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This paper shows the baseline LHC machine parameters for the 2015 start-up. Many systems have been upgraded during LS1 and in 2015 the LHC will operate at a higher energy than before and with a tighter filling scheme. Therefore, the 2015 commissioning phase risks to be less smooth than in 2012. The proposed starting configuration puts the focus on feasibility rather than peak performance and includes margins for operational uncertainties. Instead, once beam experience and a better machine knowledge has been obtained, a push in β* and performance can be envisaged. In this paper, the focus is on collimation settings and reach in β*---other parameters are covered in greater depth by other papers in these proceedings.
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This paper summarises the presentations and the subsequent discussions during the second session of the LHC Performance Workshop in Chamonix 2014.
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During LS1 a number of consolidations and upgrades have been undertaken in the LHC RF, including replacement of a cryomodule (four cavities, beam 2), upgrade of klystron collectors and new solid state crowbar systems. The RF parameters will be outlined in view of the consequences of the increased beam current and energy, and the exotic bunch spacing for the scrubbing beams. The LHC Transverse feedback system (ADT) is also undergoing a major upgrade during LS1, with double the total number of pickups to reduce the noise floor of the system, new beam position electronics and an upgraded digital signal processing system to accommodate all of the extra functionality that had been introduced during LHC Run I, and more sophisticated signal processing algorithms to be deployed for Run II. An external “observation box” to record transverse and longitudinal data from the RF and ADT systems is being implemented.
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During this talk, the scope and mandate of the Long Shutdown 2 (LS2) has been introduced, emphasising on the major differences with respect to LS1. The flexibility to use the winter shutdown to advance part of the works initially planned for LS2 will be considered in the frame of the LS2 discussions, the reporting line has been presented. Finally, the main dates for the LS2 preparation have been presented and will be followed carefully in order to ensure a smooth preparation of the LS2 shutdown.
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The variety of beams, needed to set-up in the injectors as requested in the LHC, are reviewed, in terms of priority but also performance expectations and reach during 2015. This includes the single bunch beams for machine commissioning and measurements (probe, Indiv) but also the standard physics beams with 50 ns and 25 ns bunch spacing and their high brightness variants using the Bunch Compression Merging and Splitting (BCMS) scheme. The required parameters and target performance of special beams like the doublet for electron cloud enhancement and the more exotic 8b+4e beam, compatible with some post-scrubbing scenarios are also described. The progress and plans for the LHC ion production beams during 2014-2015 are detailed. Highlights on the current progress of the setting up of the various beams are finally presented with special emphasis on potential performance issues across the proton and ion injector chain.
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The LHC Injectors Upgrade (LIU) project aims at extending the brightness and intensity reach of the injector complex. After the implementation of all LIU upgrades, beam loading and longitudinal instabilities in the SPS will likely remain the main limitations for the achievable intensity of the 25 ns beam. The goal of this paper is to present options to circumvent this limitation and increase the intensity of the 25 ns beams out of the SPS. In particular, two aspects will be addressed: 1) Alternative SPS optics configurations with intermediate transition energy between Q20 and Q26. Although the presently operational Q20 optics pushed the TMCI threshold from 1.6×1011 p/b to 4×1011 p/b, it might not be the optimal choice for maximizing the intensity of the 25 ns beam due to the RF power limitations. Possible optics configurations with intermediate transition energy are investigated, aiming at a better balance between TMCI threshold and RF power requirements. 2) Increase of the number of colliding bunches in the LHC by transferring a larger number of bunches between the PS and the SPS. In this context, schemes for transferring 80 or more bunches per PS batch and their operational implications are discussed, together with possible advantages for mitigating other limits in the SPS and LHC. Finally, machine development studies during Run 2 for evaluating the feasibility and potential of these schemes are addressed.
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After a second period of operation of more than three years, the accelerator complex will be stopped for about 18 months, from July 2018. The main purpose of the Long Shutdown 2 (LS2) is the LHC injectors upgrade (LIU). Nevertheless LHC will profit from this period to perform full maintenance of all the equipment, to consolidate part of the machine and to anticipate activities, where possible, of the LHC High Luminosity (HL-LHC) project. During LS2 activities across LHC, Injectors and LHC Experiments will be performed. This paper reviews all the major LS2 activities (maintenance, consolidation and HL-LHC), identifying those which are on the critical path, those which can be anticipated during End of Year Technical Stops, and those which will have to be postponed to Long Shutdown 3. The support needed from infrastructure services and logistics will be highlighted, as well as those requiring technical expertise from the Accelerator and Technology sector. A preliminary LS2 schedule is proposed, including the driving activities and the critical path.
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In these lectures we present a few topics in Quantum Field Theory in detail. Some of them are conceptual and some more practical. They have been selected because they appear frequently in current applications to Particle Physics and String Theory.
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The summary session of the LHC Performance Workshop in Chamonix, 22-25 September 2014 [1], held at CERN on 8 October 2014 [2] synthesized one week of presentations and intense discussions on the near-, medium- and long-term strategy for the LHC, including the upgrades of the LHC and its injectors. In particular, Chamonix 2014 discussed the lessons from, and the end of the Long Shutdown 1 (LS1) up to powering tests and cold checkout, the injector status, the beam commissioning in 2015, the challenges and strategy for LHC Run 2, the LHC Injector Upgrade (LIU), the High-Luminosity LHC (HL-LHC), the consolidation of accelerator and non-LHC experiment areas through Long Shutdown 3 (LS3), as well as the strategy and preparation for the Long Shutdown 2 (LS2). We report the main points and actions which have emerged at the Chamonix 2014 workshop.
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This paper introduces the requirements for power converters needed for particle accelerators. It describes the role of power converters and the challenges and constraints when powering magnets. The different circuit layouts are presented as well as the operating cycles. The power converter control and high precision definition are also introduced. This paper lists the key circuit parameters to be taken into consideration to properly specify a power converter that can be compiled in a functional specification.
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