Fine-tuning to minimize emittances of J-PARC RF-driven H⁻ ion source

Area of Science:

• Particle Accelerators
• Plasma Physics
• Ion Source Technology

Background:

• The Japan Proton Accelerator Research Complex (J-PARC) utilizes a cesiated RF-driven H(-) ion source.
• Achieving high beam power is crucial for J-PARC's research capabilities.

Purpose of the Study:

• To optimize the rod-filter-field (RFF) configuration for minimizing transverse emittances.
• To investigate factors contributing to emittance degradation.
• To enhance the peak beam intensity and overall performance of the ion source.

Main Methods:

• Optimized the triple-gap-lengths of five rod-filter-magnets in the RFF system.
• Analyzed the impact of impurity gases on beam emittance.
• Modified the beam-hole-diameter of the extraction electrode.

Main Results:

• Successfully operated the H(-) ion source for approximately one year, demonstrating 1 MW beam power.
• Identified impurity gases as a significant cause of emittance degradation, potentially more so than the RFF.
• Observed unexpected improvements in both emittances and peak beam intensity with a smaller extraction electrode beam-hole-diameter.

Conclusions:

• The J-PARC H(-) ion source achieved its design beam power of 1 MW.
• RFF optimization and extraction electrode design are critical for beam quality.
• Controlling impurity gases is essential for further emittance reduction.