Bitter electromagnet

A Bitter electromagnet or Bitter solenoid is a type of electromagnet invented in 1933 by American physicist Francis Bitter used in scientific research to create extremely strong magnetic fields. Bitter electromagnets have been used to achieve the strongest continuous manmade magnetic fields on earth (up to 45 teslas - as of 2011).

Bitter electromagnets are used where extremely strong fields are required. The iron cores used in conventional electromagnets saturate and cease to provide any advantage at fields above a few teslas, so iron core electromagnets are limited to fields of about 2 teslas. Superconducting electromagnets can produce stronger magnetic fields but are limited to fields of 10 to 20 teslas, due to flux creep, though theoretical limits are higher. For stronger fields resistive solenoid electromagnets of the Bitter design are used. Their disadvantage is that they require very high drive currents, and dissipate large quantities of heat.

Bitter magnets are constructed of circular conducting metal plates and insulating spacers stacked in a helical configuration, rather than coils of wire. The current flows in a helical path through the plates. This design was invented in 1933 by American physicist Francis Bitter. In his honor the plates are known as Bitter plates. The purpose of the stacked plate design is to withstand the enormous outward mechanical pressure produced by Lorentz forces due to the magnetic field acting on the moving electric charges in the plate, which increase with the square of the magnetic field strength. Additionally, water circulates through holes in the plates as a coolant, to carry away the enormous heat created in the plates due to resistive heating by the large currents flowing through them. The heat dissipation also increases with the square of the magnetic field strength.

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