| Paper | Title | Page |
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| TUPEC018 | Gallium Arsenide Preparation and QE Lifetime Studies using the ALICE Photocathode Preparation Facility | 1752 |
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Gallium Arsenide (GaAs) photocathodes have in recent year been widely used and have become the focus for use in modern accelerators and light sources such as the Accelerators and Lasers in Combined Experiments (ALICE) and the International Linear Collider (ILC). Once activated to a Negative Electron Affinity (NEA) state and illuminated by a laser, these materials can be used as a high-brightness source of both polarised and un-polarised electrons. This work presents an effective preparation procedure including heat cleaning, atomic hydrogen cleaning and the activation process for NEA GaAs photocathode. The stability of quantum efficiency (QE) and lifetime of NEA GaAs photocathode have been studied in the load-lock and photocathode preparation system for the ALICE photo- electron gun which has a base pressure in the order of 10-11 mbar. These studies are also supported with experimental evidence from surface science techniques such as Photoelectron Spectroscopy (XPS) and Low Energy Electron Diffraction (LEED) to demonstrate the processes at the atomic level. |
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| WEPEC052 | Higher Order Modes in Third Harmonic Cavities for XFEL/FLASH | 3007 |
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We analyse the higher order modes in the 3.9GHz bunch shaping cavities recently installed in the XFEL/FLASH facility at DESY. We report on recent experimental results on the frequency spectrum, both beam and probe based. These are compared to those predicted by finite element computer codes, globalised scattering matrix calculations and a two-band circuit model. This study is focused on the dipole component of the multiband expansion of the wakefield. |
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| WEPEC053 | High Gradient Superconducting Cavity with Low Surface EM Fields and Well-suppressed HOMs for The ILC | 3010 |
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We present an optimized geometry for a 1.3 GHz superconducting cavity in which the surface electromagnetic fields have been minimized and the bandwidth of the fundamental mode has been maximized. We refer to this design as the New Low Surface Field (NLSF) cavity*. Earlier work* focused the fundamental mode properties. Here we study higher order modes (HOMs), means of damping them, and short range wakefields. A two-band circuit model is employed in order to facilitate rapid characteristic of the HOMs in the cavity. * N. Juntong and R.M. Jones, High-Gradient SRF Cavity with Minimized Surface E.M. Fields and Superior Bandwidth for The ILC, SRF2009, THPPO024, 2009. |
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| WEPE032 | Recent Progress on a Manifold Damped and Detuned Structure for CLIC | 3425 |
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Our earlier design* for an accelerating structure to suppress the wakefields in the CLIC main accelerating cavities has been modified. This structure combines strong detuning of the cell frequencies with waveguide-like damping by providing the structure with four attached manifolds which loosely couple a portion of the wakefields from each cell. The amended geometry reduces the surface pulse temperature heating by approximately 20%. We report on the overall parameters of the fundamental mode, together with details on damping higher order dipole modes. In order to adequately suppress the wakefield we interleave the frequencies of eight successive structures. * Khan and Jones, TU5PFP007, PAC'09, Vancouver, Canada 2009. |
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| THPE078 | Beam Dynamics Investigation of the 101.28 MHz IH Structure as Injector for the HIE-ISOLDE SC Linac | 4701 |
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The first phase of the HIE-ISOLDE project at CERN consists of a superconducting (SC) linac upgrade in order to increase the energy of post-accelerated radioactive ion beams from 2.8 MeV/u to over 10 MeV/u (for A/q = 4.5). In preparation for the upgrade, we present beam dynamics studies of the booster section of the normal conducting (NC) REX-ISOLDE linac, focused on the longitudinal development of the beam in the 101.28 MHz IH cavity, employing a Combined Zero Degree Structure* (KONUS), pulsing at a high gradient of over 3 MV/m. The evolution of the transverse emittance in the superconducting linac depends critically on the injected phase space distribution of particles from the existing linac and, with a better understanding of the longitudinal beam dynamics upstream, the performance of the upgrade can be optimised. Data taken during the commissioning phase of the REX-ISOLDE linac is analysed to understand the properties of the beam in the booster and combined with beam dynamics simulations which include the realistic fields of the IH structure, determined from both simulation and perturbation measurement. The matching of the NC and SC machines is also discussed. *Ratzinger, U., "The IH-structure and its capability to accelerate high current beams," Particle Accelerator Conference, 1991. |
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| WEPD018 | Status of COLDDIAG: a Cold Vacuum Chamber for Diagnostics | 3126 |
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One of the still open issues for the development of superconducting insertion devices is the understanding of the beam heat load. With the aim of measuring the beam heat load to a cold bore and the hope to gain a deeper understanding in the beam heat load mechanisms, a cold vacuum chamber for diagnostics is under construction. The following diagnostics will be implemented: i) retarding field analyzers to measure the electron flux, ii) temperature sensors to measure the total heat load, iii) pressure gauges, iv) and mass spectrometers to measure the gas content. The inner vacuum chamber will be removable in order to test different geometries and materials. This will allow the installation of the cryostat in different synchrotron light sources. COLDDIAG will be built to fit in a short straight section at ANKA. A first installation at the synchrotron light source DIAMOND is under discussion. Here we describe the technical design report of this device and the planned measurements with beam. |