As physicists developed plans for building an Electron-Ion Collider (EIC) — a next-generation nuclear physics facility to be built at the U.S. Department of Energy’s Brookhaven National Laboratory for nuclear physics research — they explored various options for accelerating the beams of electrons. One approach, developed by scientists at Stony Brook University and Brookhaven National Laboratory, was to use an energy-recovery linear accelerator (ERL).
The ERL would bring the electrons up to the energy needed to probe the inner structure of protons and atomic nuclei, and then decelerate the electrons and reuse most of their energy. The R&D to develop the innovative ERL may end up having a major impact in a different area of physics — high-energy particle physics, where the power needs make its energy-saving features particularly attractive.
In a paper just published in the journal Physics Letters B, the authors describe how their innovations could tame the power requirements of an electron-positron (e-e+) collider — a next-generation high-energy particle physics research facility under discussion for possible future construction in Europe.
The ERL would be made of superconducting radiofrequency (SRF) cavities, and act as “a perpetuum-mobile of some kind invented in 1960s by Maury Tigner at Cornell University,” explained Vladimir Litvinenko, a professor of physics at Stony Brook with a joint appointment at Brookhaven Lab. “The main advantage of SRF cavities is that they consume very little energy while operating. They are perfectly suited to accelerate new particles by taking energy back from used particles,” he explained.
The particle physics community is in the early stages of planning for a possible future electron-positron collider, including discussing various designs and locations. In each of these setups, the facility would bring beams of negatively charged electrons (e-) into collisions with their positively charged antimatter counterparts, known as positrons (e+), to conduct precision studies of the properties of the Higgs boson. That’s the particle discovered at the Large Hadron Collider (LHC) in Europe in 2012 that is responsible for imparting mass to most fundamental particles in the Standard Model of particle physics.
“Learning more about the Higgs particle’s properties and interactions with other particles would help scientists unravel the mechanism behind this important foundation of how our universe works, and possibly uncover discrepancies that point to the existence of new particles or ‘new physics,’” said Brookhaven physicist Maria Chamizo-Llatas, a co-author on the paper.
One of the possible designs is a “storage ring” 100-kilometers in circumference based at Europe’s CERN laboratory (home to the 27-kilometer circular LHC). Beams of electrons and positrons would circulate through the storage ring continuously and collide repeatedly to produce the desired data. An alternate design would consist of two large linear accelerators that produce straight-line, head-on smashups.
Power requirements for both of these setups are approaching hundreds of megawatts, Roser said — enough energy to power hundreds of thousands of homes.
In a storage ring, Roser noted, lots of energy gets lost as “synchrotron” radiation, a type of energy emitted by charged particles as they change direction moving around the circle (picture the way water sprays off a wet towel if you swirl it around above your head). “The higher the energy, the greater the synchrotron energy loss,” Roser said — and the greater the need to make up that loss by adding more energy to keep particles colliding.