A microtron is a type of

particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel electric charge, charged particles to very high speeds and energies, and to contain them in well-defined particle beam, beams. Large accelerators are used for fun ...

concept originating from the

cyclotron A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: J ...

in which the accelerating field is not applied through large D-shaped electrodes, but through a

linear accelerator A linear particle accelerator (often shortened to linac) is a type of particle accelerator that accelerates charged subatomic particles or ions to a high speed by subjecting them to a series of oscillating electric potentials along a linear b ...

structure. The classic microtron was invented by

Vladimir Veksler Vladimir Iosifovich Veksler (russian: Владимир Иосифович Векслер; ; March 4, 1907 – September 22, 1966) was a prominent Soviet experimental physicist. Biography Veksler was born in Zhitomir on March 4, 1907 in the ...

around 1944. The kinetic energy of the particles is increased by a constant amount per field change (one half or a whole revolution). Microtrons are designed to operate at constant field

frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from '' angular frequency''. Frequency is measured in hertz (Hz) which is ...

and

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and t ...

in the

ultrarelativistic limit In physics, a particle is called ultrarelativistic when its speed is very close to the speed of light . The expression for the relativistic energy of a particle with rest mass and momentum is given by :E^2 = m^2 c^4 + p^2 c^2. The energy of an ...

. Thus they are especially suited for very light elementary particles, namely

electrons The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary partic ...

. In a microtron, due to the electrons' increasing momentum, the particle paths are different for each pass. The time needed for that is proportional to the pass number. The slow electrons need one electric field oscillation, the faster electrons need an integer multiple of this oscillation.

Racetrack microtron

A racetrack microtron is a larger-scale microtron which uses two electromagnets instead of one. Both electromagnets supply a homogeneous magnetic field in a half-circle formed region, and the particles path between both magnets is thus straight. One advantage of this is that the accelerator cavity can be larger, enabling the use of different

(linac) forms, and is not installed in a region with large magnetic fields. The linac is placed near the edge of the gap between the dee-shaped magnets. The remainder of the gap is used for focusing devices. The electron is readmitted to the linac after each revolution. This procedure can be repeated until the increasing

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

of the particle's path makes further acceleration impossible. The particle beam is then deflected into an experiment area or a further accelerator stage. The world's largest racetrack-microtron is the

Mainz Microtron The Mainz Microtron (German name: ''Mainzer Mikrotron''), abbreviated MAMI, is a microtron (particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel electric charge, charged particles to very high ...

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MAMI-Prospectus
p. 13ff

Applications

Microtrons provide high-energy electron beams with a low

beam emittance In accelerator physics, emittance is a property of a charged particle beam. It refers to the area occupied by the beam in a position-and-momentum phase space. Each particle in a beam can be described by its position and momentum along each of ...

(no radiation equilibrium) and a high repetition rate (equal to the operation frequency of the linac).

References

Accelerator physics Soviet inventions