Karel Cornelis

Performance and Operational Experience of the CNGS Facility

The CNGS facility (CERN Neutrinos to Gran Sasso) aims at directly detecting muon to tau neutrino oscillations. An intense muon-neutrino beam (1.0·1017 muon neutrinos/day) is generated at CERN and directed over 732km towards the Gran Sasso National Laboratory, LNGS, in Italy, where two large and complex detectors, OPERA and ICARUS, are located. CNGS is the first long-baseline neutrino facility in which the measurement of the oscillation parameters is performed by observation of the tau-neutrino appearance. The facility is approved for a physics program of five years with a total of 22.5·1019 protons on target. Having resolved successfully some initial issues that occurred since its commissioning in 2006, the facility had its first complete year of physics in 2008. By the end of 2009 the facility delivered in total 5.4·1019 protons on target corresponding to an expected ~2-3 tau neutrino events in the OPERA detector, according to the most probable physics parameter oscillation model of today. The experiences gained in operating this 500 kW neutrino beam facility along with highlights of the beam performance in 2009 are discussed.

Transverse behaviour of the LHC proton beam in the SPS: an update

During the 1999 SPS run, strong transverse instabilities were observed with the LHC beam. Both the instability characteristics and the identical threshold current as for beam-induced electron multipacting led to consider the interaction of the beam with the electron cloud as a likely source. In 2000, we have measured the dependence of beam motion, beam loss, and emittance growth on bunch intensity, number of bunches, octupole strength, chromaticity, and gaps in the bunch train. We report on these recent studies and compare the beam observations with simulations of electron cloud build up and electron-induced single-bunch instabilities.

Present understanding of electron cloud effects in the Large Hadron Collider

We discuss the predicted electron cloud build up in the arcs and the long straight sections of the LHC, and its possible consequences on heat load, beam stability, long-term emittance preservation, and vacuum. Our predictions are based on computer simulations and analytical estimates, parts of which have been benchmarked against experimental observations at the SPS.

Can the proton injectors meet the HL-LHC requirements after LS2?

The LIU project has as mandate the upgrade of the LHC injector chain to match the requirements of HLLHC. The present planning assumes that the upgrade work will be completed in LS2, for commissioning in the following operational year. The known limitations in the different injectors are described, together with the various upgrades planned to improve the performance. The expected performance reach after the upgrade with 25 and 50 ns beams is examined. The project planning is discussed in view of the present LS1 and LS2 planning. The main unresolved questions and associated decision points are presented, and the key issues to be addressed by the end of 2012 are detailed in the context of the machine development programs and hardware construction activities. HL-LHC REQUIREMENTS AFTER LS2 The stated performance objective of HL-LHC is to accumulate 3000 fb of integrated p-p luminosity at 14 TeV centre of mass collision energy [1]. In order to achieve this, an annual figure of 250-300 fb has been posited, requiring instantaneous luminosity capability of around 7–8×10 cms, levelling to 5×10 cms and high machine efficiency [2]. The present paper covers the first of these challenging requirements: how to deliver the beam from the injector complex for these luminosities almost an order of magnitude above LHC design. The HL-LHC project has previously outlined possible parameter sets for 25 and 50 ns spacing which give the required luminosity, summarised in Tab. 1, adapted from [2]. Strictly speaking the HL-LHC needs the specified beams from the SPS after LS3, when the major work for the HL-LHC project is planned. The LIU work will take place largely in LS2, so that the period LS2 to LS3 will be an important one in terms of achieving the maximum performance from the injector chain. The figures quoted are for beams at the start of the collision process at 7 TeV – any beam loss or emittance dilution after extraction from the SPS is not included. The assumptions on the beam loss and emittance dilution for all machines are given in Tab. 2, where it can be seen that the total assumed beamloss -ΔI/I0 is 27%, and the emittance growth Δε/ε0 is 33%, corresponding to a brightness which is reduced to 55% of the original value. Table 1: Parameters and requirements from HL-LHC Parameter Nom. HL 25 ns HL 50 ns N [e11 p+] 1.15 2.0 3.3

JACoW : Phase Space Folding Studies for Beam Loss Reduction During Resonant Slow Extraction at the CERN SPS

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.

Analysis and Operational Feedback on the New Design of the High Energy Beam Dump in the CERN SPS

The CERN’s Super Proton Synchrotron (SPS) high energy internal dump (Target Internal Dump Vertical Graphite, known as -TIDVG) is required to intercept beam dumps from 102.2 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) performed 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).

Analysis of the SPS Long Term Orbit Drifts

The Super Proton Synchrotron (SPS) is the last accelerator in the Large Hadron Collider (LHC) injector chain, and has to deliver the two high-intensity 450 GeV proton beams to the LHC. The transport from SPS to LHC is done through the two Transfer Lines (TL), TI2 and TI8, for Beam 1 (B1) and Beam 2 (B2) respectively. During the first LHC operation period Run 1, a long term drift of the SPS orbit was observed, causing changes in the LHC injection due to the resulting changes in the TL trajectories. This translated into longer LHC turnaround because of the necessity to periodically correct the TL trajectories in order to preserve the beam quality at injection into the LHC. Different sources for the SPS orbit drifts have been investigated: each of them can account only partially for the total orbit drift observed. In this paper, the possible sources of such drift are described, together with the simulated and measured effect they cause. Possible solutions and countermeasures are also discussed.

The performance of the SPS as LEP injector

The injection of positrons into the first octant of the LEP (Large Electron Positron Collider) during the LEP injection tests in 1988, required the SPS (Super Proton Synchrotron) to operate as an injector for the LEP. Positrons were accelerated in the SPS from an energy of 3.5 GeV to about 18 GeV and extracted into LEP during the one-week test. This test, as well as the further commissioning of the SPS with leptons, could be made without perturbation to the physics program. The leptons were accelerated in three cycles, interleaved between the proton cycles, and four bunches of positrons or electrons were accelerated on each of them. Bunches with intensities exceeding the design value of 0.8*10/sup 10/ were accelerated. Following preliminary studies, countermeasures against various collective effects allowed the acceleration of up to 2.6*10/sup 10/ particles per bunch. The required momentum for LEP injection of 20 GeV could also be achieved.<<ETX>>