Two-dimensional wave-number spectral analysis techniques for phase contrast imaging turbulence imaging data on large...

Area of Science:

• Plasma Physics
• Fusion Energy Research
• Diagnostic Techniques

Background:

• Understanding plasma turbulence is crucial for magnetic confinement fusion.
• Accurate measurement of wave-number spectra and phase velocity is essential for characterizing turbulence.
• Existing methods for analyzing 2D CO2 laser phase contrast imaging data have limitations in spatial resolution.

Purpose of the Study:

• To develop and validate an improved analysis method for spatially resolved wave-number spectra and phase velocity.
• To enhance the characterization of plasma turbulence in the Large Helical Device (LHD).
• To compare different spectral analysis techniques for phase contrast imaging data.

Main Methods:

• Utilized magnetic shear technique for propagation direction identification.
• Applied 2D spatial Fourier analysis to images from a 6x8 detector array.
• Employed multiple-spatial point cross-correlation averaging before power spectrum calculation.
• Compared conventional Fourier analysis with the Maximum Entropy Method (MEM).

Main Results:

• The Maximum Entropy Method (MEM) provided superior results compared to other techniques.
• MEM significantly improved spatial resolution (Δρ ~ 0.1) compared to conventional Fourier analysis (Δρ ~ 0.5).
• Artifacts from spectral narrowing were investigated and found to be non-significant.

Conclusions:

• The developed MEM-based analysis method offers significantly enhanced spatial resolution for wave-number spectra.
• This improved resolution facilitates more accurate physical interpretation of plasma turbulence.
• The technique is valuable for analyzing data from 2D CO2 laser phase contrast imaging systems in fusion devices.