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Development of 3D microwave imaging reflectometry in LHD (invited)
Y Nagayama1, D Kuwahara, T Yoshinaga
1National Institute for Fusion Science, Toki, Japan.
The Review of Scientific Instruments
|November 7, 2012
Summary
Three-dimensional microwave imaging reflectometry visualizes plasma density fluctuations using four frequencies. A narrow structure along field lines was observed during edge harmonic oscillations (EHO).
Area of Science:
- Plasma physics
- Fusion energy research
- Microwave diagnostics
Background:
- Density fluctuations in plasma affect stability and performance.
- Visualizing these fluctuations is crucial for understanding plasma behavior.
- Edge Harmonic Oscillations (EHO) are important MHD modes in edge plasma.
Purpose of the Study:
- To develop and apply a 3D microwave imaging reflectometry system.
- To visualize fluctuating reflection surfaces caused by plasma density fluctuations.
- To observe the Edge Harmonic Oscillation (EHO) in the edge plasma.
Main Methods:
- Utilized 3D microwave imaging reflectometry in a large helical device.
- Employed probe waves at four frequencies for radial position mapping.
- Used imaging optics to project cut-off surfaces onto 2D horn antenna mixer arrays (7x7 channels).
- Developed multi-channel receivers with micro-strip-line technology.
Main Results:
- Successfully visualized fluctuating reflection surfaces caused by density fluctuations.
- Observed the Edge Harmonic Oscillation (EHO) using the developed system.
- Identified a narrow structure aligned with field lines during EHO.
Conclusions:
- The 3D microwave imaging reflectometry system is effective for visualizing plasma density fluctuations.
- The system provides valuable insights into MHD modes like EHO.
- The observed narrow structure offers new information about EHO characteristics.
