Unlike the spiral motion of a cyclotron, particles move around a circle inside a synchrotron. (Think NASCAR races on a circular track.) As the particles accelerate, the electromagnetic field in the ring increases to keep pace.
A synchrotron beam isn’t continuous. Instead, particles are clustered into “bunches.” Each bunch is shaped like a small, ultrathin noodle. The bunch could be a few centimeters long, but only a tenth of a millimeter wide.
These bunches contain something like 1012 particles, a density that still falls far short of the number of atoms that would be in an actual noodle of that size.
The Next Frontier: Higher Luminosity and Smaller Machines
From CERN’s massive and complex LHC, which holds the record for largest machine ever built, to comparatively run-of-the-mill linacs in hospital X-ray rooms, we’ve become very good at building particle accelerators.
So, where do we go from here? Have we reached the limit on what we can build or what accelerators can do? The answer is a resounding no.
There are many roads for advancing accelerator physics. Two with far-reaching potential are increasing beam luminosity and making accelerators very, very tiny.
Why luminosity matters
One indicator of accelerator performance is luminosity. It provides a metric for how many interactions you can see and how much data you can produce, which means more potential for discoveries of new physics.
That potential is the focus of the High Luminosity LHC (HL-LHC) project. According to CERN, the project “will allow physicists to study [known] mechanisms in greater detail, such as the Higgs boson, and observe rare new phenomena that might reveal themselves.”
Scheduled to start operation in 2027, it aims to increase luminosity by a factor of 10 over the original LHC’s design value. Experts estimate the upgrade will produce 15 million Higgs bosons annually. That’s up from the three million the LHC made in 2017. Increasing this number is important for scientists at CERN, as detectors can only clearly observe a small fraction of the Higgs bosons that are produced.
Making many more bosons could lead to observations that expand on the Standard Model of particle physics, changing our understanding of the most basic building blocks of matter.
Researchers are also making accelerators smaller than ever. One example is the accelerator-on-a-chip—a nanoscale particle accelerator made by Stanford University researchers. Presently in the proof-of-concept stage, it demonstrates that accelerators can be made cheaper and smaller than behemoths like the LHC.
“The largest accelerators are like powerful telescopes. There are only a few in the world and scientists must come to places like SLAC to use them,” electrical engineer and team lead on this project Jelena Vuckovic said in a Sci Tech Daily article. “We want to miniaturize accelerator technology in a way that makes it a more accessible research tool.”
Along with that accessibility, making accelerators more compact has manifold possibilities in other applications. Today, X-ray machines take up whole rooms, perhaps with technology like this they could be made portable. Perhaps cancer therapies could be made cheaper with easier-to-manufacture equipment.
One thing is certain, from the largest to the smallest, the future of accelerators is one of vast possibility for both fundamental science and industry application.