Magnesium Film Photocathodes for High Brilliance Electron Injectors (original) (raw)
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Improvement of the Photoemission Efficiency of Magnesium Photocathodes
2017
To improve the quality of photocathodes is one of the critical issues in enhancing the stability and reliability of photo-injector systems. Presently the primary choice is to use metallic photocathodes for the ELBE SRF Gun-II to reduce the risk of contamination of the superconducting cavity. Magnesium has a low work function (3.6 eV) and shows high quantum efficiency (QE) up to 0.3 % after laser cleaning. The SRF Gun II with an Mg photocathode has successfully provided electron beam for ELBE users. However, the present cleaning process with a high intensi-ty laser (activation) is time consuming and generates unwanted surface roughness. This paper presents the investigation of alternative surface cleaning procedures, such as thermal treatment. The QE and topography of Mg samples after treatment are reported.
High-brightness photocathode electron sources
AIP Conference Proceedings, 1995
Most present and future electron accelerators require bright sources. Invented less than ten years ago, the photo-injector the principle of which is briefly recalled, has already demonstrated that it can provide very bright beams. In this paper, the most advanced photo-injector projects are reviewed, their specific features are outlined, and their major issues are examined. The state-of-the-art in photocathode and laser technologies is presented. Beam dynamics issues are also considered since they are essential in the production of bright beams. Finally, the question of the maturity of photo-injector technology is addressed.
Ablated Mg films with a graphite cover as photocathodes
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005
Mg films deposited by pulsed laser ablation on a Cu substrate were tested as photocathodes in a DC diode. They showed features of robustness and a quantum efficiency of 3 Â 10 À4 at low accelerating field when illuminated by 266 nm light at normal incidence. A graphite protective layer of about 20 nm thickness deposited by laser ablation just after the Mg deposition made the cathode stable and of easy handling. The cathodes could stay for several weeks in air before being inserted in the test chamber. The preparation procedure and the tests are presented. r
R & D ACTIVITY ON HIGH QE ALKALI PHOTOCATHODES FOR RF GUNS
1996
R&D on high quantum efficiency (QE) alkali photocathode is in progress at Milano in the context of the ARES-TTF (Tesla Test Facility) program. High QE multialkali antimonide and cesium telluride cathodes have been produced in an advanced preparation system. Photoemitter's preparation procedures have been set-up, in collaboration with the SESAMO lab. of the University of Modena, using Auger Electron Spectroscopy (AES): AES technique was used, in conjunction with sputter erosion, to obtain the in-depth profile of the photoemissive film. In this way photocathode preparation parameters (substratum cleaning procedure and temperature, alkali metal deposition rate, etc.) have been optimised. The spectral response of the photocathodes and the QE spatial distribution over the cathode surface has been measured using different light sources (254 nm < λ < 670 nm) and an optical scanning system. The photocathode poisoning effect and the changes in the photoemissive response due to the reaction with different gases have been investigated exposing the photoemitters, in a controlled way, to methane, carbon monoxide, carbon dioxide and oxygen. The good results so far obtained brought in Milano the responsibility of the production of cesium telluride photocathodes for the TTF Injector II. A preparation system for this application will be operative at Argonne within the end of 1995.
Journal of physics, 2011
Accelerator drivers for Energy Recovery Linac (ERL) and Free-Electron Laser (FEL) based light sources demand electron injectors which deliver high brightness bunches on the several hundreds of picocoulomb scale, at repetition rates between 1 MHz and 1 GHz (or higher), corresponding to an average current between 0.1 and 100 mA. Simultaneous satisfaction of these injector requirements is considerably beyond the current state-of-the-art. Daresbury Laboratory is concentrating efforts on the development of high average current III-V and X n Y 3-n Sb photocathode-based DC and SRF photocathode guns for ERL applications. The ultimate goal of this research is their integration with the ALICE ERL.
Pulsed laser deposition of Mg thin films on Cu substrates for photocathode applications
Applied Surface Science, 2005
In this study, pulsed laser ablation of pure Mg targets (99.99%) using an XeCl excimer laser (l = 308 nm, t = 30 ns) was used to grow Mg coatings on Cu substrates. A thin layer of Mg (100-200 nm) was deposited in UHV of 5 Â 10 À6 Pa to ensure high purity. A second ultra-thin layer of MgO of 10-20 nm was deposited in oxygen at 10 À2 Pa pressure to protect the previous layer from atmospheric contamination.
Experimental characterization of the high-brightness electron photoinjector
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1996
Operational experience of the emittance compensated photoinjector at the Brookhaven Accelerator Test Facility (ATF) is presented in this paper. The photoinjector has demonstrated the stability and reliability required for UV and X-ray FEL applications. The RF gun has been routinely running at more than 100 MV/m peak acceleration field; the laser system of the photoinjector has achieved 2% peak to peak energy stability, 0.5 % point stability and better than 2 ps timing jitter. The highest measured quantum efficiency of the Cu cathode is 0.05%. The electron beam bunch length was measured to be 10 ps using a linac RF phase scan. The normalized rms emittance for a 0.5 nC charge was measured, to be from 1 to 2 mm-mad, which agrees with PARMELA simulations.
Design of a high-brightness, high-duty factor photocathode electron gun
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 1992
The proposed UV-FEL user's facility at Brookhaven National Laboratory will require a photocathode gun capable of producing short (< 6 psec) bunches of electrons at high repetition rates (5 kHz), low energy spread (< 1.5 %), a peak current of 300 A (after compression) and a total bunch charge of up to 2 nC. At the highest charge the normalized transverse emittance should be less than 7 Jt mm-mrad. We are presently designing a gun that is expected to exceed these requirements. This gun will consist of 3 V2 cells, constructed of GlidCop-15, an aluminum oxide dispersion strengthened copper alloy. The gun will be capable of operating at duty factors in excess of 1%. Extensive beam dynamics studies of the gun were used to determine the effect of varying the length of the first cell, shaping the apertures between cells, and increasing the number of cells. In addition, a detailed thermal and mechanical study of the gun was performed to ensure that the thermal stresses were well within the allowable limits and that copper erosion of the water channels would not occur.