NSTX

NSTX, the National Spherical Torus Experiment, is a magnetic confinement fusion device operated by the Princeton Plasma Physics Laboratory (PPPL) in Princeton, New Jersey. It investigates the physics of spherical tokamaks, a compact variant of the tokamak design characterized by a low aspect ratio and the potential to achieve high beta plasmas.

The device is a spherical tokamak with a relatively low aspect ratio, featuring a center stack, toroidal field coils, and poloidal field coils to shape and control the plasma. NSTX employs heating methods such as neutral beam injection and radiofrequency heating to raise plasma temperature and drive current, while wall conditioning techniques help maintain plasma purity. A suite of diagnostics, including Thomson scattering, interferometry, spectroscopy, and magnetic probes, provides detailed measurements of plasma performance and stability.

Scientific goals center on exploring high-beta operation, non-inductive current drive, and advanced plasma configurations. NSTX has contributed to understanding how spherical tokamaks behave at elevated pressure, how plasma shape and current profiles influence confinement, and how to manage stability and transport in compact devices.

NSTX underwent a major upgrade to form NSTX-U in the 2010s. The upgrade expanded the magnetic system, heating capabilities, and diagnostic coverage, enabling higher plasma currents, longer pulse lengths, and greater experimental flexibility. NSTX-U resumed operations with the aim of advancing spherical tokamak physics and informing the development of future fusion reactors.

Overall, NSTX remains a leading center for spherical tokamak research, supporting international collaboration in the effort to evaluate compact, cost-effective approaches to fusion energy.