Thomson scattering diagnostic system design for the Compact Toroidal Hybrid experiment

Area of Science:

• Plasma Physics
• Fusion Energy Research
• Optical Diagnostics

Background:

• Non-axisymmetric plasmas present unique challenges for diagnostic measurements.
• Accurate characterization of plasma parameters is crucial for fusion energy development.
• Existing diagnostic systems may not be suitable for the specific geometry of the Compact Toroidal Hybrid (CTH) device.

Purpose of the Study:

• To design and implement a novel Thomson scattering system for the CTH device.
• To enable precise measurements of electron temperature and density in non-axisymmetric plasmas.
• To utilize standard, commercially available components for cost-effectiveness and accessibility.

Main Methods:

• A vertically aligned beam from a frequency-doubled Nd:YAG laser is directed through the CTH plasma.
• Careful optical design, including Brewster windows and baffle systems, minimizes stray laser light.
• An f/1 aspheric lens, Holospec spectrometer, and intensified camera are used for light collection and spectral analysis.

Main Results:

• The system is optimized for an 8m beam path with a <3mm beam diameter within the plasma.
• It is capable of measuring core electron temperatures from 20-300 eV.
• Electron densities can be determined in the range of 5 x 10^18 to 5 x 10^19 m^-3.

Conclusions:

• A functional Thomson scattering system has been successfully developed for the CTH device.
• The system's design effectively mitigates stray laser light interference.
• This diagnostic capability is vital for understanding and controlling non-axisymmetric plasma behavior in fusion research.