reversedfield

Reversed-field is a general term used to describe a situation in which a physical field—such as a magnetic or electric field—has a direction opposite to a chosen reference orientation.

In plasma physics, the reversed-field pinch (RFP) is a magnetic confinement concept in which the toroidal magnetic field reverses sign near the edge of a toroidal plasma. The reversal results from self-generated currents and magnetic reconnection; RFPs exhibit a low-shear, helical magnetic state and can reach high beta. Early experiments were conducted in the 1970s–1980s; modern devices include the Madison Symmetric Torus (MST) and other tokamak derivatives; RFPs have contributed to understanding magnetic self-organization and fusion confinement, though they face confinement and steady-state challenges.

In direct current machines, reversing the field direction—by reversing the field winding connections—can reverse the direction of rotation of the motor; this technique is used to control direction. In some configurations the combined reversal of field and armature yields the same rotation, per torque equations; the effect depends on the machine type (series vs shunt).

In astrophysics and geophysics, magnetic field reversals describe the flipping of a field's polarity, such as solar magnetic reversals during the solar cycle or geomagnetic reversals in Earth's history.

The term can also describe any experimental or device-specific reversal of a field direction relative to a reference.