Paper |
Title |
Page |
MOPS072 |
Broadband Electromagnetic Characterization of Materials for Accelerator Components |
769 |
|
- C. Zannini, A. Grudiev, E. Métral, T. Pieloni, G. Rumolo
CERN, Geneva, Switzerland
- G. De Michele
PSI, Villigen, Switzerland
- C. Zannini
EPFL, Lausanne, Switzerland
|
|
|
Electromagnetic (EM) characterization of materials up to high frequencies is a major requirement for the correct modeling of many accelerator components: collimators, kickers, high order modes damping devices for accelerating cavities. In this scenario, the coaxial line method has gained much importance compared to other methods because of its applicability in a wide range of frequencies. In this paper we describe a new coaxial line method that allows using only one measurement setup to characterize the material in a range of frequency from few MHz up to several GHz. A coaxial cable fed at one side is filled with the material under test and closed on a known load on the other side. The properties of the material are obtained from the measured reflection coefficient by using it as input for a transmission line (TL) model or for 3D EM simulations, which describe the measurements setup. We have applied this method to characterize samples of SiC (Silicon Carbide) which could be used for LHC collimators and for CLIC accelerating structures and NiZn ferrite used for kicker magnets.
|
|
|
TUPZ023 |
Observation of Bunch to Bunch Differences due to Beam-beam Effects |
1855 |
|
- G. Papotti, R. Alemany-Fernandez, R. Giachino, W. Herr, T. Pieloni, M. Schaumann, G. Trad
CERN, Geneva, Switzerland
|
|
|
Due to the bunch filling schemes in the LHC the bunches experience a very different collision schedule and therefore different beam-beam effects. These differences and the effect on the performance have been observed and compared with the expectations. Possible limitations due to these effects are discussed.
|
|
|
TUPZ025 |
Experience with Offset Collisions in the LHC |
1858 |
|
- G. Papotti, R. Alemany-Fernandez, F. Follin, R. Giachino, W. Herr, T. Pieloni, M. Schaumann
CERN, Geneva, Switzerland
- R. Calaga, R. Miyamoto
BNL, Upton, Long Island, New York, USA
|
|
|
To keep the luminosity under control, some experiments require the adjustment of the luminosity during a fill, so-called luminosity leveling. One option is the separate the beams transversely and adjust the separation to the desired collision rate. The results from controlled experiments are reported and interpreted. The feasibility of this method for ultimate luminosities is discussed.
|
|
|
TUPZ029 |
Observation of Coherent Beam-beam Effects in the LHC |
1870 |
|
- X. Buffat
EPFL, Lausanne, Switzerland
- R. Calaga, S.M. White
BNL, Upton, Long Island, New York, USA
- R. Giachino, W. Herr, G. Papotti, T. Pieloni
CERN, Geneva, Switzerland
|
|
|
Early collisions in the LHC with a very limited number of bunches with high intensities indicated the presence of coherent beam-beam driven oscillations. Here we discuss the experimental results and compare with the expectations.
|
|
|
WEODA01 |
Observations of Beam-beam Effects at High Intensities in the LHC |
1936 |
|
- W. Herr, R. Alemany-Fernandez, R. Giachino, G. Papotti, T. Pieloni
CERN, Geneva, Switzerland
- R. Calaga
BNL, Upton, Long Island, New York, USA
- E. Laface
ESS, Lund, Sweden
- M. Schaumann
RWTH, Aachen, Germany
|
|
|
First observations with colliding beams in the LHC with bunch intensities close to nominal and above are reported. In 2010 the LHC initially operated with few bunches spaced around the circumference. Beam-beam tune shifts exceeding significantly the design value have been observed. In a later stage crossing angles were introduced around the experiments to allow the collisions of bunch trains. We report the first experience with head-on as well as long range interactions of high intensity bunches and discuss the possible performance reach.
|
|
|
Slides WEODA01 [0.409 MB]
|
|
|
THOBA01 |
Electron Cloud Observations in LHC |
2862 |
|
- G. Rumolo, G. Arduini, V. Baglin, H. Bartosik, P. Baudrenghien, N. Biancacci, G. Bregliozzi, S.D. Claudet, R. De Maria, J. Esteban Muller, M. Favier, C. Hansen, W. Höfle, J.M. Jimenez, V. Kain, E. Koukovini, G. Lanza, K.S.B. Li, G.H.I. Maury Cuna, E. Métral, G. Papotti, T. Pieloni, F. Roncarolo, B. Salvant, E.N. Shaposhnikova, R.J. Steinhagen, L.J. Tavian, D. Valuch, W. Venturini Delsolaro, F. Zimmermann
CERN, Geneva, Switzerland
- C.M. Bhat
Fermilab, Batavia, USA
- U. Iriso
CELLS-ALBA Synchrotron, Cerdanyola del Vallès, Spain
- N. Mounet, C. Zannini
EPFL, Lausanne, Switzerland
|
|
|
Operation of LHC with bunch trains different spacings has revealed the formation of an electron cloud inside the machine. The main observations of electron cloud build-up are the pressure rise measured at the vacuum gauges in the warm regions, as well as the increase of the beam screen temperature in the cold regions due to an additional heat load. The effects of the electron cloud were also visible as a strong instability and emittance growth affecting the last bunches of longer trains, which could be improved running with higher chromaticity and/or larger transverse emittances. A summary of the 2010 and 2011 observations and measurements and a comparison with existing models will be presented. The efficiency of scrubbing and scrubbing strategies to improve the machine running performance will be also briefly discussed.
|
|
|
Slides THOBA01 [2.911 MB]
|
|
|