Dipole magnet

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Dipole magnet from the Advanced Photon Source.

Image:Half cell dipole electromagnet.JPG

A "half cell" dipole electromagnet showing almost exposed beamline.

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 to it. Thus, a particle injected into a dipole magnet will travel on a circular or helical trajectory. By adding several dipole sections on the same plane, the bending radial effect of the beam increases.

In particle accelerators, dipole magnets are used to realize bends in the design trajectory (or 'orbit') of the particles, as in circular accelerators. Other uses include:

Injection of particles into the accelerator
Ejection of particles from the accelerator
Correction of orbit errors
Production of synchrotron radiation

Such magnets are also used in traditional televisions, which contain a cathode ray tube, which is essentially a small particle accelerator. Their magnets are called deflecting coils. The magnets move a single spot on the screen of the TV tube in a controlled way all over the screen. The screen has many lines, and "interlacing" is used. That means that on one pass the light spot is moved very quickly along all of the odd-numbered lines (1,3,5 ...), then along all of the even-numbered lines (2,4,6 ...) during the next pass, and so on.