Efficient electron cyclotron current drive regime for plasma current start-up in fusion reactors.

Area of Science:

• Plasma Physics
• Fusion Energy Engineering

Background:

• Tokamak reactors require efficient methods for plasma current start-up.
• Conventional electron cyclotron heating (ECH) methods face limitations in current drive efficiency at relevant temperatures.
• Developing solenoid-free tokamak designs is crucial for economical fusion energy.

Purpose of the Study:

• To identify an enhanced electron cyclotron heating (ECH) regime for efficient current start-up in reactor-like magnetic fields.
• To compare the current drive efficiency of this new regime against conventional ECH methods.
• To assess the potential of this regime for solenoid-free tokamak reactor designs.

Main Methods:

• Investigated an accessibility-enhanced X-mode electron cyclotron heating (ECH) regime.
• Analyzed electron cyclotron interaction with unidirectional passing electrons under specific wave accessibility conditions.
• Evaluated performance in a reactor-like toroidal magnetic field range at relevant start-up temperatures.

Main Results:

• Identified an ECH current start-up regime with over 100 times higher current drive efficiency than conventional methods.
• Achieved very high current drive efficiency by leveraging strong cyclotron interaction with constrained unidirectional passing electrons.
• Demonstrated the effectiveness of the regime within a reactor-like toroidal magnetic field range.

Conclusions:

• The identified ECH regime offers a highly efficient method for tokamak current start-up.
• This efficient electron cyclotron current drive may enable innovative, economical, solenoid-free tokamak fusion reactor designs.
• The findings contribute to advancing practical fusion energy solutions.