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Published on: August 1, 2017
Sawtooth oscillation in current-carrying plasma in the large helical device
Y Nagayama1, K Kawahata, S Inagaki
1National Institute for Fusion Science, Toki 509-5292, Japan.
Physical Review Letters
|June 6, 2003
Summary
Plasma current in helical devices triggers sawtooth oscillations, impacting core or edge plasma regions. These crashes, likely reconnection events, occur without observed precursors, advancing fusion energy research.
Area of Science:
- Plasma physics
- Fusion energy research
- Helical confinement
Background:
- Sawtooth oscillations are a common phenomenon in magnetically confined plasmas.
- Understanding sawtooth behavior is crucial for achieving stable fusion conditions.
- Previous studies often observed precursor oscillations before sawtooth crashes.
Purpose of the Study:
- To investigate sawtooth oscillations in current-carrying helical plasmas.
- To determine the effect of plasma current on sawtooth behavior and thresholds.
- To analyze the nature of sawtooth crashes and their precursors.
Main Methods:
- Utilizing electron-cyclotron-emission diagnostics.
- Conducting experiments in the Large Helical Device (LHD).
- Analyzing plasma behavior under varying plasma currents driven by neutral beam injection.
Main Results:
- Sawtooth oscillations were observed in current-carrying helical plasmas.
- Plasma current reduced the beta threshold for sawtooth oscillations.
- Increasing central q led to core crashes; decreasing q resulted in annular edge crashes.
- Rapid plasma mixing observed, suggesting reconnection phenomena.
- No precursor oscillations were detected, differing from prior experiments.
Conclusions:
- Plasma current significantly influences sawtooth oscillation dynamics in helical devices.
- Sawtooth crashes in this context are likely driven by magnetic reconnection.
- The absence of precursors offers new insights into crash mechanisms.
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