductors at room temperature, rather than superconducting wire, are able to ramp up at far greater speeds. These include the world's highest intensity neutron beam at J-PARC in Japan, which charges up at a rate of 70 tesla per second, and Fermilab's own 8-GeV booster ring, which ramps up at 30 tesla per second.
One problem with using superconducting magnetics for these purposes is the formation of large hot spots that increase with the field amplitude and the rate of ramping. There is also an inherently small margin for error in terms of the operating temperature of traditional superconducting materials, with it only taking a small increase in temperature for them to transition to their normal conducting and resistive state.
The Fermilab scientists believe they have found a solution to this problem in a material known as yttrium barium copper oxide (YBCO), known for its high-temperature superconductivity and, as we saw back in 2011, its potential in the field of magnetic levitation. Using this material, the team built a magnet that could operate at temperatures between six and 20 Kelvin, and could handle 1,000 amps of electrical current.
Putting this new high-temperature, superconducting magnet to the test, the team showed it could ramp up at a rate of 290 tesla per second, and achieve a peak magnetic field strength of around 0.5 tesla. This is obviously a far cry from the eight tesla on show at the LHC, but the scientists say a higher field strength can be achieved by dialing up the electrical current running through the magnet.
The scientists will continue experimenting with their creation, working to expand the power supply and possibly achieve even higher ramping rates. They see the technology playing a role in all sorts of future experiments, including neutrino research and the planned 100-km (62-mile) Future Circular Collider that could be up and running by 2040.
Source: Fermilab