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. A beam transport system will only allow particles that are close to its design momentum, and of course they have to fit through the beam pipe and magnets that make up the system. In a colliding beam accelerator, keeping the emittance small means that the likelihood of particle interactions will be greater resulting in higher luminosity.

Emittance has units of length, but is usually referred to as "length/angle", for example, "millimeter/milli-radians". It can be measured in all three spatial dimensions. The dimension parallel to the motion of the particle is called the longitudinal emittance. The other two dimensions are referred to as the transverse emittances.

The arithmetic definition of a transverse emittance is:

$emittance = frac\left\{6pi \left( width^2 - D\left(frac\left\{dp\right\}\left\{p\right\}\right)^2\right)\right\}\left\{B\right\}$

Where:
* width is the width of the particle beam
* dp/p is the momentum spread of the particle beam
* D is the value of the dispersion function at the measurement point in the particle accelerator
* B is the value of the beta function at the measurement point in the particle accelerator

Since it is difficult to measure the full width of the beam, either the RMS width of the beam or the value of the width that encompasses a specific percentage of the beam (for example, 95%) is measured. The emittance from these width measurements is then referred to as the "RMS emittance" of the "95% emittance", respectively.

Lenses can focus a beam, reducing its size while increasing its angular spread, but cannot change the total emittance. Ways of reducing the beam emittance include radiation damping, stochastic cooling, and electron cooling.

Acceptance

The acceptance is the maximum emittance that a beam transport system or analysing system is able to transmit.

Wikimedia Foundation. 2010.

См. также в других словарях:

• Emittance — may refer to: *Beam emittance *Thermal emittance …   Wikipedia

• Charged particle beam — A charged particle beam is a spatially localized group of electrically charged particles that have approximately the same velocity (speed and direction). The kinetic energies of the particles are typically measured in keV or MeV, much larger than …   Wikipedia

• RFQ Beam Coolers — RFQ stands for Radio Frequency Quadrupole (also known as a Quadrupole mass analyzer when used as a mass filter), an instrument that is used in mass spectrometry. The RFQ was invented by Prof. Wolfgang Paul in the late 50 s / early 60 s at the… …   Wikipedia

• Particle beam cooling — To be developed as a jump page related to particle accelerators Cooling techniques are important for the control the emittance of particle beams in particle accelerators. Usually, these techniques take advantage, in some way, of the electric or… …   Wikipedia

• International Muon Ionization Cooling Experiment — The International Muon Ionization Cooling Experiment (or MICE) 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… …   Wikipedia

• Intrabeam Scattering — (IBS) is an effect in accelerator physics where collisions between particles couple the beam emittance in all three dimensions. This generally causes the beam size to grow. In proton accelerators, intrabeam scattering causes the beam to grow… …   Wikipedia

• Ionization cooling — Physical Principle = Ionization cooling is a process by which the beam emittance of a beam of particles may be reduced [G.I. Budker, in: Proceedings of 15th International Conference on High Energy Physics, Kiev, 1970A.N. Skrinsky, Intersecting… …   Wikipedia

• Radiation damping — in accelerator physics is a way of reducing the beam emittance of a high velocity beam of charged particles. More specifically, it reduces the momentum spread of the particles making up the beam.There are two main ways of using radiation damping… …   Wikipedia

• Eurisol — The EURISOL project is aimed at the design and eventual construction of a next generation European ISOL radioactive ion beam (RIB) facility capable of extending current research in atomic and nuclear physics by providing users with a wide variety …   Wikipedia

• 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 (according to the objectives of the experiments) to… …   Wikipedia

Поделиться ссылкой на выделенное

Прямая ссылка:
Нажмите правой клавишей мыши и выберите «Копировать ссылку»