Steady-state fully noninductive current driven by electron cyclotron waves in a magnetically confined plasma

Area of Science:

• Plasma Physics
• Fusion Energy Research
• Tokamak Technology

Background:

• Tokamaks are key devices for fusion energy, traditionally relying on inductive current drive.
• Achieving steady-state operation requires noninductive current drive methods to sustain plasma current indefinitely.
• Electron cyclotron current drive (ECCD) is a promising noninductive technique.

Purpose of the Study:

• To demonstrate sustained, fully noninductive plasma current in a tokamak using only electron cyclotron current drive.
• To investigate the feasibility of steady-state operation in tokamaks via ECCD.
• To analyze the spatial distribution of power deposition and its effect on current drive efficiency.

Main Methods:

• Utilized three 0.5-MW gyrotrons for electron cyclotron current drive.
• Carefully controlled the spatial distribution of deposited power across the plasma minor radius.
• Sustained a plasma current of 123 kA for 2 seconds.
• Performed transient current replacement experiments up to 153 kA for 100 ms.

Main Results:

• Achieved a steady-state, fully noninductive plasma current of 123 kA for 2 seconds using ECCD exclusively.
• Demonstrated transient current replacement of up to 153 kA for 100 ms with central ECCD.
• Confirmed the noninductive nature of the scenario by successfully recharging the Ohmic transformer.
• Showcased the dependence of current drive efficiency on the radial power deposition profile.

Conclusions:

• Electron cyclotron current drive alone can sustain a steady-state plasma current in a tokamak.
• Optimized power deposition profiles are crucial for achieving steady-state conditions with ECCD.
• This breakthrough paves the way for future steady-state tokamak reactors.