No abstract

In the FRX-C/T experiment [Proceedings of the 9th Symposium for Engineering Problems of Fusion Research (IEEE, New York, 1981), p. 1751], field-reversed configuration (FRC) plasmas have been formed in, and launched from, a field-reversed theta-pinch source and subsequently trapped in an adjacent confinement region. No destructive instabilities or enhanced losses of poloidal flux, particles, or thermal energy are observed for FRC total trajectories of up to 16 m. The observed translation dynamics agree with two-dimensional magnetohydrodynamic (MHD) simulations. When translated into reduced external magnetic fields, FRC’s are observed to accelerate, expand, and cool in partial agreement with adiabatic theory. The plasmas reflect from an external mirror and after each reflection, the axial kinetic energy is reduced by approximately 50%. Because of this reduction, FRC’s are readily trapped without the need of pulsed gate magnet coils.

No abstract

A zero-dimensional theoretical model is developed to study energy, particle, and magnetic flux confinement during the equilibrium phase in field-reversed configurations. The plasma is heated by adiabatic compression from the external magnetic field and by ohmic dissipation. Energy is lost from lower-hybrid-drift induced particle transport, classical and anomalous thermal conduction, and impurity line radiation. As an example, the model is used to analyze data measured in the FRX-C experiment.

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.