thumb The thumb is the first digit of the hand, next to the index finger. When a person is standing in the medical anatomical position (where the palm is facing to the front), the thumb is the outermost digit. The Medical Latin English noun for thumb ...

A subtype of a magnetic lens ( quadrupole magnet) in the Maier-Leibnitz laboratory, Munich A magnetic lens is a device for the focusing or deflection of moving

charged particles In physics, a charged particle is a particle with an electric charge. It may be an ion, such as a molecule or atom with a surplus or deficit of electrons relative to protons. It can also be an electron or a proton, or another elementary particle, ...

, such as

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kn ...

s or

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

s, by use of the magnetic Lorentz force. Its strength can often be varied by usage of

electromagnet An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the ...

s. Magnetic lenses are used in diverse applications, from

cathode ray tube A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms ( oscilloscope), pictu ...

s over electron microscopy to

particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams. Large accelerators are used for fundamental research in particle ...

Design

A magnetic lens typically consists of several electromagnets arranged in a

quadrupole A quadrupole or quadrapole is one of a sequence of configurations of things like electric charge or current, or gravitational mass that can exist in ideal form, but it is usually just part of a multipole expansion of a more complex structure refl ...

(see

quadrupole magnet Quadrupole magnets, abbreviated as Q-magnets, consist of groups of four magnets laid out so that in the planar multipole expansion of the field, the dipole terms cancel and where the lowest significant terms in the field equations are quadrupole. ...

), sextupole, or higher format; the

electromagnetic coil An electromagnetic coil is an electrical Electrical conductivity, conductor such as a wire in the shape of a wiktionary:coil, coil (spiral or helix). Electromagnetic coils are used in electrical engineering, in applications where electric curre ...

s are placed at the vertices of a square or another

regular polygon In Euclidean geometry, a regular polygon is a polygon that is Equiangular polygon, direct equiangular (all angles are equal in measure) and Equilateral polygon, equilateral (all sides have the same length). Regular polygons may be either convex p ...

. From this configuration a customized magnetic field can be formed to manipulate the

particle beam A particle beam is a stream of charged or neutral particles. In particle accelerators, these particles can move with a velocity close to the speed of light. There is a difference between the creation and control of charged particle beams and neu ...

. The passing particle is subjected to two vector forces

H_Z

(parallel to the core), and

H_R

(parallel to the radius of the lens).

H_R

causes the particle to spiral through the lens, and this spiraling expose the electron to

H_Z

which in turn focus the electron. Note that the magnetic field is inhomogeneous, particles close to the center are less strongly deflected than those passing the lens far from the axis.Hafner B., 2008, ''Introductory Transmission Electron Microscopy Primer,'' Characterization Facility, University of Minnesota –
Reference

Uses

Television sets employing

s use a magnetic lens in the form of a ''

deflection yoke A deflection yoke is a kind of magnetic lens, used in cathode ray tubes to scan the electron beam both vertically and horizontally over the whole screen. In a CRT television, the electron beam is moved in a raster scan on the screen. By adjusti ...

'' to enable an electron beam to

scan Scan may refer to: Acronyms * Schedules for Clinical Assessment in Neuropsychiatry (SCAN), a psychiatric diagnostic tool developed by WHO * Shared Check Authorization Network (SCAN), a database of bad check writers and collection agency for bad ...

the image by deflecting it vertically and horizontally.

Notes

References

* *

External links

* Accelerator physics Cathode ray tube Electromagnetic coils Television technology Types of magnets {{Electronics-stub

Design

Uses

See also

Notes

References

External links