| Paper | Title | Page |
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| MOPMF053 | Observations, Analysis and Mitigation of Recurrent LHC Beam Dumps Caused by Fast Losses in Arc Half-Cell 16L2 | 228 |
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| Recurrent beam dumps significantly perturbed the operation of the CERN LHC in the summer months of 2017, especially in August. These unexpected beam dumps were triggered by fast beam losses that built up in the cryogenic beam vacuum at the half-cell 16 left of LHC-IP2 and were detected either at that location but mainly in the collimation insertions. This contribution details the experimental observables (beam losses, coherent instabilities, heat load to cryogenic system, vacuum signals), the extent of the understanding of the beam loss and instability mechanisms and the mitigation steps and new settings that allowed recovering the luminosity performance of the LHC for the rest of the Run. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF053 | |
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| MOPMF061 | Emittance Growth in Coast in the SPS at CERN | 257 |
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Funding: Research supported by the HL-LHC project. The HL-LHC prototype crab-cavities are installed in the CERN SPS, which will allow for a comprehensive beam test with high energy protons for the first time. As the time available for experimental beam dynamics studies with the crab cavities installed in the machine will be limited, a very good preparation is required. One of the main concerns is the induced emittance growth, driven by phase amplitude jitter in the crab cavities. In this respect, several machine development (MD) studies were performed during the past years to quantify and characterize the long term emittance evolution of proton beams in the SPS. In these proceedings, the experimental observations from past years are summarized and the MD studies from 2016 and 2017 are presented. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF061 | |
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| THPAF035 | Single-Collimator Tune Shift Measurement of the Three-Stripe Collimator at the LHC | 3036 |
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| Several options of low resistivity coating have been proposed for the collimator upgrade of the Large Hadron Collider. In order to study their effect on the beam dynamics a special collimator has been built and installed in the machine. Its jaws are coated with three different materials and can be moved transversely to selectively expose the beam to the chosen coating. We have measured the resistive wall tune shifts of each coating material and compared them with that of a standard Carbon Fibre Composite (CFC) collimator jaw. A resolution of the tune shift of the order of 10-5 has been achieved in the measurement. The results show a significant reduction of the resistive wall tune shift with novel materials. The largest improvement is obtained with a 5 μm Molybdenum coating of a Molybdenum-Graphite jaw. The observed tune shifts show a good agreement with the impedance model and the bench impedance and resistivity measurements. Obtained results can be used to further improve the precision of the impedance model. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF035 | |
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| THPAF057 | Instability Observations in the Large Hadron Collider During Run 2 | 3099 |
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| Instabilities of many different types and characteristics have been observed in the LHC during Run 2. The origin of these instabilities come from a variety of stabilising and destabilising mechanisms. Efforts to understand these instabilities and prevent their occurrence has improved the performance of the LHC in all stages of the machine cycle. This paper aims to give an overview into some of the instability observations and details the operational steps to prevent them. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF057 | |
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| THPAF058 | Experimental Characterisation of a Fast Instability Linked to Losses in the 16L2 Cryogenic Half-Cell in the CERN LHC | 3103 |
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| The operation during the summer months of the 2017 Run of the CERN LHC was plagued with fast beam losses that repeatedly occurred in the 16th arc half-cell at the left of IP2 as well as in the collimation insertion, leading to unwanted beam dumps. Transverse coherent oscillations were observed during this fast process. We detail here the experimental observations of coherent motion that al-lowed shedding light upon parts of the mechanism and identify the potential mitigations that were successfully implemented in the second half of the Run. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF058 | |
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