Distinct Turbulence Saturation Regimes in Stellarators

Area of Science:

• Plasma physics
• Fusion energy research
• Computational fluid dynamics

Background:

• Ion-temperature-gradient (ITG) turbulence is a key driver of energy loss in fusion devices.
• Previous studies in tokamaks identified a single saturation regime for ITG turbulence.
• Stellarators, with their complex 3D magnetic fields, present unique challenges for understanding plasma turbulence.

Purpose of the Study:

• To investigate the behavior of ITG turbulence in stellarator magnetic fields.
• To identify distinct saturation regimes of ITG turbulence in stellarators.
• To develop a theoretical explanation for observed turbulence behaviors.

Main Methods:

• Petascale numerical simulations of plasma turbulence in stellarator geometries.
• Development of a simplified turbulence theory to explain simulation results.
• Comparison of simulation findings with existing tokamak turbulence observations.

Main Results:

• Two distinct saturation regimes for ITG turbulence were identified in stellarators.
• The first regime, characterized by strong zonal flows, aligns with tokamak observations.
• A novel second regime was discovered, featuring quasi-two-dimensional turbulence, weak zonal flows, and reduced heat flux scaling.

Conclusions:

• Stellarator magnetic geometry significantly influences ITG turbulence dynamics.
• The newly identified second regime offers insights into optimizing stellarator performance.
• Understanding these regimes is crucial for advancing fusion energy development.