The National Spherical Torus Experiment Upgrade, or NSTX-U, is the most powerful spherical tokamak in the world. With its nearly spherical plasma shape, it provides a test of the theory of toroidal magnetic confinement as the spherical limit is approached. During experimental studies in the original NSTX, plasma with a spherical torus shape (viz. a shape resembling a cored apple) was found to be stable even when ratios of plasma-to-magnetic pressure and self-driven current fraction were large. Beyond stability, NSTX-U will test the impact of the spherical torus shape on plasma energy confinement properties. If present theoretical predictions are verified, it would indicate that spherical tori use applied magnetic fields more efficiently than most other magnetic confinement systems and could, therefore, be expected to lead to more cost-effective fusion power systems in the long term. The NSTX-U construction was complete in 2015 and plasma operations began in 2016. This upgrade project included a new center stack and a second neutral beam injection system. Together this hardware upgrade has doubled the magnetic field, plasma current, and auxiliary heating power of the device, while extending the plasma pulse length by nearly a factor of five
Original Mission Need Statement (2009)
An improved understanding of the Spherical Torus (ST) magnetic confinement configuration is needed to establish the physics basis for next-step ST facilities, broaden the scientific understanding of plasma confinement for ITER, and maintain U.S. world leadership in ST research capabilities. In particular, operation at higher magnetic field with reduced plasma collisionality is needed to extend the plasma physics understanding of the ST toward next-step ST facilities and ITER. Controllable fully-non-inductive current-drive will also contribute to assessing the ST as a potentially cost-effective path to fusion energy.
Updated Mission Need Statement (2018)
Advances in the physics and technologies of magnetically confined fusion plasmas, since design and construction of the NSTX-U project, opened new pathways to contribute to burning plasma science. The NSTX-U project is a world leading device that will address critical areas in magnetic confinement, notably in conjunction with the MAST-U spherical tokamak operated at the Culham Centre for Fusion Energy (CCFE), UK. Recent developments in high-performance computing (HPC) pave new ways for plasma simulation, data analysis, and machine learning. The development of new software requires benchmarking with a well-characterized plasma device. NSTX-U will be well-positioned to make important contributions, especially in key fields as plasma turbulence, fast particles interacting with plasmas, and avoidance of sudden disruptions of the plasma current. Finding solutions to the challenges of how to deal with the high thermal wall loads is a critical area of fusion research, and NSTX-U will enable world leading research with lithium as an advanced wall material. New developments in high temperature superconductivity hold the potential to revolutionize magnetic confinement fusion. Spherical tokamak experiments with normal conducting magnets remain important to establish the physics basis for next-step devices that would use superconducting magnets
Columbia research at the NSTX-U facility takes place in the following areas:
Research aimed to find robust methods of disruption event characterization and forecasting.
Research to develop the physical basis enabling high pressure in the spherical tokamak configuration.