Tilting stability of field‐reversed configurations

Tilting in field‐reversed configurations (FRC) has long been regarded as the most dangerous instability threatening FRC confinement. Tilting is analogous to the internal kink in a tokamak. The tilting stability of FRC experiments can be explained by a combination of ideal‐MHD and finite ion gyro‐radius effects. Experiments to date have employed approximately straight magnetic coils (θ‐pinches) to produce equilbrium. Other equilibria have been found theoretically which are ideal‐MHD stable to tilting. Although not consistent with a conventional θ‐pinch coil these could be produced by a more sophisticated equilibrium field coil system such as is commonly used in tokamak devices. The significance of discovering FRC equilbria that are ideal‐MHD tilting stable is clear: stability does not require the injection of a large population of highly energetic ions and the associated technological burden.