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This Report gives a full description of the ELENA Ring to be built within the circumference of the Antiproton Decelarator (AD) Ring, in Building 193 at CERN. The ELENA ring will further decelerate the antiprotons coming from the AD at the momentum of 100 MeV/c down to 13.7 MeV/c, which corresponds to the kinetic energy of 100 keV before extracting to the physics experiments in the same building. The history of such an extra low energy antiproton ring at CERN goes a long way back, and even to the Decelerator’s previous incarnation, the Low Energy Antiproton Ring (LEAR), which came into operation in 1983. Already at that time, there were physics’ requests to further decelerate the antiprotons expected from LEAR by proposals for ELENA. Appendix I illustrates the cover pages of two such CERN documents from 1982.

Chromatic coupling was regularly measured in the LHC throughout 2012. A first beam-based correction of chromatic coupling was applied during a dedicated MD. In this note we summarise the measurements and results showing a significant reduction in the chromatic coupling for both beams.

The future ELENA ring at CERN will decelerate the AD anti-proton beam further from 5.3 MeV to 100 keV kinetic energy, to increase the efficiency of anti-proton trapping. At present there are four experiments in the AD hall which will be complemented with the installation of ELENA by additional three experiments and an additional source for commissioning. This paper describes the optimization of the transfer line geometry, ring rotation and source position. The optics of the transfer lines and error studies to define field and alignment tolerances are shown, and the optics particularities of electrostatic elements and their optimization highlighted.

A new optics was introduced in the SPS for improving beam stability at high intensity. For transferring the beam to the LHC, the extraction bumps, extraction kickers and transfer lines needed to be adapted to the new optics. In particular, the transfer lines were re-matched and re-commissioned with the new optics. The first operational results are discussed for the SPS extraction, the transfer lines and the LHC injection. A detailed comparison is presented between the old and the new optics of the trajectories, dispersion, losses and other performance aspects.

In 2011 the ELENA decelerator was approved as a CERN project. Initially one extraction was foreseen, which should use a kicker and a magnetic septum which can be recuperated from an earlier installation. Since then a second extraction has been approved and a new solution was studied using only electric fields to extract the beam. This will be achieved by fast pulsing a separator, allowing single-bunch but also a full single-turn extraction from ELENA towards the experiments. The extraction and transfer requirements of ELENA are described, followed by the principal differences between the magnetic and electric field concepts. The design of electrostatic focussing and bending devices for the transfer lines will be presented. Finally the field quality which can be achieved with the separator and the concept of its power supply will be discussed.

An optics in the SPS with lower integer tunes (20 versus 26) was proposed and introduced in machine studies since 2010, as a measure for increasing transverse and longitudinal instability thresholds, especially at low energy, for the LHC proton beams. After two years of machine studies and careful optimisation, the new Q20 optics became operational in September 2012 and steadily delivered beam to the LHC until the end of the run. This paper reviews the operational performance of the Q20 optics with respect to transverse and longitudinal beam characteristics in the SPS, enabling high brightness beams injected into the LHC. Aspects of longitudinal beam stability, transmission, high-energy orbit control and beam transfer are discussed.

The LHC is filled from the SPS via two 3 km long transfer lines: TI2 for beam 1 and TI8 for beam 2. In the first years of LHC operation large trajectory variationswere discovered. The sources of bunch-by-bunch and shot-by-shot trajectory variations had been identified and improved by the 2012 LHC run. The origins of the longer term drifts were however still unclear and significant time was spent correcting the trajectories. In the last part of the 2012 run the optics in the SPS was changed to lower transition energy. Trajectory stability and correction frequency will be compared between before and after the optics change in the SPS. The sources of the variations have now been identified and will be discussed in this paper. Remedies for operation after the long shutdown will be proposed.

Glenn Vanbavinckhove ontwikkelde onder meer een nieuw algoritme, de segment-by-segment-techniek, om sterke lokale fouten voor belangrijke optische parameters te identificeren in versnellers en andere opslagringen. Vanbavinckhove presenteert methodes en technieken voor de meting en correctie van de lineaire optica in versnellers en andere opslagringen. De segment-by-segment-techniek bleek zeer nuttig te zijn tijdens de ingebruikname van de LHC (Large Hadron Collider, ondergrondse deeltjesversneller). Door een meer geautomatiseerde manier van het identificeren van lokale fouten, bijvoorbeeld door gebruik te maken van een lokaal matching script of lokale responsmatrix, kan de segment-by-segment-techniek verbeterd worden. Ook beschrijft Vanbavinckhove in detail de modus operandi voor het meten en corrigeren van de optiek. De turn by turn-data verkregen in de beam position monitors (monitoren die de positie van de bundel waarnemen) werden gebruikt om de optische parameters te meten.

This note summarizes the results obtained at injection during the 2nd MD block and the floating MD block in July. Highlights are presented for injection in the LHC with the Q20 SPS optics, influence of the supercycle and injection with 25 ns bunch spacing. Beams were successfully injected into the LHC using the Q20 optics [1, 3]. Small corrections were needed to steer the beam in the transfer lines. Dispersion measurements were conducted for both beams. The horizontal normalized dispersion in TI2 was a factor 2 smaller for Q20 with respect to Q26, for TI8 on the other hand the opposite was observed. The results for injection loss dependency on super cycle composition show only a small increase in losses for beam 2. The losses observed must therefore mainly come from other sources such as shot-by-shot stability or quality of scraping. For the injection with 25 ns bunch spacing bunches were injected for both beams. For B1 up to the maximum of 288 bunches. For B2 on the other only up to 144 bunches were injected, due to the higher number of voltage breakdowns for a P8 injection kicker magnet. There is enough margin for increasing the bunch intensity and at the same time keeping losses below 30% for operational flexibility.

This note summarizes the commissioning of the betatron squeeze from 1.5 m to 1 m performed during MD3. The MD3 work included measurements of the optics, setting up of the collimation system for tight settings, validation of the collimation settings and a test ramp with higher intensity to probe long-range beam-beam effects.

ISBN 978-3-95450-115-1 - http://accelconf.web.cern.ch/AccelConf/IPAC2012/papers/moppc006.pdf; International audience; A high β* = 90 m optics was commissioned and used for first very forward physics operation in the LHC in 2011. The experience gained from working with this optics in 5 studies and operation periods in 2011 was very positive. The target β* = 90 m was reached by a de-squeeze from the standard 11 m injection and ramp optics on the first attempt and collisions and first physics results obtained in the second study. The optics was measured and corrected with good precision. The running conditions were very clean and allowed for measurements with roman pots very close to the beam.

In 2011, the LHC has delivered collisions with different optics configurations in the four interaction points, at an operating energy of 3.5 TeV. The performance has been pushed during the year until a final configuration with 3 IPs squeezed to 1 m was achieved. Correspondingly, the machine aperture has been measured in the different configurations at injection and at top energy, to ensure a safe operation in all conditions of $\beta^*$ and crossing angle configuration. In this paper, the 2011 commissioning experience of LHC optics is reviewed and the results of aperture measurements are presented. Measurement requirements for 2012 and possible improvements are also discussed.

The performance of the LHC injection and extraction systems and the main problems encountered during 2012 operation are described. Special attention is dedicated to the stability of the transfer lines, steering frequency, sensitivity to beam and machine changes, injection protection collimators setup and the consequent impact on operation and possible machine protection issues. The improvements foreseen for operation with injection of up to 288 bunches after LS1 in terms of stability, availability and safety are explored. The modifications foreseen to strengthen the reliability of the LHC Beam Dumping System and the new TCDQ hardware for operation at 6.5 TeV with high intensity beams are introduced.

This note highlights the results obtained during the third so-called ATS MD which took place in 2011. The goal of this MD was extremely challenging, targeting a pre-squeezed beta* of 40 cm in ATLAS and CMS, followed by a telescopic squeeze of these two insertions to finally reach a beta* of 10 cm both at IP1 and IP5. Due to the rather poor machine availability during the MD period, the time initially allocated to the ATS studies was hardly cut by a factor of 2, and "only" the achromatic pre-squeeze down to beta*=40 cm was demonstrated with beam.

This paper reports on the first successful attempt to measure and correct the on-momentum optics close to the half integer resonance in LHC at injection energy. This tune working point is traditionally preferred by colliders for providing the largest resonance-free space in the tune diagram [1, 2]. It is also considered as an option for the HL-LHC upgrade [3].

Two methods for deriving the Beta-functions were studied, as a discrepancy occured when approaching the half integer resonance. Several simulations have been performed to study the behaviour of the two methods under different controlled circumstances. An ideal accelerator without any errors of the magnetic components was simulated before magnetic field errors were added to the simulation. A new algorithm was devoloped in order to improve the computation of the Beta-functions.

The phase advance between the two interaction points in RHIC is optimized for dynamic aperture for a initial design beta-star. This may not hold true as RHIC presently operates with a considerably reduced beta-star. Additionally the reduction of the available beam aperture due to an enlarged chromatic beta-beating is evident. Measurements of the chromatic optics in the RHIC are presented along with the proposal to optimize the arc phase advance between the two IPs to adjust the chromatic beta-beating. Measurements of chromatic optics from the LHC at injection and top energy are presented.

The non-linear chromaticity of the LHC has been studied. Measurements of variation in tune with dp/p on both beams at injection optics are being compared with Q′′ and Q′′′ as calculated with the LHC effective model. This model uses the best currently available measurements of magnetic field harmonics. An attempt is being made to optimize the b4 and b5 spool-pieces corrections in view of the corresponding chromaticity terms.

At present, the LHC operates with a different fractional tunes at injection and at collision energy due to improved dynamic aperture indicated by tracking studies. Therefore, a tune swing crossing the 10th order resonance is needed during the beta-squeeze. A new proposal to alter the working point to collision tunes already at injection and during an energy ramp is foreseen to avoid the tune jump. Simulations and measurements of the optics along with the beam emittances and lifetime are compared to the nominal injection tunes. Feasibility for a working point close to the 1/2 integer is also attempted.

Transverse betatron coupling in the LHC is measured from Fourier analysis of turn-by-turn beam oscillations excited by AC dipoles. The use of the AC dipole for optics measurements induces a small systematic error which can be corrected with an appropriate data interpretation. An algorithm to apply this correction to the measurement of the coupling resonance driving terms is developed. This paper will review this new algorithm and present results of its application to the LHC.

During the 2011 LHC run several measurements and cor- rection campaigns were conducted. As a result a peak β- beat of 10% level was achieved. This level, well below the specified tolerances of the LHC, improves the aperture margins and helps minimize the luminosity imbalance be- tween the different experiments. A combination of local corrections at the insertion regions and an overall global correction were used to achieve this record low beta-beat. The sequence of the optics corrections and stability along the 2011 run are reported.

Higher order effects can play an important role in the performance of the LHC. Lack of knowledge of these pa- rameters can increase the tune footprint and compromise the beam lifetime. First measurements of these parameters at injection and flattop have been conducted. Detailed sim- ulations are compared to the measurements together with discussions on the measurement limitations.

Accurate knowledge of the collision point optics is crucial to equalize the luminosities at the different experiments. K-modulation was successfully applied at several accelerators for measuring the lattice beta functions. In the LHC, it was proposed as an alternative method to compute the beta* at the collision points. Results of beta* measurements in the LHC based on the K-modulation technique are presented with comparisons to nominal segment-bysegment method.

The tight tolerances in the LHC requires optics measurement with very good accuracy. Therefore, AC dipoles are employed as the primary devices to measure the LHC optics. The accuracy of the measurement is mainly determined by the length of the coherent signal, signal-to-noise ratio of the measurement, and the data processing to effectively suppress the noise. This paper presents numerical and experimental studies of how these factors affect the accuracy of the LHC optics measurement using the AC dipoles.

Excessive beta-beat, deviation of measured beta function from the calculated beta functions based on an model, in high energy colliders can lead to large deviation of beta function at collision point as well as other adverse ef- fects. The segment-by-segment technique was successfully demonstrated in the LHC operation for reducing the beta- beat. It was then applied to RHIC polarized proton opera- tion in 2011. This paper reports the experimental results of optics correction at RHIC. Future plan is also presented.

http://accelconf.web.cern.ch/AccelConf/IPAC2011/papers/tupz001.pdf; International audience; Special β∗ = 90 m optics have been developed for the two very high luminosity insertions of the LHC [1] [2], as a rst step to allow for very low angle precision measure- ments of the proton-proton collisions in the LHC. These optics were developed to be compatible with the stan- dard LHC injection and ramp optics. The target value of β∗ = 90 m is reached by an un-squeeze from the injection β∗ = 11 m. We report about the implementation of this op- tics and the rst experience gained in commissioning with beam during two machine studies.

TBC

This note describes the results obtained during the first so-called ATS MD where a new injection optics was commissioned and ramped to 3.5 TeV.

This paper reports on the first successful attempt to inject and ramp LHC beams with collision tunes. Using the same tunes throughout the entire LHC cycle has three clear advantages: • Shorter squeeze sequence and hence saving time for luminosity production. • Less complexity in the operation of feed-backs. • Absence of tune swing crossing 7th and 10th order resonances.

We describe the first machine study on high-Beta optics performed in the LHC. Beams were un-squeezed in the interactions regions 1 and 5 from Beta* = 11m to 90m in steps with external tune compensation using the main quadrupoles.

Consolidation of the coupling correction scheme in the LHC is challenged by a missing skew quadrupole family in Sector 3-4 at the start-up in 2009-2010. Simultaneous coupling and vertical dispersion correction using vertical orbit bumps at the sextupoles, was studied by analyzing turn-byturn data. This scheme was tested in the CERN SPS where the optical structure of arc cells is quite similar to the LHC. In the SPS, horizontal and vertical beam positions are measured separately with single plane BPMs, thus a technique to construct ”pseudo double plane BPM” is also discussed.

Optics stability during all phases of operation is crucial for the LHC. The optical properties of the machine have been optimized based on a detailed magnetic model of the SC magnets and on their sorting. Tools and procedures have been developed for rapid checks of beta beating, dispersion, and linear coupling, as well as for prompt optics correction. Initial optics errors, correction performance and optics stability from the first LHC run will be reported, and compared with expectations.

The knowledge of the distribution of the nonlinear components in a ring is important for the resonance compensation. A method to measure the lattice nonlinear components based on the nonlinear tune response to a controlled closed orbit deformation (NTRM) was suggested in [1]. First benchmarking of this method was carried out with controlled sextupolar errors in the SIS18 synchrotron at GSI. We present here a further benchmarking of NTRM by using controlled octupolar errors at CERN SPS.

The 2009 LHC run has made it possible to collect an extensive set of beam-based measurements. A good fraction of the LHC magnets, aperture and optics models has been validated with these measurements. However, a few localized optical errors remain. Appropriate corrections are necessary to reach machine specifications and to safely operate the LHC at higher intensities. The measurements, model predictions and proposed optics corrections are summarized

For several years optics measurement and correction algorithms have been developed for the LHC. During 2008 these algorithms have been tested in the SPS and RHIC. The experimental results proving the readiness of the applications are presented.

In 2008 beam successfully circulated in the LHC. Thanks to an excellent functioning of the beam position monitor (BPM) system and the related software, injection oscillations were recorded for the first 90 turns at all BPMs. The analysis of these data gives the unique opportunity of evaluating the periodic optics and inferring possible error sources.

The constraints in the LHC machine protection impose tighter optics tolerances than in any other hadron collider. A variety of beam-based measurements in the first days of LHC operation was effective to measure aperture clearance, magnet polarities and machine optics. A summary of these measurements is given together with model insights.

Optics correction in the LHC is challenged by the tight aperture constrains and the demand of a highly performing BPM system. To guarantee that the LHC optics remains within a maximum allowable beta-beating of 20% several methods are being investigated through computer simulations and experiments at existing hadron machines. A software package to consolidate the implementation of the various techniques during LHC operation is underway (or nearing completion).

The Achromatic Telescopic Squeezing (ATS) scheme is a novel squeezing mechanism enabling the production of very low β* in circular colliders. The basic principles of the ATS scheme will be reviewed together with its strong justification for the High-Luminosity LHC Project. In this context, a few dedicated experiments with beam were meticulously prepared and took place at the LHC in 2011. The results obtained will be highlighted, demonstrating the potential of the ATS scheme for any upgrade project relying on a strong reduction of β*.