| Paper | Title | Page |
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| MOPIK044 | The Use of a Passive Scatterer for SPS Slow Extraction Beam Loss Reduction | 607 |
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| A significant reduction in the fraction of protons lost on the SPS electrostatic septum ES during resonant slow extraction is highly desirable for present Fixed-Target beam operation, and will become mandatory for the proposed SHiP experiment, which is now being studied in the framework of CERN's Physics Beyond Colliders program. In this paper the possible use of a passive scattering device (diffuser) is investigated. The physics processes underlying the use of a diffuser are described, and the dependence on the diffuser geometry, material and location of the potential loss reduction on the electrostatic septum (ES) wires is investigated with a semi-analytical approach. Numerical simulations to quantify the expected performance gain for the optimum configuration are presented, and the results discussed in view of the feasibility of a potential realisation in the SPS. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPIK044 | |
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| MOPIK045 | SPS Slow Extraction Losses and Activation: Challenges and Possibilities for Improvement | 611 |
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In 2015 the highest integrated number of protons in the history of the North Area was slow extracted from the CERN Super Proton Synchrotron (SPS) for the Fixed Target physics programme. At well over 1.1019 protons on target (POT), this represented the highest annual figure at SPS for almost two decades, since the West Area Neutrino Facility was operational some 20 years ago. The high intensity POT requests have continued into 2016-17 and look set to do so for the foreseeable future, especially in view of the proposed SPS Beam Dump Facility and experiments, e.g. SHiP*, which are requesting up to 4·1019 POT per year. Without significant improvements, the attainable annual POT will be limited to well below the total the SPS machine could deliver, due to activation of accelerator equipment and associated personnel dose limitations. In this contribution, the issues arising from the recent high activation levels are discussed along with the steps taken to understand, manage and mitigate these issues. The research avenues being actively pursued to improve the slow extraction related beam loss for present operation and future requests are outlined, and their relative merits discussed.
*A. Golutvin et al., ‘‘A Facility to Search for Hidden Particles (SHiP) at the CERN SPS'', CERN, Geneva, Switzerland, Rep. CERN-SPSC-2015-016 (SPSC-P-350), Apr. 2015. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPIK045 | |
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| MOPIK046 | Phase Space Folding Studies for Beam Loss Reduction During Resonant Slow Extraction at the CERN SPS | 615 |
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| The requested number of protons slow-extracted from the CERN Super Proton Synchrotron (SPS) for Fixed Target (FT) physics is expected to continue increasing in the coming years, especially if the proposed SPS Beam Dump Facility is realised. Limits on the extracted intensity are already being considered to mitigate the dose to personnel during interventions required to maintain the extraction equipment, especially the electrostatic extraction septum. In addition to other on-going studies and technical developments, a reduction of the beam loss per extracted proton will play a crucial role in the future performance reach of the FT experimental programme at the SPS. In this paper a concept is investigated to reduce the fraction of beam impacting the extraction septum by folding the arm of the phase space separatrix. Beam dynamics simulations for the concept are presented and compared to the phase space acceptance of the extraction channel. The performance potential of the concept at SPS is evaluated and discussed alongside the necessary changes to the non-linear optical elements in the machine. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPIK046 | |
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| MOPIK048 | Experimental Results of Crystal-Assisted Slow Extraction at the SPS | 623 |
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| The possibility of extracting highly energetic particles from the Super Proton Synchrotron (SPS) by means of silicon bent crystals has been explored since the 1990's. The channelling effect of a bent crystal can be used to strongly deflect primary protons and eject them from the synchrotron. Many studies and experiments have been carried out to investigate crystal channelling effects. The extraction of 120 and 270 GeV proton beams has already been demonstrated in the SPS with dedicated experiments located in the ring. Presently in the SPS, the UA9 experiment is performing studies to evaluate the possibility to use bent silicon crystals to steer particle beams in high energy accelerators. Recent studies on the feasibility of extraction from the SPS have been made using the UA9 infrastructure with a longer-term view of using crystals to help mitigate slow extraction induced activation of the SPS. In this paper, the possibility to eject particles into the extraction channel in LSS2 using the bent crystals already installed in the SPS is presented. Details of the concept, simulations and measurements carried out with beam are presented, before the outlook for the future is discussed. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPIK048 | |
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| MOPIK049 | SPS Slow Extracted Spill Quality During the 2016 Run | 627 |
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| The flux of particles slow extracted with the 1/3 integer resonance from the Super Proton Synchrotron at CERN should ideally be constant over the length of the extraction plateau, for optimum use of the beam by the fixed target experiments. The extracted intensity is controlled in feed-forward correction of the horizontal tune via the main SPS quadrupoles. The Mains power supply noise at 50 Hz and harmonics is also corrected in feed-forward by small amplitude tune modulation at the respective frequencies with a dedicated additional quadrupole circuit. In 2016 the spill quality could be much improved with respect to the situation of the previous year with more performant algorithms. In this paper the improved tools are described and the characteristics of the SPS slow extracted spill in terms of macro structure and typical frequency content are shown. Other sources of perturbation were, however, also present in 2016 which frequently caused the spill quality to be much reduced. The different effects are discussed and possible or actual solutions detailed. Finally, the evolution of the spill quality during characteristic periods in the 2016 run is presented. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPIK049 | |
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| MOPIK050 | Reduction of Resonant Slow Extraction Losses with Shadowing of Septum Wires by a Bent Crystal | 631 |
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| A new experiment, SHiP, is being studied at CERN to investigate the existence of three Heavy Neutral Leptons in order to give experimental proof to the proposed neutrino minimal Standard Model. High-intensity slow-extraction of protons from the SPS is a pre-requisite for SHiP. The experiment requires a resonant extraction with in a 7.2 s cycle, and about 4·1013 protons extracted at 400 GeV in a 1 s flat-top, to achieve the needed 2·1020 protons on target in five years. Although the SPS has delivered this in the past to the CNGS experiment with fast extraction, for SHiP beam losses and activation of the SPS electrostatic extraction septum (ZS) could be a serious performance limitation, since the target number of protons to resonantly extract per year is a factor of two higher than ever achieved before and a factor of four than ever reached with the third-integer slow extraction. In this paper, a novel extraction technique to significantly reduce the losses at the ZS is proposed, based on the use of a bent crystal to shadow the septum wires. Theoretical concepts are developed, the performance gain quantified and a possible layout proposed. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPIK050 | |
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| TUPVA007 | Impact of LHC and SPS Injection Kicker Rise Times on Lhc Filling Schemes and Luminosity Reach | 2043 |
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| The 2016 LHC proton filling schemes generally used a spacing between injections of batches of bunches into SPS and LHC corresponding to the design report specification for the SPS and LHC injection kicker rise times, respectively. A reduction of the batch spacing can be directly used to increase luminosity without detrimental effects on beam stability, and with no increase in the number of events per crossing seen by the experiments. Measurements and simulations were performed in SPS and LHC to understand if a shorter injection kicker rise time and associated tighter batch spacing would lead to increased injection oscillations of the first and last bunches of a bunch train and eventually also a systematic growth of the transverse emittance. The results were used to define the minimum possible batch spacing for an acceptable emittance growth in LHC, with gains of reductions of about 10% possible in both machines. The results are discussed, including the potential improvement of the LHC luminosity for different filling schemes. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPVA007 | |
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| TUPVA128 | Performance of the CERN Injector Complex and Transmission Studies into the LHC during the Second Proton-Lead Run | 2395 |
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| The LHC performance during the proton-lead run in 2016 fully relied on a permanent monitoring and systematic improvement of the beam quality in all the injectors. The beam production and characteristics are explained in this paper, together with the improvements realized during the run from the source up to the flat top of the LHC. Transmission studies from one accelerator to the next as well as beam quality evolution studies during the cycle at each accelerator, have been carried out and are summarized in this paper. In 2016, the LHC had to deliver the beams to the experiments at two different energies, 4 Z TeV and 6.5 Z TeV. The properties of the beams at these two energies are also presented | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPVA128 | |
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| WEPVA110 | Analysis and Operational Feedback on the New Design of the High Energy Beam Dump in the CERN SPS | 3524 |
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| CERN's Super Proton Synchrotron (SPS) high-energy internal dump (Target Internal Dump Vertical Graphite, known as TIDVG) is required to intercept beams from 102 to 450 GeV. The equipment installed in 2014 (TIDVG#3) featured an absorbing core composed of different materials surrounded by a water-cooled copper jacket, which hold the UHV of the machine. An inspection of a previous equipment (TIDVG#2) in 2013 revealed significant beam induced damage to the aluminium section of the dump, which required imposing operational limitations to minimise the risk of reproducing this phenomenon. Additionally, in 2016 a vacuum leak was detected in the dump assembly, which imposed further limitations, i.e. a reduction of the beam intensity that could be dumped per SPS supercycle. This paper presents a new design (TIDVG#4), which focuses on improving the operational robustness of the device. Moreover, thanks to the added instrumentation, a careful analysis of its performance (both experimentally and during operation) will be possible. These studies will help validating technical solutions for the design of the future SPS dump to be installed during CERN's Long Shutdown 2 in 2020 (TIDVG#5). | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA110 | |
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| THPAB146 | Investigation of the Remanent Field of the SPS Main Dipoles and Possible Solutions for Machine Operation | 4069 |
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| The CERN Super Proton Synchrotron (SPS) provides different types of beams at different extraction energies. The main magnets of the SPS are regulated with a current loop, but it has turned out that hysteresis effects from the main dipoles have a significant impact on reproducibility and hence efficiency and availability. Beam and machine parameters were found to depend on the programmed sequence of magnetic cycles - the so-called super cycle - representing the production of the different beams. The scientific program of the SPS requires frequent changes of the supercycle composition and the effect of the main magnet hysteresis has to be understood, modelled and used in accelerator control system. This paper summarises the first main field measurements carried out with the currently available systems during operational conditions as well as measurements of vital machine and beam parameters as a function of the super cycle composition. Finally, ideas will be presented to provide reproducibility by automatically correcting different parameters taking the magnetic history of the main magnets into account. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPAB146 | |
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| THPAB147 | Automatic Local Aperture Measurements in the SPS | 4073 |
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| The CERN SPS (Super Proton Synchrotron) serves as LHC injector and provides beam for the North Area fixed target experiments. It is equipped with flat vacuum chambers to accommodate the large horizontal beam size required during transition crossing and slow extraction. At low energy, the vertical acceptance becomes critical with high intensity large emittance fixed target beams. Optimizing the vertical available aperture is a key ingredient to optimize transmission and reduce activation around the ring. Aperture measurements are routinely carried out after each shutdown. Global vertical aperture measurements are followed by detailed bump scans at the locations with the loss peaks. During the 2016 run a tool was developed to provide an automated local aperture scan around the entire ring. This allowed to establish detailed reference measurements of the vertical aperture and identify directly the SPS aperture bottlenecks. The methodology applied for the scans will be briefly described in this paper and the analysis discussed. Finally, the 2016 SPS measured vertical aperture will be presented and compared to the results obtained with the previous method. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPAB147 | |
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