Optical measurements for turbulence characterization in RFX-mod edge

Area of Science:

• Plasma Physics
• Fusion Energy Research
• Magnetic Confinement Fusion

Background:

• The edge of the Reversed Field Pinch experiment RFX-mod exhibits complex magnetic topology and significant pressure gradients.
• Understanding plasma edge parameters and turbulence is crucial for controlling fusion processes.

Purpose of the Study:

• To characterize main plasma edge parameters and turbulence in RFX-mod.
• To investigate coherent structures (blobs) and radial profiles of thermodynamic variables.
• To achieve high-frequency measurements of plasma edge dynamics.

Main Methods:

• Utilized a thermal helium beam diagnostic for local measurements of electron density (n(e)), temperature (T(e)), and pressure (P(e)) via spectral line ratios.
• Employed a gas puff imaging system for high-frequency (1 MHz bandwidth) measurements of He I emissivity fluctuations.
• Integrated triaxial magnetic coils for simultaneous characterization of the edge magnetic field.

Main Results:

• Obtained measurements of edge radial profiles for n(e), T(e), and P(e) using the helium beam diagnostic.
• Measured intermittent edge turbulence and the profiles of n(e), T(e), and P(e) for coherent structures with 6 μs resolution.
• Successfully correlated optical diagnostic data with magnetic field measurements.

Conclusions:

• The developed fast spectroscopic diagnostics effectively characterize plasma edge parameters and turbulence in RFX-mod.
• Detailed insights into coherent structures and thermodynamic profiles were achieved.
• The study provides valuable data for understanding and controlling plasma behavior in reversed field pinch devices.