Rotating magnetic fields (RMF) have been used to both form and maintain field reversed configurations (FRC) in quasisteady state. These experiments differ from steady-state rotamaks in that the FRCs are similar to those formed in theta-pinch devices, that is elongated and confined inside a flux conserver. The RMF creates an FRC by driving an azimuthal current which reverses an initial positive bias field. The FRC then expands radially, compressing the initial axial bias flux and raising the plasma density, until a balance is reached between the RMF drive force and the electron–ion friction. This generally results in a very high ratio of separatrix to flux conserver radius. The achievable final conditions are compared with simple analytic models to estimate the effective plasma resistivity. The RMF torque on the electrons is quickly transferred to the ions, but ion spin-up is limited in these low density experiments, presumably by ion-neutral friction, and does not influence the basic current drive process. However, the ion rotation can result in a rotating n=2 distortion if the separatrix radius is too far removed from the plasma tube wall.

Flux, energy and particle lifetimes have been measured in the new Large s Experiment field reversed configuration (FRC) facility. By careful control of the formation process, it was possible to form symmetric, quiescent FRCs, with s values higher than 4, in the one year of operation of the device. A wide range of plasma conditions was achieved, with ion temperatures varying between 0.1 and 1.5 keV. The lifetimes continue to scale approximately with the rs2/ρi parameter found in earlier work, with a coefficient proportional to xs to a power between 0.5 and 1

Flux and particle life-times of field-reversed configurations (FRC) have been measured in the TRX-1 field-reversed theta pinch. These measurements have been correlated with detailed numerical transport calculations based on classical and lower-hybrid-drift (LHD) resistivity. The data appear to imply spatially uniform resistivity profiles with a magnitude somewhat lower than that given by the wave energy bound of LHD fluctuations. Using a programmed formation technique it has been possible to form FRCs with large amounts of poloidal flux, and thus large separatrix radii. The particle confinement time has been found to scale approximately linearly with the amount of poloidal flux, and 150 μs particle confinement times have been achieved in 3 X 1015 cm−3 density FRCs with separatrix radii of only 7 cm. The linear scaling with poloidal flux is highly encouraging for scaling to higher-field, larger-size devices.

After extensive experimentation on the Translation, Confinement, and Sustainment rotating magnetic-field (RMF)-driven field reversed configuration (FRC) device [A. L. Hoffman et al., Fusion Sci. Technol. 41, 92 (2002)], the principal physics of RMF formation and sustainment of standard prolate FRCs inside a flux conserver is reasonably well understood. If the RMF magnitude Bω at a given frequency ω is high enough compared to other experimental parameters, it will drive the outer electrons of a plasma column into near synchronous rotation, allowing the RMF to penetrate into the plasma. If the resultant azimuthal current is strong enough to reverse an initial axial bias field Bo a FRC will be formed. A balance between the RMF applied torque and electron-ion friction will determine the peak plasma density nm∝Bω∕η1∕2ω1∕2rs, where rs is the FRC separatrix radius and η is an effective weighted plasma resistivity. The plasma total temperature Tt is free to be any value allowed by power balance as long as the ratio of FRC diamagnetic current, I′dia≈2Be∕μo, is less than the maximum possible synchronous current, I′sync=⟨ne⟩eωrs2∕2. The RMF will self-consistently penetrate a distance δ* governed by the ratio ζ=I′dia∕I′sync. Since the FRC is a diamagnetic entity, its peak pressure pm=nmkTt determines its external magnetic field Be≈(2μopm)1∕2. Higher FRC currents, magnetic fields, and poloidal fluxes can thus be obtained, with the same RMF parameters, simply by raising the plasma temperature. Higher temperatures have also been noted to reduce the effective plasma resistivity, so that these higher currents can be supported with surprisingly little increase in absorbed RMF power.