Demonstration of Tokamak Discharge Shutdown with Shell Pellet Payload Impurity Dispersal.

Area of Science:

• Fusion Energy Research
• Plasma Physics
• Tokamak Engineering

Background:

• Tokamak disruptions pose a significant risk to reactor operation and integrity.
• Conventional disruption mitigation methods often result in high heat loads and undesirable impurity effects.
• A new approach is needed for effective tokamak disruption mitigation with reduced wall damage.

Purpose of the Study:

• To demonstrate the efficacy of shell pellets for rapid tokamak discharge shutdown.
• To investigate the potential of shell pellets for low heat load and slow current quench disruption mitigation.
• To explore the formation of hollow temperature profiles during disruption mitigation.

Main Methods:

• Development and testing of shell pellets containing a dispersive payload (boron powder) within a diamond shell.
• Implementation of shell pellet injection into the DIII-D tokamak for rapid discharge shutdown.
• Spectroscopic analysis to confirm payload release and temperature profile measurements.

Main Results:

• Successful rapid (<10 ms) tokamak discharge shutdown was achieved using shell pellets.
• Low conducted divertor heat fluence (approximately 0.1 MJ/m²) was observed.
• Spectroscopic data confirmed massive release of the boron payload into the plasma core.
• Evidence of a hollow temperature profile during the shutdown was obtained.

Conclusions:

• Shell pellets represent a promising new method for tokamak disruption mitigation.
• This technique offers potential for reduced wall heat loads and slower current quench.
• Further research into shell pellets could lead to improved disruption control in future fusion reactors.