Upgraded millimeter-wave interferometer for measuring the electron density during the beam extraction in the negative...

Area of Science:

• Plasma physics
• Fusion energy research

Background:

• Accurate measurement of electron density is crucial for optimizing negative ion sources used in fusion energy research.
• Previous measurement techniques faced limitations during high-voltage beam extraction.

Purpose of the Study:

• To upgrade a millimeter-wave interferometer for precise electron density measurements in a large-scaled negative ion source.
• To investigate the behavior of electron density during beam extraction.

Main Methods:

• Installed an upgraded 70 GHz millimeter-wave interferometer on a large-scaled negative ion source.
• Implemented several improvements including shorter wavelength probing, specialized horn antenna, digital phase detection, and insulator insertion.
• Performed measurements in front of the plasma grid, covering electron densities from 2 × 10^15 to 3 × 10^18 m^-3.

Main Results:

• Successfully measured line-averaged electron density during beam extraction.
• Observed a linear increase in electron density with increasing arc power.
• Detected a sudden drop in electron density upon initiation of high-voltage beam extraction.

Conclusions:

• The upgraded interferometer enables reliable electron density measurements in challenging negative ion source environments.
• Electron density is strongly correlated with operational parameters like arc power and beam extraction.
• These findings provide valuable data for optimizing negative ion source performance.