Reversed field pin
Reversed field pinch
A reversed-field pinch (RFP) is a device used to produce and contain near-thermonuclear plasmas. It is a toroidal pinch which uses a unique magnetic field configuration as a scheme to magnetically confine a plasma, primarily to study magnetic fusion energy. Its magnetic geometry is somewhat different from that of the more common tokamak. As one moves out radially, the portion of the magnetic field pointing toroidally (see inset) reverses its direction, giving rise to the term "reversed field". This configuration can be sustained with comparatively lower fields than that of a tokamak of similar power density. One of the disadvantages of this configuration is that it tends to be more susceptible to non-linear effects and turbulence. This makes it a perfect laboratory for non-ideal (resistive) magnetohydrodynamics. RFPs are also used in the study of astrophysical plasmas as they share many features.
The largest Reversed Field Pinch device presently in operation is called the Reversed-Field eXperiment (RFX) in Padua, Italy. Others include the Madison Symmetric Torus, EXTRAP T2R in Sweden, and TPE-RX in Japan.