Abstract
The thermally assisted photoemission (TAPE) effect was investigated for the hexaboride thermionic cathodes (${\mathrm{LaB}}_{6}$ and ${\mathrm{CeB}}_{6}$). It was found that the quantum efficiency of these cathodes can be increased by raising the cathode temperature along with the thermionic emission. In addition both materials can emit a measurable photoemission current by being irradiated with a laser having a photon energy below the work function at sufficiently high cathode temperatures. Our measurements indicate that this process is linear. These results show the significance of the TAPE effect. An additional effect of cathode heating is surface cleaning. This effect was detected as the hysteresis of the quantum efficiency which can be observed by heating up and cooling down the cathode. This effect slightly changes the quantum efficiency but not as much as the TAPE effect.
Highlights
Thermionic and photoelectron injectors are widely adopted in FEL facilities
In this work we investigate the possibility of increasing the quantum efficiency (QE) of thermionic cathode materials using a thermally assisted photoemission (TAPE) process
The main point of interest is to understand the effects of thermal excitation on the photoemission properties of metal hexaboride materials. Another point is the feasibility of electron extraction by photon energy below the work function of the cathode material using the TAPE effect
Summary
Thermionic and photoelectron injectors are widely adopted in FEL facilities. The use of photocathodes for the generation of high brightness electron beams has the advantages of a high peak current and flexible control of emission timing; in some cases it has the disadvantages of high sensitivity to vacuum conditions and short lifetime. By heating up a cathode, electrons can obtain a higher energy state than the work function and can be extracted via thermionic current. In this study we focus on two representative hexaboride thermionic cathode materials, LaB6 and CeB6, and investigate their photoemission properties under various temperature and incident photon energy conditions. In this work we focus on the TAPE phenomenon on itself and treat the dark current as the background in data evaluation Another point of interest would be the application of the TAPE effect for electron extraction by laser with photon energy below the work function of the cathode material. Consideration of emittance and complexity of laser systems are beyond the scope of this paper
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
