First Results for the Beam Commissioning of the CERN Multi-Turn Extraction

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 singleand 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

OPERATIONAL PERFORMANCE OF THE LHC PROTON BEAMS WITH THE SPS LOW TRANSITION ENERGY OPTICS

Abstract 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

OPERATIONAL PERFORMANCE OF THE LHC PROTON BEAMS WITH THE SPS LOW TRANSITION ENERGY OPTICS

Abstract 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

Optics measurements and transfer line matching for the SPS injection of the CERN Multi-Turn Extraction beam

Dispersion and beam optics measurements were carried out in the transfer line between the CERN PS and SPS for the new Multi-Turn Extraction beam. Since the extraction conditions of the four islands and the core are different and strongly dependent on the non-linear effects used to split the beam in the transverse plane, a special care was taken during the measurement campaigns. Furthermore, an appropriate strategy was devised to minimize the overall optical mismatch at SPS injection. All this led to a new optical configuration that will be presented in the paper

Fixed target beams

The CERN SPS (Super Proton Synchrotron) serves asLHC injector and provides beam for the North Area fixedtarget experiments. At low energy, the vertical acceptancebecomes critical with high intensity large emittance fixed tar-get beams. Optimizing the vertical available aperture is a keyingredient to optimize transmission and reduce activationaround the ring. During the 2016 run a tool was developed toprovide an automated local aperture scan around the entirering.The flux of particles slow extracted with the1/3inte-ger resonance from the Super Proton Synchrotron at CERNshould ideally be constant over the length of the extractionplateau, for optimum use of the beam by the fixed target ex-periments in the North Area. The extracted intensity is con-trolled in feed-forward correction of the horizontal tune viathe main SPS quadrupoles. The Mains power supply noiseat 50 Hz and harmonics is also corrected in feed-forwardby small amplitude tune modulation at the respective fre-quencies with a dedicated additional quadrupole circuit. Thecharacteristics of the SPS slow extracted spill in terms ofmacro structure and typical frequency content are shown.Other sources of perturbation were, however, also present in2016 which frequently caused the spill quality to be muchreduce

Non-linear beam dynamics tests in the LHC: measurement of intensity decay for probing dynamic aperture at injection

For a second year in a row dynamic aperture experiments have been performed at the LHC. These studies have been carried out by two teams following alternative techniques: On Beam 1 a novel approach has been tested which heats the beam until the emittance becomes large, and derives the dynamic aperture from beam losses assuming an inverse logarithm model for the time-dependence of the intensity. On Beam 2, the traditional approach of sampling the dynamic aperture with large amplitude kicks has been pursued [1]. In 2011, considerable progress was made and impressive results have been reported. In 2012 a further Machine Development (MD) session was scheduled during which both teams have benefited from an improved availability of the beams and more optimal performance of the instrumentation. Observations and analysis are presented as two MD reports of the LHC dynamic aperture experiment MD. This note describes the observations made on Beam 1, when the strength of the spool pieces have been varied. The key quantity is the intensity evolution. Clear differences have been recorded and a preliminary analysis is reported in this note. The considerable set of data will be analysed in details later on

Losses on SPS flat bottom and beam loading with LHC beams

Losses at SPS flat bottom with the LHC proton beams hadbeen studied since the earliest days the LHC beams becameavailable in the SPS. Some of the loss mechanisms involvedcould be identified and over the years of operation with thenominal 25ns LHC beam, the losses could be gradually re-duced. Nevertheless, in machine studies with high intensity25ns LHC beams it is still observed that the transmissiondegrades with intensity. As summarised in this paper, a se-ries of studies have been performed in 2016 with the aim offurther characterising the loss mechanisms and eventuallyfinding mitigation measures in view of the LHC injectorupgrade project (LIU

Experimental studies with low transition energy optics in the SPS

The optics of the SPS can be tuned to lower transition energy such that the slippage factor at injection is raised by a factor of almost 3. From theory, an increase of the intensity thresholds for transverse mode coupling, longitudinal coupled bunch and longitudinal instabilities due to the loss of Landau damping can be expected. In this paper, experimental studies in the SPS with single bunches of protons with intensities of up to 3.5e11 p/b on the flat bottom and at 450 GeV/c are presented. Longitudinal instabilities were studied with LHC-type beams with 50 ns spacing and injected intensities up to 1.8e11 p/b. The measurements address the increase of intensity thresholds and the achievable transverse emittances in the new low gamma transition optics with respect to the nominal SPS optics. The obtained results are compared with numerical simulations

Increasing instability thresholds in the SPS by lowering transition energy

A new optics for the SPS with lower transition energy was tested experimentally during 2010-2011, showing a significant increase of the single bunch instability thresholds at injection due to the 3-fold increase of the slip factor. The performed machine studies for different LHC beams and intensities are summarized in this paper. In particular, the search for the single bunch TMCI threshold in the new optics is presented. Observations on the longitudinal multibunch stability are compared between the nominal and the low-transition optics. Finally, optics variants with higher vertical tunes are discussed, which could allow to further increase the thresholds for TMCI and other vertical instabilities by reducing the vertical beta function

Experimental Studies for Future LHC Beams in the SPS

The High Luminosity LHC (HL-LHC) project requires significantly higher beam intensity than presently accessible in the LHC injector chain. The aim of the LHC injectors upgrade project (LIU) is to prepare the CERN accelerators for the future needs of the LHC. Therefore a series of SPS machine studies with high brightness beams were performed, assessing the present performance reach and identifying remaining limitations. Of particular concern are beam loading and longitudinal instabilities at high energy, space charge for beams with 50 ns bunch spacing and electron cloud effects for beams with 25 ns bunch spacing. This paper provides a summary of the performed studies that have been possible thanks to the implementation of the SPS low gamma-transition optics