Enhanced localized energetic-ion losses resulting from single-pass interactions with Alfvén eigenmodes
X Chen1, M E Austin, R K Fisher
1University of California-Irvine, Irvine, California 92697, USA. chenxi@fusion.gat.com
Physical Review Letters
|February 26, 2013
Summary
We observed prompt neutral beam-ion losses in the DIII-D tokamak caused by Alfvén eigenmodes. These losses expel full energy beam ions on their first orbit, exceeding nominal levels.
Area of Science:
- Plasma physics
- Fusion energy research
- Astrophysical particle acceleration
Background:
- Energetic particle behavior is crucial for fusion reactor performance.
- Toroidal and reversed shear Alfvén eigenmodes can destabilize energetic particles.
- Understanding particle scattering mechanisms is key to controlling fusion plasmas.
Purpose of the Study:
- To report the first observation of prompt neutral beam-ion losses induced by nonresonant scattering from Alfvén eigenmodes.
- To characterize the nature and magnitude of these losses.
- To use these observations to probe energetic particle scattering.
Main Methods:
- Utilizing the DIII-D tokamak to generate and diagnose plasma conditions.
- Observing prompt neutral beam-ion losses.
- Correlating losses with toroidal and reversed shear Alfvén eigenmodes.
Main Results:
- Observed coherent, full-energy beam-ion losses on the first poloidal orbit.
- Demonstrated that these first-orbit losses exceed nominal prompt losses.
- Established a linear scaling of loss amplitude with mode amplitude.
Conclusions:
- Nonresonant scattering by Alfvén eigenmodes causes significant prompt beam-ion losses.
- This provides a direct measure of particle radial excursion due to specific modes.
- Findings may inform understanding of energetic particle scattering in fusion and astrophysical contexts.
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