High-bandwidth polarimeter for a high density, accelerated spheromak.

Area of Science:

• Plasma physics
• Fusion energy research
• Optical diagnostics

Background:

• The PI-1 plasma injector requires advanced diagnostics for performance evaluation.
• Accurate measurement of plasma density and magnetic fields is crucial for fusion research.
• Heterodyne polarimetry offers a non-invasive method for plasma characterization.

Purpose of the Study:

• To develop and calibrate a three-beam heterodyne polarimeter for the PI-1 plasma injector.
• To measure plasma density and Faraday rotation for magnetic field estimation.
• To validate the polarimeter's performance against other diagnostics and models.

Main Methods:

• Construction of a three-beam heterodyne polarimeter.
• Calibration procedures including beam ellipticity measurement and ensuring collinearity.
• Measurement of Faraday rotation and plasma density.
• Comparison of polarimeter data with existing diagnostics and theoretical models.

Main Results:

• The calibrated polarimeter shows improved agreement with other diagnostics.
• The noise floor for Faraday rotation measurement is 0.1° at 0.5 MHz bandwidth.
• Maximum error in spheromak Faraday rotation measurements is approximately 0.3° at 0.5 MHz bandwidth.
• Axial resolution of 6 cm to 30 cm achieved at 0.5 MHz bandwidth.

Conclusions:

• The three-beam heterodyne polarimeter is a valuable diagnostic tool for plasma injectors.
• Calibration is essential for accurate Faraday rotation measurements.
• The polarimeter provides reliable data on plasma density and magnetic field characteristics.
• Future upgrades will include additional polarimeter chords for enhanced spatial coverage.