Ionization cooling
Encyclopedia
Ionization cooling is a process by which the beam emittance
of a beam of particles may be reduced
.
In ionization cooling, particles are passed through some material. The momentum of the particles is reduced as they ionize atomic electrons in the material. Thus the normalised beam emittance is reduced. By re-accelerating the beam, for example in an RF cavity, the longitudinal momentum may be restored without replacing transverse momentum. Thus overall the angular spread and hence the geometric emittance in the beam will be reduced.
Ionization cooling can be spoiled by stochastic physical processes. Multiple Coulomb scattering in muons as well as nuclear scattering in protons and ions can reduce the cooling or even lead to net heating transverse to the direction of beam motion. In addition, energy straggling can cause heating parallel to the direction of beam motion.
and a Muon Collider. Muon ionization cooling is expected to be demonstrated for the first time by the Proof of Principle International Muon Ionization Cooling Experiment
. Other PoP muon ionization cooling experiments have been devised.
as a dispersive prism
to divide the particles by energy, and then passing the resultant "rainbow" beam though a tapered wedge of cooling material. Thus, faster particles are cooled more and slower particles are cooled less. A simple way is to fill the dipole itself with cooling material, so that more energetic particles following a larger orbit pass are cooled more.
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 beam of particles may be reduced
.
In ionization cooling, particles are passed through some material. The momentum of the particles is reduced as they ionize atomic electrons in the material. Thus the normalised beam emittance is reduced. By re-accelerating the beam, for example in an RF cavity, the longitudinal momentum may be restored without replacing transverse momentum. Thus overall the angular spread and hence the geometric emittance in the beam will be reduced.
Ionization cooling can be spoiled by stochastic physical processes. Multiple Coulomb scattering in muons as well as nuclear scattering in protons and ions can reduce the cooling or even lead to net heating transverse to the direction of beam motion. In addition, energy straggling can cause heating parallel to the direction of beam motion.
Muon cooling
The primary use of ionization cooling is envisaged to be for cooling of muon beams. This is because ionization cooling is the only technique that works on the timescale of the muon lifetime. Ionization cooling channels have been designed for use in a Neutrino FactoryNeutrino Factory
The Neutrino Factory is a proposed particle accelerator complex intended to measure in detail the properties of neutrinos, which are extremely weakly interacting fundamental particles that can travel in straight lines through normal matter for thousands of kilometres...
and a Muon Collider. Muon ionization cooling is expected to be demonstrated for the first time by the Proof of Principle International Muon Ionization Cooling Experiment
International Muon Ionization Cooling Experiment
The International Muon Ionization Cooling Experiment is a high energy physics experiment dedicated to observing ionization cooling of muons for the first time. This is a process where by the beam emittance of a beam is reduced in order to reduce the beam size, so that more muons can be accelerated...
. Other PoP muon ionization cooling experiments have been devised.
Other particles
Ionization cooling has also been proposed for use in low energy ion beams and proton beams.Longitudinal cooling
The technique can be adapted to provide longitudinal as well as transverse cooling by using a dipole magnetDipole magnet
A dipole magnet, in particle accelerators, is a magnet constructed to create a homogeneous magnetic field over some distance. Particle motion in that field will be circular in a plane perpendicular to the field and collinear to the direction of particle motion and free in the direction orthogonal...
as a dispersive prism
Dispersive prism
In optics, a dispersive prism is a type of optical prism, normally having the shape of a geometrical triangular prism. It is the most widely-known type of optical prism, although perhaps not the most common in actual use. Triangular prisms are used to disperse light, that is, to break light up into...
to divide the particles by energy, and then passing the resultant "rainbow" beam though a tapered wedge of cooling material. Thus, faster particles are cooled more and slower particles are cooled less. A simple way is to fill the dipole itself with cooling material, so that more energetic particles following a larger orbit pass are cooled more.