Control of neoclassical tearing modes by sawtooth control

Area of Science:

• Plasma physics
• Fusion energy research
• Magnetohydrodynamics

Background:

• Neoclassical tearing modes (NTMs) are a significant concern in magnetic confinement fusion devices.
• The onset of NTMs is contingent upon the presence of a sufficiently large seed island.
• Sawteeth, a common magnetohydrodynamic instability, can influence NTM stability.

Purpose of the Study:

• To investigate the relationship between sawtooth behavior and the destabilization of NTMs.
• To explore methods for controlling NTMs in fusion plasmas.
• To assess the implications for future burning plasma scenarios.

Main Methods:

• Experiments were conducted on the Joint European Torus (JET).
• Sawtooth stabilization techniques, including ion-cyclotron heating and current drive, were employed.
• Heating and current drive were applied strategically outside the inversion radius.

Main Results:

• Long-period sawteeth, achieved through stabilization methods, were found to readily destabilize NTMs.
• Alpha particles, relevant to burning plasmas, were observed to strongly stabilize sawteeth.
• Targeted heating and current drive outside the inversion radius destabilized sawteeth, leading to shorter periods.
• This destabilization allowed for higher beta values without the onset of NTMs.

Conclusions:

• Sawtooth dynamics play a crucial role in the onset and control of NTMs.
• Fusion alpha particles have a stabilizing effect on sawteeth, posing challenges for NTM control in burning plasmas.
• Precisely applied heating and current drive can be used to manage sawtooth behavior and avoid NTMs, improving fusion performance.