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A new correlation polarimeter-interferometer system enhances plasma diagnostics in the DIII-D tokamak. This advanced system achieves a significantly lower noise floor for detecting magnetic and density fluctuations.

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Area of Science:

  • Plasma physics
  • Fusion energy research
  • Advanced diagnostic techniques

Background:

  • Tokamak devices require precise measurements of plasma properties.
  • Detecting small-amplitude magnetic and density fluctuations is crucial for understanding plasma behavior.
  • Existing polarimeter-interferometer systems have limitations in sensitivity and noise levels.

Purpose of the Study:

  • To develop and demonstrate a novel correlation polarimeter-interferometer system.
  • To achieve a lower noise floor for enhanced detection of plasma fluctuations.
  • To measure magnetic and density fluctuations in DIII-D tokamak plasmas.

Main Methods:

  • Utilizing two collinear, frequency-offset, orthogonally polarized electromagnetic waves (650 GHz) to measure the Faraday effect.
  • Employing a third, linearly polarized wave as a local oscillator for line-averaged density measurement.
  • Implementing correlation techniques between two detectors for polarimetry and two intermediate frequencies for interferometry.

Main Results:

  • The developed system exhibits a noise floor more than one order of magnitude lower than standard systems.
  • Successfully detected broadband magnetic and density fluctuations in DIII-D H-mode plasmas.
  • Measured fluctuation amplitudes as low as 0.03 Gauss/kHz for magnetic fields and 4x10^13 m^-3/kHz for density.

Conclusions:

  • The correlation polarimeter-interferometer is a highly sensitive diagnostic for plasma fluctuations.
  • This technology offers significant improvements for plasma research in fusion devices.
  • The system enables detailed characterization of turbulent phenomena in tokamak plasmas.