| Paper | Title | Page |
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| MOPPC003 | Very Fast LHC Crab Cavity Failures and their Mitigation | 121 |
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For the high-luminosity LHC upgrade program (HL-LHC), the installation of crab cavities (CCs) is needed to compensate the geometric luminosity loss due to the crossing angle and for luminosity leveling [*]. The baseline is a local scheme with CCs around the ATLAS and CMS experiments. In a failure case (e.g. a control failure or arcing in the coupler), the voltage and/or phase of a CC can change significantly with a very fast time constant of the order of 1 to 10 LHC turns. This can lead to large, global betatron oscillations of the beam. The impact of CC failures on the beam dynamics is discussed and the results from dedicated simulations are presented. Mitigation strategies to limit the impact of CC failures to an acceptable level are proposed.
* F. Zimmermann and O. Brüning, “Parameter Space for the LHC High-Luminosity Upgrade”, IPAC'12, MOPPC005, May 2012. |
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| MOPPC027 | Synchro-Betatron Effects in the Presence of Large Piwinski Angle and Crab Cavities at the HL-LHC | 190 |
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Funding: This work partially supported by the US Department of Energy through the US LHC Accelerator Research Program (LARP). The reduction of beta-star at the collision points for the high luminosity LHC (HL-LHC) requires an increment in the crossing angle to maintain the normalized beam separation to suppress the effects of long-range beam-beam interactions. However, increase in crossing angle may give rise to synchro-betatron resonances which may negatively affect the beam emittance and lifetime. 6D weak-strong and strong-strong simulations are performed to study the effect of synchro-betatron resonances in the context of the HL-LHC layout and its suppression via crab crossing. |
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| TUPPR027 | Study of Multipolar RF Kicks from the Main Deflecting Mode in Compact Crab Cavities for LHC | 1873 |
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| A crab cavity system is under design in the frame work of the High Luminosity LHC project. Due to transverse space constraints on one hand and the RF frequency requirements on the other hand, the design of the crab cavities has to be compact. This results in the crab cavity shape being far from axially symmetric and, as a consequence, higher order multipolar components of the main deflecting mode are non-zero. In this paper, multipolar RF kicks from the main deflecting mode have been calculated in the compact crab cavities for LHC. They are compared to the multipolar error in magnetic elements of LHC. The influence of the RF kicks on the beam dynamics has been investigated and possible acceptable tolerances are presented. | ||
| TUPPR084 | HOM Damping and Multipacting Analysis of the Quarter-wave Crab Cavity | 2020 |
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| The Quarter-Wave Crab Cavity design has been analyzed further to accommodate LHC requirements. The goal for the design is to provide strong deflecting voltage to the proton bunches at the IP, while keeping the effective length as short as possible. We will evaluate the Higher Order Mode damping with two magnetic coupling dampers of 90 degrees apart. In this paper, we also show possible multipacting locations which are simulated by 3D code. | ||
| WEEPPB008 | HOM Coupler Optimisation for the Superconducting RF Cavities in ESS | 2182 |
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| The European Spallation Source (ESS) will be the world’s most powerful next generation neutron source. It consists of a linear accelerator, target, and instruments for neutron experiments. The linac is designed to accelerate protons to a final energy of 2.5 GeV , with an average design beam power of 5 MW, for collision with a target used to produce a high neutron flux. A section of the linac will contain Superconducting RF (SCRF) cavities designed to resonate at 704 MHz. Dangerous beam induced modes in these cavities may make the beam unstable and increase the cryogenic load and so couplers are usually installed to provide damping. Previous studies have shown potential designs are susceptible to multipacting, a resonant process which can absorb RF power and lead to heating effects. This paper will show how a coupler suffering from multipacting has been redesigned to limit this effect. Optimisation of the RF damping is also discussed. | ||
| WEPPC027 | A Quarter Wave Design for Crab Crossing in the LHC | 2260 |
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Funding: This work partially supported by the US Department of Energy through the US LHC Accelerator Research Program (LARP). The aperture constraints of the LHC interaction region and the alternating crossing schemes at two collision points calls for a superconducting deflecting cavity with very compact dimensions at low frequencies for the purpose of crab crossing. A new concept of using a superconducting 1/4-wave design, ideally suited to address the LHC constraints at 400 MHz, is proposed. The optimized RF cavity design and associated advantages of using a 1/4 wave resonator are presented. Aspects related to higher order mode damping, multipacting and frequency tuning are also addressed. |
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| THPPP007 | Proton-Beam Emittance Growth in SPS Coasts | 3737 |
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Funding: This work partially supported by the US Department of Energy through the US LHC Accelerator Research Program (LARP). Proton-beam transverse emittance growth rates have been measured during SPS coasts to assess the possibility of using the SPS as a testbed for the LHC prototype crab cavities. The SPS measurements in coasts were performed at different beam energies, for varying RF voltage, beam intensity, and chromaticity. Results from these measurements are presented with potential explanations for the observed emittance growth. |
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