| Paper | Title | Page |
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| MOPME074 | High Voltage Performance of the Beam Screen of the LHC Injection Kicker Magnets | 541 |
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| The LHC injection kicker magnets include beam screens to shield the ferrite yokes against wakefields resulting from the high intensity beam. The screening is provided by conductors lodged in the inner wall of a ceramic support tube. The design of the beam screen has been upgraded to overcome limitations and permit LHC operation with increasingly higher bunch intensity and short bunch lengths: the new design also significantly reduces the electric field associated with the screen conductors, decreasing the probability of electrical breakdown. The high voltage conditioning process for the upgraded kicker magnets is presented and discussed. In addition a test setup has been utilized to study flashover, on the inner wall of the ceramic tube, as a function of both applied voltage and vacuum pressure: results from the test setup are presented. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-MOPME074 | |
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| WEPME005 | Enhanced Field Emission and Emitter Activation on Flat Dry-ice Cleaned Cu Samples | 2261 |
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Enhanced field emission (EFE), resulting in dark currents and electric breakdowns, is one of the main gradient limitations for the CLIC accelerating structures (actual design Eacc = 100 MV/m, Epeak = 240 MV/m *). Measurements on diamond-turned, flat (Ra = 158 nm) Cu samples showed first EFE at surface fields Es = 130 MV/m. In order to reduce EFE, we have installed a commercial dry ice cleaning (DIC) system in a clean room environment (class iso 5). Accordingly, the number density of emitters (N) was significantly decreased by DIC from N = 52 /cm² to N = 12 /cm² at Es = 190 MV/m. Furthermore we have tested two diamond-turned and chemically etched (SLAC treatment, Ra = 150 nm) Cu samples after DIC resulting in EFE onset at 230 MV/m. Locally measured I(V) curves of the strongest emitters yielded field enhancement factors b = 10 – 90 (10 – 85) on the diamond-turned (chemically etched), respectively. SEM and EDX investigations of the located emission sites revealed surface defects and few particulates (Al, Ca, Si) as origin of the EFE. Moreover, strong emitter activation effects were observed. A possible breakdown mechanism based on this EFE activation will be discussed.
* A. Grudiev and W. Wuensch, Proceedings of LINAC2010, Tsukuba, Japan, pp. 211 - 213 |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPME005 | |
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| WEPRI042 | Nb Coated HIE-ISOLDE QWR Superconducting Accelerating Cavities: From Process Development to Series Production | 2571 |
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| The new HIE-ISOLDE accelerator at CERN requires the production of 32 superconducting cavities (20 high-beta and 12 low-beta) in order to increase the energy of the rare isotope beam delivered to the experiments. The Quarter Wave Resonators (QWRs) cavities (0.3m diameter and 0.8m height) are made of OFE 3D-forged copper and are coated by DC-bias diode sputtering with a thin superconducting layer of niobium. Following a preliminary process development phase, the series production of the high-beta cavities has started. An overview of the development phase is presented, describing the key parameters varied to match the HIE-ISOLDE specifications (operation at 4.5 K with an accelerating field of 6 MV/m at 10W RF losses and Q0=4.5x108) and the resulting niobium film characteristics. The first series of cavities, produced using the baseline coating recipe, and their RF performance is reviewed. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI042 | |
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| WEPRI048 | Testing and Dressed Cavity Design for the HL-LHC 4R Crab Cavity | 2589 |
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| The High luminosity upgrade to the LHC (HL-LHC) calls for crab cavities to reduce the luminosity loss due to the crossing angle and help provide luminosity levelling. The 4 Rod Crab Cavity (4RCC) is one of three proposed options under consideration. A bare cavity has been prototyped and has undergone recent vertical tests and the results are presented. The dressed cavity includes a power coupler, a lower order mode coupler and two HOM couplers will be presented and discussed. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI048 | |
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