Role of surface microgeometries on electron escape probability and secondary electron yield of metal surfaces

The influence of microgeometries on the Secondary Electron Yield (SEY) of surfaces is investigated. Laser written structures of different aspect ratio (height to width) on a copper surface tuned the SEY of the surface and reduced its value to less than unity. The aspect ratio of microstructures was methodically controlled by varying the laser parameters. The results obtained corroborate a recent theoretical model of SEY reduction as a function of the aspect ratio of microstructures. Nanostructures - which are formed inside the microstructures during the interaction with the laser beam - provided further reduction in SEY comparable to that obtained in the simulation of structures which were coated with an absorptive layer suppressing secondary electron emission

Low secondary electron yield engineered surface for electron cloud mitigation

Secondary electron yield (SEY or δ) limits the performance of a number of devices. Particularly, in high-energy charged particle accelerators, the beam-induced electron multipacting is one of the main sources of electron cloud (e-cloud) build up on the beam path; in radio frequency wave guides, the electron multipacting limits their lifetime and causes power loss; and in detectors, the secondary electrons define the signal background and reduce the sensitivity. The best solution would be a material with a low SEY coating and for many applications δ < 1 would be sufficient. We report on an alternative surface preparation to the ones that are currently advocated. Three commonly used materials in accelerator vacuum chambers (stainless steel, copper, and aluminium) were laser processed to create a highly regular surface topography. It is shown that this treatment reduces the SEY of the copper, aluminium, and stainless steel from δmax of 1.90, 2.55, and 2.25 to 1.12, 1.45, and 1.12, respectively. The δmax further reduced to 0.76-0.78 for all three treated metals after bombardment with 500 eV electrons to a dose between 3.5 × 10-3 and 2.0 × 10-2 C·mm-2

The impacts of situational factors on consumer misbehaviour in service outlets (on the example of Iranian chain stores)

The aim of the article. The aim of this study is to identify and explore the situational factors, which lead customers to misbehave in service settings. This study is designed to develop a better understanding of different drivers of misbehaviours from situational factors' perspective and examines the relationship of past misbehaviour and future misbehaviour intentions. The results of the analysis. In this study, the conceptual model is outlined. This model comprises five hypotheses between theses constructs: loyalty intentions, severity of misbehaviour, perceived opportunity, perceived risk, past customer misbehaviour and future misbehaviour intentions. Using survey responses from 384 customers of Iranian chain stores, the empirical results offer the support for the forwarded research hypothesis. Structural equation modelling is used to examine these associations. The data suggest that situational factors have impacts on the customer misbehaviour. The results show that the relationships between loyalty intentions, severity of misbehaviour, perceived risk and past misbehaviours are statistically significant. In addition to above hypothesis, the results provide support for the positive association between past customer misbehaviour and future misbehaviour intentions. However, the relationship between perceived opportunity and past misbehaviour is not statistically supported. Thus, utilizing the structural equation modelling to analyze the survey data indicates strong support for 4 of the 5 hypothesized associations. The research findings have the range of key implications for both academia and industry by focusing on the factors associated with both past and future customer misbehaviour. The results of this study outline the point that service manager should be cautious about the episodes of customer misbehaviour and its severity as the mechanism to control or manage the frequency of future occurrences. The findings also highlight the importance of customers to chain stores (by supporting the link of customer loyalty intentions and past misbehavior). In addition, it might be beneficial to train front employees to act peacefully and respectfully toward customers. Conclusions and directions of further researches. The novelty point of this study is to illuminate the impact of situational factors on misbehaviours for the first time based on the background of Iranian culture. As the matter of fact that customer misbehaviour is prevalent in the Iranian chain stores, identifying the related antecedents especially from situation side is on the great center of attention

Generation of a VUV-to-visible Raman frequency comb in hydrogen-filled kagom\'e photonic crystal fiber

We report the generation of a purely vibrational Raman comb, extending from the vacuum ultraviolet (184 nm) to the visible (478 nm), in hydrogen-filled kagom\'e-style photonic crystal fiber pumped at 266 nm. Stimulated Raman scattering and molecular modulation processes are enhanced by higher Raman gain in the ultraviolet. Owing to the pressure-tunable normal dispersion landscape of the fiber-gas system in the ultraviolet, higher-order anti-Stokes bands are generated preferentially in higher-order fiber modes. The results pave the way towards tunable fiber-based sources of deep- and vacuum ultraviolet light for applications in, e.g., spectroscopy and biomedicine.Comment: 4 pages, 5 figures, 1 tabl

RF Characterisation of Laser Treated Copper Surfaces for the Mitigation of Electron Cloud in Accelerators

In accelerator beam chambers and RF waveguides, electron cloud and multipacting can be mitigated effectively by reducing the secondary electron yield (SEY). In recent years, it has been established that laser-engineered surface structuring is a very efficient method to create a copper surface with a SEY maximum close to or even below unity. Different laser pulse durations, from nanoseconds to picoseconds, can be used to change surface morphology. Conversely, the characteristics that minimise the SEY, such as the moderately deep grooves and the redeposited nanoparticles, might have unfavourable consequences, including increased RF surface resistance. In this study, we describe the techniques used to measure the surface resistance of laser-treated copper samples using an enhanced dielectric resonator with 12 cm diameter sample sizes operating in the GHz range. The quantification basis lies in a non-contact measurement of the high-frequency losses, focusing on understanding the variation of surface resistance levels depending on the specifics of the treatment and possible post-treatment cleaning procedures.</p

RF Characterisation of Laser Treated Copper Surfaces for the Mitigation of Electron Cloud in Accelerators

In accelerator beam chambers and RF waveguides, electron cloud and multipacting can be mitigated effectively by reducing the secondary electron yield (SEY). In recent years, it has been established that laser-engineered surface structuring is a very efficient method to create a copper surface with a SEY maximum close to or even below unity. Different laser pulse durations, from nanoseconds to picoseconds, can be used to change surface morphology. Conversely, the characteristics that minimise the SEY, such as the moderately deep grooves and the redeposited nanoparticles, might have unfavourable consequences, including increased RF surface resistance. In this study, we describe the techniques used to measure the surface resistance of laser-treated copper samples using an enhanced dielectric resonator with 12 cm diameter sample sizes operating in the GHz range. The quantification basis lies in a non-contact measurement of the high-frequency losses, focusing on understanding the variation of surface resistance levels depending on the specifics of the treatment and possible post-treatment cleaning procedures.</p

Out of focus ultrafast processing of metals for reduced secondary electron yield

We have demonstrated out-of-focus ultrafast pulsed laser processing of copper with a variable working distance, without the need for mechanical movement. This was achieved by employing a diffractive optical element. The method has been demonstrated in a practical application to reduce the secondary electron yield (SEY) of copper to below 1.3. We show that using an extended focus element not only increases the consistency of processing across a range of working distances, but also changes the topography of the produced structures, reducing the SEY. This presented approach shows promise in facilitating the Large Hadron Collider’s (LHC’s) upcoming high luminosity upgrade by preventing electron clouds