Particle model of full-size ITER-relevant negative ion source

Area of Science:

• Plasma Physics
• Fusion Energy Research

Background:

• Accurate modeling of negative ion sources is crucial for fusion energy development.
• Previous models have not fully captured the complexities of full-size ITER-relevant negative ion sources.

Purpose of the Study:

• To develop and utilize a detailed 2.5D particle-in-cell Monte Carlo collision model for the ITER negative ion source.
• To investigate the impact of magnetic fields and plasma grid geometry on ion extraction.

Main Methods:

• A 2.5D particle-in-cell Monte Carlo collision model was employed.
• The model included expansion, extraction, and partial acceleration regions with fine mesh resolution.
• Magnetic filter and electron deflection fields were incorporated.

Main Results:

• A significant asymmetry in electron current was observed across the plasma grid apertures.
• This asymmetry is driven by electron Hall drift perpendicular to the filter field.
• A negative ion current density of 660 A/m² was used as a parameter for neutral conversion.

Conclusions:

• The developed model highlights critical design challenges related to plasma uniformity in negative ion sources.
• Electron Hall drift is a key factor causing inhomogeneity in extracted electron currents.
• Achieving a steady state within 15 μs was not yet realized, indicating the need for further model refinement and longer simulation times.