The Extra Low ENergy Antiproton ring ELENA is a small synchrotron recently constructed and commissioned to decelerate antiprotons injected from the Antiproton Decelerator AD with a kinetic energy of 5.3 MeV down to 100 keV. Controlled deceleration in the synchrotron, equipped with an electron cooler to reduce losses and generate dense bunches, allows the experiments, typically capturing the antiprotons in traps and manipulating them further, to improve the trapping efficiency by one to two orders of magnitude. During 2018, bunches with an energy of 100 keV with parameters close to nominal have been demonstrated, and first beams have been provided to an experiment in a new experimental zone. The magnetic transfer lines from the AD to the experiments have been replaced by electrostatic lines from ELENA. Commissioning of the new transfer lines and, in parallel, studies to better understand the ring with H− beams from a dedicated source, have started in autumn 2020. The first 100 keV antiproton physics run using ELENA will start in late summer 2021.

ELENA (Extra Low ENergy Antiproton ring) is an upgrade project at the CERN AD (Antiproton Decelerator). The smaller ELENA ring will further decelerate 5.3 MeV antiprotons from the AD ring down to 100 keV using electron cooling to obtain good deceleration efficiency and dense beams. An increase of up to two orders of magnitude in trapping efficiency is expected at the AD experiments. This paper will report on the current status of ELENA where beam commissioning of the ring is now taking place. Phase one of the project installation has been completed with ring and injection lines in place, while phase two will finalize the project with installation of 100 keV transfer lines connecting the experiments to ELENA and is planned to take place in 2019/2020.

D. Manglunki, M.E. Angoletta, J. Axensalva, G. Bellodi, A. Blas, M. Bodendorfer, T. Bohl, S. Cettour-Cave, K. Cornelis, H. Damerau, I. Efthymiopoulos, A. Fabich, J.A. Ferreira Somoza, A. Findlay, P. Freyermuth, S. Gilardoni, S.B. Hancock, E.B. Holzer, S. Jensen, V. Kain, D. Küchler, A.M. Lombardi, A.I. Michet, M. O'Neil, S. Pasinelli, R. Scrivens, R. Steerenberg, G. Tranquille, CERN, Geneva, Switzerland

The increase of luminosity demanded by the High Luminosity LHC (HL-LHC) requires an increase of beam intensity, which might result in instabilities appearing at injection energy in the CERN PS. Transverse head-tail instabilities have already been observed on operational LHC beams and a stabilizing mechanism as an alternative to linear coupling is currently being studied. It consists of reducing the mode number of the transverse oscillation by changing linear chromaticity and in succession completely suppressing the instability by a transverse damper system with appropriate bandwidth. Therefore, a chromaticity correction scheme at low energy exploiting the intrinsic possibilities offered by special circuits mounted on top of the main magnet poles, the Pole Face Windings (PFW), has been examined. The presence of destructive betatron resonances, which restrict the choice of the injection working point and the maximum acceptable tune spread, forms an additional limitation for high-brightness and high-intensity beams in the CERN PS. To improve the current working point control scheme, the influence of the PFW on the machine resonances is presented in this paper.

The base-line scenario for the High-Luminosity LHC upgrade foresees an intensity increase delivered by the injectors. With its 53 years, the CERN PS would have to operate beyond the limit of its performance to match the future requirements. Beam instabilities driven by transverse impedance are an important issue for the operation with high intensity beams as for the high-brightness LHC beams. Measurements of transverse tune dependence with beam intensity were performed at injection kinetic energy 1.4 GeV and at LHC beam extraction momentum 26 GeV/c. This allows deducing the low frequency inductive broad-band impedance of the machine. Then an estimation of the real part of the impedance is made by the rise time measurement of a fast transverse instability at transition energy believed to be a TMCI type. Those are the first step towards a global machine impedance characterization in order to push forward the performances of the accelerator.

Some of the upgrade scenarios of the high-luminosity LHC require large intensity per bunch from the injector chain. Single bunch beams with intensities of up to 3.5 to 4e11 protons per bunch (p/b) and nominal emittances were successfully produced in the PS Complex and delivered to the SPS in 2010. This contribution presents results of studies with this new intense beam in the SPS to probe single bunch intensity limitations with nominal gamma transition. In particular, the vertical Transverse Mode Coupling Instability (TMCI) threshold with low chromaticity was observed at 1.6e11 p/b for single nominal LHC bunches in the SPS. With increased vertical chromaticity, larger intensities could be injected, stored along the flat bottom and accelerated up to 450 GeV/c. However, significant losses and/or transverse emittance blow-up were then observed. Longitudinal and transverse optimization efforts in the PSB, PS and SPS were put in place to minimize this beam degradation and succeeded to obtain single 2.5e11 p/b LHC-type bunches with satisfying parameters at extraction of the SPS.

The current 1.4 GeV CERN PS injection energy limits the maximum intensity required by the future HighLuminosity LHC. The bare-machine large chromaticity combined with the non-linear space charge forces make high-brightness and high-intensity beams cross betatron resonances along the injection flat bottom, inducing transverse emittance blow-up and beam losses. A scan of the working point plane (Qx,Qy) was done in order to identify beam destructive resonances, in the framework of a possible 2 GeV injection energy upgrade which would reduce the space charge effect on the tune. Experiments were carried out in order to review the maximum space charge tune shift for which no transverse emittance blow-up is observed. The results of measurements and simulations will be presented in this paper.

Some of the upgrade scenarios of the high-luminosity LHC require large intensity per bunch from the injector chain. Single bunch beams with intensities of up to 3.5 to 4e11 p/b and nominal emittances were successfully produced in the PS Complex and delivered to the SPS in 2010. This contribution presents results of studies with this new intense beam in the SPS to probe single bunch intensity limitations with nominal gamma transition. In particular, the vertical Transverse Mode Coupling Instability (TMCI) threshold with low chromaticity was observed at 1.6e11 p/b for single nominal LHC bunches in the SPS. With increased vertical chromaticity, larger intensities could be injected, stored along the flat bottom and accelerated up to 450 GeV/c. However, significant losses and/or transverse emittance blow up were then observed. Longitudinal and transverse optimization efforts in the PSB, PS and SPS were put in place to minimize this beam degradation and succeeded to obtain single 2.5e11 p/b LHC type bunches with satisfying parameters at extraction of the SPS. PROBING INTENSITY LIMITS OF LHC-TYPE BUNCHES IN CERN SPS WITH NOMINAL OPTICS G. Adrian, D. Allen, O. Andujar, T. Argyropoulos, J. Axensalva, J. Baldy, H. Bartosik, S. Cettour Cave, F. Chapuis, J. F. Comblin, K. Cornelis, D. Cotte, K. Cunnington, H. Damerau, M. Delrieux, J.-L. DuranLopez, J. Esteban Mueller, A. Findlay, J. Fleuret, F. Follin, P. Freyermuth, H. Genoud, S. Gilardoni, A. Guerrero, S. Hancock, K. Hanke, O. Hans, R. Hazelaar, W. Höfle, L. Jensen, J. Kuczerowski, Y. Le Borgne, R. Maillet, D. Manglunki, S. Massot, E. Matli, G. Métral, E. Métral, B. Mikulec, J.-M. Nonglaton, E. Ovalle, Y. Papaphilippou, L. Pereira, F. Peters, A. Rey, J. Ridewood, G. Rumolo, B. Salvant, J.-L. Sanchez Alvarez, E. Shaposhnikova, R. Steerenberg, R. Steinhagen, J. Tan, B. Vandorpe, E. Veyrunes (CERN, Geneva) Abstract Some of the upgrade scenarios of the high-luminosity LHC require large intensity per bunch from the injector chain. Single bunch beams with intensities of up to 3.5 to 4e11 p/b and nominal emittances were successfully produced in the PS Complex and delivered to the SPS in 2010. This contribution presents results of studies with this new intense beam in the SPS to probe single bunch intensity limitations with nominal gamma transition. In particular, the vertical Transverse Mode Coupling Instability (TMCI) threshold with low chromaticity was observed at 1.6e11 p/b for single nominal LHC bunches in the SPS. With increased vertical chromaticity, larger intensities could be injected, stored along the flat bottom and accelerated up to 450 GeV/c. However, significant losses and/or transverse emittance blow up were then observed. Longitudinal and transverse optimization efforts in the PSB, PS and SPS were put in place to minimize this beam degradation and succeeded to obtain single 2.5e11 p/b LHC type bunches with satisfying parameters at extraction of the SPS.Some of the upgrade scenarios of the high-luminosity LHC require large intensity per bunch from the injector chain. Single bunch beams with intensities of up to 3.5 to 4e11 p/b and nominal emittances were successfully produced in the PS Complex and delivered to the SPS in 2010. This contribution presents results of studies with this new intense beam in the SPS to probe single bunch intensity limitations with nominal gamma transition. In particular, the vertical Transverse Mode Coupling Instability (TMCI) threshold with low chromaticity was observed at 1.6e11 p/b for single nominal LHC bunches in the SPS. With increased vertical chromaticity, larger intensities could be injected, stored along the flat bottom and accelerated up to 450 GeV/c. However, significant losses and/or transverse emittance blow up were then observed. Longitudinal and transverse optimization efforts in the PSB, PS and SPS were put in place to minimize this beam degradation and succeeded to obtain single 2.5e11 p/b LHC type bunches with satisfying parameters at extraction of the SPS. INTRODUCTION In the frame of the foreseen LHC injector upgrade, CERN is currently probing the brightness limits of the LHC injectors with LHC type beams [1]. The efficient ramp-up of the LHC performance over the past months is now pushing for more improvements of the injected proton beam, in particular in terms of bunch intensity and transverse emittance. This contribution presents the studies performed in the injector chain to increase the bunch intensity beyond nominal (1.15e11 p/b) and ultimate (1.7e11 p/b) at extraction of the SPS. PREPARING HIGH INTENSITY SINGLE BUNCHES IN ALL MACHINES PS Booster (PSB) The nominal LHC type single proton bunch (LHCINDIV) is produced by injecting 1.1 turn from LINAC2 into ring 3 of the PSB. The bunch population at injection in the PSB is of the order of 1.3 10 protons per bunch (p/b). Capture losses and controlled longitudinal shaving with the cavity C02 reduce this intensity by more than a factor 10 to obtain the nominal 1.15 10p/b LHCtype single bunch intensity at extraction of ring 3. Two methods were used to increase the extracted intensity from the PSB: (1) a reduction of the longitudinal shaving right after capture, which enabled to significantly increase the intensity extracted from the PSB, (2) an increase of the number of injected turns from LINAC2, which generates an increased transverse emittance. Thanks to this method, the operation team of the PSB can choose to extract a wide range of single bunch intensities (0.05 to 3 10 p/b) with conserved longitudinal and transverse emittances. This range can be extended to higher intensities per bunch if the emittance constraints are relaxed. PS (Proton Synchrotron) The injection of these high intensity single bunches in the PS was performed without major issues. When these high intensity single bunches extracted from the PS were injected into the SPS in 2010, very high losses and transverse emittance blow up were observed despite optimization of the orbit, working point, RF voltage and chromaticity ξ. One efficient cure to these issues was blowing up the transverse emittance extracted from the PS (above 2 mm.mrad instead of less than 1.5 mm.mrad, 1σ normalised). This blow up was first achieved by crudely inserting a screen into the beam in the TT10 transfer line from the PS to the SPS (as seen in Fig. 1). Then, a more controlled blow up was achieved by missteering the beam at injection of the PS with the injection kicker KFA45 and injection septum SMH42. In fact, it appeared that the emittance blow-up in both planes was difficult to control simultaneously and the blow-up was then performed by sweeping betatron tunes across resonances at injection energy. In 2011, this need to blow up the beams in the PS disappeared without an obvious reason. Finally, following the strong interest to inject smaller emittances in the LHC, a thorough campaign to simultaneously measure transverse emittances in the PSB, PS and SPS was performed and enabled to calibrate the fast wire scanners in the three machines to observe where emittance blow up was generated. It is important to note that this crucial measurement obtained from the beam size and the optics model is however technically complicated and unfortunately still suffers from repeatability and reliability issues in all 3 considered machines [2]. Fig. 1: One of the first attempts to inject high intensity single bunches in SPS with the MDPS beam. Compared to the nominal cycle LHCINDIV, intensity at PS ejection (yellow line) is 3 times higher and shows large intensity variation (already present at PSB extraction). Large losses are observed between PS ejection and SPS injection currents (dark blue line), except when the BTV was put in TT10 (blue box). Decreasing the vertical chromaticity ξy (red boxes) can be observed to generate large losses between SPS injection and the end of SPS flat bottom (magenta line). SPS (Super Proton Synchrotron) Contrary to the PSB and PS, the injection and acceleration of high intensity single bunches in the SPS required significant tuning besides the usual correction of the transverse oscillations, orbit, working point, energy error, RF phase and capture voltage at injection. Indeed, clear bottlenecks were observed with the nominal gamma transition optics, for which the integer part of the horizontal and vertical tunes Qx,y is equal to 26. LONGITUDINAL PLANE IN THE SPS A slow longitudinal instability was observed when the single bunch intensity is larger than 1.9e11 p/b. The 800 MHz RF system was then turned on but the bunch was more unstable longitudinally. Scanning the phase between the two RF systems (200 MHz and 800 MHz) did not help. It is important to note that the 800 MHz RF system may be needed to damp significant synchrotron oscillations of a single bunch with nominal intensity (1.15e11 p/b). If it is not used, these oscillations can be clearly observed over the whole cycle with the wall current monitor and significantly affect the transverse position signals. TRANSVERSE PLANE IN THE SPS Chromaticity settings As observed on Figs. 1 and 2, large losses at injection were observed on SPS flat bottom if the vertical chromaticity was not significantly increased at injection. It is important to note that the first measurement point of the SPS beam current transformer (BCT) is the result of beam current integration over the first 9ms (i.e. the first 400 turns). As a consequence, fast losses that significantly reduce the bunch intensity in 100 to 200 turns cannot be easily observed if the SPS BCT is not compared to the PS BCT measurement at extraction (as in Fig. 1). Besides, the BCT data integrates on all the buckets and may also include longitudinally uncaptured beam. In that case crosschecks with the Fast BCT or the integrated Wall current monitor signal are needed to assess fast losses, in particular when the beam is not accelerated. Fig. 2: SPS BCT intensity data as a function of vertical chromaticity. The

The CERN Proton Synchrotron has been continuously improving its beam performances since 1959. The working point parameters of the accelerator are mainly controlled by dedicated windings installed on the poles of the main combined function magnets. In 2007, the power supplies of these windings were renovated and extended from three to five independent groups, allowing exploration of new working point settings. This configuration offers the flexibility of several adjustment strategies such as leaving one current free or to control an additional physical parameter, like Q''_h. A non-linear chromaticity measurement campaign, at different beam energies, resulted in matrices defining the relationship between the five pole face winding currents and the four beam parameters Q_h, Q_v, Xi_h, and Xi_v. Each cell of these matrices was fitted against energy. The final result is a single matrix which is now used by the operational software to trim the working point. This paper summarises this measurement campaign by presenting the resulting matrix with a brief overview of the adjustment tools and strategy. Furthermore a few future possible benefits of this control enhancement will be discussed.

The Multi-Turn Extraction (MTE), a new type of extraction based on beam trapping inside stable islands in horizontal phase space, has been commissioned during the 2008 run of the CERN Proton Synchrotron. Both single and multi-bunch beams with a total intensity up to 1.4 1013 protons have been extracted with efficiencies up to 98%. Furthermore, injection tests in the CERN Super Proton Synchrotron were performed, with the beam then accelerated and extracted to produce neutrinos for the CERN Neutrino-to-Gran Sasso experiments. The results of the extensive measurement campaign are presented and discussed in detail.

Following the analysis of the results obtained during the first year of beam commissioning of the CERN multiturn extraction, a number of changes have been introduced in the beam manipulations performed in the CERN Proton Synchrotron. This includes a different control of the linear chromaticity, the setting of the nonlinear magnets used to split the beam, and the longitudinal structure in the PS. The results obtained during the 2009 run are presented and discussed in detail, including the beam performance in both the PS and the SPS.