The National Spherical Torus Experiment Upgrade (NSTX-U) delivered important scientific results during its first research campaign prior to shutting down for repairs. The upgrade doubled the magnetic field strength, current, and heating power of its predecessor and made the NSTX-U the most powerful fusion facility of its kind. Principal results of the initial operations included:

• Quickly surpassing the maximum magnetic field strength and pulse duration of its predecessor prior to the upgrade.
• Achieving high plasma confinement, or H-mode, on just the eighth day of the 10 weeks of experiments. H-mode is a superior regime for fusion performance.
• Reducing plasma instabilities with beams from a second neutral beam injector that was installed to increase the heating of the plasma. This device fired beams at different angles than the first injector, which generated the initial instabilities.
• Changing the direction in which other instabilities propagate using the second neutral beam injector. This result is consistent with the new beam significantly modifying the distribution of energetic ions. Providing increased flexibility in the distribution of energetic ions was a major scientific motivation for the new beam.
• Advancing development of methods to prevent plasma disruptions and to ramp down plasma when disruptions can no longer be avoided. Such methods will be critical for ITER, the international fusion experiment under construction in France, and for all future tokamaks.
• Identifying and learning to correct conditions called error fields that are common to tokamaks and can hinder the performance of fusion plasmas.
• Commissioning all magnetic diagnostics needed to gauge control of the plasma and demonstrating advanced diagnosis of the surface composition of the reactor walls.

Researchers now look forward to continuing their investigation of key issues needed to develop fusion energy as soon as NSTX-U repairs are completed and the spherical tokamak resumes operation.