Large charge extraction from metallic multifilamentary Nb3Sn photocathode

Area of Science:

• Materials Science
• Plasma Physics
• Accelerator Physics

Background:

• Conventional metallic photocathodes have a current density limit below 10^9 A/m^2 in RF photoguns.
• High current density is crucial for generating bright, short electron bunches.

Purpose of the Study:

• To develop a new photocathode material and structure to overcome the current density limitations of conventional metals.
• To investigate a new electron emission regime at high laser fluence.

Main Methods:

• Fabrication of a metallic-composite, multifilamentary Nb3Sn wire photocathode with a micrometer arrayed structure.
• Photoemission measurements using a 266 nm picosecond laser pulse and a 50 kV accelerating voltage.
• Characterization of charge extraction, quantum efficiency, and emittance.

Main Results:

• Achieved a current density of 1.6×10^11 A/m^2, exceeding the conventional limit by over 100 times.
• Stable extraction of up to 4800 pC of charge with 0.9% quantum efficiency, 100 times higher than conventional cathodes.
• Observed a new electron emission regime at high laser fluence (100 mJ/cm^2) without surface ablation.

Conclusions:

• The novel Nb3Sn photocathode enables unprecedented current densities and charge extraction, surpassing the 3-step model predictions.
• The low emittance achieved, despite high current density, is attributed to the small emitting area.
• This advanced photocathode technology is promising for applications requiring short and bright electron bunches.