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| MOPRO116 | Mechanical Engineering and Design of Novel Collimators for HL-LHC | 369 |
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| In view of LHC intensity upgrades, collimator materials may become a limit to the machine performance: the high RF impedance of Carbon-Carbon composites can lead to beam instabilities, while the Tungsten alloy adopted in tertiary collimators exhibits low robustness in case of beam-induced accidents. An R&D program has been pursued to develop new materials overcoming such limitations. Molybdenum-Graphite, in addition to its outstanding thermal conductivity, can be coated with pure molybdenum, reducing collimator impedance by a factor of 10. A new secondary collimator is being designed around this novel composite. New high-melting materials are also proposed to improve the robustness of tertiary collimators. All the new collimators will be equipped with BPMs, significantly enhancing the alignment speed and the beta-star reach. This implies additional constraints of space, as well as detailed static and fatigue calculations on cables and connectors. This paper describes the mechanical design and the engineering calculations of such future collimators, focusing on the study via state-of-the-art numerical methods of interactions between the particle beams and the new materials adopted. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-MOPRO116 | |
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| TUPRI049 | Geometric Beam Coupling Impedance of LHC Secondary Collimators | 1677 |
| SUSPSNE059 | use link to see paper's listing under its alternate paper code | |
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Funding: Work supported by European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404 The High Luminosity LHC project is aimed at increasing the LHC luminosity by an order of magnitude. One of the key ingredients to achieve the luminosity goal is the beam intensity increase. In order to keep under control beam instabilities and to avoid excessive power losses a careful design of new vacuum chamber components and an improvement of the present LHC impedance model are required. Collimators are the main impedance contributors. Measurements with beam have revealed that the betatron coherent tune shifts were by about a factor of 2 higher with respect to the theoretical predictions based on the current model. Up to now the resistive wall impedance has been considered as the major impedance contribution for collimators. By carefully simulating their geometric impedance we show that for the graphite collimators with half-gaps higher than 10 mm the geometric impedance exceeds the resistive wall one. In turn, for the tungsten collimators the geometric impedance dominates for all used gap values. Hence, including the geometric collimator impedance into the LHC impedance model enabled us to reach a better agreement between the measured and simulated collimator tune shifts. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI049 | |
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| TUPRI056 | Beam Measurements of the LHC Impedance and Validation of the Impedance Model | 1698 |
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| Different measurements of the longitudinal impedance of the LHC done with single bunches with various intensities and longitudinal emittances during measurement sessions in 2011-2012 are compared with particle simulations based on the existing LHC impedance model. The very low reactive impedance of the LHC, with Im(Z/n) around 0.1 Ohm, is not easy to measure. The most sensitive observation is the loss of Landau damping during acceleration, which shows at which energy bunches become unstable depending on their parameters. In addition, the synchrotron frequency shift due to the reactive impedance was estimated following two methods. Firstly, it was obtained from the peak-detected Schottky spectrum. Secondly, a sine modulation in the RF phase was applied to the bunches with different intensities and the modulation frequency was scanned. In both cases, the synchrotron frequency shift was of the order of the measurement precision. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI056 | |
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