An improved procedure for energy matching between PS and SPS at CERN

Energy matching between two hadron synchrotrons is the adjustment of the magnetic bending fields and beam momentum to obtain a correct transfer between the two. Conventionally, energy matching is achieved by turning off the RF system and measuring the revolution frequency of the de-bunching beam in the receiving accelerator. For an ideal circumference ratio, the orbits would then be centred in the two rings. However, this procedure is non transparent, seen that the de-bunched beam cannot be accelerated anymore. Thanks to the Low-Level RF (LLRF) upgrade in the Super Proton Synchrotron (SPS) during the 2019-2021 long shutdown, most LLRF signals have become available in digital form, allowing easy online display, analysis, and storage. In this contribution, we look at the possibility of performing energy matching between the PS and the SPS in a more transparent way, without disabling the RF system. The signals from the beam phase and synchronization loops reveal information on the energy of the beam injected into the SPS. This allows to continuously monitor the transfer frequency error, as well as identify and correct potential long-term drifts

Automatic Local Aperture Measurements in the SPS

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

Identification and Removal of SPS Aperture Limitations

The CERN SPS (Super Proton Synchrotron) serves as LHC injector and provides beam for the North Area fixed target experiments. Since the 2016 run automated local aperture scans have been performed with the main focus on the vertical plane where limitations typically arise due to the flat vacuum chambers in most SPS elements. For LHC beams the aperture limitations with the present low integer tune optics also occur at locations with large dispersion. Aperture measurements in the horizontal plane using a variety of techniques were performed and showed surprising results, which could partially explain the unexpected losses of high intensity LHC beams at the SPS flat bottom. In this paper, reference measurements from 2016 are compared with the ones taken at the beginning of the run in 2017. Several aperture restrictions in the vertical plane could be found and cured, and a potential systematic restriction in the horizontal plane has been identified. The results of the measurements and the origin of the restrictions are presented in this paper, and the outlook for partial mitigation is discussed

Approaching the High-Intensity Frontier Using the Multi-Turn Extraction at the CERN Proton Synchrotron

Complementary to the physics research at the LHC, several fixed target facilities receive beams from the LHC injector complex. In the scope of the fixed target physics program at the Super Proton Synchrotron, high-intensity proton beams from the Proton Synchrotron are extracted using the Multi-Turn Extraction scheme, which is based on particle trapping in stable islands of the horizontal phase space. Considering the number of protons requested by future experimental fixed target facilities, such as the Search for Hidden Particles experiment, the currently operationally delivered beam intensities are insufficient. Therefore, experimental studies have been conducted to optimize the Multi-Turn Extraction technique and to exploit the possible intensity reach. The results of these studies along with the operational performance of high-intensity beams during the 2017 run are presented in this paper. Furthermore, the impact of the hardware changes pursued in the framework of the LHC Injectors Upgrade project on the high-intensity beam properties is briefly mentioned.Complementary to the physics research at the LHC, sev- eral fixed target facilities receive beams from the LHC in- jector complex. To serve the fixed target physics program at the Super Proton Synchrotron, high-intensity proton beams from the Proton Synchrotron are extracted using the Multi- Turn Extraction technique based on trapping parts of the beam in stable resonance islands. Considering the num- ber of protons requested by future experimental fixed target facilities, such as the Search for Hidden Particles experi- ment, the currently operationally delivered beam intensities are insufficient. Therefore, experimental studies have been conducted to optimize the Multi-Turn Extraction technique and to exploit the possible intensity reach. The results of these studies along with the operational performance of high- intensity beams during the 2017 run are presented in this paper. Furthermore, the impact of the hardware changes pur- sued in the framework of the LHC Injectors Upgrade project on the high-intensity beam properties is briefly mentioned

Design of a Magnetic Bump Tail Scraping System for the CERN SPS

The LHC injectors are being upgraded to meet the demanding beam specification required for High Luminosity LHC (HL-LHC) operation. In order to reduce the beam losses which can trigger the sensitive LHC beam loss interlocks during the SPS-to-LHC beam injection process, it is important that the beam tails are properly scraped away in the SPS. The current SPS tail cleaning system relies on a moveable scraper blade, with the positioning of the scraper adjusted over time according to the orbit variations of the SPS. A new robust beam tail cleaning system has been designed which will use a fixed scraper block towards which the beam will be moved by a local magnetic orbit bump. The design proposal is presented, together with the related beam dynamics studies and results from machine studies with beam

Development of fragmented low-Z ion beams for the NA61 fixed-target experiment at the CERN SPS

The NA61 ex­per­i­ment, aims to study the prop­er­ties of the onset of de­con­fine­ment at low SPS en­er­gies and to find sig­na­tures of the crit­i­cal point of strong­ly in­ter­act­ing mat­ter. A broad range in T-μB phase di­a­gram will be cov­ered by per­form­ing an en­er­gy (13A-158A GeV/c) and sys­tem size (p+p, Be+Be, Ar+Ca, Xe+La) scan. In a first phase, frag­ment­ed ion beams of 7Be or 11C pro­duced as sec­on­daries with the same mo­men­tum per nu­cle­on when the in­ci­dent pri­ma­ry Pb-ion beam hits a thin Be tar­get will be used. The H2 beam line that trans­ports the beam to the ex­per­i­ment acts as a dou­ble spec­trom­e­ter which com­bined with a new thin tar­get (de­grad­er) where frag­ments loose en­er­gy pro­por­tion­al to the square of their charge al­lows the sep­a­ra­tion of the want­ed A/Z frag­ments. Thin scin­til­la­tors and TOF mea­sure­ment for the low en­er­gy points are used as par­ti­cle iden­ti­fi­ca­tion de­vices. In this paper re­sults from the first test of the frag­ment­ed ion beam done in 2010 will be pre­sent­ed show­ing that a pure Be beam can be ob­tained sat­is­fy­ing the needs of the ex­per­i­ment

Lifetime and Beam Losses Studies of Partially Strip Ions in the SPS (129^{129}Xe39+^{39+})

International audienceThe CERN multipurpose Gamma Factory proposal relies on using Partially Stripped Ion (PSI) beams, instead of electron beams, as the drivers of its light source. If such beams could be successfully stored in the LHC ring, fluxes of the order of $10^{17}$ photons/s, in the $\gamma$-ray energy domain of $1 \leq \rm{E}_{\gamma} \leq 400$ MeV could be achieved. This energy domain is out of reach for the FEL-based light sources as long as the multi TeV electron beams are not available. The CERN Gamma Factory proposal has the potential of increasing by 7 orders of magnitude the intensity limits of the present Inverse Compton Scattering sources. In 2017 the CERN accelerator complex demonstrated its flexibility by producing a new, xenon ion beam. The Gamma Factory study group, based on this achievement, requested special studies. It aimed to inject and to accelerate, in the SPS, partially stripped xenon ions ($^{129}$Xe$^{39+}$) measure their life time, and determine the relative strength of the processes responsible for the PSI beam losses. The study presented in this contribution was an preparatory step in view of the the future studies programmed for 2018 with lead PSI beams

AWAKE Proton Beam Commissioning

AWAKE will be the first proton driven plasma wakefield acceleration experiment worldwide. The facility is located in the former CNGS area at CERN and includes a proton, laser and electron beam line merging in a 10 m long plasma cell, which is followed by the experimental diagnostics. In the first phase of the AWAKE physics program, which started at the end of 2016, the effect of the plasma on a high energy proton beam is being studied. A proton bunch is expected to experience the so called self-modulation instability, which leads to the creation of micro-bunches within the long proton bunch. The plasma channel is created in a rubidium vapor via field ionization by a TW laser pulse. This laser beam has to overlap with the proton beam over the full length of the plasma cell, resulting in tight requirements for the stability of the proton beam at the plasma cell in the order of 0.1 mm. In this paper the beam commissioning results of the 810 m long transfer line for proton bunches with $3 \cdot 10^{11}$ protons/bunch and a momentum of 400 GeV/c will be presented with a focus on the challenges of the parallel operation of the laser and proton beam

CERN's Fixed Target Primary Ion Programme

The renewed availability of heavy ions at CERN for the needs of the LHC programme has triggered the interest of the fixed-target community. The project, which involves sending several species of primary ions at various energies to the North Area of the Super Proton Synchrotron, has now entered its operational phase. The first argon run, with momenta ranging from 13 AGeV/c to 150 AGeV/c, took place from February 2015 to April 2015. This paper presents the status of the project, the performance achieved thus far and an outlook on future plans

Performance of the CERN Injector Complex and Transmission Studies into the LHC during the Second Proton-Lead Run

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 presente