Massive Matter Injection into the Ultrahigh-vacuum of thermonuclear Fusion Systems: Control of Plasma Stability and Ensuring good Vacuum Conditions

Massive matter injection in ultra-high vacuum environment for thermonuclear fusion devices The injection of large quantities of material in fusion plasmas is one of the technical challenges of today's fusion research. The aims of depositing different materials are plasma fueling, controlling instabilities, improving energy confinement and vacuum quality or mitigating consequences of disruptions (high heat loads, strong electromagnetic forces, relativistic electrons). To prevent unnecessary load on the vacuum system of the fusion device, the injection is performed with pellets or concentrated gas pulses. Pellets are solids with a volume of a few mm(3) which are either composed of solid material at room temperature or of cryogenic gases. The pellets are accelerated by centrifuges or gas canons to speeds of up to 1500 m/s and are fired into the plasma with repetition rates of up 140 pellets/s. The gas pulses are generated using high speed gas valves which are operated a few centimeters from the plasma edge.