Diamagnetic forces acting upon the water within its body levitated a live frog inside the 3.2 cm vertical bore of a Bitter solenoid. The magnetic field was about 16 teslas at the Nijmegen High Field Magnet Laboratory.

A Bitter electromagnet or Bitter solenoid is a type of electromagnet made of circular metal plates and insulating spacers stacked in a helical configuration, rather than coils of wire. This design was invented and built in 1933 by American physicist Francis Bitter. In his honor the plates are known as Bitter plates.

Bitter electromagnets are used to produce extremely strong magnetic fields (up to 60 teslas^{[citation needed]} as of 2006). The stacked plate design is mechanically very sturdy, to withstand the outward pressure produced by Lorentz forces, which increase with the square of the magnetic field strength. Additionally, water circulates through holes in the plates as a coolant, since resistive heating also increases with the square of the magnetic field strength.

Despite the drawback of resistive heating, Bitter electromagnets are used where extremely strong fields are required because superconducting electromagnets cannot operate above the field strength at which the magnet materials cease to be superconducting (typically on the order of 10 to 20 teslas, due to flux creep, though theoretical limits are higher).

[edit] External links

• National High Magnetic Field Laboratory Magnet Projects Page at Florida State University
• Magnets at Nijmegen High Field Magnet Laboratory
• The Frog That Learned to Fly and a ball of water inside a Bitter solenoid at the High Field Magnet Laboratory
• Diagrams and description of the Bitter solenoid used in the frog levitation demonstration

[edit] See also

• superconducting magnet