Wolfgang Bartmann

The ELENA facility

The CERN Antiproton Decelerator (AD) provides antiproton beams with a kinetic energy of 5.3 MeV to an active user community. The experiments would profit from a lower beam energy, but this extraction energy is the lowest one possible under good conditions with the given circumference of the AD. The Extra Low Energy Antiproton ring (ELENA) is a small synchrotron with a circumference a factor of 6 smaller than the AD to further decelerate antiprotons from the AD from 5.3 MeV to 100 keV. Controlled deceleration in a synchrotron equipped with an electron cooler to reduce emittances in all three planes will allow the existing AD experiments to increase substantially their antiproton capture efficiencies and render new experiments possible. ELENA ring commissioning is taking place at present and first beams to a new experiment installed in a new experimental area are foreseen in 2017. The transfer lines from ELENA to existing experiments in the old experimental area will be installed during CERN Long Shutdown 2 (LS2) in 2019 and 2020. The status of the project and ring commissioning will be reported. This article is part of the Theo Murphy meeting issue ‘Antiproton physics in the ELENA era’.

Linear Optics Design for PS2

The design considerations and key parameters for the replacement of the CERN Proton Synchrotron (PS) with a new ring (PS2), as part of the upgrade of the LHC injector complex are summarized. Classical linear optics solutions including standard FODO, doublet and triplet cells with real transition energy, are studied. Particular emphasis is given to the tuning and optimisation of Negative Momentum Compaction (NMC) cells with imaginary transition energy. The optics of the high energy transfer line is also presented.

Beam Simulation Studies for the Upgrade of the SPS Beam Dumping System

The SPS at CERN currently uses a beam dumping system that is installed in the long straight section 1 (LSS1) of the SPS. This system consists of two beam stopper blocks for low and high energy beams, as well as two vertical and three horizontal kicker magnets, which deflect and dilute the beam on the dumps. Within the frame of the LHC injector upgrade project (LIU) the beam dumping system will be relocated to long straight section 5 (LSS5) and upgraded with an additional vertical kicker, new main switches and a single new beam dump, which covers the full energy range. The impact of a possible increase of the vertical kicker rise time on the beam has been studied in simulations with MAD-X for the different optics in the SPS. Furthermore, the impact on the beam in failure scenarios such as the non-firing of one kicker has been investigated. The results of these studies will be presented and discussed in this paper. Operational mitigation methods to deal with an increased rise time will also be discussed. INTRODUCTION The SPS presently uses an internal beam dumping system, which consists of two separate beam dump blocks for low and high energy beams installed in the long straight section 1 (LSS1, Fig. 1) [1]:  TIDH, energy range 14 – 28.9 GeV  TIDVG, energy range 102.2 – 450 GeV There exists a forbidden zone for beam energies between 28.9 GeV and 102.2 GeV, where no programmed beam dump is possible. The deflection onto the dump blocks is performed with two vertical kicker magnets (MKDV). Three horizontal kicker magnets (MKDH) dilute the beam on the dump blocks to reduce the beam density on their front faces. Figure 1: Layout of the present SPS beam dumping system (Figure courtesy of F. M. Velotti). The present SPS beam dumping system (SBDS) has several limitations and issues [1, 2]:  Incompatibility of upgrading present TIDVG for High-Luminosity LHC (HL-LHC) beam parameters;  Production of high air activation;  High activation of the narrow area around the TIDVG without the possibility of full shielding;  Interference with SPS injection system, which is also located in LSS1;  The above mentioned forbidden energy zone;  MKDV magnet reliability issues at high energy. These limitations will be addressed in an upgrade of the SBDS [2, 3] in the frame of the LHC injector upgrade project (LIU) [4], which aims for upgrading the LHC injector chain to enable the production of high-brightness beams required for the HL-LHC era. For the LIU SBDS upgrade, the following changes are planned [2]:  The relocation of the SBDS from LSS1 to LSS5. This will solve the interferences with the injection system;  Replacing the two separate beam dump blocks by one newly designed for the entire energy range;  Installation of an additional MKDV magnet with the full system operated with reduced voltage to decrease the risk of high-voltage breakdowns;  Upgrade of MKDV main generators with new solid state switches;  A new dump external shielding to reduce the surrounding dose. The upgrade of the generators is currently under development and it is not clear if the present MKDV rise time of 1.1 μs can be preserved with the new system. A slight increase of the rise time to 1.3 μs might be necessary. To study the impact of the increased rise time on the beam, tracking simulations were performed using MAD-X [5]. MKDV RISE TIME The studies were performed using the present kicker waveforms, shown in Fig. 2, since the new waveforms are not yet available, scaled to the expected operational voltage. For the 3rd MKDV, which will be installed during the Figure 2: Waveforms of the vertical (MKDV) and horizontal kickers (MKDH) used for the simulation. ________________________________________ * Email: christoph.hessler@cern.ch 9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW Publishing ISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-TUPAF031 04 Hadron Accelerators T12 Beam Injection/Extraction and Transport TUPAF031 747 Co nt en tf ro m th is w or k m ay be us ed un de rt he te rm so ft he CC BY 3. 0 lic en ce (© 20 18 ). A ny di str ib ut io n of th is w or k m us tm ai nt ai n at tri bu tio n to th e au th or (s ), tit le of th e w or k, pu bl ish er ,a nd D O I.

Injection and Dump Systems for a 13.5 TeV Hadron Synchrotron HE-LHC

One option for a future circular collider at CERN is to build a 13.5 TeV hadron synchrotron, or High Energy LHC (HE-LHC) in the LHC tunnel. Injection and dump systems will have to be upgraded to cope with the higher beam rigidity and increased damage potential of the beam. The required modifications of the beam transfer hardware are highlighted in view of technology advancements in the field of kicker switch technology. An optimised straight section optics is shown.

Machine development studies for PSB extraction at 160 MeV and PSB to PS beam transfer

This paper collects the machine development (MD) activities for the beam transfer studies in 2016 concerning the PSB extraction and the PSB-to-PS transfer. Many topics are covered: from the 160 MeV extraction from the PSB, useful for the future commissioning activities after the connection with Linac4, to new methodologies for measuring the magnetic waveforms of kickers and dispersion reduction schemes at PS injection, which are of great interest for the LHC Injectors Upgrade (LIU) [1] project.

JACoW : Machine Development Studies in the CERN PS Booster, in 2016

The paper presents the outstanding studies performed in 2016 in preparation of the PS Booster upgrade, within the LHC Injector Upgrade project (LIU), to provide twice higher brightness and intensity to the High-Luminosity LHC.Major changes include the increase of injection and extraction energy, the implementation of a H− charge-exchange injection system, the replacement of the present Main Power Supply and the deployment of a new RF system (and related Low-Level), based on the Finemet technology. Although the major improvements will be visible only after the upgrade, the present machine can already benefit of the work done, in terms of better brightness, transmission and improved reproducibility of the present operational beams. Studies address the space-charge limitations at low energy, for which a detailed optics model is needed and for which mitigation measurements are under study, and the blow-up reduction at injection in the downstream machine, for which the beams need careful preparation and transmission. Moreover they address the requirements and the reliability of new beam instrumentation and hardware that is being installed in view of LIU.

Sources of Emittance Growth at the CERN PS Booster to PS Transfer

The CERN PS Booster (PSB) has four vertically stacked rings. After extraction from each ring, the bunches are recombined in two stages, comprising septum and kicker systems, such that the accumulated bunch train is injected through a single line into the PS. Bunches from the four rings go through a different number of vertical bends, which leads to differences in the betatron and dispersion functions due to edge focussing. The fast pulsed systems at PSB extraction, recombination and PS injection lead to systematic errors of delivery precision at the injection point. These error sources are quantified in terms of emittance growth and particle loss. Mitigations to reduce the overall emittance growth at the PSB to PS transfer within the LHC injectors upgrade are presented. ERROR SOURCES AND STABILITY CALCULATION For this study the error sources at the PSB to PS transfer have been divided into correctable and uncorrectable or dynamic errors. Correctable errors comprise magnet misalignments, magnet systematic errors such as different laminations or steel, and magnet random errors, e.g. different transfer function within a production series. Also long term drifts of the trajectory due to temperature and humidity are considered correctable. Uncorrectable errors can be random, such as shot-to-shot stability, in particular in view of the pulse-to-pulse modulated energy levels (1.4 and 2.0 GeV) of the transfer, and systematic like power converter ripple and fast pulsed kicker waveforms. Initially, only correctable errors were assigned in the transfer line model and its correction feasibility verified. During this transfer, four lines are combined into one line within a relatively short distance compared to the vertical offset. Due to the important deflection angles there are strong error sources which have to be compensated by few instrumentation and correction elements. The study showed that failure of beam position monitors are detrimental to the correction capability, and it is required to include the extraction septum as correction knob into the automatic trajectory algorithm used in the control room. Figure 1: Layout of the PSB recombination [1]. After this verification the machine was assumed to be free of correctable errors and dynamic errors were assigned separately to identify the main contributors to delivery imprecision. The effect of these errors was evaluated firstly, by their impact on the beam envelope of the line and consequently losses and activation of material, secondly, by comparison of trajectory variations and beta beating with the forseen margins in the envelope calculation and thirdly, by calculation of emittance growth due to offsets in position and angle at PS injection. Due to the different number of deflections seen by each bunch in the vertical recombination, Fig. 1, edge focussing from the vertical dipoles causes the optics to be different for each line [2]. This leads to an unavoidable emittance growth from betatron and dispersion mismatch at PS injection. The optics of the four lines can be perfectly matched to the PS injection optics for one of the four lines, but it is deliberately mismatched for all lines with the aim to minimize the overall emittance growth for all four lines. The optics for the transfer line coming from ring 4 is shown in Fig. 2. Figure 2: Present (thin) and new (thick) optics for the PSB to PS transfer in the top part. Horizontal betatron and dispersion functions are denoted in black and green, vertical betatron and dispersion functions in red and blue, respectively. In the bottom part the 3 σ horizontal LHC beam envelope is shown.