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Métral, E.

Paper Title Page
WGA02 Transverse Mode-Coupling Instability in the CERN SPS: Comparing HEADTAIL Simulations with Beam Measurements 45
 
  • B. Salvant
    EPFL, Lausanne
  • G. Arduini, E. Métral, G. Papotti, D. Quatraro, G. Rumolo, R.J. Steinhagen, R. Tomás
    CERN, Geneva
  • R. Calaga
    BNL, Upton, Long Island, New York
 
 

Since 2003, single bunches of protons with high intensity and low longitudinal emittance have been observed to suffer from heavy losses in less than one synchrotron period after injection in the CERN Super Proton Synchrotron (SPS) when the vertical chromaticity is corrected. This fast instability does not limit the current performance of the SPS, but would be a major limitation in case of an anticipated upgrade of the SPS, which requires bunches of 4·1011 protons (p). Besides, the characteristics of this instability are also complementary indicators of the value of the SPS beam coupling impedance. MOSES analytical calculations, HEADTAIL macroparticle tracking simulations, as well as several measurement campaigns in the SPS indicate that this instability may be due to a coupling between transverse modes ‘-2’ and ‘-3’. The aim of this contribution is to report improvements of the SPS impedance model used by HEADTAIL simulations, and to find out more characteristics of the measured instability in order to assess whether the observed instability in the SPS is indeed a Transverse Mode Coupling Instability (TMCI).

 

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WGA03 Measurement of the Transverse Resistive Wall Impedance of a LHC Graphite Collimator at Low Frequency 48
 
  • F. Roncarolo
    UMAN, Manchester
  • F. Caspers, T. Kroyer, E. Métral
    CERN, Geneva
  • B. Salvant
    EPFL, Lausanne
 
 

The largest contribution to the LHC transverse resistive wall impedance is given by the graphite collimators. Such a contribution is predicted by analytical calculations. A series of laboratory measurements were performed to experimentally validate the analytical results in the case of small gaps and in a low frequency regime where the skin depth becomes comparable to the collimator thickness. The measurement method consists in determining the dependence of a probe coil input impedance on the surrounding materials and was applied to sample graphite plates, stand alone LHC collimator jaws and a full collimator assembly. After reviewing the measurement procedures, problematics and stages, the results are compared to analytical predictions and numerical simulations.

 

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WGA29 Achievable Space-Charge Tune Shift with Long Lifetime in the CERN PS and SPS 153
 
  • E. Métral, H. Burkhardt
    CERN, Geneva
 
 

In the CERN Proton Synchrotron (PS), a slow beam loss of few percents is still observed on the long injection flat-bottom with the nominal beam for LHC after fine tuning of the working point. The understanding of space-charge effects is therefore of paramount importance to try and alleviate this limitation. This is why controlled benchmarking space-charge experiments were performed in the last few years. The results are presented in detail with a particular emphasis on the maximum achievable space-charge tune shift with long lifetime. On the contrary, space-charge effects usually play a minor role in high-energy machines like the CERN Super Proton Synchrotron (SPS). However, they could potentially become a limitation for the heavy ion beams needed for the LHC. Therefore, experimental studies on space-charge limitations were also performed in the SPS in the last few years. The results are discussed in detail in the present paper. Furthermore, it is worth mentioning that observations similar to the ones measured in the PS in the presence of space-charge were also measured in the SPS with electron cloud.

 

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CPL01 Summary of Group A: Beam Dynamics in High Intensity Circular Machines 482
 
  • R.A. Baartman
    TRIUMF, Vancouver
  • G. Franchetti
    GSI, Darmstadt
  • E. Métral
    CERN, Geneva
 
 

32 papers were presented. Rather than summarizing each one individually, we give a few highlights, conditioned by the items in the working group charge, namely:

  1. Summarize the state of the art in simulation capabilities. What developments are needed?
  2. Summarize the state of the art in theory. What developments are needed?
  3. Summarize recent developments in benchmarking experimental data with simulations. What critical experiments and diagnostic developments are needed to further refine the theory and simulations?
  4. Summarize the state of the art in instability mitigation techniques. What further technology developments are needed?
  5. Summarize the primary limitations to beam intensity in existing circular machines.
  6. Summarize the key beam dynamics questions for high-intensity circular machines
  7. Summarize opportunities for advancing the field.

 

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