1,720,983 research outputs found
Overview on development of metallic and superconducting photocathodes by the PLD technique for linear accelerator sources
No full textIn this paper, we report on the current status of the different configurations that have been suggested for the preparation of metallic and superconducting photocathodes (MPs and SCPs, respectively) by pulsed laser deposition. These strategic devices are used in the new generation of free-electron lasers and in research and development into plasma-based accelerators. To date, three different types of photocathodes have been used: conventional, hybrid and non-conventional configurations. In the case of the conventional configuration, the photocathode consists of a metallic bulk, typically Cu for normal conducting radio-frequency guns and Nb for superconducting radio-frequency guns. In the hybrid configuration, a thin emitting film with high photoemission performance, like Y or Mg, is located in the centre of the Cu flange of the photoinjector. For hybrid SCPs, the emitting material is a thin film of Pb, which has a quantum efficiency higher than that of Nb. Non-conventional configurations of MPs and SCPs have recently been engineered that consist respectively of a Y disc partially covered by a film of Cu and a Pb disc partially covered by a film of Nb. The central surfaces of the Y and Pb discs are not coated, thus providing an emitting area of the materials with higher quantum efficiency. These last devices inserted into a RF gun offer both the photoemission properties and work function of Y and the advantages of Cu in the case of MPs. In the case of SCPs, this new approach offers the relatively high photo-emissive properties of Pb and at the same time preserves all the advantages of Nb as a superconducting material
Characterisation of Pb thin films prepared by the nanosecond pulsed laser deposition technique for photocathode application
No full textAbstract Pb thin films were prepared by the nanosecond pulsed laser deposition technique on Si (100) and polycrystalline Nb substrates for photocathode application. As the photoemission performances of a cathode are strongly affected by its surface characteristics, the Pb films were grown at different substrate temperatures with the aim of modifying the morphology and structure of thin films. An evident morphological modification in the deposited films with the formation of spherical grains at higher temperatures has been observed. X-ray diffraction measurements showed that a preferred orientation of Pb (111) normal to the substrate was achieved at 30 C while the Pb (200) plane became strongly pronounced with the increase in the substrate temperature. Finally, a Pb thin film deposited on Nb substrate at 30 C and tested as the photocathode showed interesting results for the application of such a device in superconducting radio frequency guns
Characterisation of Pb thin films prepared by the nanosecond pulsed laser deposition technique for photocathode application
No full textMorphology and Structure of Nb Thin Films Grown by Pulsed Laser Deposition at Different Substrate Temperatures
No full textTight comparison of Mg and Y thin film photocathodes obtained by the pulsed laser deposition technique
No full textIn this work Magnesium (Mg) and Yttrium (Y) thin films have been deposited on Copper (Cu) polycrystalline substrates by the pulsed laser ablation technique for photocathode application. Such metallic materials are studied for their interesting photoemission properties and are proposed as a good alternative to the Cu photocathode, which is generally used in radio-frequency guns. Mg and Y films were uniform with no substantial differences in morphology; a polycrystalline structure was found for both of them. Photoemission measurements of such cathodes based on thin films were performed, revealing a quantum efficiency higher than Cu bulk. Photoemission theory according to the three-step model of Spicer is invoked to explain the superior photoemission performance of Mg with respect to Y. (C) 2016 Elsevier B.V. All rights reserved.</p
Nanomechanical and microtribological properties of yttrium thin films for photocathode engineering
No full textThe authors study the nanomechanical and microtribological properties of yttrium (Y) thin films deposited by pulsed laser deposition on Cu polycrystalline substrates. Nanoindentation tests reveal that such films have a high hardness of H = 2.3 GPa and a reduced elastic modulus of 71.7 GPa with respect to the Cu substrates. The friction coefficient between a diamond tip and the Y film reaches a steady state value of μ ∼ 0.34, lower than that for the Cu (μ ∼ 0.38). Moreover, nanoscratch experiments show that Y films are more scratch-resistant than the Cu substrates, probably due to their greater hardness, higher elastic recovery, and lower friction coefficient. Their results confirm that the mechanical and tribological properties of the Y films are suitable for designing and fabricating scratch-resistant hybrid photocathodes and can reduce instabilities and unwanted discharges in the cavity of the radio-frequency gun. Furthermore, the low surface roughness and the low work function of the material are important characteristics for a photocathode based on the Y thin film for the production of high-brightness electron beams
Growth of poly-crystalline Cu films on Y substrates by picosecond pulsed laser deposition for photocathode applications
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Structural and morphological properties of metallic thin films grown by pulsed laser deposition for photocathode application
Get PDFIn this work yttrium and lead thin films have been deposited by pulsed laser deposition technique and characterized by ex situ different diagnostic methods. All the films were adherent to the substrates and revealed a polycrystalline structure. Y films were uniform with a very low roughness and droplet density, while Pb thin films were characterized by a grain morphology with a relatively high roughness and droplet density. Such metallic materials are studied because they are proposed as a good alternative to copper and niobium photocathodes which are generally used in radiofrequency and superconducting radiofrequency guns, respectively. The photoemission performances of the photocathodes based on Y and Pb thin films have been also studied and discussed.Funding agencies: Italian National Institute of Nuclear Physics (INFN); Italian Ministry of Research [RBFR12NK5 k]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]</p
- …
