We have demonstrated the formation of stable, symmetric, compact-torus (CT) plasma rings and the subsequent stable, twofold radial compression in coaxial conical electrodes with the ring accelerator experiment. The CT is compressed by J×B forces from a capacitor bank discharging across the conical electrodes. During compression, the force of the ${\mathbf{B}}_{\mathrm{\theta }}$ acceleration field balances the force of the CT poloidal field against the cones, in good agreement with a 2D code. Power amplification factors of ∼100 may be possible with an opening switch based on this technique.

• Received 1 October 1990

DOI:https://doi.org/10.1103/PhysRevLett.66.165