Storage ring

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A small storage ring at SLAC. This particular storage ring is one of two small storage rings or circular cyclotrons. This section is located in the beginning of the machine and is called the south damping ring used to damp the beams down to suitable dimensions.

A storage ring consists of a circular ring in which a particle beam or charged particles on a beamline from a particle accelerator can be kept circulating almost indefinitely. Storage of a particular particle is based on the mass of the particle being stored. These rings are typically used to store electrons (or their anti-matter partners, positrons) or protons. It is very common that two storage rings will be combined in such a way that the particles rotate in opposite directions, and are deliberately brought in order to create particle collisions. A detector will be located at this point for the purposes of observing the results of the collisions. Another very common use for storage rings is in the generation of synchrotron light for biological or chemical experiments.

A storage ring is a type of synchrotron.

1 Important Considerations for Storage of a particle beam
2 See also

[edit] Important Considerations for Storage of a particle beam

[edit] Magnets

A force must be applied to the beam in such a way that it moves in the (almost) circular orbit required to keep it in the machine. Since the particles are charged, they will experience a force as they move through a magnetic field, so specific arrangements of magnets may be used for this purpose. Dipole magnets are used for beam steering.

Since bunches of particles have a tendency to grow apart with time -- due to the initial random motion of the particles, the bunch will grow larger and larger until it hits the wall of the vacuum chamber and is lost -- magnets must be installed in order to focus the beam. Quadrupole magnets are used for this, as the charged particles in the bunch will experience a larger force (towards the centre of the bunch) the further they are from the magnetic axis as they pass through the quadrupole. Thus particles a long way from the centre of the bunch will experience a large force back to the correct position.

As dipole and quadrupole magnets will have a stronger effect on lower energy particles, any energy spread in the bunch will begin to appear as a spread in the transverse and longitudinal size of the bunch. Sextupole magnets (and higher order magnets) are used to correct this effect -- known as chromaticity.

For a synchrotron, the magnets are sequenced according to the Chasman-Green lattice.

[edit] Vacuum

As the bunches will travel many thousands of kilometers (considering that they will be moving at near the speed of light for many hours), any residual gas in the beam pipe will result in many, many collisions. This will have the effect of increasing the size of the bunch, and increasing the energy spread. Therefore, a better vacuum yields better beam dynamics.

[edit] Timing

The timing of the release of the beam and the storage duration are important.

Typically there are pulsed magnets in a storage ring to kick a beam into the ring (called Injection kicker magnets) and to kick a beam out of the ring (called Extraction kicker magnets). These magnets are driven by a high voltage modulator to produce magnetic fields with very fast rise and fall times (so that the field is only present when the bunch chosen for extraction/injection is passing, and not the previous or subsequent bunches).

An accumulator ring is slightly different from a storage ring.