Abstract
A high-voltage pulsed electron gun has been developed for the low-emittance injector system of the x-ray free electron laser (FEL) project at SPring-8. A single-crystal ${\mathrm{CeB}}_{6}$ cathode was chosen as a thermionic emitter because of its excellent emission properties, i.e., smooth surface, high emission density, uniform emission density, and high resistance to contamination. A gun voltage of $\ensuremath{-}500\text{ }\text{ }\mathrm{kV}$ was determined as a compromise between the need for suppressing emittance growth and reducing the risks of high-voltage arcing. We have succeeded in producing a 500 keV beam with 1 A peak current and $3\text{ }\ensuremath{\mu}\mathrm{s}$ width. We have also measured the beam emittance by means of the double-slit method and obtained an extremely low emittance of $1.1\ensuremath{\pi}\text{ }\text{ }\mathrm{mm}\text{ }\mathrm{mrad}$ (normalized, rms). These results are very promising for the x-ray FEL. In this paper, we describe the design and basic performance of the ${\mathrm{CeB}}_{6}$ electron gun, and report the emittance measurement experiments.
Highlights
Nowadays, the generation of a low-emittance highintensity electron beam is an indispensable and key technology for future electron accelerators, e.g., x-ray free electron lasers (FEL), energy recovery linacs, and eeÿ linear colliders
In the case of the x-ray FEL based on the process of self-amplified spontaneous emission (SASE), it is well known that the fine structure of the beam dominates the FEL gain
A small tail at the profile edge is the source of the emittance increase, which may be generated by the space-charge effect
Summary
The generation of a low-emittance highintensity electron beam is an indispensable and key technology for future electron accelerators, e.g., x-ray free electron lasers (FEL), energy recovery linacs, and eeÿ linear colliders. In the x-ray FEL, the electron beam generated by the gun is accelerated in the main linac; it is directly injected into the long undulator and an x-ray beam is generated there. In the SPring-8 Compact SASE Source (SCSS) project, we decided to use a thermionic cathode followed by a buncher system [1,2,3]. This is a conventional injector system used in many types of electron accelerators. (iii) Application of 500 kV to the cathode.—In order to minimize emittance growth due to space-charge effects, a higher gun voltage is desirable. The design details and basic performance of the CeB6 electron gun are described, and the emittance measurement experiments are reported
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