The new single crystal dispersion interferometer installed on KSTAR and its first measurement

Area of Science:

• Plasma physics
• Fusion energy research
• Optical diagnostics

Background:

• Dispersion interferometers are crucial for measuring line-integrated electron densities in fusion devices.
• Conventional setups using two nonlinear crystals face challenges with optical alignment and focusing, especially with small crystal apertures.
• Mechanical vibrations can introduce noise, necessitating effective optical suppression methods.

Purpose of the Study:

• To introduce and demonstrate a new heterodyne dispersion interferometer concept: the single crystal dispersion interferometer (SCDI).
• To overcome the optical alignment and focusing difficulties associated with conventional dispersion interferometers.
• To validate the SCDI's performance for measuring electron density, particularly during dynamic plasma events.

Main Methods:

• Development and installation of a single crystal dispersion interferometer (SCDI) on the KSTAR tokamak.
• Utilizing a 1064 nm laser wavelength for measurements.
• Comparison of SCDI measurements with data from an existing two-color interferometer.

Main Results:

• The KSTAR SCDI was successfully installed and operated.
• The SCDI demonstrated its capability to measure abrupt and large changes in electron density during shattered pellet injection.
• Measurements from the SCDI showed good agreement with the existing two-color interferometer, validating its feasibility.

Conclusions:

• The single crystal dispersion interferometer (SCDI) offers a simplified and effective approach for electron density measurements in fusion devices.
• The SCDI overcomes key optical alignment challenges inherent in conventional dispersion interferometers.
• This technology shows promise for advanced plasma diagnostics, especially in dynamic scenarios.