Electron cooling is a method to shrink the

emittance Emittance may refer to: *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 ...

(size,

divergence In vector calculus, divergence is a vector operator that operates on a vector field, producing a scalar field giving the quantity of the vector field's source at each point. More technically, the divergence represents the volume density of t ...

, and energy spread) of a charged particle beam without removing particles from the beam. Since the number of particles remains unchanged and the space coordinates and their derivatives (angles) are reduced, this means that the

phase space In dynamical system theory, a phase space is a space in which all possible states of a system are represented, with each possible state corresponding to one unique point in the phase space. For mechanical systems, the phase space usual ...

occupied by the stored particles is compressed. It is equivalent to reducing the temperature of the beam. See also stochastic cooling. The method was invented by

Gersh Budker Gersh Itskovich Budker (Герш Ицкович Будкер), also named Andrey Mikhailovich Budker (1 May 1918 – 4 July 1977), was a Soviet physicist, specialized in nuclear physics and accelerator physics. Biography He was elected a Correspo ...

at INP, Novosibirsk, in 1966 for the purpose of increasing luminosity of

hadron In particle physics, a hadron (; grc, ἁδρός, hadrós; "stout, thick") is a composite subatomic particle made of two or more quarks held together by the strong interaction. They are analogous to molecules that are held together by the ele ...

collider A collider is a type of particle accelerator which brings two opposing particle beams together such that the particles collide. Colliders may either be ring accelerators or linear accelerators. Colliders are used as a research tool in particle ...

s. It was first tested in 1974 with 68 MeV protons at NAP-M storage ring at INP. It is used at both operating ion colliders: the

Relativistic Heavy Ion Collider The Relativistic Heavy Ion Collider (RHIC ) is the first and one of only two operating heavy- ion colliders, and the only spin-polarized proton collider ever built. Located at Brookhaven National Laboratory (BNL) in Upton, New York, and used by ...

and in the Low Energy Ion Ring at CERN. Basically, electron cooling works as follows: * A beam of dense quasi-monoenergetic electrons is produced and merged with the ion beam to be cooled. * The

velocity Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity i ...

of the electrons is made equal to the average velocity of the ions. * The ions undergo

Coulomb scattering In particle physics, Rutherford scattering is the elastic scattering of charged particles by the Coulomb interaction. It is a physical phenomenon explained by Ernest Rutherford in 1911 that led to the development of the planetary Rutherford model ...

in the electron “gas” and exchange

momentum In Newtonian mechanics, momentum (more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If is an object's mass ...

with the electrons.

Thermodynamic equilibrium Thermodynamic equilibrium is an axiomatic concept of thermodynamics. It is an internal state of a single thermodynamic system, or a relation between several thermodynamic systems connected by more or less permeable or impermeable walls. In ther ...

is reached when the particles have the same momentum, which requires that the much lighter electrons have much higher velocities. Thus, thermal energy is transferred from the ions to the electrons. * The electron beam is finally bent away from the ion beam.

References

*: The

Fermilab Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a United States Department of Energy United States Department of Energy National Labs, national laboratory specializing in high-energy parti ...

br> Electron Cooling Project
Accelerator physics Soviet inventions {{accelerator-stub