Plasma Physics Seminar

Advancing Fusion Energy: The National Spherical Torus Experiment Upgrade    

Speaker Name: Mate Lampert, NSTX

Abstract : 

The National Spherical Torus Experiment (NSTX) at the Princeton Plasma Physics Laboratory has been crucial in exploring the potential of the spherical tokamak (ST) design for fusion energy. This type of magnetic plasma confinement is now being considered for future fusion pilot plants.

Currently, the NSTX is undergoing significant upgrades. Researchers are working to deepen their understanding of how ST plasmas behave to ensure that, once the upgraded device (NSTX-U) is operational, it will provide maximum benefits. This research also aims to improve our confidence in the performance of future fusion     devices.

Spherical tokamaks (STs) offer several advantages over traditional tokamaks. Their low aspect ratio (the ratio of the torus' minor to major radius) and resulting higher toroidicity contribute to greater stability and enable higher beta (the ratio of plasma     pressure to magnetic pressure). Additionally, the higher toroidicity also results in the natural suppression of microinstabilities that lead to particle and energy transport. However, STs also present unique challenges, such as managing high heat flux, starting and sustaining the plasma without room for an induction coil, and dealing     with plasma instabilities.

Elevated heat fluxes on plasma-facing components (PFCs) are primarily induced by     turbulence at the plasma edge and within the scrape-off layer (SOL). The turbulence in the SOL is characterized by its intermittent nature, which gives rise to field-aligned     structures known as filaments. These filaments are responsible for transporting significant quantities of plasma density and thermal energy from the confined core     to the PFCs, potentially leading to erosion or damage of these components. Consequently, it is imperative to thoroughly investigate this phenomenon to develop     effective control and mitigation strategies to reduce the adverse impacts on PFCs to acceptable levels.

To this end, a data analysis tool was developed to systematically characterize filaments by estimating key parameters such as their position, velocity, orientation,     angular velocity, and morphology. These parameters were subsequently analyzed to establish correlations with one another, as well as with the overall plasma shape and profile characteristics.