Ring Accelerator Experiment (RACE)

Earlier work on the RACE experiment has demonstrated acceleration and inertial focusing of spheromak-type compact toroids of low mass (10 μg), low density (10
¹⁹
m
^-3
), and low magnetic field (0.2 T) to high velocity (2 x 10
⁶
m/sec) and kinetic energy (10 kJ). The plasma rings were accelerated in a 0.5 m diameter / 6 m long coaxial railgun. Two end configurations were used-one straight, and the other with the final 2 meters tapered to form a converging nozzle. Rings could be focused to one third of the original diameter in the tapered section using the kinetic energy acquired during acceleration. Computer modeling and measurements gave reasonably good accounting of ring mass, momentum, and energy. Recent work has been directed toward increasing the ring magnetic field by utilizing slower formation times and precompressing the ring from 0.32 m O.D. to 0.16 m O.D. prior to a short 1.5 m acceleration. The precompression dynamics are dominated by acceleration magnetic forces balancing ring internal magnetic equilibrium forces. Kinetic pressure and ring inertia are apparently less important. Ring density and magnetic field were increased in the precompression cone (n
_e
˜10
²¹
m
^-3
, B˜0.5-1.0 T), and increased further after compression (n
_e
˜10
²²
m
^-3
, B˜-2.0 T), Final velocities (0.5 x 10
⁶
m/sec) are lower due to the shorter acceleration section, but still consistent with computer modeling.