synchrotron

The synchrotron is the design behind essentially every high-energy accelerator today, from the Large Hadron Collider down to the bright X-ray light sources used by chemists and biologists. Its name comes from the key idea: everything stays synchronized. Picture a fixed circular racetrack — not a spiral like the cyclotron, but a single ring of constant radius — around which a bunch of particles is steered lap after lap, gaining energy each time.

The cyclotron's spiral has a built-in size limit, so the synchrotron throws it away and keeps the particles on one fixed ring. The catch is that, as the particles speed up, you must steer them harder to keep them on the same circle. So the bending magnets are ramped up in strength in perfect step with the rising beam energy, and the timing of the radio-frequency pushes is adjusted too — that synchronized ramping of magnets, accelerating fields, and beam is exactly what the name describes. Because the ring radius is fixed, the magnets can hug a thin doughnut-shaped beam pipe rather than fill a huge disk, which is far more economical at large size.

This is why the highest-energy machines are synchrotrons. They reuse the same accelerating cavities and bending magnets thousands of times per second, so a beam can pile up to enormous energy over many laps. The trade-off is that bending a beam in a circle makes it radiate energy (synchrotron radiation), a loss that grows fast for light particles and ultimately limits how high a circular electron machine can go. For heavy protons that loss is far smaller, which is why the very highest-energy colliders accelerate protons in rings.