Fringe jump analysis and implementation of polarimetry on the ASDEX Upgrade DCN interferometer

Area of Science:

• Plasma physics
• Fusion energy research
• Diagnostic techniques

Background:

• The ASDEX Upgrade tokamak uses a 5-channel DCN interferometer (195 μm wavelength) for plasma density measurements.
• Traditional phase measurement and density calculation rely on hard-wired electronics, susceptible to errors like fringe jumps.

Purpose of the Study:

• To introduce a fast digitizer for acquiring raw interferometer signals.
• To enable analysis of fringe jump causes and develop digital signal processing (DSP) based phase reconstruction.
• To test a prototype polarimeter for Faraday rotation measurements.

Main Methods:

• Installation of a fast digitizer to capture raw DCN interferometer signals.
• Development of digital signal processing algorithms for phase reconstruction.
• Integration of a prototype polarimeter for Faraday rotation measurements on one channel.

Main Results:

• The new system allows detailed analysis of fringe jump origins.
• Digital signal processing enables the development of improved phase reconstruction schemes.
• The prototype polarimeter successfully measures Faraday rotation.

Conclusions:

• The implemented digital system enhances the accuracy and analytical capabilities of plasma density diagnostics.
• This advancement supports more precise control and understanding of tokamak plasma behavior.
• The integration of polarimetry opens new avenues for plasma state characterization.