Baking the perfect pie one piece at a time: PPPL makes progress on central magnet of NSTX‑U

Jeanne Jackson DeVoe
Oct. 25, 2024

The U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) achieved a major milestone recently when it completed the intricate process of building the first quadrant of the magnet at the heart of the National Spherical Torus Experiment-Upgrade (NSTX-U).

PPPL is assembling two high-current magnets to create the toroidal field-ohmic heating coil (TF-OH) bundle. The magnets make up the core of the NSTX-U, similar to the core of an apple. They are designed to produce the highest magnetic field strength of any large spherical torus.

The toroidal field (TF) coil is a 19-foot tall inner magnet resembling a telephone pole that carries up to four megaamps of electric current or 4 million amps to stabilize and confine the hot plasma in fusion experiments. The outer magnet, the ohmic heating (OH) coil, is a 4-kilovolt magnet that wraps around the TF coil like thread around a bobbin. It uses up to 24,000 amps to induce an electric field that drives an electric current within the vessel and helps heat the plasma.

“These magnets are critical to the NSTX-U experiment, and the team has been laser focused on this assembly,” said Steve Cowley, Laboratory director. “Constructing the first quadrant is a big achievement.”

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