• B. Mikulec, A. Blas, C. Carli, A. Findlay, K. Hanke, G. Rumolo, J. Tan
  CERN, Geneva

The CERN PS Booster (PSB) produces a variety of beam flavours for the LHC. While the nominal LHC physics beams require 6 Booster bunches with intensities up to 1.6·10¹² protons per bunch, during the LHC commissioning single bunch beams with variable intensities as low as 5·10⁹ protons have to be provided reproducibly. The final transverse and in many cases also the final longitudinal beam characteristics have to be achieved already in the PSB and can be very demanding in terms of beam brightness and stability. The optimized production schemes for the different LHC beam flavours in the PSB and the achieved machine performance are presented. Experience with the first beams sent to the LHC in September 2008 is discussed. An overview of the first measured results with a new production scheme of the nominal LHC beam using single instead of double-batch beam transfer from the PSB to the PS is also given.

• B. Mikulec, M. Chanel, A. Findlay, K. Hanke, D. Quatraro, G. Rumolo, J. Tan, R. Tomás
  CERN, Geneva

The CERN Proton Synchrotron Booster (PSB) has been running for more than 30 years. Originally designed to accelerate particles from 50 to 800 MeV, later upgraded to an energy of 1 GeV and finally 1.4 GeV, it is steadily being pushed to its operational limits. One challenge is the permanent demand for intensity increase, in particular for CNGS and ISOLDE, but also in view of LINAC4. As it is an accelerator working with very high space charge during the low energy part of its cycle, its operational conditions have to be precisely tuned. Amongst other things resonances must be avoided, stop band crossings optimized and the machine impedance minimized. Recently, an operational intensity record was achieved with >4.25·10¹³ protons accelerated. An orbit correction campaign performed during the 2007/2008 shutdown was a major contributing factor to achieving this intensity. As the PSB presently has very few orbit correctors available, the orbit correction has to be achieved by displacing and/or tilting some of the defocusing quadrupoles common to all 4 PSB rings. The contributing factors used to optimize performance will be reviewed.

• D. Quatraro, A. Findlay, B. Mikulec, G. Rumolo
  CERN, Geneva

The usual approach and treatment for the interaction of a particle beam with wake fields start from the assumption of ultrarelativistic beams. This is not the case, for example, for the Proton Synchrotron Booster (PSB) whose particles have a kinetic energy up to 1.4 GeV, with a relativistic gamma close to 2.5. There are some examples in literature which derive non ultrarelativistic formulas for the resistive wall impedance. In this paper we have extended the Broad-Band resonator model, allowing the impedance to have poles even in the half upper complex plane, in order to obtain a wake function different from zero for z greater than zero. The Haissinski equation has been numerically solved showing longitudinal bunch shape changes with the energy. In addition some longitudinal bunch profile measurements, taken for different energies and bunch intensities at the PSB, are shown.

• D. Quatraro, A. Blas, M. Chanel, A. Findlay, B. Mikulec, G. Rumolo
  CERN, Geneva

To understand one contribution to the intensity limitations of the CERN Proton Synchrotron Booster (PSB) in view of its operation with beams from Linac 4, the impedance of the machine has been characterized. Measurements of tune shift as a function of the intensity have been carried out in order to estimate the low frequency imaginary part of the impedance. Since the PSB is a low energy machine, these measurements have been done at two different energies,so as to enable us to disentangle the effect of the indirect space charge and resistive wall from the contribution of the machine impedance. An estimation of the possible resonant peaks in the impedance spectrum has been made by measuring a fast instability in Ring 4.

• C. Carli, A. Blas, A. Findlay, R. Garoby, S. Hancock, K. Hanke, B. Mikulec, M. Schokker
  CERN, Geneva

At present, for most LHC type physics beams, six buckets of the PS operated with harmonic number h=7 are filled in two transfers, and each of the PS Booster rings provides only one bunch. The scheme presented aims at replacing the double batch transfer by a single batch transfer and is of interest (i) for the nominal 25 ns LHC beams once the Booster injection energy has been increased after completion of Linac4 and (ii) already now for 50 ns and 75 ns LHC beams less demanding for the Booster in terms of beam brightness. Two bunches with the correct spacing must be generated in the Booster rings by superposition of an h=2 RF system and a smaller h=1 component. Theoretical considerations and first experimental results will be presented.

• 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.

• B. Mikulec, G. Bellodi, M. Eshraqi, K. Hanke, T. Hermanns, S. Lanzone, A.M. Lombardi, U. Raich
  CERN, Geneva

Construction work for the new CERN linear accelerator, Linac4, started in October 2008. Linac4 will replace the existing Linac2 and provide an H^- beam at 160 MeV (as opposed to the present 50 MeV proton beam) for injection into the CERN PS Booster (PSB). The charge-exchange H^- injection combined with the higher beam energy will allow for an increase in beam brightness required for reaching the ultimate LHC luminosity. Commissioning of Linac4 and of the transfer line to the PSB is planned for the last quarter of 2012. Appropriate beam instrumentation is foreseen to provide transverse and longitudinal beam characterization at the exit of Linac4 and in two dedicated measurement lines located before injection into the PSB. A detailed description of the diagnostics set, especially of spectrometer and emittance meter, and the upgrade of the measurement lines for Linac4 commissioning and operation is presented.