page_title: Particle accelerator
section_title: Electrostatic particle accelerators
hierarchical_section_title: Particle accelerator / Electrostatic particle accelerators
caption_attribution_description: English: Photo of a Cockcroft–Walton generator in the london science museum
context_page_description: A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams.
  Large accelerators are used for basic research in particle physics. The largest accelerator currently operating is the Large Hadron Collider near Geneva, Switzerland, operated by the CERN. It is a collider accelerator, which can accelerate two beams of protons to an energy of 6.5 TeV and cause them to collide head-on, creating center-of-mass energies of 13 TeV. Other powerful accelerators are SuperKEKB at KEK in Japan, RHIC at Brookhaven National Laboratory in New York and, formerly, the Tevatron at Fermilab, Batavia, Illinois. Accelerators are also used as synchrotron light sources for the study of condensed matter physics. Smaller particle accelerators are used in a wide variety of applications, including particle therapy for oncological purposes, radioisotope production for medical diagnostics, ion implanters for manufacture of semiconductors, and accelerator mass spectrometers for measurements of rare isotopes such as radiocarbon.
context_section_description: Historically, the first accelerators used simple technology of a single static high voltage to accelerate charged particles.  The charged particle was accelerated through an evacuated tube with an electrode at either end, with the static potential across it.   Since the particle passed only once through the potential difference, the output energy was limited to the accelerating voltage of the machine.  While this method is still extremely popular today, with the electrostatic accelerators greatly out-numbering any other type, they are more suited to lower energy studies owing to the practical voltage limit of about 1 MV for air insulated machines, or 30 MV when the accelerator is operated in a tank of pressurized gas with high dielectric strength, such as sulfur hexafluoride.  In a tandem accelerator the potential is used twice to accelerate the particles, by reversing the charge of the particles while they are inside the terminal.  This is possible with the acceleration of atomic nuclei by using anions (negatively charged ions), and then passing the beam through a thin foil to strip electrons off the anions inside the high voltage terminal, converting them to cations (positively charged ions), which are accelerated again as they leave the terminal.
  The two main types of electrostatic accelerator are the Cockcroft-Walton accelerator, which uses a diode-capacitor voltage multiplier to produce high voltage, and the Van de Graaff accelerator, which uses a moving fabric belt to carry charge to the high voltage electrode.  Although electrostatic accelerators accelerate particles along a straight line, the term linear accelerator is more often used for accelerators that employ oscillating rather than static electric fields.
caption: A Cockcroft-Walton generator (Philips, 1937), residing in Science Museum (London).
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