Tomographic imaging system for measuring impurity line emission in a field-reversed configuration

Area of Science:

• Plasma Physics
• Optical Diagnostics
• Fusion Energy Research

Background:

• Field-reversed configurations (FRCs) are a promising magnetic confinement fusion approach.
• Accurate measurement of impurity ion transport is essential for optimizing FRC plasma stability and confinement.
• Existing diagnostic methods may have limitations in spatial and temporal resolution for FRC plasmas.

Purpose of the Study:

• To develop and implement a 16-chord optical tomography system for FRC plasmas.
• To measure the 2D emissivity profiles of impurity ions (singly ionized argon).
• To determine the radial, cross-field diffusion coefficients of impurity ions during FRC equilibrium.

Main Methods:

• A 16-chord optical tomography system with two fans of eight chords was implemented.
• Photomultiplier tubes (PMTs) with narrow band-pass filters centered at 434.8 nm measured argon emission.
• Argon gas was introduced via a puff valve during FRC formation.
• Reconstruction algorithms generated time-dependent, 2D emissivity profiles.

Main Results:

• The system achieved a spatial resolution of 1.5 cm.
• Background noise was less than 10% of the argon emission signal.
• Radial, cross-field diffusion coefficients were determined to be in the range of 10–10^3 m²/s during FRC equilibrium.

Conclusions:

• The developed optical tomography system is effective for diagnosing FRC plasmas.
• The measured diffusion coefficients provide critical data for FRC plasma modeling and improvement.
• This diagnostic capability advances the understanding of impurity transport in FRCs.