Magnetic compression heating experiments at the 1 GW level on field-reversed configuration (FRC) compact toroid plasmas are reported. FRC’s formed in a tapered theta-pinch coil have been translated into a single-turn compression coil, where the external magnetic field is slowly raised up to seven times its initial value. Significant electron and ion heating consistent with the expected B4/5 adiabatic scaling is observed, despite significant particle diffusion, which is enhanced during compression. The n=2 rotational instability is enhanced during compression, but has been controlled to an extent by the application of an external quadrupole field. The particle and flux confinement times, τN and τφ, remain approximately equal and decrease roughly with the square of the plasma radius R during compression, implying a constant nonclassical field-null resistivity. The observed τN and τφ magnitudes and scalings are compared with classical and anomalous transport theories, and existing empirical models. Particle diffusion dominates the energy confinement, accounting for three-fourths of the total losses. Upper bounds on the electron thermal diffusivities are estimated.

Detailed stability studies are made with new diagnostics in the FRX-C/LSM field-reversed theta pinch [Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1989), Vol. II, p. 517]. These studies seek the origin of a degradation of the confinement properties of field-reversed configurations (FRC’s) that appears associated with strong axial dynamics during plasma formation. Several instabilities are observed, including rotational modes, interchanges, and tilt instabilities. Only the latter are strongly correlated with FRC confinement. Tilt instabilities are observed for FRC’s with larger average number of ion gyroradii (s∼3–5) and smaller separatrix elongations (e∼3–4). Coincidently, strong axial dynamics occurs for cases with larger s and smaller e values, through increases in either reversed bias field or fill pressure. These data provide some understanding of FRC stability. In agreement with finite Larmor radius theory, there is a regime of gross stability for the very kinetic and elongated FRC’s with s/e<0.2–0.3. This is the regime that has been studied in most FRC experiments. However, tilt and other instabilities are observed for FRC’s with s/e∼1. Additional stabilization techniques will be required for future large-size FRC’s.

We report the first consistent observations of internal tilt instabilities in field-reversed configurations. Detailed comparisons with numerical calculations establish that data from an array of external magnetic probes are signatures of these destructive plasma instabilities. As suggested by finite-Larmor-radius theory, field-reversed configurations appear grossly stable when s/e [(average number of ion gyroradii)/(separatrix elongation)] is less than 0.2-0.3 and show MHD-like tilt instabilities when s/e-~\.

Data from an array of external probes provide the first clear evidence for the n=1 rotational instability in field-reversed configurations. The time evolution and the axial structure of this instability are clarified.

Electron energy transport in field reversed configuration (FRC) equilibria is studied experimentally for a variety of conditions. Up to 37% of the global plasma power loss is attributed to non-convective processes by electrons. The electron temperatures are approximately two times larger than those measured without reversed bias field, which indicates confinement by the poloidal magnetic field in the FRC. The inferred average cross-field thermal diffusivities χ⊥e are anomalous, ranging between 35 and 140 times classical, and are consistent with transport from turbulent magnetic fluctuations of 1 to 2%.