Applications and progress of dust injection to fusion energy

Three regimes of dust injection are proposed for different applications to fusion energy. In the 'low-speed' regime (< 5 km/s), basic dust transport study, edge plasma diagnostics, edge-localized-mode (ELM) pacing in magnetic fusion devices call be realized by injecting dust of known properties into today's fusion experiments. ELM pacing, as all alternative to mini-pellet injection, is a promising scheme to prevent disruptions and type I ELM's that can cause catastrophic damage to fusion devices. Different schemes are available to inject dust. In the 'intermediate-speed regime (10 - 200 km/s), possible applications of dust injection include fueling of the next-step fusion devices, core-diagnostics of the next-step fusion devices, and compression of plasma and solid targets to aid fusion energy production. Promising laboratory results of dust moving at 10-50 km/s do exist. Significant advance in this regime may be expected in the near term to achieve higher dust speeds. In the 'high-speed regime (> 500 km/s). dust injection call potentially be used to directly produce fusion energy through impact. Ideas on how to achieve these extremely high speeds are mostly on paper. No plan exists today to realize them in laboratory. Some experimental results, including electrostatic, electromagnetic, gas-dragged, plasma-dragged, and laser-ablation-based acceleration, are summarized and compared. Some features and limitations of the different acceleration methods will be discussed. A necessary component of all dust injectors, is the dust dropper (also known as dust dispenser). A computer-controlled piezoelectric crystals has been developed to dropped dust in a systematic and reproducible manner. Particle fluxes ranges front a few tens of particles per second tip to thousands of particles per second by this simple device.