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Island dynamics in the large-helical-device plasmas
1National Institute for Fusion Science, Toki, Gifu 509-5292, Japan.
Physical Review Letters
|February 28, 2002
Summary
In Large Helical Device plasma, collisionless conditions with finite beta significantly reduce externally imposed 1/1 islands. Collisional plasmas with finite beta enlarge islands above a specific vacuum island size threshold.
Area of Science:
- Plasma Physics
- Fusion Energy Research
- Magnetohydrodynamics
Background:
- Understanding plasma behavior in fusion devices is crucial.
- Externally imposed magnetic islands can affect plasma confinement.
- Plasma collisionality and beta (plasma pressure to magnetic pressure ratio) are key parameters influencing plasma stability.
Purpose of the Study:
- To investigate the impact of plasma collisionality and finite beta on externally imposed magnetic islands.
- To determine the conditions under which magnetic island size changes in the Large Helical Device.
- To identify thresholds for magnetic island enlargement in fusion plasmas.
Main Methods:
- Analysis of plasma discharges in the Large Helical Device.
- Measurement of externally imposed island size.
- Correlation of island size with plasma parameters like collisionality (nu*) and beta.
Main Results:
- A substantial decrease in 1/1 island size was observed in collisionless plasmas (nu* < 1) with finite beta (> 0.1%).
- In collisional plasmas with finite beta, island size increased.
- A threshold in vacuum island size was identified, below which enlargement did not occur.
Conclusions:
- Plasma collisionality and finite beta play critical roles in magnetic island dynamics.
- Collisionless regimes with finite beta can suppress magnetic islands, potentially improving plasma confinement.
- The existence of a threshold for island enlargement suggests complex nonlinear interactions within the plasma.