Millimeter-wave interferometry and far-forward scattering for density fluctuation measurements on LTX-β

Area of Science:

• Plasma physics
• Fusion energy research
• Diagnostic instrumentation

Background:

• Accurate electron density measurements are crucial for understanding plasma behavior in fusion devices.
• Existing interferometry techniques can be complex and require multiple components.

Purpose of the Study:

• To document the hardware of a novel interferometer for the Lithium Tokamak Experiment-β (LTX-β).
• To evaluate the system's capability as a far-forward collective scattering diagnostic.
• To assess its potential for measuring high-frequency density oscillations and turbulence.

Main Methods:

• Utilizing a unique narrow-band chirped-frequency interferometry system with a single source and beam splitter.
• Employing a centerstack-mounted retro-reflector mirror for radial chord measurements.
• Characterizing the system's scattering diagnostic capabilities for perpendicular wavenumbers (k⊥).

Main Results:

• The interferometer provides electron line density measurements along a midplane radial chord.
• The current optical setup has a detection range of 0.4 ≲ k⊥ ≲ 1.7 cm⁻¹.
• An improved layout is projected to extend the upper k⊥ limit to approximately 3 cm⁻¹.
• Initial measurements on LTX demonstrate both interferometry and scattered signal data.

Conclusions:

• The developed interferometer is a unique and capable diagnostic for LTX-β.
• The system is expected to provide routine measurements of coherent density oscillations and broadband turbulence.
• This diagnostic advancement contributes to the understanding of plasma dynamics in fusion experiments.