• S.S. Gilardoni, F. Arnold Malandain, E. Benedetto, T. Bohl, S. Cettour Cave, K. Cornelis, H. Damerau, F. Follin, T. Fowler, F. Franchi, P. Freyermuth, H. Genoud, R. Giachino, M. Giovannozzi, S. Hancock, Y. Le Borgne, D. Manglunki, G. Metral, L. Pereira, J.P. Ridewood, Y. Riva, M. Schokker, L. Sermeus, R.R. Steerenberg, B. Vandorpe, J. Wenninger
  CERN, Geneva

The Multi-Turn Extraction, a new type of extraction based on beam trapping inside stable islands in the 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 details.

• B. Salvant
  EPFL, Lausanne
• G. Arduini, H. Burkhardt, H. Damerau, W. Höfle, E. Métral, G. Papotti, G. Rumolo, B. Salvant, R. Tomás, S.M. White
  CERN, Geneva
• R. Calaga, R. De Maria
  BNL, Upton, Long Island, New York

The upgrade of the CERN Large Hadron Collider (LHC) would require a four- to fivefold increase of the single bunch intensity presently obtained in the Super Proton Synchrotron (SPS). Operating at such high single bunch intensities requires a detailed knowledge of the sources of SPS beam coupling impedance, so that longitudinal and transverse impedance reduction campaigns can be planned and performed effectively if needed. In this paper, the transverse impedance of the SPS is studied by injecting a single long bunch into the SPS, and observing its decay without RF. This particular setup enhances the resolution of the frequency analysis of the longitudinal and transverse bunch signals acquired with strip line couplers connected to a fast data acquisition. It also gives access to the frequency content of the transverse impedance. Results from measurements with short and long bunches in the SPS performed in 2008 are compared with simulations and theoretical predictions.

• E.N. Shaposhnikova, T. Bohl, H. Damerau, K. Hanke, T.P.R. Linnecar, B. Mikulec, J. Tan, J. Tuckmantel
  CERN, Geneva

First reference measurements of the longitudinal impedance were made with beam in the SPS machine in 1999 to quantify the results of the impedance reduction programme, completed in 2001. The 2001 data showed that the low-frequency inductive impedance had been reduced by a factor 2.5 and that bunch lengthening due to the microwave instability was absent up to the ultimate LHC bunch intensity. Measurements of the quadrupole frequency shift with intensity in the following years suggest a significant increase in impedance (which nevertheless remains below the 1999 level) due to the installation of eight extraction kickers for beam transfer to the LHC. Microwave instability is still not observed up to the maximum bunch intensities available from injector. The experimental results are compared with expectations based on the known longitudinal impedance of the different machine elements in the SPS.

• C.M. Bhat
  Fermilab, Batavia
• F. Caspers, H. Damerau, S. Hancock, E. Mahner, F. Zimmermann
  CERN, Geneva

Funding: Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy and CARE-HHH

Motivated by the discussions on scenarios for LHC upgrades, beam studies on the stability of flat bunches in a double-harmonic RF system have been conducted in the CERN Proton Synchrotron (PS). Injecting nearly nominal LHC beam intensity per cycle, 18 bunches are accelerated on harmonic h=21 to 26 GeV with the 10 MHz RF system. On the flat-top, all bunches are then transformed to flat bunches by adiabatically adding RF voltage at h=42 from a 20 MHz cavity in anti-phase to the h=21 system. The voltage ratio V(h42)/V(h21) of about 0.5 was set according to simulations. For the next 140 ms, longitudinal profiles show stable bunches in the double harmonic RF bucket until extraction. Without the second harmonic component, coupled-bunch oscillations are observed. The flatness of the bunches along the batch is analyzed as a measure of the relative phase error between the RF systems due to beam loading. Measurements of electron cloud effects induced by the beam are also discussed. The results of beam dynamics simulations and their comparison with the measured data are presented.