Métral, E.

Paper	Title	Page
MOPCH097	CERN Proton Synchrotron Working Point Control Using an Improved Version of the Pole-face-windings and Figure-of-eight Loop Powering	264
	R.R. Steerenberg, J.-P. Burnet, M. Giovannozzi, O. Michels, E. Métral, B. Vandorpe CERN, Geneva
	The working point of the CERN Proton Synchrotron, which is equipped with combined function magnets, is controlled using pole-face-windings. Each main magnet consists of one focusing and one de-focusing half-unit on which four pole-face-winding plates are mounted containing two separate coils each, called narrow and wide. At present they are connected in series, but can be powered independently. In addition, a winding called the figure-of-eight loop, contours the pole faces and crosses between the two half units, generating opposite fields in each half-unit. The four optical parameters, horizontal and vertical tune and chromaticity, are adjusted by acting on the pole-face-winding currents in both half units and in the figure-of-eight loop, leaving one physical quantity free. The power supply consolidation project opened the opportunity to use five independent power supplies, to adjust the four parameters plus an additional degree of freedom. This paper presents the results of the measurements that have been made in the five-current mode together with the influence of the magnetic nonlinearities, due to the unbalance in the narrow and wide winding currents, on the beam dynamics.
THPCH057	The Fast Vertical Single-bunch Instability after Injection into the CERN Super Proton Synchrotron	2913
	E. Métral, G. Arduini, T. Bohl, H. Burkhardt, G. Rumolo CERN, Geneva B. Spataro INFN/LNF, Frascati (Roma)
	Since 2003, high-intensity single-bunch proton beams with low longitudinal emittance have been affected by heavy losses after less than one synchrotron period after injection. The effects of the resonance frequency of the responsible impedance, longitudinal emittance and chromaticity on the intensity threshold were already discussed in detail in 2004, comparing analytical predictions with simulation results. In this paper the evolution of the instability between injection and the time of beam loss is our main concern. Measurements are compared with HEADTAIL simulations. A travelling-wave pattern propagating along the bunch, which is the signature of a Beam Break-Up or Transverse Mode Coupling Instability (TMCI), is clearly identified. The oscillating frequency, near ~1 GHz, is in good agreement with the usual broad-band impedance model deduced from beam-based measurements like the head-tail growth rate vs. chromaticity.
THPCH058	Simulation Study on the Beneficial Effect of Linear Coupling for the Transverse Mode Coupling Instability in the CERN Super Proton Synchrotron	2916
	E. Métral, G. Rumolo CERN, Geneva
	The intensity threshold of the transverse mode coupling instability in a flat vertical chamber, as in the CERN Super Proton Synchrotron, is much higher in the horizontal plane than in the vertical one. This asymmetry between the transverse planes led us to the idea that linear coupling from skew quadrupoles could be used to increase the intensity threshold. This technique is already applied, for instance, in the CERN Proton Synchrotron, where a slow head-tail horizontal instability due to the resistive-wall impedance is stabilized by linear coupling only, i.e. with neither octupoles nor feedbacks. This paper presents the results of the study of the effect of linear coupling on the transverse mode coupling instability, using the HEADTAIL simulation code.
THPCH059	Kicker Impedance Measurements for the Future Multi-turn Extraction of the CERN Proton Synchrotron	2919
	E. Métral, F. Caspers, M. Giovannozzi, A. Grudiev, T. Kroyer, L. Sermeus CERN, Geneva
	In the context of the novel multi-turn extraction, where charged particles are trapped into stable islands in transverse phase space, the ejection of five beamlets will be performed by means of a set of three new kickers. Before installing them into the machine, a measurement campaign has been launched to evaluate the impedance of such devices. Two measurement techniques were used to try to disentangle the driving and detuning impedances. The first consists in measuring the longitudinal impedance for different transverse offsets using a single displaced wire. The sum of the transverse driving and detuning impedances is then deduced applying Panofsky-Wenzel theorem. The second uses two wires excited in opposite phase and yields the driving transverse impedance only. Finally, the consequences on the beam dynamics are also analyzed.
THPCH060	Simulation Study on the Energy Dependence of the TMCI Threshold in the CERN-SPS	2922
	G. Rumolo, E. Métral, E.N. Shaposhnikova CERN, Geneva
	This paper concentrates on theoretical studies of Transverse Mode Coupling Instability at the SPS. It shows the expected thresholds based on a HEADTAIL tracking model and on impedance values estimated from previous measurements. First, the effect of space charge is addressed as an important ingredient at the low energies. Subsequently, the change of TMCI threshold possibly induced by a higher injection energy into the SPS (plausible according to the upgrade studies) is investigated and a scaling law with energy is derived.
THPCH061	Tune Shift Induced by Nonlinear Resistive Wall Wake Field of Flat Collimator	2925
	F. Zimmermann, G. Arduini, R.W. Assmann, H. Burkhardt, F. Caspers, M. Gasior, O.R. Jones, T. Kroyer, E. Métral, S. Redaelli, G. Robert-Demolaize, F. Roncarolo, G. Rumolo, R.J. Steinhagen, J. Wenninger CERN, Geneva
	We present formulae for the coherent and incoherent tune shifts due to the nonlinear resistive wall wake field for a single beam traveling between two parallel plates. In particular, we demonstrate that the nonlinear terms of the resistive wall wake field become important if the gap between the plates is comparable to the transverse rms beam size. We also compare the theoretically predicted tune shift as a function of gap size with measurements for an LHC prototype graphite collimator in the CERN SPS and with simulations.
TUODFI01	The Final Collimation System for the LHC	986
	R.W. Assmann, O. Aberle, G. Bellodi, A. Bertarelli, C.B. Bracco, H.-H. Braun, M. Brugger, S. Calatroni, R. Chamizo, A. Dallocchio, B. Dehning, A. Ferrari, P. Gander, A. Grudiev, E.B. Holzer, J.-B. Jeanneret, J.M. Jimenez, M. Jonker, Y. Kadi, K. Kershaw, J. Lendaro, J. Lettry, R. Losito, M. Magistris, A.M. Masi, M. Mayer, E. Métral, R. Perret, C. Rathjen, S. Redaelli, G. Robert-Demolaize, S. Roesler, F. Ruggiero, M. Santana-Leitner, P. Sievers, M. Sobczak, E. Tsoulou, V. Vlachoudis, Th. Weiler CERN, Geneva I. Baishev, I.L. Kurochkin IHEP Protvino, Protvino, Moscow Region
	The LHC collimation system has been re-designed over the last three years in order to address the unprecedented challenges that are faced with the 360 MJ beams at 7 TeV. The layout of the LHC has now been fixed and a final approach for collimation and cleaning has been adopted. In total 132 collimator locations have been reserved in the two LHC rings and can be installed in a phased approach. Ninety collimators of five different types will be available for initial beam operation. The system has been fully optimized for avoiding quenches of super-conducting magnets during beam losses and for sufficient survival of beamline components against radioactive dose. The phased approach for LHC collimation is described, the various collimators and their functionalities are explained, and the expected system performance is summarized.
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