Experimental demonstration of compact torus compression and acceleration

Tests of compact torus (CT) compression on the RACE device [Phys. Rev. Lett. 61, 2843 (1988)] have successfully demonstrated stable compression by a factor of 2 in radius, field amplification by factors of 2–3 to 20 kG, and compressed densities exceeding 1016 cm−3. The results are in good agreement with two-dimensional magnetohydrodynamic simulations of the CT dynamics. The CT is formed between a pair of coaxial conical conductors that serve as both a flux conserver for stable, symmetric formation and as electrodes for the compression and acceleration phases. The CT is compressed by J×B forces (poloidal current, toroidal field) when a 120 kV, 260 kJ capacitor bank is discharged across the electrodes. The CT reaches two-fold compression to a radius of 8 cm and a length of 20–30 cm near the time of peak current, 10 μsec (many Alfvén times) after the accelerator fire time, and is subsequently accelerated in a 150 cm straight coaxial section to velocities in the range 1.5–6.5×107 cm/sec. A new set of acceleration/focusing electrodes 740 cm in length are projected to give an additional factor of 3 in radial compression with final velocities of 1–3×108 cm/sec (similar to previously achieved on RACE) and incident power densities of a few ×1011 W/cm2. Compact torus accelerators scaled to multimegajoules have the potential to achieve unprecedented plasma velocities and power densities with many applications in high-energy-density physics.