Pellet acceleration using an ablation-controlled electrothermal launcher

The NCSU ablation-controlled electrothermal launcher SIRENS has been used to accelerate plastic (Lexan polycarbonate) pellets to investigate the possibility of using electrothermal launchers as frozen pellet injectors for tokamak fueling. Successful installation of such a device would include a protective shell (sabot) to shield the hydrogenic pellet from ablation and allow it to maintain its integrity throughout the acceleration. The SIRENS device has been modified to include specially designed barrel sections equipped with diagnostic ports. A pulse forming network (PFN), provides a longer pulse length of 250 μs, which allows for an extended period of pellet acceleration. Pellet masses between 300 and 1000 milligrams were used, and plastic sabots with 70 milligram plastic payloads were also tested. Measured velocities are in the range of 1500 m/s for the short pulse shots and 2000 m/s for the PFN long pulse shots. The 1D, time dependent gas dynamics code “ODIN” was modified to include a section to model the pellet´s movement, and the additional pellet terms were included in the set of governing equations. The pellet movement as predicted by the code compared favorably with experimental results, and the plasma parameters within the electrothermal launcher behaved as predicted