linacs

A linear accelerator, or linac, is a device that uses oscillating electric fields to accelerate charged particles along a straight, evacuated tube. Particles gain energy each time they pass through an accelerating gap, with the radio frequency field synchronized to the particle’s arrival. Linacs can accelerate electrons, protons, or other ions, and their output beams are used directly or as injectors for larger accelerators.

Typical linac designs include an electron gun or ion source, a chain of RF cavities arranged in accelerating sections, focusing elements such as magnets or solenoids, beam diagnostics, and a vacuum and RF power system. Structures may operate in traveling-wave or standing-wave modes and use normal-conducting or superconducting cavities. The choice of frequency, gradient, and technology influences efficiency, cost, and beam quality.

Applications span medicine, industry, and research. In medicine, linacs generate high-energy electron or photon beams for external-beam radiotherapy, enabling treatments for a wide range of cancers. In industry, electron linacs are used for sterilization, materials processing, and non-destructive testing. In physics, linacs serve as injectors for larger accelerators, drive free-electron lasers, or enable experiments in beam dynamics and accelerator technology.

Historically, the concept dates to early 20th-century work by Widerøe and later development by Lawrence and others. Modern clinical linacs deliver energy ranges suited to therapy, typically several MeV for electrons and photon energies up to around 25 MV, while proton and heavier-ion linacs provide hundreds of MeV to GeV-scale energies for advanced therapy and research.