A stream of accelerated particles used in experiments.A particle beam is a directed stream of charged or neutral particles, such as electrons, protons, or ions, that are accelerated to high speeds, often close to the speed of light. Particle beams are the primary tools for probing the fundamental structure of matter in particle physics, but they also have applications in medicine, materials science, and even industrial processing. The behavior of particle beams is governed by electromagnetism and special relativity, and their manipulation requires precise magnetic and electric fields.
The concept of a particle beam emerged in the early 20th century with the development of cathode ray tubes, but the modern era began with Ernest Lawrence's invention of the cyclotron in 1931, which allowed particles to be accelerated to high energies for nuclear physics experiments.
Particles are generated in a source, then accelerated by electric fields in a linear accelerator or a circular ring. Magnetic fields steer and focus the beam, keeping the particles on a defined trajectory. As the particles gain energy, their speed approaches the speed of light, and relativistic effects become significant. The beam can be directed at a target to produce collisions, or extracted for use in experiments or applications. Beam quality is characterized by parameters like intensity, emittance (spread in position and momentum), and polarization.
Particle beams are used in cancer therapy (proton therapy), in synchrotron light sources for materials research, and in industrial accelerators for ion implantation in semiconductors.
Particle beams can be used to produce attosecond X-ray flashes, allowing scientists to capture the motion of electrons in real time.