Dual-angle, self-calibrating Thomson scattering measurements in RFX-MOD

Area of Science:

• Plasma Physics
• Fusion Energy Research
• Optical Diagnostics

Background:

• The RFX-MOD experiment utilizes multipoint Thomson scattering (TS) for plasma diagnostics.
• Accurate calibration of spectral channels is crucial for reliable TS measurements.
• Simultaneous observation at multiple spatial positions and scattering angles is challenging.

Purpose of the Study:

• To develop and validate a self-calibrating TS measurement technique for the RFX-MOD experiment.
• To simultaneously determine electron temperature (Te), electron density (ne), and relative spectral channel sensitivity coefficients (Ci).
• To assess the feasibility of using dual-angle scattering data for in-situ calibration.

Main Methods:

• Utilizing a multipoint TS system capable of simultaneous measurements at two different scattering angles.
• Employing optical multiplexing with fiber optic signal delays to route signals to a single polychromator.
• Analyzing dual-angle TS spectra to extract plasma parameters and calibration coefficients.

Main Results:

• Demonstrated the simultaneous determination of Te, ne, and Ci from dual-angle TS data.
• Showed that reliable relative calibration coefficients can be obtained even with small spectral differences.
• Confirmed the feasibility of the method with good signal-to-noise ratio spectra from a limited number of plasma shots.

Conclusions:

• The dual-angle TS technique provides a robust method for self-calibration of plasma diagnostics.
• This approach simplifies and enhances the accuracy of electron temperature and density measurements.
• The findings suggest that calibrating all TS polychromators using a dual-laser TS technique in RFX-MOD is feasible.