| Paper | Title | Page |
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| MOPWA030 | Upgrade of the LHC Injection Kicker Magnets | 729 |
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| The two LHC injection kicker systems, comprising 4 magnets per ring, produce a kick of 1.3 T.m with a rise-time of less than 900 ns and a flattop ripple of less than ±0.5%. A beam screen is placed in the aperture of each magnet, to provide a path for the image current of the high intensity LHC beam and screen the ferrite yoke against wake fields. The screen consists of a ceramic tube with conductors in the inner wall. The initially implemented beam screen ensured a low rate of electrical breakdowns while providing an adequate beam coupling impedance. Operation with increasingly higher intensity beams, stable for many hours at a time, now results in substantial heating of the ferrite yoke, sometimes requiring cool down over several hours before the LHC can be refilled. During the long shutdown in 2013/2014 all 8 kicker magnets will be upgraded with an improved beam screen and an increased emissivity of the vacuum tank. In addition equipment adjacent to the injection kickers and various vacuum components will also be modified to help reduce the vacuum pressure in the kickers during high-intensity operation. This paper discusses the upgrades as well as their preparation and planning. | ||
| MOPWA031 | Beam Induced Ferrite Heating of the LHC Injection Kickers and Proposals for Improved Cooling | 732 |
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| The two LHC injection kicker systems produce a kick of 1.3 T.m with a flattop duration variable up to 7860 ns, and rise and fall times of less than 900 ns and 3000 ns, respectively. A beam screen is placed in the aperture of each magnet, which consists of a ceramic tube with conductors in the inner wall. The conductors provide a path for the beam image current and screen the ferrite yoke against wake fields. Recent LHC operation, with high intensity beam stable for many hours, resulted in significant heating of both the ferrite yoke and beam impedance reduction ferrites. For one kicker magnet the ferrite yoke approached its Curie temperature. As a result of a long thermal time-constant the ferrites can require several hours to cool enough to re-inject beam, thus limiting the availability of the LHC. Thermal measurement data has been analysed, a thermal model developed and emissivity measurements carried out. The effects of various measures to improve the ferrite cooling have been simulated, including an improved emissivity of the vacuum tank and active cooling on the outside of the tank. | ||
| MOPWA032 | Reduction of Surface Flashover of the Beam Screen of the LHC Injection Kickers | 735 |
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| The LHC injection kicker magnets include beam screens to shield the ferrite yokes against wake fields resulting from the high intensity beam. The screening is provided by conductors lodged in the inner wall of a ceramic support tube. Operation with increasingly higher bunch intensity, and narrow bunches, now requires improved ferrite screening. This will be implemented by additional conductors; however the good high-voltage behaviour of the kicker magnets must not be compromised by the supplementary screening. Extensive studies and optimisations have been carried out, to better satisfy the often conflicting requirements for low beam coupling impedance, fast magnetic field rise-time, high vacuum and good high voltage behaviour. A new configuration is proposed which reduces significantly the electric field associated with the screen conductors and the secondary electron yield of the surface of the ceramic tube. Results of high voltage test results are also presented. | ||
| TUPWA042 | Lessons Learned and Mitigation Measures for the CERN LHC Equipment with RF Fingers | 1802 |
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| Beam-induced RF heating has been observed in several LHC components when the bunch/beam intensity was increased and/or the bunch length reduced. In particular eight bellows, out of the ten double-bellows modules present in the machine in 2011, were found with the spring, which should keep the RF fingers in good electrical contact with the central insert, broken. Following these observations, the designs of all the components of the LHC equipped with RF fingers have been reviewed. The lessons learnt and mitigation measures are presented in this paper. | ||
| WEPWO044 | RF Characterization of Niobium Films for Superconducting Cavities | 2399 |
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Funding: Work supported by the Wolfgang-Gentner-Programme of the Bundesministerium für Bildung und Forschung (BMBF) The surface resistance RS of superconductors shows a complex dependence on the external parameters such as temperature, frequency or radio-frequency (RF) field. The excited modes of 400, 800 and 1200 MHz allow measurements at actual operating frequencies of superconducting cavities. Niobium films on copper substrates have several advantages over bulk niobium cavities. HiPIMS (High-power impulse magnetron sputtering) is a promising technique to increase the quality and therefore the performance of niobium films. This contribution will introduce CERNs recently developed HiPIMS coating apparatus. Moreover, first results of niobium coated copper samples will be presented, revealing the dominant loss mechanisms. |
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| WEPWO046 | First Test Results of the 4-rod Crab Cavity | 2405 |
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Funding: The HiLumi LHC Design Study (a sub-system of HL-LHC) is cofunded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404. The first prototype crab cavity with the 4-rod geometry has undergone surface treatment and cold testing. Due to the complex geometry and unique fabrication procedure, RF validation of the field at beyond the nominal operating voltage at a sufficiently high Q0 is an important pre-requiste. Preliminary results of the first cold tests are presented along with cavity performance at different stages of the cavity processing is described. |
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| THPFI044 | NEG Thin Film Coating Development for the MAX IV Vacuum System | 3385 |
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| The new synchrotron radiation facility of the MAX IV laboratories is under construction and expected to deliver the first light beam in 2016. To cope with the small aperture, the intense photon bombardment and the low-pressure requirement, most of the beam pipes for the 3-GeV ring are going to be coated with Ti-Zr-V non-evaporable getter (NEG) thin films. To take advantage from the experience acquired during the construction of the Large Hadron Collider (LHC), collaboration between CERN and MAX IV Laboratories has been set up. The choice of the extruded Cu tubes, the preliminary surface treatments, the coating configuration, and the performance validation of the small-diameter vacuum chambers have been addressed. In parallel, an intense development has been tackled at CERN for the coating of vacuum chambers where photon and electron beams circulate in separate pipes. The most important results of the collaboration are presented and future perspectives pointed out. | ||
| THPFI051 | Radio-Frequency Multipacting as Quality Control of Coatings for e-Cloud Suppression | 3403 |
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| To mitigate electron clouds in particle accelerators, a carbon coating with low SEY has been developed. In the case of the SPS (Super Proton Synchrotron), which belongs to the LHC injector chain, testing the performance of coated beam pipes directly in the accelerator must cope with the schedule of the regular machine operation. For this reason an alternative instrument based on RF induced multipacting in a coaxial configuration has been designed for ex-situ characterization of the main bending dipoles of the SPS. In this contribution we report the results obtained before and after coating for two 6.4 meter dipoles with different cross sections of the vacuum chambers. The multipacting is monitored by measuring the pressure rise and the RF reflected power. After coating, the power threshold to induce multipacting is strongly reduced indicating a lower propensity for electron cloud. The impact of the RF coupling on the sensitivity of the technique is discussed. | ||