IPAC2014 - List of Authors (Zannini, C.)

Paper	Title	Page
TUPME026	TMCI Thresholds for LHC Single Bunches in the CERN-SPS and Comparison with Simulations	1407
	H. Bartosik, G. Iadarola, Y. Papaphilippou, G. Rumolo, B. Salvant, C. Zannini CERN, Geneva, Switzerland
	At the beginning of 2013 an extensive measurement campaign was carried out at the SPS in order to determine the Transverse Mode Coupling Instability thresholds of LHC-type bunches in a wide range of intensities and longitudinal emittances. The measurements were performed in two different configurations of machine optics (nominal and low gamma transition) with the goal to characterize the differences in behavior and performance. The purpose of this paper is to describe in detail the measurement procedure and results, as well as the comparison of the experimental data with HEADTAIL simulations based on the latest SPS impedance model. Beside the impedances of the resistive wall, the beam position monitors (BPMs), the RF cavities, and the flanges, an advanced model of the impedance of the kicker magnets is included, which are found to play a major role in the definition of the stability region of the LHC-type bunches in the two optics configurations studied.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME026
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TUPME027	Analysis of the Electron Cloud Observations with 25 ns Bunch Spacing at the LHC	1410
	G. Iadarola Naples University Federico II, Science and Technology Pole, Napoli, Italy G. Arduini, V. Baglin, D. Banfi, H. Bartosik, S.D. Claudet, C.O. Domínguez, J.F. Esteban Müller, G. Iadarola, T. Pieloni, G. Rumolo, E.N. Shaposhnikova, L.J. Tavian, C. Zannini, F. Zimmermann CERN, Geneva, Switzerland
	Electron Cloud (EC) effects have been identified as a major performance limitation for the Large Hadron Collider (LHC) when operating with the nominal bunch spacing of 25 ns. During the LHC Run 1 (2010 - 2013) the luminosity production mainly used beams with 50 ns spacing, while 25 ns beams were only employed for short periods in 2011 and 2012 for test purposes. On these occasions, observables such as pressure rise, heat load in the cold sections as well as clear signatures on bunch-by-bunch emittance blow up, particle loss and energy loss indicated the presence of an EC in a large portion of the LHC. The analysis of the recorded data, together with EC build up simulations, has led to a significant improvement of our understanding of the EC effect in the different components of the LHC. Studies were carried out both at injection energy (450 GeV) and at top energy (4 TeV) aiming at determining the energy dependence of the EC formation and its impact on the quality of the proton beam.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME027
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TUPRI054	FEM Analysis of Beam-coupling Impedance and RF Contacts Criticality on the LHC UA9 Piezo Goniometer	1692
	A. Danisi, R. Losito, A. Masi, A. Passarelli, B. Salvant, C. Zannini CERN, Geneva, Switzerland
	The UA9 piezo-goniometer has been designed to guarantee micro-radians-accuracy angular positioning of a silicon crystal for a crystal collimation experiment in the LHC, and to minimize the impact on the LHC beam-coupling impedance. This paper presents a Finite Element Method (FEM) study of the device, in both parking and operational positions, to evaluate its impact on the LHC impedance budget. The study has been a progressive simulation work, started from the simplification of the original detailed design, and aimed at highlighting the effect of single details (e.g. objects in confining chambers) on the longitudinal and transverse components of beam-coupling impedance. In addition, the shielding contribution of the RF gaskets has been carefully evaluated, with the objective to assess the consequences for operation in case of their failure. Sensitivity analyses to simulation parameters are also performed, in order to test the FEM model robustness. A final word is drawn on the overall device impedance criticality.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI054
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TUPRI055	Theoretical Analysis of Metamaterial Insertions for Resistive-wall Beam-coupling Impedance Reduction	1695
	A. Danisi, R. Losito, A. Masi, B. Salvant, C. Zannini CERN, Geneva, Switzerland
	Resistive-wall impedance usually constitutes a significant percentage of the total beam-coupling impedance budget of many accelerator structures (e.g. for LHC, it can be more than 50%). Reduction techniques for resistive-wall components entail high electrical-conductivity coatings. This paper proposes the use of metamaterials, having negative values of magnetic permeability or dielectric permittivity (or both), for sensibly reducing or theoretically nearly cancelling the resistive-wall component of beam-coupling impedance. The proposed approach is developed by means of an equivalent transmission-line model, whose results show the potential reduction of both longitudinal and transverse impedance when using metamaterial insertions. The effects on the real and imaginary part have been singled out. The effectiveness of such materials is discussed both for negative-permittivity and for negative-permeability cases, which actually show different impacts and can be then target of proper engineering. This first-stage study opens the possibility of considering metamaterials for impedance mitigation or for setting up proper experimental setups.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI055
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TUPRI061	Power Loss Calculation in Separated and Common Beam Chambers of the LHC	1711
	C. Zannini, G. Iadarola, G. Rumolo CERN, Geneva, Switzerland G. Iadarola Naples University Federico II, Science and Technology Pole, Napoli, Italy
	The performance of 25 ns beams in the LHC is strongly limited by the electron cloud. To determine the amount electron cloud in the cold sections of the machine, it is very important to be able to disentangle the beam induced heating due to the beam coupling impedance from that attributable to electron cloud. This paper will focus on the calculation of the first contribution. First, the impedance model used for the calculation of the beam induced power loss is briefly discussed. Then, the methods for the calculation of the beam induced power loss in regions with one or two beams are also described. Finally, the calculated power loss is compared with the measured heat loads for both 25 and 50 ns beams in both the LHC arcs and in the inner triplets (ITs).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI061
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TUPRI062	The Mode Matching Technique Applied to the Transverse Beam Coupling Impedance Calculation of Azimuthally Symmetric Devices of Finite Length	1714
	N. Biancacci, E. Métral, B. Salvant, C. Zannini CERN, Geneva, Switzerland M. Migliorati, L. Palumbo URLS, Rome, Italy V.G. Vaccaro Naples University Federico II and INFN, Napoli, Italy
	The infinite length approximation is often used to simplify the calculation of the beam coupling impedance of accelerator elements. This is expected to be a reasonable assumption for devices whose length is greater than the transverse dimension but may be a less accurate approximation for segmented devices. In this contribution we present the extension of the study of the beam coupling impedance of a finite length device to the transverse plane. In order to take into account the finite length, we decompose the fields in the cavity and in the beam pipe into a set of orthonormal modes and apply the Mode Matching method to obtain the impedance. To validate our method, we will present comparisons between analytical formulas and 3D electromagnetic CST simulations.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI062
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TUPRI063	Electromagnetic Simulations for Non-ultrarelativistic Beams and Application to the CERN Low Energy Machines	1718
	C. Zannini, N. Biancacci, T.L. Rijoff, G. Rumolo CERN, Geneva, Switzerland T.L. Rijoff TU Darmstadt, Darmstadt, Germany
	In the framework of the PS-Booster upgrade project an accurate impedance model is needed in order to determine the effect on the beam stability and assess the impact of the new devices to be installed in the machine. CST 3-D EM simulations are widely used to estimate the impedance contribution of the different devices along the CERN accelerator complex. Unlike the highly relativistic case, in which the reliability of the EM solver has been proved in many specific cases by comparing simulations with analytical results, the nonrelativistic case has been so far not yet benchmarked. In order to use systematically CST 3-D EM simulations for the PS-Booster, or even lower energy machines like the antiproton decelerator ELENA, a validation campaign has been carried out. The main complication to single out the beam coupling impedance, as resulting from the interaction of the beam with the surroundings, consisted of removing reliably the strong contribution of the direct space charge of the source bunch, which is included in the EM calculation. The simulation results were then benchmarked with the analytical results for the case of a PEC cylindrical tube and of a ferrite loaded kicker.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI063
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WEPME050	High Frequency Electromagnetic Characterization of NEG properties for the CLIC Damping Rings	2384
SUSPSNE103	use link to see paper's listing under its alternate paper code
	E. Koukovini-Platia, G. Rumolo, C. Zannini CERN, Geneva, Switzerland
	Coating materials will be used in the CLIC damping rings (DR) to suppress two-stream effects. In particular, NEG coating is necessary to suppress fast beam ion instabilities in the electron damping ring (EDR). The electromagnetic (EM) characterization of the material properties up to high frequencies is required for the impedance modeling of the CLIC DR components. The EM properties for frequencies of few GHz are determined with the waveguide method, based on a combination of experimental measurements of the complex transmission coefficient S21 and CST 3D EM simulations. The results obtained from a NEG coated copper (Cu) waveguide are presented in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPME050
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

TMCI Thresholds for LHC Single Bunches in the CERN-SPS and Comparison with Simulations

1407

H. Bartosik, G. Iadarola, Y. Papaphilippou, G. Rumolo, B. Salvant, C. Zannini
CERN, Geneva, Switzerland

At the beginning of 2013 an extensive measurement campaign was carried out at the SPS in order to determine the Transverse Mode Coupling Instability thresholds of LHC-type bunches in a wide range of intensities and longitudinal emittances. The measurements were performed in two different configurations of machine optics (nominal and low gamma transition) with the goal to characterize the differences in behavior and performance. The purpose of this paper is to describe in detail the measurement procedure and results, as well as the comparison of the experimental data with HEADTAIL simulations based on the latest SPS impedance model. Beside the impedances of the resistive wall, the beam position monitors (BPMs), the RF cavities, and the flanges, an advanced model of the impedance of the kicker magnets is included, which are found to play a major role in the definition of the stability region of the LHC-type bunches in the two optics configurations studied.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME026

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPME027

Analysis of the Electron Cloud Observations with 25 ns Bunch Spacing at the LHC

1410

G. Iadarola
Naples University Federico II, Science and Technology Pole, Napoli, Italy
G. Arduini, V. Baglin, D. Banfi, H. Bartosik, S.D. Claudet, C.O. Domínguez, J.F. Esteban Müller, G. Iadarola, T. Pieloni, G. Rumolo, E.N. Shaposhnikova, L.J. Tavian, C. Zannini, F. Zimmermann
CERN, Geneva, Switzerland

Electron Cloud (EC) effects have been identified as a major performance limitation for the Large Hadron Collider (LHC) when operating with the nominal bunch spacing of 25 ns. During the LHC Run 1 (2010 - 2013) the luminosity production mainly used beams with 50 ns spacing, while 25 ns beams were only employed for short periods in 2011 and 2012 for test purposes. On these occasions, observables such as pressure rise, heat load in the cold sections as well as clear signatures on bunch-by-bunch emittance blow up, particle loss and energy loss indicated the presence of an EC in a large portion of the LHC. The analysis of the recorded data, together with EC build up simulations, has led to a significant improvement of our understanding of the EC effect in the different components of the LHC. Studies were carried out both at injection energy (450 GeV) and at top energy (4 TeV) aiming at determining the energy dependence of the EC formation and its impact on the quality of the proton beam.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME027

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPRI054

FEM Analysis of Beam-coupling Impedance and RF Contacts Criticality on the LHC UA9 Piezo Goniometer

1692

A. Danisi, R. Losito, A. Masi, A. Passarelli, B. Salvant, C. Zannini
CERN, Geneva, Switzerland

The UA9 piezo-goniometer has been designed to guarantee micro-radians-accuracy angular positioning of a silicon crystal for a crystal collimation experiment in the LHC, and to minimize the impact on the LHC beam-coupling impedance. This paper presents a Finite Element Method (FEM) study of the device, in both parking and operational positions, to evaluate its impact on the LHC impedance budget. The study has been a progressive simulation work, started from the simplification of the original detailed design, and aimed at highlighting the effect of single details (e.g. objects in confining chambers) on the longitudinal and transverse components of beam-coupling impedance. In addition, the shielding contribution of the RF gaskets has been carefully evaluated, with the objective to assess the consequences for operation in case of their failure. Sensitivity analyses to simulation parameters are also performed, in order to test the FEM model robustness. A final word is drawn on the overall device impedance criticality.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI054

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPRI055

Theoretical Analysis of Metamaterial Insertions for Resistive-wall Beam-coupling Impedance Reduction

1695

A. Danisi, R. Losito, A. Masi, B. Salvant, C. Zannini
CERN, Geneva, Switzerland

Resistive-wall impedance usually constitutes a significant percentage of the total beam-coupling impedance budget of many accelerator structures (e.g. for LHC, it can be more than 50%). Reduction techniques for resistive-wall components entail high electrical-conductivity coatings. This paper proposes the use of metamaterials, having negative values of magnetic permeability or dielectric permittivity (or both), for sensibly reducing or theoretically nearly cancelling the resistive-wall component of beam-coupling impedance. The proposed approach is developed by means of an equivalent transmission-line model, whose results show the potential reduction of both longitudinal and transverse impedance when using metamaterial insertions. The effects on the real and imaginary part have been singled out. The effectiveness of such materials is discussed both for negative-permittivity and for negative-permeability cases, which actually show different impacts and can be then target of proper engineering. This first-stage study opens the possibility of considering metamaterials for impedance mitigation or for setting up proper experimental setups.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI055

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPRI061

Power Loss Calculation in Separated and Common Beam Chambers of the LHC

1711

C. Zannini, G. Iadarola, G. Rumolo
CERN, Geneva, Switzerland
G. Iadarola
Naples University Federico II, Science and Technology Pole, Napoli, Italy

The performance of 25 ns beams in the LHC is strongly limited by the electron cloud. To determine the amount electron cloud in the cold sections of the machine, it is very important to be able to disentangle the beam induced heating due to the beam coupling impedance from that attributable to electron cloud. This paper will focus on the calculation of the first contribution. First, the impedance model used for the calculation of the beam induced power loss is briefly discussed. Then, the methods for the calculation of the beam induced power loss in regions with one or two beams are also described. Finally, the calculated power loss is compared with the measured heat loads for both 25 and 50 ns beams in both the LHC arcs and in the inner triplets (ITs).

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI061

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPRI062

The Mode Matching Technique Applied to the Transverse Beam Coupling Impedance Calculation of Azimuthally Symmetric Devices of Finite Length

1714

N. Biancacci, E. Métral, B. Salvant, C. Zannini
CERN, Geneva, Switzerland
M. Migliorati, L. Palumbo
URLS, Rome, Italy
V.G. Vaccaro
Naples University Federico II and INFN, Napoli, Italy

The infinite length approximation is often used to simplify the calculation of the beam coupling impedance of accelerator elements. This is expected to be a reasonable assumption for devices whose length is greater than the transverse dimension but may be a less accurate approximation for segmented devices. In this contribution we present the extension of the study of the beam coupling impedance of a finite length device to the transverse plane. In order to take into account the finite length, we decompose the fields in the cavity and in the beam pipe into a set of orthonormal modes and apply the Mode Matching method to obtain the impedance. To validate our method, we will present comparisons between analytical formulas and 3D electromagnetic CST simulations.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI062

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPRI063

Electromagnetic Simulations for Non-ultrarelativistic Beams and Application to the CERN Low Energy Machines

1718

C. Zannini, N. Biancacci, T.L. Rijoff, G. Rumolo
CERN, Geneva, Switzerland
T.L. Rijoff
TU Darmstadt, Darmstadt, Germany

In the framework of the PS-Booster upgrade project an accurate impedance model is needed in order to determine the effect on the beam stability and assess the impact of the new devices to be installed in the machine. CST 3-D EM simulations are widely used to estimate the impedance contribution of the different devices along the CERN accelerator complex. Unlike the highly relativistic case, in which the reliability of the EM solver has been proved in many specific cases by comparing simulations with analytical results, the nonrelativistic case has been so far not yet benchmarked. In order to use systematically CST 3-D EM simulations for the PS-Booster, or even lower energy machines like the antiproton decelerator ELENA, a validation campaign has been carried out. The main complication to single out the beam coupling impedance, as resulting from the interaction of the beam with the surroundings, consisted of removing reliably the strong contribution of the direct space charge of the source bunch, which is included in the EM calculation. The simulation results were then benchmarked with the analytical results for the case of a PEC cylindrical tube and of a ferrite loaded kicker.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI063

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPME050

High Frequency Electromagnetic Characterization of NEG properties for the CLIC Damping Rings

2384

SUSPSNE103

use link to see paper's listing under its alternate paper code

E. Koukovini-Platia, G. Rumolo, C. Zannini
CERN, Geneva, Switzerland

Coating materials will be used in the CLIC damping rings (DR) to suppress two-stream effects. In particular, NEG coating is necessary to suppress fast beam ion instabilities in the electron damping ring (EDR). The electromagnetic (EM) characterization of the material properties up to high frequencies is required for the impedance modeling of the CLIC DR components. The EM properties for frequencies of few GHz are determined with the waveguide method, based on a combination of experimental measurements of the complex transmission coefficient S21 and CST 3D EM simulations. The results obtained from a NEG coated copper (Cu) waveguide are presented in this paper.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPME050

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)