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Experimental Validation of a Kinetic Ballooning Mode in High-Performance High-Bootstrap Current Fraction Fusion
1General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
Physical Review Letters
|October 20, 2023
Summary
High-frequency electromagnetic fluctuations were observed in DIII-D plasma, revealing a self-regulating phenomenon. These kinetic ballooning modes (KBM) play a key role in internal transport barrier (ITB) saturation.
Area of Science:
- Plasma Physics
- Fusion Energy Research
- Magnetohydrodynamics
Background:
- High bootstrap current fraction plasmas in devices like DIII-D are crucial for fusion energy.
- Internal transport barriers (ITBs) are essential for achieving high performance in fusion plasmas.
- Understanding plasma turbulence and its self-regulating mechanisms is key to controlling fusion reactions.
Purpose of the Study:
- To investigate the nature and impact of high-frequency electromagnetic fluctuations in DIII-D plasmas.
- To identify the specific type of fluctuations and their location within the plasma.
- To determine the role of these fluctuations in the saturation of internal transport barriers.
Main Methods:
- Observation and characterization of high-frequency electromagnetic fluctuations using diagnostic tools.
- Analysis of fluctuation properties such as frequency, poloidal wavelength, and phase velocity.
- Experimental validation of the identified fluctuations as kinetic ballooning modes (KBM).
- Quasilinear estimation to predict particle and thermal fluxes driven by KBM.
Main Results:
- Observation of coherent high-frequency electromagnetic fluctuations (130-220 kHz) in DIII-D.
- Fluctuations characterized by poloidal wavelength (16-30 m⁻¹) and phase velocity (~30 km/s).
- Experimental validation identifying these as kinetic ballooning modes (KBM) in the ITB region.
- KBM predicted to drive significant particle and thermal fluxes.
Conclusions:
- The observed KBM are responsible for a turbulence-induced self-regulating phenomenon.
- These KBM play a significant role in the saturation of internal transport barriers (ITBs).
- Findings contribute to understanding plasma transport and control in fusion devices.
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