US NSTX-U lowers central magnet assembly into place as 2027 restart approaches

A large piece of the U.S. National Spherical Torus Experiment-Upgrade (NSTX-U) is finally inside the machine. Princeton Plasma Physics Laboratory (PPPL) reported on November 10 that crews lifted the central magnet assembly by crane and lowered it into NSTX-U on October 27. It is a tangible step toward restarting major spherical-tokamak research in the United States.

PPPL's June announcement concerned the arrival of the central magnet bundle. The new development is different: a larger assembly incorporating the toroidal-field magnet and the magnet used to induce plasma current and ohmic heating, together with protective structures and divertor magnets, has now been lowered into the device. Fitting magnets, cooling connections and a vacuum boundary into a constrained central region is one of the engineering challenges of a spherical tokamak.

PPPL has not yet declared installation complete. Engineers still have to align the assembly using laser measurements and verify vacuum seals; the laboratory expected those steps to conclude in November. Cooling lines, electrical connections and protective tiles must then be installed. Full machine assembly is expected in early 2027, with experimental operations planned for later that year. This is not a demonstration of electricity generation.

NSTX-U is intended to examine how far a compact tokamak geometry can support high-performance plasma operation. Lowering the magnet assembly is not itself a new plasma-physics result; it is engineering progress toward resuming experiments. Alongside PPPL's research programme, the next things to watch are alignment, vacuum integrity and integrated commissioning.