Design of a cavity ring-down spectroscopy diagnostic for negative ion rf source SPIDER.

Area of Science:

• Plasma physics
• Fusion energy research
• Atomic and molecular physics

Background:

• The SPIDER facility is crucial for testing and optimizing neutral beam injection systems for ITER.
• Accurate measurement of negative ion density is essential for efficient fusion plasma heating.

Purpose of the Study:

• To present the design and simulated performance of a Cavity Ring-Down Spectroscopy (CRDS) diagnostic for the SPIDER facility.
• To validate the CRDS diagnostic for measuring line-of-sight integrated negative ion (H(-) and D(-)) densities.

Main Methods:

• Cavity Ring-Down Spectroscopy (CRDS) utilizing the photodetachment process.
• Negative ions are converted to neutral atoms via laser-induced electron stripping.
• Design and simulation of the CRDS diagnostic for the SPIDER source extraction region.

Main Results:

• CRDS diagnostic design and performance simulations are presented.
• A prototype operated without plasma yielded reference CRDS signals.
• Validation of the diagnostic design and assessment of signal-to-noise ratio were achieved.

Conclusions:

• The CRDS diagnostic is a viable method for measuring negative ion densities in fusion plasma sources.
• The presented design and prototype results support the optimization of ITER's neutral beam injection systems.
• Further validation with plasma is expected to confirm the diagnostic's effectiveness.