Maximum-J capability in a quasiaxisymmetric stellarator

Area of Science:

• Plasma physics
• Fusion energy research
• Magnetohydrodynamics

Background:

• Quasiaxisymmetric (QA) stellarators offer potential for stable plasma confinement in fusion energy devices.
• Achieving improved confinement is crucial for the viability of stellarator-based fusion reactors.
• Understanding particle transport mechanisms is key to optimizing plasma performance.

Purpose of the Study:

• To investigate the Maximum-J condition in QA stellarators for enhanced plasma confinement.
• To analyze the role of magnetic field nonaxisymmetry in creating local J maxima and drift reversal.
• To demonstrate external control over the Maximum-J condition for studying turbulent transport.

Main Methods:

• Theoretical analysis of the second adiabatic invariant (J) and its radial derivative.
• Computational modeling of magnetic field configurations in QA stellarators.
• Investigation of drift reversal phenomena induced by nonaxisymmetric magnetic fields.

Main Results:

• The Maximum-J condition, defined by the radial derivative of J matching the pressure gradient sign, was investigated.
• Nonaxisymmetry in magnetic field strength was found to create local J maxima, leading to drift reversal.
• External controllability of the Maximum-J condition was successfully demonstrated.

Conclusions:

• The Maximum-J condition is a viable strategy for improving plasma confinement in QA stellarators.
• Magnetic field nonaxisymmetry plays a critical role in enabling Maximum-J and drift reversal.
• The ability to externally control this condition opens new avenues for studying and mitigating turbulent transport in fusion devices.