National Spherical Torus Experiment: engineering overview and research results 1999–2000

The National Spherical Torus Experiment (NSTX) is a new US facility for the study of plasma confinement, heating, and current drive in a low aspect ratio, spherical torus (ST) configuration. The ST configuration is an alternate magnetic confinement concept which is characterized by high β (ratio plasma pressure to magnetic field pressure) and low toroidal field compared to conventional tokamaks, and could provide a pathway to the realization of a practical fusion power source. NSTX achieved first plasma in February 1999, and since that time has completed and commissioned all components and systems within the machine proper. Routine operation with inductively driven plasma current ≤1 MA and flat top ≤0.3 s has been established, and the ohmic characterization phase of the research program is underway. Radio frequency (RF) and neutral beam injection (NBI) systems have been installed and are presently being commissioned. This paper describes the NSTX mission, gives an overview of the engineering design, and summarizes the research results obtained thus far.