Multiscale Chirping Modes Driven by Thermal Ions in a Plasma with Reactor-Relevant Ion Temperature

Area of Science:

• Plasma Physics
• Fusion Energy Research
• Magnetohydrodynamics

Background:

• Tokamak devices are crucial for fusion energy research.
• Understanding plasma instabilities is key to controlling fusion reactions.
• High-ion-temperature regimes in tokamaks can exhibit complex behaviors.

Purpose of the Study:

• To report the first observation of a specific thermal ion-driven instability.
• To characterize the properties and spatial scales of this instability.
• To assess the implications for future fusion reactors.

Main Methods:

• Experimental observation in the DIII-D tokamak.
• Analysis of plasma behavior in reactor-relevant temperature regimes.
• Investigation of instabilities in high-ion-temperature and high-beta plasma.

Main Results:

• Observed a thermal ion-driven bursting instability with rapid frequency chirping.
• The instability, identified as an Alfvénic ion temperature gradient mode, spans multiple spatial scales.
• Demonstrated destabilization of the Alfvén continuum due to ion compressibility at reactor-relevant temperatures.

Conclusions:

• The observed instability can cause magnetic topology changes and minor disruptions.
• Its occurrence in high-temperature, high-beta plasmas necessitates further study for future reactors.
• This finding is the first to link Alfvén continuum destabilization to ion compressibility in this regime.