Strong focusing


Strong focusing

In accelerator physics strong focusing or alternating-gradient focusing is the principle that the net effect on a particle beam of charged particles passing through alternating field gradients is to make the beam converge. By contrast "Weak focusing" is the principle that nearby circles, described by charged particles moving in a uniform magnetic field, only intersect once per revolution.

Earnshaw's theorem shows that simultaneous focussing in two directions at once is impossible. However, ridged poles of a cyclotron or two or more spaced quadrupole magnets (arranged in quadrature) alternately focus horizontally and vertically. [ [http://www.bnl.gov/bnlweb/history/focusing.asp The Alternating Graident Concept ] ]

Strong focusing was first invented at Brookhaven National Laboratory and deployed on the Alternating Gradient Synchrotron there. The theory was developed in 1957 by E. D. Courant and H. S. Snyder. [ [http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/AP-literature/Courant-Snyder-1958.pdf Theory of the Alternating-Gradient Synchrotron] ] Courant and Snyder found that the net effect of alternating the field gradient was that both the vertical and horizontal focusing of protons could be made strong at the same time, allowing tight control of proton paths in the machine. This increased beam intensity while reducing the overall construction cost of a more powerful accelerator. The theory revolutionised cyclotron design, and permitted very high field strengths to be employed, while massively reducing the size of the magnets needed by minimising the size of the beam. All current cyclotrons use strong focusing.

Multipole magnets

Modern systems often use multipole magnets, such as quadrupole and sextupole magnets, to focus the beam down, as magnets give a more powerful deflection effect than earlier electrostatic systems at high beam kinetic energies. The multipole magnets refocus the beam after each deflection section, as deflection sections have a defocusing effect that can be countered with a convergent magnet 'lens'.

This can be shown schematically as a sequence of divergent and convergent lenses. The quadrupoles are often laid out in what are called FODO patterns (where F focusses vertically and defocusses horizontally, and D focusses horizontally and defocusses vertically and O is a space or deflection magnet). Following the beam particles in their trajectories through the focussing arrangement, an oscillating pattern would be seen.

Mathematical modelling

The effect of a set of focusing magnets can be expressed as a matrix. [ [http://www-linux.gsi.de/~boine/vorlesung/skript/html/node9.html Beam focusing ] ]

ee also

*Electron gun uses cylindrical symmetric fields such as provided by a Wehnelt cylinder to focus an electron beam
*Maglev has also been a suggested use of strong focusing
*Quadrupole magnet
*Sextupole magnet

External links

* [http://bc1.lbl.gov/CBP_pages/educational/WoB/home.htm Lawrence Berkeley National Laboratory: World of Beams]

References


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • strong focusing — stiprusis fokusavimas statusas T sritis fizika atitikmenys: angl. strong focusing vok. starke Fokussierung, f rus. жёсткая фокусировка, f; сильная фокусировка, f pranc. focalisation à gradient alterné, f; focalisation dure, f; focalisation… …   Fizikos terminų žodynas

  • strong-focusing principle — stipriojo fokusavimo principas statusas T sritis radioelektronika atitikmenys: angl. strong focusing principle vok. Prinzip der starken Fokussierung, n rus. принцип жёсткой фокусировки, m; принцип сильной фокусировки, m pranc. principe de… …   Radioelektronikos terminų žodynas

  • strong-focusing synchrotron — stipriosios fokusuotės sinchrotronas statusas T sritis radioelektronika atitikmenys: angl. strong focusing synchrotron vok. Synchrotron mit starker Fokussierung, n rus. синхротрон с сильной фокусировкой, m pranc. synchrotron à focalisation… …   Radioelektronikos terminų žodynas

  • strong-focusing accelerator — stipriosios fokusuotės greitintuvas statusas T sritis fizika atitikmenys: angl. strong focusing accelerator vok. starkfokussierender Teilchenbeschleuniger, m rus. сильнофокусирующий ускоритель, m; ускоритель жёсткой фокусировки, m pranc.… …   Fizikos terminų žodynas

  • Strong National Museum of Play — in Rochester, New York, USA, is a museum founded in 1982 that documents the history of play in American culture. Based on the personal collection of Margaret Woodbury Strong, the museum is a Smithsonian affiliate. It is also home to the National… …   Wikipedia

  • Strong AI — For John Searle s Strong AI hypothesis, see Philosophy of artificial intelligence Strong AI is artificial intelligence that matches or exceeds human intelligence the intelligence of a machine that can successfully perform any intellectual task… …   Wikipedia

  • Weak focusing — In particle accelerators Weak focusing occurs when particles are kept in reasonably strong, uniform magnetic fields that causes them to move in circles under the influence of the Lorentz force.Weak focusing is a name for the fact that the… …   Wikipedia

  • Self-focusing — is a non linear optical process induced by the change in refractive index of materials exposed to intense electromagnetic radiation. [Cumberbatch, E. Self focusing in Non linear optics , J. Inst. Maths Applics 6, 250 (1970)] Mourou, G. A. et al.… …   Wikipedia

  • Self-focusing transducers — Acoustic waves emitted by ultrasonics transducer crystals exhibit a property known as self focusing (or natural focusing ). Note that this is distinct from the electronically controlled focusing employed in diagnostic ultrasound devices which… …   Wikipedia

  • Nolan Strong & The Diablos — Further information: Fortune Records Nolan Strong The Diablos were a Detroit based R B and doo wop vocal group best known for its hit songs The Wind and Mind Over Matter. The group was one of the most popular, pre Motown, R B acts in Detroit… …   Wikipedia