Comparison of an electrothermal plasma source to a light gas gun for launching large cryogenic pellets for tokamak disruption mitigation

Future large tokamaks, such as ITER, will require a reliable technique for rapid energy dissipation to mitigate harmful effects from disruptions. Two main methods developed for disruption mitigation are massive gas injection and shattered pellet injection (SPI). Argon and neon are favorable materials for both injection methods. When launching pellets with SPI, it has proven difficult to launch intact pellets of pure argon and/or neon owing to their high material strength at cryogenic temperatures. In this work, we compare two methods of launching relatively high-Z pellets. An electrothermal plasma source is an experimental alternative to the fast opening, high-pressure, gas valve. The electrothermal source was used to launch Lexan™ pellets with approximately the same size and mass of comparable mixed gas (D2 and Ne) cryogenic pellets launched by gas guns. We describe comparisons of achieved pellet velocities, energy efficiencies of each system, and the implications of implementing each respective method on an operating tokamak.