Observation Of Repetition-Rate Dependent Emission From an Un-Gated Thermionic Cathode RF Gun

TL;DR

This study investigates how RF repetition rate affects emission in an un-gated thermionic cathode RF gun, revealing an inverse relationship contrary to existing models, likely due to cathode surface damage.

Contribution

The paper presents experimental evidence of an inverse relationship between RF repetition rate and average current, challenging existing theories and highlighting cathode surface degradation effects.

Findings

Inverse relationship observed between RF repetition rate and average current

Cathode surface damage impacts emission behavior

Challenges identified for scaling high-current RF guns

Abstract

Recent work at Fermilab in collaboration with the Advanced Photon Source and members of other national labs, designed an experiment to study the relationship between the RF repetition rate and the average current per RF pulse. While existing models anticipate a direct relationship between these two parameters we observed an inverse relationship. We believe this is a result of damage to the barium coating on the cathode surface caused by a change in back-bombardment power that is unaccounted for in the existing theories. These observations shed new light on the challenges and fundamental limitations associated with scaling an un-gated thermionic cathode RF gun to high average current machines.