Particle accelerator

A particle accelerator is a machine that uses electromagnetic fields to propel ions to very high speeds. These ions are contained in well-defined beams. Scientists use these machines to study the fundamental structure of matter, space, and time. By creating high-energy collisions, researchers can investigate how the smallest building blocks of the universe behave.

There are more than 30,000 accelerators operating around the world today. They range from tiny devices to massive machines stretching for miles.

There are two basic classes of accelerators: electrostatic and electrodynamic. Electrostatic accelerators use static electric fields to move particles. In these machines, the particle passes through the potential difference only once. Because of this, the energy is limited by the accelerating voltage. This voltage is restricted by electrical breakdown. Common examples include the Cockcroft–Walton generator and the Van de Graaff generator.

Even old television sets used a small electrostatic accelerator called a cathode-ray tube.

Electrodynamic accelerators, also called electromagnetic accelerators, use changing electromagnetic fields. These fields can be created through magnetic induction or oscillating radio frequency (RF) fields. Because particles can pass through the same accelerating field multiple times, the output energy is not limited by the strength of the field. This class of technology was first developed in the 1920s. It serves as the foundation for most modern, large-scale accelerators.

Many scientists helped pioneer the field of electrodynamic acceleration. These pioneers include Rolf Widerøe, Gustav Ising, Leó Szilárd, Max Steenbeck, and Ernest Lawrence. They were responsible for building the first operational linear particle accelerator and the cyclotron.

In the 20th century, these machines were often called "atom smashers." This was because they targeted the atoms of matter to study their nuclei. Today, many machines collide subatomic particles instead of whole nuclei.

Particle physics research requires extremely high energies. Physicists often use beams of leptons, such as electrons and positrons, or quarks. Because quarks cannot be isolated due to color confinement, scientists study them by colliding nucleons. Nucleons are composed of quarks and gluons. To achieve these studies, machines create beams of protons and antiprotons at energies of hundreds of GeV or more. The Large Hadron Collider (LHC) at CERN is the largest and highest-energy machine used for this purpose.

It can accelerate proton beams to 6.5 TeV and cause them to collide head-on, creating center-of-mass energies of 13 TeV.

Accelerators are vital for many different scientific fields. In nuclear physics, scientists use beams of bare atomic nuclei to study the structure of nuclei. They also study condensed matter at extreme temperatures and densities, similar to the early Big Bang. The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory is a major tool for this work. Additionally, electrons moving through magnetic fields emit synchrotron radiation. This bright light is used to study biology, chemistry, and atomic structure.

Many synchrotron light sources exist globally, such as the ESRF in France or the Diamond facility in the UK.

Beyond fundamental research, accelerators have many practical applications. About 44% of all accelerators are used for radiotherapy to treat cancer. This is known as particle therapy. Another 41% are used for ion implantation, which is necessary to manufacture semiconductors and integrated circuits.

They are also used for industrial processing and biomedical research. For example, electron beams are used for the sterilization of medical devices. Because electron beams provide a high dose rate, they can sterilize items quickly while reducing polymer degradation.