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Title |
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| MOPLT033 |
Experimental Studies of Controlled Longitudinal Emittance Blow-up in the SPS as LHC Injector and LHC Test-Bed
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617 |
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- J. Tuckmantel, T. Bohl, T.P.R. Linnecar, E.N. Shaposhnikova
CERN, Geneva
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The longitudinal emittance of the LHC beam must be increased in a controlled way both in the SPS and the LHC itself. In the first case a small increase is sufficient to help prevent coupled bunch instabilities but in the second a factor three is required to also reduce intra-beam scattering effects. This has been achieved in the SPS by exciting the beam at the synchrotron frequency through the phase loop of the main RF system using bandwidth-limited noise, a method that is particularly suitable for the LHC which will have only one RF system. We describe the tests that have been done in the SPS both for low and high intensity beams, the hardware used and the influence of parameters such as time of excitation, bandwidth, frequency and amplitude on the resulting blow-up. After taking into account intensity effects it was possible to achieve a controlled emittance increase by a factor of about 2.5 without particle loss or the creation of visible tails in the distribution.
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| MOPLT035 |
Beam Induced Heating of the SPS Fast Pulsed Magnets
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623 |
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- J.A. Uythoven, G. Arduini, T. Bohl, F. Caspers, E.H.R. Gaxiola, T. Kroyer, M. Timmins, L. Vos
CERN, Geneva
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Fast pulsed magnets with ferrite yokes are used in CERN?s SPS accelerator for beam injection, extraction and excitation for tune measurements. The impedance of the ferrite structures can provoke significant beam induced heating, especially for beams with high peak currents as for LHC operation, even beyond the Curie temperature. The expected heating in the different kicker systems for various operational modes is compared with beam measurements. Estimates of the beam induced power have been derived from measured beam spectra. A fast extraction kicker system has recently been equipped with a cooling system. The measured cooling performance is compared with data from laboratory setups and numerical simulations.
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| WEPLT035 |
Capture Loss of the LHC Beam in the CERN SPS
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1903 |
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- E.N. Shaposhnikova, T. Bohl, T.P.R. Linnecar, J. Tuckmantel
CERN, Geneva
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The matched voltage of the LHC beam at injection into the SPS is 750 kV. However, even with RF feedback and feed forward systems in operation, the relative particle losses on the flat bottom for nominal LHC parameters with this capture voltage can reach the 30% level. With voltages as high as 2 MV these losses are still around 15% pushing the intensity in the SPS injectors to the limit to obtain nominal intensity beam for the LHC. Beam losses grow with intensity and are always asymmetric in energy (lost particles are seen main in front of the batch). The asymmetry can be explained by the energy loss of particles due to the SPS impedance which is also responsible for a non-zero synchronous phase on the flat bottom leading to large gaps between buckets. In this paper the measurements of the dependence of particles loss on the beam and machine parameters are presented and discussed together with possible loss mechanisms.
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| WEPLT036 |
Energy Loss of a Single Bunch in the CERN SPS
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1906 |
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- E.N. Shaposhnikova, T. Bohl, T.P.R. Linnecar, J. Tuckmantel
CERN, Geneva
- A. Hofmann
Honorary CERN Staff Member, Grand-Saconnex
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The dependence of energy loss on bunch length was determined experimentally for a single proton bunch in the SPS at 26 GeV/c. This was done from measurements of the synchronous phase as a function of intensity for different capture voltages. The results are compared with the expected dependence calculated from the resistive part of the SPS impedance below 1 GHz. Two impedance sources, the cavities of the 200 MHz RF system and the extraction kickers, give the main contributions to particle energy loss in very good agreement with experiment. The results obtained allow a better understanding of some mechanisms leading to capture loss of the high intensity LHC beam in the SPS.
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| WEPLT041 |
RF Amplitude Modulation to Suppress Longitudinal Coupled Bunch Instabilities in the SPS
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1921 |
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- E. Vogel, T. Bohl, U. Wehrle
CERN, Geneva
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In the SPS, even after a considerable impedance reduction including the removal of all RF cavities used for lepton acceleration in the past, longitudinal coupled bunch instabilities develop with an LHC beam of about one fifth of the nominal bunch intensity. The nominal LHC beam is stabilised using both, the 800 MHz Landau damping cavities, in bunch shortening mode, and pre-emptive emittance blow-up. An alternative method to increase the synchrotron frequency spread and thus stabilise the beam is amplitude modulation of the accelerating RF voltage. This method might be especially suitable in accelerators without a higher harmonic RF system, as will be the case in LHC. The main results of recent studies using this method in the SPS and considerations about its use in LHC are presented.
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| WEPLT044 |
Electron-cloud Build-up Simulations and Experiments at CERN
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1930 |
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- F. Zimmermann, G. Arduini, V. Baglin, T. Bohl, B.J. Jenninger, J.M. Jimenez, J.-M. Laurent, F. Ruggiero, D. Schulte
CERN, Geneva
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We compare the predications of electron-cloud build-up simulations with measurements at the CERN SPS. Specifically, we compare the electron flux at the wall, electron-energy spectra, heat loads, and the spatial distribution of the electrons for two different bunch spacings, with variable magnetic fields, and for several chamber temperatures and associated surface conditions. The simulations employ a modified, improved version of the ECLOUD code. The main changes are briefly described. We finally present updated simulation results for the heat load in the cold LHC arcs.
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