Year: 2025
Type: article
Abstract: Understanding the kinetic ballooning mode (KBM) is crucial for optimizing plasma performance in high- β spherical tokamaks. Global gyrokinetic simulations of KBMs in a projected NSTX-U shot are presented using realistic magnetic geometry and plasma profiles. Linear simulations across varying plasma β values show that the KBM is unstable in NSTX-U at significantly higher plasma β than conventional tokamaks due to the plasma shaping effects. Isotope effects on KBM are more pronounced at higher plasma β but remain relatively weak near the KBM stability threshold. Without flow shear, KBMs are unstable in both the core and pedestal regions. In the core, the investigated toroidal mode numbers in the range n = [ 15 , … , 31 ] are observed to be unstable. In the pedestal, on the other hand, the n = 15 mode is the most unstable mode due to local β values lower than those in the core. Parameter scans of plasma profile gradients and plasma β demonstrate that the linear KBM in the core exhibits a high sensitivity to β , whereas KBM in the pedestal shows a lower sensitivity. A reduction of β by approximately 15% from the projected value stabilizes KBMs in the core. Nonlinear simulations reveal that self-generated zonal flows play a crucial role in regulating KBM-driven turbulence, reducing the size of turbulent eddies, shortening the radial correlation length by nearly threefold, and decreasing turbulent transport by approximately 35%. These findings provide valuable insights into KBM stability and turbulent transport, offering guidance for optimizing operational scenarios in future experiments.
Source: Nuclear Fusion
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,595
Awards: HIGH-PERFORMANCE SCENARIO DEVELOPMENT IN NSTX-U VIA PHYSICS-BASED MODELING AND MODEL-BASED CONTROL, G122673668, G1286236842, G1677143136, G3083819904, G419881185, G42916606, G4501827968, G498139845, G5076365615, ADVANCES IN THE THEORY OF REDUCED ANOMALOUS TRANSPORT MODELING AND CONFINEMENT OF TOKAMAK PLASMAS, ADVANCES IN THE THEORY OF REDUCED ANOMALOUS TRANSPORT MODELING AND CONFINEMENT OF TOKAMAK PLASMAS, G8003822989, ADVANCING UNDERSTANDING AND PREDICTIVE CAPABILITY FOR FAST-ION DRIVEN INSTABILITIES AND ASSOCIATED ANOMALOUS TRANSPORT IN NSTX-U, G8935046309, G969889393
OpenAlex ID: W4414273372