FRCs

FRCs, or field-reversed configurations, are a class of magnetized plasma configurations used in magnetic confinement fusion research. They form compact toroids in which the magnetic field is primarily poloidal and generated by a toroidal current within the plasma. The configuration lacks a strong externally applied toroidal field, and the magnetic field inside the plasma reverses direction relative to the field outside, giving the name field-reversed. The resulting closed magnetic field lines create a separatrix that confines the plasma within a localized, elongated torus.

FRCs can be formed by pulsed, high-current methods that reverse the magnetic field in a preexisting plasma. Common formation approaches include theta-pinch and coaxial plasma gun techniques, sometimes involving merging or injecting helicity to produce the field reversal. After formation, the plasma tends to be high beta, with pressure comparable to the magnetic pressure, which is attractive for potential fusion gain. The field geometry yields a relatively simple coil system but also presents unique stability and confinement challenges.

Key properties of FRCs include their high beta, compact size, and predominantly poloidal magnetic field structure. They typically exhibit closed field lines with a boundary defined by the last closed flux surface. Confinement times in many experiments are limited by plasma instabilities, including tilt and shift modes, along with resistive and kinetic effects. Various stabilization strategies have been explored, such as end plugs, external bias fields, rotational effects, and active control schemes, to prolong confinement and move toward steady-state operation.

Research on FRCs continues worldwide, motivated by the potential for a simpler, cost-effective path to fusion energy due to reduced magnetic coil requirements and the high beta regime. Challenges remain in achieving long-lived, stable confinement and sustained steady-state operation. See also magnetic confinement fusion, spheromak, and theta pinch.