TOKAMAK PLASMAS

INJECTION OF SOLID FUEL PELLETS INTO A TOKAMAK REACTOR IS ANATTRACTIVE TECHNIQUE FOR REFUELING. THE CONCEPT IS BASED ONTHE UNIFORM EVAPORATION OF THE CRYOGENIC MATERIAL DURING ITSTRAVEL ACROSS THE MINOR DIAMETER OF THE MACHINE. THE ABLATION RATE IS DETERMINED BY THE PHYSICS OF THE HEAT CONDUCTION FROM THE LOW-DENSITY, HIGH-TEMPERATURE TOKAMAK PLASMA. THE INJECTION VELOCITY REQUIRED IS DETERMINED BY THE PELLET MASS, THE MACHINE'S MINOR DIAMETER AND THE ABLATION RATE. RECENT EXPERIMENTS SUGGEST THE EVAPORATION RATE TO BE LARGE, THUS REQUIRING INJECTION VELOCITIES IN EXCESS OF 10 KM/SEC. ACHIEVEMENT OF THESE HIGH VELOCITIES IS A TECHNOLOGICAL CHALLENGE. BEFORE A REALISTIC INJECTION PROCESS CAN BE DESIGNED, A BETTER UNDERSTANDING OF THE ABLATION PHYSICS MUST BE OBTAINED. TO DATE, ONLY SIMPLY STEADY-STATE MODELS HAVE BEEN USED TO EXPLAIN THE EXPERIMENTAL RESULTS. ABLATION PHYSICS IS A COMPLICATED PROCESS WHICH IS BEST HANDLED IN A TIME-DEPENDENT FASHION VIA NUMERICAL SIMULATION STUDIES. WE PROPOSE TO CONSTRUCT SUCH A CODE IN PHASE I WHICH WILL BE A POWERFUL TOOL IN DESIGNING EXPERIMENTS FOR LARGER MACHINES.