Interpreting the dynamic equilibrium during evaporation in a cesium environment.

Area of Science:

• Plasma physics
• Fusion energy research
• Materials science

Background:

• The ITER neutral beam injectors require precise control of cesium (Cs) vapor for optimal performance.
• The CAesium Test Stand (CATS) facility is used to test prototype Cs ovens under vacuum conditions (10⁻⁶ mbar).
• Understanding Cs behavior within the test chamber, particularly its interaction with surfaces, is essential for accurate modeling and experimental validation.

Purpose of the Study:

• To develop and validate a dynamic equilibrium model for Cs evaporation within the CATS facility.
• To determine the Cs sticking coefficient at the chamber walls.
• To provide a method for calculating Cs atom density and flux at various locations.

Main Methods:

• Implementation of a dynamic equilibrium model incorporating Cs atom sticking and energy accommodation at walls.
• Utilizing diagnostics such as Langmuir-Taylor detectors, laser absorption spectroscopy, and a quartz crystal microbalance.
• Simulating Cs evaporation and equilibrium density, comparing model predictions with experimental data.

Main Results:

• The study successfully modeled the dynamic equilibrium of Cs evaporation in the CATS facility.
• A Cs sticking coefficient of 2% at the chamber walls was determined through model-experiment comparison.
• The model provides accurate predictions of Cs atom density and flux distribution.

Conclusions:

• The developed model accurately describes Cs behavior in the CATS facility.
• The determined Cs sticking coefficient is a key parameter for refining ITER neutral beam injector source design.
• This work validates the experimental approach and modeling strategy for future tests.