An upgraded interferometer-polarimeter system for broadband fluctuation measurements

Area of Science:

• Plasma Physics
• Fusion Energy Research
• Diagnostic Techniques

Background:

• High-frequency fluctuations are crucial for understanding plasma instabilities and transport.
• Previous diagnostic limitations hindered detailed analysis of these phenomena.

Purpose of the Study:

• To upgrade the Madison Symmetric Torus interferometer-polarimeter system for more sensitive high-frequency fluctuation measurements.
• To improve the diagnosis of plasma instabilities and transport phenomena.

Main Methods:

• Implementation of improved planar-diode mixer technology.
• Reduction of phase noise in the interferometer-polarimeter system.
• Verification of probe beam alignment tolerances for accurate polarimetry.

Main Results:

• Achieved typical polarimeter root-mean-square (rms) phase noise values of 0.05°-0.07° with a 400 kHz bandwidth.
• Enabled resolution of fluctuations up to 250 kHz for polarimetry and 600 kHz for interferometry.
• Confirmed that probe beam alignment tolerances of ≤0.1 mm minimize spatial misalignment contamination.

Conclusions:

• The upgraded system provides significantly enhanced sensitivity for high-frequency fluctuation measurements.
• Improved diagnostics are vital for advancing the understanding of plasma behavior in fusion devices.
• Precise alignment is critical for reliable polarimetric measurements, especially near the magnetic axis.