Editing Electromagnet (section)

===Lorentz forces===
In powerful electromagnets, the magnetic field exerts a force on each turn of the windings, due to the [[Lorentz force]] <math>q\mathbf{v}\times\mathbf{B}</math> acting on the moving charges within the wire. The Lorentz force is perpendicular to both the axis of the wire and the magnetic field. It can be visualized as a pressure between the [[magnetic field lines]], pushing them apart. It has two effects on an electromagnet's windings:
* The field lines within the axis of the coil exert a radial force on each turn of the windings, tending to push them outward in all directions. This causes a [[tensile stress]] in the wire.
* The leakage field lines between each turn of the coil exert an attractive force between adjacent turns, tending to pull them together.{{cn|date=July 2020}}
The Lorentz forces increase with ''<math>B^2</math>''. In large electromagnets the windings must be firmly clamped in place, to prevent motion on power-up and power-down from causing [[metal fatigue]] in the windings. In the [[Bitter electromagnet]] design (Fig. 2), used in very high-field research magnets, the windings are constructed as flat disks to resist the radial forces, and clamped in an axial direction to resist the axial ones.