Abstract
A photo-cathode able to generate a high-performance electron beam with large operability is one of the most important devices in an advanced accelerator. In particular, the $$\rm CsK_2Sb$$ photo-cathode is of interest because it has high robustness and can be driven by visible light. In this study, we performed cathode evaporation on Si(100), Si(111), and GaAs(100) substrates to evaluate the performance dependence on the substrate material and surface state. For each substrate, the cathode performance on the as-received and cleaned substrates were compared. We found that the cathode performance on the cleaned substrate was superior to that on the as-received substrate for all materials. The cathode performance on the cleaned GaAs(100) and Si(100) substrates were similar, but that on the cleaned Si(111) was significantly much lower. This result gives experimental evidence about the substrate surface direction dependence of $$\rm CsK_2Sb$$ photo-cathode performance.
Highlights
In linear-accelerator-based advanced accelerators such as the Energy Recovery Linac (ERL) [1,2], Free Electron Laser (FEL) [3], and Linear Collider (LC) [4], the performance of the accelerated beam strongly depends on the initial beam property
The multi-alkali cathode is considered to be the strongest candidate as a high-brightness electron source because it can be operated by green light (532 nm) with 10% quantum efficiency (QE) [14,15], which is obtained from the second harmonics of a solid-state laser
We found that the QE was maximized around 100 ◦C on Si(100) and Si(111) with good reproducibility
Summary
In linear-accelerator-based advanced accelerators such as the Energy Recovery Linac (ERL) [1,2], Free Electron Laser (FEL) [3], and Linear Collider (LC) [4], the performance of the accelerated beam strongly depends on the initial beam property. The multi-alkali cathode is considered to be the strongest candidate as a high-brightness electron source because it can be operated by green light (532 nm) with 10% QE [14,15], which is obtained from the second harmonics of a solid-state laser. The quantum efficiency of the cathode in these studies was relatively low (3%), and cathode performance dependence on the surface direction of the substrate or CsK2Sb crystal was not significantly observed. This suggests that the cathode evaporation condition was not fully optimized in these studies. We describe the experiment, and provide the results and discussion
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