Formation, spin-up, and stability of field-reversed configurations

Formation, spontaneous spin-up, and stability of θ-pinch formed field-reversed configurations are studied self-consistently in three dimensions with a multiscale hybrid model that treats all plasma ions as full-orbit collisional macroparticles and the electrons as a massless quasineutral fluid. The end-to-end hybrid simulations reveal poloidal profiles of implosion-driven fast toroidal plasma rotation and demonstrate three well-known discharge regimes as a function of experimental parameters: the decaying stable configuration, the tilt unstable configuration, and the nonlinear evolution of a fast growing tearing mode.

Figure 1

Temporal evolution of the plasma density $n_e$ and self-generated toroidal field $B_t$ in a stable, axisymmetric field reversed θ-pinch discharge.

Figure 2

Stable FRC profiles at ${\mathrm{\Omega }}_{ci}t=140$ cut radially through one of the toroidal field maxima: (a) plasma density (black line) and toroidal velocity [light gray (green) line] and (b) axial (black line) and toroidal [light gray (red) line] magnetic fields.

Figure 3

Temporal evolution of the plasma toroidal velocity $v_t$ (left) and local field time increment $\mathrm{\Delta }{t}_f$ (right) in a stable, axisymmetric field-reversed θ-pinch discharge.

Figure 4

Temporal evolution of the plasma density $n_e$ (isovolumes) in two unstable discharges where axisymmetric configurations are disrupted by (a) a late tilt instability of the FRC with $S^{*}/E\approx 4$ and (b) an early magneto-Taylor instability of the plasma column.