Escape dynamics in a Hamiltonian map for double-null diverted tokamaks

Area of Science:

• Plasma Physics
• Fusion Energy
• Dynamical Systems

Background:

• Tokamak magnetic confinement fusion relies on understanding complex magnetic field line structures.
• Diverted tokamaks, crucial for managing heat and particles, exhibit intricate phase-space dynamics.
• Modeling these dynamics is key to optimizing fusion reactor performance.

Purpose of the Study:

• To introduce and analyze a simple symmetric Hamiltonian map for double-null diverted tokamak magnetic fields.
• To compare the phase-space structure and magnetic field line behavior of double-null and single-null models.
• To elucidate the origins of distinct escape fraction oscillations in these models.

Main Methods:

• Development of a symmetric Hamiltonian map for magnetic field line modeling.
• Characterization of phase-space structure using finite-time Lyapunov exponent and escape time analysis.
• Analysis of mean transient measure and invariant manifolds of hyperbolic fixed points.

Main Results:

• The chaotic layer area increases with perturbation strength in both double-null and single-null models.
• Distinct oscillatory behaviors were observed in the escape fractions of the two models.
• Escape fraction variations are linked to changes in escape channel formation and stickiness near island chains.

Conclusions:

• The study provides a simplified yet effective model for tokamak magnetic field line dynamics.
• Differences in escape dynamics between double-null and single-null configurations are quantitatively characterized.
• Understanding stickiness and escape channels is crucial for predicting plasma behavior in fusion devices.