Measurements of intrinsic emittance dependence on rf field for copper photocathodes

Eduard Prat,Hans-Heinrich Braun,Simona Bettoni,Thomas Schietinger,Marta Csatari Divall

doi:10.1103/physrevstab.18.063401

Eduard Prat, Hans-Heinrich Braun + Show 3 more

Open Access

https://doi.org/10.1103/physrevstab.18.063401

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Abstract

Radio-frequency (rf) photoinjectors are used to generate high-brightness electron beams for a wide range of applications. Because of their outstanding beam quality, they are particularly well-suited as sources for X-ray free-electron lasers (FELs). The beam emittance, which is significantly influenced by the intrinsic emittance of the cathode, is fundamental for FELs, since it has a strong impact on the lasing performance and it defines the length and cost of the facility. In this paper we present measurements of the intrinsic emittance as a function of the rf field for a copper photocathode. Our measurements match with the theoretical expectations, showing that the intrinsic emittance can be reduced by decreasing the rf field at the cathode. We obtained normalized intrinsic emittances down to $350\text{ }\text{ }\mathrm{nm}/\mathrm{mm}$, the lowest values ever measured in a rf photoinjector.

Highlights

Radio-frequency photoinjectors [1] are the most adequate instruments to produce high brightness electron beams of energies up to several MeV
Rf photoinjectors have various applications, mainly as drivers for future linear colliders and especially X-ray free-electron laser (FEL) facilities, and as direct sources for electron diffraction experiments [2,3] or in compact gamma-ray or X-ray sources based on inverse Compton scattering [4,5]
The electron beam emittance is a key parameter for FELs

Summary

Introduction

Radio-frequency (rf) photoinjectors [1] are the most adequate instruments to produce high brightness electron beams of energies up to several MeV. The electron beam emittance is a key parameter for FELs. To produce diffraction-limited transverse-coherent radiation, the electron transverse emittance should be εn=γ ≈ λ=4π for an efficient electron-radiation interaction, where εn is the normalized beam emittance, γ is the Lorentz factor and λ is the FEL radiation wavelength. To produce diffraction-limited transverse-coherent radiation, the electron transverse emittance should be εn=γ ≈ λ=4π for an efficient electron-radiation interaction, where εn is the normalized beam emittance, γ is the Lorentz factor and λ is the FEL radiation wavelength This condition indicates that by reducing the normalized emittance the required final beam energy can be decreased, which allows a shorter and more economical accelerator.

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