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A Fast Shutdown Technique for Large Tokamaks

Authors: S.C. Jardin, G.L. Schmidt, E.D. Fredrickson, K.W. Hill, J. Hyun, B.J. Merrill, and R. Sayer

Date: September 1999

Published in: Nucl. Fusion 40 (May 2000) 923-933.

A practical method is proposed for the fast shutdown of a large, ignited tokamak. The method consists of injecting a rapid series of 30-50 deuterium pellets doped with a small (0.0005%) concentration of Krypton impurity, and simultaneously ramping the plasma current and shaping fields down over a period of several seconds using the poloidal field system. Detailed modeling with the Tokamak Simulation Code using a newly developed pellet mass deposition model shows that this method should terminate the discharge in a controlled and stable way without producing significant numbers of runaway electrons. A partial prototyping of this technique was accomplished in TFTR.