Dark-ground illumination as a quantitative diagnostic for plasma density.

Area of Science:

• Plasma Physics
• Optical Diagnostics

Background:

• Toroidal belt pinch plasmas are crucial for fusion energy research.
• Accurate measurement of electron density profiles is essential for understanding plasma behavior.

Purpose of the Study:

• To develop and apply a novel optical diagnostic technique for measuring radial electron density profiles in toroidal belt pinch plasmas.
• To characterize the electron density of plasma produced in the Columbia Torus I belt pinch.

Main Methods:

• Utilized a collimated ruby laser focused to a 100-micrometer spot.
• Employed a modified dark-ground microscope technique, masking the central diffraction pattern with a wire.
• Recorded interference fringe patterns on photographic film to determine phase shifts and electron density.

Main Results:

• Successfully obtained radial electron density profiles of the toroidal belt pinch plasma.
• Measured an elliptical plasma cross-section with dimensions 2a ~ 2 cm and 2b ~ 30 cm.
• Determined peak electron densities (n(0)) around 3x10^16/cm^3 and average densities as low as 2x10^15/cm^3.

Conclusions:

• The developed optical technique provides a sensitive method for measuring plasma electron density.
• The results offer valuable data for theoretical models and further experiments on toroidal belt pinch plasmas.