CERN Accelerating science

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Acceleration: the process which consists of giving energy to a particle beam. This is achieved by the radio-frequency (RF) cavities

Antiproton The antimatter equivalent of the proton, with the same mass but opposite charge.

Atomic energy levels The possible energy of electronic orbitals in an atom are restricted to well-defined and discrete values. They are called the "energy levels of the atom". Their value is measured relative to the energy required to remove an electron, which is called the ionization potential of the atom

Beam: a collection of particles traveling in an accelerator, storage ring, or transfer line.

Bubble Chamber A detector filled with a liquid close to its boiling point, where the ionizing particles' trajectories materialize in the form of tracks made of bubbles.

Cloud Chamber A detector filled with a gas close to its condensation point, where the ionizing particles' trajectories materialize in the form of tracks made of droplets.

Cooling By analogy with the kinetic theory of gases where heat is equivalent to disorder, the term "cooling" designates the reduction of the beam's transverse dimensions and energy spread. Different techniques can be used to this effect. Electron cooling, more effective at low energy, uses an electron beam merged with the antiproton beam, and acts as a heat exchanger between the two beams. In the case of stochastic cooling, an error signal generated in a monitor is fed back, via a corrector, to the beam sample which created it, eventually centering the sample's characteristics towards the average value, after a large number of passages through the apparatus.

Deceleration: the process which consists of taking energy from a particle beam, analogous to "slowing it down".

Dirac, Paul Adrien Maurice British physicist (1902-1984). He worked out a version of quantum mechanics consistent with special relativity. His computations led him to predict the existence of the positron (positive electron). He shared the Nobel Prize for physics in 1933 with E.Schr´┐Żdinger.

Penning trap Device able to trap charged particles in a small volume for long periods of time (several months), thanks to an appropriate configuration of electric and magnetic fields.

Quantum mechanics The theory that energy does not have a continuous range of values, but is, instead, absorbed or radiated discontinuously, in multiples of definite, indivisible units called quanta.

Quarks Subatomic particles which possess a fractional electric charge, and of which protons, neutrons, and other hadrons are believed to be composed.

Radio-Frequency, or RF: The alternating voltage that provides (or takes) energy to (or from) the beam to accelerate (or decelerate) it.

Special Relativity The theory that the laws of nature are the same for all observers in unaccelerated motion and the speed of light is independent of the motion of its source. Einstein postulated that the time interval between two events was longer for an observer in whose frame of reference the events occur in different places than for the observer for whom they occur at the same place.

Synchrotron Modern circular accelerator, where the particles are guided by dipole magnets, focused by quadrupole magnets, and accelerated by radio-frequency electric fields.

eV,MeV,GeV The electron-Volt (eV) is the energy unit which corresponds to the acceleration of a particle having the charge of the electron through a voltage difference of one Volt. Its multiples the mega-electron-Volt (MeV) and giga-electron-Volt (GeV) respectively amount to one million and one billion electron-volts.

LEAR LEAR: CERN's Low Energy Antiproton Ring (1982-1996), where the first nine atoms of anti-hydrogen were observed.

PS CERN's Proton Synchrotron, which accelerated protons to its nominal energy of 25 GeV for the first time in 1959, it has since been upgraded to also accelerate heavy ions, leptons (electrons and positrons), and antiprotons. It is now at the heart of CERN's accelerator complex.

SPS CERN's 450 GeV Super Proton Synchrotron, which reached its nominal energy for the first time in 1976. In the eighties it was converted into a proton-antiproton collider. It is now also used as a lepton injector for LEP, and will be used as a proton injector for LHC.

ISR CERN's 30 GeV Intersecting Storage Rings (1967-1984). The first proton collider.

LEP CERN's 100 GeV Large Electron-Positron collider, started in 1989, and due to stop at the end of 2000. Its collision energy has now been upgraded to 202 GeV.