Edge scanning reflectometry for density profile measurement on the SPARC tokamak

Area of Science:

• Plasma physics
• Fusion energy research
• Microwave diagnostics

Background:

• Accurate electron density measurements are crucial for understanding and controlling plasma behavior in fusion devices.
• The scrape-off layer and H-mode pedestal regions in tokamaks are critical for confinement and performance, requiring detailed density profiling.

Purpose of the Study:

• To develop and implement an Edge Scanning Reflectometry (ESRL) system for the SPARC tokamak.
• To measure electron density profiles from the far scrape-off layer to the H-mode pedestal top.
• To provide real-time density data essential for active plasma control.

Main Methods:

• Utilizes a frequency-modulated continuous wave (FMCW) technique operating from 18 to 90 GHz.
• Employs both O-mode and left-hand-cutoff X-mode reflectometry to cover a density range of approximately 4 × 10^18 to 4 × 10^20 m^-3 at 12 T.
• Leverages frequency multiplication and amplification to generate signals in K, Ka, U, and E bands, combined using quasi-optical techniques.
• Incorporates oversized waveguides and a bi-static arrangement to minimize signal loss and distortion.

Main Results:

• The ESRL system is designed to provide comprehensive electron density measurements across critical plasma regions.
• Simulations using a COMSOL Multiphysics RF model aid in optimizing antenna placement.
• Engineering analyses support the preliminary design of key system components.

Conclusions:

• The ESRL system is a viable diagnostic for detailed electron density profiling in SPARC.
• The multi-band FMCW approach enables measurements across a wide density range relevant to H-mode plasmas.
• Real-time density data from ESRL will significantly enhance plasma control capabilities for fusion research.