Radiation damping
Encyclopedia
Radiation damping in accelerator physics
is a way of reducing the beam emittance
of a high-velocity beam of charged particles.
There are two main ways of using radiation damping to reduce the emittance of a particle beam—damping rings and undulators—and both rely on the same principle. They induce synchrotron radiation
to reduce the particles' momentum, then replace that with momentum in the desired direction of motion.
, thereby reducing the size of their momentum vectors without changing their orientation (ignoring quantum effects for the moment). Included around the ring are accelerating sections that replace the energy lost to the synchrotron radiation in such a way that the momentum vector of the particle will be restored to its original size, but will make a smaller angle with the desired trajectory.
Because tight corners enhance synchrotron radiation, damping rings are often small. When a long beam of particles is needed, to fill a large particle accelerator, the damping ring may be extended with long straight sections.
or wiggler
magnets to induce more synchrotron radiation. These are devices with periodic magnetic fields that cause the particles to oscillate transversely, equivalent to many small tight turns. These operate using the same principle as damping rings and this oscillation causes the charged particles to emit synchrotron radiation, which is then replaced in accelerating sections.
The many small turns in an undulator have the advantage that the cone of synchrotron radiation is all in one direction, forward. This is easier to shield than the broad fan produced by a large turn.
Accelerator physics
Accelerator physics deals with the problems of building and operating particle accelerators.The experiments conducted with particle accelerators are not regarded as part of accelerator physics. These belong to particle physics, nuclear physics, condensed matter physics, materials physics, etc...
is a way of reducing the beam emittance
Beam emittance
The beam emittance of a particle accelerator is the extent occupied by the particles of the beam in space and momentum phase space as it travels. A low emittance particle beam is a beam where the particles are confined to a small distance and have nearly the same momentum...
of a high-velocity beam of charged particles.
There are two main ways of using radiation damping to reduce the emittance of a particle beam—damping rings and undulators—and both rely on the same principle. They induce synchrotron radiation
Synchrotron radiation
The electromagnetic radiation emitted when charged particles are accelerated radially is called synchrotron radiation. It is produced in synchrotrons using bending magnets, undulators and/or wigglers...
to reduce the particles' momentum, then replace that with momentum in the desired direction of motion.
Damping Rings
As particles are steered around a closed loop ( not necessarily circular), the lateral acceleration causes them to give off synchrotron radiationSynchrotron radiation
The electromagnetic radiation emitted when charged particles are accelerated radially is called synchrotron radiation. It is produced in synchrotrons using bending magnets, undulators and/or wigglers...
, thereby reducing the size of their momentum vectors without changing their orientation (ignoring quantum effects for the moment). Included around the ring are accelerating sections that replace the energy lost to the synchrotron radiation in such a way that the momentum vector of the particle will be restored to its original size, but will make a smaller angle with the desired trajectory.
Because tight corners enhance synchrotron radiation, damping rings are often small. When a long beam of particles is needed, to fill a large particle accelerator, the damping ring may be extended with long straight sections.
Undulators and Wigglers
When faster damping is required than can be provided by the turns inherent in a damping ring, it is common to add undulatorUndulator
An undulator is an insertion device from high-energy physics and usually part of a largerinstallation, a synchrotron storage ring. It consists of a periodic structure of dipole magnets . The static magnetic field is alternating along the length of the undulator with a wavelength \lambda_u...
or wiggler
Wiggler (synchrotron)
A wiggler is an insertion device in a synchrotron. It is a series of magnets designed to periodically laterally deflect a beam of charged particles inside a storage ring of a synchrotron...
magnets to induce more synchrotron radiation. These are devices with periodic magnetic fields that cause the particles to oscillate transversely, equivalent to many small tight turns. These operate using the same principle as damping rings and this oscillation causes the charged particles to emit synchrotron radiation, which is then replaced in accelerating sections.
The many small turns in an undulator have the advantage that the cone of synchrotron radiation is all in one direction, forward. This is easier to shield than the broad fan produced by a large turn.
External links
- SLAC damping rings home page, including a non-technical description of the damping rings at SLAC.
- Studies Pertaining to a Small Damping Ring for the International Linear Collider, a report describing the constraints on minimum damping ring size.