Improved density profile measurements in the C-2U advanced beam-driven Field-Reversed Configuration (FRC) plasmas

Area of Science:

• Plasma physics
• Interferometry
• Fusion energy research

Background:

• Previous C-2 experiment utilized a CO2/HeNe interferometer for electron density measurements.
• High-frequency common mode phase noise was identified as a challenge in prior measurements.
• A reference chord construction was found to reduce this noise by a factor of 3.

Purpose of the Study:

• To present improved plasma density profile measurement results from the upgraded C-2U system.
• To demonstrate the capabilities of the new 4-chord far-infrared laser interferometer.
• To investigate the influence of fast ions on plasma density and plasma stability.

Main Methods:

• Development of a 4-chord far-infrared laser interferometer for the C-2U upgrade.
• Utilizing superior sensitivity (>1 MHz bandwidth, 1 x 10^16 m^-2) to overcome spatial undersampling issues.
• Analysis of electron density profiles and plasma dynamics.

Main Results:

• The new interferometer demonstrated superior sensitivity and resolved spatial undersampling.
• Evidence of fast-ion modified density profiles was observed.
• Stabilization of the n = 1 plasma wobble mode was achieved.

Conclusions:

• The C-2U far-infrared interferometer provides enhanced electron density measurements.
• The system successfully captured fast-ion driven density modifications.
• The findings contribute to understanding plasma stability and control in fusion research.