19 research outputs found
Study of the Powerful Nd:YLF Laser Amplifiers for the CTF3 Photoinjectors
No full textA high-power neodymium-doped yttrium lithium fluoride (Nd:YLF) mode-locked 1.5-GHz laser currently used to drive the two photoinjectors of the Compact Linear Collider Test Facility project at the European Organization for Nuclear Research is described. A phenomenological characterization of the two powerful Nd:YLF amplifiers is presented and compared with the measurements. The laser system operates in a saturated steady-state mode. This mode provides good shot-to-shot stability with pulse train mean power in the 10 kW range
New method for full field measurement of pore water pressures
No full textA cost effective method to measure pore water pressures in mixed granular media is described using 40 miniature MEMS pore pressure transducers. High accuracy in a single point is exchanged for lower accuracy full field measurements adjacent to the strongbox wall. The system is easily de-aired and calibrated due to the fact that the transducers are installed inside the strongbox wall. Additionally, the proof of concept test shows that the transducers are sufficiently accurate for problems with large pressure difference such as consolidation of clay while being subjected to elevated stress levels in the geotechnical centrifuge
Fast phase switching within the bunch train of the PHIN photo-injector at CERN using fiber-optic modulators on the drive laser
No full textThe future Compact Linear Collider (CLIC) e^-/e^+ collider is based on the two-beam acceleration concept, whereby interleaving electron bunches of the drive beam through a delay loop and combiner rings as well as high peak RF power at 12GHz are created locally to accelerate a second beam, the main beam. One of the main objectives of the currently operational CLIC Test Facility (CTF3) is to demonstrate beam combination from 1.5GHz to 12GHz, which requires satellite-free fast phase-switching of the drive beam with sub-ns speed. The PHIN photo-injector, with the photo-injector laser, provides flexibility in the time structure of the electron bunches produced, by direct manipulation of the laser pulses. A novel fiber modulator-based phase-switching technique allows clean and fast phase-switch at 1.5GHz. This paper describes the switching system based on fiber-optic modulators, and the measurements carried out on both the laser and the electron beam to verify the scheme
Lifetime Studies of Cs2Te Cathodes at the Phin RF Photoinjector at CERN
No full textThe PHIN photoinjector has been developed to study the feasibility of a photoinjector option for the CLIC (Compact LInear Collider) drive beam as an alternative to the baseline design, using a thermionic gun. The CLIC drive beam requires a high charge of 8.4 nC per bunch in 0.14 ms long trains, with 2 ns bunch spacing and 50 Hz macro pulse repetition rate, which corresponds to a total charge per macro pulse of 0.59 mC. This means unusually high peak and average currents for photoinjectors and is challenging concerning the cathode lifetime. In this paper detailed studies of the lifetime of Cs2Te cathodes, produced by the co-evaporation technique, are presented with respect to bunch charge, train length and vacuum level. Furthermore, the impact of the train length and bunch charge on the vacuum level will be discussed and steps to extend the lifetime will be outlined
The London Geotechnical Centrifuge Centre at City University London
No full textThe London Geotechnical Centrifuge Centre located at City University, London is one of four currently active centrifuges in the UK. The centrifuge is well used and much of the geotechnical research at City University employs physical modelling but supported by a large element testing facility and numerical modelling capability. The centre was established in 1990 and the facility was extensively upgraded to provide more space for sample preparation and model making in 2004. In 2012 the centre is supporting 4 doctoral research projects in addition to visitors from China, Italy and UK. The focus of research is urban construction processes with an underlying theme of sustainability. Over the last 10 years the group has established a capability for tackling complex modelling problems and is currently investigating the application of smart instrumentation and control at high g
The CLIC Feasibility Demonstration in CTF3
No full textThe objective of the CLIC Test Facility CTF3 is to demonstrate the feasibility issues of the CLIC two-beam technology: the efficient generation of a very high current drive beam, used as the power source to accelerate the main beam to multi-TeV energies with gradients of over 100 MeV/m, and stable drive beam deceleration. Results of successful beam acceleration with over 100 MeV/m energy gain are shown. Measurements of drive beam deceleration over a chain of Power Extraction Structures (PETS) are presented. The achieved RF power levels, the stability of the power production and of the deceleration are discussed. Finally, we give an overview of the remaining issues to be addressed by the end of 2011
Impact of laser stacking and photocathode materials on microbunching stability in photoinjectors
No full textMicrobunching instability is a well-known phenomenon that may deteriorate the performance of accelerators. The instability may be triggered by a shot-noise mechanism or by some initial intensity modulations at the generation of the electron bunch (or both) and can be amplified all along the machine. At SwissFEL, the free-electron laser (FEL) facility operating at the Paul Scherrer Institute (PSI), the initial design stipulated a shaping of the photocathode laser output to obtain a flat-top longitudinal profile. This scheme is attractive in terms of the uniformity of the beam properties along the bunch. The drawback of this approach is that some unavoidable modulations are generated along the laser pulse. We investigate, both experimentally and by numerical simulations, the longitudinal dynamics of a beam obtained illuminating a copper cathode with a laser profile shaped by the stacking technique. We repeat the analysis for several compression factors and initial laser profile modulations. We find that the microbunching instability gain renders the use of the stacking technique not efficient to run a free-electron laser facility using as photocathode a material with a short response time. We experimentally demonstrate that the use of a material with a longer response time efficiently damps the structures originating from the laser profile obtained with stacking, and helps to improve the performance of the facility. In general, this is an approach to minimize the microbunching instability at any FEL (also not using stacking) or at least reduce the use of other countermeasures, which, such as the laser heater, may degrade the final FEL performance
Praziquantel coverage in schools and communities targeted for the elimination of urogenital schistosomiasis in Zanzibar: a cross-sectional survey
No full text© 2015 Knopp et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. The attached file is the published version of the article.NHM Repositor
Study and implementation of urogenital schistosomiasis elimination in Zanzibar (Unguja and Pemba islands) using an integrated multidisciplinary approach
No full textABSTRACT: BACKGROUND: Schistosomiasis is a parasitic infection that continues to be a major public health problem in many developing countries being responsible for an estimated burden of at least 1.4 million disability-adjusted life years (DALYs) in Africa alone. However, morbidity due to schistosomiasis has been greatly reduced in some parts of the world, including Zanzibar. The Zanzibar government is now committed to eliminate urogenital schistosomiasis. Over the next 3--5 years, the whole at-risk population will be administered praziquantel (40 mg/kg) biannually. Additionally, snail control and behaviour change interventions will be implemented in selected communities and the impact measured in a randomized intervention trial. METHODS: In this 5-year research study, on both Unguja and Pemba islands, urogenital schistosomiasis will be assessed in 45 communities with urine filtration and reagent strips in 4,500 schoolchildren aged 9--12 years annually, and in 4,500 first-year schoolchildren and 2,250 adults in years 1 and 5. Additionally, from first-year schoolchildren, a finger-prick blood sample will be collected and examined for Schistosoma haematobium infection biomarkers. Changes in prevalence and infection intensity will be assessed annually. Among the 45 communities, 15 were randomized for biannual snail control with niclosamide, in concordance with preventive chemotherapy campaigns. The reduction of Bulinus globosus snail populations and S. haematobium-infected snails will be investigated. In 15 other communities, interventions triggering behaviour change have been designed and will be implemented in collaboration with the community. A change in knowledge, attitudes and practices will be assessed annually through focus group discussions and in-depth interviews with schoolchildren, teachers, parents and community leaders. In all 45 communities, changes in the health system, water and sanitation infrastructure will be annually tracked by standardized questionnaire-interviews with community leaders. Additional issues potentially impacting on study outcomes and all incurring costs will be monitored and recorded. DISCUSSION: Elimination of schistosomiasis has become a priority on the agenda of the Zanzibar government and the international community. Our study will contribute to identifying what, in addition to preventive chemotherapy, needs to be done to prevent, control, and ultimately eliminate schistosomiasis, and to draw lessons for current and future schistosomiasis elimination programmes in Africa and elsewhere.Trial registrationISRCTN4883768
