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Resonance cone interaction with a self-consistent radio-frequency sheath.
1Lodestar Research Corporation, 2400 Central Avenue P-5, Boulder, Colorado 80301, USA.
Physical Review Letters
|December 31, 2008
Summary
Lower-hybrid resonance cones can strongly interact with tokamak walls, potentially causing damage during radio-frequency heating. A critical parameter threshold determines if these harmful interactions occur, offering a way to avoid them.
Area of Science:
- Plasma physics
- Fusion energy research
- Radio-frequency heating
Background:
- Lower-hybrid resonance cones are key wave phenomena in magnetized plasmas.
- Plasma sheaths near conducting walls can affect wave propagation and energy deposition.
- Radio-frequency (RF) heating in tokamaks can inadvertently excite these resonance cones.
Purpose of the Study:
- To investigate the interaction and reflection of lower-hybrid resonance cones with plasma sheaths.
- To analyze the impact of these interactions on radio-frequency wall effects in tokamaks.
- To identify conditions that mitigate or exacerbate radio-frequency-induced wall damage.
Main Methods:
- Modeling the plasma sheath as a Child-Langmuir law-defined vacuum gap.
- Calculating the voltage transmission fraction from resonance cones to the plasma sheath.
- Analyzing the dependence of this transmission on a critical plasma parameter.
Main Results:
- A sensitive, threshold-like behavior was observed in the voltage transmission to the sheath.
- Above a critical parameter threshold, voltage transmission is near unity, indicating strong sheath interaction.
- Below the threshold, interactions are significantly reduced, minimizing potential wall damage.
Conclusions:
- Strong radio-frequency wall interactions are possible when resonance cones reach the plasma sheath above a critical threshold.
- These interactions can be detrimental to tokamak fusion experiments.
- Operating below the identified threshold can prevent deleterious radio-frequency-wall effects, ensuring safer and more efficient tokamak operation.
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