ACCELERATION OF NEON PELLETS TO HIGH SPEEDS FOR FUSION APPLICATIONS

The injection of impurity pellets into the plasmas of tokamak fusion r eactors has been proposed as a technique to lessen the deleterious eff ects of plasma disruptions. Equipment and techniques that were previou sly developed for pneumatic hydrogen pellet injection systems and used for plasma fueling applications were employed for a limited experimen tal study with neon pellets. Isotopic hydrogen pellets doped with neon have previously been used for injection into fusion plasmas to study impurity particle transport, and pure neon pellets are applicable for disruption studies. Using a repeating pneumatic injector in the labora tory, it was found that the formation and acceleration of 2.7-mm-diam neon pellets were relatively straightforward; reliable operation was d emonstrated with both a single- and a two-stage light gas gun, includi ng velocities of similar to 700 m/s with a single-stage injector and u p to 1740 m/s with a two-stage injector. Based on the operating sequen ces and successful tests demonstrated in the laboratory experiments, a three-barrel repeating pneumatic injector installed on the DIII-D tok amak was equipped with the necessary components for neon operation and has been used in initial disruption experiments with 1.8-mm-diam neon pellets. (C) 1996 American Institute of Physics.