Electromagnetic Launch of mm-Size Pellets to Great Velocities

Small body launching that uses gas or plasma faces the fundamental problem caused by excess energy loss that is due to the great wall surface/volume ratio of the barrel. For example, the efficiency of the plasma armature (PA) rail-gun acceleration is maximum for 8–10 mm-size bodies and drops as their size decreases.¹ That is why in the case of nuclear fusion applications, where 1–2 mm-size pellets at 5–10 km/s velocity are desirable, electromagnetic launchers have not yet demonstrated an advantage over light-gas guns and one is now forced to search for a compromise between the pellet size (increasing it up to #3–4 mm) and its velocity (decreasing it down to ≈3 km/s).. As a whole, the probability of attaining 5–10 km/s velocity for 1–2 mm pellets seems to be rather remote at the present. When designing the 1 mm railgun that exploits the PA, we made use of our concept of dielectric pellet launching at the greatest constant acceleration, which is close to the strength or the electrode skin-layer explosion limits.² That shortened the barrel length sufficiently. The system become highly compact, with the electrode length ≈10–16 cm, thus permitting the rapid test of new operation modes as well as modifications of the design, including magnetic field augmentation and the use of a compacted PA.³ As a result of these refinements, the difficulties caused by the catastrophic supply of mass ablated from the electrodes were overcome and regimes of 1–2 mm plastic pellets without sabot accelerated to 5 km/s were found. No pre-accelerator is used. The launcher operates in air at atmospheric conditions. The potentials and prospects of the small system created are far from being exhausted and deserve further elaboration.