A controller for plasma motion in a Tokamak based on model estimation

A simple model and its application in designing the plasma position control system in the Saskatoon Torus Medium (STOR-M ) Tokamak are described. Estimating the model parameters, the design of a controller, plasma position measurement, the design of a power driver, and the implementation and testing of the complete system are included. The following assumptions are made to simplify the plasma position model: the plasma is treated as a moving axisymmetric, current-carrying filament; the iron-core of the transformer is approximated by an infinitely long cylinder; and the STOR-M vacuum vessel is constructed of type-304L stainless steel, is circular in cross-section, and is 4 mm in thickness. The model was very useful in the early stages of the design, but due to practical constraints the parameters of the model could not be determined very accurately. A least-squares-error algorithm was used offline to determine revised estimates of the model's parameters. Based on these values, the PID (proportional-integral-derivative) controller was tuned. A 30 kA plasma has been successfully contained for a time of 50 ms, which is the maximum time required for this machine.<
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