Evidence for fast-ion transport by microturbulence
W W Heidbrink1, J M Park, M Murakami
1University of California, Irvine, CA 92697, USA.
Physical Review Letters
|November 13, 2009
Summary
Turbulence causes energetic ion diffusion in DIII-D tokamak plasmas. Anomalies from classical predictions were observed, especially in hotter, lower-energy, and larger-radius plasmas.
Area of Science:
- Plasma physics
- Fusion energy research
- Ion transport phenomena
Background:
- Energetic ions are crucial for heating fusion plasmas.
- Understanding their diffusion is key to controlling plasma stability and performance.
- Neutral-beam injection (NBI) is a primary method for creating energetic ions in tokamaks.
Purpose of the Study:
- To experimentally measure the cross-field diffusion of energetic ions driven by microturbulence.
- To compare experimental observations with theoretical predictions of fast-ion transport.
- To identify plasma conditions that influence the magnitude of anomalous diffusion.
Main Methods:
- Utilized DIII-D tokamak experiments with neutral-beam injection.
- Employed Fast-ion D-alpha spectroscopy, neutron measurements, and motional Stark effect diagnostics.
- Analyzed the fast-ion distribution function to quantify diffusion.
Main Results:
- Measured cross-field diffusion of energetic ions due to plasma microturbulence.
- Observed that diffusion anomalies compared to classical theory are most pronounced in high-temperature plasmas.
- Anomalies were also greater at lower fast-ion energies and larger minor radii.
Conclusions:
- Experimental measurements confirm the significant role of microturbulence in energetic ion diffusion.
- The observed diffusion characteristics align with theoretical expectations for turbulent transport.
- Findings provide crucial data for validating and improving theoretical models of fast-ion behavior in fusion plasmas.
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