Accelerator physics

The Tevatron (background circle) was a synchrotron collider-type particle accelerator at the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, USA. It was shut down in 2011. Before that, until 2007, it was the most powerful particle accelerator in the world. It could speed up protons to over 1 TeV (tera electron volts). Protons and antiprotons moved in opposite directions in the ring at the back and crashed into each other at two points controlled by magnets.

Animation showing the operation of a linear accelerator, widely used in both physics research and cancer treatment.

Accelerator physics is a part of science that deals with how to build and understand particle accelerators. These are special machines that use electric and magnetic fields to make tiny particles, like electrons or protons, move very fast, almost as fast as light. They also help guide and control these particles in a beam. Scientists in this field study how to design these machines, how the particles move inside them, and how to keep the beams strong and focused. This work is a mix of physics and engineering. Particle accelerators are important tools. They are used to learn more about the universe in high-energy physics, to study atoms and materials, and even to help with medical treatments, like cancer therapy.

Particle accelerators are used in many different ways. In science, they help us study the tiniest parts of matter by smashing particles together at very high speeds. Big machines like the Large Hadron Collider (LHC) in Europe and the Tevatron in the U.S. have helped scientists make big discoveries, like finding the Higgs boson. These experiments test important ideas in physics about how the universe works. In practical uses, accelerators do other helpful things. Some are used to make very strong X-rays (called synchrotron light) that help scientists study things like proteins, viruses, and materials. In medicine, special types of particle beams can be used to treat cancer, such as with proton therapy. In factories, they are also used to change materials or kill germs on products to keep them clean and safe.

Accelerator physics is all about understanding how beams of tiny particles move when they are pushed or guided by electric and magnetic fields. These fields help speed up, steer, and focus the particles. Scientists in this field study things like how to keep the beam stable and focused, how particles spread out or stay together, how to deal with energy loss (like when particles give off light called synchrotron radiation), and how to avoid problems that can make the beam unstable. They also design special equipment, like radiofrequency (RF) cavities that boost particle speed, magnets arranged in patterns (called lattices) to control the beam, and tools for getting the beam in and out of the accelerator. A big part of their job is making sure the beam is strong, precise, and does not lose too many particles along the way.

Accelerator physics has different areas, depending on the type of particle accelerator. Linear accelerators (linacs) make particles go faster in a straight line. Circular accelerators, like cyclotrons and synchrotrons, speed up particles in a circle using magnets. Plasma-based accelerators are a newer kind of technology. They use powerful lasers and plasma (a hot, charged gas) to push particles very quickly over short distances. These might lead to smaller and cheaper accelerators in the future. Scientists also use computer programs to model and test how particles will move inside an accelerator. These simulations help them improve how the machines work before building them or turning them on.

In recent years, accelerator physics has helped create special tools called free-electron lasers (FELs) and X-ray free-electron lasers (XFELs). These machines make extremely fast and powerful flashes of light, so fast they can capture events that happen in just femtoseconds (a femtosecond is a millionth of a billionth of a second). Scientists use these lasers to watch very tiny things happen in real time, like chemical reactions, how proteins move, or how atoms behave in quantum physics. One famous example is the LCLS (Linac Coherent Light Source) at SLAC in the U.S., which is one of the most advanced machines of this kind in the world.