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.

A new device, the Inductive Plasma Accelerator, was employed to simultaneously form and accelerate two oppositely directed field reversed configurations (FRCs) where the relative velocity (600 km s−1) of the plasmoids was much larger than their internal thermal motion. Upon collision all of the FRC directional energy was observed to be rapidly thermalized concurrent with complete magnetic reconnection of the two FRCs. Upon merging, the resulting FRC was compressed to kilovolt ion temperatures exhibiting a configuration lifetime better than predicted by past scaling of in situ formed FRCs. With the improved FRC confinement scaling, a pulsed plasma device based on this approach capable of achieving fusion gain is examined. For an FRC with a poloidal flux 20 mWb or greater, the fusion energy yield per pulse exceeds the plasma energy for compression fields of 10 T or more. The scaling is insensitive to the compression chamber radial scale, providing for the possibility of a very compact fusion neutron source.

Interchange modes have been a key limiting instability for many magnetic confinement fusion configurations. In previous studies intended to deal with these ubiquitous instabilities, complex, transport enhancing, minimum-B producing coils were added to the otherwise simple linear mirror plasma. Possible solutions for returning to a simple symmetric mirror configuration, such as ponderomotive fields, are weak and difficult to apply. A new method is demonstrated here for the first time, utilizing rotating magnetic fields that are simple to apply and highly effective. A simple and easily comprehensible theory has also been developed to explain the remarkable stabilizing properties. Although this work has been performed on field reversed configurations, it should have a wide application to other confinement schemes, and could become a cornerstone for high-beta plasma stability.

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