Continuous-wave photoinjectors operating at high accelerating gradients promise to revolutionize many areas of science and applications. They can establish the basis for a new generation of monochromatic x-ray free electron lasers, high-brightness hadron beams, or a new generation of microchip production. In this Letter we report on the record-performing superconducting rf electron gun with CsK_{2}Sb photocathode. The gun is generating high charge electron bunches (up to 10  nC/bunch) and low transverse emittances, while operating for months with a single photocathode. This achievement opens a new era in generating high-power beams with a very high average brightness.

High-Brightness Continuous-Wave Electron Beams from Superconducting Radio-Frequency Photoemission Gun.

A superconducting radio frequency (RF) photoelectron injector (SRF gun) is under development at the Research Center Dresden–Rossendorf. This project aims mainly at replacing the present thermionic gun of the superconducting electron linac ELBE. Thereby the beam quality is greatly improved. Especially, the normalized transverse emittance can be reduced by up to one order of magnitude depending on the operating conditions. The length of the electron bunches will be shortened by about two orders of magnitude making the present bunchers in the injection beam line dispensable. The maximum obtainable bunch charge of the present thermionic gun amounts to 80 pC. The SRF gun is designed to deliver also higher bunch charge values up to 2.5 nC. Therefore, this gun can be used also for advanced facilities such as energy recovery linacs (ERLs) and soft X-ray FELs. The SRF gun is designed as a 3 1 2 cell cavity structure with three cells basically TESLA cells supplemented by a newly developed gun cell and a choke filter. The exit energy is projected to be 9.5 MeV. In this paper, we present a description of the design of the SRF gun with special emphasis on the physical and technical problems arising from the necessity of integrating a photocathode into the superconducting cavity structure. Preparation, transfer, cooling and alignment of the photocathode are discussed. In designing the SRF gun cryostat for most components wherever possible the technical solutions were adapted from the ELBE cryostat in some cases with major modifications. As concerns the status of the project the design is finished, most parts are manufactured and the gun is being assembled. Some of the key components are tested in special test arrangements such as cavity warm tuning, cathode cooling, the mechanical behavior of the tuners and the effectiveness of the magnetic screening of the cavity.

Development of a superconducting radio frequency photoelectron injector

The proposed FELs at CEBAF require an electron source delivering 120 pC bunches at a repetition rate of 7.485 MHz, corresponding to an average current of 0.9 mA. To meet this requirement we will employ a 500 kV DC photoemission electron gun to produce nominal 100 psec bunches of modest peak current. The subsequent injector system will bunch and accelerate this beam, producing 60 A, 2 psec bunches for the FELs. The photoemission gun will use a negative electron affinity GaAs photocathode, which provides good quantum efficiency and an adequate temporal response. The optical beam will be provided by a frequency doubled Nd:YLF laser system, actively mode locked to a subharmonic of the fundamental accelerator frequency. The principal technical difficulties associated with an electron source of this type involve the operating lifetime of the photocathode, and the operation of a high voltage gun in the presence of the alkali metals necessary to produce the photocathode. Various design a

/pdf/a-500-kv-photoemission-electron-gun-for-the-cebaf-fel-4rk4p3qw8a.pdf

A 500 kV photoemission electron gun for the CEBAF FEL

Currently available, fully coherent (laser) light sources emit radiation only in a limited range of wavelengths in the infrared, visible and near-ultraviolet range, excluding their use in all the measurements needing tunable photons of energy higher than a few eV. Consequentially, the strong scientific need for tunable, coherent radiation sources from the vacuum ultraviolet (VUV) to the X-ray in the femtosecond and picosecond time domain has spurred international research efforts to develop a new generation of research facilities. Laser-driven light sources that use non-linear processes to create very high harmonics and the interaction between an ultra-short laser pulse and an electron bunch in a storage ring are both able to produce radiation pulses in the femtosecond time domain and in the soft EUV and X-ray region, but with a relatively low useful photon flux on the sample. In contrast Free-Electron Lasers (FELs) can produce light pulses with peak brilliance as much as ten orders of magnitude higher than the pulses generated in present third-generation synchrotron light sources and with photon energies ranging from the VUV to the hard X-rays, i.e. from about 10eV (120nm) to 10keV (0.12nm). This manuscript reviews the scientific fields that can be opened or extended by the new techniques along with the progress of FEL physics and the supporting accelerator physics and technology.

/pdf/vuv-and-x-ray-free-electron-lasers-the-technology-and-its-4l3q3bh9cg.pdf

VUV and X-ray free-electron lasers: The technology and its scientific promise

At the radiation source ELBE a superconducting radio-frequency photoinjector (SRF gun) was developed and put into operation Since 2010 the gun has delivered beam into the ELBE linac A new driver laser with 13 MHz pulse repetition rate allows now to operate the free-electron lasers (FELs) with the SRF gun This paper reports on the first lasing experiment with the far-infrared FEL at ELBE, describes the hardware, the electron beam parameters and the measurement of the FEL infrared radiation output

Free-electron laser operation with a superconducting radio-frequency photoinjector at ELBE

We describe the design of an electron injector for the production of a bunched cw electron beam of high brightness, low energy spread, and potentially high beam power. Electron beams of this kind are required for high efficiency and short wavelength free electron lasers. The injector consists of a superconducting reentrant cavity housing a photoemission cathode evaporated on a superconducting substrate. The cathode is illuminated with short light pulses of a mode-locked frequency doubled Nd: YAG laser. The experimental layout of the “superconducting photoemission source” is described together with its components: the photocathode preparation chamber, the cavity, the cryogenic setup, and the beam analysis system. The conceptual beam parameters are discussed and first results of calculations on beam dynamics using a particle-in-cell computer code are given.

/pdf/a-proposed-superconducting-photoemission-source-of-high-3rkvezfh6q.pdf

A proposed superconducting photoemission source of high brightness

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A proposed superconducting photoemission source of high brightness