New ORNL Pellet Injection System and Installation/Initial Operations on MST

A compact pellet injection system that was recently developed at the Oak Ridge National Laboratory has been installed on the Madison Symmetric Torus (MST) at the University of Wisconsin and used in initial plasma fueling experiments. The system, referred to as a "pellet injector in a suitcase," is a pipe gun device with a four-barrel capability (presently equipped with two 1.0-mm-bore barrels), and it uses a cryogenic refrigerator for in-situ hydrogen pellet formation (typically, D₂ pellets). This new, portable, stand-alone pellet injection system was developed to provide a flexible means of plasma fueling on a wide variety of magnetic confinement devices, with relatively low costs for installation and operation. The injector has already been used to produce useful results with pellets on MST plasmas, including significant and rapid increases (almost 100%) in the line average density, and effectively depositing fuel in the plasma core (central densities of [approximately equal to] 1.4 × 10¹⁹ m^-3). In this paper, the injection system, its performance, and reliability will be described, and results from some initial MST pellet experiments will be highlighted.