Measurements of work function and surface conditions in cesiated negative ion sources

Area of Science:

• Plasma Physics
• Surface Science
• Ion Source Technology

Background:

• Negative hydrogen ion sources are vital for fusion energy research.
• Cesium injection is used to reduce coextracted electron currents in these sources.
• The surface work function of electrodes influences ion generation efficiency.

Purpose of the Study:

• To investigate the role of electrode surface work function in negative hydrogen ion sources.
• To measure the work function of extraction electrode surfaces under operational conditions.
• To understand the fundamental processes governing negative hydrogen ion generation.

Main Methods:

• Work function measurement using a work function diode.
• Kelvin probe measurements for surface potential.
• Photoelectric method for work function determination.
• Addressing challenges in measuring work function in plasma environments.

Main Results:

• Cesium deposition alters the work function of the extraction electrode surface.
• Work function is a critical parameter influencing electron transfer and H- ion yield.
• Difficulties in direct work function measurement within the ion source were encountered.

Conclusions:

• Optimizing the electrode surface work function through cesium injection is key to improving negative hydrogen ion source performance.
• Accurate work function measurement is essential for fundamental understanding and operational enhancement.
• Further research is needed to overcome measurement challenges and refine surface condition monitoring.