Charge exchange spectroscopy as a fast ion diagnostic on TEXTOR

Area of Science:

• Plasma Physics
• Fusion Energy Research
• Spectroscopy

Background:

• Fast ions are crucial for heating and sustaining fusion plasmas.
• Accurate measurement of fast ion density profiles is essential for understanding plasma confinement and stability.
• Existing diagnostics have limitations in measuring fast ion behavior in tokamaks.

Purpose of the Study:

• To introduce and evaluate an upgraded charge exchange spectroscopy (CES) diagnostic at the TEXTOR tokamak.
• To demonstrate a novel method for simultaneously measuring fast ion populations using two neutral beam injectors.
• To improve the accuracy of absolute fast ion density profile measurements.

Main Methods:

• Utilizing an upgraded charge exchange spectroscopy diagnostic with specific viewing angles aligned with fast ion birth pitch angles.
• Employing two neutral beam injectors: one for fast ion generation and another for active spectroscopy.
• Simultaneously measuring the D-alpha spectrum, capturing both the fast ion tail and the Doppler-shifted beam emission spectrum.
• Developing a spectral analysis method to model and fit background noise and the slowing-down feature.

Main Results:

• The new diagnostic setup allows simultaneous measurement of the fast ion tail (blue wing) and Doppler-shifted beam emission (red wing) of the D-alpha spectrum.
• The combined spectral analysis offers enhanced accuracy for determining absolute fast ion density profiles.
• Background subtraction challenges were addressed by modeling and fitting spectral components.

Conclusions:

• The upgraded CES diagnostic at TEXTOR is operational and effective for fast ion studies.
• The novel dual-beam injection technique significantly improves the accuracy of fast ion density measurements.
• This advancement contributes to a better understanding of fast ion dynamics in fusion plasmas.