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Two-dimensional structure and particle pinch in tokamak H mode
Naohiro Kasuya1, Kimitaka Itoh
1National Institute for Fusion Science, Toki, Gifu, Japan.
Physical Review Letters
|August 11, 2005
Summary
Investigating tokamak edge plasma, this study reveals how a strong electric field creates a solitary wave, driving an inward particle pinch. This mechanism explains the rapid density buildup during the L- to H-mode transition for improved confinement.
Area of Science:
- Plasma physics
- Fusion energy research
- Magnetohydrodynamics
Background:
- Tokamak edge plasma exhibits complex structures crucial for confinement.
- Understanding transport barriers is key to achieving fusion energy.
- Nonlinear viscosity effects influence plasma dynamics.
Purpose of the Study:
- To investigate 2D structures of electrostatic potential, density, and flow velocity at the tokamak edge.
- To model the impact of nonlinear bulk-ion and turbulence-driven shear viscosity.
- To explain the formation of transport barriers and density pedestals.
Main Methods:
- Developed a 2D model incorporating nonlinear viscosity terms.
- Analyzed plasma behavior under strong radial electric fields (H-mode).
- Simulated electrostatic potential, density, and flow velocity profiles.
Main Results:
- A 2D transport barrier structure was obtained in H-mode, featuring a poloidal shock and solitary radial electric field.
- An inward particle pinch was induced by the poloidally asymmetric electric field, strengthening with the electric field.
- An abrupt increase in inward ion and electron flux was observed at the L- to H-mode transition.
Conclusions:
- The poloidal shock and resulting inward particle pinch are key to forming the density pedestal.
- This mechanism drives the spontaneous self-reorganization into an improved confinement regime (H-mode).
- The model provides insights into the fundamental physics of tokamak edge plasma dynamics and confinement transitions.