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Multiresonance effect in type-I edge-localized mode control with low n fields on JET.
Y Liang1, C G Gimblett, P K Browning
1Forschungszentrum Jülich GmbH, Association EURATOM-FZ Jülich, Institut für Energieforschung--Plasmaphysik, Trilateral Euregio Cluster, D-52425 Jülich, Germany. y.liang@fz-juelich.de
Physical Review Letters
|September 28, 2010
Summary
Researchers observed new resonances in edge-localized mode (ELM) frequency on the JET tokamak using applied low n fields. These findings reveal how magnetic field perturbations influence ELM behavior and plasma stability.
Area of Science:
- Plasma physics
- Fusion energy research
- Tokamak operations
Background:
- Edge-localized modes (ELMs) are crucial plasma instabilities in tokamak fusion devices.
- Controlling ELM frequency (f(ELM)) is vital for stable fusion reactions.
- Previous studies lacked detailed understanding of ELM frequency dependence on edge safety factors under specific magnetic field conditions.
Purpose of the Study:
- To investigate the effect of applied low toroidal mode number (n=1,2) magnetic fields on edge-localized mode (ELM) frequency.
- To identify and characterize resonances in ELM frequency as a function of the edge safety factor q(95).
- To explore the predictive capability of a theoretical model for observed ELM frequency behavior.
Main Methods:
- Experiments were conducted on the JET tokamak using type-I ELMy H-mode plasma.
- Varying the edge safety factor q(95) from 4 to 5.
- Applying low toroidal mode number (n=1,2) magnetic fields and observing changes in ELM frequency (f(ELM)).
- Comparing experimental results with a theoretical model based on ideal external peeling modes.
Main Results:
- Without applied fields, f(ELM) showed a slight increase from 20 to 30 Hz with increasing q(95).
- With an applied n=1 field, resonant q(95) values led to a 4-5 fold increase in f(ELM).
- Non-resonant q(95) values with the n=1 field resulted in only a 2-fold increase in f(ELM).
Conclusions:
- The study demonstrates the existence of multiple resonances in ELM frequency related to the edge safety factor when low n fields are applied.
- The observed resonances suggest a strong interaction between applied magnetic fields and plasma edge stability.
- A theoretical model, incorporating localized relaxation triggered by unstable ideal external peeling modes, qualitatively predicts these observed resonances.
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